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    SubjectRe: [PATCH][RFC] asm-generic:remove calling flush_write_buffers() in dma_sync_*_for_cpu
    On Tue, Jul 07, 2009 at 04:06:48PM +0200, Arnd Bergmann wrote:
    > Note that actually you need to do writeback+invalidate in DMA_TO_DEVICE

    Rubbish. DMA _to_ the device just needs any data held in the cache to
    be pushed out into the hardware RAM. There's absolutely no point in
    invalidating it - that's a complete waste of time.

    > and at least an invalidate in DMA_FROM_DEVICE during dma_map_*.
    > For the unmap, I don't think you ever need to invalidate the cache.

    As I've already explained, you do if you have speculative prefetching
    which can bring in data into the cache from _any_ memory location at
    _any_ time. We _are_ going to have to do this, no questions asked.

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      Last update: 2009-07-07 19:39    [W:0.021 / U:0.240 seconds]
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