linux-kernel - RE: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

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Date:   Fri, 26 May 2017 11:57:59 +0000
From:   "Deucher, Alexander" <Alexander.Deucher@....com>
To:     'Joerg Roedel' <jroedel@...e.de>
CC:     'David Woodhouse' <dwmw2@...radead.org>,
        'Joerg Roedel' <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Daniel Drake <drake@...lessm.com>,
        "Samuel Sieb" <samuel@...b.net>
Subject: RE: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

> -----Original Message-----
> From: Joerg Roedel [mailto:jroedel@...e.de]
> Sent: Wednesday, May 24, 2017 4:45 AM
> To: Deucher, Alexander
> Cc: 'David Woodhouse'; 'Joerg Roedel'; Bjorn Helgaas; linux-
> pci@...r.kernel.org; linux-kernel@...r.kernel.org; Daniel Drake; Samuel
> Sieb
> Subject: Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs
> 
> 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.

FWIW, the GPU driver does not actually use ATS at the moment so I don't think we should see any ATS transactions.

Alex