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

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Date:	Wed, 30 Jun 2010 21:27:37 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	linux-pm@...ts.linux-foundation.org,
	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 Hjønnevåg <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: [update] Re: [PATCH] PM: Make it possible to avoid wakeup events from being lost

On Wednesday, June 30, 2010, Alan Stern wrote:
> On Mon, 28 Jun 2010, Rafael J. Wysocki wrote:
> 
> > +/*
> > + * The functions below use the observation that each wakeup event starts a
> > + * period in which the system should not be suspended.  The moment this period
> > + * will end depends on how the wakeup event is going to be processed after being
> > + * detected and all of the possible cases can be divided into two distinct
> > + * groups.
> > + *
> > + * First, a wakeup event may be detected by the same functional unit that will
> > + * carry out the entire processing of it and possibly will pass it to user space
> > + * for further processing.  In that case the functional unit that has detected
> > + * the event may later "close" the "no suspend" period associated with it
> > + * directly as soon as it has been dealt with.  The pair of pm_stay_awake() and
> > + * pm_relax(), balanced with each other, is supposed to be used in such
> > + * situations.
> > + *
> > + * Second, a wakeup event may be detected by one functional unit and processed
> > + * by another one.  In that case the unit that has detected it cannot really
> > + * "close" the "no suspend" period associated with it, unless it knows in
> > + * advance what's going to happen to the event during processing.  This
> > + * knowledge, however, may not be available to it, so it can simply specify time
> > + * to wait before the system can be suspended and pass it as the second
> > + * argument of pm_wakeup_event().
> > + */
> 
> Since there's no longer any way to cancel a call to pm_wakeup_event()  
> or close the "no suspend" period early, there is no need to use
> dynamically-allocated delayed_work structures.  You can make do with a
> single static timer; always keep it set to expire at the latest time
> passed to pm_wakeup_event().

The decremenations of events_in_progress wouldn't be balanced with
incrementations this way.  Or do you have any clever way of dealing with
that in mind?

Rafael
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