Documentation/power/runtime_pm.rst

2 Runtime Power Management Framework for I/O Devices
14 Support for runtime power management (runtime PM) of I/O devices is provided
19   used for queuing all work items related to runtime PM, because this allows
24 * A number of runtime PM fields in the 'power' member of 'struct device' (which
26   be used for synchronizing runtime PM operations with one another.
28 * Three device runtime PM callbacks in 'struct dev_pm_ops' (defined in
31 * A set of helper functions defined in drivers/base/power/runtime.c that can be
32   used for carrying out runtime PM operations in such a way that the
36 The runtime PM callbacks present in 'struct dev_pm_ops', the device runtime PM
38 runtime PM are described below.
40 2. Device Runtime PM Callbacks
43 There are three device runtime PM callbacks defined in 'struct dev_pm_ops'::
98     RAM until the appropriate resume callback is executed for it.  The runtime
102   * If the suspend callback returns -EBUSY or -EAGAIN, the device's runtime PM
131     I/O operations as needed.  The runtime PM status of the device is then
155 0, then the PM core will attempt to carry out a runtime suspend of the device,
164 that the following constraints are met with respect to runtime PM callbacks for
176     ->runtime_suspend() for the devices the runtime PM status of which is
185     PM core will only execute ->runtime_resume() for the devices the runtime
205 3. Runtime PM Device Fields
208 The following device runtime PM fields are present in 'struct dev_pm_info', as
240       equal to zero); the initial value of it is 1 (i.e. runtime PM is
264     - the runtime PM status of the device; this field's initial value is
275     - indicates that the device does not use the runtime PM callbacks (see
302 4. Runtime PM Device Helper Functions
305 The following runtime PM helper functions are defined in
306 drivers/base/power/runtime.c and include/linux/pm_runtime.h:
309     - initialize the device runtime PM fields in 'struct dev_pm_info'
312     - make sure that the runtime PM of the device will be disabled after
323       success, 1 if the device's runtime PM status was already 'suspended', or
336       success, 1 if the device's runtime PM status was already 'active' or
357       runtime status was already 'suspended', or error code if the request
365       success, 1 if the device's runtime PM status was already 'active', or
381       runtime PM status is RPM_ACTIVE and the runtime PM usage counter is
387       runtime PM status is RPM_ACTIVE, and either ign_usage_count is true
416       to zero, the runtime PM helper functions can execute subsystem-level
421       field was previously zero, this prevents subsystem-level runtime PM
423       pending runtime PM operations on the device are either completed or
430       (synchronously) in that case, cancel any other pending runtime PM requests
431       regarding it and wait for all runtime PM operations on it in progress to
440     - clear the device's 'power.runtime_error' flag, set the device's runtime
448     - clear the device's 'power.runtime_error' flag, set the device's runtime
455     - return true if the device's runtime PM status is 'active' or its
459     - return true if the device's runtime PM status is 'suspended' and its
463     - return true if the device's runtime PM status is 'suspended'
476     - set the power.no_callbacks flag for the device and remove the runtime
481     - set the power.irq_safe flag for the device, causing the runtime-PM
486       the runtime-PM callbacks to be invoked with interrupts off
503       milliseconds); if 'delay' is negative then runtime suspends are
549 5. Runtime PM Initialization, Device Probing and Removal
552 Initially, the runtime PM is disabled for all devices, which means that the
553 majority of the runtime PM helper functions described in Section 4 will return
556 In addition to that, the initial runtime PM status of all devices is
559 runtime PM status must be changed to 'active', with the help of
562 However, if the device has a parent and the parent's runtime PM is enabled,
567 runtime PM is still disabled (i.e. pm_runtime_enable() hasn't been called for
570 should be called for it too as soon as reasonably possible or its runtime PM
574 If the default initial runtime PM status of the device (i.e. 'suspended')
578 should be used.  Of course, for this purpose the device's runtime PM has to be
590 time.  A driver that makes use of the runtime autosuspend feature, may want to
593 Moreover, the driver core prevents runtime PM callbacks from racing with the bus
596 runtime PM functionality.  It does so by calling pm_runtime_get_sync() before
605 drivers to make their ->remove() callbacks avoid races with runtime PM directly,
609 Drivers in ->remove() callback should undo the runtime PM changes done
617 runtime power management of the device until the user space turns it on.
618 Namely, during the initialization the driver can make sure that the runtime PM
625 6. Runtime PM and System Sleep
628 Runtime PM and system sleep (i.e., system suspend and hibernation, also known
633 The device may have different wake-up settings for runtime PM and system sleep.
634 For example, remote wake-up may be enabled for runtime suspend but disallowed
640 or other settings for runtime suspend and system sleep.
659     likely it would need a runtime resume in the near future anyway.
662 brought back to full power during resume, then its runtime PM status will have
670 The PM core always increments the runtime usage counter before calling the
672 Hence disabling runtime PM temporarily like this will not cause any runtime
692 that the device appears to be runtime-suspended and its state is fine, so it
693 may be left in runtime suspend provided that all of its descendants are also
694 left in runtime suspend.  If that happens, the PM core will not execute any
702 the runtime PM and system suspend/resume (and hibernation) callbacks by carrying
744       if successful, change the device's runtime PM status to 'active'
781       if successful, change the device's runtime PM status to 'active'
794 poweroff and runtime suspend callback, and similarly for system resume, thaw,
795 restore, and runtime resume, can achieve this with the help of the
806 need of runtime PM callbacks; if the callbacks did exist, ->runtime_suspend()
814 prevent the non-debugging runtime PM sysfs attributes from being created.
822 or driver about runtime power changes.  Instead, the driver for the device's
834 at runtime until they have been inactive for some minimum period.  Even when
840 the appropriate PM routines); rather it means that runtime suspends will