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    SubjectRe: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver
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    On Thu, 2011-09-08 at 14:36 +0800, Barry Song wrote:
    > 2011/9/8 Jassi Brar <jassisinghbrar@gmail.com>:
    > > On Thu, Sep 8, 2011 at 8:47 AM, Jassi Brar <jassisinghbrar@gmail.com> wrote:
    > >> On Thu, Sep 8, 2011 at 7:42 AM, Barry Song <21cnbao@gmail.com> 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} ?
    > >>
    > > Perhaps 2d-dma.PNG is inaccurate - it shouldn't depict any deltaX.
    > > Doesn't xlen and width always start together ? If no, please don't read ahead.
    > >
    > > According to figures, {xlen > width} is to be set _only_ when a transfer
    > > is divided into _exactly_ two chunks separated by gap _exactly_
    > > equal to length of the second chunk (an extremely rare case).
    >
    > Sorry i didn't list related full information in datasheet in my early reply.
    > we don't have the case of xlen > dma_width.
    But is it theoretically possible or just an error case?? Looks like its
    latter, right?

    --
    ~Vinod Koul
    Intel Corp.

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