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

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Date:   Sat, 10 Apr 2021 21:48:15 +0100
From:   Roy Spliet <nouveau@...iet.org>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Karol Herbst <kherbst@...hat.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        "moderated list:SOUND" <alsa-devel@...a-project.org>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Takashi Iwai <tiwai@...e.de>,
        nouveau <nouveau@...ts.freedesktop.org>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        tiwai@...e.com, Alex Deucher <alexander.deucher@....com>,
        Alan Stern <stern@...land.harvard.edu>,
        Mike Rapoport <rppt@...nel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        open list <linux-kernel@...r.kernel.org>,
        Aaron Plattner <aplattner@...dia.com>
Subject: Re: [Nouveau] [PATCH v2] ALSA: hda: Continue to probe when codec
 probe fails

Op 10-04-2021 om 20:23 schreef Lukas Wunner:
> On Sat, Apr 10, 2021 at 04:51:27PM +0100, Roy Spliet wrote:
>> Can I ask someone with more
>> technical knowledge of snd_hda_intel and vgaswitcheroo to brainstorm about
>> the possible challenges of nouveau taking matters into its own hand rather
>> than keeping this PCI quirk around?
> 
> It sounds to me like the HDA is not powered if no cable is plugged in.
> What is reponsible then for powering it up or down, firmware code on
> the GPU or in the host's BIOS?

Sometimes the BIOS, but definitely unconditionally the PCI quirk code: 
https://github.com/torvalds/linux/blob/master/drivers/pci/quirks.c#L5289

(CC Aaron Plattner)

> 
> Ideally, we should try to find out how to control HDA power from the
> operating system rather than trying to cooperate with whatever firmware
> is doing.  If we have that capability, the OS should power the HDA up
> and down as it sees fit.
> 
> Thanks,
> 
> Lukas
>