[Nouveau] [PATCH] PCI: add prefetch quirk to work around Asus/Nvidia suspend issues

[Daniel Drake]

On Sat, Sep 1, 2018 at 3:12 AM, Bjorn Helgaas <helgaas at kernel.org> wrote:
> If true, this sounds like some sort of erratum, so it would be good to
> get some input from Intel, and I cc'd a few Intel folks.

Yes, it would be great to get their input.

> It's interesting that all the systems below are from Asus.  That makes
> me think there's some BIOS or SMM connection, e.g., SMM traps the
> register write and does something magic.

Is there a way I can check if there is a SMM trap active for this address?

> Does this problem happen after a full system suspend/resume, or does
> it happen after runtime suspend of only the GPU?  Or runtime suspend
> of only the GPU and the upstream bridge?

runtime suspend/resume works fine. It only happens after S3 suspend.

> Can we tell whether Windows rewrites this register unconditionally at
> resume-time?  If so, it may be more robust for Linux to do the same.
> The whole thing is black magic, which I hate, but if it's our only
> choice, it may be better to have this applied everywhere so we don't
> keep stubbing our toes on new systems that require the quirk.

Any suggestions for how to make this happen? Booting windows in
virt-manager (hoping that I could then spy on PCI config space reg
accesses), I don't see an option for S3 suspend, but I'll keep looking
into this.

Thanks
Daniel