From 2f24ac8dd87983a55f0498898f34a5f2b735b802 Mon Sep 17 00:00:00 2001 From: Ricardo Ribalda Date: Mon, 23 Mar 2026 09:53:53 +0000 Subject: [PATCH] media: uvcvideo: Fix buffer sequence in frame gaps 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: stable@kernel.org Fixes: 650b95feee35 ("[media] uvcvideo: Generate discontinuous sequence numbers when frames are lost") Signed-off-by: Ricardo Ribalda Reviewed-by: Hans de Goede Signed-off-by: Hans de Goede Signed-off-by: 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; }