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    SubjectRe: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver
    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.

    >
    > Anyways, every case can be easily expressed using the generic api
    > I proposed. See 'struct xfer_template' in https://lkml.org/lkml/2011/8/12/128

    i think it is the interleaved DMA case and there is a
    inter-chunk-gap(ICG) between every chunk while dma_width > xlen,
    then your new generic API can definitely cover this case.

    >
    > Roughly speaking, the following should be done...
    > Client driver :-
    > **************
    > For a 'Rectangular' transfer (2d-dma.PNG) :-
    >      xfer_template.numf = Ylen;  /* height of rectangle */
    >      xfer_template.frame_size = 1;
    >      xfer_template.sgl[0].size = Xlen; /* width of rectangle */
    >      xfer_template.sgl[0].icg = start_addr_Y(n) - end_addr_Y(n-1);
    >
    > For the "A Line and some" transfer (2d-dma2.PNG) :-
    >      xfer_template.numf = 1;
    >      xfer_template.frame_size = 2;
    >      xfer_template.sgl[0].size = xlen1; /* a line */
    >      xfer_template.sgl[1].size = xlen2;  /* and some */
    >      xfer_template.sgl[0].icg = start_addr_Y(n) - end_addr_Y(n-1);
    >      xfer_template.sgl[1].icg = 0; /* doesn't matter */
    >
    > DMAC driver :-
    > ***************
    >      if (xfer_template.frame_size == 1) {
    >           /* rectangle */
    >           schan->xlen = xfer_template.sgl[0].size;
    >           schan->width = schan->xlen + xfer_template.sgl[0].icg;
    >      } else if (xfer_template.frame_size == 2 &&
    >                  xfer_template.numf == 1 &&
    >                  xfer_template.sgl[1].size == xfer_template.sgl[0].icg){
    >           /* a line and some */
    >           schan->xlen = xfer_template.sgl[0].size +  xfer_template.sgl[1].size.
    >           schan->width = xfer_template.sgl[0].size;
    >      } else {
    >           /* _Hardware_ doesn't support the transfer as such. *
    >           return -EINVAL;
    >      }
    >      schan->ylen = xfer_template.numf /* -1? */;
    >

    Thanks
    barry
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