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From:   Karol Herbst <kherbst@redhat.com>
Date:   Wed, 20 Nov 2019 13:09:51 +0100
Message-ID: <CACO55tupFbq0T1DcR+C+YxtPR=csPBQhwVXz_SHWT5F8bRK8JA@mail.gmail.com>
Subject: Re: [PATCH v4] pci: prevent putting nvidia GPUs into lower device
 states on certain intel bridges
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Mika Westerberg <mika.westerberg@intel.com>,
        Bjorn Helgaas <helgaas@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Lyude Paul <lyude@redhat.com>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Linux PCI <linux-pci@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        nouveau <nouveau@lists.freedesktop.org>,
        Dave Airlie <airlied@gmail.com>,
        Mario Limonciello <Mario.Limonciello@dell.com>
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On Wed, Nov 20, 2019 at 1:06 PM Rafael J. Wysocki <rafael@kernel.org> wrote=
:
>
> On Wed, Nov 20, 2019 at 12:51 PM Karol Herbst <kherbst@redhat.com> wrote:
> >
> > On Wed, Nov 20, 2019 at 12:48 PM Rafael J. Wysocki <rafael@kernel.org> =
wrote:
> > >
> > > On Wed, Nov 20, 2019 at 12:22 PM Mika Westerberg
> > > <mika.westerberg@intel.com> wrote:
> > > >
> > > > On Wed, Nov 20, 2019 at 11:52:22AM +0100, Rafael J. Wysocki wrote:
> > > > > On Wed, Nov 20, 2019 at 11:18 AM Mika Westerberg
> > > > > <mika.westerberg@intel.com> wrote:
> > > > > >
>
> [cut]
>
> > > > >
> > > > > Oh, so does it look like we are trying to work around AML that tr=
ied
> > > > > to work around some problematic behavior in Linux at one point?
> > > >
> > > > Yes, it looks like so if I read the ASL right.
> > >
> > > OK, so that would call for a DMI-based quirk as the real cause for th=
e
> > > issue seems to be the AML in question, which means a firmware problem=
.
> > >
> >
> > And I disagree as this is a linux specific workaround and windows goes
> > that path and succeeds. This firmware based workaround was added,
> > because it broke on Linux.
>
> Apparently so at the time it was added, but would it still break after
> the kernel changes made since then?
>
> Moreover, has it not become harmful now?  IOW, wouldn't it work after
> removing the "Linux workaround" from the AML?
>
> The only way to verify that I can see would be to run the system with
> custom ACPI tables without the "Linux workaround" in the AML in
> question.
>

the workaround is not enabled by default, because it has to be
explicitly enabled by the user.