Messages in this thread | | | From | Barry Song <> | Date | Fri, 9 Sep 2011 10:52:38 +0800 | Subject | Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver |
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2011/9/9 Barry Song <21cnbao@gmail.com>: > 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. >
For example, if we set xlen = 7, dma_width =4, ylen > 0 then dma will happen like: 0~6 4~10 8~14 12~18 ....
But for ylen=0, it has no issue. there is no next line to overlap with the extra data.
in case we set xlen = 0, something funny will happen: i will copy the same memory again and again(ylen+1 times).
-barry -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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