Re: Hibernation considerations

Rafael J. Wysocki
2007-07-17T21:24:31Z

On Tuesday, 17 July 2007 22:37, david@lang.hm wrote:
> On Tue, 17 Jul 2007, Jeremy Maitin-Shepard wrote:
>
> > "Rafael J. Wysocki" <rjw@sisk.pl> writes:
> >
> > [snip]
> >
> >>> Rafael, for those of us who aren't thoroughly familiar with all the ins
> >>> and outs of the ACPI spec, could you please summarize a list of the
> >>> ACPI calls needed in the second and third cases above? Indicate which
> >>> ones need to be done from within the original kernel and which should
> >>> be done from within a kexec'd hibernation kernel.
> >
> >> Sure.
> >
> >> In the third case (ie. transition to S4) we are supposed to do the following:
> >
> >> (1) Upon entering the sleep state, which IMO can be done _after_ the image
> >> has been saved:
> >
> > I assume you mean "in order to enter the sleep state", rather than "upon
> > entering the sleep state". I still don't understand what you mean by
> > "which IMO can be done _after_ the image has been saved"; as far as I
> > understand, the last step of this process, "make the platform enter S4",
> > is almost like a shutdown as far as the kernel is concerned (except for
> > the tiny detail of having to call those special ACPI methods on resume);
> > consequently, it would seem that nothing can be done after that step.
> >
> >> * figure out which devices can wake up
> >> * put devices into low power states (wake-up devices are placed in the Dx
> >> states compatible with the wake capability, the others are powered off)
>
> this can't be done by the image-saving kernel if that kernel doesn't know
> about the device.

Good observation. :-)

Greetings,
Rafael

--
"Premature optimization is the root of all evil." - Donald Knuth