[PATCH 2/2] media: uvcvideo: Avoid partial metadata buffers

[Ricardo Ribalda]

If the metadata queue that is empty receives a new buffer while we are
in the middle of processing a frame, the first metadata buffer will
contain partial information.

Avoid this by tracking the state of the metadata buffer and making sure
that it is in sync with the data buffer.

Now that we are at it, simplify the code a bit by not getting a metadata
buffer if there is no data buffer ready.

Fixes: 088ead255245 ("media: uvcvideo: Add a metadata device node")
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_video.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 4feb3699f520..f339d6d19a39 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1517,6 +1517,8 @@ static void uvc_video_next_buffers(struct uvc_streaming *stream,
 						  *meta_buf);
 	}
 	*video_buf = uvc_queue_next_buffer(&stream->queue, *video_buf);
+	if (*video_buf && *meta_buf)
+		(*meta_buf)->state = UVC_BUF_STATE_ACTIVE;
 }
 
 static void uvc_video_decode_isoc(struct uvc_urb *uvc_urb,
@@ -1718,9 +1720,23 @@ static void uvc_video_complete(struct urb *urb)
 
 	buf = uvc_queue_get_current_buffer(queue);
 
-	if (vb2_qmeta)
+	if (buf && vb2_qmeta)
 		buf_meta = uvc_queue_get_current_buffer(qmeta);
 
+	/*
+	 * Avoid partial metadata buffers, by making sure that the data buffer
+	 * and metadata buffer state is in sync.
+	 *
+	 * A new (QUEUED) buffer is only allowed to become ACTIVE if we are also
+	 * at the start of a new data buffer.
+	 */
+	if (buf_meta && buf_meta->state == UVC_BUF_STATE_QUEUED) {
+		if (buf->state != UVC_BUF_STATE_QUEUED)
+			buf_meta = NULL;
+		else
+			buf_meta->state = UVC_BUF_STATE_ACTIVE;
+	}
+
 	/* Re-initialise the URB async work. */
 	uvc_urb->async_operations = 0;
 

-- 
2.54.0.rc1.513.gad8abe7a5a-goog