Messages in this thread | | | From | Barry Song <> | Date | Thu, 8 Sep 2011 14:14:01 +0800 | Subject | Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver |
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Hi Jassi,
2011/9/8 Jassi Brar <jassisinghbrar@gmail.com>: > 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} ?
DMA_WIDTH is the size address will increase after every DMA line. For example: if xlen = 4, dma_width=8, ylen=5; Then DMA will run as(suppose DMA address start from 0): 0~3 8~11 16~19 24~27 ...
This feature can help us to do DMA operation to non-continuous memory area, for example, pick a part of a image.
The DMA X-length is in the 32-bit D-word boundary. This value specifies the number of D-words transferred in each line. The value should be less than or equal to the value of DMA width register.
The DMA Y-length specifies the number of lines in DMA transfers. The number of the lines in DMA transfer is Y-length + 1.
Each channel has dedicated DMA Width registers. Each DMA channel should not use other channel’s DMA width. To enable a correct 2-D DMA, the DMA Width register must be correctly set. The value of the DMA Width register must be greater than or equal to the X-length, otherwise, the data is overlapped. DMA_WIDTH should not be set to 0.
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