9cad9c95d7
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Rob Clark <rob.clark@linaro.org>
2486 lines
113 KiB
XML
2486 lines
113 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
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<book id="drmDevelopersGuide">
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<bookinfo>
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<title>Linux DRM Developer's Guide</title>
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<authorgroup>
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<author>
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<firstname>Jesse</firstname>
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<surname>Barnes</surname>
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<contrib>Initial version</contrib>
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<affiliation>
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<orgname>Intel Corporation</orgname>
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<address>
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<email>jesse.barnes@intel.com</email>
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</address>
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</affiliation>
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</author>
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<author>
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<firstname>Laurent</firstname>
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<surname>Pinchart</surname>
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<contrib>Driver internals</contrib>
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<affiliation>
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<orgname>Ideas on board SPRL</orgname>
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<address>
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<email>laurent.pinchart@ideasonboard.com</email>
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</address>
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</affiliation>
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</author>
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</authorgroup>
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<copyright>
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<year>2008-2009</year>
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<year>2012</year>
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<holder>Intel Corporation</holder>
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<holder>Laurent Pinchart</holder>
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</copyright>
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<legalnotice>
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<para>
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The contents of this file may be used under the terms of the GNU
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General Public License version 2 (the "GPL") as distributed in
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the kernel source COPYING file.
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</para>
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</legalnotice>
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<revhistory>
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<!-- Put document revisions here, newest first. -->
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<revision>
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<revnumber>1.0</revnumber>
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<date>2012-07-13</date>
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<authorinitials>LP</authorinitials>
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<revremark>Added extensive documentation about driver internals.
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</revremark>
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</revision>
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</revhistory>
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</bookinfo>
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<toc></toc>
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<!-- Introduction -->
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<chapter id="drmIntroduction">
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<title>Introduction</title>
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<para>
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The Linux DRM layer contains code intended to support the needs
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of complex graphics devices, usually containing programmable
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pipelines well suited to 3D graphics acceleration. Graphics
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drivers in the kernel may make use of DRM functions to make
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tasks like memory management, interrupt handling and DMA easier,
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and provide a uniform interface to applications.
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</para>
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<para>
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A note on versions: this guide covers features found in the DRM
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tree, including the TTM memory manager, output configuration and
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mode setting, and the new vblank internals, in addition to all
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the regular features found in current kernels.
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</para>
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<para>
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[Insert diagram of typical DRM stack here]
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</para>
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</chapter>
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<!-- Internals -->
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<chapter id="drmInternals">
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<title>DRM Internals</title>
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<para>
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This chapter documents DRM internals relevant to driver authors
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and developers working to add support for the latest features to
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existing drivers.
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</para>
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<para>
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First, we go over some typical driver initialization
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requirements, like setting up command buffers, creating an
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initial output configuration, and initializing core services.
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Subsequent sections cover core internals in more detail,
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providing implementation notes and examples.
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</para>
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<para>
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The DRM layer provides several services to graphics drivers,
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many of them driven by the application interfaces it provides
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through libdrm, the library that wraps most of the DRM ioctls.
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These include vblank event handling, memory
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management, output management, framebuffer management, command
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submission & fencing, suspend/resume support, and DMA
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services.
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</para>
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<!-- Internals: driver init -->
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<sect1>
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<title>Driver Initialization</title>
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<para>
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At the core of every DRM driver is a <structname>drm_driver</structname>
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structure. Drivers typically statically initialize a drm_driver structure,
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and then pass it to one of the <function>drm_*_init()</function> functions
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to register it with the DRM subsystem.
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</para>
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<para>
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The <structname>drm_driver</structname> structure contains static
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information that describes the driver and features it supports, and
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pointers to methods that the DRM core will call to implement the DRM API.
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We will first go through the <structname>drm_driver</structname> static
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information fields, and will then describe individual operations in
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details as they get used in later sections.
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</para>
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<sect2>
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<title>Driver Information</title>
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<sect3>
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<title>Driver Features</title>
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<para>
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Drivers inform the DRM core about their requirements and supported
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features by setting appropriate flags in the
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<structfield>driver_features</structfield> field. Since those flags
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influence the DRM core behaviour since registration time, most of them
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must be set to registering the <structname>drm_driver</structname>
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instance.
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</para>
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<synopsis>u32 driver_features;</synopsis>
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<variablelist>
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<title>Driver Feature Flags</title>
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<varlistentry>
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<term>DRIVER_USE_AGP</term>
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<listitem><para>
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Driver uses AGP interface, the DRM core will manage AGP resources.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_REQUIRE_AGP</term>
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<listitem><para>
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Driver needs AGP interface to function. AGP initialization failure
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will become a fatal error.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_USE_MTRR</term>
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<listitem><para>
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Driver uses MTRR interface for mapping memory, the DRM core will
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manage MTRR resources. Deprecated.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_PCI_DMA</term>
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<listitem><para>
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Driver is capable of PCI DMA, mapping of PCI DMA buffers to
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userspace will be enabled. Deprecated.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_SG</term>
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<listitem><para>
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Driver can perform scatter/gather DMA, allocation and mapping of
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scatter/gather buffers will be enabled. Deprecated.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_HAVE_DMA</term>
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<listitem><para>
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Driver supports DMA, the userspace DMA API will be supported.
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Deprecated.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
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<listitem><para>
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DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler. The
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DRM core will automatically register an interrupt handler when the
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flag is set. DRIVER_IRQ_SHARED indicates whether the device &
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handler support shared IRQs (note that this is required of PCI
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drivers).
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_IRQ_VBL</term>
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<listitem><para>Unused. Deprecated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_DMA_QUEUE</term>
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<listitem><para>
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Should be set if the driver queues DMA requests and completes them
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asynchronously. Deprecated.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_FB_DMA</term>
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<listitem><para>
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Driver supports DMA to/from the framebuffer, mapping of frambuffer
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DMA buffers to userspace will be supported. Deprecated.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_IRQ_VBL2</term>
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<listitem><para>Unused. Deprecated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_GEM</term>
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<listitem><para>
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Driver use the GEM memory manager.
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_MODESET</term>
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<listitem><para>
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Driver supports mode setting interfaces (KMS).
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</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>DRIVER_PRIME</term>
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<listitem><para>
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Driver implements DRM PRIME buffer sharing.
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</para></listitem>
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</varlistentry>
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</variablelist>
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</sect3>
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<sect3>
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<title>Major, Minor and Patchlevel</title>
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<synopsis>int major;
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int minor;
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int patchlevel;</synopsis>
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<para>
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The DRM core identifies driver versions by a major, minor and patch
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level triplet. The information is printed to the kernel log at
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initialization time and passed to userspace through the
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DRM_IOCTL_VERSION ioctl.
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</para>
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<para>
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The major and minor numbers are also used to verify the requested driver
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API version passed to DRM_IOCTL_SET_VERSION. When the driver API changes
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between minor versions, applications can call DRM_IOCTL_SET_VERSION to
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select a specific version of the API. If the requested major isn't equal
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to the driver major, or the requested minor is larger than the driver
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minor, the DRM_IOCTL_SET_VERSION call will return an error. Otherwise
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the driver's set_version() method will be called with the requested
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version.
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</para>
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</sect3>
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<sect3>
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<title>Name, Description and Date</title>
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<synopsis>char *name;
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char *desc;
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char *date;</synopsis>
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<para>
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The driver name is printed to the kernel log at initialization time,
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used for IRQ registration and passed to userspace through
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DRM_IOCTL_VERSION.
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</para>
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<para>
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The driver description is a purely informative string passed to
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userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
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the kernel.
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</para>
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<para>
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The driver date, formatted as YYYYMMDD, is meant to identify the date of
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the latest modification to the driver. However, as most drivers fail to
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update it, its value is mostly useless. The DRM core prints it to the
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kernel log at initialization time and passes it to userspace through the
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DRM_IOCTL_VERSION ioctl.
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</para>
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</sect3>
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</sect2>
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<sect2>
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<title>Driver Load</title>
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<para>
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The <methodname>load</methodname> method is the driver and device
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initialization entry point. The method is responsible for allocating and
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initializing driver private data, specifying supported performance
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counters, performing resource allocation and mapping (e.g. acquiring
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clocks, mapping registers or allocating command buffers), initializing
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the memory manager (<xref linkend="drm-memory-management"/>), installing
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the IRQ handler (<xref linkend="drm-irq-registration"/>), setting up
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vertical blanking handling (<xref linkend="drm-vertical-blank"/>), mode
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setting (<xref linkend="drm-mode-setting"/>) and initial output
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configuration (<xref linkend="drm-kms-init"/>).
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</para>
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<note><para>
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If compatibility is a concern (e.g. with drivers converted over from
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User Mode Setting to Kernel Mode Setting), care must be taken to prevent
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device initialization and control that is incompatible with currently
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active userspace drivers. For instance, if user level mode setting
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drivers are in use, it would be problematic to perform output discovery
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& configuration at load time. Likewise, if user-level drivers
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unaware of memory management are in use, memory management and command
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buffer setup may need to be omitted. These requirements are
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driver-specific, and care needs to be taken to keep both old and new
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applications and libraries working.
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</para></note>
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<synopsis>int (*load) (struct drm_device *, unsigned long flags);</synopsis>
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<para>
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The method takes two arguments, a pointer to the newly created
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<structname>drm_device</structname> and flags. The flags are used to
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pass the <structfield>driver_data</structfield> field of the device id
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corresponding to the device passed to <function>drm_*_init()</function>.
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Only PCI devices currently use this, USB and platform DRM drivers have
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their <methodname>load</methodname> method called with flags to 0.
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</para>
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<sect3>
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<title>Driver Private & Performance Counters</title>
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<para>
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The driver private hangs off the main
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<structname>drm_device</structname> structure and can be used for
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tracking various device-specific bits of information, like register
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offsets, command buffer status, register state for suspend/resume, etc.
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At load time, a driver may simply allocate one and set
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<structname>drm_device</structname>.<structfield>dev_priv</structfield>
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appropriately; it should be freed and
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<structname>drm_device</structname>.<structfield>dev_priv</structfield>
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set to NULL when the driver is unloaded.
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</para>
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<para>
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DRM supports several counters which were used for rough performance
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characterization. This stat counter system is deprecated and should not
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be used. If performance monitoring is desired, the developer should
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investigate and potentially enhance the kernel perf and tracing
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infrastructure to export GPU related performance information for
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consumption by performance monitoring tools and applications.
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</para>
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</sect3>
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<sect3 id="drm-irq-registration">
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<title>IRQ Registration</title>
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<para>
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The DRM core tries to facilitate IRQ handler registration and
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unregistration by providing <function>drm_irq_install</function> and
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<function>drm_irq_uninstall</function> functions. Those functions only
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support a single interrupt per device.
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</para>
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<!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
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<para>
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Both functions get the device IRQ by calling
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<function>drm_dev_to_irq</function>. This inline function will call a
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bus-specific operation to retrieve the IRQ number. For platform devices,
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<function>platform_get_irq</function>(..., 0) is used to retrieve the
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IRQ number.
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</para>
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<para>
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<function>drm_irq_install</function> starts by calling the
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<methodname>irq_preinstall</methodname> driver operation. The operation
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is optional and must make sure that the interrupt will not get fired by
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clearing all pending interrupt flags or disabling the interrupt.
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</para>
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<para>
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The IRQ will then be requested by a call to
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<function>request_irq</function>. If the DRIVER_IRQ_SHARED driver
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feature flag is set, a shared (IRQF_SHARED) IRQ handler will be
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requested.
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</para>
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<para>
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The IRQ handler function must be provided as the mandatory irq_handler
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driver operation. It will get passed directly to
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<function>request_irq</function> and thus has the same prototype as all
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IRQ handlers. It will get called with a pointer to the DRM device as the
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second argument.
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</para>
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<para>
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Finally the function calls the optional
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<methodname>irq_postinstall</methodname> driver operation. The operation
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usually enables interrupts (excluding the vblank interrupt, which is
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enabled separately), but drivers may choose to enable/disable interrupts
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at a different time.
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</para>
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<para>
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<function>drm_irq_uninstall</function> is similarly used to uninstall an
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IRQ handler. It starts by waking up all processes waiting on a vblank
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interrupt to make sure they don't hang, and then calls the optional
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<methodname>irq_uninstall</methodname> driver operation. The operation
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must disable all hardware interrupts. Finally the function frees the IRQ
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by calling <function>free_irq</function>.
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</para>
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</sect3>
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<sect3>
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<title>Memory Manager Initialization</title>
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<para>
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Every DRM driver requires a memory manager which must be initialized at
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load time. DRM currently contains two memory managers, the Translation
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Table Manager (TTM) and the Graphics Execution Manager (GEM).
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This document describes the use of the GEM memory manager only. See
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<xref linkend="drm-memory-management"/> for details.
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</para>
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</sect3>
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<sect3>
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<title>Miscellaneous Device Configuration</title>
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<para>
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Another task that may be necessary for PCI devices during configuration
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is mapping the video BIOS. On many devices, the VBIOS describes device
|
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configuration, LCD panel timings (if any), and contains flags indicating
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device state. Mapping the BIOS can be done using the pci_map_rom() call,
|
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a convenience function that takes care of mapping the actual ROM,
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whether it has been shadowed into memory (typically at address 0xc0000)
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or exists on the PCI device in the ROM BAR. Note that after the ROM has
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been mapped and any necessary information has been extracted, it should
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be unmapped; on many devices, the ROM address decoder is shared with
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other BARs, so leaving it mapped could cause undesired behaviour like
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hangs or memory corruption.
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<!--!Fdrivers/pci/rom.c pci_map_rom-->
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</para>
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</sect3>
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</sect2>
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</sect1>
|
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|
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<!-- Internals: memory management -->
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|
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<sect1 id="drm-memory-management">
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<title>Memory management</title>
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<para>
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Modern Linux systems require large amount of graphics memory to store
|
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frame buffers, textures, vertices and other graphics-related data. Given
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the very dynamic nature of many of that data, managing graphics memory
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|
efficiently is thus crucial for the graphics stack and plays a central
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role in the DRM infrastructure.
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</para>
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<para>
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The DRM core includes two memory managers, namely Translation Table Maps
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(TTM) and Graphics Execution Manager (GEM). TTM was the first DRM memory
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|
manager to be developed and tried to be a one-size-fits-them all
|
|
solution. It provides a single userspace API to accomodate the need of
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all hardware, supporting both Unified Memory Architecture (UMA) devices
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|
and devices with dedicated video RAM (i.e. most discrete video cards).
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This resulted in a large, complex piece of code that turned out to be
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hard to use for driver development.
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|
</para>
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|
<para>
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|
GEM started as an Intel-sponsored project in reaction to TTM's
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|
complexity. Its design philosophy is completely different: instead of
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|
providing a solution to every graphics memory-related problems, GEM
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|
identified common code between drivers and created a support library to
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|
share it. GEM has simpler initialization and execution requirements than
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|
TTM, but has no video RAM management capabitilies and is thus limited to
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UMA devices.
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|
</para>
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<sect2>
|
|
<title>The Translation Table Manager (TTM)</title>
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<para>
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|
TTM design background and information belongs here.
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</para>
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|
<sect3>
|
|
<title>TTM initialization</title>
|
|
<warning><para>This section is outdated.</para></warning>
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|
<para>
|
|
Drivers wishing to support TTM must fill out a drm_bo_driver
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|
structure. The structure contains several fields with function
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pointers for initializing the TTM, allocating and freeing memory,
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|
waiting for command completion and fence synchronization, and memory
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|
migration. See the radeon_ttm.c file for an example of usage.
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|
</para>
|
|
<para>
|
|
The ttm_global_reference structure is made up of several fields:
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|
</para>
|
|
<programlisting>
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|
struct ttm_global_reference {
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enum ttm_global_types global_type;
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size_t size;
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void *object;
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int (*init) (struct ttm_global_reference *);
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void (*release) (struct ttm_global_reference *);
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|
};
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|
</programlisting>
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|
<para>
|
|
There should be one global reference structure for your memory
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|
manager as a whole, and there will be others for each object
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|
created by the memory manager at runtime. Your global TTM should
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|
have a type of TTM_GLOBAL_TTM_MEM. The size field for the global
|
|
object should be sizeof(struct ttm_mem_global), and the init and
|
|
release hooks should point at your driver-specific init and
|
|
release routines, which probably eventually call
|
|
ttm_mem_global_init and ttm_mem_global_release, respectively.
|
|
</para>
|
|
<para>
|
|
Once your global TTM accounting structure is set up and initialized
|
|
by calling ttm_global_item_ref() on it,
|
|
you need to create a buffer object TTM to
|
|
provide a pool for buffer object allocation by clients and the
|
|
kernel itself. The type of this object should be TTM_GLOBAL_TTM_BO,
|
|
and its size should be sizeof(struct ttm_bo_global). Again,
|
|
driver-specific init and release functions may be provided,
|
|
likely eventually calling ttm_bo_global_init() and
|
|
ttm_bo_global_release(), respectively. Also, like the previous
|
|
object, ttm_global_item_ref() is used to create an initial reference
|
|
count for the TTM, which will call your initialization function.
|
|
</para>
|
|
</sect3>
|
|
</sect2>
|
|
<sect2 id="drm-gem">
|
|
<title>The Graphics Execution Manager (GEM)</title>
|
|
<para>
|
|
The GEM design approach has resulted in a memory manager that doesn't
|
|
provide full coverage of all (or even all common) use cases in its
|
|
userspace or kernel API. GEM exposes a set of standard memory-related
|
|
operations to userspace and a set of helper functions to drivers, and let
|
|
drivers implement hardware-specific operations with their own private API.
|
|
</para>
|
|
<para>
|
|
The GEM userspace API is described in the
|
|
<ulink url="http://lwn.net/Articles/283798/"><citetitle>GEM - the Graphics
|
|
Execution Manager</citetitle></ulink> article on LWN. While slightly
|
|
outdated, the document provides a good overview of the GEM API principles.
|
|
Buffer allocation and read and write operations, described as part of the
|
|
common GEM API, are currently implemented using driver-specific ioctls.
|
|
</para>
|
|
<para>
|
|
GEM is data-agnostic. It manages abstract buffer objects without knowing
|
|
what individual buffers contain. APIs that require knowledge of buffer
|
|
contents or purpose, such as buffer allocation or synchronization
|
|
primitives, are thus outside of the scope of GEM and must be implemented
|
|
using driver-specific ioctls.
|
|
</para>
|
|
<para>
|
|
On a fundamental level, GEM involves several operations:
|
|
<itemizedlist>
|
|
<listitem>Memory allocation and freeing</listitem>
|
|
<listitem>Command execution</listitem>
|
|
<listitem>Aperture management at command execution time</listitem>
|
|
</itemizedlist>
|
|
Buffer object allocation is relatively straightforward and largely
|
|
provided by Linux's shmem layer, which provides memory to back each
|
|
object.
|
|
</para>
|
|
<para>
|
|
Device-specific operations, such as command execution, pinning, buffer
|
|
read & write, mapping, and domain ownership transfers are left to
|
|
driver-specific ioctls.
|
|
</para>
|
|
<sect3>
|
|
<title>GEM Initialization</title>
|
|
<para>
|
|
Drivers that use GEM must set the DRIVER_GEM bit in the struct
|
|
<structname>drm_driver</structname>
|
|
<structfield>driver_features</structfield> field. The DRM core will
|
|
then automatically initialize the GEM core before calling the
|
|
<methodname>load</methodname> operation. Behind the scene, this will
|
|
create a DRM Memory Manager object which provides an address space
|
|
pool for object allocation.
|
|
</para>
|
|
<para>
|
|
In a KMS configuration, drivers need to allocate and initialize a
|
|
command ring buffer following core GEM initialization if required by
|
|
the hardware. UMA devices usually have what is called a "stolen"
|
|
memory region, which provides space for the initial framebuffer and
|
|
large, contiguous memory regions required by the device. This space is
|
|
typically not managed by GEM, and must be initialized separately into
|
|
its own DRM MM object.
|
|
</para>
|
|
</sect3>
|
|
<sect3>
|
|
<title>GEM Objects Creation</title>
|
|
<para>
|
|
GEM splits creation of GEM objects and allocation of the memory that
|
|
backs them in two distinct operations.
|
|
</para>
|
|
<para>
|
|
GEM objects are represented by an instance of struct
|
|
<structname>drm_gem_object</structname>. Drivers usually need to extend
|
|
GEM objects with private information and thus create a driver-specific
|
|
GEM object structure type that embeds an instance of struct
|
|
<structname>drm_gem_object</structname>.
|
|
</para>
|
|
<para>
|
|
To create a GEM object, a driver allocates memory for an instance of its
|
|
specific GEM object type and initializes the embedded struct
|
|
<structname>drm_gem_object</structname> with a call to
|
|
<function>drm_gem_object_init</function>. The function takes a pointer to
|
|
the DRM device, a pointer to the GEM object and the buffer object size
|
|
in bytes.
|
|
</para>
|
|
<para>
|
|
GEM uses shmem to allocate anonymous pageable memory.
|
|
<function>drm_gem_object_init</function> will create an shmfs file of
|
|
the requested size and store it into the struct
|
|
<structname>drm_gem_object</structname> <structfield>filp</structfield>
|
|
field. The memory is used as either main storage for the object when the
|
|
graphics hardware uses system memory directly or as a backing store
|
|
otherwise.
|
|
</para>
|
|
<para>
|
|
Drivers are responsible for the actual physical pages allocation by
|
|
calling <function>shmem_read_mapping_page_gfp</function> for each page.
|
|
Note that they can decide to allocate pages when initializing the GEM
|
|
object, or to delay allocation until the memory is needed (for instance
|
|
when a page fault occurs as a result of a userspace memory access or
|
|
when the driver needs to start a DMA transfer involving the memory).
|
|
</para>
|
|
<para>
|
|
Anonymous pageable memory allocation is not always desired, for instance
|
|
when the hardware requires physically contiguous system memory as is
|
|
often the case in embedded devices. Drivers can create GEM objects with
|
|
no shmfs backing (called private GEM objects) by initializing them with
|
|
a call to <function>drm_gem_private_object_init</function> instead of
|
|
<function>drm_gem_object_init</function>. Storage for private GEM
|
|
objects must be managed by drivers.
|
|
</para>
|
|
<para>
|
|
Drivers that do not need to extend GEM objects with private information
|
|
can call the <function>drm_gem_object_alloc</function> function to
|
|
allocate and initialize a struct <structname>drm_gem_object</structname>
|
|
instance. The GEM core will call the optional driver
|
|
<methodname>gem_init_object</methodname> operation after initializing
|
|
the GEM object with <function>drm_gem_object_init</function>.
|
|
<synopsis>int (*gem_init_object) (struct drm_gem_object *obj);</synopsis>
|
|
</para>
|
|
<para>
|
|
No alloc-and-init function exists for private GEM objects.
|
|
</para>
|
|
</sect3>
|
|
<sect3>
|
|
<title>GEM Objects Lifetime</title>
|
|
<para>
|
|
All GEM objects are reference-counted by the GEM core. References can be
|
|
acquired and release by <function>calling drm_gem_object_reference</function>
|
|
and <function>drm_gem_object_unreference</function> respectively. The
|
|
caller must hold the <structname>drm_device</structname>
|
|
<structfield>struct_mutex</structfield> lock. As a convenience, GEM
|
|
provides the <function>drm_gem_object_reference_unlocked</function> and
|
|
<function>drm_gem_object_unreference_unlocked</function> functions that
|
|
can be called without holding the lock.
|
|
</para>
|
|
<para>
|
|
When the last reference to a GEM object is released the GEM core calls
|
|
the <structname>drm_driver</structname>
|
|
<methodname>gem_free_object</methodname> operation. That operation is
|
|
mandatory for GEM-enabled drivers and must free the GEM object and all
|
|
associated resources.
|
|
</para>
|
|
<para>
|
|
<synopsis>void (*gem_free_object) (struct drm_gem_object *obj);</synopsis>
|
|
Drivers are responsible for freeing all GEM object resources, including
|
|
the resources created by the GEM core. If an mmap offset has been
|
|
created for the object (in which case
|
|
<structname>drm_gem_object</structname>::<structfield>map_list</structfield>::<structfield>map</structfield>
|
|
is not NULL) it must be freed by a call to
|
|
<function>drm_gem_free_mmap_offset</function>. The shmfs backing store
|
|
must be released by calling <function>drm_gem_object_release</function>
|
|
(that function can safely be called if no shmfs backing store has been
|
|
created).
|
|
</para>
|
|
</sect3>
|
|
<sect3>
|
|
<title>GEM Objects Naming</title>
|
|
<para>
|
|
Communication between userspace and the kernel refers to GEM objects
|
|
using local handles, global names or, more recently, file descriptors.
|
|
All of those are 32-bit integer values; the usual Linux kernel limits
|
|
apply to the file descriptors.
|
|
</para>
|
|
<para>
|
|
GEM handles are local to a DRM file. Applications get a handle to a GEM
|
|
object through a driver-specific ioctl, and can use that handle to refer
|
|
to the GEM object in other standard or driver-specific ioctls. Closing a
|
|
DRM file handle frees all its GEM handles and dereferences the
|
|
associated GEM objects.
|
|
</para>
|
|
<para>
|
|
To create a handle for a GEM object drivers call
|
|
<function>drm_gem_handle_create</function>. The function takes a pointer
|
|
to the DRM file and the GEM object and returns a locally unique handle.
|
|
When the handle is no longer needed drivers delete it with a call to
|
|
<function>drm_gem_handle_delete</function>. Finally the GEM object
|
|
associated with a handle can be retrieved by a call to
|
|
<function>drm_gem_object_lookup</function>.
|
|
</para>
|
|
<para>
|
|
Handles don't take ownership of GEM objects, they only take a reference
|
|
to the object that will be dropped when the handle is destroyed. To
|
|
avoid leaking GEM objects, drivers must make sure they drop the
|
|
reference(s) they own (such as the initial reference taken at object
|
|
creation time) as appropriate, without any special consideration for the
|
|
handle. For example, in the particular case of combined GEM object and
|
|
handle creation in the implementation of the
|
|
<methodname>dumb_create</methodname> operation, drivers must drop the
|
|
initial reference to the GEM object before returning the handle.
|
|
</para>
|
|
<para>
|
|
GEM names are similar in purpose to handles but are not local to DRM
|
|
files. They can be passed between processes to reference a GEM object
|
|
globally. Names can't be used directly to refer to objects in the DRM
|
|
API, applications must convert handles to names and names to handles
|
|
using the DRM_IOCTL_GEM_FLINK and DRM_IOCTL_GEM_OPEN ioctls
|
|
respectively. The conversion is handled by the DRM core without any
|
|
driver-specific support.
|
|
</para>
|
|
<para>
|
|
Similar to global names, GEM file descriptors are also used to share GEM
|
|
objects across processes. They offer additional security: as file
|
|
descriptors must be explictly sent over UNIX domain sockets to be shared
|
|
between applications, they can't be guessed like the globally unique GEM
|
|
names.
|
|
</para>
|
|
<para>
|
|
Drivers that support GEM file descriptors, also known as the DRM PRIME
|
|
API, must set the DRIVER_PRIME bit in the struct
|
|
<structname>drm_driver</structname>
|
|
<structfield>driver_features</structfield> field, and implement the
|
|
<methodname>prime_handle_to_fd</methodname> and
|
|
<methodname>prime_fd_to_handle</methodname> operations.
|
|
</para>
|
|
<para>
|
|
<synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
|
|
struct drm_file *file_priv, uint32_t handle,
|
|
uint32_t flags, int *prime_fd);
|
|
int (*prime_fd_to_handle)(struct drm_device *dev,
|
|
struct drm_file *file_priv, int prime_fd,
|
|
uint32_t *handle);</synopsis>
|
|
Those two operations convert a handle to a PRIME file descriptor and
|
|
vice versa. Drivers must use the kernel dma-buf buffer sharing framework
|
|
to manage the PRIME file descriptors.
|
|
</para>
|
|
<para>
|
|
While non-GEM drivers must implement the operations themselves, GEM
|
|
drivers must use the <function>drm_gem_prime_handle_to_fd</function>
|
|
and <function>drm_gem_prime_fd_to_handle</function> helper functions.
|
|
Those helpers rely on the driver
|
|
<methodname>gem_prime_export</methodname> and
|
|
<methodname>gem_prime_import</methodname> operations to create a dma-buf
|
|
instance from a GEM object (dma-buf exporter role) and to create a GEM
|
|
object from a dma-buf instance (dma-buf importer role).
|
|
</para>
|
|
<para>
|
|
<synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
|
|
struct drm_gem_object *obj,
|
|
int flags);
|
|
struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
|
|
struct dma_buf *dma_buf);</synopsis>
|
|
These two operations are mandatory for GEM drivers that support DRM
|
|
PRIME.
|
|
</para>
|
|
</sect3>
|
|
<sect3 id="drm-gem-objects-mapping">
|
|
<title>GEM Objects Mapping</title>
|
|
<para>
|
|
Because mapping operations are fairly heavyweight GEM favours
|
|
read/write-like access to buffers, implemented through driver-specific
|
|
ioctls, over mapping buffers to userspace. However, when random access
|
|
to the buffer is needed (to perform software rendering for instance),
|
|
direct access to the object can be more efficient.
|
|
</para>
|
|
<para>
|
|
The mmap system call can't be used directly to map GEM objects, as they
|
|
don't have their own file handle. Two alternative methods currently
|
|
co-exist to map GEM objects to userspace. The first method uses a
|
|
driver-specific ioctl to perform the mapping operation, calling
|
|
<function>do_mmap</function> under the hood. This is often considered
|
|
dubious, seems to be discouraged for new GEM-enabled drivers, and will
|
|
thus not be described here.
|
|
</para>
|
|
<para>
|
|
The second method uses the mmap system call on the DRM file handle.
|
|
<synopsis>void *mmap(void *addr, size_t length, int prot, int flags, int fd,
|
|
off_t offset);</synopsis>
|
|
DRM identifies the GEM object to be mapped by a fake offset passed
|
|
through the mmap offset argument. Prior to being mapped, a GEM object
|
|
must thus be associated with a fake offset. To do so, drivers must call
|
|
<function>drm_gem_create_mmap_offset</function> on the object. The
|
|
function allocates a fake offset range from a pool and stores the
|
|
offset divided by PAGE_SIZE in
|
|
<literal>obj->map_list.hash.key</literal>. Care must be taken not to
|
|
call <function>drm_gem_create_mmap_offset</function> if a fake offset
|
|
has already been allocated for the object. This can be tested by
|
|
<literal>obj->map_list.map</literal> being non-NULL.
|
|
</para>
|
|
<para>
|
|
Once allocated, the fake offset value
|
|
(<literal>obj->map_list.hash.key << PAGE_SHIFT</literal>)
|
|
must be passed to the application in a driver-specific way and can then
|
|
be used as the mmap offset argument.
|
|
</para>
|
|
<para>
|
|
The GEM core provides a helper method <function>drm_gem_mmap</function>
|
|
to handle object mapping. The method can be set directly as the mmap
|
|
file operation handler. It will look up the GEM object based on the
|
|
offset value and set the VMA operations to the
|
|
<structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
|
|
field. Note that <function>drm_gem_mmap</function> doesn't map memory to
|
|
userspace, but relies on the driver-provided fault handler to map pages
|
|
individually.
|
|
</para>
|
|
<para>
|
|
To use <function>drm_gem_mmap</function>, drivers must fill the struct
|
|
<structname>drm_driver</structname> <structfield>gem_vm_ops</structfield>
|
|
field with a pointer to VM operations.
|
|
</para>
|
|
<para>
|
|
<synopsis>struct vm_operations_struct *gem_vm_ops
|
|
|
|
struct vm_operations_struct {
|
|
void (*open)(struct vm_area_struct * area);
|
|
void (*close)(struct vm_area_struct * area);
|
|
int (*fault)(struct vm_area_struct *vma, struct vm_fault *vmf);
|
|
};</synopsis>
|
|
</para>
|
|
<para>
|
|
The <methodname>open</methodname> and <methodname>close</methodname>
|
|
operations must update the GEM object reference count. Drivers can use
|
|
the <function>drm_gem_vm_open</function> and
|
|
<function>drm_gem_vm_close</function> helper functions directly as open
|
|
and close handlers.
|
|
</para>
|
|
<para>
|
|
The fault operation handler is responsible for mapping individual pages
|
|
to userspace when a page fault occurs. Depending on the memory
|
|
allocation scheme, drivers can allocate pages at fault time, or can
|
|
decide to allocate memory for the GEM object at the time the object is
|
|
created.
|
|
</para>
|
|
<para>
|
|
Drivers that want to map the GEM object upfront instead of handling page
|
|
faults can implement their own mmap file operation handler.
|
|
</para>
|
|
</sect3>
|
|
<sect3>
|
|
<title>Dumb GEM Objects</title>
|
|
<para>
|
|
The GEM API doesn't standardize GEM objects creation and leaves it to
|
|
driver-specific ioctls. While not an issue for full-fledged graphics
|
|
stacks that include device-specific userspace components (in libdrm for
|
|
instance), this limit makes DRM-based early boot graphics unnecessarily
|
|
complex.
|
|
</para>
|
|
<para>
|
|
Dumb GEM objects partly alleviate the problem by providing a standard
|
|
API to create dumb buffers suitable for scanout, which can then be used
|
|
to create KMS frame buffers.
|
|
</para>
|
|
<para>
|
|
To support dumb GEM objects drivers must implement the
|
|
<methodname>dumb_create</methodname>,
|
|
<methodname>dumb_destroy</methodname> and
|
|
<methodname>dumb_map_offset</methodname> operations.
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>int (*dumb_create)(struct drm_file *file_priv, struct drm_device *dev,
|
|
struct drm_mode_create_dumb *args);</synopsis>
|
|
<para>
|
|
The <methodname>dumb_create</methodname> operation creates a GEM
|
|
object suitable for scanout based on the width, height and depth
|
|
from the struct <structname>drm_mode_create_dumb</structname>
|
|
argument. It fills the argument's <structfield>handle</structfield>,
|
|
<structfield>pitch</structfield> and <structfield>size</structfield>
|
|
fields with a handle for the newly created GEM object and its line
|
|
pitch and size in bytes.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>int (*dumb_destroy)(struct drm_file *file_priv, struct drm_device *dev,
|
|
uint32_t handle);</synopsis>
|
|
<para>
|
|
The <methodname>dumb_destroy</methodname> operation destroys a dumb
|
|
GEM object created by <methodname>dumb_create</methodname>.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>int (*dumb_map_offset)(struct drm_file *file_priv, struct drm_device *dev,
|
|
uint32_t handle, uint64_t *offset);</synopsis>
|
|
<para>
|
|
The <methodname>dumb_map_offset</methodname> operation associates an
|
|
mmap fake offset with the GEM object given by the handle and returns
|
|
it. Drivers must use the
|
|
<function>drm_gem_create_mmap_offset</function> function to
|
|
associate the fake offset as described in
|
|
<xref linkend="drm-gem-objects-mapping"/>.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect3>
|
|
<sect3>
|
|
<title>Memory Coherency</title>
|
|
<para>
|
|
When mapped to the device or used in a command buffer, backing pages
|
|
for an object are flushed to memory and marked write combined so as to
|
|
be coherent with the GPU. Likewise, if the CPU accesses an object
|
|
after the GPU has finished rendering to the object, then the object
|
|
must be made coherent with the CPU's view of memory, usually involving
|
|
GPU cache flushing of various kinds. This core CPU<->GPU
|
|
coherency management is provided by a device-specific ioctl, which
|
|
evaluates an object's current domain and performs any necessary
|
|
flushing or synchronization to put the object into the desired
|
|
coherency domain (note that the object may be busy, i.e. an active
|
|
render target; in that case, setting the domain blocks the client and
|
|
waits for rendering to complete before performing any necessary
|
|
flushing operations).
|
|
</para>
|
|
</sect3>
|
|
<sect3>
|
|
<title>Command Execution</title>
|
|
<para>
|
|
Perhaps the most important GEM function for GPU devices is providing a
|
|
command execution interface to clients. Client programs construct
|
|
command buffers containing references to previously allocated memory
|
|
objects, and then submit them to GEM. At that point, GEM takes care to
|
|
bind all the objects into the GTT, execute the buffer, and provide
|
|
necessary synchronization between clients accessing the same buffers.
|
|
This often involves evicting some objects from the GTT and re-binding
|
|
others (a fairly expensive operation), and providing relocation
|
|
support which hides fixed GTT offsets from clients. Clients must take
|
|
care not to submit command buffers that reference more objects than
|
|
can fit in the GTT; otherwise, GEM will reject them and no rendering
|
|
will occur. Similarly, if several objects in the buffer require fence
|
|
registers to be allocated for correct rendering (e.g. 2D blits on
|
|
pre-965 chips), care must be taken not to require more fence registers
|
|
than are available to the client. Such resource management should be
|
|
abstracted from the client in libdrm.
|
|
</para>
|
|
</sect3>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<!-- Internals: mode setting -->
|
|
|
|
<sect1 id="drm-mode-setting">
|
|
<title>Mode Setting</title>
|
|
<para>
|
|
Drivers must initialize the mode setting core by calling
|
|
<function>drm_mode_config_init</function> on the DRM device. The function
|
|
initializes the <structname>drm_device</structname>
|
|
<structfield>mode_config</structfield> field and never fails. Once done,
|
|
mode configuration must be setup by initializing the following fields.
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>int min_width, min_height;
|
|
int max_width, max_height;</synopsis>
|
|
<para>
|
|
Minimum and maximum width and height of the frame buffers in pixel
|
|
units.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>struct drm_mode_config_funcs *funcs;</synopsis>
|
|
<para>Mode setting functions.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<sect2>
|
|
<title>Frame Buffer Creation</title>
|
|
<synopsis>struct drm_framebuffer *(*fb_create)(struct drm_device *dev,
|
|
struct drm_file *file_priv,
|
|
struct drm_mode_fb_cmd2 *mode_cmd);</synopsis>
|
|
<para>
|
|
Frame buffers are abstract memory objects that provide a source of
|
|
pixels to scanout to a CRTC. Applications explicitly request the
|
|
creation of frame buffers through the DRM_IOCTL_MODE_ADDFB(2) ioctls and
|
|
receive an opaque handle that can be passed to the KMS CRTC control,
|
|
plane configuration and page flip functions.
|
|
</para>
|
|
<para>
|
|
Frame buffers rely on the underneath memory manager for low-level memory
|
|
operations. When creating a frame buffer applications pass a memory
|
|
handle (or a list of memory handles for multi-planar formats) through
|
|
the <parameter>drm_mode_fb_cmd2</parameter> argument. This document
|
|
assumes that the driver uses GEM, those handles thus reference GEM
|
|
objects.
|
|
</para>
|
|
<para>
|
|
Drivers must first validate the requested frame buffer parameters passed
|
|
through the mode_cmd argument. In particular this is where invalid
|
|
sizes, pixel formats or pitches can be caught.
|
|
</para>
|
|
<para>
|
|
If the parameters are deemed valid, drivers then create, initialize and
|
|
return an instance of struct <structname>drm_framebuffer</structname>.
|
|
If desired the instance can be embedded in a larger driver-specific
|
|
structure. The new instance is initialized with a call to
|
|
<function>drm_framebuffer_init</function> which takes a pointer to DRM
|
|
frame buffer operations (struct
|
|
<structname>drm_framebuffer_funcs</structname>). Frame buffer operations are
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>int (*create_handle)(struct drm_framebuffer *fb,
|
|
struct drm_file *file_priv, unsigned int *handle);</synopsis>
|
|
<para>
|
|
Create a handle to the frame buffer underlying memory object. If
|
|
the frame buffer uses a multi-plane format, the handle will
|
|
reference the memory object associated with the first plane.
|
|
</para>
|
|
<para>
|
|
Drivers call <function>drm_gem_handle_create</function> to create
|
|
the handle.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>void (*destroy)(struct drm_framebuffer *framebuffer);</synopsis>
|
|
<para>
|
|
Destroy the frame buffer object and frees all associated
|
|
resources. Drivers must call
|
|
<function>drm_framebuffer_cleanup</function> to free resources
|
|
allocated by the DRM core for the frame buffer object, and must
|
|
make sure to unreference all memory objects associated with the
|
|
frame buffer. Handles created by the
|
|
<methodname>create_handle</methodname> operation are released by
|
|
the DRM core.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>int (*dirty)(struct drm_framebuffer *framebuffer,
|
|
struct drm_file *file_priv, unsigned flags, unsigned color,
|
|
struct drm_clip_rect *clips, unsigned num_clips);</synopsis>
|
|
<para>
|
|
This optional operation notifies the driver that a region of the
|
|
frame buffer has changed in response to a DRM_IOCTL_MODE_DIRTYFB
|
|
ioctl call.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
<para>
|
|
After initializing the <structname>drm_framebuffer</structname>
|
|
instance drivers must fill its <structfield>width</structfield>,
|
|
<structfield>height</structfield>, <structfield>pitches</structfield>,
|
|
<structfield>offsets</structfield>, <structfield>depth</structfield>,
|
|
<structfield>bits_per_pixel</structfield> and
|
|
<structfield>pixel_format</structfield> fields from the values passed
|
|
through the <parameter>drm_mode_fb_cmd2</parameter> argument. They
|
|
should call the <function>drm_helper_mode_fill_fb_struct</function>
|
|
helper function to do so.
|
|
</para>
|
|
</sect2>
|
|
<sect2>
|
|
<title>Output Polling</title>
|
|
<synopsis>void (*output_poll_changed)(struct drm_device *dev);</synopsis>
|
|
<para>
|
|
This operation notifies the driver that the status of one or more
|
|
connectors has changed. Drivers that use the fb helper can just call the
|
|
<function>drm_fb_helper_hotplug_event</function> function to handle this
|
|
operation.
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<!-- Internals: kms initialization and cleanup -->
|
|
|
|
<sect1 id="drm-kms-init">
|
|
<title>KMS Initialization and Cleanup</title>
|
|
<para>
|
|
A KMS device is abstracted and exposed as a set of planes, CRTCs, encoders
|
|
and connectors. KMS drivers must thus create and initialize all those
|
|
objects at load time after initializing mode setting.
|
|
</para>
|
|
<sect2>
|
|
<title>CRTCs (struct <structname>drm_crtc</structname>)</title>
|
|
<para>
|
|
A CRTC is an abstraction representing a part of the chip that contains a
|
|
pointer to a scanout buffer. Therefore, the number of CRTCs available
|
|
determines how many independent scanout buffers can be active at any
|
|
given time. The CRTC structure contains several fields to support this:
|
|
a pointer to some video memory (abstracted as a frame buffer object), a
|
|
display mode, and an (x, y) offset into the video memory to support
|
|
panning or configurations where one piece of video memory spans multiple
|
|
CRTCs.
|
|
</para>
|
|
<sect3>
|
|
<title>CRTC Initialization</title>
|
|
<para>
|
|
A KMS device must create and register at least one struct
|
|
<structname>drm_crtc</structname> instance. The instance is allocated
|
|
and zeroed by the driver, possibly as part of a larger structure, and
|
|
registered with a call to <function>drm_crtc_init</function> with a
|
|
pointer to CRTC functions.
|
|
</para>
|
|
</sect3>
|
|
<sect3>
|
|
<title>CRTC Operations</title>
|
|
<sect4>
|
|
<title>Set Configuration</title>
|
|
<synopsis>int (*set_config)(struct drm_mode_set *set);</synopsis>
|
|
<para>
|
|
Apply a new CRTC configuration to the device. The configuration
|
|
specifies a CRTC, a frame buffer to scan out from, a (x,y) position in
|
|
the frame buffer, a display mode and an array of connectors to drive
|
|
with the CRTC if possible.
|
|
</para>
|
|
<para>
|
|
If the frame buffer specified in the configuration is NULL, the driver
|
|
must detach all encoders connected to the CRTC and all connectors
|
|
attached to those encoders and disable them.
|
|
</para>
|
|
<para>
|
|
This operation is called with the mode config lock held.
|
|
</para>
|
|
<note><para>
|
|
FIXME: How should set_config interact with DPMS? If the CRTC is
|
|
suspended, should it be resumed?
|
|
</para></note>
|
|
</sect4>
|
|
<sect4>
|
|
<title>Page Flipping</title>
|
|
<synopsis>int (*page_flip)(struct drm_crtc *crtc, struct drm_framebuffer *fb,
|
|
struct drm_pending_vblank_event *event);</synopsis>
|
|
<para>
|
|
Schedule a page flip to the given frame buffer for the CRTC. This
|
|
operation is called with the mode config mutex held.
|
|
</para>
|
|
<para>
|
|
Page flipping is a synchronization mechanism that replaces the frame
|
|
buffer being scanned out by the CRTC with a new frame buffer during
|
|
vertical blanking, avoiding tearing. When an application requests a page
|
|
flip the DRM core verifies that the new frame buffer is large enough to
|
|
be scanned out by the CRTC in the currently configured mode and then
|
|
calls the CRTC <methodname>page_flip</methodname> operation with a
|
|
pointer to the new frame buffer.
|
|
</para>
|
|
<para>
|
|
The <methodname>page_flip</methodname> operation schedules a page flip.
|
|
Once any pending rendering targetting the new frame buffer has
|
|
completed, the CRTC will be reprogrammed to display that frame buffer
|
|
after the next vertical refresh. The operation must return immediately
|
|
without waiting for rendering or page flip to complete and must block
|
|
any new rendering to the frame buffer until the page flip completes.
|
|
</para>
|
|
<para>
|
|
If a page flip is already pending, the
|
|
<methodname>page_flip</methodname> operation must return
|
|
-<errorname>EBUSY</errorname>.
|
|
</para>
|
|
<para>
|
|
To synchronize page flip to vertical blanking the driver will likely
|
|
need to enable vertical blanking interrupts. It should call
|
|
<function>drm_vblank_get</function> for that purpose, and call
|
|
<function>drm_vblank_put</function> after the page flip completes.
|
|
</para>
|
|
<para>
|
|
If the application has requested to be notified when page flip completes
|
|
the <methodname>page_flip</methodname> operation will be called with a
|
|
non-NULL <parameter>event</parameter> argument pointing to a
|
|
<structname>drm_pending_vblank_event</structname> instance. Upon page
|
|
flip completion the driver must fill the
|
|
<parameter>event</parameter>::<structfield>event</structfield>
|
|
<structfield>sequence</structfield>, <structfield>tv_sec</structfield>
|
|
and <structfield>tv_usec</structfield> fields with the associated
|
|
vertical blanking count and timestamp, add the event to the
|
|
<parameter>drm_file</parameter> list of events to be signaled, and wake
|
|
up any waiting process. This can be performed with
|
|
<programlisting><![CDATA[
|
|
struct timeval now;
|
|
|
|
event->event.sequence = drm_vblank_count_and_time(..., &now);
|
|
event->event.tv_sec = now.tv_sec;
|
|
event->event.tv_usec = now.tv_usec;
|
|
|
|
spin_lock_irqsave(&dev->event_lock, flags);
|
|
list_add_tail(&event->base.link, &event->base.file_priv->event_list);
|
|
wake_up_interruptible(&event->base.file_priv->event_wait);
|
|
spin_unlock_irqrestore(&dev->event_lock, flags);
|
|
]]></programlisting>
|
|
</para>
|
|
<note><para>
|
|
FIXME: Could drivers that don't need to wait for rendering to complete
|
|
just add the event to <literal>dev->vblank_event_list</literal> and
|
|
let the DRM core handle everything, as for "normal" vertical blanking
|
|
events?
|
|
</para></note>
|
|
<para>
|
|
While waiting for the page flip to complete, the
|
|
<literal>event->base.link</literal> list head can be used freely by
|
|
the driver to store the pending event in a driver-specific list.
|
|
</para>
|
|
<para>
|
|
If the file handle is closed before the event is signaled, drivers must
|
|
take care to destroy the event in their
|
|
<methodname>preclose</methodname> operation (and, if needed, call
|
|
<function>drm_vblank_put</function>).
|
|
</para>
|
|
</sect4>
|
|
<sect4>
|
|
<title>Miscellaneous</title>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>void (*gamma_set)(struct drm_crtc *crtc, u16 *r, u16 *g, u16 *b,
|
|
uint32_t start, uint32_t size);</synopsis>
|
|
<para>
|
|
Apply a gamma table to the device. The operation is optional.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>void (*destroy)(struct drm_crtc *crtc);</synopsis>
|
|
<para>
|
|
Destroy the CRTC when not needed anymore. See
|
|
<xref linkend="drm-kms-init"/>.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect4>
|
|
</sect3>
|
|
</sect2>
|
|
<sect2>
|
|
<title>Planes (struct <structname>drm_plane</structname>)</title>
|
|
<para>
|
|
A plane represents an image source that can be blended with or overlayed
|
|
on top of a CRTC during the scanout process. Planes are associated with
|
|
a frame buffer to crop a portion of the image memory (source) and
|
|
optionally scale it to a destination size. The result is then blended
|
|
with or overlayed on top of a CRTC.
|
|
</para>
|
|
<sect3>
|
|
<title>Plane Initialization</title>
|
|
<para>
|
|
Planes are optional. To create a plane, a KMS drivers allocates and
|
|
zeroes an instances of struct <structname>drm_plane</structname>
|
|
(possibly as part of a larger structure) and registers it with a call
|
|
to <function>drm_plane_init</function>. The function takes a bitmask
|
|
of the CRTCs that can be associated with the plane, a pointer to the
|
|
plane functions and a list of format supported formats.
|
|
</para>
|
|
</sect3>
|
|
<sect3>
|
|
<title>Plane Operations</title>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>int (*update_plane)(struct drm_plane *plane, struct drm_crtc *crtc,
|
|
struct drm_framebuffer *fb, int crtc_x, int crtc_y,
|
|
unsigned int crtc_w, unsigned int crtc_h,
|
|
uint32_t src_x, uint32_t src_y,
|
|
uint32_t src_w, uint32_t src_h);</synopsis>
|
|
<para>
|
|
Enable and configure the plane to use the given CRTC and frame buffer.
|
|
</para>
|
|
<para>
|
|
The source rectangle in frame buffer memory coordinates is given by
|
|
the <parameter>src_x</parameter>, <parameter>src_y</parameter>,
|
|
<parameter>src_w</parameter> and <parameter>src_h</parameter>
|
|
parameters (as 16.16 fixed point values). Devices that don't support
|
|
subpixel plane coordinates can ignore the fractional part.
|
|
</para>
|
|
<para>
|
|
The destination rectangle in CRTC coordinates is given by the
|
|
<parameter>crtc_x</parameter>, <parameter>crtc_y</parameter>,
|
|
<parameter>crtc_w</parameter> and <parameter>crtc_h</parameter>
|
|
parameters (as integer values). Devices scale the source rectangle to
|
|
the destination rectangle. If scaling is not supported, and the source
|
|
rectangle size doesn't match the destination rectangle size, the
|
|
driver must return a -<errorname>EINVAL</errorname> error.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>int (*disable_plane)(struct drm_plane *plane);</synopsis>
|
|
<para>
|
|
Disable the plane. The DRM core calls this method in response to a
|
|
DRM_IOCTL_MODE_SETPLANE ioctl call with the frame buffer ID set to 0.
|
|
Disabled planes must not be processed by the CRTC.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>void (*destroy)(struct drm_plane *plane);</synopsis>
|
|
<para>
|
|
Destroy the plane when not needed anymore. See
|
|
<xref linkend="drm-kms-init"/>.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect3>
|
|
</sect2>
|
|
<sect2>
|
|
<title>Encoders (struct <structname>drm_encoder</structname>)</title>
|
|
<para>
|
|
An encoder takes pixel data from a CRTC and converts it to a format
|
|
suitable for any attached connectors. On some devices, it may be
|
|
possible to have a CRTC send data to more than one encoder. In that
|
|
case, both encoders would receive data from the same scanout buffer,
|
|
resulting in a "cloned" display configuration across the connectors
|
|
attached to each encoder.
|
|
</para>
|
|
<sect3>
|
|
<title>Encoder Initialization</title>
|
|
<para>
|
|
As for CRTCs, a KMS driver must create, initialize and register at
|
|
least one struct <structname>drm_encoder</structname> instance. The
|
|
instance is allocated and zeroed by the driver, possibly as part of a
|
|
larger structure.
|
|
</para>
|
|
<para>
|
|
Drivers must initialize the struct <structname>drm_encoder</structname>
|
|
<structfield>possible_crtcs</structfield> and
|
|
<structfield>possible_clones</structfield> fields before registering the
|
|
encoder. Both fields are bitmasks of respectively the CRTCs that the
|
|
encoder can be connected to, and sibling encoders candidate for cloning.
|
|
</para>
|
|
<para>
|
|
After being initialized, the encoder must be registered with a call to
|
|
<function>drm_encoder_init</function>. The function takes a pointer to
|
|
the encoder functions and an encoder type. Supported types are
|
|
<itemizedlist>
|
|
<listitem>
|
|
DRM_MODE_ENCODER_DAC for VGA and analog on DVI-I/DVI-A
|
|
</listitem>
|
|
<listitem>
|
|
DRM_MODE_ENCODER_TMDS for DVI, HDMI and (embedded) DisplayPort
|
|
</listitem>
|
|
<listitem>
|
|
DRM_MODE_ENCODER_LVDS for display panels
|
|
</listitem>
|
|
<listitem>
|
|
DRM_MODE_ENCODER_TVDAC for TV output (Composite, S-Video, Component,
|
|
SCART)
|
|
</listitem>
|
|
<listitem>
|
|
DRM_MODE_ENCODER_VIRTUAL for virtual machine displays
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
<para>
|
|
Encoders must be attached to a CRTC to be used. DRM drivers leave
|
|
encoders unattached at initialization time. Applications (or the fbdev
|
|
compatibility layer when implemented) are responsible for attaching the
|
|
encoders they want to use to a CRTC.
|
|
</para>
|
|
</sect3>
|
|
<sect3>
|
|
<title>Encoder Operations</title>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>void (*destroy)(struct drm_encoder *encoder);</synopsis>
|
|
<para>
|
|
Called to destroy the encoder when not needed anymore. See
|
|
<xref linkend="drm-kms-init"/>.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect3>
|
|
</sect2>
|
|
<sect2>
|
|
<title>Connectors (struct <structname>drm_connector</structname>)</title>
|
|
<para>
|
|
A connector is the final destination for pixel data on a device, and
|
|
usually connects directly to an external display device like a monitor
|
|
or laptop panel. A connector can only be attached to one encoder at a
|
|
time. The connector is also the structure where information about the
|
|
attached display is kept, so it contains fields for display data, EDID
|
|
data, DPMS & connection status, and information about modes
|
|
supported on the attached displays.
|
|
</para>
|
|
<sect3>
|
|
<title>Connector Initialization</title>
|
|
<para>
|
|
Finally a KMS driver must create, initialize, register and attach at
|
|
least one struct <structname>drm_connector</structname> instance. The
|
|
instance is created as other KMS objects and initialized by setting the
|
|
following fields.
|
|
</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><structfield>interlace_allowed</structfield></term>
|
|
<listitem><para>
|
|
Whether the connector can handle interlaced modes.
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><structfield>doublescan_allowed</structfield></term>
|
|
<listitem><para>
|
|
Whether the connector can handle doublescan.
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><structfield>display_info
|
|
</structfield></term>
|
|
<listitem><para>
|
|
Display information is filled from EDID information when a display
|
|
is detected. For non hot-pluggable displays such as flat panels in
|
|
embedded systems, the driver should initialize the
|
|
<structfield>display_info</structfield>.<structfield>width_mm</structfield>
|
|
and
|
|
<structfield>display_info</structfield>.<structfield>height_mm</structfield>
|
|
fields with the physical size of the display.
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term id="drm-kms-connector-polled"><structfield>polled</structfield></term>
|
|
<listitem><para>
|
|
Connector polling mode, a combination of
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>DRM_CONNECTOR_POLL_HPD</term>
|
|
<listitem><para>
|
|
The connector generates hotplug events and doesn't need to be
|
|
periodically polled. The CONNECT and DISCONNECT flags must not
|
|
be set together with the HPD flag.
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_CONNECTOR_POLL_CONNECT</term>
|
|
<listitem><para>
|
|
Periodically poll the connector for connection.
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_CONNECTOR_POLL_DISCONNECT</term>
|
|
<listitem><para>
|
|
Periodically poll the connector for disconnection.
|
|
</para></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
Set to 0 for connectors that don't support connection status
|
|
discovery.
|
|
</para></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>
|
|
The connector is then registered with a call to
|
|
<function>drm_connector_init</function> with a pointer to the connector
|
|
functions and a connector type, and exposed through sysfs with a call to
|
|
<function>drm_sysfs_connector_add</function>.
|
|
</para>
|
|
<para>
|
|
Supported connector types are
|
|
<itemizedlist>
|
|
<listitem>DRM_MODE_CONNECTOR_VGA</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_DVII</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_DVID</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_DVIA</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_Composite</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_SVIDEO</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_LVDS</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_Component</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_9PinDIN</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_DisplayPort</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_HDMIA</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_HDMIB</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_TV</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_eDP</listitem>
|
|
<listitem>DRM_MODE_CONNECTOR_VIRTUAL</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
<para>
|
|
Connectors must be attached to an encoder to be used. For devices that
|
|
map connectors to encoders 1:1, the connector should be attached at
|
|
initialization time with a call to
|
|
<function>drm_mode_connector_attach_encoder</function>. The driver must
|
|
also set the <structname>drm_connector</structname>
|
|
<structfield>encoder</structfield> field to point to the attached
|
|
encoder.
|
|
</para>
|
|
<para>
|
|
Finally, drivers must initialize the connectors state change detection
|
|
with a call to <function>drm_kms_helper_poll_init</function>. If at
|
|
least one connector is pollable but can't generate hotplug interrupts
|
|
(indicated by the DRM_CONNECTOR_POLL_CONNECT and
|
|
DRM_CONNECTOR_POLL_DISCONNECT connector flags), a delayed work will
|
|
automatically be queued to periodically poll for changes. Connectors
|
|
that can generate hotplug interrupts must be marked with the
|
|
DRM_CONNECTOR_POLL_HPD flag instead, and their interrupt handler must
|
|
call <function>drm_helper_hpd_irq_event</function>. The function will
|
|
queue a delayed work to check the state of all connectors, but no
|
|
periodic polling will be done.
|
|
</para>
|
|
</sect3>
|
|
<sect3>
|
|
<title>Connector Operations</title>
|
|
<note><para>
|
|
Unless otherwise state, all operations are mandatory.
|
|
</para></note>
|
|
<sect4>
|
|
<title>DPMS</title>
|
|
<synopsis>void (*dpms)(struct drm_connector *connector, int mode);</synopsis>
|
|
<para>
|
|
The DPMS operation sets the power state of a connector. The mode
|
|
argument is one of
|
|
<itemizedlist>
|
|
<listitem><para>DRM_MODE_DPMS_ON</para></listitem>
|
|
<listitem><para>DRM_MODE_DPMS_STANDBY</para></listitem>
|
|
<listitem><para>DRM_MODE_DPMS_SUSPEND</para></listitem>
|
|
<listitem><para>DRM_MODE_DPMS_OFF</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
<para>
|
|
In all but DPMS_ON mode the encoder to which the connector is attached
|
|
should put the display in low-power mode by driving its signals
|
|
appropriately. If more than one connector is attached to the encoder
|
|
care should be taken not to change the power state of other displays as
|
|
a side effect. Low-power mode should be propagated to the encoders and
|
|
CRTCs when all related connectors are put in low-power mode.
|
|
</para>
|
|
</sect4>
|
|
<sect4>
|
|
<title>Modes</title>
|
|
<synopsis>int (*fill_modes)(struct drm_connector *connector, uint32_t max_width,
|
|
uint32_t max_height);</synopsis>
|
|
<para>
|
|
Fill the mode list with all supported modes for the connector. If the
|
|
<parameter>max_width</parameter> and <parameter>max_height</parameter>
|
|
arguments are non-zero, the implementation must ignore all modes wider
|
|
than <parameter>max_width</parameter> or higher than
|
|
<parameter>max_height</parameter>.
|
|
</para>
|
|
<para>
|
|
The connector must also fill in this operation its
|
|
<structfield>display_info</structfield>
|
|
<structfield>width_mm</structfield> and
|
|
<structfield>height_mm</structfield> fields with the connected display
|
|
physical size in millimeters. The fields should be set to 0 if the value
|
|
isn't known or is not applicable (for instance for projector devices).
|
|
</para>
|
|
</sect4>
|
|
<sect4>
|
|
<title>Connection Status</title>
|
|
<para>
|
|
The connection status is updated through polling or hotplug events when
|
|
supported (see <xref linkend="drm-kms-connector-polled"/>). The status
|
|
value is reported to userspace through ioctls and must not be used
|
|
inside the driver, as it only gets initialized by a call to
|
|
<function>drm_mode_getconnector</function> from userspace.
|
|
</para>
|
|
<synopsis>enum drm_connector_status (*detect)(struct drm_connector *connector,
|
|
bool force);</synopsis>
|
|
<para>
|
|
Check to see if anything is attached to the connector. The
|
|
<parameter>force</parameter> parameter is set to false whilst polling or
|
|
to true when checking the connector due to user request.
|
|
<parameter>force</parameter> can be used by the driver to avoid
|
|
expensive, destructive operations during automated probing.
|
|
</para>
|
|
<para>
|
|
Return connector_status_connected if something is connected to the
|
|
connector, connector_status_disconnected if nothing is connected and
|
|
connector_status_unknown if the connection state isn't known.
|
|
</para>
|
|
<para>
|
|
Drivers should only return connector_status_connected if the connection
|
|
status has really been probed as connected. Connectors that can't detect
|
|
the connection status, or failed connection status probes, should return
|
|
connector_status_unknown.
|
|
</para>
|
|
</sect4>
|
|
<sect4>
|
|
<title>Miscellaneous</title>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>void (*destroy)(struct drm_connector *connector);</synopsis>
|
|
<para>
|
|
Destroy the connector when not needed anymore. See
|
|
<xref linkend="drm-kms-init"/>.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect4>
|
|
</sect3>
|
|
</sect2>
|
|
<sect2>
|
|
<title>Cleanup</title>
|
|
<para>
|
|
The DRM core manages its objects' lifetime. When an object is not needed
|
|
anymore the core calls its destroy function, which must clean up and
|
|
free every resource allocated for the object. Every
|
|
<function>drm_*_init</function> call must be matched with a
|
|
corresponding <function>drm_*_cleanup</function> call to cleanup CRTCs
|
|
(<function>drm_crtc_cleanup</function>), planes
|
|
(<function>drm_plane_cleanup</function>), encoders
|
|
(<function>drm_encoder_cleanup</function>) and connectors
|
|
(<function>drm_connector_cleanup</function>). Furthermore, connectors
|
|
that have been added to sysfs must be removed by a call to
|
|
<function>drm_sysfs_connector_remove</function> before calling
|
|
<function>drm_connector_cleanup</function>.
|
|
</para>
|
|
<para>
|
|
Connectors state change detection must be cleanup up with a call to
|
|
<function>drm_kms_helper_poll_fini</function>.
|
|
</para>
|
|
</sect2>
|
|
<sect2>
|
|
<title>Output discovery and initialization example</title>
|
|
<programlisting><![CDATA[
|
|
void intel_crt_init(struct drm_device *dev)
|
|
{
|
|
struct drm_connector *connector;
|
|
struct intel_output *intel_output;
|
|
|
|
intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
|
|
if (!intel_output)
|
|
return;
|
|
|
|
connector = &intel_output->base;
|
|
drm_connector_init(dev, &intel_output->base,
|
|
&intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
|
|
|
|
drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
|
|
DRM_MODE_ENCODER_DAC);
|
|
|
|
drm_mode_connector_attach_encoder(&intel_output->base,
|
|
&intel_output->enc);
|
|
|
|
/* Set up the DDC bus. */
|
|
intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
|
|
if (!intel_output->ddc_bus) {
|
|
dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
|
|
"failed.\n");
|
|
return;
|
|
}
|
|
|
|
intel_output->type = INTEL_OUTPUT_ANALOG;
|
|
connector->interlace_allowed = 0;
|
|
connector->doublescan_allowed = 0;
|
|
|
|
drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
|
|
drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
|
|
|
|
drm_sysfs_connector_add(connector);
|
|
}]]></programlisting>
|
|
<para>
|
|
In the example above (taken from the i915 driver), a CRTC, connector and
|
|
encoder combination is created. A device-specific i2c bus is also
|
|
created for fetching EDID data and performing monitor detection. Once
|
|
the process is complete, the new connector is registered with sysfs to
|
|
make its properties available to applications.
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<!-- Internals: mid-layer helper functions -->
|
|
|
|
<sect1>
|
|
<title>Mid-layer Helper Functions</title>
|
|
<para>
|
|
The CRTC, encoder and connector functions provided by the drivers
|
|
implement the DRM API. They're called by the DRM core and ioctl handlers
|
|
to handle device state changes and configuration request. As implementing
|
|
those functions often requires logic not specific to drivers, mid-layer
|
|
helper functions are available to avoid duplicating boilerplate code.
|
|
</para>
|
|
<para>
|
|
The DRM core contains one mid-layer implementation. The mid-layer provides
|
|
implementations of several CRTC, encoder and connector functions (called
|
|
from the top of the mid-layer) that pre-process requests and call
|
|
lower-level functions provided by the driver (at the bottom of the
|
|
mid-layer). For instance, the
|
|
<function>drm_crtc_helper_set_config</function> function can be used to
|
|
fill the struct <structname>drm_crtc_funcs</structname>
|
|
<structfield>set_config</structfield> field. When called, it will split
|
|
the <methodname>set_config</methodname> operation in smaller, simpler
|
|
operations and call the driver to handle them.
|
|
</para>
|
|
<para>
|
|
To use the mid-layer, drivers call <function>drm_crtc_helper_add</function>,
|
|
<function>drm_encoder_helper_add</function> and
|
|
<function>drm_connector_helper_add</function> functions to install their
|
|
mid-layer bottom operations handlers, and fill the
|
|
<structname>drm_crtc_funcs</structname>,
|
|
<structname>drm_encoder_funcs</structname> and
|
|
<structname>drm_connector_funcs</structname> structures with pointers to
|
|
the mid-layer top API functions. Installing the mid-layer bottom operation
|
|
handlers is best done right after registering the corresponding KMS object.
|
|
</para>
|
|
<para>
|
|
The mid-layer is not split between CRTC, encoder and connector operations.
|
|
To use it, a driver must provide bottom functions for all of the three KMS
|
|
entities.
|
|
</para>
|
|
<sect2>
|
|
<title>Helper Functions</title>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>int drm_crtc_helper_set_config(struct drm_mode_set *set);</synopsis>
|
|
<para>
|
|
The <function>drm_crtc_helper_set_config</function> helper function
|
|
is a CRTC <methodname>set_config</methodname> implementation. It
|
|
first tries to locate the best encoder for each connector by calling
|
|
the connector <methodname>best_encoder</methodname> helper
|
|
operation.
|
|
</para>
|
|
<para>
|
|
After locating the appropriate encoders, the helper function will
|
|
call the <methodname>mode_fixup</methodname> encoder and CRTC helper
|
|
operations to adjust the requested mode, or reject it completely in
|
|
which case an error will be returned to the application. If the new
|
|
configuration after mode adjustment is identical to the current
|
|
configuration the helper function will return without performing any
|
|
other operation.
|
|
</para>
|
|
<para>
|
|
If the adjusted mode is identical to the current mode but changes to
|
|
the frame buffer need to be applied, the
|
|
<function>drm_crtc_helper_set_config</function> function will call
|
|
the CRTC <methodname>mode_set_base</methodname> helper operation. If
|
|
the adjusted mode differs from the current mode, or if the
|
|
<methodname>mode_set_base</methodname> helper operation is not
|
|
provided, the helper function performs a full mode set sequence by
|
|
calling the <methodname>prepare</methodname>,
|
|
<methodname>mode_set</methodname> and
|
|
<methodname>commit</methodname> CRTC and encoder helper operations,
|
|
in that order.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>void drm_helper_connector_dpms(struct drm_connector *connector, int mode);</synopsis>
|
|
<para>
|
|
The <function>drm_helper_connector_dpms</function> helper function
|
|
is a connector <methodname>dpms</methodname> implementation that
|
|
tracks power state of connectors. To use the function, drivers must
|
|
provide <methodname>dpms</methodname> helper operations for CRTCs
|
|
and encoders to apply the DPMS state to the device.
|
|
</para>
|
|
<para>
|
|
The mid-layer doesn't track the power state of CRTCs and encoders.
|
|
The <methodname>dpms</methodname> helper operations can thus be
|
|
called with a mode identical to the currently active mode.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
|
|
uint32_t maxX, uint32_t maxY);</synopsis>
|
|
<para>
|
|
The <function>drm_helper_probe_single_connector_modes</function> helper
|
|
function is a connector <methodname>fill_modes</methodname>
|
|
implementation that updates the connection status for the connector
|
|
and then retrieves a list of modes by calling the connector
|
|
<methodname>get_modes</methodname> helper operation.
|
|
</para>
|
|
<para>
|
|
The function filters out modes larger than
|
|
<parameter>max_width</parameter> and <parameter>max_height</parameter>
|
|
if specified. It then calls the connector
|
|
<methodname>mode_valid</methodname> helper operation for each mode in
|
|
the probed list to check whether the mode is valid for the connector.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect2>
|
|
<sect2>
|
|
<title>CRTC Helper Operations</title>
|
|
<itemizedlist>
|
|
<listitem id="drm-helper-crtc-mode-fixup">
|
|
<synopsis>bool (*mode_fixup)(struct drm_crtc *crtc,
|
|
const struct drm_display_mode *mode,
|
|
struct drm_display_mode *adjusted_mode);</synopsis>
|
|
<para>
|
|
Let CRTCs adjust the requested mode or reject it completely. This
|
|
operation returns true if the mode is accepted (possibly after being
|
|
adjusted) or false if it is rejected.
|
|
</para>
|
|
<para>
|
|
The <methodname>mode_fixup</methodname> operation should reject the
|
|
mode if it can't reasonably use it. The definition of "reasonable"
|
|
is currently fuzzy in this context. One possible behaviour would be
|
|
to set the adjusted mode to the panel timings when a fixed-mode
|
|
panel is used with hardware capable of scaling. Another behaviour
|
|
would be to accept any input mode and adjust it to the closest mode
|
|
supported by the hardware (FIXME: This needs to be clarified).
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>int (*mode_set_base)(struct drm_crtc *crtc, int x, int y,
|
|
struct drm_framebuffer *old_fb)</synopsis>
|
|
<para>
|
|
Move the CRTC on the current frame buffer (stored in
|
|
<literal>crtc->fb</literal>) to position (x,y). Any of the frame
|
|
buffer, x position or y position may have been modified.
|
|
</para>
|
|
<para>
|
|
This helper operation is optional. If not provided, the
|
|
<function>drm_crtc_helper_set_config</function> function will fall
|
|
back to the <methodname>mode_set</methodname> helper operation.
|
|
</para>
|
|
<note><para>
|
|
FIXME: Why are x and y passed as arguments, as they can be accessed
|
|
through <literal>crtc->x</literal> and
|
|
<literal>crtc->y</literal>?
|
|
</para></note>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>void (*prepare)(struct drm_crtc *crtc);</synopsis>
|
|
<para>
|
|
Prepare the CRTC for mode setting. This operation is called after
|
|
validating the requested mode. Drivers use it to perform
|
|
device-specific operations required before setting the new mode.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>int (*mode_set)(struct drm_crtc *crtc, struct drm_display_mode *mode,
|
|
struct drm_display_mode *adjusted_mode, int x, int y,
|
|
struct drm_framebuffer *old_fb);</synopsis>
|
|
<para>
|
|
Set a new mode, position and frame buffer. Depending on the device
|
|
requirements, the mode can be stored internally by the driver and
|
|
applied in the <methodname>commit</methodname> operation, or
|
|
programmed to the hardware immediately.
|
|
</para>
|
|
<para>
|
|
The <methodname>mode_set</methodname> operation returns 0 on success
|
|
or a negative error code if an error occurs.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>void (*commit)(struct drm_crtc *crtc);</synopsis>
|
|
<para>
|
|
Commit a mode. This operation is called after setting the new mode.
|
|
Upon return the device must use the new mode and be fully
|
|
operational.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect2>
|
|
<sect2>
|
|
<title>Encoder Helper Operations</title>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>bool (*mode_fixup)(struct drm_encoder *encoder,
|
|
const struct drm_display_mode *mode,
|
|
struct drm_display_mode *adjusted_mode);</synopsis>
|
|
<note><para>
|
|
FIXME: The mode argument be const, but the i915 driver modifies
|
|
mode->clock in <function>intel_dp_mode_fixup</function>.
|
|
</para></note>
|
|
<para>
|
|
Let encoders adjust the requested mode or reject it completely. This
|
|
operation returns true if the mode is accepted (possibly after being
|
|
adjusted) or false if it is rejected. See the
|
|
<link linkend="drm-helper-crtc-mode-fixup">mode_fixup CRTC helper
|
|
operation</link> for an explanation of the allowed adjustments.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>void (*prepare)(struct drm_encoder *encoder);</synopsis>
|
|
<para>
|
|
Prepare the encoder for mode setting. This operation is called after
|
|
validating the requested mode. Drivers use it to perform
|
|
device-specific operations required before setting the new mode.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>void (*mode_set)(struct drm_encoder *encoder,
|
|
struct drm_display_mode *mode,
|
|
struct drm_display_mode *adjusted_mode);</synopsis>
|
|
<para>
|
|
Set a new mode. Depending on the device requirements, the mode can
|
|
be stored internally by the driver and applied in the
|
|
<methodname>commit</methodname> operation, or programmed to the
|
|
hardware immediately.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>void (*commit)(struct drm_encoder *encoder);</synopsis>
|
|
<para>
|
|
Commit a mode. This operation is called after setting the new mode.
|
|
Upon return the device must use the new mode and be fully
|
|
operational.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect2>
|
|
<sect2>
|
|
<title>Connector Helper Operations</title>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>struct drm_encoder *(*best_encoder)(struct drm_connector *connector);</synopsis>
|
|
<para>
|
|
Return a pointer to the best encoder for the connecter. Device that
|
|
map connectors to encoders 1:1 simply return the pointer to the
|
|
associated encoder. This operation is mandatory.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>int (*get_modes)(struct drm_connector *connector);</synopsis>
|
|
<para>
|
|
Fill the connector's <structfield>probed_modes</structfield> list
|
|
by parsing EDID data with <function>drm_add_edid_modes</function> or
|
|
calling <function>drm_mode_probed_add</function> directly for every
|
|
supported mode and return the number of modes it has detected. This
|
|
operation is mandatory.
|
|
</para>
|
|
<para>
|
|
When adding modes manually the driver creates each mode with a call to
|
|
<function>drm_mode_create</function> and must fill the following fields.
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>__u32 type;</synopsis>
|
|
<para>
|
|
Mode type bitmask, a combination of
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>DRM_MODE_TYPE_BUILTIN</term>
|
|
<listitem><para>not used?</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_TYPE_CLOCK_C</term>
|
|
<listitem><para>not used?</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_TYPE_CRTC_C</term>
|
|
<listitem><para>not used?</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>
|
|
DRM_MODE_TYPE_PREFERRED - The preferred mode for the connector
|
|
</term>
|
|
<listitem>
|
|
<para>not used?</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_TYPE_DEFAULT</term>
|
|
<listitem><para>not used?</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_TYPE_USERDEF</term>
|
|
<listitem><para>not used?</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_TYPE_DRIVER</term>
|
|
<listitem>
|
|
<para>
|
|
The mode has been created by the driver (as opposed to
|
|
to user-created modes).
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
Drivers must set the DRM_MODE_TYPE_DRIVER bit for all modes they
|
|
create, and set the DRM_MODE_TYPE_PREFERRED bit for the preferred
|
|
mode.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>__u32 clock;</synopsis>
|
|
<para>Pixel clock frequency in kHz unit</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>__u16 hdisplay, hsync_start, hsync_end, htotal;
|
|
__u16 vdisplay, vsync_start, vsync_end, vtotal;</synopsis>
|
|
<para>Horizontal and vertical timing information</para>
|
|
<screen><![CDATA[
|
|
Active Front Sync Back
|
|
Region Porch Porch
|
|
<-----------------------><----------------><-------------><-------------->
|
|
|
|
//////////////////////|
|
|
////////////////////// |
|
|
////////////////////// |.................. ................
|
|
_______________
|
|
|
|
<----- [hv]display ----->
|
|
<------------- [hv]sync_start ------------>
|
|
<--------------------- [hv]sync_end --------------------->
|
|
<-------------------------------- [hv]total ----------------------------->
|
|
]]></screen>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>__u16 hskew;
|
|
__u16 vscan;</synopsis>
|
|
<para>Unknown</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>__u32 flags;</synopsis>
|
|
<para>
|
|
Mode flags, a combination of
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_PHSYNC</term>
|
|
<listitem><para>
|
|
Horizontal sync is active high
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_NHSYNC</term>
|
|
<listitem><para>
|
|
Horizontal sync is active low
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_PVSYNC</term>
|
|
<listitem><para>
|
|
Vertical sync is active high
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_NVSYNC</term>
|
|
<listitem><para>
|
|
Vertical sync is active low
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_INTERLACE</term>
|
|
<listitem><para>
|
|
Mode is interlaced
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_DBLSCAN</term>
|
|
<listitem><para>
|
|
Mode uses doublescan
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_CSYNC</term>
|
|
<listitem><para>
|
|
Mode uses composite sync
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_PCSYNC</term>
|
|
<listitem><para>
|
|
Composite sync is active high
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_NCSYNC</term>
|
|
<listitem><para>
|
|
Composite sync is active low
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_HSKEW</term>
|
|
<listitem><para>
|
|
hskew provided (not used?)
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_BCAST</term>
|
|
<listitem><para>
|
|
not used?
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_PIXMUX</term>
|
|
<listitem><para>
|
|
not used?
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_DBLCLK</term>
|
|
<listitem><para>
|
|
not used?
|
|
</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_MODE_FLAG_CLKDIV2</term>
|
|
<listitem><para>
|
|
?
|
|
</para></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</para>
|
|
<para>
|
|
Note that modes marked with the INTERLACE or DBLSCAN flags will be
|
|
filtered out by
|
|
<function>drm_helper_probe_single_connector_modes</function> if
|
|
the connector's <structfield>interlace_allowed</structfield> or
|
|
<structfield>doublescan_allowed</structfield> field is set to 0.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>char name[DRM_DISPLAY_MODE_LEN];</synopsis>
|
|
<para>
|
|
Mode name. The driver must call
|
|
<function>drm_mode_set_name</function> to fill the mode name from
|
|
<structfield>hdisplay</structfield>,
|
|
<structfield>vdisplay</structfield> and interlace flag after
|
|
filling the corresponding fields.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
<para>
|
|
The <structfield>vrefresh</structfield> value is computed by
|
|
<function>drm_helper_probe_single_connector_modes</function>.
|
|
</para>
|
|
<para>
|
|
When parsing EDID data, <function>drm_add_edid_modes</function> fill the
|
|
connector <structfield>display_info</structfield>
|
|
<structfield>width_mm</structfield> and
|
|
<structfield>height_mm</structfield> fields. When creating modes
|
|
manually the <methodname>get_modes</methodname> helper operation must
|
|
set the <structfield>display_info</structfield>
|
|
<structfield>width_mm</structfield> and
|
|
<structfield>height_mm</structfield> fields if they haven't been set
|
|
already (for instance at initilization time when a fixed-size panel is
|
|
attached to the connector). The mode <structfield>width_mm</structfield>
|
|
and <structfield>height_mm</structfield> fields are only used internally
|
|
during EDID parsing and should not be set when creating modes manually.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>int (*mode_valid)(struct drm_connector *connector,
|
|
struct drm_display_mode *mode);</synopsis>
|
|
<para>
|
|
Verify whether a mode is valid for the connector. Return MODE_OK for
|
|
supported modes and one of the enum drm_mode_status values (MODE_*)
|
|
for unsupported modes. This operation is mandatory.
|
|
</para>
|
|
<para>
|
|
As the mode rejection reason is currently not used beside for
|
|
immediately removing the unsupported mode, an implementation can
|
|
return MODE_BAD regardless of the exact reason why the mode is not
|
|
valid.
|
|
</para>
|
|
<note><para>
|
|
Note that the <methodname>mode_valid</methodname> helper operation is
|
|
only called for modes detected by the device, and
|
|
<emphasis>not</emphasis> for modes set by the user through the CRTC
|
|
<methodname>set_config</methodname> operation.
|
|
</para></note>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<!-- Internals: vertical blanking -->
|
|
|
|
<sect1 id="drm-vertical-blank">
|
|
<title>Vertical Blanking</title>
|
|
<para>
|
|
Vertical blanking plays a major role in graphics rendering. To achieve
|
|
tear-free display, users must synchronize page flips and/or rendering to
|
|
vertical blanking. The DRM API offers ioctls to perform page flips
|
|
synchronized to vertical blanking and wait for vertical blanking.
|
|
</para>
|
|
<para>
|
|
The DRM core handles most of the vertical blanking management logic, which
|
|
involves filtering out spurious interrupts, keeping race-free blanking
|
|
counters, coping with counter wrap-around and resets and keeping use
|
|
counts. It relies on the driver to generate vertical blanking interrupts
|
|
and optionally provide a hardware vertical blanking counter. Drivers must
|
|
implement the following operations.
|
|
</para>
|
|
<itemizedlist>
|
|
<listitem>
|
|
<synopsis>int (*enable_vblank) (struct drm_device *dev, int crtc);
|
|
void (*disable_vblank) (struct drm_device *dev, int crtc);</synopsis>
|
|
<para>
|
|
Enable or disable vertical blanking interrupts for the given CRTC.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<synopsis>u32 (*get_vblank_counter) (struct drm_device *dev, int crtc);</synopsis>
|
|
<para>
|
|
Retrieve the value of the vertical blanking counter for the given
|
|
CRTC. If the hardware maintains a vertical blanking counter its value
|
|
should be returned. Otherwise drivers can use the
|
|
<function>drm_vblank_count</function> helper function to handle this
|
|
operation.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
<para>
|
|
Drivers must initialize the vertical blanking handling core with a call to
|
|
<function>drm_vblank_init</function> in their
|
|
<methodname>load</methodname> operation. The function will set the struct
|
|
<structname>drm_device</structname>
|
|
<structfield>vblank_disable_allowed</structfield> field to 0. This will
|
|
keep vertical blanking interrupts enabled permanently until the first mode
|
|
set operation, where <structfield>vblank_disable_allowed</structfield> is
|
|
set to 1. The reason behind this is not clear. Drivers can set the field
|
|
to 1 after <function>calling drm_vblank_init</function> to make vertical
|
|
blanking interrupts dynamically managed from the beginning.
|
|
</para>
|
|
<para>
|
|
Vertical blanking interrupts can be enabled by the DRM core or by drivers
|
|
themselves (for instance to handle page flipping operations). The DRM core
|
|
maintains a vertical blanking use count to ensure that the interrupts are
|
|
not disabled while a user still needs them. To increment the use count,
|
|
drivers call <function>drm_vblank_get</function>. Upon return vertical
|
|
blanking interrupts are guaranteed to be enabled.
|
|
</para>
|
|
<para>
|
|
To decrement the use count drivers call
|
|
<function>drm_vblank_put</function>. Only when the use count drops to zero
|
|
will the DRM core disable the vertical blanking interrupts after a delay
|
|
by scheduling a timer. The delay is accessible through the vblankoffdelay
|
|
module parameter or the <varname>drm_vblank_offdelay</varname> global
|
|
variable and expressed in milliseconds. Its default value is 5000 ms.
|
|
</para>
|
|
<para>
|
|
When a vertical blanking interrupt occurs drivers only need to call the
|
|
<function>drm_handle_vblank</function> function to account for the
|
|
interrupt.
|
|
</para>
|
|
<para>
|
|
Resources allocated by <function>drm_vblank_init</function> must be freed
|
|
with a call to <function>drm_vblank_cleanup</function> in the driver
|
|
<methodname>unload</methodname> operation handler.
|
|
</para>
|
|
</sect1>
|
|
|
|
<!-- Internals: open/close, file operations and ioctls -->
|
|
|
|
<sect1>
|
|
<title>Open/Close, File Operations and IOCTLs</title>
|
|
<sect2>
|
|
<title>Open and Close</title>
|
|
<synopsis>int (*firstopen) (struct drm_device *);
|
|
void (*lastclose) (struct drm_device *);
|
|
int (*open) (struct drm_device *, struct drm_file *);
|
|
void (*preclose) (struct drm_device *, struct drm_file *);
|
|
void (*postclose) (struct drm_device *, struct drm_file *);</synopsis>
|
|
<abstract>Open and close handlers. None of those methods are mandatory.
|
|
</abstract>
|
|
<para>
|
|
The <methodname>firstopen</methodname> method is called by the DRM core
|
|
when an application opens a device that has no other opened file handle.
|
|
Similarly the <methodname>lastclose</methodname> method is called when
|
|
the last application holding a file handle opened on the device closes
|
|
it. Both methods are mostly used for UMS (User Mode Setting) drivers to
|
|
acquire and release device resources which should be done in the
|
|
<methodname>load</methodname> and <methodname>unload</methodname>
|
|
methods for KMS drivers.
|
|
</para>
|
|
<para>
|
|
Note that the <methodname>lastclose</methodname> method is also called
|
|
at module unload time or, for hot-pluggable devices, when the device is
|
|
unplugged. The <methodname>firstopen</methodname> and
|
|
<methodname>lastclose</methodname> calls can thus be unbalanced.
|
|
</para>
|
|
<para>
|
|
The <methodname>open</methodname> method is called every time the device
|
|
is opened by an application. Drivers can allocate per-file private data
|
|
in this method and store them in the struct
|
|
<structname>drm_file</structname> <structfield>driver_priv</structfield>
|
|
field. Note that the <methodname>open</methodname> method is called
|
|
before <methodname>firstopen</methodname>.
|
|
</para>
|
|
<para>
|
|
The close operation is split into <methodname>preclose</methodname> and
|
|
<methodname>postclose</methodname> methods. Drivers must stop and
|
|
cleanup all per-file operations in the <methodname>preclose</methodname>
|
|
method. For instance pending vertical blanking and page flip events must
|
|
be cancelled. No per-file operation is allowed on the file handle after
|
|
returning from the <methodname>preclose</methodname> method.
|
|
</para>
|
|
<para>
|
|
Finally the <methodname>postclose</methodname> method is called as the
|
|
last step of the close operation, right before calling the
|
|
<methodname>lastclose</methodname> method if no other open file handle
|
|
exists for the device. Drivers that have allocated per-file private data
|
|
in the <methodname>open</methodname> method should free it here.
|
|
</para>
|
|
<para>
|
|
The <methodname>lastclose</methodname> method should restore CRTC and
|
|
plane properties to default value, so that a subsequent open of the
|
|
device will not inherit state from the previous user.
|
|
</para>
|
|
</sect2>
|
|
<sect2>
|
|
<title>File Operations</title>
|
|
<synopsis>const struct file_operations *fops</synopsis>
|
|
<abstract>File operations for the DRM device node.</abstract>
|
|
<para>
|
|
Drivers must define the file operations structure that forms the DRM
|
|
userspace API entry point, even though most of those operations are
|
|
implemented in the DRM core. The <methodname>open</methodname>,
|
|
<methodname>release</methodname> and <methodname>ioctl</methodname>
|
|
operations are handled by
|
|
<programlisting>
|
|
.owner = THIS_MODULE,
|
|
.open = drm_open,
|
|
.release = drm_release,
|
|
.unlocked_ioctl = drm_ioctl,
|
|
#ifdef CONFIG_COMPAT
|
|
.compat_ioctl = drm_compat_ioctl,
|
|
#endif
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
Drivers that implement private ioctls that requires 32/64bit
|
|
compatibility support must provide their own
|
|
<methodname>compat_ioctl</methodname> handler that processes private
|
|
ioctls and calls <function>drm_compat_ioctl</function> for core ioctls.
|
|
</para>
|
|
<para>
|
|
The <methodname>read</methodname> and <methodname>poll</methodname>
|
|
operations provide support for reading DRM events and polling them. They
|
|
are implemented by
|
|
<programlisting>
|
|
.poll = drm_poll,
|
|
.read = drm_read,
|
|
.fasync = drm_fasync,
|
|
.llseek = no_llseek,
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
The memory mapping implementation varies depending on how the driver
|
|
manages memory. Pre-GEM drivers will use <function>drm_mmap</function>,
|
|
while GEM-aware drivers will use <function>drm_gem_mmap</function>. See
|
|
<xref linkend="drm-gem"/>.
|
|
<programlisting>
|
|
.mmap = drm_gem_mmap,
|
|
</programlisting>
|
|
</para>
|
|
<para>
|
|
No other file operation is supported by the DRM API.
|
|
</para>
|
|
</sect2>
|
|
<sect2>
|
|
<title>IOCTLs</title>
|
|
<synopsis>struct drm_ioctl_desc *ioctls;
|
|
int num_ioctls;</synopsis>
|
|
<abstract>Driver-specific ioctls descriptors table.</abstract>
|
|
<para>
|
|
Driver-specific ioctls numbers start at DRM_COMMAND_BASE. The ioctls
|
|
descriptors table is indexed by the ioctl number offset from the base
|
|
value. Drivers can use the DRM_IOCTL_DEF_DRV() macro to initialize the
|
|
table entries.
|
|
</para>
|
|
<para>
|
|
<programlisting>DRM_IOCTL_DEF_DRV(ioctl, func, flags)</programlisting>
|
|
<para>
|
|
<parameter>ioctl</parameter> is the ioctl name. Drivers must define
|
|
the DRM_##ioctl and DRM_IOCTL_##ioctl macros to the ioctl number
|
|
offset from DRM_COMMAND_BASE and the ioctl number respectively. The
|
|
first macro is private to the device while the second must be exposed
|
|
to userspace in a public header.
|
|
</para>
|
|
<para>
|
|
<parameter>func</parameter> is a pointer to the ioctl handler function
|
|
compatible with the <type>drm_ioctl_t</type> type.
|
|
<programlisting>typedef int drm_ioctl_t(struct drm_device *dev, void *data,
|
|
struct drm_file *file_priv);</programlisting>
|
|
</para>
|
|
<para>
|
|
<parameter>flags</parameter> is a bitmask combination of the following
|
|
values. It restricts how the ioctl is allowed to be called.
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
DRM_AUTH - Only authenticated callers allowed
|
|
</para></listitem>
|
|
<listitem><para>
|
|
DRM_MASTER - The ioctl can only be called on the master file
|
|
handle
|
|
</para></listitem>
|
|
<listitem><para>
|
|
DRM_ROOT_ONLY - Only callers with the SYSADMIN capability allowed
|
|
</para></listitem>
|
|
<listitem><para>
|
|
DRM_CONTROL_ALLOW - The ioctl can only be called on a control
|
|
device
|
|
</para></listitem>
|
|
<listitem><para>
|
|
DRM_UNLOCKED - The ioctl handler will be called without locking
|
|
the DRM global mutex
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
<sect1>
|
|
<title>Command submission & fencing</title>
|
|
<para>
|
|
This should cover a few device-specific command submission
|
|
implementations.
|
|
</para>
|
|
</sect1>
|
|
|
|
<!-- Internals: suspend/resume -->
|
|
|
|
<sect1>
|
|
<title>Suspend/Resume</title>
|
|
<para>
|
|
The DRM core provides some suspend/resume code, but drivers wanting full
|
|
suspend/resume support should provide save() and restore() functions.
|
|
These are called at suspend, hibernate, or resume time, and should perform
|
|
any state save or restore required by your device across suspend or
|
|
hibernate states.
|
|
</para>
|
|
<synopsis>int (*suspend) (struct drm_device *, pm_message_t state);
|
|
int (*resume) (struct drm_device *);</synopsis>
|
|
<para>
|
|
Those are legacy suspend and resume methods. New driver should use the
|
|
power management interface provided by their bus type (usually through
|
|
the struct <structname>device_driver</structname> dev_pm_ops) and set
|
|
these methods to NULL.
|
|
</para>
|
|
</sect1>
|
|
|
|
<sect1>
|
|
<title>DMA services</title>
|
|
<para>
|
|
This should cover how DMA mapping etc. is supported by the core.
|
|
These functions are deprecated and should not be used.
|
|
</para>
|
|
</sect1>
|
|
</chapter>
|
|
|
|
<!-- TODO
|
|
|
|
- Add a glossary
|
|
- Document the struct_mutex catch-all lock
|
|
- Document connector properties
|
|
|
|
- Why is the load method optional?
|
|
- What are drivers supposed to set the initial display state to, and how?
|
|
Connector's DPMS states are not initialized and are thus equal to
|
|
DRM_MODE_DPMS_ON. The fbcon compatibility layer calls
|
|
drm_helper_disable_unused_functions(), which disables unused encoders and
|
|
CRTCs, but doesn't touch the connectors' DPMS state, and
|
|
drm_helper_connector_dpms() in reaction to fbdev blanking events. Do drivers
|
|
that don't implement (or just don't use) fbcon compatibility need to call
|
|
those functions themselves?
|
|
- KMS drivers must call drm_vblank_pre_modeset() and drm_vblank_post_modeset()
|
|
around mode setting. Should this be done in the DRM core?
|
|
- vblank_disable_allowed is set to 1 in the first drm_vblank_post_modeset()
|
|
call and never set back to 0. It seems to be safe to permanently set it to 1
|
|
in drm_vblank_init() for KMS driver, and it might be safe for UMS drivers as
|
|
well. This should be investigated.
|
|
- crtc and connector .save and .restore operations are only used internally in
|
|
drivers, should they be removed from the core?
|
|
- encoder mid-layer .save and .restore operations are only used internally in
|
|
drivers, should they be removed from the core?
|
|
- encoder mid-layer .detect operation is only used internally in drivers,
|
|
should it be removed from the core?
|
|
-->
|
|
|
|
<!-- External interfaces -->
|
|
|
|
<chapter id="drmExternals">
|
|
<title>Userland interfaces</title>
|
|
<para>
|
|
The DRM core exports several interfaces to applications,
|
|
generally intended to be used through corresponding libdrm
|
|
wrapper functions. In addition, drivers export device-specific
|
|
interfaces for use by userspace drivers & device-aware
|
|
applications through ioctls and sysfs files.
|
|
</para>
|
|
<para>
|
|
External interfaces include: memory mapping, context management,
|
|
DMA operations, AGP management, vblank control, fence
|
|
management, memory management, and output management.
|
|
</para>
|
|
<para>
|
|
Cover generic ioctls and sysfs layout here. We only need high-level
|
|
info, since man pages should cover the rest.
|
|
</para>
|
|
|
|
<!-- External: vblank handling -->
|
|
|
|
<sect1>
|
|
<title>VBlank event handling</title>
|
|
<para>
|
|
The DRM core exposes two vertical blank related ioctls:
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term>DRM_IOCTL_WAIT_VBLANK</term>
|
|
<listitem>
|
|
<para>
|
|
This takes a struct drm_wait_vblank structure as its argument,
|
|
and it is used to block or request a signal when a specified
|
|
vblank event occurs.
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term>DRM_IOCTL_MODESET_CTL</term>
|
|
<listitem>
|
|
<para>
|
|
This should be called by application level drivers before and
|
|
after mode setting, since on many devices the vertical blank
|
|
counter is reset at that time. Internally, the DRM snapshots
|
|
the last vblank count when the ioctl is called with the
|
|
_DRM_PRE_MODESET command, so that the counter won't go backwards
|
|
(which is dealt with when _DRM_POST_MODESET is used).
|
|
</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<!--!Edrivers/char/drm/drm_irq.c-->
|
|
</para>
|
|
</sect1>
|
|
|
|
</chapter>
|
|
|
|
<!-- API reference -->
|
|
|
|
<appendix id="drmDriverApi">
|
|
<title>DRM Driver API</title>
|
|
<para>
|
|
Include auto-generated API reference here (need to reference it
|
|
from paragraphs above too).
|
|
</para>
|
|
</appendix>
|
|
|
|
</book>
|