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    SubjectRe: PCI DMA to small buffers on cache-incoherent arch
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       From: Oliver Neukum <Oliver.Neukum@lrz.uni-muenchen.de>
    Date: Sun, 9 Jun 2002 08:45:49 +0200

    Am Sonntag, 9. Juni 2002 07:29 schrieb David S. Miller:
    > From: Roland Dreier <roland@topspin.com>
    > Date: 08 Jun 2002 18:26:12 -0700
    >
    > Just to make sure I'm reading this correctly, you're saying that as
    > long as a buffer is OK for DMA, it should be OK to use a
    > sub-cache-line chunk as a DMA buffer via pci_map_single(), and
    > accessing the rest of the cache line should be OK at any time before,
    > during and after the DMA.
    >
    > Yes.

    Does this mean that this piece of memory does have to be declared
    uncacheable until DMA is finished ?
    How else do you solve th problem of validity during DMA and
    especially after DMA ?

    You flush either before/after depending upon whether the cpu caches
    are writeback in nature or not, and the cpu is not allowed to touch
    those addresses while the device is doing the DMA.
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