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    SubjectRe: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver
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    On Fri, 2011-09-09 at 10:52 +0800, Barry Song wrote:
    > >
    > > Actually, there is no real case for xlen > dma_width. this picture is
    > > only explaining what will happen if we set xlen > dma_width.
    > > when xlen > dma_width, for every line, dma will transfer only
    > > dma_width. Then the extra data is wrapped around
    > > to the next data line, it will corrupt the DMA transfer for
    > > multiple-line 2-D DMA since the extra data will overlap with the real
    > > next line.
    > >
    > > if we set ylen to 0, the DMA becomes 1D, the wrap-around of the extra
    > > data has no issue nobody will overlap with it.
    > >
    >
    > For example, if we set xlen = 7, dma_width =4, ylen > 0
    > then dma will happen like:
    > 0~6
    > 4~10
    > 8~14
    > 12~18
    > ....
    Is there a real world use case of this??

    >
    > But for ylen=0, it has no issue. there is no next line to overlap with
    > the extra data.
    >
    > in case we set xlen = 0, something funny will happen:
    > i will copy the same memory again and again(ylen+1 times).


    --
    ~Vinod Koul
    Intel Corp.



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