Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend

[Pavel Machek <pavel@ucw.cz>]

On Wed 2015-09-09 11:20:25, Alan Stern wrote:
> On Wed, 9 Sep 2015, Rafael J. Wysocki wrote:
> 
> > > The best example and actually the very specific problem we want to
> > > solve is handling touchscreens on a phone / tablet. When the screen is
> > > turned off, it is ideal to suspend the touchscreen for two reasons: to
> > > lower the power consumption as much as possible and to prevent
> > > interrupts to wake-up the CPU when the user touches the device, and
> > > thus save even more power as we allow the CPU to stay in deep idle
> > > states for longer periods.
> > >
> > > Note that when the screen is turned-on again, we want to resume the
> > > touchscreen so that it can send events again.
> > 
> > In fact, then, what you need seems to be the feature discussed by Alan
> > and me some time ago allowing remote wakeup do be disabled for runtime
> > PM from user space as that in combination with autosuspend should
> > address your use case.
> 
> That, plus they want the touchscreen to go into runtime suspend 
> whenever the screen is off (was this not the main reason for the 
> patch?).
> 
> It seems to me that it should be possible to arrange for this to happen 
> simply by making userspace close the touchscreen device when the screen 
> is turned off.  Or am I missing something?

Well... that's not what existing userspace expects. Your X windows
server will not close the touchscreen.

..and it would be nice to have enough hardware abstraction in the
kernel so that X can be used on phones...
									
									Pavel
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