media: v4l: Support obtaining link frequency via get_mbus_config

Add link_freq field to struct v4l2_mbus_config in order to pass the link
frequency to the receiving sub-device.

Signed-off-by: Sakari Ailus <[e-mail]>
Reviewed-by: Tomi Valkeinen <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/v4l2-core/v4l2-common.c

···
 s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul,
 			     unsigned int div)
 {
+	struct v4l2_mbus_config mbus_config = {};
 	struct v4l2_subdev *sd;
+	int ret;
 
 	sd = media_entity_to_v4l2_subdev(pad->entity);
-	if (!sd)
-		return -ENODEV;
+	ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index,
+			       &mbus_config);
+	if (ret < 0 && ret != -ENOIOCTLCMD)
+		return ret;
 
+	if (mbus_config.link_freq)
+		return mbus_config.link_freq;
+
+	/*
+	 * Fall back to using the link frequency control if the media bus config
+	 * doesn't provide a link frequency.
+	 */
 	return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div);
 }
 EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad);

include/media/v4l2-mediabus.h

···
 /**
  * struct v4l2_mbus_config - media bus configuration
  * @type: interface type
+ * @link_freq: The link frequency. See also V4L2_CID_LINK_FREQ control.
  * @bus: bus configuration data structure
  * @bus.parallel: embedded &struct v4l2_mbus_config_parallel.
  *		  Used if the bus is parallel or BT.656.
···
  */
 struct v4l2_mbus_config {
 	enum v4l2_mbus_type type;
+	u64 link_freq;
 	union {
 		struct v4l2_mbus_config_parallel parallel;
 		struct v4l2_mbus_config_mipi_csi1 mipi_csi1;