On Thu, Oct 18, 2012 at 5:29 AM, Jassi Brar <jaswinder.singh@xxxxxxxxxx> wrote: > On 18 October 2012 12:15, Huang Shijie <b32955@xxxxxxxxxxxxx> wrote: >> 于 2012年10月18日 14:18, Vinod Koul 写道: >> >>> Why cant you do start (prepare clock etc) when you submit the descriptor >>> to dmaengine. Can be done in tx_submit callback. >>> Similarly remove the clock when dma transaction gets completed. >> >> I ever thought this method too. >> >> But it will become low efficient in the following case: >> >> Assuming the gpmi-nand driver has to read out 1024 pages in one _SINGLE_ >> read operation. >> The gpmi-nand will submit the descriptor to dmaengine per page. So with your >> method, >> the system will repeat the enable/disable dma clock 1024 time. At every >> enable/disable dma clock, >> the system has to enable the clock chain and it's parents ... >> >> But with this patch, we only need to enable/disable dma clock one time, just >> at we select the nand chip. >> > If the clock is the dmac's property (not channels'), the toggling > seems too aggressive. > You could try using runtime_suspend/resume for clock > disabling/enabling. How about employing autosuspend with a few ms > delay? Yes, employing the autosuspend is workable method too.o But it's a little more complicated then this patch. You have to create a thread or workqueue to do the job. What's more, I think other DMA engine may also meets the same issue as the mxs-dma, such as the imx-sdma. It's somehow a common issue to disable the clocks when no one use the DMA engine. Do you also suggest employing the autosuspend? Why not use a simple way to handle this issue? When the dma device want to use a DMA engine, it just needs to issue a DMA_START command. thanks Huang Shijie Huang Shijie -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
