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

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Message-ID: <20150927170217.GA3303@xo-6d-61-c0.localdomain>
Date:	Sun, 27 Sep 2015 19:02:17 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oneukum@...e.de>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Irina Tirdea <irina.tirdea@...el.com>,
	Len Brown <len.brown@...el.com>,
	Octavian Purdila <octavian.purdila@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing
 runtime suspend

Hi!

> > > > That, or there may be an additional value, say "aggressive", to write to the
> > > > control file in which case it becomes just
> > > > 
> > > > echo aggressive >/sys/.../power/control
> > > 
> > > That said I suppose that the "off" value for the "wakeup" file might also be
> > > useful in some other cases, so it likely is a better approach.
> > 
> > We still need some sort of "inhibit" callback for cases where the
> > driver doesn't want to go into runtime suspend but does want to turn
> > off all I/O.  Should this callback be triggered when the user writes
> > "off" to power/wakeup, or when the user writes "inhibit" to
> > power/control, or should there be a separate sysfs attribute?
> 
> My first thought is that if there is a separate attribute, then it only actually
> makes sense for devices that generate input events, while the "off" thing may
> be generally useful in principle (eg. it may indicate to disable PME for the
> device to the PCI layer etc).
> 
> OTOH, the additional "inhibit" attribute may only be exposed if the corresponding
> callback is present, so I'm not really sure.
> 
> Question is, though, what's the use case for turning off I/O when we don't
> go into runtime suspend.  After all, runtime suspend need not mean putting

Well... In "cellphone goes to pocket" case, you want to turn off I/O even if
the touchscreen can not support runtime suspend.

See parents in the thread for explanation.

									Pavel
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