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    SubjectRe: USB transfer_buffer allocations on 64bit systems
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    Am Freitag, 9. April 2010 00:20:36 schrieb Alan Stern:
    > > > That would work, but it doesn't match the way existing drivers use the
    > > > interface. For example, the audio driver allocates a 16-byte coherent
    > > > buffer and then uses four bytes from it for each of four different
    > > > URBs.
    > >
    > > That will not work with any fallback that does not yield a coherent buffer.
    >
    > What you mean isn't entirely clear. But it certainly does work in
    > various circumstances that don't yield coherent buffers. For example,
    > it works if the controller uses PIO instead of DMA. It also works if
    > the controller uses DMA and the URBs have to be bounced.

    It'll work on x86. On incoherent architectures this violates the cacheline
    rules for DMA-mapping if you have to bounce. So it seems to me that
    if you want to share a buffer between URBs, it must be coherent.

    Regards
    Oliver


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