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

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Message-ID: <1650089.1kJ4DQOsm3@avalon>
Date:	Fri, 28 Mar 2014 12:18:12 +0100
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Hans Verkuil <hverkuil@...all.nl>
Cc:	linux-media@...r.kernel.org, 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 Hans,

On Friday 28 March 2014 09:50:42 Hans Verkuil wrote:
> 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()?

No reason at all. I'll fix that.

> > +
> >  	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.

Good point. Will be fixed in v2.

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

-- 
Regards,

Laurent Pinchart

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