Re: [PATCH] PM: Make it possible to avoid wakeup events from being lost

From: Rafael J. Wysocki
Date: Mon Jun 28 2010 - 08:52:06 EST

On Monday, June 28, 2010, mark gross wrote:
> Looks good to me!

Great, thanks! May I add your "Acked-by" to the patch, then?


> On Sat, Jun 26, 2010 at 03:14:13PM +0200, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rjw@xxxxxxx>
> >
> > One of the arguments during the suspend blockers discussion was that
> > the mainline kernel didn't contain any mechanisms making it possible
> > to avoid losing wakeup events during system suspend.
> >
> > Generally, there are two problems in that area. First, if a wakeup
> > event occurs exactly when /sys/power/state is being written to, it
> > may be delivered to user space right before the freezer kicks in, so
> > the user space consumer of the event may not be able to process it
> > before the system is suspended. Second, if a wakeup event occurs
> > after user space has been frozen, it is not generally guaranteed that
> > the ongoing transition of the system into a sleep state will be
> > aborted.
> >
> > To address these issues introduce a new global sysfs attribute,
> > /sys/power/wakeup_count, associated with a running counter of wakeup
> > events and three helper functions, pm_stay_awake(), pm_relax(), and
> > pm_wakeup_event(), that may be used by kernel subsystems to control
> > the behavior of this attribute and to request the PM core to abort
> > system transitions into a sleep state already in progress.
> >
> > The /sys/power/wakeup_count file may be read from or written to by
> > user space. Reads will always succeed (unless interrupted by a
> > signal) and return the current value of the wakeup events counter.
> > Writes, however, will only succeed if the written number is equal to
> > the current value of the wakeup events counter. If a write is
> > successful, it will cause the kernel to save the current value of the
> > wakeup events counter and to abort the subsequent system transition
> > into a sleep state if any wakeup events are reported after the write
> > has returned.
> >
> > [The assumption is that before writing to /sys/power/state user space
> > will first read from /sys/power/wakeup_count. Next, user space
> > consumers of wakeup events will have a chance to acknowledge or
> > veto the upcoming system transition to a sleep state. Finally, if
> > the transition is allowed to proceed, /sys/power/wakeup_count will
> > be written to and if that succeeds, /sys/power/state will be written
> > to as well. Still, if any wakeup events are reported to the PM core
> > by kernel subsystems after that point, the transition will be
> > aborted.]
> >
> > Additionally, put a wakeup events counter into struct dev_pm_info and
> > make these per-device wakeup event counters available via sysfs,
> > so that it's possible to check the activity of various wakeup event
> > sources within the kernel.
> >
> > To illustrate how subsystems can use pm_wakeup_event(), make the
> > low-level PCI runtime PM wakeup-handling code use it.
> >
> > Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
> > ---
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