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

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Message-ID: <20150921123055.GB16589@amd>
Date:	Mon, 21 Sep 2015 14:30:55 +0200
From:	Pavel Machek <pavel@....cz>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Octavian Purdila <octavian.purdila@...el.com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"Tirdea, Irina" <irina.tirdea@...el.com>,
	Oliver Neukum <oneukum@...e.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Brown, Len" <len.brown@...el.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing
 runtime suspend

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