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

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Date:   Fri, 16 Jun 2017 18:29:23 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Daniel Drake <drake@...lessm.com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Samuel Sieb <samuel@...b.net>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH v2] PCI: Add ATS-disable quirk for AMD Stoney GPUs

Hi Bjorn,

On Thu, Jun 15, 2017 at 02:15:45PM -0500, Bjorn Helgaas wrote:
> It was marked "superseded" in patchwork and thus off my radar.  I
> don't remember if I did that or why.  I changed it back to "New" so I
> won't forget about it.

Great!

> You mention (May 24) the original bug report.  Can you include the URL
> for that?

I think there were multiple reports, here is one I could still find:

	https://lists.linuxfoundation.org/pipermail/iommu/2017-March/020836.html

> I admit I just don't have warm fuzzies that the problem is well
> understood.

The current understanding (without my ability to debug the hardware
involved) is that the GPU in the Stoney systems gets into a weird state
when ATS invalidations are sent too fast and stops responding to the
iommu.

The iommu then can't complete the invalidation commands and the driver
throws completion-wait loop timeout messages out.

	Joerg