[PATCH] dmaengine: add CSR SiRFprimaII DMAC driver
vkoul at infradead.org
Fri Sep 9 12:25:08 EDT 2011
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:
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).
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