media: vb2: add vb2_find_timestamp()

Use v4l2_timeval_to_ns instead of timeval_to_ns to ensure that
both kernelspace and userspace will use the same conversion
function.

Next add a new vb2_find_timestamp() function to find buffers
with a specific timestamp.

This function will only look at DEQUEUED and DONE buffers, i.e.
buffers that are already processed.

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

include/media/videobuf2-v4l2.h

@@ -55,6 +55,23 @@ struct vb2_v4l2_buffer {
 #define to_vb2_v4l2_buffer(vb) \
 	container_of(vb, struct vb2_v4l2_buffer, vb2_buf)
 
+/**
+ * vb2_find_timestamp() - Find buffer with given timestamp in the queue
+ *
+ * @q:		pointer to &struct vb2_queue with videobuf2 queue.
+ * @timestamp:	the timestamp to find. Only buffers in state DEQUEUED or DONE
+ *		are considered.
+ * @start_idx:	the start index (usually 0) in the buffer array to start
+ *		searching from. Note that there may be multiple buffers
+ *		with the same timestamp value, so you can restart the search
+ *		by setting @start_idx to the previously found index + 1.
+ *
+ * Returns the buffer index of the buffer with the given @timestamp, or
+ * -1 if no buffer with @timestamp was found.
+ */
+int vb2_find_timestamp(const struct vb2_queue *q, u64 timestamp,
+		       unsigned int start_idx);
+
 int vb2_querybuf(struct vb2_queue *q, struct v4l2_buffer *b);
 
 /**