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    SubjectRe: [PATCH] asm-generic: add a dma-mapping.h file
    On Friday 22 May 2009, FUJITA Tomonori wrote:
    > I don't think that this works for all architectures because a returned
    > buffer of alloc_pages_node might not be DMA-capable. Needs to use the
    > coherent_dma_mask here. See x86's dma_alloc_coherent and Alpha's
    > pci-noop.c (there might be other examples).

    Right, Grant also made the same comment.

    > I think that having a generic header for simple mapping functions
    > (dma_map_single, dma_map_page, dma_map_sg, etc) would be useful but
    > I'm not sure if we can't have a generic version of
    > dma_alloc_coherent.
    > There are lots of architectures that do
    > architecture-specific things. For example, you replaced avr32
    > dma-mapping.h except for dma_alloc_coherent, which seems to be can't
    > be generic.

    I agree that it won't be fully generic, because all architectures
    with non-coherent DMA will have to do architecture specific setup
    to get uncached mappings here. I believe that it can be generic
    enough to support all architectures that have a cache-coherent PCI
    bus, hence the #ifdef CONFIG_DMA_COHERENT around this function.

    E.g. cris could use a one-line redirect to
    asm-generic/dma-mapping-linear.h if it did not have the
    special dma_get_cache_alignment function. I still would
    like to find a better way to handle this one than to
    redefine the function.

    > BTW, it looks odd to add dma_debug to dma_map_single, etc but not
    > dma_alloc_coherent. ;)

    hehe, sure. I copied the dma_debug stuff from sh, the comments
    from avr32 and the dma_alloc_coherent implementation from powerpc,
    so I missed this one.

    Thanks for the review.

    Arnd <><

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