Messages in this thread |  | | Date | Tue, 23 Jun 2009 14:26:22 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [patch update 3] PM: Introduce core framework for run-time PM of I/O devices |
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On Tue, 23 Jun 2009, Rafael J. Wysocki wrote:
> In short, I think suspending (or queuing a suspend request) should fail if the > usage counter is nonzero, but the resuming (or queuing up a resume request) > should be possible regardless of its value. The reason is that multiple > threads may in theory attempt to resume the device at the same time.
Agreed. Suspends and resumes aren't symmetrical -- a single resume request must outweigh numerous suspend requests.
> However, I'm not sure if the core should manipulate the usage counter by > itself, because it's sort of problematic (there's no good approach to decide > when to decrement the counter).
Yes. The idea behind my previous message was that it's not really so easy for the core to decide when to _increment_ the counter either.
> So, I'd let the callers use pm_runtime_get() to increment the counter > and pm_runtime_put() to decrement it, possibly queuing up an idle notification > if the counter happens to reach 0. Also, I'm not sure if unbalanced > pm_runtime_put() should be regarded as a bug.
It should be. Once the counter is messed up, runtime PM wouldn't be able to work properly. But maybe you should add a pm_set_counter call so that drivers can recover from imbalances.
One question still remains: If the counter is 0 at the end of a successful pm_runtime_resume, should the core then call pm_notify_idle? Or should we make the driver responsible for that too?
> At the same time, I'd like the core to use runtime_status and the other > fields in dev_pm_info, except for the usage counter, to ensure that all > operations are only carried out when it makes sense.
Yes. In fact, I'd say that when the counter is positive it doesn't make sense to allow a runtime suspend -- so you don't need that exception in your statement above. :-)
Alan Stern
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