Re: Hibernation considerations

[david@lang.hm]

On Mon, 16 Jul 2007, Al Boldi wrote:

> david@lang.hm wrote:
> > On Mon, 16 Jul 2007, Al Boldi wrote:
> > > david@lang.hm wrote:
> > > > suspend-to-RAM should not involve kexec, the only reason for doing the
> > > > kexec to to get a seperate userspace to use for suspend-to-disk
> > > > operations instead of trying to partially freeze the sustem and keep
> > > > useing it.
> > >
> > > Or you could do suspend-to-disk-and-RAM.  But in the above case, it was
> > > meant to test kexec compatibility with device suspend/resume calls.
> >
> > the point I am trying to make here is that there is no reason that the
> > kexec approach needs to do _any_ suspend/resume calls.
>
> When you go through ACPI, then that implies calling suspend/resume calls.

then don't go through ACPI

> > all that is needed is the ability of the new kernel to initialize the
> > devices it needs.
>
> We have to go through ACPI, for wakeup functions to succeed.  A simple
> power-off won't do.

the kexec switch being posted requires ACPI be disabled, so it's clearly 
possible to switch kernels and initialize devices without ACPI

> > suspend-to-disk-and-ram could be implemented as three
> > seperate steps
> >
> > 1. suspend-to-disk
> >
> > 2. resume-from-disk
> >
> > 3. suspend-to-ram
> >
> > followed by either
> >
> > 4. resume-from-ram
> >
> > or
> >
> > 4. battery dies and loptop powers off completely
> >
> > 5. power-on boot.
> >
> > 6. resume-from-disk
> >
> > all that you need to do is to make sure that the system doesn't run
> > anything that would affect permanent media or the outside world between
> > steps #2 and #3
>
> Exactly, which is why your scheme would break down on #3, and that's why you
> need to call S3 from within the kexec'd hibernation kernel after saving the
> hibernation image.

when a kexec is called, how does the kernel know what to execute? 
something needs to tell it what to do, and I think that something is 
either something in the kexec image, or it's something passed as a 
parameter to that image.

all that would be needed to do #3 safely is to have the kernel that you 
restarted on #2 do a suspend-to-ram before it does anything else.

David Lang
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