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    SubjectRe: SCSI breakage on non-cache coherent architectures
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     > 2) Add the __dma_cacheline_aligned tag.
    >
    > But note that with #2 it could get quite ugly because the
    > alignment and size both have a minimum that needs to be
    > enforced, not just the alignment alone. So either:
    >
    > struct foo {
    > unsigned int other_unrelated_stuff;
    >
    > struct object dma_thing __dma_cacheline_aligned;
    >
    > unsigned int more_nondma_stuff __dma_cacheline_aligned;
    > };
    >
    > or:
    >
    > struct foo {
    > unsigned int other_unrelated_stuff;
    >
    > union {
    > struct object dma_thing __dma_cacheline_aligned;
    > char __pad[(sizeof(object) + DMA_CACHELINE_SIZE &
    > ~DMA_CACHELINE_SIZE)];
    > } u;
    >
    > unsigned int more_nondma_stuff __dma_cacheline_aligned;
    > };

    I wrapped this ugliness up inside the macro back in what I posted in
    2002 (http://lkml.org/lkml/2002/6/12/234):

    #define __dma_buffer __dma_buffer_line(__LINE__)
    #define __dma_buffer_line(line) __dma_buffer_expand_line(line)
    #define __dma_buffer_expand_line(line) \
    __attribute__ ((aligned(L1_CACHE_BYTES))); \
    char __dma_pad_ ## line [0] __attribute__ ((aligned(L1_CACHE_BYTES)))

    then you just need to tag the actual member like:

    char foo[3] __dma_buffer;

    - R.
    -
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