[libcamera-devel] [PATCH 2/3] libcamera: v4l2_videodevice: Clarify setting of v4l2_buffer timestamp

[Laurent Pinchart]

Hi Umang,

Thank you for the patch.

On Thu, Mar 17, 2022 at 04:17:39PM +0530, Umang Jain via libcamera-devel wrote:
> 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 <umang.jain at ideasonboard.com>
> ---
>  src/libcamera/v4l2_videodevice.cpp | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> index 5580269f..a6c54b19 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-men,

s/mem-to-men/mem-to-mem/

> +		 * there is no harm in setting the timestamps as they will be
> +		 * ignored (and over-written).

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> +		 */
>  		buf.timestamp.tv_sec = metadata.timestamp / 1000000000;
>  		buf.timestamp.tv_usec = (metadata.timestamp / 1000) % 1000000;
>  	}

-- 
Regards,

Laurent Pinchart