linux-kernel - Re: [PATCH 1/2] usb: gadget: uvc: Switch to monotonic clock for buffer timestamps

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Date:	Fri, 28 Mar 2014 09:50:42 +0100
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-media@...r.kernel.org
CC:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Fengguang Wu <fengguang.wu@...el.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Roland Scheidegger <rscheidegger_lists@...peed.ch>
Subject: Re: [PATCH 1/2] usb: gadget: uvc: Switch to monotonic clock for buffer
 timestamps

Hi Laurent,

I have a few comments:

On 03/23/2014 04:32 PM, Laurent Pinchart wrote:
> The wall time clock isn't useful for applications as it can jump around
> due to time adjustement. Switch to the monotonic clock.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> ---
>  drivers/usb/gadget/uvc_queue.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/usb/gadget/uvc_queue.c b/drivers/usb/gadget/uvc_queue.c
> index 0bb5d50..d4561ba 100644
> --- a/drivers/usb/gadget/uvc_queue.c
> +++ b/drivers/usb/gadget/uvc_queue.c
> @@ -364,6 +364,7 @@ static struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
>  						struct uvc_buffer *buf)
>  {
>  	struct uvc_buffer *nextbuf;
> +	struct timespec ts;
>  
>  	if ((queue->flags & UVC_QUEUE_DROP_INCOMPLETE) &&
>  	     buf->length != buf->bytesused) {
> @@ -379,14 +380,11 @@ static struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
>  	else
>  		nextbuf = NULL;
>  
> -	/*
> -	 * FIXME: with videobuf2, the sequence number or timestamp fields
> -	 * are valid only for video capture devices and the UVC gadget usually
> -	 * is a video output device. Keeping these until the specs are clear on
> -	 * this aspect.
> -	 */
> +	ktime_get_ts(&ts);

Why not use the v4l2-common.c helper v4l2_get_timestamp()?

> +
>  	buf->buf.v4l2_buf.sequence = queue->sequence++;
> -	do_gettimeofday(&buf->buf.v4l2_buf.timestamp);
> +	buf->buf.v4l2_buf.timestamp.tv_sec = ts.tv_sec;
> +	buf->buf.v4l2_buf.timestamp.tv_usec = ts.tv_nsec / NSEC_PER_USEC;

You should also add:

	buf->buf.v4l2_buf.field = V4L2_FIELD_NONE;

I noticed that that was never set, which is wrong.

Regards,

	Hans

>  
>  	vb2_set_plane_payload(&buf->buf, 0, buf->bytesused);
>  	vb2_buffer_done(&buf->buf, VB2_BUF_STATE_DONE);
> 

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