linux-kernel - Re: [RFD] Automatic suspend

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Message-ID: <20090216224741.GE1370@ucw.cz>
Date:	Mon, 16 Feb 2009 23:47:41 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Arve Hj??nnev??g <arve@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <mgross@...ux.intel.com>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

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
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