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    SubjectRe: [PATCH] Xen/i386 cleanups - AGP bus/phys cleanups
    On Wednesday, March 16, 2005 10:35 am, Keir Fraser wrote:
    > On 16 Mar 2005, at 18:10, Christoph Hellwig wrote:
    > > On Wed, Mar 16, 2005 at 10:01:07AM -0500, Rik van Riel wrote:
    > >> In the case of AGP, the AGPGART effectively _is_ the
    > >> IOMMU. Calculating the addresses right for programming
    > >> the AGPGART is probably worth fixing.
    > >
    > > Well, it's a half-assed one. And some systems have a real one.
    > >
    > > But the real problem is that virt_to_bus doesn't exist at all
    > > on architectures like ppc64, and this patch touches files like
    > > generic.c and backend.c that aren't PC-specific. So you
    > > effectively break agp support for them.
    > The AGP driver is only configurable for ppc32, alpha, x86, x86_64 and
    > ia64, all of which have virt_to_bus.

    Yeah, but that doesn't mean it makes sense on all those platforms. The
    biggest problem with virt_to_bus (well, depending on who you talk to) is that
    it can't handle systems where the address translation must be done
    differently depending on *which* bus we're getting a bus address for. Not
    sure what makes sense in this case though... is the DMA mapping interface

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