Re: [RFC PATCH 1/2] drm/amd/display: fix wrong color value mapping on DCN32 shaper LUT

[Alex Hung <alex.hung@amd.com>]

On 1/16/26 13:29, Harry Wentland wrote:
> 
> 
> On 2025-12-08 18:44, Melissa Wen wrote:
>> We've seen some shimmer points on DCN32 when using the steamOS color
>> pipeline for HDR on gaming. Looks like black values being wrongly mapped
>> to red/blue/green values. Fiz that by using the exact number of
>> hw_points computed in the LUT segmentation. Probably the whole logic
>> that adds +1 to the latest points should be revisited.
>>
>> Signed-off-by: Melissa Wen <mwen@igalia.com>
> 
> I haven't had a chance to trace the hw_points logic but am
> inclined to take the patch if it fixes things. My only concern
> is that it reverts part of Kruno's change to increase the points
> by 1 so I wonder if it could break something else subtly.
> 
> Alex Hung will follow up and get back on it.

I will check with Kruno and forward this to next week's promotion test.

> 
> Harry
> 
>> ---
>>   drivers/gpu/drm/amd/display/dc/dcn30/dcn30_cm_common.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_cm_common.c b/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_cm_common.c
>> index 0690c346f2c5..ba20575be214 100644
>> --- a/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_cm_common.c
>> +++ b/drivers/gpu/drm/amd/display/dc/dcn30/dcn30_cm_common.c
>> @@ -225,7 +225,7 @@ bool cm3_helper_translate_curve_to_hw_format(
>>   
>>   	// DCN3+ have 257 pts in lieu of no separate slope registers
>>   	// Prior HW had 256 base+slope pairs
>> -	lut_params->hw_points_num = hw_points + 1;
>> +	lut_params->hw_points_num = hw_points;
>>   
>>   	k = 0;
>>   	for (i = 1; i < MAX_REGIONS_NUMBER; i++) {
>