linux-kernel - Re: Attempted summary of suspend-blockers LKML thread

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Date:	Sun, 8 Aug 2010 19:25:42 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Matthew Garrett <mjg59@...f.ucam.org>, david@...g.hm,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	pavel@....cz, florian@...kler.org, swetland@...gle.com,
	peterz@...radead.org, tglx@...utronix.de, alan@...rguk.ukuu.org.uk
Subject: Re: Attempted summary of suspend-blockers LKML thread

On Saturday, August 07, 2010, Alan Stern wrote:
> On Sat, 7 Aug 2010, Rafael J. Wysocki wrote:
> 
> > > Arguably not every PCI interrupt should be regarded as a wakeup event, so
> > > I think we can simply say in the cases when that's necessary the driver should
> > > be responsible for using pm_wakeup_event() or pm_stay_awake() / pm_relax() as
> > > appropriate.
> > > 
> > > My patch only added it to the bus-level code which covered the PME-based
> > > wakeup events that _cannot_ be handled by device drivers.
> 
> In other words, your bus-level changes were a necessary but not
> sufficient start.  I can buy that.
> 
> > 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.

Thanks,
Rafael
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