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

    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

    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? */;
    --
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