linux-kernel - Re: [update] Re: [RFC][PATCH] PM: Avoid losing wakeup events during suspend

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Date:	Tue, 22 Jun 2010 16:34:49 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Florian Mickler <florian@...kler.org>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Neil Brown <neilb@...e.de>, mark gross <640e9920@...il.com>
Subject: Re: [update] Re: [RFC][PATCH] PM: Avoid losing wakeup events during
 suspend

On Tue, 22 Jun 2010, Rafael J. Wysocki wrote:

> Anyway, below's an update that addresses this particular case.
> 
> It adds two more functions, pm_wakeup_begin() and pm_wakeup_end()
> that play similar roles to suspend_block() and suspend_unblock(), but they
> don't operate on suspend blocker objects.  Instead, the first of them increases
> a counter of events in progress and the other one decreases this counter.
> Together they have the same effect as pm_wakeup_event(), but the counter
> of wakeup events in progress they operate on is also checked by
> pm_check_wakeup_events().
> 
> Thus there are two ways kernel subsystems can signal wakeup events.  First,
> if the event is not explicitly handed over to user space and "instantaneous",
> they can simply call pm_wakeup_event() and be done with it.  Second, if the
> event is going to be delivered to user space, the subsystem that processes
> the event can call pm_wakeup_begin() right when the event is detected and
> pm_wakeup_end() when it's been handed over to user space.

Or if the event is going to be handled entirely in the kernel but over
a prolonged period of time.

> Please tell me what you think.

I like it a lot.  It addresses the main weakness in the earlier 
version.  With this, you could essentially duplicate the in-kernel part 
of the wakelocks/suspend blockers stuff.  All except the timed 
wakelocks -- you might want to consider adding a 
pm_wakeup_begin_timeout() convenience routine.

Here's another possible enhancement (if you can figure out a way to do
it without too much effort): After a suspend begins, keep track of the
first wakeup event you get.  Then when the suspend is aborted, print a
log message saying why and indicating which device was responsible for
the wakeup.

One little thing: You have the PCI subsystem call pm_wakeup_event().  
If the driver then wants to call pm_wakeup_begin(), the event will get 
counted twice.  I guess this doesn't matter much, but it does seem 
peculiar.

Alan Stern

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