linux-kernel - Re: [RFC][PATCH -mm 1/3] PM: Hibernation and suspend notifiers

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Message-ID: <20070530153740.GA4772@ucw.cz>
Date:	Wed, 30 May 2007 15:37:40 +0000
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Oliver Neukum <oliver@...kum.org>
Subject: Re: [RFC][PATCH -mm 1/3] PM: Hibernation and suspend notifiers

Hi!

> +Suspend notifiers
> +	(C) 2007 Rafael J. Wysocki <rjw@...k.pl>, GPL
> +
> +There are some operations that device drivers may want to carry out in their
> +.suspend() routines, but shouldn't, because they can cause the hibernation or
> +suspend to fail. For example, a driver may want to allocate a substantial amount
> +of memory (like 50 MB) in .suspend(), but that shouldn't be done after the
> +swsusp's memory shrinker has run.
> +
> +Also, there may be some operations, that subsystems want to carry out before a
> +hibernation/suspend or after a restore/resume, requiring the system to be fully
> +functional, so the drivers' .suspend() and .resume() routines are not suitable
> +for this purpose.  For example, device drivers may want to upload firmware to
> +their devices after a restore from a hibernation image, but they cannot do it by
> +calling request_firmware() from their .resume() routines (user land processes
> +are frozen at this point).  The solution may be to load the firmware into
> +memory before processes are frozen and upload it from there in the .resume()
> +routine.  Of course, a hibernation notifier may be used for this purpose.
> +
> +The subsystems that have such needs can register suspend notifiers that will be
> +called upon the following events by the suspend core:
> +
> +PM_PRE_FREEZE		The system is going to hibernate or suspend, tasks will
> +			be frozen immediately

Hmm, looks like bad idea if we are going to remove freezer from
suspend...?

> +PM_POST_THAW		Tasks have just been thawed after a resume or restore
> +			from a hibernation image
> +
> +PM_HIBERNATION_PREPARE	The system is preparing for hibernation.  Tasks have
> +			been frozen, memory is going to be freed and devices
> +			are going to be suspended.

Is not PRE_FREEZE enough? We can allocate memory for drivers there,
too...

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