mirror of
https://github.com/torvalds/linux.git
synced 2024-11-13 23:51:39 +00:00
e066e9aa4d
Also fix a few places in gpu docs that are still relevant, and add a bunch of .mailmap entries. Acked-by: Dave Airlie <airlied@redhat.com> Signed-off-by: Simona Vetter <simona.vetter@ffwll.ch>
177 lines
9.3 KiB
ReStructuredText
177 lines
9.3 KiB
ReStructuredText
============
|
||
Introduction
|
||
============
|
||
|
||
The Linux DRM layer contains code intended to support the needs of
|
||
complex graphics devices, usually containing programmable pipelines well
|
||
suited to 3D graphics acceleration. Graphics drivers in the kernel may
|
||
make use of DRM functions to make tasks like memory management,
|
||
interrupt handling and DMA easier, and provide a uniform interface to
|
||
applications.
|
||
|
||
A note on versions: this guide covers features found in the DRM tree,
|
||
including the TTM memory manager, output configuration and mode setting,
|
||
and the new vblank internals, in addition to all the regular features
|
||
found in current kernels.
|
||
|
||
[Insert diagram of typical DRM stack here]
|
||
|
||
Style Guidelines
|
||
================
|
||
|
||
For consistency this documentation uses American English. Abbreviations
|
||
are written as all-uppercase, for example: DRM, KMS, IOCTL, CRTC, and so
|
||
on. To aid in reading, documentations make full use of the markup
|
||
characters kerneldoc provides: @parameter for function parameters,
|
||
@member for structure members (within the same structure), &struct structure to
|
||
reference structures and function() for functions. These all get automatically
|
||
hyperlinked if kerneldoc for the referenced objects exists. When referencing
|
||
entries in function vtables (and structure members in general) please use
|
||
&vtable_name.vfunc. Unfortunately this does not yet yield a direct link to the
|
||
member, only the structure.
|
||
|
||
Except in special situations (to separate locked from unlocked variants)
|
||
locking requirements for functions aren't documented in the kerneldoc.
|
||
Instead locking should be check at runtime using e.g.
|
||
``WARN_ON(!mutex_is_locked(...));``. Since it's much easier to ignore
|
||
documentation than runtime noise this provides more value. And on top of
|
||
that runtime checks do need to be updated when the locking rules change,
|
||
increasing the chances that they're correct. Within the documentation
|
||
the locking rules should be explained in the relevant structures: Either
|
||
in the comment for the lock explaining what it protects, or data fields
|
||
need a note about which lock protects them, or both.
|
||
|
||
Functions which have a non-\ ``void`` return value should have a section
|
||
called "Returns" explaining the expected return values in different
|
||
cases and their meanings. Currently there's no consensus whether that
|
||
section name should be all upper-case or not, and whether it should end
|
||
in a colon or not. Go with the file-local style. Other common section
|
||
names are "Notes" with information for dangerous or tricky corner cases,
|
||
and "FIXME" where the interface could be cleaned up.
|
||
|
||
Also read the :ref:`guidelines for the kernel documentation at large <doc_guide>`.
|
||
|
||
Documentation Requirements for kAPI
|
||
-----------------------------------
|
||
|
||
All kernel APIs exported to other modules must be documented, including their
|
||
datastructures and at least a short introductory section explaining the overall
|
||
concepts. Documentation should be put into the code itself as kerneldoc comments
|
||
as much as reasonable.
|
||
|
||
Do not blindly document everything, but document only what's relevant for driver
|
||
authors: Internal functions of drm.ko and definitely static functions should not
|
||
have formal kerneldoc comments. Use normal C comments if you feel like a comment
|
||
is warranted. You may use kerneldoc syntax in the comment, but it shall not
|
||
start with a /** kerneldoc marker. Similar for data structures, annotate
|
||
anything entirely private with ``/* private: */`` comments as per the
|
||
documentation guide.
|
||
|
||
Getting Started
|
||
===============
|
||
|
||
Developers interested in helping out with the DRM subsystem are very welcome.
|
||
Often people will resort to sending in patches for various issues reported by
|
||
checkpatch or sparse. We welcome such contributions.
|
||
|
||
Anyone looking to kick it up a notch can find a list of janitorial tasks on
|
||
the :ref:`TODO list <todo>`.
|
||
|
||
Contribution Process
|
||
====================
|
||
|
||
Mostly the DRM subsystem works like any other kernel subsystem, see :ref:`the
|
||
main process guidelines and documentation <process_index>` for how things work.
|
||
Here we just document some of the specialities of the GPU subsystem.
|
||
|
||
Feature Merge Deadlines
|
||
-----------------------
|
||
|
||
All feature work must be in the linux-next tree by the -rc6 release of the
|
||
current release cycle, otherwise they must be postponed and can't reach the next
|
||
merge window. All patches must have landed in the drm-next tree by latest -rc7,
|
||
but if your branch is not in linux-next then this must have happened by -rc6
|
||
already.
|
||
|
||
After that point only bugfixes (like after the upstream merge window has closed
|
||
with the -rc1 release) are allowed. No new platform enabling or new drivers are
|
||
allowed.
|
||
|
||
This means that there's a blackout-period of about one month where feature work
|
||
can't be merged. The recommended way to deal with that is having a -next tree
|
||
that's always open, but making sure to not feed it into linux-next during the
|
||
blackout period. As an example, drm-misc works like that.
|
||
|
||
Code of Conduct
|
||
---------------
|
||
|
||
As a freedesktop.org project, dri-devel, and the DRM community, follows the
|
||
Contributor Covenant, found at: https://www.freedesktop.org/wiki/CodeOfConduct
|
||
|
||
Please conduct yourself in a respectful and civilised manner when
|
||
interacting with community members on mailing lists, IRC, or bug
|
||
trackers. The community represents the project as a whole, and abusive
|
||
or bullying behaviour is not tolerated by the project.
|
||
|
||
Simple DRM drivers to use as examples
|
||
=====================================
|
||
|
||
The DRM subsystem contains a lot of helper functions to ease writing drivers for
|
||
simple graphic devices. For example, the `drivers/gpu/drm/tiny/` directory has a
|
||
set of drivers that are simple enough to be implemented in a single source file.
|
||
|
||
These drivers make use of the `struct drm_simple_display_pipe_funcs`, that hides
|
||
any complexity of the DRM subsystem and just requires drivers to implement a few
|
||
functions needed to operate the device. This could be used for devices that just
|
||
need a display pipeline with one full-screen scanout buffer feeding one output.
|
||
|
||
The tiny DRM drivers are good examples to understand how DRM drivers should look
|
||
like. Since are just a few hundreds lines of code, they are quite easy to read.
|
||
|
||
External References
|
||
===================
|
||
|
||
Delving into a Linux kernel subsystem for the first time can be an overwhelming
|
||
experience, one needs to get familiar with all the concepts and learn about the
|
||
subsystem's internals, among other details.
|
||
|
||
To shallow the learning curve, this section contains a list of presentations
|
||
and documents that can be used to learn about DRM/KMS and graphics in general.
|
||
|
||
There are different reasons why someone might want to get into DRM: porting an
|
||
existing fbdev driver, write a DRM driver for a new hardware, fixing bugs that
|
||
could face when working on the graphics user-space stack, etc. For this reason,
|
||
the learning material covers many aspects of the Linux graphics stack. From an
|
||
overview of the kernel and user-space stacks to very specific topics.
|
||
|
||
The list is sorted in reverse chronological order, to keep the most up-to-date
|
||
material at the top. But all of them contain useful information, and it can be
|
||
valuable to go through older material to understand the rationale and context
|
||
in which the changes to the DRM subsystem were made.
|
||
|
||
Conference talks
|
||
----------------
|
||
|
||
* `An Overview of the Linux and Userspace Graphics Stack <https://www.youtube.com/watch?v=wjAJmqwg47k>`_ - Paul Kocialkowski (2020)
|
||
* `Getting pixels on screen on Linux: introduction to Kernel Mode Setting <https://www.youtube.com/watch?v=haes4_Xnc5Q>`_ - Simon Ser (2020)
|
||
* `Everything Great about Upstream Graphics <https://www.youtube.com/watch?v=kVzHOgt6WGE>`_ - Simona Vetter (2019)
|
||
* `An introduction to the Linux DRM subsystem <https://www.youtube.com/watch?v=LbDOCJcDRoo>`_ - Maxime Ripard (2017)
|
||
* `Embrace the Atomic (Display) Age <https://www.youtube.com/watch?v=LjiB_JeDn2M>`_ - Simona Vetter (2016)
|
||
* `Anatomy of an Atomic KMS Driver <https://www.youtube.com/watch?v=lihqR9sENpc>`_ - Laurent Pinchart (2015)
|
||
* `Atomic Modesetting for Drivers <https://www.youtube.com/watch?v=kl9suFgbTc8>`_ - Simona Vetter (2015)
|
||
* `Anatomy of an Embedded KMS Driver <https://www.youtube.com/watch?v=Ja8fM7rTae4>`_ - Laurent Pinchart (2013)
|
||
|
||
Slides and articles
|
||
-------------------
|
||
|
||
* `The Linux graphics stack in a nutshell, part 1 <https://lwn.net/Articles/955376/>`_ - Thomas Zimmermann (2023)
|
||
* `The Linux graphics stack in a nutshell, part 2 <https://lwn.net/Articles/955708/>`_ - Thomas Zimmermann (2023)
|
||
* `Understanding the Linux Graphics Stack <https://bootlin.com/doc/training/graphics/graphics-slides.pdf>`_ - Bootlin (2022)
|
||
* `DRM KMS overview <https://wiki.st.com/stm32mpu/wiki/DRM_KMS_overview>`_ - STMicroelectronics (2021)
|
||
* `Linux graphic stack <https://studiopixl.com/2017-05-13/linux-graphic-stack-an-overview>`_ - Nathan Gauër (2017)
|
||
* `Atomic mode setting design overview, part 1 <https://lwn.net/Articles/653071/>`_ - Simona Vetter (2015)
|
||
* `Atomic mode setting design overview, part 2 <https://lwn.net/Articles/653466/>`_ - Simona Vetter (2015)
|
||
* `The DRM/KMS subsystem from a newbie’s point of view <https://bootlin.com/pub/conferences/2014/elce/brezillon-drm-kms/brezillon-drm-kms.pdf>`_ - Boris Brezillon (2014)
|
||
* `A brief introduction to the Linux graphics stack <https://blogs.igalia.com/itoral/2014/07/29/a-brief-introduction-to-the-linux-graphics-stack/>`_ - Iago Toral (2014)
|
||
* `The Linux Graphics Stack <https://blog.mecheye.net/2012/06/the-linux-graphics-stack/>`_ - Jasper St. Pierre (2012)
|