linux-kernel - Re: Hibernation considerations

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Message-Id: <200707172324.33285.rjw@sisk.pl>
Date:	Tue, 17 Jul 2007 23:24:31 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	david@...g.hm
Cc:	Jeremy Maitin-Shepard <jbms@....edu>,
	Alan Stern <stern@...land.harvard.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	Kyle Moffett <mrmacman_g4@....com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Al Boldi <a1426z@...ab.com>
Subject: Re: Hibernation considerations

On Tuesday, 17 July 2007 22:37, david@...g.hm wrote:
> On Tue, 17 Jul 2007, Jeremy Maitin-Shepard wrote:
> 
> > "Rafael J. Wysocki" <rjw@...k.pl> writes:
> >
> > [snip]
> >
> >>> Rafael, for those of us who aren't thoroughly familiar with all the ins
> >>> and outs of the ACPI spec, could you please summarize a list of the
> >>> ACPI calls needed in the second and third cases above?  Indicate which
> >>> ones need to be done from within the original kernel and which should
> >>> be done from within a kexec'd hibernation kernel.
> >
> >> Sure.
> >
> >> In the third case (ie. transition to S4) we are supposed to do the following:
> >
> >> (1) Upon entering the sleep state, which IMO can be done _after_ the image
> >>     has been saved:
> >
> > I assume you mean "in order to enter the sleep state", rather than "upon
> > entering the sleep state".  I still don't understand what you mean by
> > "which IMO can be done _after_ the image has been saved"; as far as I
> > understand, the last step of this process, "make the platform enter S4",
> > is almost like a shutdown as far as the kernel is concerned (except for
> > the tiny detail of having to call those special ACPI methods on resume);
> > consequently, it would seem that nothing can be done after that step.
> >
> >>   * figure out which devices can wake up
> >>   * put devices into low power states (wake-up devices are placed in the Dx
> >>     states compatible with the wake capability, the others are powered off)
> 
> this can't be done by the image-saving kernel if that kernel doesn't know 
> about the device.

Good observation. :-)

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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