Re: [RFD] Automatic suspend

Pavel Machek
2009-02-16T22:47:41Z

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.

--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html