Date:   Tue, 13 Apr 2021 09:24:24 +0100
From:   Roy Spliet <nouveau@...iet.org>
To:     Karol Herbst <kherbst@...hat.com>
Cc:     Aaron Plattner <aplattner@...dia.com>,
        Lukas Wunner <lukas@...ner.de>,
        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>
Subject: Re: [Nouveau] [PATCH v2] ALSA: hda: Continue to probe when codec
 probe fails

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

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
>>
> 

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