From b24e39be48ffa581ef93044084bc3b4d20053804 Mon Sep 17 00:00:00 2001 From: Umang Jain Date: Thu, 17 Mar 2022 16:17:39 +0530 Subject: libcamera: v4l2_videodevice: Clarify setting of v4l2_buffer timestamp Add a comment to clarify why we set v4l2_buffer timestamp while queuing the buffer (VIDIOC_QBUF). The timstamps are required to be supplied for memory-to-memory devices for output streams which then are copied to capture stream buffers with the help of V4L2_BUF_FLAG_TIMESTAMP_COPY (set by the driver). Signed-off-by: Umang Jain Reviewed-by: Laurent Pinchart Reviewed-by: Kieran Bingham --- src/libcamera/v4l2_videodevice.cpp | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'src') diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp index 5580269f..95b9c38b 100644 --- a/src/libcamera/v4l2_videodevice.cpp +++ b/src/libcamera/v4l2_videodevice.cpp @@ -1600,6 +1600,14 @@ int V4L2VideoDevice::queueBuffer(FrameBuffer *buffer) buf.length = planes[0].length; } + /* + * Timestamps are to be supplied if the device is a mem-to-mem + * device. The drivers will have V4L2_BUF_FLAG_TIMESTAMP_COPY + * set hence these timestamps will be copied from the output + * buffers to capture buffers. If the device is not mem-to-mem, + * there is no harm in setting the timestamps as they will be + * ignored (and over-written). + */ buf.timestamp.tv_sec = metadata.timestamp / 1000000000; buf.timestamp.tv_usec = (metadata.timestamp / 1000) % 1000000; } -- cgit v1.2.1