linux-kernel - Re: A minimally power-aware driver treats all messages as SUSPEND?

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Message-ID: <20080701151415.GA17688@digi.com>
Date:	Tue, 1 Jul 2008 17:14:15 +0200
From:	Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Andrew Morton <akpm@...l.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: A minimally power-aware driver treats all messages as SUSPEND?

Hello Rafael,

Rafael J. Wysocki wrote:
> On Tuesday, 1 of July 2008, Uwe Kleine-König wrote:
> > include/linux/pm.h claims:
> >
> >       A minimally power-aware driver treats all messages as SUSPEND
> >       [...].
> >
> > This was introduced in commit 82bb67f2 by David Brownell.  At this time
> > PM_EVENT_HIBERNATE didn't exist.  This was added in 3a2d5b70 by Rafael
> > J. Wysocki without updating the above sentence.  I think a minimally
> > power-aware driver should treat all messages as HIBERNATE, shouldn't it?
> 
> No, I don't think so.  In the majority of cases, SUSPEND is equivalent to the
> combination of FREEZE and HIBERNATE.
I didn't get that.  I thought SUSPEND is suspend-to-ram and HIBERNATE is
suspend-to-disk, so HIBERNATE is the "deeper sleep".
With that I might have to do less on SUSPEND because some state might be
preserved after the machine comes up again.

> Still, this is going to change anyway with the introduction of the new
> suspend/hibernation callbacks that are scheduled for 2.6.27.
in next?

Best regards
Uwe

-- 
Uwe Kleine-König, Software Engineer
Digi International GmbH Branch Breisach, Küferstrasse 8, 79206 Breisach, Germany
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