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

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Date:	Wed, 5 Aug 2009 16:57:51 +1000
From:	Dave Airlie <airlied@...il.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Keir Fraser <kier.fraser@...citrix.com>,
	xen-devel@...ts.xensource.com, Joerg Roedel <joerg.roedel@....com>,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Zhenyu Wang <zhenyu.z.wang@...el.com>
Subject: Re: [Xen-devel] Re: [RFC] Make AGP work with IOMMU

On Wed, Aug 5, 2009 at 4:44 PM, David Woodhouse<dwmw2@...radead.org> wrote:
> On Tue, 2009-08-04 at 16:52 -0700, Jeremy Fitzhardinge wrote:
>> And just when I have patches to use them for their original purpose...
>>
>> Looking back over the thread, are you saying that most users are already
>> using the DMA API correctly for AGP accesses?  If that's true then we
>> should be just fine.
>
> No, not 'most users'. But perhaps we should.
>
> 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. 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.

Dave.
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