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@@ -501,13 +501,29 @@ helper functions described in Section 4. In that case, pm_runtime_resume()
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should be used. Of course, for this purpose the device's run-time PM has to be
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enabled earlier by calling pm_runtime_enable().
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-If the device bus type's or driver's ->probe() or ->remove() callback runs
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+If the device bus type's or driver's ->probe() callback runs
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pm_runtime_suspend() or pm_runtime_idle() or their asynchronous counterparts,
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they will fail returning -EAGAIN, because the device's usage counter is
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-incremented by the core before executing ->probe() and ->remove(). Still, it
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-may be desirable to suspend the device as soon as ->probe() or ->remove() has
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-finished, so the PM core uses pm_runtime_idle_sync() to invoke the
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-subsystem-level idle callback for the device at that time.
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+incremented by the driver core before executing ->probe(). Still, it may be
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+desirable to suspend the device as soon as ->probe() has finished, so the driver
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+core uses pm_runtime_put_sync() to invoke the subsystem-level idle callback for
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+the device at that time.
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+
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+Moreover, the driver core prevents runtime PM callbacks from racing with the bus
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+notifier callback in __device_release_driver(), which is necessary, because the
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+notifier is used by some subsystems to carry out operations affecting the
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+runtime PM functionality. It does so by calling pm_runtime_get_sync() before
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+driver_sysfs_remove() and the BUS_NOTIFY_UNBIND_DRIVER notifications. This
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+resumes the device if it's in the suspended state and prevents it from
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+being suspended again while those routines are being executed.
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+
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+To allow bus types and drivers to put devices into the suspended state by
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+calling pm_runtime_suspend() from their ->remove() routines, the driver core
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+executes pm_runtime_put_sync() after running the BUS_NOTIFY_UNBIND_DRIVER
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+notifications in __device_release_driver(). This requires bus types and
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+drivers to make their ->remove() callbacks avoid races with runtime PM directly,
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+but also it allows of more flexibility in the handling of devices during the
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+removal of their drivers.
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The user space can effectively disallow the driver of the device to power manage
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it at run time by changing the value of its /sys/devices/.../power/control
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