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    SubjectRe: [PATCH 09/10] swiotlb: add support for non-coherent DMA
    On Mon, Oct 22, 2018 at 06:11:04PM +0100, Robin Murphy wrote:
    >> + if (!dev_is_dma_coherent(dev) &&
    >> + (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
    >
    > Nit: other parts of the file are already using the "!(...)" style rather
    > than "(...) == 0".

    Indeed. Probably some kind of copy and past error..

    > I had a quick play at moving the cache maintenance here out into the
    > callers, which comes out arguably looking perhaps a little cleaner (only +1
    > source line overall, and actually reduces text size by 32 bytes for my
    > build), but sadly I can't really see any way of doing the equivalent for
    > map/unmap short of duplicating the whole 3-line arch_sync_*() block, which
    > just makes for a different readability problem. As you mentioned on patch
    > #7, I guess this really is just one of those things which has no nice
    > solution, so cosmetics aside,

    It looks pretty ok, but given that I want to send this version to
    Linus for the merge window I don't really dare to touch it.

    The master plan for 4.21 is to actually merge swiotlb into dma-direct
    and to allow direct calls to dma-direct given how expensive indirect
    calls are with spectre, and dma mappings show up badly in various
    benchmarks. I'll see if I can do that in a way following what you've
    done.

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