linux-kernel - Re: [PATCH] PCI: Blacklist AMD Stoney GPU devices for ATS

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Date:   Wed, 29 Mar 2017 11:42:18 +0200
From:   'Joerg Roedel' <jroedel@...e.de>
To:     "Nath, Arindam" <Arindam.Nath@....com>
Cc:     "Deucher, Alexander" <Alexander.Deucher@....com>,
        '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>
Subject: Re: [PATCH] PCI: Blacklist AMD Stoney GPU devices for ATS

Hi Arindam,

On Wed, Mar 29, 2017 at 07:15:42AM +0000, Nath, Arindam wrote:
> Joerg, as per my limited understanding of ATS, the ATC will respond to
> invalidation requests after making sure there are no in-flight DMA
> transactions with the address requested by IOMMU to be invalidated.
> Now since the IOMMU was sending invalidate command to GPU even though
> there was no explicit page unmapping request from the graphics
> subsystem, we _might_ end up in a situation where the ATC takes longer
> than the invalidation timeout to respond to IOMMU.

The maximum wait-time in the loop is 100ms. This should be more than
enough for the ATC to complete any in-flight transaction and flush its
internal TLB.

If that is not enough, there is almost certainly something wrong with
the hardware.



	Joerg