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drm/amd/display: Fix OGAM LUT calculation precision 

[Why]
The OGAM LUT precision was accumulating too much error
in the higher end.

[How]
Instead of calculating all points of the LUT in relation
to the previous ones, perform a full calculation in one
of the intermediate segments to stop error propagation.

Signed-off-by: Felipe Clark <Felipe.Clark@amd.com>
Reviewed-by: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Felipe 2020-11-30 17:38:02 -05:00 committed by Alex Deucher
parent 610c4974ad
commit e10777a679
1 changed files with 17 additions and 5 deletions
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22
drivers/gpu/drm/amd/display/modules/color/color_gamma.c
View File

@ -30,6 +30,14 @@
#include "opp.h"
#include "color_gamma.h"
/* When calculating LUT values the first region and at least one subsequent
* region are calculated with full precision. These defines are a demarcation
* of where the second region starts and ends.
* These are hardcoded values to avoid recalculating them in loops.
*/
#define PRECISE_LUT_REGION_START 224
#define PRECISE_LUT_REGION_END 239
static struct hw_x_point coordinates_x[MAX_HW_POINTS + 2];
// these are helpers for calculations to reduce stack usage
@ -346,7 +354,13 @@ static struct fixed31_32 translate_from_linear_space(
dc_fixpt_recip(args->gamma));
}
scratch_1 = dc_fixpt_add(one, args->a3);
if (cal_buffer->buffer_index < 16)
/* In the first region (first 16 points) and in the
* region delimited by START/END we calculate with
* full precision to avoid error accumulation.
*/
if ((cal_buffer->buffer_index >= PRECISE_LUT_REGION_START &&
cal_buffer->buffer_index <= PRECISE_LUT_REGION_END) ||
(cal_buffer->buffer_index < 16))
scratch_2 = dc_fixpt_pow(args->arg,
dc_fixpt_recip(args->gamma));
else
@ -397,9 +411,7 @@ static struct fixed31_32 translate_from_linear_space_long(
dc_fixpt_recip(args->gamma))),
args->a2);
else
return dc_fixpt_mul(
args->arg,
args->a1);
return dc_fixpt_mul(args->arg, args->a1);
}
static struct fixed31_32 calculate_gamma22(struct fixed31_32 arg, bool use_eetf, struct calculate_buffer *cal_buffer)
@ -717,7 +729,6 @@ static struct fixed31_32 calculate_mapped_value(
BREAK_TO_DEBUGGER();
result = dc_fixpt_zero;
} else {
BREAK_TO_DEBUGGER();
result = dc_fixpt_one;
}
@ -976,6 +987,7 @@ static bool build_freesync_hdr(struct pwl_float_data_ex *rgb_regamma,
cal_buffer->buffer_index = 0; // see var definition for more info
rgb += 32; // first 32 points have problems with fixed point, too small
coord_x += 32;
for (i = 32; i <= hw_points_num; i++) {
if (!is_clipped) {
if (use_eetf) {