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

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Date:	Wed, 9 Sep 2015 11:20:25 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
cc:	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>, Pavel Machek <pavel@....cz>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing
 runtime suspend

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?

Alan Stern

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