Messages in this thread | | | Subject | Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver | From | Vinod Koul <> | Date | Fri, 09 Sep 2011 03:21:16 +0530 |
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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. What is intended usage of the 2D dma?
In first diagram you sent, x length is first block length to transfer and (dma_width - x_len) is length to skip, right?
So what is the second diagram about? Is this juts a case when notion of xlen > dma_width? How much you transfer and how much you skip?
-- ~Vinod Koul Intel Corp.
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