drm/amd/display: Create fake sink and stream for writeback connector

[WHAT]
Writeback connectors don't have a physical sink but DC still
needs a sink to function. Create a fake sink and stream for
writeback connectors
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -5755,13 +5755,13 @@ decide_crtc_timing_for_drm_display_mode(struct drm_display_mode *drm_mode,
 }
 
 static struct dc_sink *
-create_fake_sink(struct amdgpu_dm_connector *aconnector)
+create_fake_sink(struct dc_link *link)
 {
 	struct dc_sink_init_data sink_init_data = { 0 };
 	struct dc_sink *sink = NULL;
 
-	sink_init_data.link = aconnector->dc_link;
-	sink_init_data.sink_signal = aconnector->dc_link->connector_signal;
+	sink_init_data.link = link;
+	sink_init_data.sink_signal = link->connector_signal;
 
 	sink = dc_sink_create(&sink_init_data);
 	if (!sink) {
@@ -6132,6 +6132,7 @@ create_stream_for_sink(struct drm_connector *connector,
 	enum color_transfer_func tf = TRANSFER_FUNC_UNKNOWN;
 	struct dsc_dec_dpcd_caps dsc_caps;
 
+	struct dc_link *link = NULL;
 	struct dc_sink *sink = NULL;
 
 	drm_mode_init(&mode, drm_mode);
@@ -6145,14 +6146,24 @@ create_stream_for_sink(struct drm_connector *connector,
 	if (connector->connector_type != DRM_MODE_CONNECTOR_WRITEBACK) {
 		aconnector = NULL;
 		aconnector = to_amdgpu_dm_connector(connector);
-		if (!aconnector->dc_sink) {
-			sink = create_fake_sink(aconnector);
-			if (!sink)
-				return stream;
-		} else {
-			sink = aconnector->dc_sink;
-			dc_sink_retain(sink);
-		}
+		link = aconnector->dc_link;
+	} else {
+		struct drm_writeback_connector *wbcon = NULL;
+		struct amdgpu_dm_wb_connector *dm_wbcon = NULL;
+
+		wbcon = drm_connector_to_writeback(connector);
+		dm_wbcon = to_amdgpu_dm_wb_connector(wbcon);
+		link = dm_wbcon->link;
+	}
+
+	if (!aconnector || !aconnector->dc_sink) {
+		sink = create_fake_sink(link);
+		if (!sink)
+			return stream;
+
+	} else {
+		sink = aconnector->dc_sink;
+		dc_sink_retain(sink);
 	}
 
 	stream = dc_create_stream_for_sink(sink);