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

[Roy Spliet]

Op 13-04-2021 om 01:10 schreef Karol Herbst:
> On Mon, Apr 12, 2021 at 9:36 PM Roy Spliet <nouveau@xxxxxxxxxx> 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.

The problem, as stated a few e-mails earlier, is that the HDA errors 
currently prevent snd_hda_intel from properly probing the device and 
registering it with vgaswitcheroo. As a result, the GPU always stays in 
DynPwr rather than DynOff even when it's unused, keeping the PCIe bus 
and the CPU package powered. Basically burning through a charged battery 
a lot quicker than need be.
If we go back a mile on the e-mail thread, I think the problem was 
narrowed down to snd_hda_intel reading an invalid codec mask on the 
config space, and using it anyway. That being said, I believe there are 
also reports of users that don't get HDMI audio unless the cable was 
plugged in at boot-time, with similar messages in their logs. The codec 
might in such cases be hiding themselves until a cable is plugged in?
@Aaron Plattner: does that latter observation sound right to you?

> > 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.

Right. Are there situations where nouveau needs to? Or is this a 
misunderstanding of the problem from my end?

> > - 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