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

[Rafael J. Wysocki]

On Wed, Nov 20, 2019 at 1:10 PM Karol Herbst <kherbst@xxxxxxxxxx> wrote:
>
> On Wed, Nov 20, 2019 at 1:06 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> >
> > On Wed, Nov 20, 2019 at 12:51 PM Karol Herbst <kherbst@xxxxxxxxxx> wrote:
> > >
> > > On Wed, Nov 20, 2019 at 12:48 PM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> > > >
> > > > On Wed, Nov 20, 2019 at 12:22 PM Mika Westerberg
> > > > <mika.westerberg@xxxxxxxxx> 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@xxxxxxxxx> 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.

I'm not sure what you are talking about.

I'm taking specifically about the ((OSYS == 0x07DF) && (_REV == 0x05))
check mentioned by Mika which doesn't seem to depend on user input in
any way.