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

[David Brownell <david-b@pacbell.net>]

On Thursday 27 April 2006 9:55 am, Patrick Mochel wrote:
> On Thu, Apr 27, 2006 at 10:34:16AM -0400, Alan Stern wrote:
> > 
> > 		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".

As a rule swsusp (or firmware suspend-to-disk) power off everything except
what's needed to power up the motherboard ... or to provide "5 AM wakeup"
type events using a battery-backed realtime clock.  Maintaining VBUS power
sessions from USB host controllers is one of those "theoretically allowed,
but never observed in the wild" cases.

Right, not "completely" off ... but certainly nowhere as close to "on" as
would be true of suspend-to-RAM.  And regardless, the problem in $SUBJECT is
when Linux trashes the state which the limited "on" is there to maintain.

- Dave



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