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

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Message-Id: <201007012102.27495.rjw@sisk.pl>
Date:	Thu, 1 Jul 2010 21:02:27 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
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 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.

> 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.

Rafael
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