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    SubjectRe: [patch update] Re: [linux-pm] Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code)
    Date
    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.

    Regards
    Oliver

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