linux-kernel - Re: [PATCH v4] pci: prevent putting nvidia GPUs into lower device states on certain intel bridges

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Date:   Wed, 20 Nov 2019 13:09:51 +0100
From:   Karol Herbst <kherbst@...hat.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Mika Westerberg <mika.westerberg@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lyude Paul <lyude@...hat.com>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        nouveau <nouveau@...ts.freedesktop.org>,
        Dave Airlie <airlied@...il.com>,
        Mario Limonciello <Mario.Limonciello@...l.com>
Subject: Re: [PATCH v4] pci: prevent putting nvidia GPUs into lower device
 states on certain intel bridges

On Wed, Nov 20, 2019 at 1:06 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Wed, Nov 20, 2019 at 12:51 PM Karol Herbst <kherbst@...hat.com> wrote:
> >
> > On Wed, Nov 20, 2019 at 12:48 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
> > >
> > > On Wed, Nov 20, 2019 at 12:22 PM Mika Westerberg
> > > <mika.westerberg@...el.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@...el.com> wrote:
> > > > > >
>
> [cut]
>
> > > > >
> > > > > Oh, so does it look like we are trying to work around AML that tried
> > > > > 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 the
> > > 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.