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

[Harry Wentland <harry.wentland@amd.com>]

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.

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++) {