Re: [PATCH 05/13] PM: Add option to disable /sys/power/state interface

Pavel Machek
2009-02-09T09:15:06Z

Hi!

> >> > Also, please observe that if there is a mechanism allowing us to put individual
> >> > devices, or entire subsystems (such as a bus with devices attached to it), into
> >> > low power states at run time, without placing the entire system in a sleep
> >> > state, and put them back into the full power state as needed, we won't need
> >> > anything like the "early suspend" introduced by this series of patches.
> >>
> >> While early-suspend is not needed, it is still convenient on an
> >> embedded device where some drivers are clearly only used when the
> >> screen is on.
> >
> > Ah, that's interesting. So in fact you want some devices to go into low power
> > states as soon as the screen is off and that's why you fint the early-suspend
> > useful. Is this correct?
>
> Yes. We turn off the touchscreen and trackball when the screen turns
> off since both these devices use additional power when enabled.
> Neither of these devices can be turned off (after a timeout) while the
> screen is on.

Ok, first: It is not at all clear to me that trackball / touchscreen
is unusable with screen off. For weird cases (using android to
remotely control PC?) screen-off trackball-on makes
sense. Actually... if you are charging than maybe waking up the device
by touching the screen is a good idea? So maybe you are putting a bit
too much policy into kernel.

OTOH, as long as you do it in android-specific code, that's probably
okay.

So lets assume that trackball is unusable with screen off. Stuff is
easy, then either

1) make your useland close trackball/touchscreen devices when they
turn the screen off.

(This is actually preffered, as it keeps policy out of the kernel)

or

2) Just use notifier chain to notify trackball/touchscreen when the
screen is going off.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html