[PATCH] dma: add new DMA control commands

[Russell King - ARM Linux]

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?