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

Pavel Machek
2008-07-11T18:50:58Z

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?

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