linux-kernel - Re: [RFC][PATCH 1/3] PM: Introduce new top level suspend and hibernation callbacks (rev. 7)

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Message-ID: <20080402131215.GC5295@ucw.cz>
Date:	Wed, 2 Apr 2008 15:12:15 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg KH <greg@...ah.com>, Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	David Brownell <david-b@...bell.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Oliver Neukum <oliver@...kum.org>,
	Nigel Cunningham <ncunningham@...a.org.au>
Subject: Re: [RFC][PATCH 1/3] PM: Introduce new top level suspend and hibernation callbacks (rev. 7)

On Wed 2008-04-02 02:09:46, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> Introduce 'struct pm_ops' and 'struct pm_ext_ops' ('ext' meaning
> 'extended') representing suspend and hibernation operations for bus
> types, device classes, device types and device drivers.
> 
> Modify the PM core to use 'struct pm_ops' and 'struct pm_ext_ops'
> objects, if defined, instead of the ->suspend() and ->resume(),
> ->suspend_late(), and ->resume_early() callbacks (the old callbacks
> will be considered as legacy and gradually phased out).
> 
> The main purpose of doing this is to separate suspend (aka S2RAM and
> standby) callbacks from hibernation callbacks in such a way that the
> new callbacks won't take arguments and the semantics of each of them
> will be clearly specified.  This has been requested for multiple
> times by many people, including Linus himself, and the reason is that
> within the current scheme if ->resume() is called, for example, it's
> difficult to say why it's been called (ie. is it a resume from RAM or
> from hibernation or a suspend/hibernation failure etc.?).
> 
> The second purpose is to make the suspend/hibernation callbacks more
> flexible so that device drivers can handle more than they can within
> the current scheme.  For example, some drivers may need to prevent
> new children of the device from being registered before their
> ->suspend() callbacks are executed or they may want to carry out some
> operations requiring the availability of some other devices, not
> directly bound via the parent-child relationship, in order to prepare
> for the execution of ->suspend(), etc.
> 
> Ultimately, we'd like to stop using the freezing of tasks for suspend
> and therefore the drivers' suspend/hibernation code will have to take
> care of the handling of the user space during suspend/hibernation.
> That, in turn, would be difficult within the current scheme, without
> the new ->prepare() and ->complete() callbacks.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>

ACK.

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