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    Subject[PATCH 3/4] dma: document dma_flags_set_dmaflush()

    Document dma_flags_set_dmaflush().

    Signed-off-by: Arthur Kepner <akepner@sgi.com>
    --
    DMA-mapping.txt | 25 ++++++++++++++++++++++++-
    1 file changed, 24 insertions(+), 1 deletion(-)

    diff --git a/Documentation/DMA-mapping.txt b/Documentation/DMA-mapping.txt
    index e07f253..31e3234 100644
    --- a/Documentation/DMA-mapping.txt
    +++ b/Documentation/DMA-mapping.txt
    @@ -745,7 +745,30 @@ to "Closing".
    2.5., page+offset is always used, and the "address" field has been
    deleted.

    -2) More to come...
    +2) Platforms that permit DMA reordering
    +
    + At least one platform (SGI SN2) allows DMA to be reordered between
    + device and host memory. This reordering can happen in the NUMA
    + interconnect, and it usually results in correct operation and improved
    + performance. In some situations it may be necessary to explicitly
    + synchronize DMA from the device. For example, if the device does a DMA
    + write to indicate that data is ready, the DMA of the "completion
    + indication" can race with DMA of data. In this situation,
    + dma_flags_set_dmaflush() can be used to associate a "dmaflush"
    + attribute with a memory region. The dmaflush attribute will cause in-
    + flight DMA from the device to be flushed to host memory when the
    + associated memory region is written. (On platforms that don't permit
    + DMA reordering, this is a no-op.)
    +
    + For example, you might map the memory region used for completion
    + indications as follows:
    +
    + int count, flags = dma_flags_set_dmaflush(DMA_BIDIRECTIONAL);
    + .....
    + count = dma_map_sg(dev, sglist, nents, flags);
    +
    +
    +3) More to come...

    Handling Errors

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