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SubjectRe: [PATCH v3 2/2] PM / Runtime: Add pm_runtime_enable_recursive
On Thu, 2 Jul 2015, Tomeu Vizoso wrote:

> > Just because these sub-devices are virtual, it doesn't mean you can
> > ignore the way they interact with runtime PM.
>
> Fair enough, but then, how are we expected to be able to use the
> direct_complete facility if the core bails out if a descendant doesn't
> have runtime PM enabled?
>
> > In the case of ep_87 this doesn't matter. Endpoint devices (like all
> > devices) are in the SUSPENDED state by default when they are created,
> > and they never leave that state.
>
> I don't see why it doesn't matter for endpoints or the others. They
> don't have runtime PM enabled, so no ancestor will be able to do
> direct_complete.

Ah, you're concerned about these lines near the start of
__device_suspend():

if (dev->power.direct_complete) {
if (pm_runtime_status_suspended(dev)) {
pm_runtime_disable(dev);
if (pm_runtime_suspended_if_enabled(dev))
goto Complete;

pm_runtime_enable(dev);
}
dev->power.direct_complete = false;
}

Perhaps the pm_runtime_suspended_if_enabled() test should be changed to
pm_runtime_status_suspended(). Then it won't matter whether the
descendant devices are enabled for runtime PM.

> > A possible way around the problem is to use pm_suspend_ignore_children
> > on the uvcvideo interface. But I'm not sure that would be the right
> > thing to do.
>
> Would that mean that if a device has ignore_children then it could
> still do direct_complete even if its descendants weren't able to?

I think we could justify that. The ignore_children flag means we can
communicate with the children even when the device is in runtime
suspend, so there's no reason to force the device to leave runtime
suspend during a system sleep.

Alan Stern



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