linux-kernel - Re: [PATCH v3] pci: prevent putting nvidia GPUs into lower device states on certain intel bridges

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Message-ID: <20191021154606.GT2819@lahna.fi.intel.com>
Date:   Mon, 21 Oct 2019 18:46:06 +0300
From:   Mika Westerberg <mika.westerberg@...el.com>
To:     Karol Herbst <kherbst@...hat.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Lyude Paul <lyude@...hat.com>,
        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>,
        Linux ACPI Mailing List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v3] pci: prevent putting nvidia GPUs into lower device
 states on certain intel bridges

On Mon, Oct 21, 2019 at 04:49:09PM +0200, Karol Herbst wrote:
> On Mon, Oct 21, 2019 at 4:09 PM Mika Westerberg
> <mika.westerberg@...el.com> wrote:
> >
> > On Mon, Oct 21, 2019 at 03:54:09PM +0200, Karol Herbst wrote:
> > > > I really would like to provide you more information about such
> > > > workaround but I'm not aware of any ;-) I have not seen any issues like
> > > > this when D3cold is properly implemented in the platform.  That's why
> > > > I'm bit skeptical that this has anything to do with specific Intel PCIe
> > > > ports. More likely it is some power sequence in the _ON/_OFF() methods
> > > > that is run differently on Windows.
> > >
> > > yeah.. maybe. I really don't know what's the actual root cause. I just
> > > know that with this workaround it works perfectly fine on my and some
> > > other systems it was tested on. Do you know who would be best to
> > > approach to get proper documentation about those methods and what are
> > > the actual prerequisites of those methods?
> >
> > Those should be documented in the ACPI spec. Chapter 7 should explain
> > power resources and the device power methods in detail.
> 
> either I looked up the wrong spec or the documentation isn't really
> saying much there.

Well it explains those methods, _PSx, _PRx and _ON()/_OFF(). In case of
PCIe device you also want to check PCIe spec. PCIe 5.0 section 5.8 "PCI
Function Power State Transitions" has a picture about the supported
power state transitions and there we can find that function must be in
D3hot before it can be transitioned into D3cold so if the _OFF() for
example blindly assumes that the device is in D0 when it is called, it
is a bug in the BIOS.

BTW, where can I find acpidump of such system?