linux-kernel - Re: ALSA: intel8x0: div by zero in snd_intel8x0

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Date:   Wed, 07 Jul 2021 20:14:13 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Max Filippov <jcmvbkbc@...il.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        alsa-devel@...a-project.org, Leon Romanovsky <leon@...nel.org>,
        Takashi Iwai <tiwai@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: Re: ALSA: intel8x0: div by zero in snd_intel8x0_update()

On Wed, 07 Jul 2021 19:50:07 +0200,
Max Filippov wrote:
> 
> On Wed, Jul 7, 2021 at 12:02 AM Takashi Iwai <tiwai@...e.de> wrote:
> > On Tue, 06 Jul 2021 19:50:08 +0200, Max Filippov wrote:
> > > linux v5.13 booting on qemu-system-xtensa virt board gets stuck inside
> > > snd_intel8x0_probe -> intel8x0_measure_ac97_clock with this patch.
> > > Prior to it it boots successfully for me.
> > > I'm curious if this issue has been reported yet.
> > >
> > > What I see is an IRQ flood, at some point snd_intel8x0_interrupt
> > > and timer ISR  are called in loop and execution never returns to
> > > the interrupted function intel8x0_measure_ac97_clock.
> > >
> > > Any idea what it could be?
> >
> > That's something odd with the VM.  As the chip itself has never shown
> > such a problem on real systems, maybe the best action would be to just
> > skip the clock measurement on VM.  The measurement itself is
> > unreliable on VM, so it makes more sense.
> >
> > That said, something like below would work?
> 
> It didn't change anything in my case. My further observation is that
> the snd_intel8x0_update is called before the ichdev->prepared
> is set to one and as a result IRQ is apparently never cleared.

So it's broken in anyway no matter whether
intel8x0_measure_ac97_clock() is called or not, right?
I'm afraid that something is wrong in VM, then.  The driver has been
working over decades on thousands of real different boards.

Skipping the clock measurement on VM would be still useful,
independent from your problem, though.


Takashi

> Perhaps because intel8x0_measure_ac97_clock is called from the
> snd_intel8x0_probe, well before the snd_intel8x0_pcm_prepare
> that sets ichdev->prepared is called.
> 
> > thanks,
> >
> > Takashi
> >
> > ---
> > diff --git a/sound/pci/intel8x0.c b/sound/pci/intel8x0.c
> > index 2d1bfbcba933..b75f832d7777 100644
> > --- a/sound/pci/intel8x0.c
> > +++ b/sound/pci/intel8x0.c
> > @@ -2199,6 +2199,9 @@ static int snd_intel8x0_mixer(struct intel8x0 *chip, int ac97_clock,
> >         pbus->private_free = snd_intel8x0_mixer_free_ac97_bus;
> >         if (ac97_clock >= 8000 && ac97_clock <= 48000)
> >                 pbus->clock = ac97_clock;
> > +       else if (chip->inside_vm)
> > +               pbus->clock = 48000;
> > +
> >         /* FIXME: my test board doesn't work well with VRA... */
> >         if (chip->device_type == DEVICE_ALI)
> >                 pbus->no_vra = 1;
> 
> -- 
> Thanks.
> -- Max
>