[PATCH 19/31] staging: bcm2835-camera: Ensure timestamps never go backwards.

Stefan Wahren wahrenst at gmx.net
Thu Jun 27 18:56:16 UTC 2019

From: Dave Stevenson <dave.stevenson at raspberrypi.org>

There is an awkward situation with H264 header bytes. Currently
they are returned with a PTS of 0 because they aren't associated
with a timestamped frame to encode. These are handled by either
returning the timestamp of the last buffer to have been received,
or in the case of the first buffer the timestamp taken at
This results in a race where the current frame may have started
before we take the start time, which results in the first encoded
frame having an earlier timestamp than the header bytes.

Ensure that we never return a negative delta to the user by checking
against the previous timestamp.

Signed-off-by: Dave Stevenson <dave.stevenson at raspberrypi.org>
 drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
index 9967df9..6205793 100644
--- a/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
+++ b/drivers/staging/vc04_services/bcm2835-camera/bcm2835-camera.c
@@ -387,6 +387,11 @@ static void buffer_cb(struct vchiq_mmal_instance *instance,
 			 dev->capture.vc_start_timestamp, pts,
+		if (timestamp < dev->capture.last_timestamp) {
+			v4l2_dbg(1, bcm2835_v4l2_debug, &dev->v4l2_dev,
+				 "Negative delta - using last time\n");
+			timestamp = dev->capture.last_timestamp;
+		}
 		buf->vb.vb2_buf.timestamp = ktime_to_ns(timestamp);
 	} else {
 		if (dev->capture.last_timestamp) {

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