linux-kernel - RE: [PATCH] ASoC: sti: sti

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Date:   Tue, 15 Mar 2022 15:27:40 +0000
From:   Arnaud POULIQUEN <arnaud.pouliquen@...com>
To:     Takashi Iwai <tiwai@...e.de>
CC:     Daniel Palmer <daniel@...f.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "tiwai@...e.com" <tiwai@...e.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] ASoC: sti: sti_uniperif: Remove driver




ST Restricted

> -----Original Message-----
> From: Takashi Iwai <tiwai@...e.de>
> Sent: mardi 15 mars 2022 15:35
> To: Arnaud POULIQUEN <arnaud.pouliquen@...com>
> Cc: Daniel Palmer <daniel@...f.com>; broonie@...nel.org; tiwai@...e.com;
> alsa-devel@...a-project.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] ASoC: sti: sti_uniperif: Remove driver
> 
> On Tue, 15 Mar 2022 14:15:20 +0100,
> Arnaud POULIQUEN wrote:
> >
> > Hello,
> >
> >
> > ST Restricted
> >
> > > -----Original Message-----
> > > From: Takashi Iwai <tiwai@...e.de>
> > > Sent: mardi 15 mars 2022 11:28
> > > To: Daniel Palmer <daniel@...f.com>
> > > Cc: broonie@...nel.org; tiwai@...e.com; Arnaud POULIQUEN
> > > <arnaud.pouliquen@...com>; alsa-devel@...a-project.org; linux-
> > > kernel@...r.kernel.org
> > > Subject: Re: [PATCH] ASoC: sti: sti_uniperif: Remove driver
> > >
> > > On Tue, 15 Mar 2022 10:13:19 +0100,
> > > Daniel Palmer wrote:
> > > >
> > > > This driver seems to be in the "only good for attracting bot
> > > > generated patches" phase of it's life.
> > > >
> > > > It doesn't seem like anyone actually tested the patches that have
> > > > been applied in the last few years as uni_reader_irq_handler() had
> > > > a dead lock added to it (it locks the stream, then calls
> > > > snd_pcm_stop_xrun() which will also lock the stream).
> > >
> > > Mea culpa, that was an obvious deadlock I overlooked in the patch
> > > series.
> > >
> > > > Seems best just to remove it.
> > > >
> > > > Signed-off-by: Daniel Palmer <daniel@...f.com>
> > > > ---
> > > >  I've never used this driver, don't have the hardware etc.
> > > >  I just noticed that this looks broken when debugging my  own
> > > > driver that uses snd_pcm_stop_xrun() and was looking  at other
> > > > users to see if I was using it wrong and noticed  this was the
> > > > only place that locked the stream before  calling
> > > > snd_pcm_stop_xrun().
> > > >
> > > >  There are probably some other bits of the driver that  should be
> > > > removed but I didn't look that hard.
> > > >
> > > >  TL;DR; This driver seems broken, seems like nobody uses  it.
> > > > Maybe it should be deleted?
> > >
> > > Yeah, that looks dead.
> > >
> >
> > The platform is still used for instance:
> > https://lore.kernel.org/all/1d95209f-9cb4-47a3-2696-7a93df7cdc05@foss.
> > st.com/
> >
> > So please do not remove the driver
> 
> Ah, it's always good to see a vital sign!
> 
> > The issue has not been detected because it is related to an error that
> > occurs only when we reach the limit of the platform, with application
> > that stop the stream at same time.
> > So almost no chance to occur.
> >
> > > OTOH, if anyone really wants to keep the stuff, please revert the
> > > commit dc865fb9e7c2251c9585ff6a7bf185d499db13e4.
> >
> > Yes reverting the commit is one solution.
> > The other is to clean-up the snd_pcm_stream_lock/
> > snd_pcm_stream_unlock in the Handler.
> 
> That would work, but maybe it's safer to keep that lock, as the state change
> isn't protected by irq_lock but only implicitly by stream lock in start/stop
> callbacks.
 
You are right, trying to use the snd_pcm_stop_xrun needs deeper update
that could introduce regression. 
It seems wiser to revert your commit  dc865fb9e7c2 as you propose.

Thanks,
Arnaud

> 
> 
> thanks,
> 
> Takashi