[media] V4L: Add s_rx_buffer subdev video operation

The s_rx_buffer callback allows the host to set buffer for a data being
received by the subdev, e.g. non-image frame (meta) data. This callback
can be implemented by subdevice like a MIPI CSI2 receiver, allowing the
host driver to gather additional data into frame buffer passed to user
space.
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

include/media/v4l2-subdev.h

@@ -274,6 +274,10 @@ struct v4l2_subdev_audio_ops {
    s_mbus_config: set a certain mediabus configuration. This operation is added
 	for compatibility with soc-camera drivers and should not be used by new
 	software.
+
+   s_rx_buffer: set a host allocated memory buffer for the subdev. The subdev
+	can adjust @size to a lower value and must not write more data to the
+	buffer starting at @data than the original value of @size.
  */
 struct v4l2_subdev_video_ops {
 	int (*s_routing)(struct v4l2_subdev *sd, u32 input, u32 output, u32 config);
@@ -327,6 +331,8 @@ struct v4l2_subdev_video_ops {
 			     struct v4l2_mbus_config *cfg);
 	int (*s_mbus_config)(struct v4l2_subdev *sd,
 			     const struct v4l2_mbus_config *cfg);
+	int (*s_rx_buffer)(struct v4l2_subdev *sd, void *buf,
+			   unsigned int *size);
 };
 
 /*