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    SubjectRe: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver
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    On Thu, Sep 8, 2011 at 11:44 AM, Barry Song <21cnbao@gmail.com> wrote:
    >> Sorry, the role of DMA_WIDTH is not clear to me yet.
    >> In which case the user _must_ set {xlen > width} ?
    >
    > DMA_WIDTH is the size address will increase after every DMA line.
    > For example:
    > if xlen = 4, dma_width=8, ylen=5;
    > Then DMA will run as(suppose DMA address start from 0):
    > 0~3
    > 8~11
    > 16~19
    > 24~27
    > ...
    Ok, so I guessed right. 2d-dma.PNG is indeed inaccurate, unless
    there is some separate start-address of the 'width-window' which
    you haven't mentioned.

    > This feature can help us to do DMA operation to non-continuous memory
    > area, for example, pick a part of a image.
    That's just a small part of what the proposed api can do.

    > The DMA X-length is in the 32-bit D-word boundary. This value
    > specifies the number of D-words transferred
    > in each line. The value should be less than or equal to the value of
    > DMA width register.
    >
    > The DMA Y-length specifies the number of lines in DMA transfers. The
    > number of the lines in DMA transfer
    > is Y-length + 1.
    >
    > Each channel has dedicated DMA Width registers. Each DMA channel
    > should not use other channel’s DMA
    > width.
    > To enable a correct 2-D DMA, the DMA Width register must be correctly
    > set. The value of the DMA Width
    > register must be greater than or equal to the X-length, otherwise, the
    > data is overlapped. DMA_WIDTH
    > should not be set to 0.
    >
    Ok, so what I said in my last post [https://lkml.org/lkml/2011/9/8/10] seems
    quite accurate. Maybe you only need to additionally take care of
    conversion of sizes between bytes and words.
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