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

From: Gustavo Padovan <gustavo@padovan.org>
To: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Cc: Alexandre Courbot <acourbot@chromium.org>,
	linux-media@vger.kernel.org, Hans Verkuil <hverkuil@xs4all.nl>,
	Shuah Khan <shuahkh@osg.samsung.com>,
	Pawel Osciak <pawel@osciak.com>,
	Sakari Ailus <sakari.ailus@iki.fi>,
	Brian Starkey <brian.starkey@arm.com>,
	Thierry Escande <thierry.escande@collabora.com>,
	linux-kernel@vger.kernel.org,
	Gustavo Padovan <gustavo.padovan@collabora.com>
Subject: Re: [RFC v5 07/11] [media] vb2: add in-fence support to QBUF
Date: Fri, 17 Nov 2017 11:08:01 -0200	[thread overview]
Message-ID: <20171117130801.GH19033@jade> (raw)
In-Reply-To: <20171117110025.2a49db49@vento.lan>

2017-11-17 Mauro Carvalho Chehab <mchehab@osg.samsung.com>:

> Em Fri, 17 Nov 2017 15:49:23 +0900
> Alexandre Courbot <acourbot@chromium.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.

Gustavo