On Thu, Oct 18, 2012 at 02:45:41PM +0800, Huang Shijie 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 ... And what if you stop using clk_prepare_enable(), and prepare the clock when the channel is requested and only use clk_enable() in the tx_submit method? -- 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
