[PATCH v3 2/2] media: uvcvideo: Fix sequence number when no EOF

[Ricardo Ribalda]

If the driver could not detect the EOF, the sequence number is increased
twice:
 1) When we enter uvc_video_decode_start() with the old buffer and FID has
   fliped => We return -EAGAIN and last_fid is not flipped
 2) When we enter uvc_video_decode_start() with the new buffer.

Fix this issue by saving last_fid on the first FID flip.

Cc: stable@xxxxxxxxxx
Fixes: 650b95feee35 ("[media] uvcvideo: Generate discontinuous sequence numbers when frames are lost")
Reported-by: Hans de Goede <hansg@xxxxxxxxxx>
Closes: https://lore.kernel.org/linux-media/CANiDSCuj4cPuB5_v2xyvAagA5FjoN8V5scXiFFOeD3aKDMqkCg@xxxxxxxxxxxxxx/T/#me39fb134e8c2c085567a31548c3403eb639625e4
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_video.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 9e06b1d0f0f9..3e6ded69388f 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1254,6 +1254,12 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
 		uvc_dbg(stream->dev, FRAME,
 			"Frame complete (FID bit toggled)\n");
 		buf->state = UVC_BUF_STATE_READY;
+
+		/*
+		 * If the EOF detection has failed, we need to save the last_fid
+		 * to avoid increasing the sequence number twice.
+		 */
+		stream->last_fid = fid;
 		return -EAGAIN;
 	}
 

-- 
2.53.0.851.ga537e3e6e9-goog