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3 (C) 2009-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
13 put their PM-related work items. It is strongly recommended that pm_wq be
15 them to be synchronized with system-wide power transitions (suspend to RAM,
47 The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks
51 1. PM domain of the device, if the device's PM domain object, dev->pm_domain,
54 2. Device type of the device, if both dev->type and dev->type->pm are present.
56 3. Device class of the device, if both dev->class and dev->class->pm are
59 4. Bus type of the device, if both dev->bus and dev->bus->pm are present.
63 dev->driver->pm directly (if present).
67 and bus type. Moreover, the high-priority one will always take precedence over
68 a low-priority one. The PM domain, bus type, device type and class callbacks
69 are referred to as subsystem-level callbacks in what follows.
73 the PM core that it is safe to run the ->runtime_suspend(), ->runtime_resume()
74 and ->runtime_idle() callbacks for the given device in atomic context with
80 The subsystem-level suspend callback, if present, is _entirely_ _responsible_
82 include executing the device driver's own ->runtime_suspend() callback (from the
83 PM core's point of view it is not necessary to implement a ->runtime_suspend()
84 callback in a device driver as long as the subsystem-level suspend callback
87 * Once the subsystem-level suspend callback (or the driver suspend callback,
96 * If the suspend callback returns -EBUSY or -EAGAIN, the device's runtime PM
100 * If the suspend callback returns an error code different from -EBUSY and
101 -EAGAIN, the PM core regards this as a fatal error and will refuse to run
109 device, then ->runtime_suspend() should return -EBUSY. On the other hand, if
111 low-power state during the execution of the suspend callback, it is expected
113 should be enabled for all input devices put into low-power states at run time.
115 The subsystem-level resume callback, if present, is _entirely_ _responsible_ for
117 include executing the device driver's own ->runtime_resume() callback (from the
118 PM core's point of view it is not necessary to implement a ->runtime_resume()
119 callback in a device driver as long as the subsystem-level resume callback knows
122 * Once the subsystem-level resume callback (or the driver resume callback, if
134 The idle callback (a subsystem-level one, if present, or the driver one) is
147 suspending the device are satisfied) and to queue up a suspend request for the
154 started a delayed suspend), the routine must return a non-zero value. Negative
162 ->runtime_suspend() in parallel with ->runtime_resume() or with another
163 instance of ->runtime_suspend() for the same device) with the exception that
164 ->runtime_suspend() or ->runtime_resume() can be executed in parallel with
165 ->runtime_idle() (although ->runtime_idle() will not be started while any
168 (2) ->runtime_idle() and ->runtime_suspend() can only be executed for 'active'
169 devices (i.e. the PM core will only execute ->runtime_idle() or
170 ->runtime_suspend() for the devices the runtime PM status of which is
173 (3) ->runtime_idle() and ->runtime_suspend() can only be executed for a device
178 (4) ->runtime_resume() can only be executed for 'suspended' devices (i.e. the
179 PM core will only execute ->runtime_resume() for the devices the runtime
185 * If ->runtime_suspend() is about to be executed or there's a pending request
186 to execute it, ->runtime_idle() will not be executed for the same device.
188 * A request to execute or to schedule the execution of ->runtime_suspend()
189 will cancel any pending requests to execute ->runtime_idle() for the same
192 * If ->runtime_resume() is about to be executed or there's a pending request
195 * A request to execute ->runtime_resume() will cancel any pending or
205 - timer used for scheduling (delayed) suspend and autosuspend requests
208 - timer expiration time, in jiffies (if this is different from zero, the
213 - work structure used for queuing up requests (i.e. work items in pm_wq)
216 - wait queue used if any of the helper functions needs to wait for another
220 - lock used for synchronization
223 - the usage counter of the device
226 - the count of 'active' children of the device
229 - if set, the value of child_count is ignored (but still updated)
232 - used for disabling the helper functions (they work normally if this is
237 - if set, there was a fatal error (one of the callbacks returned error code
243 - if set, ->runtime_idle() is being executed
246 - if set, there's a pending request (i.e. a work item queued up into pm_wq)
249 - type of request that's pending (valid if request_pending is set)
252 - set if ->runtime_resume() is about to be run while ->runtime_suspend() is
257 - the runtime PM status of the device; this field's initial value is
262 - if set, indicates that the user space has allowed the device driver to
268 - indicates that the device does not use the runtime PM callbacks (see
273 - indicates that the ->runtime_suspend() and ->runtime_resume() callbacks
277 - indicates that the device's driver supports delayed autosuspend (see
282 - indicates that the PM core should attempt to carry out an autosuspend
286 - the delay time (in milliseconds) to be used for autosuspend
289 - the time (in jiffies) when the pm_runtime_mark_last_busy() helper
301 - initialize the device runtime PM fields in 'struct dev_pm_info'
304 - make sure that the runtime PM of the device will be disabled after
308 - execute the subsystem-level idle callback for the device; returns an
309 error code on failure, where -EINPROGRESS means that ->runtime_idle() is
314 - execute the subsystem-level suspend callback for the device; returns 0 on
316 error code on failure, where -EAGAIN or -EBUSY means it is safe to attempt
317 to suspend the device again in future and -EACCES means that
321 - same as pm_runtime_suspend() except that the autosuspend delay is taken
327 - execute the subsystem-level resume callback for the device; returns 0 on
329 error code on failure, where -EAGAIN means it may be safe to attempt to
331 checked additionally, and -EACCES means that 'power.disable_depth' is
335 - submit a request to execute the subsystem-level idle callback for the
340 - schedule the execution of the subsystem-level suspend callback for the
345 - schedule the execution of the subsystem-level suspend callback for the
351 ->runtime_suspend() is already scheduled and not yet expired, the new
355 - submit a request to execute the subsystem-level resume callback for the
361 - increment the device's usage counter
364 - increment the device's usage counter, run pm_request_resume(dev) and
368 - increment the device's usage counter, run pm_runtime_resume(dev) and
372 - return -EINVAL if 'power.disable_depth' is nonzero; otherwise, if the
378 - decrement the device's usage counter
381 - decrement the device's usage counter; if the result is 0 then run
385 - decrement the device's usage counter; if the result is 0 then run
389 - decrement the device's usage counter; if the result is 0 then run
393 - decrement the device's usage counter; if the result is 0 then run
397 - decrement the device's usage counter; if the result is 0 then run
401 - decrement the device's 'power.disable_depth' field; if that field is equal
402 to zero, the runtime PM helper functions can execute subsystem-level
406 - increment the device's 'power.disable_depth' field (if the value of that
407 field was previously zero, this prevents subsystem-level runtime PM
411 necessary to execute the subsystem-level resume callback for the device
415 - check if there's a resume request pending for the device and resume it
419 necessary to execute the subsystem-level resume callback for the device to
423 - set/unset the power.ignore_children flag of the device
426 - clear the device's 'power.runtime_error' flag, set the device's runtime
434 - clear the device's 'power.runtime_error' flag, set the device's runtime
441 - return true if the device's runtime PM status is 'active' or its
445 - return true if the device's runtime PM status is 'suspended' and its
449 - return true if the device's runtime PM status is 'suspended'
452 - set the power.runtime_auto flag for the device and decrease its usage
457 - unset the power.runtime_auto flag for the device and increase its usage
462 - set the power.no_callbacks flag for the device and remove the runtime
467 - set the power.irq_safe flag for the device, causing the runtime-PM
471 - return true if power.irq_safe flag was set for the device, causing
472 the runtime-PM callbacks to be invoked with interrupts off
475 - set the power.last_busy field to the current time
478 - set the power.use_autosuspend flag, enabling autosuspend delays; call
483 - clear the power.use_autosuspend flag, disabling autosuspend delays;
488 - set the power.autosuspend_delay value to 'delay' (expressed in
497 - calculate the time when the current autosuspend delay period will expire,
539 -EAGAIN until pm_runtime_enable() is called for the device.
561 ->probe() callback will likely need to wake it up using one of the PM core's
572 It may be desirable to suspend the device once ->probe() has finished.
574 request to execute the subsystem-level idle callback for the device at that
576 update the last busy mark before returning from ->probe().
587 calling pm_runtime_suspend() from their ->remove() routines, the driver core
590 drivers to make their ->remove() callbacks avoid races with runtime PM directly,
594 Drivers in ->remove() callback should undo the runtime PM changes done
595 in ->probe(). Usually this means calling pm_runtime_disable(),
613 as suspend-to-RAM and suspend-to-disk) interact with each other in a couple of
617 The device may have different wake-up settings for runtime PM and system sleep.
618 For example, remote wake-up may be enabled for runtime suspend but disallowed
620 the subsystem-level system suspend callback is responsible for changing the
621 device's wake-up setting (it may leave that to the device driver's system
630 * The device might need to switch power levels, wake-up settings, etc.
632 * Remote wake-up events might have been lost by the firmware.
647 to be updated to reflect the actual post-system sleep status. The way to do
655 ->suspend() callback and decrements it after calling the ->resume() callback.
658 following the return of the ->resume() callback, the ->runtime_idle() callback
662 or hardware operation. Instead, all hardware components are put into low-power
676 that the device appears to be runtime-suspended and its state is fine, so it
682 related to hibernation (see Documentation/driver-api/pm/devices.rst for more
690 right before executing the subsystem-level .prepare() callback for it and
692 subsystem-level .suspend() callback for it. In addition to that the PM core
694 device right before executing the subsystem-level .suspend_late() callback
698 every device right after executing the subsystem-level .resume_early()
699 callback and right after executing the subsystem-level .complete() callback
709 - invoke the ->runtime_suspend() callback provided by the driver of this
713 - invoke the ->runtime_resume() callback provided by the driver of this
717 - if the device has not been suspended at run time, invoke the ->suspend()
722 - if pm_runtime_suspended(dev) returns "false", invoke the ->suspend_noirq()
727 - invoke the ->resume() callback provided by the driver of this device and,
731 - invoke the ->resume_noirq() callback provided by the driver of this device
734 - if the device has not been suspended at run time, invoke the ->freeze()
739 - if pm_runtime_suspended(dev) returns "false", invoke the ->freeze_noirq()
744 - if the device has not been suspended at run time, invoke the ->thaw()
749 - if pm_runtime_suspended(dev) returns "false", invoke the ->thaw_noirq()
754 - if the device has not been suspended at run time, invoke the ->poweroff()
759 - if pm_runtime_suspended(dev) returns "false", run the ->poweroff_noirq()
764 - invoke the ->restore() callback provided by the driver of this device and,
768 - invoke the ->restore_noirq() callback provided by the device's driver
771 provide its own callbacks for ->runtime_idle(), ->runtime_suspend(),
772 ->runtime_resume(), ->suspend(), ->suspend_noirq(), ->resume(),
773 ->resume_noirq(), ->freeze(), ->freeze_noirq(), ->thaw(), ->thaw_noirq(),
774 ->poweroff(), ->poweroff_noirq(), ->restore(), ->restore_noirq() in the
775 subsystem-level dev_pm_ops structure.
783 8. "No-Callback" Devices
785 Some "devices" are only logical sub-devices of their parent and cannot be
786 power-managed on their own. (The prototype example is a USB interface. Entire
787 USB devices can go into low-power mode or send wake-up requests, but neither is
789 need of runtime PM callbacks; if the callbacks did exist, ->runtime_suspend()
790 and ->runtime_resume() would always return 0 without doing anything else and
791 ->runtime_idle() would always call pm_runtime_suspend().
797 prevent the non-debugging runtime PM sysfs attributes from being created.
800 ->runtime_idle(), ->runtime_suspend(), or ->runtime_resume() callbacks.
809 9. Autosuspend, or automatically-delayed suspends
812 A device should be put in a low-power state only when there's some reason to
817 the heuristic ends up being non-optimal, it will still prevent devices from
818 "bouncing" too rapidly between low-power and full-power states.
836 of the non-autosuspend counterparts:
843 Drivers may also continue to use the non-autosuspend helper functions; they
849 autosuspend delay time has expired. If the ->runtime_suspend() callback
850 returns -EAGAIN or -EBUSY, and if the next autosuspend delay expiration time is
853 autosuspend. The ->runtime_suspend() callback can't do this rescheduling
859 synchronize ->runtime_suspend() callbacks with the arrival of I/O requests.
861 Here is a schematic pseudo-code example:
863 foo_read_or_write(struct foo_priv *foo, void *data)
865 lock(&foo->private_lock);
866 add_request_to_io_queue(foo, data);
867 if (foo->num_pending_requests++ == 0)
868 pm_runtime_get(&foo->dev);
869 if (!foo->is_suspended)
870 foo_process_next_request(foo);
871 unlock(&foo->private_lock);
874 foo_io_completion(struct foo_priv *foo, void *req)
876 lock(&foo->private_lock);
877 if (--foo->num_pending_requests == 0) {
878 pm_runtime_mark_last_busy(&foo->dev);
879 pm_runtime_put_autosuspend(&foo->dev);
881 foo_process_next_request(foo);
883 unlock(&foo->private_lock);
889 struct foo_priv foo = container_of(dev, ...);
892 lock(&foo->private_lock);
893 if (foo->num_pending_requests > 0) {
894 ret = -EBUSY;
897 foo->is_suspended = 1;
899 unlock(&foo->private_lock);
905 struct foo_priv foo = container_of(dev, ...);
907 lock(&foo->private_lock);
909 foo->is_suspended = 0;
910 pm_runtime_mark_last_busy(&foo->dev);
911 if (foo->num_pending_requests > 0)
912 foo_process_next_request(foo);
913 unlock(&foo->private_lock);
925 pm_runtime_autosuspend_expiration() from within the ->runtime_suspend()
928 -EAGAIN.