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 <mario.limonciello@amd.com> Cc: Alex Deucher <alexander.deucher@amd.com> Cc: Harry Wentland <Harry.Wentland@amd.com> Cc: Hamza Mahfooz <hamza.mahfooz@amd.com> Cc: Christian König <christian.koenig@amd.com> Cc: Aurabindo Pillai <aurabindo.pillai@amd.com> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com> Acked-by: Christian König <christian.koenig@amd.com> Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com> Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Rodrigo Siqueira
Alex Deucher
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.. _display_todos:
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==============================
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AMDGPU - Display Contributions
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==============================
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First of all, if you are here, you probably want to give some technical
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contribution to the display code, and for that, we say thank you :)
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This page summarizes some of the issues you can help with; keep in mind that
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this is a static page, and it is always a good idea to try to reach developers
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in the amdgfx or some of the maintainers. Finally, this page follows the DRM
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way of creating a TODO list; for more information, check
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'Documentation/gpu/todo.rst'.
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Gitlab issues
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=============
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Users can report issues associated with AMD GPUs at:
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- https://gitlab.freedesktop.org/drm/amd
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Usually, we try to add a proper label to all new tickets to make it easy to
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filter issues. If you can reproduce any problem, you could help by adding more
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information or fixing the issue.
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Level: diverse
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IGT
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===
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`IGT`_ provides many integration tests that can be run on your GPU. We always
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want to pass a large set of tests to increase the test coverage in our CI. If
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you wish to contribute to the display code but are unsure where a good place
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is, we recommend you run all IGT tests and try to fix any failure you see in
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your hardware. Keep in mind that this failure can be an IGT problem or a kernel
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issue; it is necessary to analyze case-by-case.
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Level: diverse
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.. _IGT: https://gitlab.freedesktop.org/drm/igt-gpu-tools
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Compilation
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===========
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Fix compilation warnings
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------------------------
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Enable the W1 or W2 warning level in the kernel compilation and try to fix the
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issues on the display side.
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Level: Starter
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Fix compilation issues when using um architecture
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-------------------------------------------------
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Linux has a User-mode Linux (UML) feature, and the kernel can be compiled to
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the **um** architecture. Compiling for **um** can bring multiple advantages
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from the test perspective. We currently have some compilation issues in this
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area that we need to fix.
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Level: Intermediate
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Code Refactor
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=============
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Add prefix to DC functions to improve the debug with ftrace
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-----------------------------------------------------------
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The Ftrace debug feature (check 'Documentation/trace/ftrace.rst') is a
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fantastic way to check the code path when developers try to make sense of a
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bug. Ftrace provides a filter mechanism that can be useful when the developer
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has some hunch of which part of the code can cause the issue; for this reason,
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if a set of functions has a proper prefix, it becomes easy to create a good
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filter. Additionally, prefixes can improve stack trace readability.
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The DC code does not follow some prefix rules, which makes the Ftrace filter
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more complicated and reduces the readability of the stack trace. If you want
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something simple to start contributing to the display, you can make patches for
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adding prefixes to DC functions. To create those prefixes, use part of the file
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name as a prefix for all functions in the target file. Check the
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'amdgpu_dm_crtc.c` and `amdgpu_dm_plane.c` for some references. However, we
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strongly advise not to send huge patches changing these prefixes; otherwise, it
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will be hard to review and test, which can generate second thoughts from
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maintainers. Try small steps; in case of double, you can ask before you put in
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effort. We recommend first looking at folders like dceXYZ, dcnXYZ, basics,
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bios, core, clk_mgr, hwss, resource, and irq.
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Level: Starter
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Reduce code duplication
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-----------------------
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AMD has an extensive portfolio with various dGPUs and APUs that amdgpu
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supports. To maintain the new hardware release cadence, DCE/DCN was designed in
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a modular design, making the bring-up for new hardware fast. Over the years,
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amdgpu accumulated some technical debt in the code duplication area. For this
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task, it would be a good idea to find a tool that can discover code duplication
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(including patterns) and use it as guidance to reduce duplications.
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Level: Intermediate
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Make atomic_commit_[check|tail] more readable
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---------------------------------------------
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The functions responsible for atomic commit and tail are intricate and
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extensive. In particular `amdgpu_dm_atomic_commit_tail` is a long function and
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could benefit from being split into smaller helpers. Improvements in this area
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are more than welcome, but keep in mind that changes in this area will affect
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all ASICs, meaning that refactoring requires a comprehensive verification; in
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other words, this effort can take some time for validation.
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Level: Advanced
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Documentation
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=============
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Expand kernel-doc
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-----------------
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Many DC functions do not have a proper kernel-doc; understanding a function and
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adding documentation is a great way to learn more about the amdgpu driver and
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also leave an outstanding contribution to the entire community.
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Level: Starter
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Beyond AMDGPU
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=============
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AMDGPU provides features that are not yet enabled in the userspace. This
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section highlights some of the coolest display features, which could be enabled
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with the userspace developer helper.
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Enable underlay
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---------------
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AMD display has this feature called underlay (which you can read more about at
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'Documentation/GPU/amdgpu/display/mpo-overview.rst') which is intended to
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save power when playing a video. The basic idea is to put a video in the
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underlay plane at the bottom and the desktop in the plane above it with a hole
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in the video area. This feature is enabled in ChromeOS, and from our data
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measurement, it can save power.
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Level: Unknown
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Adaptive Backlight Modulation (ABM)
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-----------------------------------
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ABM is a feature that adjusts the display panel's backlight level and pixel
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values depending on the displayed image. This power-saving feature can be very
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useful when the system starts to run off battery; since this will impact the
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display output fidelity, it would be good if this option was something that
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users could turn on or off.
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Level: Unknown
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HDR & Color management & VRR
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----------------------------
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HDR, Color Management, and VRR are huge topics and it's hard to put these into
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concise ToDos. If you are interested in this topic, we recommend checking some
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blog posts from the community developers to better understand some of the
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specific challenges and people working on the subject. If anyone wants to work
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on some particular part, we can try to help with some basic guidance. Finally,
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keep in mind that we already have some kernel-doc in place for those areas.
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Level: Unknown
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@ -92,4 +92,5 @@ table of content:
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dcn-blocks.rst
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mpo-overview.rst
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dc-debug.rst
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display-contributing.rst
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dc-glossary.rst
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@ -1,110 +0,0 @@
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===============================================================================
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TODOs
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===============================================================================
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1. Base this on drm-next - WIP
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2. Cleanup commit history
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3. WIP - Drop page flip helper and use DRM's version
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4. DONE - Flatten all DC objects
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* dc_stream/core_stream/stream should just be dc_stream
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* Same for other DC objects
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"Is there any major reason to keep all those abstractions?
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Could you collapse everything into struct dc_stream?
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I haven't looked recently but I didn't get the impression there was a
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lot of design around what was public/protected, more whatever needed
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to be used by someone else was in public."
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~ Dave Airlie
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5. DONE - Rename DC objects to align more with DRM
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* dc_surface -> dc_plane_state
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* dc_stream -> dc_stream_state
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6. DONE - Per-plane and per-stream validation
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7. WIP - Per-plane and per-stream commit
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8. WIP - Split pipe_ctx into plane and stream resource structs
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9. Attach plane and stream reources to state object instead of validate_context
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10. Remove dc_edid_caps and drm_helpers_parse_edid_caps
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* Use drm_display_info instead
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* Remove DC's edid quirks and rely on DRM's quirks (add quirks if needed)
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"Making sure you use the sink-specific helper libraries and kernel
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subsystems, since there's really no good reason to have 2nd
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implementation of those in the kernel. Looks likes that's done for mst
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and edid parsing. There's still a bit a midlayer feeling to the edid
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parsing side (e.g. dc_edid_caps and dm_helpers_parse_edid_caps, I
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think it'd be much better if you convert that over to reading stuff
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from drm_display_info and if needed, push stuff into the core). Also,
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I can't come up with a good reason why DC needs all this (except to
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reimplement half of our edid quirk table, which really isn't a good
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idea). Might be good if you put this onto the list of things to fix
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long-term, but imo not a blocker. Definitely make sure new stuff
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doesn't slip in (i.e. if you start adding edid quirks to DC instead of
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the drm core, refactoring to use the core edid stuff was pointless)."
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~ Daniel Vetter
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11. Remove dc/i2caux. This folder can be somewhat misleading. It's basically an
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overy complicated HW programming function for sendind and receiving i2c/aux
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commands. We can greatly simplify that and move it into dc/dceXYZ like other
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HW blocks.
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12. drm_modeset_lock in MST should no longer be needed in recent kernels
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* Adopt appropriate locking scheme
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13. get_modes and best_encoder callbacks look a bit funny. Can probably rip out
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a few indirections, and consider removing entirely and using the
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drm_atomic_helper_best_encoder default behaviour.
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14. core/dc_debug.c, consider switching to the atomic state debug helpers and
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moving all your driver state printing into the various atomic_print_state
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callbacks. There's also plans to expose this stuff in a standard way across all
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drivers, to make debugging userspace compositors easier across different hw.
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15. Move DP/HDMI dual mode adaptors to drm_dp_dual_mode_helper.c. See
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dal_ddc_service_i2c_query_dp_dual_mode_adaptor.
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16. Move to core SCDC helpers (I think those are new since initial DC review).
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17. There's still a pretty massive layer cake around dp aux and DPCD handling,
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with like 3 levels of abstraction and using your own structures instead of the
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stuff in drm_dp_helper.h. drm_dp_helper.h isn't really great and already has 2
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incompatible styles, just means more reasons not to add a third (or well third
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one gets to do the cleanup refactor).
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18. There's a pile of sink handling code, both for DP and HDMI where I didn't
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immediately recognize the standard. I think long term it'd be best for the drm
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subsystem if we try to move as much of that into helpers/core as possible, and
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share it with drivers. But that's a very long term goal, and by far not just an
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issue with DC - other drivers, especially around DP sink handling, are equally
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guilty.
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19. DONE - The DC logger is still a rather sore thing, but I know that the
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DRM_DEBUG stuff just isn't up to the challenges either. We need to figure out
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something that integrates better with DRM and linux debug printing, while not
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being useless with filtering output. dynamic debug printing might be an option.
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20. Use kernel i2c device to program HDMI retimer. Some boards have an HDMI
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retimer that we need to program to pass PHY compliance. Currently that's
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bypassing the i2c device and goes directly to HW. This should be changed.
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21. Remove vector.c from dc/basics. It's used in DDC code which can probably
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be simplified enough to no longer need a vector implementation.
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