linux - Documentation/gpu/introduction.rst

172 lines · 9.0 KiB

1	============
2	Introduction
3	============
4
5	The Linux DRM layer contains code intended to support the needs of
6	complex graphics devices, usually containing programmable pipelines well
7	suited to 3D graphics acceleration. Graphics drivers in the kernel may
8	make use of DRM functions to make tasks like memory management,
9	interrupt handling and DMA easier, and provide a uniform interface to
10	applications.
11
12	A note on versions: this guide covers features found in the DRM tree,
13	including the TTM memory manager, output configuration and mode setting,
14	and the new vblank internals, in addition to all the regular features
15	found in current kernels.
16
17	[Insert diagram of typical DRM stack here]
18
19	.. contents::
20
21	Style Guidelines
22	================
23
24	For consistency this documentation uses American English. Abbreviations
25	are written as all-uppercase, for example: DRM, KMS, IOCTL, CRTC, and so
26	on. To aid in reading, documentations make full use of the markup
27	characters kerneldoc provides: @parameter for function parameters,
28	@member for structure members (within the same structure), &struct structure to
29	reference structures and function() for functions. These all get automatically
30	hyperlinked if kerneldoc for the referenced objects exists. When referencing
31	entries in function vtables (and structure members in general) please use
32	&vtable_name.vfunc. Unfortunately this does not yet yield a direct link to the
33	member, only the structure.
34
35	Except in special situations (to separate locked from unlocked variants)
36	locking requirements for functions aren't documented in the kerneldoc.
37	Instead locking should be check at runtime using e.g.
38	``WARN_ON(!mutex_is_locked(...));``. Since it's much easier to ignore
39	documentation than runtime noise this provides more value. And on top of
40	that runtime checks do need to be updated when the locking rules change,
41	increasing the chances that they're correct. Within the documentation
42	the locking rules should be explained in the relevant structures: Either
43	in the comment for the lock explaining what it protects, or data fields
44	need a note about which lock protects them, or both.
45
46	Functions which have a non-\ ``void`` return value should have a section
47	called "Returns" explaining the expected return values in different
48	cases and their meanings. Currently there's no consensus whether that
49	section name should be all upper-case or not, and whether it should end
50	in a colon or not. Go with the file-local style. Other common section
51	names are "Notes" with information for dangerous or tricky corner cases,
52	and "FIXME" where the interface could be cleaned up.
53
54	Also read the :ref:`guidelines for the kernel documentation at large <doc_guide>`.
55
56	Documentation Requirements for kAPI
57	-----------------------------------
58
59	All kernel APIs exported to other modules must be documented, including their
60	datastructures and at least a short introductory section explaining the overall
61	concepts. Documentation should be put into the code itself as kerneldoc comments
62	as much as reasonable.
63
64	Do not blindly document everything, but document only what's relevant for driver
65	authors: Internal functions of drm.ko and definitely static functions should not
66	have formal kerneldoc comments. Use normal C comments if you feel like a comment
67	is warranted. You may use kerneldoc syntax in the comment, but it shall not
68	start with a /** kerneldoc marker. Similar for data structures, annotate
69	anything entirely private with ``/* private: */`` comments as per the
70	documentation guide.
71
72	Getting Started
73	===============
74
75	Developers interested in helping out with the DRM subsystem are very welcome.
76	Often people will resort to sending in patches for various issues reported by
77	checkpatch or sparse. We welcome such contributions.
78
79	Anyone looking to kick it up a notch can find a list of janitorial tasks on
80	the :ref:`TODO list <todo>`.
81
82	Contribution Process
83	====================
84
85	Mostly the DRM subsystem works like any other kernel subsystem, see :ref:`the
86	main process guidelines and documentation <process_index>` for how things work.
87	Here we just document some of the specialities of the GPU subsystem.
88
89	Feature Merge Deadlines
90	-----------------------
91
92	All feature work must be in the linux-next tree by the -rc6 release of the
93	current release cycle, otherwise they must be postponed and can't reach the next
94	merge window. All patches must have landed in the drm-next tree by latest -rc7,
95	but if your branch is not in linux-next then this must have happened by -rc6
96	already.
97
98	After that point only bugfixes (like after the upstream merge window has closed
99	with the -rc1 release) are allowed. No new platform enabling or new drivers are
100	allowed.
101
102	This means that there's a blackout-period of about one month where feature work
103	can't be merged. The recommended way to deal with that is having a -next tree
104	that's always open, but making sure to not feed it into linux-next during the
105	blackout period. As an example, drm-misc works like that.
106
107	Code of Conduct
108	---------------
109
110	As a freedesktop.org project, dri-devel, and the DRM community, follows the
111	Contributor Covenant, found at: https://www.freedesktop.org/wiki/CodeOfConduct
112
113	Please conduct yourself in a respectful and civilised manner when
114	interacting with community members on mailing lists, IRC, or bug
115	trackers. The community represents the project as a whole, and abusive
116	or bullying behaviour is not tolerated by the project.
117
118	Simple DRM drivers to use as examples
119	=====================================
120
121	The DRM subsystem contains a lot of helper functions to ease writing drivers for
122	simple graphic devices. For example, the `drivers/gpu/drm/tiny/` directory has a
123	set of drivers that are simple enough to be implemented in a single source file.
124	The tiny DRM drivers are good examples to understand how DRM drivers should look
125	like. Since are just a few hundreds lines of code, they are quite easy to read.
126
127	External References
128	===================
129
130	Delving into a Linux kernel subsystem for the first time can be an overwhelming
131	experience, one needs to get familiar with all the concepts and learn about the
132	subsystem's internals, among other details.
133
134	To shallow the learning curve, this section contains a list of presentations
135	and documents that can be used to learn about DRM/KMS and graphics in general.
136
137	There are different reasons why someone might want to get into DRM: porting an
138	existing fbdev driver, write a DRM driver for a new hardware, fixing bugs that
139	could face when working on the graphics user-space stack, etc. For this reason,
140	the learning material covers many aspects of the Linux graphics stack. From an
141	overview of the kernel and user-space stacks to very specific topics.
142
143	The list is sorted in reverse chronological order, to keep the most up-to-date
144	material at the top. But all of them contain useful information, and it can be
145	valuable to go through older material to understand the rationale and context
146	in which the changes to the DRM subsystem were made.
147
148	Conference talks
149	----------------
150
151	* `An Overview of the Linux and Userspace Graphics Stack <https://www.youtube.com/watch?v=wjAJmqwg47k>`_ - Paul Kocialkowski (2020)
152	* `Getting pixels on screen on Linux: introduction to Kernel Mode Setting <https://www.youtube.com/watch?v=haes4_Xnc5Q>`_ - Simon Ser (2020)
153	* `Everything Great about Upstream Graphics <https://www.youtube.com/watch?v=kVzHOgt6WGE>`_ - Simona Vetter (2019)
154	* `An introduction to the Linux DRM subsystem <https://www.youtube.com/watch?v=LbDOCJcDRoo>`_ - Maxime Ripard (2017)
155	* `Embrace the Atomic (Display) Age <https://www.youtube.com/watch?v=LjiB_JeDn2M>`_ - Simona Vetter (2016)
156	* `Anatomy of an Atomic KMS Driver <https://www.youtube.com/watch?v=lihqR9sENpc>`_ - Laurent Pinchart (2015)
157	* `Atomic Modesetting for Drivers <https://www.youtube.com/watch?v=kl9suFgbTc8>`_ - Simona Vetter (2015)
158	* `Anatomy of an Embedded KMS Driver <https://www.youtube.com/watch?v=Ja8fM7rTae4>`_ - Laurent Pinchart (2013)
159
160	Slides and articles
161	-------------------
162
163	* `The Linux graphics stack in a nutshell, part 1 <https://lwn.net/Articles/955376/>`_ - Thomas Zimmermann (2023)
164	* `The Linux graphics stack in a nutshell, part 2 <https://lwn.net/Articles/955708/>`_ - Thomas Zimmermann (2023)
165	* `Understanding the Linux Graphics Stack <https://bootlin.com/doc/training/graphics/graphics-slides.pdf>`_ - Bootlin (2022)
166	* `DRM KMS overview <https://wiki.st.com/stm32mpu/wiki/DRM_KMS_overview>`_ - STMicroelectronics (2021)
167	* `Linux graphic stack <https://studiopixl.com/2017-05-13/linux-graphic-stack-an-overview>`_ - Nathan Gauër (2017)
168	* `Atomic mode setting design overview, part 1 <https://lwn.net/Articles/653071/>`_ - Simona Vetter (2015)
169	* `Atomic mode setting design overview, part 2 <https://lwn.net/Articles/653466/>`_ - Simona Vetter (2015)
170	* `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)
171	* `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)
172	* `The Linux Graphics Stack <https://blog.mecheye.net/2012/06/the-linux-graphics-stack/>`_ - Jasper St. Pierre (2012)