Re: [PATCH] ASoC: sti: sti_uniperif: Remove driver

From: Takashi Iwai <tiwai@suse.de>
To: Arnaud POULIQUEN <arnaud.pouliquen@st.com>
Cc: Daniel Palmer <daniel@0x0f.com>,
	"broonie@kernel.org" <broonie@kernel.org>,
	"tiwai@suse.com" <tiwai@suse.com>,
	"alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ASoC: sti: sti_uniperif: Remove driver
Date: Tue, 15 Mar 2022 15:34:40 +0100	[thread overview]
Message-ID: <s5hee338etb.wl-tiwai@suse.de> (raw)
In-Reply-To: <PAXPR10MB47185B76D5F38482FB1125A5F1109@PAXPR10MB4718.EURPRD10.PROD.OUTLOOK.COM>

On Tue, 15 Mar 2022 14:15:20 +0100,
Arnaud POULIQUEN wrote:
> 
> Hello,
> 
> 
> ST Restricted
> 
> > -----Original Message-----
> > From: Takashi Iwai <tiwai@suse.de>
> > Sent: mardi 15 mars 2022 11:28
> > To: Daniel Palmer <daniel@0x0f.com>
> > Cc: broonie@kernel.org; tiwai@suse.com; Arnaud POULIQUEN
> > <arnaud.pouliquen@st.com>; alsa-devel@alsa-project.org; linux-
> > kernel@vger.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@0x0f.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.

thanks,

Takashi