Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

[David Woodhouse <dwmw2@infradead.org>]

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On Wed, 2017-05-24 at 10:44 +0200, Joerg Roedel wrote:
> Hi Alexander,
> 
> On Tue, May 23, 2017 at 07:54:12PM +0000, Deucher, Alexander wrote:
> > 
> > I finally got an answer from the hw team and we validated ATS on
> > stoney as well so in theory this patch shouldn’t actually be needed.
> > I think we may actually be papering over some other issue.  The
> > following patch seems to also fix this issue (and other issues):
> > https://www.spinics.net/lists/stable/msg172631.html
>
> Yeah, but it still looks to me like that the hardware got into some
> weird state with the storm of ATS invalidations sent to it.
> 
> The Completion-Wait loop timeouts seen in the original bug report
> indicate that the IOMMU is waiting for a response that never comes. And
> this is probably the ATS flush completion response from the GPU, as
> disabling ATS on the GPU makes the issue disappear.

The above patch doesn't actually fix any spec violation which could the
GPU an *excuse* to crash and stop responding to invalidations, does it?
It just seems to reduce the invalidation load a little, and thus paper
over the problem that the card tends to crash under load. Absent a more
coherent explanation, it still seems like the correct answer is to
blacklist these devices for ATS because they're broken.

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