mirror of
https://github.com/torvalds/linux.git
synced 2024-12-11 21:52:04 +00:00
a7983eefb6
The functions that were described in this section of
drm-internals.rst were removed in NOV-2023, along with all of the
kernel-doc comments in the source file. This now causes a
docs build warning, so remove that section of the documentation also.
drivers/gpu/drm/drm_pci.c:1: warning: no structured comments found
Fixes: 2504c7ec72 ("drm: Remove source code for non-KMS drivers")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20240112051731.15722-1-rdunlap@infradead.org
262 lines
8.1 KiB
ReStructuredText
262 lines
8.1 KiB
ReStructuredText
=============
|
|
DRM Internals
|
|
=============
|
|
|
|
This chapter documents DRM internals relevant to driver authors and
|
|
developers working to add support for the latest features to existing
|
|
drivers.
|
|
|
|
First, we go over some typical driver initialization requirements, like
|
|
setting up command buffers, creating an initial output configuration,
|
|
and initializing core services. Subsequent sections cover core internals
|
|
in more detail, providing implementation notes and examples.
|
|
|
|
The DRM layer provides several services to graphics drivers, many of
|
|
them driven by the application interfaces it provides through libdrm,
|
|
the library that wraps most of the DRM ioctls. These include vblank
|
|
event handling, memory management, output management, framebuffer
|
|
management, command submission & fencing, suspend/resume support, and
|
|
DMA services.
|
|
|
|
Driver Initialization
|
|
=====================
|
|
|
|
At the core of every DRM driver is a :c:type:`struct drm_driver
|
|
<drm_driver>` structure. Drivers typically statically initialize
|
|
a drm_driver structure, and then pass it to
|
|
drm_dev_alloc() to allocate a device instance. After the
|
|
device instance is fully initialized it can be registered (which makes
|
|
it accessible from userspace) using drm_dev_register().
|
|
|
|
The :c:type:`struct drm_driver <drm_driver>` structure
|
|
contains static information that describes the driver and features it
|
|
supports, and pointers to methods that the DRM core will call to
|
|
implement the DRM API. We will first go through the :c:type:`struct
|
|
drm_driver <drm_driver>` static information fields, and will
|
|
then describe individual operations in details as they get used in later
|
|
sections.
|
|
|
|
Driver Information
|
|
------------------
|
|
|
|
Major, Minor and Patchlevel
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
int major; int minor; int patchlevel;
|
|
The DRM core identifies driver versions by a major, minor and patch
|
|
level triplet. The information is printed to the kernel log at
|
|
initialization time and passed to userspace through the
|
|
DRM_IOCTL_VERSION ioctl.
|
|
|
|
The major and minor numbers are also used to verify the requested driver
|
|
API version passed to DRM_IOCTL_SET_VERSION. When the driver API
|
|
changes between minor versions, applications can call
|
|
DRM_IOCTL_SET_VERSION to select a specific version of the API. If the
|
|
requested major isn't equal to the driver major, or the requested minor
|
|
is larger than the driver minor, the DRM_IOCTL_SET_VERSION call will
|
|
return an error. Otherwise the driver's set_version() method will be
|
|
called with the requested version.
|
|
|
|
Name, Description and Date
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
char \*name; char \*desc; char \*date;
|
|
The driver name is printed to the kernel log at initialization time,
|
|
used for IRQ registration and passed to userspace through
|
|
DRM_IOCTL_VERSION.
|
|
|
|
The driver description is a purely informative string passed to
|
|
userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
|
|
the kernel.
|
|
|
|
The driver date, formatted as YYYYMMDD, is meant to identify the date of
|
|
the latest modification to the driver. However, as most drivers fail to
|
|
update it, its value is mostly useless. The DRM core prints it to the
|
|
kernel log at initialization time and passes it to userspace through the
|
|
DRM_IOCTL_VERSION ioctl.
|
|
|
|
Module Initialization
|
|
---------------------
|
|
|
|
.. kernel-doc:: include/drm/drm_module.h
|
|
:doc: overview
|
|
|
|
Managing Ownership of the Framebuffer Aperture
|
|
----------------------------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_aperture.c
|
|
:doc: overview
|
|
|
|
.. kernel-doc:: include/drm/drm_aperture.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_aperture.c
|
|
:export:
|
|
|
|
Device Instance and Driver Handling
|
|
-----------------------------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_drv.c
|
|
:doc: driver instance overview
|
|
|
|
.. kernel-doc:: include/drm/drm_device.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: include/drm/drm_drv.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_drv.c
|
|
:export:
|
|
|
|
Driver Load
|
|
-----------
|
|
|
|
Component Helper Usage
|
|
~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_drv.c
|
|
:doc: component helper usage recommendations
|
|
|
|
Memory Manager Initialization
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Every DRM driver requires a memory manager which must be initialized at
|
|
load time. DRM currently contains two memory managers, the Translation
|
|
Table Manager (TTM) and the Graphics Execution Manager (GEM). This
|
|
document describes the use of the GEM memory manager only. See ? for
|
|
details.
|
|
|
|
Miscellaneous Device Configuration
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Another task that may be necessary for PCI devices during configuration
|
|
is mapping the video BIOS. On many devices, the VBIOS describes device
|
|
configuration, LCD panel timings (if any), and contains flags indicating
|
|
device state. Mapping the BIOS can be done using the pci_map_rom()
|
|
call, a convenience function that takes care of mapping the actual ROM,
|
|
whether it has been shadowed into memory (typically at address 0xc0000)
|
|
or exists on the PCI device in the ROM BAR. Note that after the ROM has
|
|
been mapped and any necessary information has been extracted, it should
|
|
be unmapped; on many devices, the ROM address decoder is shared with
|
|
other BARs, so leaving it mapped could cause undesired behaviour like
|
|
hangs or memory corruption.
|
|
|
|
Managed Resources
|
|
-----------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_managed.c
|
|
:doc: managed resources
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_managed.c
|
|
:export:
|
|
|
|
.. kernel-doc:: include/drm/drm_managed.h
|
|
:internal:
|
|
|
|
Open/Close, File Operations and IOCTLs
|
|
======================================
|
|
|
|
.. _drm_driver_fops:
|
|
|
|
File Operations
|
|
---------------
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_file.c
|
|
:doc: file operations
|
|
|
|
.. kernel-doc:: include/drm/drm_file.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_file.c
|
|
:export:
|
|
|
|
Misc Utilities
|
|
==============
|
|
|
|
Printer
|
|
-------
|
|
|
|
.. kernel-doc:: include/drm/drm_print.h
|
|
:doc: print
|
|
|
|
.. kernel-doc:: include/drm/drm_print.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: drivers/gpu/drm/drm_print.c
|
|
:export:
|
|
|
|
Utilities
|
|
---------
|
|
|
|
.. kernel-doc:: include/drm/drm_util.h
|
|
:doc: drm utils
|
|
|
|
.. kernel-doc:: include/drm/drm_util.h
|
|
:internal:
|
|
|
|
|
|
Unit testing
|
|
============
|
|
|
|
KUnit
|
|
-----
|
|
|
|
KUnit (Kernel unit testing framework) provides a common framework for unit tests
|
|
within the Linux kernel.
|
|
|
|
This section covers the specifics for the DRM subsystem. For general information
|
|
about KUnit, please refer to Documentation/dev-tools/kunit/start.rst.
|
|
|
|
How to run the tests?
|
|
~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
In order to facilitate running the test suite, a configuration file is present
|
|
in ``drivers/gpu/drm/tests/.kunitconfig``. It can be used by ``kunit.py`` as
|
|
follows:
|
|
|
|
.. code-block:: bash
|
|
|
|
$ ./tools/testing/kunit/kunit.py run --kunitconfig=drivers/gpu/drm/tests \
|
|
--kconfig_add CONFIG_VIRTIO_UML=y \
|
|
--kconfig_add CONFIG_UML_PCI_OVER_VIRTIO=y
|
|
|
|
.. note::
|
|
The configuration included in ``.kunitconfig`` should be as generic as
|
|
possible.
|
|
``CONFIG_VIRTIO_UML`` and ``CONFIG_UML_PCI_OVER_VIRTIO`` are not
|
|
included in it because they are only required for User Mode Linux.
|
|
|
|
|
|
Legacy Support Code
|
|
===================
|
|
|
|
The section very briefly covers some of the old legacy support code
|
|
which is only used by old DRM drivers which have done a so-called
|
|
shadow-attach to the underlying device instead of registering as a real
|
|
driver. This also includes some of the old generic buffer management and
|
|
command submission code. Do not use any of this in new and modern
|
|
drivers.
|
|
|
|
Legacy Suspend/Resume
|
|
---------------------
|
|
|
|
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.
|
|
|
|
int (\*suspend) (struct drm_device \*, pm_message_t state); int
|
|
(\*resume) (struct drm_device \*);
|
|
Those are legacy suspend and resume methods which *only* work with the
|
|
legacy shadow-attach driver registration functions. New driver should
|
|
use the power management interface provided by their bus type (usually
|
|
through the :c:type:`struct device_driver <device_driver>`
|
|
dev_pm_ops) and set these methods to NULL.
|
|
|
|
Legacy DMA Services
|
|
-------------------
|
|
|
|
This should cover how DMA mapping etc. is supported by the core. These
|
|
functions are deprecated and should not be used.
|