> > coherent and consistent are synonyms. It's confusing because there is
 > > pci_alloc_consistent(), which is in general just a wrapper for
 > > dma_alloc_coherent().
 >
 > According to DMA-mapping.txt they are not. Alpha, M68000 wihtout MMU, PPC,
 > Sparc, Sparc64, V850 have own implementation of pci_alloc_consistent().
 >
 > Yes, on i386, the pci_alloc_consistent() is just wrapper for
 > dma_alloc_coherent().
Sorry, I was a little confusing. The implementations may be different
but in general there is no real difference between consistent and
coherent memory. Using either pci_alloc_consistent() or
dma_alloc_coherent() will exhaust the same small pool of address space
on powerpc 4xx for example.
 > So, what about some #ifdefs ? E.g., allow config option - Xen optimizations?
Seems pretty ugly, especially given that Xen is not upstream. I think
the Xen tree should just carry such patches, at least until Xen is
merged. Even then I'm quite dubious about having two code paths for this.
 - R.
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