From b2f3f5920ddb5b121cbc57ee9efc0c1ffe4d19af Mon Sep 17 00:00:00 2001 From: "Leo (Sunpeng) Li" Date: Tue, 3 Apr 2018 16:07:16 -0400 Subject: [PATCH] drm/amd/display: Fix regamma not affecting full-intensity color values Hardware understands the regamma LUT as a piecewise linear function, with points spaced exponentially along the range. We previously programmed the LUT for range [2^-10, 2^0). This causes (normalized) color values of 1 (=2^0) to miss the programmed LUT, and fall onto the end region. For DCE, the end region is extrapolated using a single (base, slope) pair, using the max y-value from the last point in the curve as base. This presents a problem, since this value affects all three color channels. Scaling down the intensity of say - the blue regamma curve - will not affect it's end region. This is especially noticiable when using RedShift. It scales down the blue and green channels, but leaves full-intensity colors unshifted. Therefore, extend the range to cover [2^-10, 2^1) by programming another hardware segment, containing only one point. That way, we won't be hitting the end region. Note that things are a bit different for DCN, since the end region can be set per-channel. Signed-off-by: Leo (Sunpeng) Li Reviewed-by: Krunoslav Kovac Acked-by: Harry Wentland Signed-off-by: Alex Deucher --- .../gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c b/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c index 1c644c7a24b7..d0575999f172 100644 --- a/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c +++ b/drivers/gpu/drm/amd/display/dc/dce110/dce110_hw_sequencer.c @@ -453,10 +453,13 @@ dce110_translate_regamma_to_hw_format(const struct dc_transfer_func *output_tf, } else { /* 10 segments - * segment is from 2^-10 to 2^0 + * segment is from 2^-10 to 2^1 + * We include an extra segment for range [2^0, 2^1). This is to + * ensure that colors with normalized values of 1 don't miss the + * LUT. */ region_start = -10; - region_end = 0; + region_end = 1; seg_distr[0] = 4; seg_distr[1] = 4; @@ -468,7 +471,7 @@ dce110_translate_regamma_to_hw_format(const struct dc_transfer_func *output_tf, seg_distr[7] = 4; seg_distr[8] = 4; seg_distr[9] = 4; - seg_distr[10] = -1; + seg_distr[10] = 0; seg_distr[11] = -1; seg_distr[12] = -1; seg_distr[13] = -1;