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

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Message-ID: <20080714062609.GD31949@elf.ucw.cz>
Date:	Mon, 14 Jul 2008 08:26:09 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Yinghai Lu <yhlu.kernel@...il.com>,
	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 Sat 2008-07-12 02:40:20, Rafael J. Wysocki wrote:
> On Friday, 11 of July 2008, Yinghai Lu wrote:
> > On Fri, Jul 11, 2008 at 1:59 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > On Friday, 11 of July 2008, Pavel Machek wrote:
> > >> On Fri 2008-07-11 21:18:34, Rafael J. Wysocki wrote:
> > >> > 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.
> > >>
> > >> Could we just call _BFS from the "loading" kernel, instead? That would
> > >> save us that copying code...
> > >
> > > I'd prefer not to, because that would require the boot kernel to support ACPI,
> > > which need not (and in fact should not IMO) be the case at present.
> > >
> > > Anyway, we'd have to either copy the NVS data into memory which is mapped and
> > > can be saved, or to map the NVS area in order to save/restore it, which I
> > > wouldn't like to do.
> > 
> > io_remap doesn't work at that time?
> 
> Yes, it does, but to use it, we would have to add extra information to the
> image header describing the location of the NVS data within the image.
> I prefer the Zhang Rui's approach to this.

Ok, I guess I prefer it now, too. Feel free to add ACK on the series.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
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