Re: [PATCH] Xen/i386 cleanups - AGP bus/phys cleanups

[Paul Mackerras]

Alan Cox writes:

> On Iau, 2005-03-17 at 09:34, Paul Mackerras wrote:
> > This code needs real physical addresses, which are not the same things
> > as bus addresses.  
> 
> Not always. The code needs platform specific goodies. We've only never
> been burned so far because there isn't a box with an IOMMU and AGPGART
> where one maps through the other.

That sounds like a good way to make AGP accesses slower. :)

Seriously, given that AGP is a technology that is being superseded by
PCI Express, I think it's reasonable to look at the range of current
implementations to see what we have to cope with.  So I don't think
it's worth worrying too much about the possibility of GARTs that go
through the IOMMU.  However, the idea of having phys_to_agp/agp_to_phys
(or virt_to_agp/agp_to_virt) sounds like it wouldn't be too much
effort, if it would help Xen.

Paul.
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