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

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Date:   Wed, 29 Mar 2017 09:47:52 +0000
From:   "Nath, Arindam" <Arindam.Nath@....com>
To:     'Joerg Roedel' <jroedel@...e.de>
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

>-----Original Message-----
>From: 'Joerg Roedel' [mailto:jroedel@...e.de]
>Sent: Wednesday, March 29, 2017 3:12 PM
>To: Nath, Arindam
>Cc: Deucher, Alexander; 'Joerg Roedel'; Bjorn Helgaas; linux-
>pci@...r.kernel.org; linux-kernel@...r.kernel.org; Daniel Drake
>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.

Actually what you said is correct. Before creating the patch, I had experimented with 1s and 10s invalidation timeout values, but none of them helped.

Thanks,
Arindam

>
>
>
>	Joerg