Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+============
+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>`_ - Daniel 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>`_ - Daniel 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>`_ - Daniel Vetter (2015)
+* `Anatomy of an Embedded KMS Driver <https://www.youtube.com/watch?v=Ja8fM7rTae4>`_ - Laurent Pinchart (2013)
+
+Slides and articles
+-------------------
+
+* `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/>`_ - Daniel Vetter (2015)
+* `Atomic mode setting design overview, part 2 <https://lwn.net/Articles/653466/>`_ - Daniel 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)