? 2012?10?18? 16:52, Russell King - ARM Linux ??:

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

quoted

? 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

yes. it's a little better.
There is nearly no difference between the clk_prepare_enable() and 
clk_enable() in actually.
the clk_gate2_ops does not have any @->prepare.

thanks
Huang Shijie

method?