linux-kernel - Re: [Intel IOMMU][patch 8/8] Preserve some Virtual Address when devices cannot address entire range.

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Date:	Tue, 24 Apr 2007 23:12:54 +0200
From:	Andi Kleen <ak@...e.de>
To:	Ashok Raj <ashok.raj@...el.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...l.org, gregkh@...e.de,
	muli@...ibm.com, asit.k.mallick@...el.com,
	suresh.b.siddha@...el.com, anil.s.keshavamurthy@...el.com,
	arjan@...ux.intel.com, shaohua.li@...el.com
Subject: Re: [Intel IOMMU][patch 8/8] Preserve some Virtual Address when devices cannot address entire range.

On Tuesday 24 April 2007 22:33:04 Ashok Raj wrote:

> With PCIE there is some benefit to keep dma addr low for performance reasons, 
> since it will use 	32bit Transaction level packets instead of 64bit.
> 
> This reservation is only required if we have some legacy device under a p2p 
> where its required to share its addr space with other devices. We could 
> implement a default when one is not specified to keep things simple.

We already have a couple of other IOMMU architectures who essentially have the same
problem. Have you checked how they solve this?

-Andi



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