Documentation/gpu: Introduce a simple contribution list for display code

This commit adds a contribution list for display under the kernel
documentation with some first suggestions. It also drops an old TODO
list from the display folder.

Cc: Mario Limonciello <[e-mail]>
Cc: Alex Deucher <[e-mail]>
Cc: Harry Wentland <[e-mail]>
Cc: Hamza Mahfooz <[e-mail]>
Cc: Christian König <[e-mail]>
Cc: Aurabindo Pillai <[e-mail]>
Reviewed-by: Mario Limonciello <[e-mail]>
Acked-by: Christian König <[e-mail]>
Acked-by: Hamza Mahfooz <[e-mail]>
Signed-off-by: Rodrigo Siqueira <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

Documentation/gpu/amdgpu/display/display-contributing.rst

···
+.. _display_todos:
+
+==============================
+AMDGPU - Display Contributions
+==============================
+
+First of all, if you are here, you probably want to give some technical
+contribution to the display code, and for that, we say thank you :)
+
+This page summarizes some of the issues you can help with; keep in mind that
+this is a static page, and it is always a good idea to try to reach developers
+in the amdgfx or some of the maintainers. Finally, this page follows the DRM
+way of creating a TODO list; for more information, check
+'Documentation/gpu/todo.rst'.
+
+Gitlab issues
+=============
+
+Users can report issues associated with AMD GPUs at:
+
+- https://gitlab.freedesktop.org/drm/amd
+
+Usually, we try to add a proper label to all new tickets to make it easy to
+filter issues. If you can reproduce any problem, you could help by adding more
+information or fixing the issue.
+
+Level: diverse
+
+IGT
+===
+
+`IGT`_ provides many integration tests that can be run on your GPU. We always
+want to pass a large set of tests to increase the test coverage in our CI. If
+you wish to contribute to the display code but are unsure where a good place
+is, we recommend you run all IGT tests and try to fix any failure you see in
+your hardware. Keep in mind that this failure can be an IGT problem or a kernel
+issue; it is necessary to analyze case-by-case.
+
+Level: diverse
+
+.. _IGT: https://gitlab.freedesktop.org/drm/igt-gpu-tools
+
+Compilation
+===========
+
+Fix compilation warnings
+------------------------
+
+Enable the W1 or W2 warning level in the kernel compilation and try to fix the
+issues on the display side.
+
+Level: Starter
+
+Fix compilation issues when using um architecture
+-------------------------------------------------
+
+Linux has a User-mode Linux (UML) feature, and the kernel can be compiled to
+the **um** architecture. Compiling for **um** can bring multiple advantages
+from the test perspective. We currently have some compilation issues in this
+area that we need to fix.
+
+Level: Intermediate
+
+Code Refactor
+=============
+
+Add prefix to DC functions to improve the debug with ftrace
+-----------------------------------------------------------
+
+The Ftrace debug feature (check 'Documentation/trace/ftrace.rst') is a
+fantastic way to check the code path when developers try to make sense of a
+bug. Ftrace provides a filter mechanism that can be useful when the developer
+has some hunch of which part of the code can cause the issue; for this reason,
+if a set of functions has a proper prefix, it becomes easy to create a good
+filter. Additionally, prefixes can improve stack trace readability.
+
+The DC code does not follow some prefix rules, which makes the Ftrace filter
+more complicated and reduces the readability of the stack trace. If you want
+something simple to start contributing to the display, you can make patches for
+adding prefixes to DC functions. To create those prefixes, use part of the file
+name as a prefix for all functions in the target file. Check the
+'amdgpu_dm_crtc.c` and `amdgpu_dm_plane.c` for some references. However, we
+strongly advise not to send huge patches changing these prefixes; otherwise, it
+will be hard to review and test, which can generate second thoughts from
+maintainers. Try small steps; in case of double, you can ask before you put in
+effort. We recommend first looking at folders like dceXYZ, dcnXYZ, basics,
+bios, core, clk_mgr, hwss, resource, and irq.
+
+Level: Starter
+
+Reduce code duplication
+-----------------------
+
+AMD has an extensive portfolio with various dGPUs and APUs that amdgpu
+supports. To maintain the new hardware release cadence, DCE/DCN was designed in
+a modular design, making the bring-up for new hardware fast. Over the years,
+amdgpu accumulated some technical debt in the code duplication area. For this
+task, it would be a good idea to find a tool that can discover code duplication
+(including patterns) and use it as guidance to reduce duplications.
+
+Level: Intermediate
+
+Make atomic_commit_[check|tail] more readable
+---------------------------------------------
+
+The functions responsible for atomic commit and tail are intricate and
+extensive. In particular `amdgpu_dm_atomic_commit_tail` is a long function and
+could benefit from being split into smaller helpers. Improvements in this area
+are more than welcome, but keep in mind that changes in this area will affect
+all ASICs, meaning that refactoring requires a comprehensive verification; in
+other words, this effort can take some time for validation.
+
+Level: Advanced
+
+Documentation
+=============
+
+Expand kernel-doc
+-----------------
+
+Many DC functions do not have a proper kernel-doc; understanding a function and
+adding documentation is a great way to learn more about the amdgpu driver and
+also leave an outstanding contribution to the entire community.
+
+Level: Starter
+
+Beyond AMDGPU
+=============
+
+AMDGPU provides features that are not yet enabled in the userspace. This
+section highlights some of the coolest display features, which could be enabled
+with the userspace developer helper.
+
+Enable underlay
+---------------
+
+AMD display has this feature called underlay (which you can read more about at
+'Documentation/GPU/amdgpu/display/mpo-overview.rst') which is intended to
+save power when playing a video. The basic idea is to put a video in the
+underlay plane at the bottom and the desktop in the plane above it with a hole
+in the video area. This feature is enabled in ChromeOS, and from our data
+measurement, it can save power.
+
+Level: Unknown
+
+Adaptive Backlight Modulation (ABM)
+-----------------------------------
+
+ABM is a feature that adjusts the display panel's backlight level and pixel
+values depending on the displayed image. This power-saving feature can be very
+useful when the system starts to run off battery; since this will impact the
+display output fidelity, it would be good if this option was something that
+users could turn on or off.
+
+Level: Unknown
+
+
+HDR & Color management & VRR
+----------------------------
+
+HDR, Color Management, and VRR are huge topics and it's hard to put these into
+concise ToDos. If you are interested in this topic, we recommend checking some
+blog posts from the community developers to better understand some of the
+specific challenges and people working on the subject. If anyone wants to work
+on some particular part, we can try to help with some basic guidance. Finally,
+keep in mind that we already have some kernel-doc in place for those areas.
+
+Level: Unknown

Documentation/gpu/amdgpu/display/index.rst

···
    dcn-blocks.rst
    mpo-overview.rst
    dc-debug.rst
+   display-contributing.rst
    dc-glossary.rst

drivers/gpu/drm/amd/display/TODO

···
-===============================================================================
-TODOs
-===============================================================================
-
-1. Base this on drm-next - WIP
-
-
-2. Cleanup commit history
-
-
-3. WIP - Drop page flip helper and use DRM's version
-
-
-4. DONE - Flatten all DC objects
-    * dc_stream/core_stream/stream should just be dc_stream
-    * Same for other DC objects
-
-    "Is there any major reason to keep all those abstractions?
-
-    Could you collapse everything into struct dc_stream?
-
-    I haven't looked recently but I didn't get the impression there was a
-    lot of design around what was public/protected, more whatever needed
-    to be used by someone else was in public."
-    ~ Dave Airlie
-
-
-5. DONE - Rename DC objects to align more with DRM
-    * dc_surface -> dc_plane_state
-    * dc_stream -> dc_stream_state
-
-
-6. DONE - Per-plane and per-stream validation
-
-
-7. WIP - Per-plane and per-stream commit
-
-
-8. WIP - Split pipe_ctx into plane and stream resource structs
-
-
-9. Attach plane and stream reources to state object instead of validate_context
-
-
-10. Remove dc_edid_caps and drm_helpers_parse_edid_caps
-    * Use drm_display_info instead
-    * Remove DC's edid quirks and rely on DRM's quirks (add quirks if needed)
-
-    "Making sure you use the sink-specific helper libraries and kernel
-    subsystems, since there's really no good reason to have 2nd
-    implementation of those in the kernel. Looks likes that's done for mst
-    and edid parsing. There's still a bit a midlayer feeling to the edid
-    parsing side (e.g. dc_edid_caps and dm_helpers_parse_edid_caps, I
-    think it'd be much better if you convert that over to reading stuff
-    from drm_display_info and if needed, push stuff into the core). Also,
-    I can't come up with a good reason why DC needs all this (except to
-    reimplement half of our edid quirk table, which really isn't a good
-    idea). Might be good if you put this onto the list of things to fix
-    long-term, but imo not a blocker. Definitely make sure new stuff
-    doesn't slip in (i.e. if you start adding edid quirks to DC instead of
-    the drm core, refactoring to use the core edid stuff was pointless)."
-    ~ Daniel Vetter
-
-
-11. Remove dc/i2caux. This folder can be somewhat misleading. It's basically an
-overy complicated HW programming function for sendind and receiving i2c/aux
-commands. We can greatly simplify that and move it into dc/dceXYZ like other
-HW blocks.
-
-12. drm_modeset_lock in MST should no longer be needed in recent kernels
-    * Adopt appropriate locking scheme
-
-13. get_modes and best_encoder callbacks look a bit funny. Can probably rip out
-a few indirections, and consider removing entirely and using the
-drm_atomic_helper_best_encoder default behaviour.
-
-14. core/dc_debug.c, consider switching to the atomic state debug helpers and
-moving all your driver state printing into the various atomic_print_state
-callbacks. There's also plans to expose this stuff in a standard way across all
-drivers, to make debugging userspace compositors easier across different hw.
-
-15. Move DP/HDMI dual mode adaptors to drm_dp_dual_mode_helper.c. See
-dal_ddc_service_i2c_query_dp_dual_mode_adaptor.
-
-16. Move to core SCDC helpers (I think those are new since initial DC review).
-
-17. There's still a pretty massive layer cake around dp aux and DPCD handling,
-with like 3 levels of abstraction and using your own structures instead of the
-stuff in drm_dp_helper.h. drm_dp_helper.h isn't really great and already has 2
-incompatible styles, just means more reasons not to add a third (or well third
-one gets to do the cleanup refactor).
-
-18. There's a pile of sink handling code, both for DP and HDMI where I didn't
-immediately recognize the standard. I think long term it'd be best for the drm
-subsystem if we try to move as much of that into helpers/core as possible, and
-share it with drivers. But that's a very long term goal, and by far not just an
-issue with DC - other drivers, especially around DP sink handling, are equally
-guilty.
-
-19. DONE - The DC logger is still a rather sore thing, but I know that the
-DRM_DEBUG stuff just isn't up to the challenges either. We need to figure out
-something that integrates better with DRM and linux debug printing, while not
-being useless with filtering output. dynamic debug printing might be an option.
-
-20. Use kernel i2c device to program HDMI retimer. Some boards have an HDMI
-retimer that we need to program to pass PHY compliance. Currently that's
-bypassing the i2c device and goes directly to HW. This should be changed.
-
-21. Remove vector.c from dc/basics. It's used in DDC code which can probably
-be simplified enough to no longer need a vector implementation.