Hi, Xaver first reported flickering when changing GAMMA_LUT often in KDE with an HDR-enabled display: https://gitlab.freedesktop.org/drm/amd/-/issues/4444
This issue is reproducible on Fedora 42 from [1], with integrated and/or external monitors. I was able to reproduce it on DCN3.01, but other users also reported similar issue with DCN3 and DCN4 families. Besides that, when setting Night Light mode and changing a Display setting, such as Overscan, colors on the screen look like gamma LUT was lost (and it was). After further investigation, the root cause of all these problems appears to be the way DM updates the DC stream's color state at `atomic_check`, allowing test-only commit settings to override non-blocking commit settings before it is committed in `commit_tail`. Xaver explained that KWin always performs a test commit without the LUT, then another with the LUT, and finally a non-test-only commit with the same LUT value still set. This sequence makes the issue more likely to occur, as the commit_tail of a non-blocking commit can delay until a subsequent test-only commit without the LUT "removes" the gamma LUT set by the non-blocking commit at `atomic_check` from the DC stream's state. I first tried to address this issue by only programming output transfer func if and only if out_tf flag is set (v1 [2]), but this approach doesn't solve all problems, it only addressed the gamma LUT loss in the case of Night Light mode + Display settings change. Therefore, this version targets the same problem but with a completly different approach. This series resolves all reported issues by moving DC stream color changes from `atomic_check` to `atomic_setup_commit`, preventing test-only commit CRTC color properties from being programmed into `commit_tail`. I see this change in line with the kernel-doc on amdgpu_dm_atomic_check(), which says: "It is important not to modify the existing DC state. Otherwise, atomic_check may unexpectedly commit hardware changes." Adding here a shortened trace that exemplifies this bad sequence with some custom printk to track color settings in `drm_atomic_state`: [ +0.000046] DRM: non block commit call: begin [ +0.000003] amdgpu 0000:04:00.0: [drm:drm_atomic_check_only [drm]] checking 00000000183d1556 <-- non-blocking commit [ +0.000053] amdgpu: AMD DM: atomic_check: CHECK color mgmt: color change: 1, AMD regamma Tf update: 0, needs modeset: 0 for drm_atomic_state: 00000000183d1556 [ +0.000005] amdgpu: program atomic regamma? 1 for drm_atomic_state: 00000000183d1556 [ +0.000003] amdgpu: AMD DM: set_atomic_regamma: PROGRAM regamma [ +0.000699] amdgpu 0000:04:00.0: [drm:drm_atomic_nonblocking_commit [drm]] committing 00000000183d1556 nonblocking [ +0.000076] DRM: non block commit call: end [ +0.000002] amdgpu 0000:04:00.0: [drm:drm_atomic_get_connector_state [drm]] Added [CONNECTOR:93:eDP-1] 00000000c74c75cc state to 00000000bce01e59 <-- test-only commit [[ +0.000046] amdgpu 0000:04:00.0: [drm:drm_atomic_get_crtc_state [drm]] Added [CRTC:79:crtc-0] 000000004fe38ea2 state to 00000000bce01e59 [ +0.000048] amdgpu 0000:04:00.0: [drm:drm_atomic_get_plane_state [drm]] Added [PLANE:76:plane-6] 00000000a3ba0680 state to 00000000bce01e59 [ -0.000252] amdgpu 0000:04:00.0: [drm:amdgpu_dm_atomic_commit_tail [amdgpu]] amdgpu_crtc id:0 crtc_state_flags: enable:1, active:1, planes_changed:1, mode_changed:0,active_changed:0,connectors_changed:0 [ +0.000045] amdgpu 0000:04:00.0: [drm:drm_atomic_get_plane_state [drm]] Added [PLANE:58:plane-3] 0000000007ae0fe5 state to 00000000bce01e59 [ +0.000073] DRM: color mgmt changed for DEGAMMA? 0 [ +0.000054] DRM: color mgmt changed for CTM? 0 [ +0.000314] DRM: color mgmt changed for REGAMMA? 1 [ +0.000004] DRM: TEST ONLY call: begin [ +0.000003] amdgpu 0000:04:00.0: [drm:drm_atomic_check_only [drm]] checking 00000000bce01e59 <-- test-only commit [ +0.000055] amdgpu: AMD DM: atomic check: CHECK color mgmt: color change: 1, AMD regamma Tf update: 0, needs modeset: 0 for drm_atomic_state: 00000000bce01e59 [ +0.000005] amdgpu: program atomic regamma? 0 for drm_atomic_state 00000000bce01e59 [ +0.000003] amdgpu: AMD DM: set atomic regamma: REMOVE regamma [ +0.000247] amdgpu 0000:04:00.0: [drm:amdgpu_dm_atomic_commit_tail [amdgpu]] [HDCP_DM] pipe_ctx dispname=ANX7530 U [ +0.000441] amdgpu 0000:04:00.0: [drm:amdgpu_dm_atomic_commit_tail [amdgpu]] crtc:0, pflip_stat:AMDGPU_FLIP_SUBMITTED [ +0.000731] amdgpu: AMD DM: commit planes: color mgmt changed, out tf type: 2 for drm_atomic_commit 00000000183d1556 <-- non-blocking commit taking out TF = BYPASS [ +0.000570] DC: set_output_transfer_func? enable: 0, out_tf:1 [ +0.000005] DC: set_output_transfer_func: begin [ +0.000004] DC: set_output_transfer_func: configure output gamma: 2 <-- BYPASS [ +0.000004] DC: set_output_gamma: begin [ +0.000002] DC: set_output_gamma: DISABLE OGAM [ +0.000107] amdgpu 0000:04:00.0: [drm:drm_atomic_state_default_clear [drm]] Clearing atomic state 00000000183d1556 [ +0.000053] DRM: TEST ONLY call: end [ +0.000008] amdgpu 0000:04:00.0: [drm:drm_atomic_state_default_clear [drm]] Clearing atomic state 00000000bce01e59 [ +0.000012] amdgpu 0000:04:00.0: [drm:__drm_atomic_state_free [drm]] Freeing atomic state 00000000bce01e59 [ +0.000085] amdgpu 0000:04:00.0: [drm:__drm_atomic_state_free [drm]] Freeing atomic state 00000000183d1556 I hope this trace can illustrate the situation. [1] https://bodhi.fedoraproject.org/updates/FEDORA-2025-b58c14c454 [2] https://lore.kernel.org/amd-gfx/20250822211552.1472375-1-m...@igalia.com/ PS: maybe we should do a follow-up refactor in the amdgpu_dm_atomic_check() and move other DC state changes from `atomic_check` to `atomic_setup_commit`. Best Regards, Melissa Melissa Wen (2): drm/amd/display: update color on atomic commit time drm/amd/display: change dc stream color settings only in atomic commit .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 38 ++++++- .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h | 1 + .../amd/display/amdgpu_dm/amdgpu_dm_color.c | 105 +++++++++++++++++- 3 files changed, 139 insertions(+), 5 deletions(-) -- 2.47.2
