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Merge branch 'pm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/suspend-2.6

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* 'pm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/suspend-2.6:
  PM / Runtime: Update documentation regarding driver removal
  PM: Documentation: fix typo: pm_runtime_idle_sync() doesn't exist.
This commit is contained in:
Linus Torvalds 2011-07-03 13:33:16 -07:00
commit ba466c74d9
1 changed files with 21 additions and 5 deletions
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26
Documentation/power/runtime_pm.txt
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@ -501,13 +501,29 @@ helper functions described in Section 4. In that case, pm_runtime_resume()
should be used. Of course, for this purpose the device's run-time 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_idle_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