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

[Johannes Berg <johannes@sipsolutions.net>]

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On Fri, 2007-05-04 at 22:55 +0200, Pavel Machek wrote:

> > 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.

Sure. It just booted the machine so it must see it as 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).

I don't follow.

 * you have AC power.
 * you save system state and shut down (S5)
 * you boot up again on battery power
 * you restore system state
 * ...

vs.

 * you have AC power
 * you shut down
 * you boot up again on battery power
 * ...

where's the difference to the ACPI bios? Oh, I see, it stores it
somewhere in the memory that you've stored/restored? Well, that's your
bug then, don't touch it.

johannes

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