Commit e10777a6 authored by Felipe's avatar Felipe Committed by Alex Deucher
Browse files

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: default avatarFelipe Clark <Felipe.Clark@amd.com>
Reviewed-by: default avatarKrunoslav Kovac <Krunoslav.Kovac@amd.com>
Acked-by: default avatarQingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: default avatarAlex Deucher <alexander.deucher@amd.com>
parent 610c4974

drivers/gpu/drm/amd/display/modules/color/color_gamma.c

+17 −5
Original line number Diff line number Diff line
@@ -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) {

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