From: "Leo (Sunpeng) Li" <sunpeng.li@xxxxxxx>
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 <sunpeng.li at amd.com>
Reviewed-by: Krunoslav Kovac <Krunoslav.Kovac at amd.com>
Acked-by: Harry Wentland <harry.wentland at amd.com>
---
drivers/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 71e4812217bb..0ff2a8092782 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
@@ -456,10 +456,13 @@ 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;
@@ -471,7 +474,7 @@ 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;
--
2.15.1
