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

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Date:   Wed, 24 May 2017 10:44:50 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     "Deucher, Alexander" <Alexander.Deucher@....com>
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

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.

Regards,

	Joerg