On Thu, Oct 18, 2012 at 02:45:41PM +0800, Huang Shijie wrote:

? 2012?10?18? 14:18, Vinod Koul ??:

quoted

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?