linux-kernel - Re: [PATCH] PM: Make it possible to avoid wakeup events from being lost

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Message-ID: <20100702181449.GC16577@elf.ucw.cz>
Date:	Fri, 2 Jul 2010 20:14:49 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-pm@...ts.linux-foundation.org,
	Alan Stern <stern@...land.harvard.edu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Neil Brown <neilb@...e.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <640e9920@...il.com>,
	Arve Hj??nnev??g <arve@...roid.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Florian Mickler <florian@...kler.org>,
	linux-pci@...r.kernel.org, Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH] PM: Make it possible to avoid wakeup events from being
 lost

On Thu 2010-07-01 21:02:27, Rafael J. Wysocki wrote:
> On Thursday, July 01, 2010, Pavel Machek wrote:
> > Hi!
> > 
> > > @@ -114,3 +114,17 @@ Description:
> > >  		if this file contains "1", which is the default.  It may be
> > >  		disabled by writing "0" to this file, in which case all devices
> > >  		will be suspended and resumed synchronously.
> > > +
> > > +What:		/sys/power/wakeup_count
> > > +Date:		July 2010
> > > +Contact:	Rafael J. Wysocki <rjw@...k.pl>
> > > +Description:
> > > +		The /sys/power/wakeup_count file allows user space to avoid
> > > +		losing wakeup events when transitioning the system into a sleep
> > > +		state.  Reading from it returns the current number of registered
> > > +		wakeup events and it blocks if some wakeup events are being
> > > +		processed at the time the file is read from.  Writing to it
> > > +		will only succeed if the current number of wakeup events is
> > > +		equal to the written value and, if successful, will make the
> > > +		kernel abort a subsequent transition to a sleep state if any
> > > +		wakeup events are reported after the write has returned.
> > 
> > I assume that second suspend always succeeds?
> 
> The mechanism is one-shot if that's what you're asking for.

Yep, it would be nice to document it.

Plus maybe... should there be way to clear the wakeup_count? For
example when userspace decides that battery is low and that it wants
to go to sleep now?

> > I can't say I quite like the way two sysfs files interact with each
> > other, but it is certainly better then wakelocks...
> > 
> > Maybe we should create sys_suspend()?
> 
> Well, one can modify pm-utils to use the new sysfs file quite easily, but it
> wouldn't be that easy with sys_suspend() IMO.

Well... small C helper should be easy...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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