[PATCH 1/4] media: uvcvideo: Fix dev_sof filtering in hw timestamp

[Ricardo Ribalda]

To avoid filling the clock circular buffer with duplicated data we only
add it if the new value sof is different than the last added sof.

The issue is that we compare the unprocess sof with the processed sof.
If there is a sof_offset, or UVC_QUIRK_INVALID_DEVICE_SOF is enabled,
the comparison will not work as expected.

This patch moves the comparison to the right place.

Fixes: 141270bd95d4 ("media: uvcvideo: Refactor clock circular buffer")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_video.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 40c76c051da2..6786ca38fe5e 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -583,16 +583,7 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
 	if (!has_scr)
 		return;
 
-	/*
-	 * To limit the amount of data, drop SCRs with an SOF identical to the
-	 * previous one. This filtering is also needed to support UVC 1.5, where
-	 * all the data packets of the same frame contains the same SOF. In that
-	 * case only the first one will match the host_sof.
-	 */
 	sample.dev_sof = get_unaligned_le16(&data[header_size - 2]);
-	if (sample.dev_sof == stream->clock.last_sof)
-		return;
-
 	sample.dev_stc = get_unaligned_le32(&data[header_size - 6]);
 
 	/*
@@ -664,6 +655,16 @@ uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
 	}
 
 	sample.dev_sof = (sample.dev_sof + stream->clock.sof_offset) & 2047;
+
+	/*
+	 * To limit the amount of data, drop SCRs with an SOF identical to the
+	 * previous one. This filtering is also needed to support UVC 1.5, where
+	 * all the data packets of the same frame contains the same SOF. In that
+	 * case only the first one will match the host_sof.
+	 */
+	if (sample.dev_sof == stream->clock.last_sof)
+		return;
+
 	uvc_video_clock_add_sample(&stream->clock, &sample);
 	stream->clock.last_sof = sample.dev_sof;
 }

-- 
2.53.0.959.g497ff81fa9-goog