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

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Message-ID: <462EAB13.4040104@zytor.com>
Date:	Tue, 24 Apr 2007 18:12:51 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <ak@...e.de>
CC:	David Miller <davem@...emloft.net>, ashok.raj@...el.com,
	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.

Andi Kleen wrote:
> On Tuesday 24 April 2007 23:50:26 David Miller wrote:
>> From: Ashok Raj <ashok.raj@...el.com>
>> Date: Tue, 24 Apr 2007 14:38:35 -0700
>>
>>> Its not clear if we have a very generic device breakage.. most devices
>>> on these platforms are going to be more recent, (except maybe some
>>> legacy fd)... 
>> I'm not so sure, there are some "modern" sound cards that have
>> a 31-bit DMA addressing limitation because they use the 31st
>> bit as a status bit in their DMA descriptors :-)
> 
> There's also a 2GB only megaraid RAID controller that's pretty popular 
> because Dell shipped it for a long time.
> 

You can probably find almost any possible bitmask if you look long 
enough.  Hardware vendors are notorious for this kind of "optimizations".

	-hpa
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