On Mon Mar 23 09:53:53 2026 +0000, Ricardo Ribalda wrote:
> In UVC, the FID flips with every frame. For every FID flip, we increase
> the stream sequence number.
>
> Now, if a FID flips multiple times and there is no data transferred between
> the flips, the buffer sequence number will be set to the value of the
> stream sequence number after the first flip.
>
> Userspace uses the buffer sequence number to determine if there have been
> missing frames. With the current behaviour, userspace will think that the
> gap is in the wrong location.
>
> This patch modifies uvc_video_decode_start() to provide the correct buffer
> sequence number and timestamp.
>
> Cc: [email protected]
> Fixes: 650b95feee35 ("[media] uvcvideo: Generate discontinuous sequence
> numbers when frames are lost")
> Signed-off-by: Ricardo Ribalda <[email protected]>
> Reviewed-by: Hans de Goede <[email protected]>
> Signed-off-by: Hans de Goede <[email protected]>
> Signed-off-by: Hans Verkuil <[email protected]>
Patch committed.
Thanks,
Hans Verkuil
drivers/media/usb/uvc/uvc_video.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
---
diff --git a/drivers/media/usb/uvc/uvc_video.c
b/drivers/media/usb/uvc/uvc_video.c
index 3182f5e9d9a0..62db4db4e565 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1223,6 +1223,19 @@ static int uvc_video_decode_start(struct uvc_streaming
*stream,
stream->sequence++;
if (stream->sequence)
uvc_video_stats_update(stream);
+
+ /*
+ * On a FID flip initialize sequence number and timestamp.
+ *
+ * The driver already takes care of injecting FID flips for
+ * UVC_QUIRK_STREAM_NO_FID and UVC_QUIRK_MJPEG_NO_EOF.
+ */
+ if (buf) {
+ buf->buf.field = V4L2_FIELD_NONE;
+ buf->buf.sequence = stream->sequence;
+ buf->buf.vb2_buf.timestamp =
+ ktime_to_ns(uvc_video_get_time());
+ }
}
uvc_video_clock_decode(stream, buf, data, len);
@@ -1263,10 +1276,6 @@ static int uvc_video_decode_start(struct uvc_streaming
*stream,
return -ENODATA;
}
- buf->buf.field = V4L2_FIELD_NONE;
- buf->buf.sequence = stream->sequence;
- buf->buf.vb2_buf.timestamp = ktime_to_ns(uvc_video_get_time());
-
/* TODO: Handle PTS and SCR. */
buf->state = UVC_BUF_STATE_ACTIVE;
}
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