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Re: [Xen-devel] Using arch/x86_64/pci-dma in x86_64 Xen

To: "Muli Ben-Yehuda" <muli@xxxxxxxxxx>
Subject: Re: [Xen-devel] Using arch/x86_64/pci-dma in x86_64 Xen
From: "Christian Limpach" <christian.limpach@xxxxxxxxx>
Date: Sun, 7 May 2006 20:45:09 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, "Langsdorf, Mark" <mark.langsdorf@xxxxxxx>
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On 5/7/06, Muli Ben-Yehuda <muli@xxxxxxxxxx> wrote:
On Thu, May 04, 2006 at 09:57:35AM -0500, Langsdorf, Mark wrote:

> The current implementation of pci-dma in x86_64 Xen
> Linux is to use the i386 implementation.  I don't
> believe this is sustainable in the long term, as
> x86_64 Xen is going to need more DMA solutions than
> just SWIOTLB and plain hardware as various IOMMU
> implementations arrive.

100% agreed.

> The mainstream kernel has a clean abstraction layer
> with the dma_ops that should be portable to Xen dom0
> and domU.  I've started implementing this in a
> pci-dma-xen for x86_64 Xen Linux.  Am I stepping on
> anyone's toes or is there anyone I should be
> co-ordinating this with?

Please keep Jon and me in the loop, we added the dma_ops to the main
kernel for the Calgary IOMMU but haven't got around to porting the
various Xen dma ops to it.

Also, I believe Christian had some thoughts about the direction going
forward for the Xen specific dma ops?

I think that using the dma_ops abstraction layer on x86_64 is
definitely the way to go.  It's just not clear how the Xen specific
dma ops should be implemented in the end, whether having a common
implementation is worthwhile considering that it will require glue
code to make it fit with the different interfaces.


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