drm/msm/dsi: Migrate to drm_dsc_compute_rc_parameters()

As per the FIXME this code is entirely duplicate with what is already
provided inside drm_dsc_compute_rc_parameters(), supposedly because that
function was yielding "incorrect" results while in reality the panel
driver(s?) used for testing were providing incorrect parameters.

For example, this code from downstream assumed dsc->bits_per_pixel to
contain an integer value, whereas the upstream drm_dsc_config struct
stores it with 4 fractional bits.  drm_dsc_compute_rc_parameters()
already accounts for this feat while the panel driver used for testing
[1] wasn't, hence making drm_dsc_compute_rc_parameters() seem like it
was returning an incorrect result.
Other users of dsc->bits_per_pixel inside dsi_populate_dsc_params() also
treat it in the same erroneous way, and will be addressed in a separate
patch.
In the end, using drm_dsc_compute_rc_parameters() spares both a lot of
duplicate code and erratic behaviour.

[1]: https://git.linaro.org/people/vinod.koul/kernel.git/commit/?h=topic/pixel3_5.18-rc1&id=1d7d98ad564f1ec69e7525e07418918d90f247a1

Fixes: b908032 ("drm/msm/dsi: add support for dsc data")
Reviewed-by: Abhinav Kumar <[email protected]>
Signed-off-by: Marijn Suijten <[email protected]>
Reviewed-by: Dmitry Baryshkov <[email protected]>
Patchwork: https://patchwork.freedesktop.org/patch/508939/
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Dmitry Baryshkov <[email protected]>

Author: MarijnS95

drivers/gpu/drm/msm/dsi/dsi_host.c

@@ -21,6 +21,7 @@
 
 #include <video/mipi_display.h>
 
+#include <drm/display/drm_dsc_helper.h>
 #include <drm/drm_of.h>
 
 #include "dsi.h"
@@ -1749,14 +1750,6 @@ static char bpg_offset[DSC_NUM_BUF_RANGES] = {
 
 static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
 {
-	int mux_words_size;
-	int groups_per_line, groups_total;
-	int min_rate_buffer_size;
-	int hrd_delay;
-	int pre_num_extra_mux_bits, num_extra_mux_bits;
-	int slice_bits;
-	int data;
-	int final_value, final_scale;
 	int i;
 
 	dsc->rc_model_size = 8192;
@@ -1782,11 +1775,11 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
 	if (dsc->bits_per_pixel != 8)
 		dsc->initial_offset = 2048;	/* bpp = 12 */
 
-	mux_words_size = 48;		/* bpc == 8/10 */
-	if (dsc->bits_per_component == 12)
-		mux_words_size = 64;
+	if (dsc->bits_per_component <= 10)
+		dsc->mux_word_size = DSC_MUX_WORD_SIZE_8_10_BPC;
+	else
+		dsc->mux_word_size = DSC_MUX_WORD_SIZE_12_BPC;
 
-	dsc->mux_word_size = mux_words_size;
 	dsc->initial_xmit_delay = 512;
 	dsc->initial_scale_value = 32;
 	dsc->first_line_bpg_offset = 12;
@@ -1798,52 +1791,7 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
 	dsc->rc_quant_incr_limit0 = 11;
 	dsc->rc_quant_incr_limit1 = 11;
 
-	/* FIXME: need to call drm_dsc_compute_rc_parameters() so that rest of
-	 * params are calculated
-	 */
-	groups_per_line = DIV_ROUND_UP(dsc->slice_width, 3);
-	dsc->slice_chunk_size = DIV_ROUND_UP(dsc->slice_width * dsc->bits_per_pixel, 8);
-
-	/* rbs-min */
-	min_rate_buffer_size =  dsc->rc_model_size - dsc->initial_offset +
-				dsc->initial_xmit_delay * dsc->bits_per_pixel +
-				groups_per_line * dsc->first_line_bpg_offset;
-
-	hrd_delay = DIV_ROUND_UP(min_rate_buffer_size, dsc->bits_per_pixel);
-
-	dsc->initial_dec_delay = hrd_delay - dsc->initial_xmit_delay;
-
-	dsc->initial_scale_value = 8 * dsc->rc_model_size /
-				       (dsc->rc_model_size - dsc->initial_offset);
-
-	slice_bits = 8 * dsc->slice_chunk_size * dsc->slice_height;
-
-	groups_total = groups_per_line * dsc->slice_height;
-
-	data = dsc->first_line_bpg_offset * 2048;
-
-	dsc->nfl_bpg_offset = DIV_ROUND_UP(data, (dsc->slice_height - 1));
-
-	pre_num_extra_mux_bits = 3 * (mux_words_size + (4 * dsc->bits_per_component + 4) - 2);
-
-	num_extra_mux_bits = pre_num_extra_mux_bits - (mux_words_size -
-			     ((slice_bits - pre_num_extra_mux_bits) % mux_words_size));
-
-	data = 2048 * (dsc->rc_model_size - dsc->initial_offset + num_extra_mux_bits);
-	dsc->slice_bpg_offset = DIV_ROUND_UP(data, groups_total);
-
-	data = dsc->initial_xmit_delay * dsc->bits_per_pixel;
-	final_value =  dsc->rc_model_size - data + num_extra_mux_bits;
-	dsc->final_offset = final_value;
-
-	final_scale = 8 * dsc->rc_model_size / (dsc->rc_model_size - final_value);
-
-	data = (final_scale - 9) * (dsc->nfl_bpg_offset + dsc->slice_bpg_offset);
-	dsc->scale_increment_interval = (2048 * dsc->final_offset) / data;
-
-	dsc->scale_decrement_interval = groups_per_line / (dsc->initial_scale_value - 8);
-
-	return 0;
+	return drm_dsc_compute_rc_parameters(dsc);
 }
 
 static int dsi_host_parse_dt(struct msm_dsi_host *msm_host)