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From:   Ilia Mirkin <imirkin@alum.mit.edu>
Date:   Mon, 21 Dec 2020 12:56:38 -0500
Message-ID: <CAKb7UvjWX7xbwMKtnad5EVy16nY1M-A13YJeRWyUwHzemcVswA@mail.gmail.com>
Subject: Re: [Nouveau] [PATCH v2] ALSA: hda: Continue to probe when codec
 probe fails
To:     Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc:     Takashi Iwai <tiwai@suse.de>,
        "moderated list:SOUND" <alsa-devel@alsa-project.org>,
        Kai Vehmanen <kai.vehmanen@linux.intel.com>,
        nouveau <nouveau@lists.freedesktop.org>,
        open list <linux-kernel@vger.kernel.org>,
        Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
        tiwai@suse.com, Bjorn Helgaas <bhelgaas@google.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        Jaroslav Kysela <perex@perex.cz>,
        Mike Rapoport <rppt@kernel.org>
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On Mon, Dec 21, 2020 at 11:33 AM Kai-Heng Feng
<kai.heng.feng@canonical.com> wrote:
>
> [+Cc nouveau]
>
> On Fri, Dec 18, 2020 at 4:06 PM Takashi Iwai <tiwai@suse.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.

I don't have the full context of this discussion, but the kernel
force-enables the HDA subfunction nowadays, irrespective of nouveau or
nvidia or whatever:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pci/quirks.c?h=v5.10#n5267

Cheers,

  -ilia