On 2026-06-19 06:54, Melissa Wen wrote:
>
>
> On 31/05/2026 19:15, Harry Wentland wrote:
>> On 2026-05-21 10:50, Melissa Wen wrote:
>>>
>>>
>>> On 06/05/2026 21:11, Melissa Wen wrote:
>>>> Hi,
>>>>
>>>> With an external HDR monitor, we can see gradient banding around the sun
>>>> in the intro of Ori and the Will of the Wisps game on steamOS/Gamescope.
>>>> Gamescope uses AMD predefined transfer functions for degamma,
>>>> shaper/pre-3D-LUT and blend/post-3D-LUT plus CRTC regamma, however, only
>>>> degamma block has hardware curves. Shaper, blend, regamma predefined TFs
>>>> are software-computed by AMD color module into PWL LUTs. In addition, we
>>>> cannot use hardware curves on PRE_DEGAM with subsampled format, so that,
>>>> predefined TFs are also translated to LUTs in this situation, using
>>>> GAMCOR block instead. For this translation, the driver originally used
>>>> the same helper for EOTFs and inverse EOTFs, even though they differ in
>>>> input domain, number of regions and number of TF points per region.
>>>
>>> Hello,
>>>
>>> Can someone review this series - and merge it, if everything is okay?
>>>
>>
>> Series is
>> Reviewed-by: Harry Wentland <[email protected]>
>
> Hey Harry,
>
> Thanks for reviewing.
> Was this series applied to AMD's branch?
>
Queued th v3 for merge. Should make it in by tomorrow after going through our
CI.
Harry
> Melissa
>
>>
>> Harry
>>
>>> Thanks,
>>>
>>> Melissa
>>>
>>>>
>>>> Baring this in mind, patch 1 maps degamma predefined curves as LUT using
>>>> GAMCOR block for AMD driver-specific property that are still in use by
>>>> current gamescope. This was inspired by a similar patch from Harry for
>>>> colorop [1]. Patch 2 reverts commit 8b89acc0b2ba ("drm/amd/display:
>>>> Remove unused cm3_helper_translate_curve_to_degamma_hw_format") to
>>>> reintroduce cm3_helper_translate_curve_to_degamma_hw_format() and patch
>>>> 3 wire it up for encoded -> linear-light LUTs (degamma/blend). With 16
>>>> samples per region across 12 regions for blend LUT (where hardware
>>>> fixed-function curves are not available and predefined TFs are
>>>> software-computed into LUTs), banding becomes almost imperceptible.
>>>>
>>>> Patch 4 and 5 increase precision in the brightest half, where PQ/SRGB
>>>> EOTFs are steeper, by enabling up to 256 samples per region and halving
>>>> the per-region point count across 9 regions (128 in [0.5, 1], 64 in
>>>> [0.25, 0.5], …). This better matches the shape of PQ/SRGB EOTFs.
>>>> Although patches 4 and 5 seem conceptually correct to me, I couldn't see
>>>> clear improvement in the bright end with or without them.
>>>>
>>>> This series targets DCN3+ hw families. With this series:
>>>> - degamma and blend LUTs use
>>>> cm3_helper_translate_curve_to_degamma_hw_format(): encoded input,
>>>> non-zero end slope, up to 256 points linearly interpolated between
>>>> adjacent TF pts, fitting [0,1] encoded input range.
>>>> - shaper and regamma LUTs continue using
>>>> cm3_helper_translate_curve_to_hw_format(): linear-light input, zero
>>>> end slope, 16 points per region across 32 regions.
>>>>
>>>> [1] https://lore.kernel.org/dri-devel/20260330153451.99472-8-
>>>> [email protected]/
>>>>
>>>> [v1] https://lore.kernel.org/dri-devel/20260414220237.184289-1-
>>>> [email protected]/
>>>> Changes:
>>>> - new patch for GAMCOR usage in case of degamma predefined TF with
>>>> subsampled formats
>>>> - fix misleading information regarding degamma hw curves (Kruno)
>>>> - clarify LUT segmentation choice using 8-bit sRGB as a reference (Kruno)
>>>>
>>>> Best Regards,
>>>>
>>>> Melissa
>>>>
>>>> Melissa Wen (5):
>>>> drm/amd/display: use GAMCOR for degamma private props in subsampled
>>>> format
>>>> Revert "drm/amd/display: Remove unused
>>>> cm3_helper_translate_curve_to_degamma_hw_format"
>>>> drm/amd/display: use a separate helper to translate degamma curves
>>>> drm/amd/display: support up to 256 samples per region in degamma/blend
>>>> LUT
>>>> drm/amd/display: use halving distribution for PQ/sRGB linearizing LUT
>>>>
>>>> .../amd/display/amdgpu_dm/amdgpu_dm_color.c | 16 +-
>>>> .../amd/display/dc/dcn30/dcn30_cm_common.c | 184 ++++++++++++++++++
>>>> .../display/dc/dwb/dcn30/dcn30_cm_common.h | 4 +
>>>> .../amd/display/dc/hwss/dcn32/dcn32_hwseq.c | 10 +-
>>>> 4 files changed, 204 insertions(+), 10 deletions(-)
>>>>
>>>
>>
>
