Re: [PATCH v3 3/5] drm/amd/display: use a separate helper to translate degamma curves

On 6/23/26 09:58, Melissa Wen wrote:
> In newer DCN families, there is no hw predefined curves for shaper,
> blend and regamma. When userspace sets pre-defined curves for these
> blocks, the driver uses AMD color module to program predefined curve as
> LUT. However, it was using the same LUT segmentation for EOTF and
> inverse EOTF by using the same color management helper. This is causing
> banding on blend when PQ predefined curve is set. Besides that, degamma
> predefined HW curve cannot be used with subsampled 4:2:0/4:2:2 formats
> as it affects the linearity of color space in which HW scaler operates.
> 
> To mitigate banding when using the blend block and better support
> subsampled format on degamma, use different translation helpers when
> linearizing and delinearizing.
> 
> Tested-by: Matthew Schwartz <[email protected]>
> Reviewed-by: Harry Wentland <[email protected]>
> Signed-off-by: Melissa Wen <[email protected]>
> ---
>   .../gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c   | 11 ++++-------
>   1 file changed, 4 insertions(+), 7 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 1340f673ec3b..c2ea25927765 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
> @@ -493,11 +493,9 @@ bool dcn32_set_mcm_luts(
>   	if (plane_state->cm.blend_func.type == TF_TYPE_HWPWL)
>   		lut_params = &plane_state->cm.blend_func.pwl;
>   	else if (plane_state->cm.blend_func.type == TF_TYPE_DISTRIBUTED_POINTS) {
> -		result = cm3_helper_translate_curve_to_hw_format(
> -			plane_state->ctx,
> +		result = cm3_helper_translate_curve_to_degamma_hw_format(
>   			&plane_state->cm.blend_func,
> -			&dpp_base->regamma_params,
> -			false);
> +			&dpp_base->regamma_params);
>   		if (!result)
>   			return result;
>   

The above change broke two IGT's kms_colorop subtests (tested on DCN3.5) 
as below

=====================================
Starting subtest: plane-XR30-XR30-srgb_inv_eotf_lut-srgb_eotf_lut
i 2569 j 0 shift 10 mask 3ff comp1 3bf comp2 3ff, pixel1 3bfeffbf pixel2 
3fffffff
[79.216137] (kms_colorop:10824) CRITICAL: Test assertion failure 
function colorop_plane_test, file ../tests/kms_colorop.c:281:
[79.216143] (kms_colorop:10824) CRITICAL: Failed assertion: 
compare_with_bracket(&sw_transform_fb, output_fb)
[79.216165] (kms_colorop:10824) CRITICAL: Last errno: 38, Function not 
implemented
Stack trace: not implemented
Subtest plane-XR30-XR30-srgb_inv_eotf_lut-srgb_eotf_lut failed.

Starting subtest: plane-XR30-XR30-gamma_2_2-gamma_2_2_inv-gamma_2_2
i 15390 j 0 shift 10 mask 3ff comp1 398 comp2 3b8, pixel1 398e6398 
pixel2 3b8ee3b8
[81.747233] (kms_colorop:10824) CRITICAL: Test assertion failure 
function colorop_plane_test, file ../tests/kms_colorop.c:281:
[81.747239] (kms_colorop:10824) CRITICAL: Failed assertion: 
compare_with_bracket(&sw_transform_fb, output_fb)
[81.747256] (kms_colorop:10824) CRITICAL: Last errno: 38, Function not 
implemented
Stack trace: not implemented
Subtest plane-XR30-XR30-gamma_2_2-gamma_2_2_inv-gamma_2_2 failed.
=====================================

The root cause is from color delta increases, as also confirmed by the 
following IGT POC change:

--- tests/kms_colorop.c
+++ tests/kms_colorop.c
@@ -182,7 +182,7 @@ static bool compare_with_bracket(igt_fb_t *in, 
igt_fb_t *out)
                 return igt_cmp_fb_pixels(in, out, 1, 1);

         if (is_amdgpu_device(in->fd))
-               return igt_cmp_fb_pixels(in, out, 13, 13);
+               return igt_cmp_fb_pixels(in, out, 70, 13);


Is there any concerns on reverting above changes (or this patch)?

Note: I am looking for early feedback because I have not yet tested on 
other DCN hardware.


> @@ -554,9 +552,8 @@ bool dcn32_set_input_transfer_func(struct dc *dc,
>   	if (plane_state->in_transfer_func.type == TF_TYPE_HWPWL)
>   		params = &plane_state->in_transfer_func.pwl;
>   	else if (plane_state->in_transfer_func.type == TF_TYPE_DISTRIBUTED_POINTS &&
> -		cm3_helper_translate_curve_to_hw_format(plane_state->ctx,
> -							&plane_state->in_transfer_func,
> -							&dpp_base->degamma_params, false))
> +		cm3_helper_translate_curve_to_degamma_hw_format(&plane_state->in_transfer_func,
> +								&dpp_base->degamma_params))
>   		params = &dpp_base->degamma_params;
>   
>   	dpp_base->funcs->dpp_program_gamcor_lut(dpp_base, params);