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To: Boszormenyi Zoltan <zboszor@freemail.hu>
cc: linux-kernel@vger.kernel.org
Subject: Re: x86_64 IOMMU question
References: <1yxkz-6ct-31@gated-at.bofh.it>
From: Andi Kleen <ak@muc.de>
Date: Thu, 18 Mar 2004 00:14:09 +0100
In-Reply-To: <1yxkz-6ct-31@gated-at.bofh.it> (Boszormenyi Zoltan's message
 of "Thu, 11 Mar 2004 13:20:15 +0100")
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Boszormenyi Zoltan <zboszor@freemail.hu> writes:

> is it possible to use the IOMMU to help 32 bit devices
> that limit their capabilities with pci_set_dma_mask()?
> E.g. the emu10k1 limits itself under 256MB. Can the IOMMU
> pass the data to/from the card from/to above 256MB?

It can only remap to the AGP aperture, which is usually
just below the 4GB boundary. In theory you could move the aperture
to a very low address and remap to that (see 
arch/x86_64/kernel/aperture.c), but that would waste memory.

-Andi