media: vb2: use lock if wait_prepare/finish are NULL

If the wait_prepare or wait_finish callback is set, then call it.
If it is NULL and the queue lock pointer is not NULL, then just
unlock/lock that mutex.

This allows simplifying drivers by dropping the wait_prepare and
wait_finish ops (and eventually the vb2_ops_wait_prepare/finish helpers).

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/common/videobuf2/videobuf2-core.c

@@ -2035,7 +2035,10 @@ static int __vb2_wait_for_done_vb(struct vb2_queue *q, int nonblocking)
 		 * become ready or for streamoff. Driver's lock is released to
 		 * allow streamoff or qbuf to be called while waiting.
 		 */
-		call_void_qop(q, wait_prepare, q);
+		if (q->ops->wait_prepare)
+			call_void_qop(q, wait_prepare, q);
+		else if (q->lock)
+			mutex_unlock(q->lock);
 
 		/*
 		 * All locks have been released, it is safe to sleep now.
@@ -2045,12 +2048,16 @@ static int __vb2_wait_for_done_vb(struct vb2_queue *q, int nonblocking)
 				!list_empty(&q->done_list) || !q->streaming ||
 				q->error);
 
+		if (q->ops->wait_finish)
+			call_void_qop(q, wait_finish, q);
+		else if (q->lock)
+			mutex_lock(q->lock);
+
+		q->waiting_in_dqbuf = 0;
 		/*
 		 * We need to reevaluate both conditions again after reacquiring
 		 * the locks or return an error if one occurred.
 		 */
-		call_void_qop(q, wait_finish, q);
-		q->waiting_in_dqbuf = 0;
 		if (ret) {
 			dprintk(q, 1, "sleep was interrupted\n");
 			return ret;