linux-kernel - Re: [RFC v5 07/11] [media] vb2: add in-fence support to QBUF

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Date:   Fri, 17 Nov 2017 11:19:05 -0200
From:   Mauro Carvalho Chehab <mchehab@....samsung.com>
To:     Gustavo Padovan <gustavo@...ovan.org>
Cc:     Alexandre Courbot <acourbot@...omium.org>,
        linux-media@...r.kernel.org, Hans Verkuil <hverkuil@...all.nl>,
        Shuah Khan <shuahkh@....samsung.com>,
        Pawel Osciak <pawel@...iak.com>,
        Sakari Ailus <sakari.ailus@....fi>,
        Brian Starkey <brian.starkey@....com>,
        Thierry Escande <thierry.escande@...labora.com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [RFC v5 07/11] [media] vb2: add in-fence support to QBUF

Em Fri, 17 Nov 2017 11:08:01 -0200
Gustavo Padovan <gustavo@...ovan.org> escreveu:

> 2017-11-17 Mauro Carvalho Chehab <mchehab@....samsung.com>:
> 
> > Em Fri, 17 Nov 2017 15:49:23 +0900
> > Alexandre Courbot <acourbot@...omium.org> escreveu:
> >   
> > > > @@ -178,6 +179,12 @@ static int vb2_queue_or_prepare_buf(struct 
> > > > vb2_queue *q, struct v4l2_buffer *b,
> > > >  		return -EINVAL;
> > > >  	}
> > > >  
> > > > +	if ((b->fence_fd != 0 && b->fence_fd != -1) &&    
> > > 
> > > Why do we need to consider both values invalid? Can 0 ever be a valid fence 
> > > fd?  
> > 
> > Programs that don't use fences will initialize reserved2/fence_fd field
> > at the uAPI call to zero.
> > 
> > So, I guess using fd=0 here could be a problem. Anyway, I would, instead,
> > do:
> > 
> > 	if ((b->fence_fd < 1) &&
> > 		...
> > 
> > as other negative values are likely invalid as well.  
> 
> We are checking when the fence_fd is set but the flag wasn't. Checking
> for < 1 is exactly the opposite. so we keep as is or do it fence_fd > 0.

Ah, yes. Anyway, I would stick with:
	if ((b->fence_fd > 0) &&
		...

> 
> Gustavo


-- 
Thanks,
Mauro