media: v4l2-mem2mem: Trace on implicit un-hold

If the timestamp of the src buffer differs from the timestamp of a held
dst buffer, the held buffer is implicitly removed and marked as done.
Add a trace to help debugging if someone hits that case.
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Sebastian Fricke <sebastian.fricke@collabora.com>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/v4l2-core/v4l2-mem2mem.c

@@ -336,6 +336,7 @@ static void __v4l2_m2m_try_queue(struct v4l2_m2m_dev *m2m_dev,
 	if (src && dst && dst->is_held &&
 	    dst->vb2_buf.copied_timestamp &&
 	    dst->vb2_buf.timestamp != src->vb2_buf.timestamp) {
+		dprintk("Timestamp mismatch, returning held capture buffer\n");
 		dst->is_held = false;
 		v4l2_m2m_dst_buf_remove(m2m_ctx);
 		v4l2_m2m_buf_done(dst, VB2_BUF_STATE_DONE);