Re: Re: [PATCH] swsusp: do not use pm_ops (was: Re: suspend2 merge (was: Re: CFS and suspend2: hang in atomic copy))

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > > On the other hand, steps 6 and 7 aren't really needed for hibernation.  
> > > You _could_ shut the system off completely (ACPI S5).  Automatic wakeup
> > > wouldn't work, but the next time the user turned the computer on manually
> > > it would still resume from hibernation.
> > 
> > That's correct, with the exception that the user may find the system not fully
> > functional after the resume in that case.
> 
> Why is that anyway? Is it just a matter of the acpi code getting
> confused about the acpi bios state? How can the acpi bios possibly be
> screwed up after what it must see as a fresh boot? Does the acpi code
> poke it in ways it's not supposed to be poked after a fresh boot?

No, ACPI BIOS does not see a fresh boot.

ACPI BIOS communicates with hw, too. Suppose it generates random
number, stores it in memory and tells it to the keyboard conroller
during bootup (more specifically during ACPI enable phase).

Now, it periodically checks if number in memory is same as the number
known by keyboard controller.

If you suspend/resume without telling acpi, it will find out, because
numbers will not match.

(And now, ACPI is probably not crazy enough to store random numbers --
but it could -- but for example "I had AC power, now I do not, and I
did not see a interrupt telling me it went away" can be counted as
confusing for ACPI).
								Pavel
-- 
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