1
linux/Documentation/core-api/genericirq.rst
Linus Torvalds ac7473a179 Updates for the interrupt subsystem:
- Core:
 
     - Provide a new mechanism to create interrupt domains. The existing
       interfaces have already too many parameters and it's a pain to expand
       any of this for new required functionality.
 
       The new function takes a pointer to a data structure as argument. The
       data structure combines all existing parameters and allows for easy
       extension.
 
       The first extension for this is to handle the instantiation of
       generic interrupt chips at the core level and to allow drivers to
       provide extra init/exit callbacks.
 
       This is necessary to do the full interrupt chip initialization before
       the new domain is published, so that concurrent usage sites won't see
       a half initialized interrupt domain. Similar problems exist on
       teardown.
 
       This has turned out to be a real problem due to the deferred and
       parallel probing which was added in recent years.
 
       Handling this at the core level allows to remove quite some accrued
       boilerplate code in existing drivers and avoids horrible workarounds
       at the driver level.
 
     - The usual small improvements all over the place
 
   - Drivers
 
     - Add support for LAN966x OIC and RZ/Five SoC
 
     - Split the STM ExtI driver into a microcontroller and a SMP version to
       allow building the latter as a module for multi-platform kernels.
 
     - Enable MSI support for Armada 370XP on platforms which do not support
       IPIs.
 
     - The usual small fixes and enhancements all over the place.
 -----BEGIN PGP SIGNATURE-----
 
 iQJHBAABCgAxFiEEQp8+kY+LLUocC4bMphj1TA10mKEFAmaVJbUTHHRnbHhAbGlu
 dXRyb25peC5kZQAKCRCmGPVMDXSYoXTuD/9Tc9BhY5CW7HQkdPQu2Db1O+esprkQ
 Uo9lMpTTpPiy9btg4LONzLf4mjbufZpyKBxkRWoZFO0Zj5q4UE9NZYh7EcxrF5Tl
 CIFJmyteLsYuOyCmPrtSDSovonXjQKYBE3u2LVJNNkwEkhYbYW9sqIKeT8nneLv6
 53gd28ESFUEUjHNTblw/eXviweyUKSXc0qyg+3hgZQPMoh9RkdkEPvyaw9Y/s5Ce
 FelLLxzMqX86dR2TJMLqiaGiMpUu/kl+Yz2m5c77TwA2D68qjhHywbtKtlH7b3C6
 LMHu2dMrrKSJrLL8roVIYJdHAd1TKWVdnYhqv9WBHFTu1sDuztpR44mewbo8exUU
 L2RgVSGYNmeFC3p4wztWYSQfIVa9uOg7+TnJJdh7G0jLIeKM/TbufWqDAJAuoVPL
 QhGbZ5xNbZJZ8bvhhItjxpRN/kPs44p3mUGyRJBQzm+mDN118bqfmQzhLcwRbfE2
 smp73SQzg9alG2rGdNVEqkKmp8zhg2Crx2VCeVdgbeOxWQRet9zLWcp4FfCEUE9e
 eK3iEi8z+rmwafaf3rsxYdrdIRLaUmcni0v7R/16cJH/Cs7bU3Re8XyGhevo3lsO
 pJiP5wZDxbckwXNpLm3S/qPDW7vSCnuFPF7QmOvC3a70PsD+E4NKUgiwJuHtn/ZV
 pFBKzbQgCsowQA==
 =QCRH
 -----END PGP SIGNATURE-----

Merge tag 'irq-core-2024-07-15' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull interrupt subsystem updates from Thomas Gleixner:
 "Core:

   - Provide a new mechanism to create interrupt domains. The existing
     interfaces have already too many parameters and it's a pain to
     expand any of this for new required functionality.

     The new function takes a pointer to a data structure as argument.
     The data structure combines all existing parameters and allows for
     easy extension.

     The first extension for this is to handle the instantiation of
     generic interrupt chips at the core level and to allow drivers to
     provide extra init/exit callbacks.

     This is necessary to do the full interrupt chip initialization
     before the new domain is published, so that concurrent usage sites
     won't see a half initialized interrupt domain. Similar problems
     exist on teardown.

     This has turned out to be a real problem due to the deferred and
     parallel probing which was added in recent years.

     Handling this at the core level allows to remove quite some accrued
     boilerplate code in existing drivers and avoids horrible
     workarounds at the driver level.

   - The usual small improvements all over the place

  Drivers:

   - Add support for LAN966x OIC and RZ/Five SoC

   - Split the STM ExtI driver into a microcontroller and a SMP version
     to allow building the latter as a module for multi-platform
     kernels

   - Enable MSI support for Armada 370XP on platforms which do not
     support IPIs

   - The usual small fixes and enhancements all over the place"

* tag 'irq-core-2024-07-15' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (59 commits)
  irqdomain: Fix the kernel-doc and plug it into Documentation
  genirq: Set IRQF_COND_ONESHOT in request_irq()
  irqchip/imx-irqsteer: Handle runtime power management correctly
  irqchip/gic-v3: Pass #redistributor-regions to gic_of_setup_kvm_info()
  irqchip/bcm2835: Enable SKIP_SET_WAKE and MASK_ON_SUSPEND
  irqchip/gic-v4: Make sure a VPE is locked when VMAPP is issued
  irqchip/gic-v4: Substitute vmovp_lock for a per-VM lock
  irqchip/gic-v4: Always configure affinity on VPE activation
  Revert "irqchip/dw-apb-ictl: Support building as module"
  Revert "Loongarch: Support loongarch avec"
  arm64: Kconfig: Allow build irq-stm32mp-exti driver as module
  ARM: stm32: Allow build irq-stm32mp-exti driver as module
  irqchip/stm32mp-exti: Allow building as module
  irqchip/stm32mp-exti: Rename internal symbols
  irqchip/stm32-exti: Split MCU and MPU code
  arm64: Kconfig: Select STM32MP_EXTI on STM32 platforms
  ARM: stm32: Use different EXTI driver on ARMv7m and ARMv7a
  irqchip/stm32-exti: Add CONFIG_STM32MP_EXTI
  irqchip/dw-apb-ictl: Support building as module
  irqchip/riscv-aplic: Simplify the initialization code
  ...
2024-07-22 13:52:05 -07:00

447 lines
12 KiB
ReStructuredText

.. include:: <isonum.txt>
==========================
Linux generic IRQ handling
==========================
:Copyright: |copy| 2005-2010: Thomas Gleixner
:Copyright: |copy| 2005-2006: Ingo Molnar
Introduction
============
The generic interrupt handling layer is designed to provide a complete
abstraction of interrupt handling for device drivers. It is able to
handle all the different types of interrupt controller hardware. Device
drivers use generic API functions to request, enable, disable and free
interrupts. The drivers do not have to know anything about interrupt
hardware details, so they can be used on different platforms without
code changes.
This documentation is provided to developers who want to implement an
interrupt subsystem based for their architecture, with the help of the
generic IRQ handling layer.
Rationale
=========
The original implementation of interrupt handling in Linux uses the
__do_IRQ() super-handler, which is able to deal with every type of
interrupt logic.
Originally, Russell King identified different types of handlers to build
a quite universal set for the ARM interrupt handler implementation in
Linux 2.5/2.6. He distinguished between:
- Level type
- Edge type
- Simple type
During the implementation we identified another type:
- Fast EOI type
In the SMP world of the __do_IRQ() super-handler another type was
identified:
- Per CPU type
This split implementation of high-level IRQ handlers allows us to
optimize the flow of the interrupt handling for each specific interrupt
type. This reduces complexity in that particular code path and allows
the optimized handling of a given type.
The original general IRQ implementation used hw_interrupt_type
structures and their ``->ack``, ``->end`` [etc.] callbacks to differentiate
the flow control in the super-handler. This leads to a mix of flow logic
and low-level hardware logic, and it also leads to unnecessary code
duplication: for example in i386, there is an ``ioapic_level_irq`` and an
``ioapic_edge_irq`` IRQ-type which share many of the low-level details but
have different flow handling.
A more natural abstraction is the clean separation of the 'irq flow' and
the 'chip details'.
Analysing a couple of architecture's IRQ subsystem implementations
reveals that most of them can use a generic set of 'irq flow' methods
and only need to add the chip-level specific code. The separation is
also valuable for (sub)architectures which need specific quirks in the
IRQ flow itself but not in the chip details - and thus provides a more
transparent IRQ subsystem design.
Each interrupt descriptor is assigned its own high-level flow handler,
which is normally one of the generic implementations. (This high-level
flow handler implementation also makes it simple to provide
demultiplexing handlers which can be found in embedded platforms on
various architectures.)
The separation makes the generic interrupt handling layer more flexible
and extensible. For example, an (sub)architecture can use a generic
IRQ-flow implementation for 'level type' interrupts and add a
(sub)architecture specific 'edge type' implementation.
To make the transition to the new model easier and prevent the breakage
of existing implementations, the __do_IRQ() super-handler is still
available. This leads to a kind of duality for the time being. Over time
the new model should be used in more and more architectures, as it
enables smaller and cleaner IRQ subsystems. It's deprecated for three
years now and about to be removed.
Known Bugs And Assumptions
==========================
None (knock on wood).
Abstraction layers
==================
There are three main levels of abstraction in the interrupt code:
1. High-level driver API
2. High-level IRQ flow handlers
3. Chip-level hardware encapsulation
Interrupt control flow
----------------------
Each interrupt is described by an interrupt descriptor structure
irq_desc. The interrupt is referenced by an 'unsigned int' numeric
value which selects the corresponding interrupt description structure in
the descriptor structures array. The descriptor structure contains
status information and pointers to the interrupt flow method and the
interrupt chip structure which are assigned to this interrupt.
Whenever an interrupt triggers, the low-level architecture code calls
into the generic interrupt code by calling desc->handle_irq(). This
high-level IRQ handling function only uses desc->irq_data.chip
primitives referenced by the assigned chip descriptor structure.
High-level Driver API
---------------------
The high-level Driver API consists of following functions:
- request_irq()
- request_threaded_irq()
- free_irq()
- disable_irq()
- enable_irq()
- disable_irq_nosync() (SMP only)
- synchronize_irq() (SMP only)
- irq_set_irq_type()
- irq_set_irq_wake()
- irq_set_handler_data()
- irq_set_chip()
- irq_set_chip_data()
See the autogenerated function documentation for details.
High-level IRQ flow handlers
----------------------------
The generic layer provides a set of pre-defined irq-flow methods:
- handle_level_irq()
- handle_edge_irq()
- handle_fasteoi_irq()
- handle_simple_irq()
- handle_percpu_irq()
- handle_edge_eoi_irq()
- handle_bad_irq()
The interrupt flow handlers (either pre-defined or architecture
specific) are assigned to specific interrupts by the architecture either
during bootup or during device initialization.
Default flow implementations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Helper functions
^^^^^^^^^^^^^^^^
The helper functions call the chip primitives and are used by the
default flow implementations. The following helper functions are
implemented (simplified excerpt)::
default_enable(struct irq_data *data)
{
desc->irq_data.chip->irq_unmask(data);
}
default_disable(struct irq_data *data)
{
if (!delay_disable(data))
desc->irq_data.chip->irq_mask(data);
}
default_ack(struct irq_data *data)
{
chip->irq_ack(data);
}
default_mask_ack(struct irq_data *data)
{
if (chip->irq_mask_ack) {
chip->irq_mask_ack(data);
} else {
chip->irq_mask(data);
chip->irq_ack(data);
}
}
noop(struct irq_data *data)
{
}
Default flow handler implementations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Default Level IRQ flow handler
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
handle_level_irq provides a generic implementation for level-triggered
interrupts.
The following control flow is implemented (simplified excerpt)::
desc->irq_data.chip->irq_mask_ack();
handle_irq_event(desc->action);
desc->irq_data.chip->irq_unmask();
Default Fast EOI IRQ flow handler
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
handle_fasteoi_irq provides a generic implementation for interrupts,
which only need an EOI at the end of the handler.
The following control flow is implemented (simplified excerpt)::
handle_irq_event(desc->action);
desc->irq_data.chip->irq_eoi();
Default Edge IRQ flow handler
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
handle_edge_irq provides a generic implementation for edge-triggered
interrupts.
The following control flow is implemented (simplified excerpt)::
if (desc->status & running) {
desc->irq_data.chip->irq_mask_ack();
desc->status |= pending | masked;
return;
}
desc->irq_data.chip->irq_ack();
desc->status |= running;
do {
if (desc->status & masked)
desc->irq_data.chip->irq_unmask();
desc->status &= ~pending;
handle_irq_event(desc->action);
} while (desc->status & pending);
desc->status &= ~running;
Default simple IRQ flow handler
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
handle_simple_irq provides a generic implementation for simple
interrupts.
.. note::
The simple flow handler does not call any handler/chip primitives.
The following control flow is implemented (simplified excerpt)::
handle_irq_event(desc->action);
Default per CPU flow handler
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
handle_percpu_irq provides a generic implementation for per CPU
interrupts.
Per CPU interrupts are only available on SMP and the handler provides a
simplified version without locking.
The following control flow is implemented (simplified excerpt)::
if (desc->irq_data.chip->irq_ack)
desc->irq_data.chip->irq_ack();
handle_irq_event(desc->action);
if (desc->irq_data.chip->irq_eoi)
desc->irq_data.chip->irq_eoi();
EOI Edge IRQ flow handler
^^^^^^^^^^^^^^^^^^^^^^^^^
handle_edge_eoi_irq provides an abnomination of the edge handler
which is solely used to tame a badly wreckaged irq controller on
powerpc/cell.
Bad IRQ flow handler
^^^^^^^^^^^^^^^^^^^^
handle_bad_irq is used for spurious interrupts which have no real
handler assigned..
Quirks and optimizations
~~~~~~~~~~~~~~~~~~~~~~~~
The generic functions are intended for 'clean' architectures and chips,
which have no platform-specific IRQ handling quirks. If an architecture
needs to implement quirks on the 'flow' level then it can do so by
overriding the high-level irq-flow handler.
Delayed interrupt disable
~~~~~~~~~~~~~~~~~~~~~~~~~
This per interrupt selectable feature, which was introduced by Russell
King in the ARM interrupt implementation, does not mask an interrupt at
the hardware level when disable_irq() is called. The interrupt is kept
enabled and is masked in the flow handler when an interrupt event
happens. This prevents losing edge interrupts on hardware which does not
store an edge interrupt event while the interrupt is disabled at the
hardware level. When an interrupt arrives while the IRQ_DISABLED flag
is set, then the interrupt is masked at the hardware level and the
IRQ_PENDING bit is set. When the interrupt is re-enabled by
enable_irq() the pending bit is checked and if it is set, the interrupt
is resent either via hardware or by a software resend mechanism. (It's
necessary to enable CONFIG_HARDIRQS_SW_RESEND when you want to use
the delayed interrupt disable feature and your hardware is not capable
of retriggering an interrupt.) The delayed interrupt disable is not
configurable.
Chip-level hardware encapsulation
---------------------------------
The chip-level hardware descriptor structure :c:type:`irq_chip` contains all
the direct chip relevant functions, which can be utilized by the irq flow
implementations.
- ``irq_ack``
- ``irq_mask_ack`` - Optional, recommended for performance
- ``irq_mask``
- ``irq_unmask``
- ``irq_eoi`` - Optional, required for EOI flow handlers
- ``irq_retrigger`` - Optional
- ``irq_set_type`` - Optional
- ``irq_set_wake`` - Optional
These primitives are strictly intended to mean what they say: ack means
ACK, masking means masking of an IRQ line, etc. It is up to the flow
handler(s) to use these basic units of low-level functionality.
__do_IRQ entry point
====================
The original implementation __do_IRQ() was an alternative entry point
for all types of interrupts. It no longer exists.
This handler turned out to be not suitable for all interrupt hardware
and was therefore reimplemented with split functionality for
edge/level/simple/percpu interrupts. This is not only a functional
optimization. It also shortens code paths for interrupts.
Locking on SMP
==============
The locking of chip registers is up to the architecture that defines the
chip primitives. The per-irq structure is protected via desc->lock, by
the generic layer.
Generic interrupt chip
======================
To avoid copies of identical implementations of IRQ chips the core
provides a configurable generic interrupt chip implementation.
Developers should check carefully whether the generic chip fits their
needs before implementing the same functionality slightly differently
themselves.
.. kernel-doc:: kernel/irq/generic-chip.c
:export:
Structures
==========
This chapter contains the autogenerated documentation of the structures
which are used in the generic IRQ layer.
.. kernel-doc:: include/linux/irq.h
:internal:
.. kernel-doc:: include/linux/interrupt.h
:internal:
.. kernel-doc:: include/linux/irqdomain.h
Public Functions Provided
=========================
This chapter contains the autogenerated documentation of the kernel API
functions which are exported.
.. kernel-doc:: kernel/irq/manage.c
.. kernel-doc:: kernel/irq/chip.c
:export:
Internal Functions Provided
===========================
This chapter contains the autogenerated documentation of the internal
functions.
.. kernel-doc:: kernel/irq/irqdesc.c
.. kernel-doc:: kernel/irq/handle.c
.. kernel-doc:: kernel/irq/chip.c
:internal:
Credits
=======
The following people have contributed to this document:
1. Thomas Gleixner tglx@linutronix.de
2. Ingo Molnar mingo@elte.hu