NotForUpstream: media: video-mux: Propagate controls to source

The i.MX8MP makes calls on it's source device to determine
the link-frequency that should be configured on the CSI2 receiver.

When the source is behind a video mux, we need to pass this call through
to the connected device.

Map the control handler of the source device to the video-mux,
essentially proxying all controls on the mux to the device which has
it's link enabled.

Signed-off-by: Kieran Bingham <[email protected]>

drivers/media/platform/video-mux.c

@@ -69,6 +69,7 @@ static int video_mux_link_setup(struct media_entity *entity,
 				const struct media_pad *remote, u32 flags)
 {
 	struct v4l2_subdev *sd = media_entity_to_v4l2_subdev(entity);
+	struct v4l2_subdev *source_sd;
 	struct video_mux *vmux = v4l2_subdev_to_video_mux(sd);
 	u16 source_pad = entity->num_pads - 1;
 	int ret = 0;
@@ -111,13 +112,19 @@ static int video_mux_link_setup(struct media_entity *entity,
 		*source_mbusformat = *v4l2_subdev_get_pad_format(sd, sd_state,
 								 vmux->active);
 		v4l2_subdev_unlock_state(sd_state);
+
+		source_sd = media_entity_to_v4l2_subdev(remote->entity);
+		vmux->subdev.ctrl_handler = source_sd->ctrl_handler;
+
 	} else {
 		if (vmux->active != local->index)
 			goto out;
 
 		dev_dbg(sd->dev, "going inactive\n");
 		mux_control_deselect(vmux->mux);
 		vmux->active = -1;
+
+		vmux->subdev.ctrl_handler = NULL;
 	}
 
 out: