drm/i915/dp_mst: Set connector DSC capabilities and decompression AUX

Similarly to eDP and SST-DP connectors read out the DSC capabilities for
MST connectors as well. Atm these will match the root port's DSC caps
and only used after a follow-up change enables the decompression for
each stream separately (vs. the current way of enabling it only globally
in the first branch device downstream of the root port).
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231010112504.2156789-3-imre.deak@intel.com

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

@@ -3483,8 +3483,8 @@ static void intel_dp_read_dsc_dpcd(struct drm_dp_aux *aux,
 		    dsc_dpcd);
 }
 
-static void intel_dp_get_dsc_sink_cap(u8 dpcd_rev, struct intel_dp *intel_dp,
-				      struct intel_connector *connector)
+void intel_dp_get_dsc_sink_cap(u8 dpcd_rev, struct intel_dp *intel_dp,
+			       struct intel_connector *connector)
 {
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 

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

@@ -162,4 +162,7 @@ intel_dp_compute_config_link_bpp_limits(struct intel_dp *intel_dp,
 					bool dsc,
 					struct link_config_limits *limits);
 
+void intel_dp_get_dsc_sink_cap(u8 dpcd_rev, struct intel_dp *intel_dp,
+			       struct intel_connector *connector);
+
 #endif /* __INTEL_DP_H__ */

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

@@ -1126,6 +1126,21 @@ static int intel_dp_mst_add_properties(struct intel_dp *intel_dp,
 	return drm_connector_set_path_property(connector, pathprop);
 }
 
+static void
+intel_dp_mst_read_decompression_port_dsc_caps(struct intel_dp *intel_dp,
+					      struct intel_connector *connector)
+{
+	u8 dpcd_caps[DP_RECEIVER_CAP_SIZE];
+
+	if (!connector->dp.dsc_decompression_aux)
+		return;
+
+	if (drm_dp_read_dpcd_caps(connector->dp.dsc_decompression_aux, dpcd_caps) < 0)
+		return;
+
+	intel_dp_get_dsc_sink_cap(dpcd_caps[DP_DPCD_REV], intel_dp, connector);
+}
+
 static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topology_mgr *mgr,
 							struct drm_dp_mst_port *port,
 							const char *pathprop)
@@ -1159,6 +1174,14 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
 
 	drm_connector_helper_add(connector, &intel_dp_mst_connector_helper_funcs);
 
+	/*
+	 * TODO: set the AUX for the actual MST port decompressing the stream.
+	 * At the moment the driver only supports enabling this globally in the
+	 * first downstream MST branch, via intel_dp's (root port) AUX.
+	 */
+	intel_connector->dp.dsc_decompression_aux = &intel_dp->aux;
+	intel_dp_mst_read_decompression_port_dsc_caps(intel_dp, intel_connector);
+
 	for_each_pipe(dev_priv, pipe) {
 		struct drm_encoder *enc =
 			&intel_dp->mst_encoders[pipe]->base.base;