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linux/Documentation/PCI/endpoint/pci-vntb-howto.rst
Damien Le Moal 70b3740f2c PCI: endpoint: Automatically create a function specific attributes group 
A PCI endpoint function driver can define function specific attributes
under its function configfs directory using the add_cfs() endpoint driver
operation. This is done by tying up the mkdir operation for the function
configfs directory to a call to the add_cfs() operation.  However, there
are no checks preventing the user from repeatedly creating function
specific attribute directories with different names, resulting in the same
endpoint specific attributes group being added multiple times, which also
result in an invalid reference counting for the attribute groups. E.g.,
using the pci-epf-ntb function driver as an example, the user creates the
function as follows:

  $ modprobe pci-epf-ntb
  $ cd /sys/kernel/config/pci_ep/functions/pci_epf_ntb
  $ mkdir func0
  $ tree func0
  func0/
  |-- baseclass_code
  |-- cache_line_size
  |-- ...
  `-- vendorid

  $ mkdir func0/attrs
  $ tree func0
  func0/
  |-- attrs
  |   |-- db_count
  |   |-- mw1
  |   |-- mw2
  |   |-- mw3
  |   |-- mw4
  |   |-- num_mws
  |   `-- spad_count
  |-- baseclass_code
  |-- cache_line_size
  |-- ...
  `-- vendorid

At this point, the function can be started by linking the EP controller.
However, if the user mistakenly creates again a directory:

  $ mkdir func0/attrs2
  $ tree func0
  func0/
  |-- attrs
  |   |-- db_count
  |   |-- mw1
  |   |-- mw2
  |   |-- mw3
  |   |-- mw4
  |   |-- num_mws
  |   `-- spad_count
  |-- attrs2
  |   |-- db_count
  |   |-- mw1
  |   |-- mw2
  |   |-- mw3
  |   |-- mw4
  |   |-- num_mws
  |   `-- spad_count
  |-- baseclass_code
  |-- cache_line_size
  |-- ...
  `-- vendorid

The endpoint function specific attributes are duplicated and cause a crash
when the endpoint function device is torn down:

  refcount_t: addition on 0; use-after-free.
  WARNING: CPU: 2 PID: 834 at lib/refcount.c:25 refcount_warn_saturate+0xc8/0x144
  CPU: 2 PID: 834 Comm: rmdir Not tainted 6.3.0-rc1 #1
  Hardware name: Pine64 RockPro64 v2.1 (DT)
  pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  ...
  Call trace:
  refcount_warn_saturate+0xc8/0x144
  config_item_get+0x7c/0x80
  configfs_rmdir+0x17c/0x30c
  vfs_rmdir+0x8c/0x204
  do_rmdir+0x158/0x184
  __arm64_sys_unlinkat+0x64/0x80
  invoke_syscall+0x48/0x114
  ...

Fix this by modifying pci_epf_cfs_work() to execute the new function
pci_ep_cfs_add_type_group() which itself calls pci_epf_type_add_cfs() to
obtain the function specific attribute group and the group name (directory
name) from the endpoint function driver. If the function driver defines an
attribute group, pci_ep_cfs_add_type_group() then proceeds to register this
group using configfs_register_group(), thus automatically exposing the
function type specific configfs attributes to the user. E.g.:

  $ modprobe pci-epf-ntb
  $ cd /sys/kernel/config/pci_ep/functions/pci_epf_ntb
  $ mkdir func0
  $ tree func0
  func0/
  |-- baseclass_code
  |-- cache_line_size
  |-- ...
  |-- pci_epf_ntb.0
  |   |-- db_count
  |   |-- mw1
  |   |-- mw2
  |   |-- mw3
  |   |-- mw4
  |   |-- num_mws
  |   `-- spad_count
  |-- primary
  |-- ...
  `-- vendorid

With this change, there is no need for the user to create or delete
directories in the endpoint function attributes directory. The
pci_epf_type_group_ops group operations are thus removed.

Also update the documentation for the pci-epf-ntb and pci-epf-vntb function
drivers to reflect this change, removing the explanations showing the need
to manually create the sub-directory for the function specific attributes.

Link: https://lore.kernel.org/r/20230415023542.77601-2-dlemoal@kernel.org
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
2023-06-23 14:57:59 -05:00

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.. SPDX-License-Identifier: GPL-2.0
===================================================================
PCI Non-Transparent Bridge (NTB) Endpoint Function (EPF) User Guide
===================================================================
:Author: Frank Li <Frank.Li@nxp.com>
This document is a guide to help users use pci-epf-vntb function driver
and ntb_hw_epf host driver for NTB functionality. The list of steps to
be followed in the host side and EP side is given below. For the hardware
configuration and internals of NTB using configurable endpoints see
Documentation/PCI/endpoint/pci-vntb-function.rst
Endpoint Device
===============
Endpoint Controller Devices
---------------------------
To find the list of endpoint controller devices in the system::
# ls /sys/class/pci_epc/
5f010000.pcie_ep
If PCI_ENDPOINT_CONFIGFS is enabled::
# ls /sys/kernel/config/pci_ep/controllers
5f010000.pcie_ep
Endpoint Function Drivers
-------------------------
To find the list of endpoint function drivers in the system::
# ls /sys/bus/pci-epf/drivers
pci_epf_ntb pci_epf_test pci_epf_vntb
If PCI_ENDPOINT_CONFIGFS is enabled::
# ls /sys/kernel/config/pci_ep/functions
pci_epf_ntb pci_epf_test pci_epf_vntb
Creating pci-epf-vntb Device
----------------------------
PCI endpoint function device can be created using the configfs. To create
pci-epf-vntb device, the following commands can be used::
# mount -t configfs none /sys/kernel/config
# cd /sys/kernel/config/pci_ep/
# mkdir functions/pci_epf_vntb/func1
The "mkdir func1" above creates the pci-epf-ntb function device that will
be probed by pci_epf_vntb driver.
The PCI endpoint framework populates the directory with the following
configurable fields::
# ls functions/pci_epf_ntb/func1
baseclass_code deviceid msi_interrupts pci-epf-ntb.0
progif_code secondary subsys_id vendorid
cache_line_size interrupt_pin msix_interrupts primary
revid subclass_code subsys_vendor_id
The PCI endpoint function driver populates these entries with default values
when the device is bound to the driver. The pci-epf-vntb driver populates
vendorid with 0xffff and interrupt_pin with 0x0001::
# cat functions/pci_epf_vntb/func1/vendorid
0xffff
# cat functions/pci_epf_vntb/func1/interrupt_pin
0x0001
Configuring pci-epf-vntb Device
-------------------------------
The user can configure the pci-epf-vntb device using its configfs entry. In order
to change the vendorid and the deviceid, the following
commands can be used::
# echo 0x1957 > functions/pci_epf_vntb/func1/vendorid
# echo 0x0809 > functions/pci_epf_vntb/func1/deviceid
The PCI endpoint framework also automatically creates a sub-directory in the
function attribute directory. This sub-directory has the same name as the name
of the function device and is populated with the following NTB specific
attributes that can be configured by the user::
# ls functions/pci_epf_vntb/func1/pci_epf_vntb.0/
db_count mw1 mw2 mw3 mw4 num_mws
spad_count
A sample configuration for NTB function is given below::
# echo 4 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/db_count
# echo 128 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/spad_count
# echo 1 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/num_mws
# echo 0x100000 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/mw1
A sample configuration for virtual NTB driver for virtual PCI bus::
# echo 0x1957 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/vntb_vid
# echo 0x080A > functions/pci_epf_vntb/func1/pci_epf_vntb.0/vntb_pid
# echo 0x10 > functions/pci_epf_vntb/func1/pci_epf_vntb.0/vbus_number
Binding pci-epf-ntb Device to EP Controller
--------------------------------------------
NTB function device should be attached to PCI endpoint controllers
connected to the host.
# ln -s controllers/5f010000.pcie_ep functions/pci-epf-ntb/func1/primary
Once the above step is completed, the PCI endpoint controllers are ready to
establish a link with the host.
Start the Link
--------------
In order for the endpoint device to establish a link with the host, the _start_
field should be populated with '1'. For NTB, both the PCI endpoint controllers
should establish link with the host (imx8 don't need this steps)::
# echo 1 > controllers/5f010000.pcie_ep/start
RootComplex Device
==================
lspci Output at Host side
-------------------------
Note that the devices listed here correspond to the values populated in
"Creating pci-epf-ntb Device" section above::
# lspci
00:00.0 PCI bridge: Freescale Semiconductor Inc Device 0000 (rev 01)
01:00.0 RAM memory: Freescale Semiconductor Inc Device 0809
Endpoint Device / Virtual PCI bus
=================================
lspci Output at EP Side / Virtual PCI bus
-----------------------------------------
Note that the devices listed here correspond to the values populated in
"Creating pci-epf-ntb Device" section above::
# lspci
10:00.0 Unassigned class [ffff]: Dawicontrol Computersysteme GmbH Device 1234 (rev ff)
Using ntb_hw_epf Device
-----------------------
The host side software follows the standard NTB software architecture in Linux.
All the existing client side NTB utilities like NTB Transport Client and NTB
Netdev, NTB Ping Pong Test Client and NTB Tool Test Client can be used with NTB
function device.
For more information on NTB see
:doc:`Non-Transparent Bridge <../../driver-api/ntb>`
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