linux-kernel - Re: [linux-pm] [PATCH -mm] kexec jump -v9

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Date:	Thu, 15 May 2008 01:47:23 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Pavel Machek <pavel@....cz>, nigel@...el.suspend2.net,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pm@...ts.linux-foundation.org,
	Vivek Goyal <vgoyal@...hat.com>,
	Len Brown <len.brown@...el.com>
Subject: Re: [linux-pm] [PATCH -mm] kexec jump -v9

On Thursday, 15 of May 2008, Eric W. Biederman wrote:
> "Rafael J. Wysocki" <rjw@...k.pl> writes:
> 
> > On Saturday, 22 of March 2008, Alan Stern wrote:
> 
> > The spec doesn't say much about that, so we'll need to carry out some
> > experiments.
> 
> > Still, as far as I can figure out what the spec authors _might_ mean, I think
> > that it would be inappropriate to restore the ACPI NVS area if S5 was entered
> > on "power off".  The idea seems to be that the restoration of the ACPI NVS area
> > should complement whatever has been preserved by the platform over the
> > hibernation/resume cycle.
> 
> > IMO, if S5 was entered on "powe off", there are two possible ways to go.
> > Either ACPI is initialized by the boot kernel, in which case the image kernel
> > should not touch things like _WAK and similar, just throw away whatever
> > ACPI-related state it got from the image and try to rebuild the ACPI-related
> > data from scratch.  Or the boot kernel doesn't touch ACPI and the image kernel
> > initializes it in the same way as during a fresh boot (that might be difficult,
> > though).
> 
> Just an added data partial point.  In the kexec case I have had not heard
> anyone screaming to me that ACPI doesn't work after we switch kernels.

You don't remove power from devices while doing that.

> So I expect shutting down ACPI and restarting it should work reliably
> and that is easy to test as that is already implemented with kexec.

You can't program devices to generate wakeup events without ACPI, among
other things.

Anyway, I don't think you should focus on replacing the current hibernation
code entirely so much.

Thanks,
Rafael
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