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@@ -513,13 +513,29 @@ helper functions described in Section 4.
should be used. Of course, for this purpose the device's runtime PM has to be
enabled earlier by calling pm_runtime_enable().
-If the device bus type's or driver's ->probe() or ->remove() callback runs
+If the device bus type's or driver's ->probe() callback runs
pm_runtime_suspend() or pm_runtime_idle() or their asynchronous counterparts,
they will fail returning -EAGAIN, because the device's usage counter is
-incremented by the core before executing ->probe() and ->remove(). Still, it
-may be desirable to suspend the device as soon as ->probe() or ->remove() has
-finished, so the PM core uses pm_runtime_put_sync() to invoke the
-subsystem-level idle callback for the device at that time.
+incremented by the driver core before executing ->probe(). Still, it may be
+desirable to suspend the device as soon as ->probe() has finished, so the driver
+core uses pm_runtime_put_sync() to invoke the subsystem-level idle callback for
+the device at that time.
+
+Moreover, the driver core prevents runtime PM callbacks from racing with the bus
+notifier callback in __device_release_driver(), which is necessary, because the
+notifier is used by some subsystems to carry out operations affecting the
+runtime PM functionality. It does so by calling pm_runtime_get_sync() before
+driver_sysfs_remove() and the BUS_NOTIFY_UNBIND_DRIVER notifications. This
+resumes the device if it's in the suspended state and prevents it from
+being suspended again while those routines are being executed.
+
+To allow bus types and drivers to put devices into the suspended state by
+calling pm_runtime_suspend() from their ->remove() routines, the driver core
+executes pm_runtime_put_sync() after running the BUS_NOTIFY_UNBIND_DRIVER
+notifications in __device_release_driver(). This requires bus types and
+drivers to make their ->remove() callbacks avoid races with runtime PM directly,
+but also it allows of more flexibility in the handling of devices during the
+removal of their drivers.
The user space can effectively disallow the driver of the device to power manage
it at run time by changing the value of its /sys/devices/.../power/control