Date:   Thu, 03 Oct 2019 11:47:17 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Karol Herbst <kherbst@...hat.com>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lyude Paul <lyude@...hat.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        nouveau <nouveau@...ts.freedesktop.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [RFC PATCH] pci: prevent putting pcie devices into lower device states on certain intel bridges

On Tuesday, October 1, 2019 12:00:50 PM CEST Karol Herbst wrote:
> On Tue, Oct 1, 2019 at 11:11 AM Mika Westerberg
> <mika.westerberg@...ux.intel.com> wrote:
> >
> > On Tue, Oct 01, 2019 at 10:56:39AM +0200, Karol Herbst wrote:
> > > On Tue, Oct 1, 2019 at 10:47 AM Mika Westerberg
> > > <mika.westerberg@...ux.intel.com> wrote:
> > > >
> > > > On Mon, Sep 30, 2019 at 06:36:12PM +0200, Karol Herbst wrote:
> > > > > On Mon, Sep 30, 2019 at 6:30 PM Mika Westerberg
> > > > > <mika.westerberg@...ux.intel.com> wrote:
> > > > > >
> > > > > > On Mon, Sep 30, 2019 at 06:05:14PM +0200, Karol Herbst wrote:
> > > > > > > still happens with your patch applied. The machine simply gets shut down.
> > > > > > >
> > > > > > > dmesg can be found here:
> > > > > > > https://gist.githubusercontent.com/karolherbst/40eb091c7b7b33ef993525de660f1a3b/raw/2380e31f566e93e5ba7c87ef545420965d4c492c/gistfile1.txt
> > > > > >
> > > > > > Looking your dmesg:
> > > > > >
> > > > > > Sep 30 17:24:27 kernel: nouveau 0000:01:00.0: DRM: DCB version 4.1
> > > > > > Sep 30 17:24:27 kernel: nouveau 0000:01:00.0: DRM: MM: using COPY for buffer copies
> > > > > > Sep 30 17:24:27 kernel: [drm] Initialized nouveau 1.3.1 20120801 for 0000:01:00.0 on minor 1
> > > > > >
> > > > > > I would assume it runtime suspends here. Then it wakes up because of PCI
> > > > > > access from userspace:
> > > > > >
> > > > > > Sep 30 17:24:42 kernel: pci_raw_set_power_state: 56 callbacks suppressed
> > > > > >
> > > > > > and for some reason it does not get resumed properly. There are also few
> > > > > > warnings from ACPI that might be relevant:
> > > > > >
> > > > > > Sep 30 17:24:27 kernel: ACPI Warning: \_SB.PCI0.GFX0._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20190509/nsarguments-59)
> > > > > > Sep 30 17:24:27 kernel: ACPI Warning: \_SB.PCI0.PEG0.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20190509/nsarguments-59)
> > > > > >
> > > > >
> > > > > afaik this is the case for essentially every laptop out there.
> > > >
> > > > OK, so they are harmless?
> > > >
> > >
> > > yes
> > >
> > > > > > This seems to be Dell XPS 9560 which I think has been around some time
> > > > > > already so I wonder why we only see issues now. Has it ever worked for
> > > > > > you or maybe there is a regression that causes it to happen now?
> > > > >
> > > > > oh, it's broken since forever, we just tried to get more information
> > > > > from Nvidia if they know what this is all about, but we got nothing
> > > > > useful.
> > > > >
> > > > > We were also hoping to find a reliable fix or workaround we could have
> > > > > inside nouveau to fix that as I think nouveau is the only driver
> > > > > actually hit by this issue, but nothing turned out to be reliable
> > > > > enough.
> > > >
> > > > Can't you just block runtime PM from the nouveau driver until this is
> > > > understood better? That can be done by calling pm_runtime_forbid() (or
> > > > not calling pm_runtime_allow() in the driver). Or in case of PCI driver
> > > > you just don't decrease the reference count when probe() ends.
> > > >
> > >
> > > the thing is, it does work for a lot of laptops. We could only observe
> > > this on kaby lake and skylake ones. Even on Cannon Lakes it seems to
> > > work just fine.
> >
> > Can't you then limit it to those?
> >
> > I've experienced that Kabylake root ports can enter and exit in D3cold
> > just fine because we do that for Thunderbolt for example. But that
> > always requires help from ACPI. If the system is using non-standard ACPI
> > methods for example that may require some tricks in the driver side.
> >
> 
> yeah.. I am not quite sure what's actually the root cause. I was also
> trying to use the same PCI registers ACPI is using to trigger this
> issue on a normal desktop, no luck. Using the same registers does
> trigger the issue (hence the script).
> 
> The script is essentially just doing what ACPI does, just skipping a lot.
> 
> > > > I think that would be much better than blocking any devices behind
> > > > Kabylake PCIe root ports from entering D3 (I don't really think the
> > > > problem is in the root ports itself but there is something we are
> > > > missing when the NVIDIA GPU is put into D3cold or back from there).
> > >
> > > I highly doubt there is anything wrong with the GPU alone as we have
> > > too many indications which tell us otherwise.
> > >
> > > Anyway, at this point I don't know where to look further for what's
> > > actually wrong. And apparently it works on Windows, but I don't know
> > > why and I have no idea what Windows does on such systems to make it
> > > work reliably.
> >
> > By works you mean that Windows is able to put it into D3cold and back?
> > If that's the case it may be that there is some ACPI magic that the
> > Windows driver does and we of course are missing in Linux.
> 
> Afaik that's the case. We were talking with Nvidia about it, but they
> are not aware of any issues generally. (on Windows, nor the hardware).
> No idea if we can trust their statements though.
> 
> But yeah, it might be that on Windows they still do _DSM calls or
> something... but until today, Nvidia didn't provide any documentation
> to us for that.

So IMO in that case the right approach is to quirk the combinations of
GPU/root complex that are known problematic.

Quirking the root complex alone is likely to affect working configurations
which generally should be avoided.

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