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    SubjectRe: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver
    Hi Jassi,

    2011/9/8 Jassi Brar <>:
    > On Thu, Sep 8, 2011 at 7:42 AM, Barry Song <> wrote:
    >>>> it is much different with primacell based DMA like pl080, pl330.
    >>>> prima2 has a self-defined DMAC IP. basically it is a 2D mode dma with
    >>>> two scales X and Y and direct way to start and stop DMA.
    >>>> every channel has fixed function to serve only one perpheral. so you
    >>>> find we have a filter id.
    >>> okay, what do you mean by 2D mode? Is it similar to what TI folks, Linus
    >>> W and Jassi Brar posted RFC's on?
    >> In SiRFprimaII 2-D DMA, the system memory space is interpreted
    >> as a 2-D layout instead of a linear 1-D layout. More specifically, the
    >> system memory can be considered as
    >> multiple data lines. The length of the data line is determined by the
    >> user-selected DMA_WIDTH register.
    >> The user can specify a data window that the user wants to access using
    >> four parameters:
    >> ■ Start address
    >> ■ X length
    >> ■ Y length
    >> ■ Width
    >> The idea of a 2-D DMA is shown in figure 2d-dma.png attached.
    >> If you specifies the Y length as 0 or the X length equals to the DMA
    >> width, then this 2-D DMA reduces to
    >> 1-D. If the user configures the X length greater than the DMA width,
    >> then the extra data is wrapped around
    >> to the next data line, this may corrupt the DMA transfer for
    >> multiple-line 2-D DMA. If this is a 1-D DMA, then
    >> there is no issue. The attached diagram 2d-dma2.png shows the
    >> wrap-around of the extra data in case the X length
    >> greater than DMA width.
    > 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):

    This feature can help us to do DMA operation to non-continuous memory
    area, for example, pick a part of a image.

    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
    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.

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      Last update: 2011-09-08 08:17    [W:0.023 / U:23.556 seconds]
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