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From:   Karol Herbst <kherbst@redhat.com>
Date:   Tue, 13 Apr 2021 02:10:18 +0200
Message-ID: <CACO55tsBDov88YM7phm_SugdEUqD_1S=DWLFXSWr-4H+9wJyAQ@mail.gmail.com>
Subject: Re: [Nouveau] [PATCH v2] ALSA: hda: Continue to probe when codec
 probe fails
To:     Roy Spliet <nouveau@spliet.org>
Cc:     Aaron Plattner <aplattner@nvidia.com>,
        Lukas Wunner <lukas@wunner.de>,
        Kai-Heng Feng <kai.heng.feng@canonical.com>,
        "moderated list:SOUND" <alsa-devel@alsa-project.org>,
        Kai Vehmanen <kai.vehmanen@linux.intel.com>,
        Takashi Iwai <tiwai@suse.de>,
        nouveau <nouveau@lists.freedesktop.org>,
        Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
        tiwai@suse.com, Alex Deucher <alexander.deucher@amd.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Mike Rapoport <rppt@kernel.org>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Jaroslav Kysela <perex@perex.cz>,
        open list <linux-kernel@vger.kernel.org>
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On Mon, Apr 12, 2021 at 9:36 PM Roy Spliet <nouveau@spliet.org> wrote:
>
> Hello Aaron,
>
> Thanks for your insights. A follow-up query and some observations in-line.
>
> Op 12-04-2021 om 20:06 schreef Aaron Plattner:
> > On 4/10/21 1:48 PM, Roy Spliet wrote:
> >> 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)
> >
> > My basic understanding is that the audio function stops responding
> > whenever the graphics function is powered off. So the requirement here
> > is that the audio driver can't try to talk to the audio function while
> > the graphics function is asleep, and must trigger a graphics function
> > wakeup before trying to communicate with the audio function.
>
> I believe that vgaswitcheroo takes care of this for us.
>

yeah, and also: why would the driver want to do stuff? If the GPU is
turned off, there is no point in communicating with the audio device
anyway. The driver should do the initial probe and leave the device be
unless it's actively used. Also there is no such thing as "use the
audio function, but not the graphics one"

> > I think
> > there are also requirements about the audio function needing to be awake
> > when the graphics driver is updating the ELD, but I'm not sure.
> >

well, it's one physical device anyway, so technically the audio
function is powered on.

> > This is harder on Windows because the audio driver lives in its own
> > little world doing its own thing but on Linux we can do better.
> >
> >>> 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.
> >
> > After system boot, I don't think there's any firmware involved, but I'm
> > not super familiar with the low-level details and it's possible the
> > situation changed since I last looked at it.
> >
> > I think the problem with having nouveau write this quirk is that the
> > kernel will need to re-probe the PCI device to notice that it has
> > suddenly become a multi-function device with an audio function, and
> > hotplug the audio driver. I originally looked into trying to do that but
> > it was tricky because the PCI subsystem didn't really have a mechanism
> > for a single-function device to become a multi-function device on the
> > fly and it seemed easier to enable it early on during bus enumeration.
> > That way the kernel sees both functions all the time without anything
> > else having to be special about this configuration.

Well, we do have this pci/quirk.c thing, no? Nouveau does flip the
bit, but I am actually not sure if that's even doing something
anymore. Maybe in the runtime_resume case it's still relevant but not
sure _when_ DECLARE_PCI_FIXUP_CLASS_RESUME_EARLY is triggered, it does
seem to be called even in the runtime_resume case though.

>
> Right, so for a little more context: a while ago I noticed that my
> laptop (lucky me, Asus K501UB) has a 940M with HDA but no codec. Seems
> legit, given how this GPU has no displays attached; they're all hooked
> up to the Intel integrated GPU. That threw off the snd_hda_intel
> mid-probe, and as a result didn't permit runpm, keeping the entire GPU,
> PCIe bus and thus the CPU package awake. A bit of hackerly later we
> decided to continue probing without a codec, and now my laptop is happy,
> but...
> A new problem popped up with several other NVIDIA GPUs that expose their
> HDA subdevice, but somehow its inaccessible. Relevant lines from a
> users' log:
>
> [    3.031222] MXM: GUID detected in BIOS
> [    3.031280] ACPI BIOS Error (bug): AE_AML_PACKAGE_LIMIT, Index
> (0x000000003) is beyond end of object (length 0x0) (20200925/exoparg2-393)
> [    3.031352] ACPI Error: Aborting method \_SB.PCI0.GFX0._DSM due to
> previous error (AE_AML_PACKAGE_LIMIT) (20200925/psparse-529)
> [    3.031419] ACPI: \_SB_.PCI0.GFX0: failed to evaluate _DSM (0x300b)
> [    3.031424] ACPI Warning: \_SB.PCI0.GFX0._DSM: Argument #4 type
> mismatch - Found [Buffer], ACPI requires [Package] (20200925/nsarguments-61)
> [    3.031619] pci 0000:00:02.0: optimus capabilities: enabled, status
> dynamic power,
> [    3.031667] ACPI BIOS Error (bug): AE_AML_PACKAGE_LIMIT, Index
> (0x000000003) is beyond end of object (length 0x0) (20200925/exoparg2-393)
> [    3.031731] ACPI Error: Aborting method \_SB.PCI0.GFX0._DSM due to
> previous error (AE_AML_PACKAGE_LIMIT) (20200925/psparse-529)
> [    3.031791] ACPI Error: Aborting method \_SB.PCI0.PEG0.PEGP._DSM due
> to previous error (AE_AML_PACKAGE_LIMIT) (20200925/psparse-529)
> [    3.031856] ACPI: \_SB_.PCI0.PEG0.PEGP: failed to evaluate _DSM (0x300b)
> [    3.031859] ACPI Warning: \_SB.PCI0.PEG0.PEGP._DSM: Argument #4 type
> mismatch - Found [Buffer], ACPI requires [Package] (20200925/nsarguments-61)

If I am not wrong we are calling the _DSM method inside nouveau when
doing runpm on pre _PR3 systems. As this is all very vendor specific,
we might be doing something incorrectly.

> [    3.032058] pci 0000:01:00.0: optimus capabilities: enabled, status
> dynamic power,
> [    3.032061] VGA switcheroo: detected Optimus DSM method
> \_SB_.PCI0.PEG0.PEGP handle
> [    3.032323] checking generic (d0000000 410000) vs hw (f6000000 1000000)
> [    3.032325] checking generic (d0000000 410000) vs hw (e0000000 10000000)
> [    3.032326] checking generic (d0000000 410000) vs hw (f0000000 2000000)
> [    3.032410] nouveau 0000:01:00.0: NVIDIA GK107 (0e71f0a2)
> [    3.042385] nouveau 0000:01:00.0: bios: version 80.07.a0.00.11
> --- snip ---
> [    8.951478] snd_hda_intel 0000:01:00.1: can't change power state from
> D3cold to D0 (config space inaccessible)
> [    8.951509] snd_hda_intel 0000:01:00.1: can't change power state from
> D3hot to D0 (config space inaccessible)

This is actually a little bad, because it means that the device
doesn't come back up from D3. It's a bit weird it's D3cold and D3hot
in the messages, but maybe the device just takes quite some time to
wake up. But it does look like the device gets woken up.

> [    8.951608] snd_hda_intel 0000:01:00.1: Disabling MSI
> [    8.951621] snd_hda_intel 0000:01:00.1: Handle vga_switcheroo audio
> client
> [    8.952461] snd_hda_intel 0000:00:1b.0: bound 0000:00:02.0 (ops
> i915_audio_component_bind_ops [i915])
> [    8.952642] snd_hda_intel 0000:01:00.1: number of I/O streams is 30,
> forcing separate stream tags
>
> Now I don't know what's going on, but the snd_hda_intel messages are
> ominous. And so are the ACPI warnings. But I don't know how much these
> two are related.
>

What is the actual problem though? Seems like everything is fine
despite those messages.

> You say that it is desirable to switch on HDA at boot-time because the
> PCI subsystem doesn't play nicely with changing a device to
> multi-function. That rules out the option of only enabling the HDA
> device once a cable is plugged in. Are there any other trap doors that

yeah, we can absolutely not do that. We do quirk the device to put the
GPU into multi function state asap and the intel_hda_snd driver should
deal with it.

> snd_hda_intel needs to navigate around to make this work fault free on
> all hardware, such as:
> - Codecs not revealing themselves until a display is plugged in,
> requiring perhaps a "codec reprobe" and "codec remove" event from
> nouveau/rm to snd_hda_intel,

we could trigger the reprobe from within nouveau as we are dealing
with display hotplug events anyway.

> - Borked BIOSes just blindly assigning the MMIO space of the HDA device
> to another device, or nothing at all,

that exists? *sigh*

> - ... other things that might give any of us nightmares and heart burn?
>

hopefully there are none :p

> Thanks!
>
> Roy
>
> >
> > -- Aaron
> >
> >>> Thanks,
> >>>
> >>> Lukas
>