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    SubjectRe: problem with blk_queue_bounce_limit()
    >>>>> On Fri, 06 Jun 2003 23:44:01 -0700 (PDT), "David S. Miller" <davem@redhat.com> said:

    DaveM> But on an IOMMU system, we could end up mapping to the same
    DaveM> bogus DMA address.

    Ah, yes, just changing the buffer address doesn't guarantee a
    different bus address. I missed that.

    DaveM> So we have to solve this problem by keeping the existng bad
    DaveM> mapping, doing a new DMA mapping, then trowing away the old
    DaveM> one.

    But you're creating a new mapping for the old buffer. What if you had
    a DMA API implementation which consolidates multiple mapping attempts
    of the same buffer into a single mapping entry (along with a reference
    count)? That would break the workaround.

    Isn't the proper fix to (a) get a new buffer, (b) create a mapping for
    the new buffer, (c) destroy the mapping for the old buffer. That
    should guarantee a different bus address, no matter what the
    DMA-mapping implementation.

    Plus then you don't have to rely on PCI_DMA_BUS_IS_PHYS.

    --david
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