Re: [RFC PATCH] pci: prevent putting pcie devices into lower device states on certain intel bridges

[Karol Herbst <kherbst@redhat.com>]

On Tue, Oct 1, 2019 at 10:47 AM Mika Westerberg
<mika.westerberg@linux.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@linux.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.

> 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.