drm/i915/dp: Iterate over output bpp with fractional step size

This patch adds support to iterate over compressed output bpp as per the
fractional step, supported by DP sink.

v2:
-Avoid ending up with compressed bpp, same as pipe bpp. (Stan)
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn>
Link: https://patchwork.freedesktop.org/patch/msgid/20231110101020.4067342-7-ankit.k.nautiyal@intel.com

drivers/gpu/drm/i915/display/intel_dp.c

@@ -1737,15 +1737,15 @@ static bool intel_dp_dsc_supports_format(const struct intel_connector *connector
 	return drm_dp_dsc_sink_supports_format(connector->dp.dsc_dpcd, sink_dsc_format);
 }
 
-static bool is_bw_sufficient_for_dsc_config(u16 compressed_bpp, u32 link_clock,
+static bool is_bw_sufficient_for_dsc_config(u16 compressed_bppx16, u32 link_clock,
 					    u32 lane_count, u32 mode_clock,
 					    enum intel_output_format output_format,
 					    int timeslots)
 {
 	u32 available_bw, required_bw;
 
-	available_bw = (link_clock * lane_count * timeslots)  / 8;
-	required_bw = compressed_bpp * (intel_dp_mode_to_fec_clock(mode_clock));
+	available_bw = (link_clock * lane_count * timeslots * 16)  / 8;
+	required_bw = compressed_bppx16 * (intel_dp_mode_to_fec_clock(mode_clock));
 
 	return available_bw > required_bw;
 }
@@ -1753,7 +1753,7 @@ static bool is_bw_sufficient_for_dsc_config(u16 compressed_bpp, u32 link_clock,
 static int dsc_compute_link_config(struct intel_dp *intel_dp,
 				   struct intel_crtc_state *pipe_config,
 				   struct link_config_limits *limits,
-				   u16 compressed_bpp,
+				   u16 compressed_bppx16,
 				   int timeslots)
 {
 	const struct drm_display_mode *adjusted_mode = &pipe_config->hw.adjusted_mode;
@@ -1768,8 +1768,8 @@ static int dsc_compute_link_config(struct intel_dp *intel_dp,
 		for (lane_count = limits->min_lane_count;
 		     lane_count <= limits->max_lane_count;
 		     lane_count <<= 1) {
-			if (!is_bw_sufficient_for_dsc_config(compressed_bpp, link_rate, lane_count,
-							     adjusted_mode->clock,
+			if (!is_bw_sufficient_for_dsc_config(compressed_bppx16, link_rate,
+							     lane_count, adjusted_mode->clock,
 							     pipe_config->output_format,
 							     timeslots))
 				continue;
@@ -1882,7 +1882,7 @@ icl_dsc_compute_link_config(struct intel_dp *intel_dp,
 		ret = dsc_compute_link_config(intel_dp,
 					      pipe_config,
 					      limits,
-					      valid_dsc_bpp[i],
+					      valid_dsc_bpp[i] << 4,
 					      timeslots);
 		if (ret == 0) {
 			pipe_config->dsc.compressed_bpp_x16 =
@@ -1902,6 +1902,7 @@ icl_dsc_compute_link_config(struct intel_dp *intel_dp,
  */
 static int
 xelpd_dsc_compute_link_config(struct intel_dp *intel_dp,
+			      const struct intel_connector *connector,
 			      struct intel_crtc_state *pipe_config,
 			      struct link_config_limits *limits,
 			      int dsc_max_bpp,
@@ -1909,23 +1910,31 @@ xelpd_dsc_compute_link_config(struct intel_dp *intel_dp,
 			      int pipe_bpp,
 			      int timeslots)
 {
-	u16 compressed_bpp;
+	u8 bppx16_incr = drm_dp_dsc_sink_bpp_incr(connector->dp.dsc_dpcd);
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+	u16 compressed_bppx16;
+	u8 bppx16_step;
 	int ret;
 
+	if (DISPLAY_VER(i915) < 14 || bppx16_incr <= 1)
+		bppx16_step = 16;
+	else
+		bppx16_step = 16 / bppx16_incr;
+
 	/* Compressed BPP should be less than the Input DSC bpp */
-	dsc_max_bpp = min(dsc_max_bpp, pipe_bpp - 1);
+	dsc_max_bpp = min(dsc_max_bpp << 4, (pipe_bpp << 4) - bppx16_step);
+	dsc_min_bpp = dsc_min_bpp << 4;
 
-	for (compressed_bpp = dsc_max_bpp;
-	     compressed_bpp >= dsc_min_bpp;
-	     compressed_bpp--) {
+	for (compressed_bppx16 = dsc_max_bpp;
+	     compressed_bppx16 >= dsc_min_bpp;
+	     compressed_bppx16 -= bppx16_step) {
 		ret = dsc_compute_link_config(intel_dp,
 					      pipe_config,
 					      limits,
-					      compressed_bpp,
+					      compressed_bppx16,
 					      timeslots);
 		if (ret == 0) {
-			pipe_config->dsc.compressed_bpp_x16 =
-				to_bpp_x16(compressed_bpp);
+			pipe_config->dsc.compressed_bpp_x16 = compressed_bppx16;
 			return 0;
 		}
 	}
@@ -1963,7 +1972,7 @@ static int dsc_compute_compressed_bpp(struct intel_dp *intel_dp,
 	dsc_max_bpp = min(dsc_max_bpp, to_bpp_int(limits->link.max_bpp_x16));
 
 	if (DISPLAY_VER(i915) >= 13)
-		return xelpd_dsc_compute_link_config(intel_dp, pipe_config, limits,
+		return xelpd_dsc_compute_link_config(intel_dp, connector, pipe_config, limits,
 						     dsc_max_bpp, dsc_min_bpp, pipe_bpp, timeslots);
 	return icl_dsc_compute_link_config(intel_dp, pipe_config, limits,
 					   dsc_max_bpp, dsc_min_bpp, pipe_bpp, timeslots);