Re: [RFCv11 PATCH 00/29] Request API

[Paul Kocialkowski <paul.kocialkowski@bootlin.com>]

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Hi,

On Tue, 2018-04-17 at 06:17 +0000, Alexandre Courbot wrote:
> On Tue, Apr 17, 2018 at 3:12 PM Hans Verkuil <hverkuil@xs4all.nl>
> wrote:
> 
> > On 04/17/2018 06:33 AM, Alexandre Courbot wrote:
> > > On Mon, Apr 9, 2018 at 11:20 PM Hans Verkuil <hverkuil@xs4all.nl>
> > > wrote:
> > > 
> > > > From: Hans Verkuil <hans.verkuil@cisco.com>
> > > > Hi all,
> > > > This is a cleaned up version of the v10 series (never posted to
> > > > the list since it was messy).
> > > 
> > > Hi Hans,
> > > 
> > > It took me a while to test and review this, but finally have been
> > > able
> 
> to
> > > do it.
> > > 
> > > First the result of the test: I have tried porting my dummy vim2m
> > > test
> > > program
> > > (https://gist.github.com/Gnurou/34c35f1f8e278dad454b51578d239a42
> > > for
> > > reference),
> > > and am getting a hang when trying to queue the second OUTPUT
> > > buffer
> 
> (right
> > > after
> > > queuing the first request). If I move the calls the
> > > VIDIOC_STREAMON
> 
> after
> > > the
> > > requests are queued, the hang seems to happen at that moment.
> > > Probably a
> > > deadlock, haven't looked in detail yet.
> > > 
> > > I have a few other comments, will follow up per-patch.
> > > 
> > I had a similar/same (?) report about this from Paul:
> > https://www.mail-archive.com/linux-media@vger.kernel.org/msg129177.h
> > tml
> 
> I saw this and tried to move the call to STREAMON to after the
> requests are queued in my example program, but it then hanged there.
> So there is probably something more intricate taking place.

I figured out the issue (but forgot to report back to the list): Hans'
version of the request API doesn't set the POLLIN bit but POLLPRI
instead, so you need to select for expect_fds instead of read_fds in the
select call. That's pretty much all there is to it.

Hope this helps,

-- 
Paul Kocialkowski, Bootlin (formerly Free Electrons)
Embedded Linux and kernel engineering
https://bootlin.com

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