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

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Mon, Sep 21, 2015 at 10:38:46AM -0400, Alan Stern wrote:
> On Mon, 21 Sep 2015, Pavel Machek wrote:
> 
> > > > 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.
> 
> Surely that's a userspace issue, rather than a kernel problem?  The X
> server does have some notion of power management and power savings; why
> not extend that notion to include touchscreens?

It is not really practical: there are many consumers of input events, if
we build infrastructure to control it and proxy all users through it,
why not have it in kernel? Plus, there are users of input events
directly in the kernel, such as legacy VT/keyboard, or Android/ChromeOS
cpufreq_interactive governor that monitors user activity and bumps up
CPU speed when user actively interacts with the device. They would keep
input devices active even though user might not be actually able to
use some input devices.

Thanks.

-- 
Dmitry