Re: [PATCH 4/4] v4l: Tell user space we're using monotonic timestamps

[Sakari Ailus <sakari.ailus@iki.fi>]

Hi Kamil,

On Mon, Dec 17, 2012 at 12:48:25PM +0100, Kamil Debski wrote:
> > From: 'Sakari Ailus' [mailto:sakari.ailus@iki.fi]
> > Sent: Monday, December 17, 2012 12:35 PM
> > Subject: Re: [PATCH 4/4] v4l: Tell user space we're using monotonic
> > timestamps
> > 
> > Hi Kamil,
> > 
> > On Mon, Dec 17, 2012 at 12:19:51PM +0100, Kamil Debski wrote:
> > ...
> > > > > @@ -367,7 +368,8 @@ static void __fill_v4l2_buffer(struct
> > > > > vb2_buffer
> > > > *vb, struct v4l2_buffer *b)
> > > > >  	/*
> > > > >  	 * Clear any buffer state related flags.
> > > > >  	 */
> > > > > -	b->flags &= ~V4L2_BUFFER_STATE_FLAGS;
> > > > > +	b->flags &= ~V4L2_BUFFER_MASK_FLAGS;
> > > > > +	b->flags |= V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
> > >
> > > As far as I know, after __fill_v4l2_buffer is run driver has no means
> > > to change flags. Right?
> > 
> > Correct. Querybuf, for example, is implemented in vb2 and no driver
> > involvement is required. And we sure don't want to add it. ;)
> 
> I did not suggest that it should be added.

Good. :-)

> > 
> > > So how should a driver, which is not using the MONOTONIC timestamps
> > > inform the user space about it?
> > 
> > We currently support only monotonic timestamps. Support for different
> > kind of timestamps should be added to videobuf2 when they are needed.
> > The drivers would then be using a videobuf2 equivalent of
> > v4l2_get_timestamp().
> 
> Just as I though.
> Mind you - v4l2_get_timestamp() does not apply if the timestamp are simply
> copied.
> This is the case of some of the mem2mem devices, remember?

Yeah. Makes sense.

I guess memory-to-memory devices (apart from possibly those dealing with
compressed data which contains the timestamps) should just copy the
timestamps from output to capture buffers.

-- 
Cheers,

Sakari Ailus
e-mail: sakari.ailus@iki.fi	XMPP: sailus@retiisi.org.uk