Messages in this thread |  | | | From | David Mosberger <> | | Date | Sat, 7 Jun 2003 00:05:06 -0700 | | Subject | Re: problem with blk_queue_bounce_limit() |
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>>>>> 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.
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