drm/display: bridge_connector: handle ycbcr_420_allowed

Follow the interlace_allowed example and calculate drm_connector's
ycbcr_420_allowed flag as AND of all drm_bridge's ycbcr_420_allowed
flags in a chain. This is one of the gaps between several
bridge-specific connector implementations and drm_bridge_connector.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241019-bridge-yuv420-v1-1-d74efac9e4e6@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/display/drm_bridge_connector.c

@@ -397,11 +397,11 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 	bridge_connector->encoder = encoder;
 
 	/*
-	 * TODO: Handle doublescan_allowed, stereo_allowed and
-	 * ycbcr_420_allowed.
+	 * TODO: Handle doublescan_allowed and stereo_allowed.
 	 */
 	connector = &bridge_connector->base;
 	connector->interlace_allowed = true;
+	connector->ycbcr_420_allowed = true;
 
 	/*
 	 * Initialise connector status handling. First locate the furthest
@@ -414,6 +414,8 @@ struct drm_connector *drm_bridge_connector_init(struct drm_device *drm,
 	drm_for_each_bridge_in_chain(encoder, bridge) {
 		if (!bridge->interlace_allowed)
 			connector->interlace_allowed = false;
+		if (!bridge->ycbcr_420_allowed)
+			connector->ycbcr_420_allowed = false;
 
 		if (bridge->ops & DRM_BRIDGE_OP_EDID)
 			bridge_connector->bridge_edid = bridge;

include/drm/drm_bridge.h

@@ -802,6 +802,11 @@ struct drm_bridge {
 	 * modes.
 	 */
 	bool interlace_allowed;
+	/**
+	 * @ycbcr_420_allowed: Indicate that the bridge can handle YCbCr 420
+	 * output.
+	 */
+	bool ycbcr_420_allowed;
 	/**
 	 * @pre_enable_prev_first: The bridge requires that the prev
 	 * bridge @pre_enable function is called before its @pre_enable,