[PATCH 10/26] drm/amd/display: Fix low black values by increasing error

[Rodrigo Siqueira]

From: Peterson <peterson....@amd.com>

[WHY]
Regamma resolution for the first few black levels can have problems for
calibration.

[HOW]
HW LUT is divided into N power-of-2 regions each with K segments.  For
SDR mode we set min point at 2^-10 and increments of 2^-13. It's
generally more than 8-bit SDR needs, but some calibration tools and API
use 12-bit curves.
The fix shifts starting point to 2^-12 and starting increments at 2^-16.

Reviewed-by: Krunoslav Kovac <krunoslav.ko...@amd.com>
Signed-off-by: Peterson <peterson....@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.sique...@amd.com>
---
 .../amd/display/dc/dcn10/dcn10_cm_common.c    | 25 ++++++++-----------
 .../amd/display/dc/dcn30/dcn30_cm_common.c    | 25 ++++++++-----------
 2 files changed, 20 insertions(+), 30 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_cm_common.c 
b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_cm_common.c
index eaed5d1c398a..dcd2cdfe91eb 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_cm_common.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_cm_common.c
@@ -365,23 +365,18 @@ bool cm_helper_translate_curve_to_hw_format(struct 
dc_context *ctx,
                region_start = -MAX_LOW_POINT;
                region_end   = NUMBER_REGIONS - MAX_LOW_POINT;
        } else {
-               /* 11 segments
-                * segment is from 2^-10 to 2^1
+               /* 13 segments
+                * segment is from 2^-12 to 2^0
                 * There are less than 256 points, for optimization
                 */
-               seg_distr[0] = 3;
-               seg_distr[1] = 4;
-               seg_distr[2] = 4;
-               seg_distr[3] = 4;
-               seg_distr[4] = 4;
-               seg_distr[5] = 4;
-               seg_distr[6] = 4;
-               seg_distr[7] = 4;
-               seg_distr[8] = 4;
-               seg_distr[9] = 4;
-               seg_distr[10] = 1;
-
-               region_start = -10;
+               const uint8_t SEG_COUNT = 12;
+
+               for (i = 0; i < SEG_COUNT; i++)
+                       seg_distr[i] = 4;
+
+               seg_distr[SEG_COUNT] = 1;
+
+               region_start = -SEG_COUNT;
                region_end = 1;
        }
 
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 f31f0e3abfc0..1e1038fb04e8 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
@@ -140,23 +140,18 @@ bool cm3_helper_translate_curve_to_hw_format(
                region_start = -MAX_LOW_POINT;
                region_end   = NUMBER_REGIONS - MAX_LOW_POINT;
        } else {
-               /* 11 segments
-                * segment is from 2^-10 to 2^0
+               /* 13 segments
+                * segment is from 2^-12 to 2^0
                 * There are less than 256 points, for optimization
                 */
-               seg_distr[0] = 3;
-               seg_distr[1] = 4;
-               seg_distr[2] = 4;
-               seg_distr[3] = 4;
-               seg_distr[4] = 4;
-               seg_distr[5] = 4;
-               seg_distr[6] = 4;
-               seg_distr[7] = 4;
-               seg_distr[8] = 4;
-               seg_distr[9] = 4;
-               seg_distr[10] = 1;
-
-               region_start = -10;
+               const uint8_t SEG_COUNT = 12;
+
+               for (i = 0; i < SEG_COUNT; i++)
+                       seg_distr[i] = 4;
+
+               seg_distr[SEG_COUNT] = 1;
+
+               region_start = -SEG_COUNT;
                region_end = 1;
        }
 
-- 
2.45.2