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

[Rafael J. Wysocki]

On Thu, Nov 21, 2019 at 12:28 PM Mika Westerberg
<mika.westerberg at intel.com> wrote:
>
> On Wed, Nov 20, 2019 at 11:29:33PM +0100, Rafael J. Wysocki wrote:
> > > last week or so I found systems where the GPU was under the "PCI
> > > Express Root Port" (name from lspci) and on those systems all of that
> > > seems to work. So I am wondering if it's indeed just the 0x1901 one,
> > > which also explains Mikas case that Thunderbolt stuff works as devices
> > > never get populated under this particular bridge controller, but under
> > > those "Root Port"s
> >
> > It always is a PCIe port, but its location within the SoC may matter.
>
> Exactly. Intel hardware has PCIe ports on CPU side (these are called
> PEG, PCI Express Graphics, ports), and the PCH side. I think the IP is
> still the same.
>
> > Also some custom AML-based power management is involved and that may
> > be making specific assumptions on the configuration of the SoC and the
> > GPU at the time of its invocation which unfortunately are not known to
> > us.
> >
> > However, it looks like the AML invoked to power down the GPU from
> > acpi_pci_set_power_state() gets confused if it is not in PCI D0 at
> > that point, so it looks like that AML tries to access device memory on
> > the GPU (beyond the PCI config space) or similar which is not
> > accessible in PCI power states below D0.
>
> Or the PCI config space of the GPU when the parent root port is in D3hot
> (as it is the case here). Also then the GPU config space is not
> accessible.

Why would the parent port be in D3hot at that point?  Wouldn't that be
a suspend ordering violation?

> I took a look at the HP Omen ACPI tables which has similar problem and
> there is also check for Windows 7 (but not Linux) so I think one
> alternative workaround would be to add these devices into
> acpi_osi_dmi_table[] where .callback is set to dmi_disable_osi_win8 (or
> pass 'acpi_osi="!Windows 2012"' in the kernel command line).

I'd like to understand the facts that have been established so far
before deciding what to do about them. :-)