Messages in this thread | | | Date | Wed, 10 Jun 2009 19:42:50 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [patch update] Re: [linux-pm] Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code) |
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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.
Alan Stern
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