From: Andi Kleen <ak@muc.de>
To: Terence Ripperda <tripperda@nvidia.com>
Subject: Re: [PATCH] x86-64: Make GART_IOMMU kconfig help text more specific (trivial)
Date: Thu, 9 Mar 2006 18:47:28 +0100
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On Friday 10 March 2006 02:02, Terence Ripperda wrote:
> > Also, note that the previous help text stated that IOMMU was needed for
> > >3GB memory instead of >4GB.  This is fixed in the newer version.
> 
> note that many system bioses have memory remapping, to accomodate pci
> i/o ranges. some address space is reserved by the bios for these i/o
> ranges, and as system memory approaches this reserved space, the
> memory is remapped to >4GB. this usually happens around 3.25GB -
> 3.5GB, but probably varies based on bios and pci devices. once this
> memory is remapped to >4GB, the IOMMU kicks in.
> 
> so the original text is probably more accurate.

Yep. I already fixed this when applying the patch.

3GB is a rough round number I generally use for this.

-Andi

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