linux-kernel - Re: [REGRESSION] Too-low frequency limit for AMD GPU PCI-passed-through to Windows VM

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Date:   Tue, 15 Feb 2022 10:11:11 -0500
From:   Alex Deucher <alexdeucher@...il.com>
To:     Thorsten Leemhuis <regressions@...mhuis.info>
Cc:     Jim Turner <linuxkernel.foss@...rc-none.turner.link>,
        "Lazar, Lijo" <lijo.lazar@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Koenig, Christian" <Christian.Koenig@....com>
Subject: Re: [REGRESSION] Too-low frequency limit for AMD GPU
 PCI-passed-through to Windows VM

On Tue, Feb 15, 2022 at 9:56 AM Thorsten Leemhuis
<regressions@...mhuis.info> wrote:
>
> Top-posting for once, to make this easy accessible to everyone.
>
> Nothing happened here for two weeks now afaics. Was the discussion moved
> elsewhere or did it fall through the cracks?
>
> Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
>
> P.S.: As the Linux kernel's regression tracker I'm getting a lot of
> reports on my table. I can only look briefly into most of them and lack
> knowledge about most of the areas they concern. I thus unfortunately
> will sometimes get things wrong or miss something important. I hope
> that's not the case here; if you think it is, don't hesitate to tell me
> in a public reply, it's in everyone's interest to set the public record
> straight.
>
> On 30.01.22 01:25, Jim Turner wrote:
> > Hi Lijo,
> >
> >> Specifically, I was looking for any events happening at these two
> >> places because of the patch-
> >>
> >> https://elixir.bootlin.com/linux/v5.16/source/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c#L411
> >>
> >> https://elixir.bootlin.com/linux/v5.16/source/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c#L653
> >
> > I searched the logs generated with all drm debug messages enabled
> > (drm.debug=0x1ff) for "device_class", "ATCS", "atcs", "ATIF", and
> > "atif", for both f1688bd69ec4 and f9b7f3703ff9. Other than the few lines
> > mentioning ATIF from my previous email, there weren't any matches.
> >
> > Since "device_class" didn't appear in the logs, we know that
> > `amdgpu_atif_handler` was not called for either version.
> >
> > I also patched f9b7f3703ff9 to add the line
> >
> >   DRM_DEBUG_DRIVER("Entered amdgpu_acpi_pcie_performance_request");
> >
> > at the top (below the variable declarations) of
> > `amdgpu_acpi_pcie_performance_request`, and then tested again with all
> > drm debug messages enabled (0x1ff). That debug message didn't show up.
> >
> > So, `amdgpu_acpi_pcie_performance_request` was not called either, at
> > least with f9b7f3703ff9. (I didn't try adding this patch to
> > f1688bd69ec4.)
> >
> > Would anything else be helpful?

I guess just querying the ATIF method does something that negatively
influences the windows driver in the guest.  Perhaps the platform
thinks the driver has been loaded since the method has been called so
it enables certain behaviors that require ATIF interaction that never
happen because the ACPI methods are not available in the guest.  I
don't really have a good workaround other than blacklisting the driver
since on bare metal the driver needs to use this interface for
platform interactions.

Alex