drm/amd/display: Change DSC policy from slices per column to minimum slice height

[why] Minimum slice height is recommended by VESA DSC Spreadsheet user guide

Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
index ef5f84a144c35d7ad449a9b173367929ce9fdf2e..5995bcdfed542bc10d9a49014c40fd5f042e9dbf 100644 (file)
--- a/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
+++ b/drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c
@@ -28,6 +28,23 @@
 #include "dsc.h"
 #include <drm/drm_dp_helper.h>
 
+struct dc_dsc_policy {
+       bool use_min_slices_h;
+       int max_slices_h; // Maximum available if 0
+       int min_sice_height; // Must not be less than 8
+       int max_target_bpp;
+       int min_target_bpp; // Minimum target bits per pixel
+};
+
+const struct dc_dsc_policy dsc_policy = {
+       .use_min_slices_h = true, // DSC Policy: Use minimum number of slices that fits the pixel clock
+       .max_slices_h = 0, // DSC Policy: Use max available slices (in our case 4 for or 8, depending on the mode)
+       .min_sice_height = 108, // DSC Policy: Use slice height recommended by VESA DSC Spreadsheet user guide
+       .max_target_bpp = 16,
+       .min_target_bpp = 8,
+};
+
+
 /* This module's internal functions */
 
 static bool dsc_buff_block_size_from_dpcd(int dpcd_buff_block_size, int *buff_block_size)
@@ -241,14 +258,6 @@ static bool intersect_dsc_caps(
        return true;
 }
 
-struct dc_dsc_policy {
-       bool use_min_slices_h;
-       int max_slices_h; // Maximum available if 0
-       int num_slices_v;
-       int max_target_bpp;
-       int min_target_bpp; // Minimum target bits per pixel
-};
-
 static inline uint32_t dsc_div_by_10_round_up(uint32_t value)
 {
        return (value + 9) / 10;
@@ -270,19 +279,6 @@ static inline uint32_t calc_dsc_bpp_x16(uint32_t stream_bandwidth_kbps, uint32_t
        return dsc_target_bpp_x16;
 }
 
-const struct dc_dsc_policy dsc_policy = {
-       .use_min_slices_h = true, // DSC Policy: Use minimum number of slices that fits the pixel clock
-       .max_slices_h = 0, // DSC Policy: Use max available slices (in our case 4 for or 8, depending on the mode)
-       /* DSC Policy: Number of vertical slices set to 2 for no particular reason.
-        * Seems small enough to not affect the quality too much, while still providing some error
-        * propagation control (which may also help debugging).
-        */
-       .num_slices_v = 16,
-       .max_target_bpp = 16,
-       .min_target_bpp = 8,
-};
-
-
 /* Get DSC bandwidth range based on [min_bpp, max_bpp] target bitrate range, and timing's pixel clock
  * and uncompressed bandwidth.
  */
@@ -528,8 +524,8 @@ static bool setup_dsc_config(
        int sink_per_slice_throughput_mps;
        int branch_max_throughput_mps = 0;
        bool is_dsc_possible = false;
-       int num_slices_v;
        int pic_height;
+       int slice_height;
 
        memset(dsc_cfg, 0, sizeof(struct dc_dsc_config));
 
@@ -615,7 +611,7 @@ static bool setup_dsc_config(
        if (!is_dsc_possible)
                goto done;
 
-       // DSC slicing
+       // Slice width (i.e. number of slices per line)
        max_slices_h = get_max_dsc_slices(dsc_common_caps.slice_caps);
 
        while (max_slices_h > 0) {
@@ -678,29 +674,26 @@ static bool setup_dsc_config(
        dsc_cfg->num_slices_h = num_slices_h;
        slice_width = pic_width / num_slices_h;
 
-       // Vertical number of slices: start from policy and pick the first one that height is divisible by.
+       is_dsc_possible = slice_width <= dsc_common_caps.max_slice_width;
+       if (!is_dsc_possible)
+               goto done;
+
+       // Slice height (i.e. number of slices per column): start with policy and pick the first one that height is divisible by.
        // For 4:2:0 make sure the slice height is divisible by 2 as well.
-       num_slices_v = dsc_policy.num_slices_v;
-       if (num_slices_v < 1)
-               num_slices_v = 1;
-
-       while (num_slices_v >= 1) {
-               if (timing->pixel_encoding == PIXEL_ENCODING_YCBCR420) {
-                       int slice_height = pic_height / num_slices_v;
-                       if (pic_height % num_slices_v == 0 && slice_height % 2 == 0)
-                               break;
-               } else if (pic_height % num_slices_v == 0)
-                       break;
+       slice_height = min(dsc_policy.min_sice_height, pic_height);
 
-               num_slices_v--;
-       }
+       while (slice_height < pic_height && (pic_height % slice_height != 0 ||
+               (timing->pixel_encoding == PIXEL_ENCODING_YCBCR420 && slice_height % 2 != 0)))
+               slice_height++;
 
-       dsc_cfg->num_slices_v = num_slices_v;
+       if (timing->pixel_encoding == PIXEL_ENCODING_YCBCR420) // For the case when pic_height < dsc_policy.min_sice_height
+               is_dsc_possible = (slice_height % 2 == 0);
 
-       is_dsc_possible = slice_width <= dsc_common_caps.max_slice_width;
        if (!is_dsc_possible)
                goto done;
 
+       dsc_cfg->num_slices_v = pic_height/slice_height;
+
        // Final decission: can we do DSC or not?
        if (is_dsc_possible) {
                // Fill out the rest of DSC settings