linux-kernel - Re: [alsa-devel] [PATCH v4 3/3] ALSA: hda: Disabled unused audio controller for Dell platforms with Switchable Graphics

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Date:   Mon, 23 Apr 2018 10:08:44 +0200
From:   Pali Rohár <pali.rohar@...il.com>
To:     Kai Heng Feng <kai.heng.feng@...onical.com>
Cc:     Takashi Iwai <tiwai@...e.de>, mjg59@...f.ucam.org,
        dvhart@...radead.org, andy@...radead.org,
        Mario Limonciello <mario.limonciello@...l.com>, tiwai@...e.com,
        alsa-devel@...a-project.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org
Subject: Re: [alsa-devel] [PATCH v4 3/3] ALSA: hda: Disabled unused audio
 controller for Dell platforms with Switchable Graphics

On Monday 23 April 2018 16:04:55 Kai Heng Feng wrote:
> 
> 
> > On Apr 20, 2018, at 8:10 PM, Takashi Iwai <tiwai@...e.de> wrote:
> > 
> > On Fri, 20 Apr 2018 11:44:32 +0200,
> > Kai-Heng Feng wrote:
> > > Now it's a typical discrete-only system. HDMI audio comes from AMD audio
> > > controller, others from Intel audio controller.
> > > 
> > > When SG is enabled, the unused AMD audio contoller still exposes its
> > > sysfs, so userspace still opens the control file and stream. If
> > > userspace tries to output sound through the stream, it hangs the system.
> > 
> > Hm, could you give more information about how it hangs?
> 
> Well, I should say "it hangs the userspace process" instead.
> 
> $ speaker-test -t wav -c 2 -D hw:CARD=HDMI,DEV=3
> ...and it just stopped. Can't Ctrl+C to break it.

So userspace process cannot be killed at all? Then it is different bug
in kernel and disabling pci device is just a workaround. Not a real fix.

I would propose to find out what happen and why it cannot be killed
(probably it stuck somewhere in kernel) and fix it properly.

> > 
> > 
> > > @@ -1627,6 +1629,42 @@ static void check_msi(struct azx *chip)
> > >  	}
> > >  }
> > > 
> > > +#if IS_ENABLED(CONFIG_DELL_LAPTOP)
> > 
> > This should be IS_REACHABLE(), as both dell-laptop and HD-audio are
> > tristate.
> 
> Thanks, will update in next version.
> 
> > 
> > > +static bool check_dell_switchable_gfx(struct pci_dev *pdev)
> > 
> > I'd remove "_dell" word here.  Such a check would be likely needed for
> > other vendors, and it's quite possible that the function will be
> > extended to cover a wider DMI table.
> 
> Makes sense. Will also update this one.
> 
> Kai-Heng
> 
> > 
> > 
> > thanks,
> > 
> > Takashi

-- 
Pali Rohár
pali.rohar@...il.com