Messages in this thread | | | From | Barry Song <> | Date | Fri, 9 Sep 2011 10:35:36 +0800 | Subject | Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver |
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2011/9/9 Vinod Koul <vkoul@infradead.org>: > 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?
two cases: 1. continuous DMA: xlen = DMA_WIDTH 2. interleaved DMA: xlen < DMA_WIDTH
2 is for dma video/image or something like that. For example, you might only copy 1/9 of a nine-square grid by it.
> > In first diagram you sent, x length is first block length to transfer > and (dma_width - x_len) is length to skip, right?
(dma_width - x_len) is length to skip
> > 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?
Actually, there is no real case for xlen > dma_width. this picture is only explaining what will happen if we set xlen > dma_width. when xlen > dma_width, for every line, dma will transfer only dma_width. Then the extra data is wrapped around to the next data line, it will corrupt the DMA transfer for multiple-line 2-D DMA since the extra data will overlap with the real next line.
if we set ylen to 0, the DMA becomes 1D, the wrap-around of the extra data has no issue nobody will overlap with it.
> > -- > ~Vinod Koul > Intel Corp. > >
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