Re: Attempted summary of suspend-blockers LKML thread

Alan Stern
2010-08-08T19:07:37Z

On Sun, 8 Aug 2010, Rafael J. Wysocki wrote:

> > > Also please note that it depends a good deal on the definition of a "wakeup
> > > event". Under the definition used when my patch was being developed, ie. that
> > > wakeup events are the events that would wake up the system from a sleep state,
> > > PCI interrupts cannot be wakeup events, unless the given device remains in the
> > > full power state although the system has been suspended (standard PCI devices
> > > are not allowed to generate signals except for PME from low-power states).
> >
> > Um, what do you mean by "event"? Let's take a concrete example.
> > Suppose you have a system where you want USB plug or unplug events to
> > cause a wakeup. This is relevant to the discussion at hand if your USB
> > host controller is a PCI device.
> >
> > By your reckoning, a plug or unplug event that occurs while the system
> > is asleep would be a wakeup event by definition. And yet you say that
> > the same plug or unplug event occurring while the controller was at
> > full power would not count as a wakeup event? And in particular, it
> > should not prevent the system from suspending before the event can be
> > fully processed? That doesn't make sense. The same event is the same
> > event, regardless of the context in which it occurs. If it is treated
> > as a wakeup event in context then it should be treated as a wakeup
> > event in other contexts too.
>
> In this example the event is not a PCI interrupt itself, which is a consqeuence
> of the event, but the USB plug-unplug. So, whoever detects the plug-unplug
> should use pm_stay_awake() or pm_wakeup_event(). That may be an
> interrupt handler of a PCI USB controller, so if that is the case, the
> controller driver probably should use one of these functions in its interrupt
> handler. Still, that by no measn implies that _every_ PCI interrupt should in
> principle be regarded as a wakeup event.

Okay, agreed. I just wanted you to grant that some PCI interrupts
should be treated like wakeup events even if they don't actually wake
the system up from a sleep state. The "PCI interrupts cannot be wakeup
events" statement is a little strong.

Alan Stern