[PATCH] dma: add new DMA control commands

[Jassi Brar]

On 18 October 2012 12:15, Huang Shijie <b32955 at freescale.com> 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?