On Thursday 11 June 2009, Alan Stern wrote:
> On Thu, 11 Jun 2009, Oliver Neukum wrote:
>
> > Am Donnerstag, 11. Juni 2009 00:01:20 schrieb Rafael J. Wysocki:
> > > We have queued up resume requests for the device's parent, its parent etc.,
> > > the topmost one goes first. The workqueue is singlethread, so
> > > pm_autoresume() is going to be run for all parents before the device
> > > itself, so if that were the only resume mechanism, it would be enough to
> > > check if the parent is RPM_ACTIVE.
> >
> > A (IDLE)
> > / \
> > B (SUSPENDED) C (SUSPENDED)
> >
> > Suppose C is to be resumed. This means first in case of A the request
> > to suspend would be cancelled. Here you drop the locks:
> >
> > + && (dev->parent->power.runtime_status == RPM_IDLE
> > + || dev->parent->power.runtime_status == RPM_SUSPENDING
> > + || dev->parent->power.runtime_status == RPM_SUSPENDED)) {
> > + spin_unlock_irqrestore(&dev->power.lock, flags);
> > + spin_unlock_irqrestore(&dev->parent->power.lock, parent_flags);
> > +
> > + /* We have to resume the parent first. */
> > + pm_request_resume(dev->parent);
> >
> > But after pm_request_resume() returns there's no means to make sure
> > nothing alters it back to RPM_SUSPENDED. The workqueue doesn't help
> > you because you've scheduled nothing by that time. The suspension will
> > work because C is still in RPM_SUSPENDED.
>
> This is an example where usage counters come in handy.
Do you mean we can count suspend/resume requests for a device?
Rafael
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