linux-kernel - Re: [RFC PATCH] PM / Core: suspend_again cb for syscore

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Date:	Wed, 20 Apr 2011 12:36:41 +0200
From:	Pavel Machek <pavel@....cz>
To:	MyungJoo Ham <myungjoo.ham@...sung.com>
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Len Brown <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, kyungmin.park@...sung.com,
	myungjoo.ham@...il.com
Subject: Re: [RFC PATCH] PM / Core: suspend_again cb for syscore_ops

Hi!

> A system or a device may need to control suspend/wakeup events. It may
> want to wakeup the system after a predefined amount of time or at a
> predefined event decided while entering suspend for polling or delayed
> work. Then, it may want to enter suspend again if its predefined wakeup
> condition is the only wakeup reason and there is no outstanding events;
> thus, it does not wakeup the userspace unnecessary and keeps suspended
> as long as possible (saving the power).

Nice. Zaurus needs it, exactly due to this reason:

> 2. Execute critical "delayed work" at suspend.
>  A driver or a system/board may have a delayed work (or any similar
> things) that it wants to execute at the requested time.
>  For example, some chargers want to check the battery voltage some
> time (e.g., 30 seconds) after the battery is fully charged and the
> charger stops. Then, the charger restarts charging if the voltage has
> dropped more than a threshold, which is smaller than "restart-charger"
> voltage, which is a threshold to restart charging regardless of the
> time passed.

Yep, and zaurus also needs it to stop charging.

> The system enters the suspend again if and only if all of the following
> conditions are met:
> 1. None of suspend_again ops returned "I want to stop suspend"
> (suspend_again returns SUSPEND_AGAIN_STOP).
> 2. At least one of suspend_again ops returned "I want to suspend again"
> (suspend_again returns SUSPEND_AGAIN_CONTINUE)

Better naming  could be SUSPEND_AGAIN and VETO_RESUSPEND or
SUSPEND_AGAIN_VETO .

> Anyway, the following features may need to be added later:
> 1. An API to allow devices to express next desired wakeup-time. Then,
> the framework will combine them and setup RTC alarm accordingly and
> save/restore previously registered RTC alarms.

Yep.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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