drm/amd/display: Retrieve MST Downstream Port Status

Determine if DFP present and the type of downstream device
based on dsc_aux
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -604,6 +604,7 @@ struct amdgpu_dm_connector {
 #endif
 	bool force_yuv420_output;
 	struct dsc_preferred_settings dsc_settings;
+	union dp_downstream_port_present mst_downstream_port_present;
 	/* Cached display modes */
 	struct drm_display_mode freesync_vid_base;
 

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

@@ -209,6 +209,25 @@ static bool validate_dsc_caps_on_connector(struct amdgpu_dm_connector *aconnecto
 
 	return true;
 }
+
+bool retrieve_downstream_port_device(struct amdgpu_dm_connector *aconnector)
+{
+	union dp_downstream_port_present ds_port_present;
+
+	if (!aconnector->dsc_aux)
+		return false;
+
+	if (drm_dp_dpcd_read(aconnector->dsc_aux, DP_DOWNSTREAMPORT_PRESENT, &ds_port_present, 1) < 0) {
+		DRM_INFO("Failed to read downstream_port_present 0x05 from DFP of branch device\n");
+		return false;
+	}
+
+	aconnector->mst_downstream_port_present = ds_port_present;
+	DRM_INFO("Downstream port present %d, type %d\n",
+			ds_port_present.fields.PORT_PRESENT, ds_port_present.fields.PORT_TYPE);
+
+	return true;
+}
 #endif
 
 static int dm_dp_mst_get_modes(struct drm_connector *connector)
@@ -289,6 +308,10 @@ static int dm_dp_mst_get_modes(struct drm_connector *connector)
 			if (!validate_dsc_caps_on_connector(aconnector))
 				memset(&aconnector->dc_sink->dsc_caps,
 				       0, sizeof(aconnector->dc_sink->dsc_caps));
+
+			if (!retrieve_downstream_port_device(aconnector))
+				memset(&aconnector->mst_downstream_port_present,
+					0, sizeof(aconnector->mst_downstream_port_present));
 #endif
 		}
 	}