From 4278d65a41a2f6530437738f158f69e379bddb1c Mon Sep 17 00:00:00 2001 From: Melissa Wen Date: Thu, 20 Aug 2026 11:26:37 +0200 Subject: [PATCH] drm/amd/display: use halving distribution for all encode-to-linear curves In encode-to-linear conversions, LUT entries should be uniformly distributed across the input range: non-linear encodings are already approximately perceptually uniform, so every input code carries the same weight. A fixed count per region does the opposite, concentrating entries on the darker values and leaving few for the bright end, whereas halving distribution spaces all 256 entries uniformly. This holds for any encoded input, so remove the PQ/sRGB condition from commit "drm/amd/display: use halving distribution for PQ/sRGB linearizing LUT" and apply halving to all encode-to-linear operations (pre-defined TF or user LUTs). It fixes the following IGT kms_colorop subtests: - plane-XR30-XR30-srgb_inv_eotf_lut-srgb_eotf_lut - plane-XR30-XR30-gamma_2_2-gamma_2_2_inv-gamma_2_2 Fixes: a71d2b051f33 ("drm/amd/display: use halving distribution for PQ/sRGB linearizing LUT") Reviewed-by: Alex Hung Reviewed-by: Harry Wentland Signed-off-by: Melissa Wen Signed-off-by: Alex Deucher (cherry picked from commit 6df7c9c307e72e7f13829e94edc89134f0764775) --- .../amd/display/dc/dcn30/dcn30_cm_common.c | 34 ++++++------------- 1 file changed, 10 insertions(+), 24 deletions(-) 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 66fe7f313ea3..62ca235cd649 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 @@ -320,6 +320,8 @@ static struct fixed31_32 interp_tf_pts(const struct fixed31_32 *output_tf_channe return value; } +#define NUM_DEGAMMA_REGIONS 9 + bool cm3_helper_translate_curve_to_degamma_hw_format( const struct dc_transfer_func *output_tf, struct pwl_params *lut_params) @@ -343,31 +345,15 @@ bool cm3_helper_translate_curve_to_degamma_hw_format( memset(lut_params, 0, sizeof(struct pwl_params)); memset(seg_distr, 0, sizeof(seg_distr)); - if (output_tf->tf == TRANSFER_FUNCTION_PQ || - output_tf->tf == TRANSFER_FUNCTION_SRGB) { - /* 9 segments - * segments are from 2^-9 to 0 - */ - const uint8_t SEG_COUNT = 9; - seg_distr[0] = 0; // Since we only have one point in darkest region - for (k = 1; k < SEG_COUNT; k++) - seg_distr[k] = k - 1; // 2^(k-1) points per region; halves as k decreases + /* 9 segments + * segments are from 2^-9 to 2^0 + */ + seg_distr[0] = 0; // Since we only have one point in darkest region + for (k = 1; k < NUM_DEGAMMA_REGIONS; k++) + seg_distr[k] = k - 1; // 2^(k-1) points per region; halves as k decreases - region_start = -SEG_COUNT; - region_end = 0; - } else { - /* 12 segments - * segments are from 2^-12 to 2^0 - * There are less than 256 points, for optimization - */ - const uint8_t SEG_COUNT = 12; - - for (i = 0; i < SEG_COUNT; i++) - seg_distr[i] = 4; - - region_start = -SEG_COUNT; - region_end = 0; - } + region_start = -NUM_DEGAMMA_REGIONS; + region_end = 0; for (i = region_end - region_start; i < MAX_REGIONS_NUMBER ; i++) seg_distr[i] = -1;