linux-kernel - Re: Hibernation considerations

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Message-Id: <200707161632.02334.a1426z@gawab.com>
Date:	Mon, 16 Jul 2007 16:32:02 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	david@...g.hm
Cc:	Alan Stern <stern@...land.harvard.edu>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	Jeremy Maitin-Shepard <jbms@....edu>,
	Kyle Moffett <mrmacman_g4@....com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: Hibernation considerations

david@...g.hm wrote:
> On Mon, 16 Jul 2007, Al Boldi wrote:
> > david@...g.hm wrote:
> >> suspend-to-RAM should not involve kexec, the only reason for doing the
> >> kexec to to get a seperate userspace to use for suspend-to-disk
> >> operations instead of trying to partially freeze the sustem and keep
> >> useing it.
> >
> > Or you could do suspend-to-disk-and-RAM.  But in the above case, it was
> > meant to test kexec compatibility with device suspend/resume calls.
>
> the point I am trying to make here is that there is no reason that the
> kexec approach needs to do _any_ suspend/resume calls.

When you go through ACPI, then that implies calling suspend/resume calls.

> all that is needed is the ability of the new kernel to initialize the
> devices it needs.

We have to go through ACPI, for wakeup functions to succeed.  A simple 
power-off won't do.

> suspend-to-disk-and-ram could be implemented as three
> seperate steps
>
> 1. suspend-to-disk
>
> 2. resume-from-disk
>
> 3. suspend-to-ram
>
> followed by either
>
> 4. resume-from-ram
>
> or
>
> 4. battery dies and loptop powers off completely
>
> 5. power-on boot.
>
> 6. resume-from-disk
>
> all that you need to do is to make sure that the system doesn't run
> anything that would affect permanent media or the outside world between
> steps #2 and #3

Exactly, which is why your scheme would break down on #3, and that's why you 
need to call S3 from within the kexec'd hibernation kernel after saving the 
hibernation image.


Thanks!

--
Al

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