linux-kernel - Re: [linux-pm] [RFC PATCH 0/4] save and restore ACPI NVS memory during hibernation

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Message-Id: <200807112118.35562.rjw@sisk.pl>
Date:	Fri, 11 Jul 2008 21:18:34 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@...e.cz>
Cc:	Zhang Rui <rui.zhang@...el.com>,
	linux-pm <linux-pm@...ts.linux-foundation.org>,
	linux-acpi <linux-acpi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [linux-pm] [RFC PATCH 0/4] save and restore ACPI NVS memory during hibernation

On Friday, 11 of July 2008, Pavel Machek wrote:
> On Wed 2008-07-09 21:37:18, Rafael J. Wysocki wrote:
> > On Tuesday, 8 of July 2008, Pavel Machek wrote:
> > > Hi!
> > > 
> > > > According to the ACPI spec, ACPI NVS memory region is required to
> > > > be saved/restored by OS during hibernation.
> > > > 
> > > > Section 15.3.2 ACPI Spec 3.0b,
> > > > "OSPM will call the _PTS control method some time before entering
> > > > a sleeping state, to allow the platform???s AML code to update
> > > > this memory image before entering the sleeping state.
> > > > After the system awakes from an S4 state, OSPM will restore this
> > > > memory area and call the _WAK control method to enable the BIOS
> > > > to reclaim its memory image."
> > > > 
> > > > This patch set add the mechanism to save/restore ACPI NVS memory
> > > > during hibernation.
> > > > 
> > > > Patch 01: call platform_begin before swsusp_shrink_memory.
> > > > 	So that we can allocate enough pages for ACPI NVS memory
> > > > 	before shrink the memory.
> > > 
> > > Why is it neccessary to allocate memory for a copy? We should be able
> > > to save ACPI NVS area same way we are saving kernel pages, no?
> > 
> > Because we want to restore it from the hibernated kernel (when it gets control
> > back again).
> 
> Why is that important? So we can run some ACPI methods from hibernated
> kernel before restoring it?

We're supposed to restore it right prior to executing _WAK, which is after
we've executed _BFS.  This is a bit theoretical, because no one seems to
actaully implement _BFS, but well.

Thanks,
Rafael
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