Re: [linux-pm] [patch/rft 2.6.17-rc2] swsusp resume must not device_suspend()

Alan Stern
2006-04-27T17:41:39Z

On Thu, 27 Apr 2006, Patrick Mochel wrote:

> > According to David this shouldn't matter. During swsusp the system is
> > supposed to be completely off, with no suspend power available. Hence all
> > the power sessions are guaranteed to be interrupted, and the boot kernel
> > doesn't have to worry about destroying any of them.
>
> Not necessarily. x86 hardware implementations of suspend-to-disk retain some
> power during suspend. Not many (if any) devices will retain context, but the
> system is definitely not completely "off". Actually, the same is true for
> soft-off on x86 (aka ACPI S5). Some power may be drawn to support various power
> on events. The only time a system is truly off is when it is unplugged from
> the wall (and/or the battery taken out, if applicable).
>
> I don't think it matters much in this particular context, but it's important
> to keep in mind when making assumptions about "off-ness".

I'm perfectly happy to let you duke this out with David! :-)

Either way, there is one important observation: You can't use swsusp if
your root filesystem is on a USB disk. Not until some sort of persistent
storage manager is available...

Alan Stern

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