linux-kernel - Re: [PATCH v2] ALSA: hda: Continue to probe when codec probe fails

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Date:   Wed, 16 Dec 2020 16:58:29 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     tiwai@...e.com, Jaroslav Kysela <perex@...ex.cz>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Alex Deucher <alexander.deucher@....com>,
        Mike Rapoport <rppt@...nel.org>,
        "moderated list:SOUND" <alsa-devel@...a-project.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] ALSA: hda: Continue to probe when codec probe fails

On Wed, 16 Dec 2020 16:50:20 +0100,
Kai-Heng Feng wrote:
> 
> On Wed, Dec 16, 2020 at 11:41 PM Takashi Iwai <tiwai@...e.de> wrote:
> >
> > On Wed, 16 Dec 2020 13:47:24 +0100,
> > Kai-Heng Feng wrote:
> > >
> > > Similar to commit 9479e75fca37 ("ALSA: hda: Keep the controller
> > > initialization even if no codecs found"), when codec probe fails, it
> > > doesn't enable runtime suspend, and can prevent graphics card from
> > > getting powered down:
> > > [    4.280991] snd_hda_intel 0000:01:00.1: no codecs initialized
> > >
> > > $ cat /sys/bus/pci/devices/0000:01:00.1/power/runtime_status
> > > active
> > >
> > > So mark there's no codec and continue probing to let runtime PM to work.
> > >
> > > BugLink: https://bugs.launchpad.net/bugs/1907212
> > > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> >
> > Hm, but if the probe fails, doesn't it mean something really wrong?
> > IOW, how does this situation happen?
> 
> The HDA controller is forcely created by quirk_nvidia_hda(). So
> probably there's really not an HDA controller.

I still don't understand how non-zero codec_mask is passed.
The non-zero codec_mask means that BIOS or whatever believes that
HD-audio codecs are present and let HD-audio controller reporting the
presence.  What error did you get at probing?


> > The usual no-codec state is for the devices that have a bogus HD-audio
> > bus remaining while codecs aren't hooked or disabled by BIOS.  For
> > that, it makes to leave the controller driver and let it idle.  But if
> > you get really an error, it's something to fix there, not to just
> > ignore in general.
> 
> The best approach I can think of is to make current two steps probe
> into one. So when probe fails, the driver won't bind to the device.
> What's the reason behind the two steps approach?

It's a sort of must, as the module loading is involved with binding
with the codecs, as well as (optionally) request_firmware()
invocation.


Takashi