Re: [RFD] Automatic suspend

[Pavel Machek]

On Sun 2009-02-15 22:23:04, Roland Dreier wrote:
>  > > (2) put given subset of devices into low power states whenever they
>  > > are not used, without putting the entire system into a sleep state.
> 
>  > For (2), for me the answer is very obvious:
> 
>  > The Device Driver needs to make the decision to put the device to sleep.
>  > There are no ifs and buts about this.
> 
> For PC-like systems this is probably all that needs to be said.  However
> for highly integrated SoC systems (as Android is obviously targeting)
> there is another level of complexity due to the interdependency among
> various devices... eg things like if I know the SD controller and the
> wifi chip are both asleep then I can put my SDIO controller to sleep;
> and if the SDIO controller and the NAND controller are both asleep then
> I can stop clock X and save more power; etc etc.
> 
> This is what the PowerOp/DPM work was all about.  Unfortunately that
> doesn't seem to have made much progress upstream.  But there's no doubt
> in my mind that we need some framework beyond individual drivers that
> manages the system's power as a whole.  And the current device tree is
> probably not sufficient -- eg the bus hierarchy of a device may not
> match up with the clock tree at all.

Well, that's why clock framework exists. But none  of this is visible
to userland. 

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