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

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Message-Id: <200807092137.18966.rjw@sisk.pl>
Date:	Wed, 9 Jul 2008 21:37:18 +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 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).

Thanks,
Rafael
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