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

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Date:   Mon, 21 Dec 2020 17:47:49 +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>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Linux PCI <linux-pci@...r.kernel.org>,
        nouveau@...ts.freedesktop.org
Subject: Re: [PATCH v2] ALSA: hda: Continue to probe when codec probe fails

On Mon, 21 Dec 2020 17:33:20 +0100,
Kai-Heng Feng wrote:
> 
> [+Cc nouveau]
> 
> On Fri, Dec 18, 2020 at 4:06 PM Takashi Iwai <tiwai@...e.de> wrote:
> [snip]
> > > Quite possibly the system doesn't power up HDA controller when there's
> > > no external monitor.
> > > So when it's connected to external monitor, it's still needed for HDMI audio.
> > > Let me ask the user to confirm this.
> >
> > Yeah, it's the basic question whether the HD-audio is supposed to work
> > on this machine at all.  If yes, the current approach we take makes
> > less sense - instead we should rather make the HD-audio controller
> > working.
> 
> Yea, confirmed that the Nvidia HDA works when HDMI is connected prior boot.
> 
> > > > - The second problem is that pci_enable_device() ignores the error
> > > >   returned from pci_set_power_state() if it's -EIO.  And the
> > > >   inaccessible access error returns -EIO, although it's rather a fatal
> > > >   problem.  So the driver believes as the PCI device gets enabled
> > > >   properly.
> > >
> > > This was introduced in 2005, by Alan's 11f3859b1e85 ("[PATCH] PCI: Fix
> > > regression in pci_enable_device_bars") to fix UHCI controller.
> > >
> > > >
> > > > - The third problem is that HD-audio driver blindly believes the
> > > >   codec_mask read from the register even if it's a read failure as I
> > > >   already showed.
> > >
> > > This approach has least regression risk.
> >
> > Yes, but it assumes that HD-audio is really non-existent.
> 
> I really don't know any good approach to address this.
> On Windows, HDA PCI is "hidden" until HDMI cable is plugged, then the
> driver will flag the magic bit to make HDA audio appear on the PCI
> bus.
> IIRC the current approach is to make nouveau and device link work.

But what happens if you plug the HDMI cable later and want to use the
HDMI audio?  It won't work with your fix, right?


Takashi