On 12/9/25 7:18 AM, Melissa Wen wrote: > > > On 09/12/2025 12:12, Harry Wentland wrote: >> >> On 2025-12-09 09:44, Melissa Wen wrote: >>> >>> On 09/12/2025 11:31, Melissa Wen wrote: >>>> >>>> On 08/12/2025 22:34, Matthew Schwartz wrote: >>>>>> On Dec 8, 2025, at 3:48 PM, Melissa Wen <[email protected]> wrote: >>>>>> >>>>>> There are some unexpected banding and shimmer effects when using >>>>>> steamOS/gamescope color pipeline for HDR on DCN32 or newer families. >>>>>> Those problems are not present in Steam Deck (DCN301). It happens on >>>>>> DCN32 because plane shaper LUT uses DCN30 CM3 helper to translate curves >>>>>> instead of DCN10 CM helper. This series identifies the necessary changes >>>>>> on CM3 helper to reduce differences on color transformation made by >>>>>> those two helpers. >>>>>> >>>>>> Patch 1 aims to solve the shimmer/colorful points that looks like a >>>>>> wrong map of black values on red/green/blue colors. Patch 2 extends the >>>>>> delta clamping fix made in commit 27fc10d1095f ("drm/amd/display: Fix >>>>>> the delta clamping for shaper LUT") to solve some banding effects. >>>>>> >>>>>> Banding is not fully solved by any helper and needs further >>>>>> investigation. >>>>>> >>>>>> One easy way to check the current and expected behavior is moving the >>>>>> cursor (doing composition) to get the expected result from GFX. When the >>>>>> cursor disappears, those color transformations are back to be done by >>>>>> the display hw. >>>>> Hi Melissa, >>>>> >>>>> Could you share how you’re testing the gamescope color pipeline with HDR >>>>> on DCN32, i.e display and connection type? Are any extra gamescope or >>>>> kernel patches required? >>>>> >>>>> At least on my own DCN32 setup (AMD 7900XTX) + my primary monitor (an LG >>>>> 45gx950a-b) via DisplayPort or my DCN35 setup + integrated HDR OLED >>>>> screen (Legion Go 2), gamescope always composites when HDR is enabled. I >>>>> applied your patches on top of kernel 6.18, and my kernel is built with >>>>> CONFIG_DRM_AMD_COLOR_STEAMDECK=y (the downstream name of >>>>> AMD_PRIVATE_COLOR for SteamOS), so that shouldn't be an issue. I tried >>>>> everything from 1280x720p -> 5120x2160p, and it does not work on any >>>>> resolution. >>>> Hi Matt, >>>> >>>> You need to hack the DPP color caps to enabled SHAPER/3D and BLEND LUTs as >>>> below: >>>> >>>> diff --git >>>> i/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c >>>> w/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c >>>> index b276fec3e479..96b4f3239fb1 100644 >>>> --- i/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c >>>> +++ w/drivers/gpu/drm/amd/display/dc/resource/dcn32/dcn32_resource.c >>>> @@ -2256,8 +2256,8 @@ static bool dcn32_resource_construct( >>>> dc->caps.color.dpp.gamma_corr = 1; >>>> dc->caps.color.dpp.dgam_rom_for_yuv = 0; >>>> >>>> - dc->caps.color.dpp.hw_3d_lut = 0; >>>> - dc->caps.color.dpp.ogam_ram = 0; // no OGAM in DPP since DCN1 >>>> + dc->caps.color.dpp.hw_3d_lut = 1; >>>> + dc->caps.color.dpp.ogam_ram = 1; // no OGAM in DPP since DCN1 >>>> // no OGAM ROM on DCN2 and later ASICs >>>> dc->caps.color.dpp.ogam_rom_caps.srgb = 0; >>>> dc->caps.color.dpp.ogam_rom_caps.bt2020 = 0; >>>> >>>> In short, you need to change `caps.color.dpp.hw_3d_lut` and >>>> `caps.color.dpp.ogam_ram` to 1 in the dcnX_resource.c file to say there is >>>> a "plane" color caps. >>>> The thing is that, in DCN32+, these color caps are not part of DPP >>>> anymore, they are MPC capabilities in MCM that can be moved before or >>>> after blending. >>>> But the current kernel implementation checks DPP color caps to expose >>>> plane color proprerties. >>>> Checking MPC and where the MCM is positioned would be more complex, but >>>> not impossible. Something to improve in the future yes. >>> Just found this: dpp_color_caps.hw_3d_lut || >>> dm->dc->caps.color.mpc.preblend >>> (https://gitlab.freedesktop.org/agd5f/linux/-/blob/amd-staging-drm-next/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c#L1636) >>> >>> Should be enough for new kernel versions. So you might need only the blend >>> LUT hack. >>> >>>> You need to confirm that your `drm_info` shows all AMD plane color >>>> properties, but gamescope basically checks CTM and BLEND_TF as you can see >>>> here: >>>> https://github.com/ValveSoftware/gamescope/blob/master/src/Backends/DRMBackend.cpp#L3347 >>>> >> Are you testing this with AMD_PRIVATE_COLOR, or with the newly merged color >> pipeline API? If it's the former, then the kernel needs to be built with an >> explicit -DAMD_PRIVATE_COLOR for this to work. > > I'm testing with cflags, but AFAIU Matthew is using a downstream kernel > version where there is an extra commit that enables AMD_PRIVATE_COLOR via > config option ("CONFIG_DRM_AMD_COLOR_STEAMDECK=y"). > Depends on this kernel version, the hack for 3D LUT and BLEND LUT are both > necessary.
Thanks, I had such a change locally to add back AMD_PLANE_BLEND_TF but I was seeing some color banding in Ori and the Will of the Wisps menu around the sun in the upper left corner which gave me pause. I see you mentioned something similar in one of the threads [1] though, so we're all on the same page now. I'm not sure if you've also tried this, but gamescopectl drm_debug_disable_output_tf 1 seems to work around the color banding in that case. From what I could tell, this bypasses the hardware LUTs while HDR scanout continues working in gamescope. We lose blending on the MangoHud overlay by disabling that though. I was thinking maybe it's due to the MCM block only doing preblend unlike DPP blending, but I could definitely be on the wrong track here... [1]: https://lore.kernel.org/amd-gfx/[email protected]/ > >> >> Harry >> >>>> Let me know if it works for you. >>>> >>>> BR, >>>> >>>> Melissa >>>> >>>>> Thanks, >>>>> Matt >>>>> >>>>>> Lemme know your thoughts! >>>>>> >>>>>> Melissa >>>>>> >>>>>> Melissa Wen (2): >>>>>> drm/amd/display: fix wrong color value mapping on DCN32 shaper LUT >>>>>> drm/amd/display: extend delta clamping logic to CM3 LUT helper >>>>>> >>>>>> .../amd/display/dc/dcn30/dcn30_cm_common.c | 32 +++++++++++++++---- >>>>>> .../display/dc/dwb/dcn30/dcn30_cm_common.h | 2 +- >>>>>> .../amd/display/dc/hwss/dcn30/dcn30_hwseq.c | 9 +++--- >>>>>> .../amd/display/dc/hwss/dcn32/dcn32_hwseq.c | 17 ++++++---- >>>>>> .../amd/display/dc/hwss/dcn401/dcn401_hwseq.c | 16 ++++++---- >>>>>> 5 files changed, 50 insertions(+), 26 deletions(-) >>>>>> >>>>>> -- >>>>>> 2.51.0 >>>>>> >
