media: rcar-csi2: Serialize access to set_fmt and get_fmt

The access to the internal storage of the format rcar_csi2.mf should be
serialized, extend the existing lock mutex to also cover this.

While at it document the mutex.
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/platform/rcar-vin/rcar-csi2.c

@@ -468,9 +468,8 @@ struct rcar_csi2 {
 	struct v4l2_subdev *remote;
 	unsigned int remote_pad;
 
+	struct mutex lock; /* Protects mf and stream_count. */
 	struct v4l2_mbus_framefmt mf;
-
-	struct mutex lock;
 	int stream_count;
 
 	unsigned short lanes;
@@ -836,6 +835,8 @@ static int rcsi2_set_pad_format(struct v4l2_subdev *sd,
 	struct rcar_csi2 *priv = sd_to_csi2(sd);
 	struct v4l2_mbus_framefmt *framefmt;
 
+	mutex_lock(&priv->lock);
+
 	if (!rcsi2_code_to_fmt(format->format.code))
 		format->format.code = rcar_csi2_formats[0].code;
 
@@ -846,6 +847,8 @@ static int rcsi2_set_pad_format(struct v4l2_subdev *sd,
 		*framefmt = format->format;
 	}
 
+	mutex_unlock(&priv->lock);
+
 	return 0;
 }
 
@@ -855,11 +858,15 @@ static int rcsi2_get_pad_format(struct v4l2_subdev *sd,
 {
 	struct rcar_csi2 *priv = sd_to_csi2(sd);
 
+	mutex_lock(&priv->lock);
+
 	if (format->which == V4L2_SUBDEV_FORMAT_ACTIVE)
 		format->format = priv->mf;
 	else
 		format->format = *v4l2_subdev_get_try_format(sd, sd_state, 0);
 
+	mutex_unlock(&priv->lock);
+
 	return 0;
 }