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Re: [Xen-devel] Re: [RFC] Make AGP work with IOMMU

To: Dave Airlie <airlied@xxxxxxxxx>
Subject: Re: [Xen-devel] Re: [RFC] Make AGP work with IOMMU
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Wed, 05 Aug 2009 11:26:52 -0700
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Zhenyu Wang <zhenyu.z.wang@xxxxxxxxx>, Joerg Roedel <joerg.roedel@xxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx, David Woodhouse <dwmw2@xxxxxxxxxxxxx>, Keir Fraser <kier.fraser@xxxxxxxxxxxxx>
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On 08/04/09 23:57, Dave Airlie wrote:
>> All we've done so far is make intel-agp use the DMA API correctly. And
>> that's conditional on CONFIG_DMAR. But we could make it unconditional,
>> and make the other drivers do it too. The code is all fairly generic.
>> Without an IOMMU, the overhead would be fairly minimal.
> I'm not sure how prevalent Xen is on AGP systems, I'm going to guess
> not enough that anyone cares.

What do you mean by AGP here?  Do you mean "machine with physical AGP
port", or "machine with graphics using the AGP aperature"?  There's an
increasing interest in putting Xen on desktop machines, so the former is
debatable, but the latter (I think?) definitely isn't true.

>  Intel integrated chips are the only AGP
> codebase user that are made any more, and they don't really use AGP
> its just a legacy of the previous designs.

Plenty of people are using older machines for testing, etc, so I
wouldn't want to exclude them too lightly.  I've got bug reports from
people using older Radeons, etc.


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