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Date:   Wed, 23 Oct 2019 12:00:42 +0300
From:   Mika Westerberg <mika.westerberg@intel.com>
To:     Karol Herbst <kherbst@redhat.com>
Cc:     Bjorn Helgaas <helgaas@kernel.org>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        LKML <linux-kernel@vger.kernel.org>,
        Lyude Paul <lyude@redhat.com>,
        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>,
        Linux ACPI Mailing List <linux-acpi@vger.kernel.org>
Subject: Re: [PATCH v3] pci: prevent putting nvidia GPUs into lower device
 states on certain intel bridges
Message-ID: <20191023090042.GQ2819@lahna.fi.intel.com>
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On Tue, Oct 22, 2019 at 02:51:53PM +0200, Karol Herbst wrote:
> On Tue, Oct 22, 2019 at 2:45 PM Mika Westerberg
> <mika.westerberg@intel.com> wrote:
> >
> > On Tue, Oct 22, 2019 at 11:16:14AM +0200, Karol Herbst wrote:
> > > I think there is something I totally forgot about:
> > >
> > > When there was never a driver bound to the GPU, and if runtime power
> > > management gets enabled on that device, runtime suspend/resume works
> > > as expected (I am not 100% sure on if that always works, but I will
> > > recheck that).
> >
> > AFAIK, if there is no driver bound to the PCI device it is left to D0
> > regardless of the runtime PM state which could explain why it works in
> > that case (it is never put into D3hot).
> >
> > I looked at the acpidump you sent and there is one thing that may
> > explain the differences between Windows and Linux. Not sure if you were
> > aware of this already, though. The power resource PGOF() method has
> > this:
> >
> >    If (((OSYS <= 0x07D9) || ((OSYS == 0x07DF) && (_REV == 0x05)))) {
> >       ...
> >    }
> >
> 
> I think this is the fallback to some older method of runtime
> suspending the device, and I think it will end up touching different
> registers on the bridge controller which do not show the broken
> behaviour.

I think it actually tries to identify older Windows and then Linux (the
_REV == 0x05 check comes from that). So at least some point Dell people
have experiment this on Linux.