On 2025-12-08 19:13, Melissa Wen wrote:
>
>
> On 08/12/2025 20:59, Melissa Wen wrote:
>>
>>
>> On 28/11/2025 18:36, Harry Wentland wrote:
>>>
>>> On 2025-11-28 14:09, Melissa Wen wrote:
>>>>
>>>> On 27/11/2025 17:39, Harry Wentland wrote:
>>>>> On 2025-11-25 19:45, Melissa Wen wrote:
>>>>>> The usage of DCN30 CM helper creates some unexpected shimmer points on
>>>>>> PQ shaper TF in the steamOS HDR color pipeline. Fix it by using the same
>>>>>> DCN10 color mgmt helper of previous hw versions to translate plane
>>>>>> shaper func to hw format in DCN32 hw family.
>>>>>>
>>>>>> Signed-off-by: Melissa Wen <[email protected]>
>>>>>> ---
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Commit a953cd8cac6b ("drm/amd/display: Fix MPCC 1DLUT programming")
>>>>>> mentions some visible artifacts when using DCN10 CM helper on DCN32
>>>>>> shaper and blend LUTs. On the other hand, using DCN30 CM helper creates
>>>>>> some shimmer points on steamOS HDR pipeline. We didn't noticed any
>>>>>> visible artifacts so far, but I'd like to know more about what kind of
>>>>>> artifacts were visible at the time this helper for shaper func was
>>>>>> switched in the afore-mentioned commit for further investigation.
>>>>>>
>>>>> Thanks for the debug.
>>>>>
>>>>> Do you have more info on the unexpected shimmer points with SteamOS?
>>>>> Ideally a video and a description on what to look for and why it's
>>>>> wrong, or a comparison to a GFX-transformed example that shows the
>>>>> correct visuals?
>>>> Hi Harry,
>>>>
>>>> I took some pictures of clear unexpected scenes in HDR games.
>>>>
>>>> 1.
>>>> https://people.igalia.com/mwen/hdr-dcn321-pics/HDR-DCN321-split-fiction-game-black-loading-bkg.jpg
>>>>
>>>> Just loading Split Fiction after having turning on HDR in this game
>>>> options (Options > Graphics > HDR).
>>>> We expected a black background with the Loading <icon> in the bottom
>>>> right, this background is full of bright spots.
>>>> Friend pass is enough to reproduce the issue without having the game.
>>>>
>>>> 2.
>>>> https://people.igalia.com/mwen/hdr-dcn321-pics/HDR-DCN321-god-of-war-ragnarok-menu.jpg
>>>>
>>>> Colorful-bright points around the margin/corner of the God of War Ragnarok
>>>> game menu.
>>>>
>>>> 3. God of War Ragnarok game intro:
>>>>
>>>> -
>>>> https://people.igalia.com/mwen/hdr-dcn321-pics/HDR-DCN321-god-of-war-ragnarok-intro1.jpg
>>>> -
>>>> https://people.igalia.com/mwen/hdr-dcn321-pics/HDR-DCN321-god-of-war-ragnarok-intro2.jpg
>>>> -
>>>> https://people.igalia.com/mwen/hdr-dcn321-pics/HDR-DCN321-god-of-war-ragnarok-intro3.jpg
>>>> -
>>>> https://people.igalia.com/mwen/hdr-dcn321-pics/HDR-DCN321-god-of-war-ragnarok-PS-logo.jpg
>>>>
>>>> Same random shimmer distortions.
>>>> I think those images are good examples, but still pending screenshot/GFX
>>>> examples for comparison.
>>>> I'll take it and reply here later.
>>>>
>>> Thanks, that would still be helpful, but even as-is these images
>>> quite highlight the issue. It's more severe than I expected.
>>>
>>>>> Obviously we don't want to simply switch back to DCN10 helpers
>>>>> without understand why, and potentially regressing other use-cases.
>>>>> At least we should look at what the differences are between the
>>>>> two versions of that function, and which part of the curve programming
>>>>> causes the undesirable results.
>>>>>
>>>>> The original bug that was solved by that commit was a regression that
>>>>> sent bright values in an HDR video to black or red, so basically
>>>>> something really messed up bright PQ values. At least I suspect
>>>>> it was a PQ HDR video. The ticket doesn't state that.
>>>> I see. Looks like now we have somehow the same problem but in reverse (?)
>>>> like black values mapped into bright values (?)
>>> Yeah, if I understand your screenshots the issue seems to happen
>>> (mainly) with dark values?
>>>
>>>>> When looking at the diff between the two functions I notice that
>>>>> the cm3_ version is missing the dc_fixpt_clamp_u0d10 for the
>>>>> delta_<color>_reg assignments, toward the bottom of the function.
>>>>> I remember I had to add that to the cm_ version since it caused
>>>>> issues with SteamOS HDR. Can we try that on the cm3_ function?
>>>> Yes, I remember this issue.
>>>>
>>>> I've already tried the same changes from this commit
>>>> (https://gitlab.freedesktop.org/agd5f/linux/-/commit/27fc10d1095f) to
>>>> cm3_helper, but it doesn't help... probably because the commit was
>>>> addressing a different behaviors.
>>>>
>>>> I also noticed on cm3_ they consider a different range of hw points, as in
>>>> this comment:
>>>> "
>>>> // DCN3+ have 257 pts in lieu of no separate slope registers
>>>> // Prior HW had 256 base+slope pairs
>>>> "
>>>>
>>>> Can it be related to this problem?
>>>>
>>> Possibly. The point distribution is one potential culprit.
>>>
>>> How I would debug this is to look at the diff between the two
>>> functions and try each diff one at a time to see whether one
>>> (or two) small changes fixes this. Then look at what that change
>>> was and what it does. That can then give us a guide on how to
>>> properly fix it without affecting other use-cases.
>>
>> Hi Harry,
>>
>> Sorry for the delay. I got swamped with another debugging.
>>
>> I identified to different problems on plane shaper LUT when using the cm3
>> helper: those dark values wrong mapping and banding on some light values.
> ^^^ two
>> I followed your suggestion and found the necessary changes to address both
>> issues, I just sent two RFC patches , so we can discuss it better there.
>>
>> https://lore.kernel.org/amd-gfx/[email protected]/
>>
>> I still see a gradient banding on the game menu of Ori, but it's present
>> with the DCN10 CM helper too.
>>
>> Thanks for taking a look at these problems.
>>
Thanks, I'll have a look.
This is with the AMD_PRIVATE_COLOR stuff, right? Do you know if anyone's
working on migrating gamescope to the now-merged color pipeline API?
Harry
>> Melissa
>>>
>>> The other thing to understand is why we didn't see issues with
>>> the Color Pipeline API tests in IGT.
>>>
>>> Harry
>>>
>>>> Thanks,
>>>>
>>>> Melissa
>>>>
>>>>> Cheers,
>>>>> Harry
>>>>>
>>>>>> Thanks in advance,
>>>>>>
>>>>>> Melissa
>>>>>>
>>>>>>
>>>>>> drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c | 6 +++---
>>>>>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
>>>>>> b/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
>>>>>> index bf19ba65d09a..a28560caa1c0 100644
>>>>>> --- a/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
>>>>>> +++ b/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
>>>>>> @@ -501,9 +501,9 @@ bool dcn32_set_mcm_luts(
>>>>>> lut_params = &plane_state->in_shaper_func.pwl;
>>>>>> else if (plane_state->in_shaper_func.type ==
>>>>>> TF_TYPE_DISTRIBUTED_POINTS) {
>>>>>> // TODO: dpp_base replace
>>>>>> - ASSERT(false);
>>>>>> - cm3_helper_translate_curve_to_hw_format(&plane_state->in_shaper_func,
>>>>>> - &dpp_base->shaper_params, true);
>>>>>> + cm_helper_translate_curve_to_hw_format(plane_state->ctx,
>>>>>> + &plane_state->in_shaper_func,
>>>>>> + &dpp_base->shaper_params, true);
>>>>>> lut_params = &dpp_base->shaper_params;
>>>>>> }
>>
>
