[PATCH] media: uvcvideo: Fix buffer sequence in frame gaps

[Ricardo Ribalda]

In UVC, the FID flips with every frame. For every FID flip, we increase
the sequence number. Userpace use that information to figure out if
there has been a gap between frames.

Now, we only update the sequence number on the first FID flip, which
results in frames being incorrectly numbered just after a frame gap.

This patch rewrites the sequence number of the buffer in those
situations.

Cc: stable@xxxxxxxxxx
Fixes: 650b95feee35 ("[media] uvcvideo: Generate discontinuous sequence numbers when frames are lost")
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_video.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 40c76c051da2..ec769a504569 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1176,6 +1176,14 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
 		stream->sequence++;
 		if (stream->sequence)
 			uvc_video_stats_update(stream);
+
+		/*
+		 * If we have not received any data and FID flips, update the
+		 * sequence number of the buffer to tell userspace exactly
+		 * where the frame gap is.
+		 */
+		if (buf && !buf->bytesused)
+			buf->buf.sequence = stream->sequence;
 	}
 
 	uvc_video_clock_decode(stream, buf, data, len);

---
base-commit: a7da7fb57f2a787412da1a62292a17fa00fbfbdf
change-id: 20260310-uvc-fid-e1e55447b6f1

Best regards,
-- 
Ricardo Ribalda <ribalda@xxxxxxxxxxxx>