Messages in this thread | | | Subject | Re: [PATCH] dmaengine: add CSR SiRFprimaII DMAC driver | From | Vinod Koul <> | Date | Fri, 09 Sep 2011 21:55:08 +0530 |
| |
On Fri, 2011-09-09 at 10:52 +0800, Barry Song wrote: > > > > 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 > .... Is there a real world use case of this??
> > 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).
-- ~Vinod Koul Intel Corp.
| |