linux-kernel - Re: Hibernation considerations

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Message-ID: <Pine.LNX.4.64.0707151654420.25614@asgard.lang.hm>
Date:	Sun, 15 Jul 2007 16:58:54 -0700 (PDT)
From:	david@...g.hm
To:	Alan Stern <stern@...land.harvard.edu>
cc:	Al Boldi <a1426z@...ab.com>, "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

On Sun, 15 Jul 2007, Alan Stern wrote:

> On Sun, 15 Jul 2007, Al Boldi wrote:
>
>> Alan Stern wrote:
>>> On Sun, 15 Jul 2007, Al Boldi wrote:
>
>>>> This should be the responsibility of the kexec'd hibernating kernel.
>>>> Note though in (6), the normal kernel takes care of preparing devices,
>>>> then the hibernating kernel dumps the image and either calls S4 or S3.
>>>> On resume from S3 it can immediately switch over to the normal kernel,
>>>> and from S4 the known bootup would occur.
>>>
>>> Is it really that simple?  Somehow I doubt it.  In order for some
>>> devices to remain available for the kexec'd kernel to use, they cannot
>>> be suspended at the ACPI level.  So the kexec'd kernel will have to
>>> handle the ACPI requirements for those devices.  Likewise, it would
>>> have to handle the ACPI interactions which need to be done after all
>>> devices are prepared for the transition to S3 or S4.
>>
>> Ok, after applying the latest kexec patches, I was able to use the kexec'd
>> kernel to suspend to ram and resume to the normal kernel, while working
>> under a full-blown X session.  It went without a hitch.  All that is needed
>> now are the dump/restore hibernation-image routines.
>
> That's exactly my point.  While doing suspend-to-RAM from a kexec'd
> kernel may be simple, saving the hibernation image will add
> complications.

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.

David Lang
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