drm/amd/display: Add debug option to override DSC target bpp increment

[why]
It's required for debug purposes.

[how]
Add a dsc_bpp_increment_div debug option that overrides DPCD
BITS_PER_PIXEL_INCREMENT value. The value dsc_bpp_increment_div should
be set to is the one after parsing, i.e. it could be 1, 2, 4, 8 or 16
(meaning 1pix, 1/2pix, ..., 1/16pix).
Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -4075,7 +4075,8 @@ create_stream_for_sink(struct amdgpu_dm_connector *aconnector,
 
 	if (aconnector->dc_link && sink->sink_signal == SIGNAL_TYPE_DISPLAY_PORT) {
 #if defined(CONFIG_DRM_AMD_DC_DCN)
-		dc_dsc_parse_dsc_dpcd(aconnector->dc_link->dpcd_caps.dsc_caps.dsc_basic_caps.raw,
+		dc_dsc_parse_dsc_dpcd(aconnector->dc_link->ctx->dc,
+				      aconnector->dc_link->dpcd_caps.dsc_caps.dsc_basic_caps.raw,
 				      aconnector->dc_link->dpcd_caps.dsc_caps.dsc_ext_caps.raw,
 				      &dsc_caps);
 #endif

drivers/gpu/drm/amd/display/dc/dc.h

@@ -367,6 +367,7 @@ struct dc_debug_options {
 	bool disable_hubp_power_gate;
 	bool disable_dsc_power_gate;
 	int dsc_min_slice_height_override;
+	int dsc_bpp_increment_div;
 	bool native422_support;
 	bool disable_pplib_wm_range;
 	enum wm_report_mode pplib_wm_report_mode;

drivers/gpu/drm/amd/display/dc/dc_dsc.h

@@ -53,7 +53,8 @@ struct dc_dsc_policy {
 	uint32_t min_target_bpp;
 };
 
-bool dc_dsc_parse_dsc_dpcd(const uint8_t *dpcd_dsc_basic_data,
+bool dc_dsc_parse_dsc_dpcd(const struct dc *dc,
+		const uint8_t *dpcd_dsc_basic_data,
 		const uint8_t *dpcd_dsc_ext_data,
 		struct dsc_dec_dpcd_caps *dsc_sink_caps);
 

drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c

@@ -760,7 +760,7 @@ static bool setup_dsc_config(
 	return is_dsc_possible;
 }
 
-bool dc_dsc_parse_dsc_dpcd(const uint8_t *dpcd_dsc_basic_data, const uint8_t *dpcd_dsc_ext_data, struct dsc_dec_dpcd_caps *dsc_sink_caps)
+bool dc_dsc_parse_dsc_dpcd(const struct dc *dc, const uint8_t *dpcd_dsc_basic_data, const uint8_t *dpcd_dsc_ext_data, struct dsc_dec_dpcd_caps *dsc_sink_caps)
 {
 	if (!dpcd_dsc_basic_data)
 		return false;
@@ -813,6 +813,23 @@ bool dc_dsc_parse_dsc_dpcd(const uint8_t *dpcd_dsc_basic_data, const uint8_t *dp
 	if (!dsc_bpp_increment_div_from_dpcd(dpcd_dsc_basic_data[DP_DSC_BITS_PER_PIXEL_INC - DP_DSC_SUPPORT], &dsc_sink_caps->bpp_increment_div))
 		return false;
 
+	if (dc->debug.dsc_bpp_increment_div) {
+		/* dsc_bpp_increment_div should onl be 1, 2, 4, 8 or 16, but rather than rejecting invalid values,
+		 * we'll accept all and get it into range. This also makes the above check against 0 redundant,
+		 * but that one stresses out the override will be only used if it's not 0.
+		 */
+		if (dc->debug.dsc_bpp_increment_div >= 1)
+			dsc_sink_caps->bpp_increment_div = 1;
+		if (dc->debug.dsc_bpp_increment_div >= 2)
+			dsc_sink_caps->bpp_increment_div = 2;
+		if (dc->debug.dsc_bpp_increment_div >= 4)
+			dsc_sink_caps->bpp_increment_div = 4;
+		if (dc->debug.dsc_bpp_increment_div >= 8)
+			dsc_sink_caps->bpp_increment_div = 8;
+		if (dc->debug.dsc_bpp_increment_div >= 16)
+			dsc_sink_caps->bpp_increment_div = 16;
+	}
+
 	/* Extended caps */
 	if (dpcd_dsc_ext_data == NULL) { // Extended DPCD DSC data can be null, e.g. because it doesn't apply to SST
 		dsc_sink_caps->branch_overall_throughput_0_mps = 0;