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

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Date:   Thu, 21 Nov 2019 12:31:57 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Mika Westerberg <mika.westerberg@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Karol Herbst <kherbst@...hat.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 Thu, Nov 21, 2019 at 12:17 PM Mika Westerberg
<mika.westerberg@...el.com> wrote:
>
> On Thu, Nov 21, 2019 at 12:03:52PM +0100, Rafael J. Wysocki wrote:
> > On Thu, Nov 21, 2019 at 11:14 AM Mika Westerberg
> > <mika.westerberg@...el.com> wrote:
> > >
> > > On Wed, Nov 20, 2019 at 10:36:31PM +0100, Karol Herbst wrote:
> > > > with the branch and patch applied:
> > > > https://gist.githubusercontent.com/karolherbst/03c4c8141b0fa292d781badfa186479e/raw/5c62640afbc57d6e69ea924c338bd2836e770d02/gistfile1.txt
> > >
> > > Thanks for testing. Too bad it did not help :( I suppose there is no
> > > change if you increase the delay to say 1s?
> >
> > Well, look at the original patch in this thread.
> >
> > What it does is to prevent the device (GPU in this particular case)
> > from going into a PCI low-power state before invoking AML to power it
> > down (the AML is still invoked after this patch AFAICS), so why would
> > that have anything to do with the delays?
>
> Yes, I know what it does :) I was just thinking that maybe it's still
> the link that does not come up when we go back to D0 I guess that's not
> the case here.

I'm not sure why that would be related to putting the device into,
say, PCI D3 before invoking AML to remove power from it.  If it is not
in PCI D3 at this point, the AML still runs and still removes power
from it IIUC, so on the way back the situation is the same regardless:
the device has no power which (again) needs to be restored by AML.
That (in principle) should not depend on what happened to the device
before it lost power.