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From: Arnd Bergmann <arnd@arndb.de>
To: cbe-oss-dev@ozlabs.org
Subject: Re: [Cbe-oss-dev] [PATCH 3/3] Cell IOMMU static mapping support
Date: Mon, 28 Jan 2008 12:41:48 +0100
References: <edf2d9650b044e2bc21e9b74ad1044f4e5b6615c.1201257905.git.michael@ellerman.id.au>
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Cc: Olof Johansson <olof@lixom.net>, linuxppc-dev@ozlabs.org
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On Saturday 26 January 2008, Olof Johansson wrote:
> > 
> > So instead of having an IOMMU window that we use to temporarily map things
> > in and out of DMA'able space, at boot we create a 1:1 mapping for all of
> > memory. This obviously only works for devices that can do 64-bit DMA.
> 
> I don't get it. Why not disable the iommu instead?
> 

When you disable the iommu, the 32-bit devices stop working because
they can no longer access all of main memory.

The 1:1 mapping is in addition to the DMA window used for those devices,
not in place of it.

	Arnd <><