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SubjectRe: Streaming DMA mapping question
   From: Adam Kropelin <>
Date: Fri, 13 Sep 2002 15:39:16 -0400

According to the docs, you should either unmap or sync your DMA buffer before
touching it from the host. The i386 implementation of pci_unmap is empty --no
problem; there must not be any unmap work to do on this arch. But the
implementation of pci_dma_sync does contain a flush_write_buffers() call. This
makes me think that perhaps if I'm going to modify the buffer before I submit it
back to the controller I need to do:

Actually, rather it appears that the i386 pci_unmap_*() routines need
the write buffer flush as well.

The x86 implementation is a bad example to read if you're trying to
see what the worst case scenerio is.

Just follow the document and your driver will work properly on all
platforms. DMA-mapping.txt was meant to be written in a way such
that you should not ever need to look at an implementation of the
interfaces to figure out how to use them.
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