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Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02001Runtime Power Management Framework for I/O Devices
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +02002
Rafael J. Wysocki9659cc02011-02-18 23:20:21 +01003(C) 2009-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
Alan Stern7490e442010-09-25 23:35:15 +02004(C) 2010 Alan Stern <stern@rowland.harvard.edu>
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +02005
61. Introduction
7
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02008Support for runtime power management (runtime PM) of I/O devices is provided
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +02009at the power management core (PM core) level by means of:
10
11* The power management workqueue pm_wq in which bus types and device drivers can
12 put their PM-related work items. It is strongly recommended that pm_wq be
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020013 used for queuing all work items related to runtime PM, because this allows
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020014 them to be synchronized with system-wide power transitions (suspend to RAM,
15 hibernation and resume from system sleep states). pm_wq is declared in
16 include/linux/pm_runtime.h and defined in kernel/power/main.c.
17
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020018* A number of runtime PM fields in the 'power' member of 'struct device' (which
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020019 is of the type 'struct dev_pm_info', defined in include/linux/pm.h) that can
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020020 be used for synchronizing runtime PM operations with one another.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020021
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020022* Three device runtime PM callbacks in 'struct dev_pm_ops' (defined in
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020023 include/linux/pm.h).
24
25* A set of helper functions defined in drivers/base/power/runtime.c that can be
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020026 used for carrying out runtime PM operations in such a way that the
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020027 synchronization between them is taken care of by the PM core. Bus types and
28 device drivers are encouraged to use these functions.
29
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020030The runtime PM callbacks present in 'struct dev_pm_ops', the device runtime PM
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020031fields of 'struct dev_pm_info' and the core helper functions provided for
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020032runtime PM are described below.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020033
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200342. Device Runtime PM Callbacks
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020035
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020036There are three device runtime PM callbacks defined in 'struct dev_pm_ops':
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020037
38struct dev_pm_ops {
39 ...
40 int (*runtime_suspend)(struct device *dev);
41 int (*runtime_resume)(struct device *dev);
Rafael J. Wysockie1b19032009-12-03 21:04:08 +010042 int (*runtime_idle)(struct device *dev);
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020043 ...
44};
45
Ming Lei2fb242a2011-10-09 11:40:25 +080046The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks
Rafael J. Wysocki5841eb62011-11-23 21:18:39 +010047are executed by the PM core for the device's subsystem that may be either of
48the following:
49
50 1. PM domain of the device, if the device's PM domain object, dev->pm_domain,
51 is present.
52
53 2. Device type of the device, if both dev->type and dev->type->pm are present.
54
55 3. Device class of the device, if both dev->class and dev->class->pm are
56 present.
57
58 4. Bus type of the device, if both dev->bus and dev->bus->pm are present.
59
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010060If the subsystem chosen by applying the above rules doesn't provide the relevant
61callback, the PM core will invoke the corresponding driver callback stored in
62dev->driver->pm directly (if present).
63
Rafael J. Wysocki5841eb62011-11-23 21:18:39 +010064The PM core always checks which callback to use in the order given above, so the
65priority order of callbacks from high to low is: PM domain, device type, class
66and bus type. Moreover, the high-priority one will always take precedence over
67a low-priority one. The PM domain, bus type, device type and class callbacks
68are referred to as subsystem-level callbacks in what follows.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020069
Alan Sternc7b61de2010-12-01 00:14:42 +010070By default, the callbacks are always invoked in process context with interrupts
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010071enabled. However, the pm_runtime_irq_safe() helper function can be used to tell
72the PM core that it is safe to run the ->runtime_suspend(), ->runtime_resume()
73and ->runtime_idle() callbacks for the given device in atomic context with
74interrupts disabled. This implies that the callback routines in question must
75not block or sleep, but it also means that the synchronous helper functions
76listed at the end of Section 4 may be used for that device within an interrupt
77handler or generally in an atomic context.
Alan Sternc7b61de2010-12-01 00:14:42 +010078
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010079The subsystem-level suspend callback, if present, is _entirely_ _responsible_
80for handling the suspend of the device as appropriate, which may, but need not
81include executing the device driver's own ->runtime_suspend() callback (from the
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +010082PM core's point of view it is not necessary to implement a ->runtime_suspend()
83callback in a device driver as long as the subsystem-level suspend callback
84knows what to do to handle the device).
85
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010086 * Once the subsystem-level suspend callback (or the driver suspend callback,
87 if invoked directly) has completed successfully for the given device, the PM
88 core regards the device as suspended, which need not mean that it has been
89 put into a low power state. It is supposed to mean, however, that the
90 device will not process data and will not communicate with the CPU(s) and
91 RAM until the appropriate resume callback is executed for it. The runtime
92 PM status of a device after successful execution of the suspend callback is
93 'suspended'.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020094
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010095 * If the suspend callback returns -EBUSY or -EAGAIN, the device's runtime PM
96 status remains 'active', which means that the device _must_ be fully
97 operational afterwards.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020098
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010099 * If the suspend callback returns an error code different from -EBUSY and
100 -EAGAIN, the PM core regards this as a fatal error and will refuse to run
101 the helper functions described in Section 4 for the device until its status
102 is directly set to either'active', or 'suspended' (the PM core provides
103 special helper functions for this purpose).
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200104
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100105In particular, if the driver requires remote wakeup capability (i.e. hardware
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100106mechanism allowing the device to request a change of its power state, such as
107PCI PME) for proper functioning and device_run_wake() returns 'false' for the
108device, then ->runtime_suspend() should return -EBUSY. On the other hand, if
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100109device_run_wake() returns 'true' for the device and the device is put into a
110low-power state during the execution of the suspend callback, it is expected
111that remote wakeup will be enabled for the device. Generally, remote wakeup
112should be enabled for all input devices put into low-power states at run time.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200113
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100114The subsystem-level resume callback, if present, is _entirely_ _responsible_ for
115handling the resume of the device as appropriate, which may, but need not
116include executing the device driver's own ->runtime_resume() callback (from the
117PM core's point of view it is not necessary to implement a ->runtime_resume()
118callback in a device driver as long as the subsystem-level resume callback knows
119what to do to handle the device).
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200120
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100121 * Once the subsystem-level resume callback (or the driver resume callback, if
122 invoked directly) has completed successfully, the PM core regards the device
123 as fully operational, which means that the device _must_ be able to complete
124 I/O operations as needed. The runtime PM status of the device is then
125 'active'.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200126
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100127 * If the resume callback returns an error code, the PM core regards this as a
128 fatal error and will refuse to run the helper functions described in Section
129 4 for the device, until its status is directly set to either 'active', or
130 'suspended' (by means of special helper functions provided by the PM core
131 for this purpose).
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200132
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100133The idle callback (a subsystem-level one, if present, or the driver one) is
134executed by the PM core whenever the device appears to be idle, which is
135indicated to the PM core by two counters, the device's usage counter and the
136counter of 'active' children of the device.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200137
138 * If any of these counters is decreased using a helper function provided by
139 the PM core and it turns out to be equal to zero, the other counter is
140 checked. If that counter also is equal to zero, the PM core executes the
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100141 idle callback with the device as its argument.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200142
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100143The action performed by the idle callback is totally dependent on the subsystem
144(or driver) in question, but the expected and recommended action is to check
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100145if the device can be suspended (i.e. if all of the conditions necessary for
146suspending the device are satisfied) and to queue up a suspend request for the
Alan Stern43d51af2013-06-03 21:49:59 +0200147device in that case. If there is no idle callback, or if the callback returns
Ulf Hanssond66e6db2013-10-15 22:25:08 +02001480, then the PM core will attempt to carry out a runtime suspend of the device,
149also respecting devices configured for autosuspend. In essence this means a
150call to pm_runtime_autosuspend() (do note that drivers needs to update the
151device last busy mark, pm_runtime_mark_last_busy(), to control the delay under
152this circumstance). To prevent this (for example, if the callback routine has
153started a delayed suspend), the routine must return a non-zero value. Negative
154error return codes are ignored by the PM core.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200155
156The helper functions provided by the PM core, described in Section 4, guarantee
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100157that the following constraints are met with respect to runtime PM callbacks for
158one device:
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200159
160(1) The callbacks are mutually exclusive (e.g. it is forbidden to execute
161 ->runtime_suspend() in parallel with ->runtime_resume() or with another
162 instance of ->runtime_suspend() for the same device) with the exception that
163 ->runtime_suspend() or ->runtime_resume() can be executed in parallel with
164 ->runtime_idle() (although ->runtime_idle() will not be started while any
165 of the other callbacks is being executed for the same device).
166
167(2) ->runtime_idle() and ->runtime_suspend() can only be executed for 'active'
168 devices (i.e. the PM core will only execute ->runtime_idle() or
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200169 ->runtime_suspend() for the devices the runtime PM status of which is
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200170 'active').
171
172(3) ->runtime_idle() and ->runtime_suspend() can only be executed for a device
173 the usage counter of which is equal to zero _and_ either the counter of
174 'active' children of which is equal to zero, or the 'power.ignore_children'
175 flag of which is set.
176
177(4) ->runtime_resume() can only be executed for 'suspended' devices (i.e. the
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200178 PM core will only execute ->runtime_resume() for the devices the runtime
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200179 PM status of which is 'suspended').
180
181Additionally, the helper functions provided by the PM core obey the following
182rules:
183
184 * If ->runtime_suspend() is about to be executed or there's a pending request
185 to execute it, ->runtime_idle() will not be executed for the same device.
186
187 * A request to execute or to schedule the execution of ->runtime_suspend()
188 will cancel any pending requests to execute ->runtime_idle() for the same
189 device.
190
191 * If ->runtime_resume() is about to be executed or there's a pending request
192 to execute it, the other callbacks will not be executed for the same device.
193
194 * A request to execute ->runtime_resume() will cancel any pending or
Alan Stern15bcb91d2010-09-25 23:35:21 +0200195 scheduled requests to execute the other callbacks for the same device,
196 except for scheduled autosuspends.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200197
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02001983. Runtime PM Device Fields
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200199
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200200The following device runtime PM fields are present in 'struct dev_pm_info', as
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200201defined in include/linux/pm.h:
202
203 struct timer_list suspend_timer;
Alan Stern15bcb91d2010-09-25 23:35:21 +0200204 - timer used for scheduling (delayed) suspend and autosuspend requests
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200205
206 unsigned long timer_expires;
207 - timer expiration time, in jiffies (if this is different from zero, the
208 timer is running and will expire at that time, otherwise the timer is not
209 running)
210
211 struct work_struct work;
212 - work structure used for queuing up requests (i.e. work items in pm_wq)
213
214 wait_queue_head_t wait_queue;
215 - wait queue used if any of the helper functions needs to wait for another
216 one to complete
217
218 spinlock_t lock;
219 - lock used for synchronisation
220
221 atomic_t usage_count;
222 - the usage counter of the device
223
224 atomic_t child_count;
225 - the count of 'active' children of the device
226
227 unsigned int ignore_children;
228 - if set, the value of child_count is ignored (but still updated)
229
230 unsigned int disable_depth;
231 - used for disabling the helper funcions (they work normally if this is
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200232 equal to zero); the initial value of it is 1 (i.e. runtime PM is
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200233 initially disabled for all devices)
234
Geert Uytterhoevene1a29762014-03-24 21:31:27 +0100235 int runtime_error;
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200236 - if set, there was a fatal error (one of the callbacks returned error code
237 as described in Section 2), so the helper funtions will not work until
238 this flag is cleared; this is the error code returned by the failing
239 callback
240
241 unsigned int idle_notification;
242 - if set, ->runtime_idle() is being executed
243
244 unsigned int request_pending;
245 - if set, there's a pending request (i.e. a work item queued up into pm_wq)
246
247 enum rpm_request request;
248 - type of request that's pending (valid if request_pending is set)
249
250 unsigned int deferred_resume;
251 - set if ->runtime_resume() is about to be run while ->runtime_suspend() is
252 being executed for that device and it is not practical to wait for the
253 suspend to complete; means "start a resume as soon as you've suspended"
254
Rafael J. Wysocki7a1a8eb2009-12-03 21:19:18 +0100255 unsigned int run_wake;
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200256 - set if the device is capable of generating runtime wake-up events
Rafael J. Wysocki7a1a8eb2009-12-03 21:19:18 +0100257
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200258 enum rpm_status runtime_status;
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200259 - the runtime PM status of the device; this field's initial value is
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200260 RPM_SUSPENDED, which means that each device is initially regarded by the
261 PM core as 'suspended', regardless of its real hardware status
262
Rafael J. Wysocki87d1b3e2010-03-06 21:28:17 +0100263 unsigned int runtime_auto;
264 - if set, indicates that the user space has allowed the device driver to
265 power manage the device at run time via the /sys/devices/.../power/control
266 interface; it may only be modified with the help of the pm_runtime_allow()
267 and pm_runtime_forbid() helper functions
268
Alan Stern7490e442010-09-25 23:35:15 +0200269 unsigned int no_callbacks;
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200270 - indicates that the device does not use the runtime PM callbacks (see
Alan Stern7490e442010-09-25 23:35:15 +0200271 Section 8); it may be modified only by the pm_runtime_no_callbacks()
272 helper function
273
Alan Sternc7b61de2010-12-01 00:14:42 +0100274 unsigned int irq_safe;
275 - indicates that the ->runtime_suspend() and ->runtime_resume() callbacks
276 will be invoked with the spinlock held and interrupts disabled
277
Alan Stern15bcb91d2010-09-25 23:35:21 +0200278 unsigned int use_autosuspend;
279 - indicates that the device's driver supports delayed autosuspend (see
280 Section 9); it may be modified only by the
281 pm_runtime{_dont}_use_autosuspend() helper functions
282
283 unsigned int timer_autosuspends;
284 - indicates that the PM core should attempt to carry out an autosuspend
285 when the timer expires rather than a normal suspend
286
287 int autosuspend_delay;
288 - the delay time (in milliseconds) to be used for autosuspend
289
290 unsigned long last_busy;
291 - the time (in jiffies) when the pm_runtime_mark_last_busy() helper
292 function was last called for this device; used in calculating inactivity
293 periods for autosuspend
294
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200295All of the above fields are members of the 'power' member of 'struct device'.
296
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02002974. Runtime PM Device Helper Functions
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200298
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200299The following runtime PM helper functions are defined in
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200300drivers/base/power/runtime.c and include/linux/pm_runtime.h:
301
302 void pm_runtime_init(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200303 - initialize the device runtime PM fields in 'struct dev_pm_info'
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200304
305 void pm_runtime_remove(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200306 - make sure that the runtime PM of the device will be disabled after
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200307 removing the device from device hierarchy
308
309 int pm_runtime_idle(struct device *dev);
Alan Stern43d51af2013-06-03 21:49:59 +0200310 - execute the subsystem-level idle callback for the device; returns an
311 error code on failure, where -EINPROGRESS means that ->runtime_idle() is
312 already being executed; if there is no callback or the callback returns 0
Ulf Hanssond66e6db2013-10-15 22:25:08 +0200313 then run pm_runtime_autosuspend(dev) and return its result
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200314
315 int pm_runtime_suspend(struct device *dev);
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100316 - execute the subsystem-level suspend callback for the device; returns 0 on
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200317 success, 1 if the device's runtime PM status was already 'suspended', or
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200318 error code on failure, where -EAGAIN or -EBUSY means it is safe to attempt
Rafael J. Wysocki632e2702011-07-01 22:29:15 +0200319 to suspend the device again in future and -EACCES means that
320 'power.disable_depth' is different from 0
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200321
Alan Stern15bcb91d2010-09-25 23:35:21 +0200322 int pm_runtime_autosuspend(struct device *dev);
323 - same as pm_runtime_suspend() except that the autosuspend delay is taken
324 into account; if pm_runtime_autosuspend_expiration() says the delay has
325 not yet expired then an autosuspend is scheduled for the appropriate time
326 and 0 is returned
327
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200328 int pm_runtime_resume(struct device *dev);
Thadeu Lima de Souza Cascardode8164f2010-01-17 19:22:28 -0200329 - execute the subsystem-level resume callback for the device; returns 0 on
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200330 success, 1 if the device's runtime PM status was already 'active' or
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200331 error code on failure, where -EAGAIN means it may be safe to attempt to
332 resume the device again in future, but 'power.runtime_error' should be
Rafael J. Wysocki632e2702011-07-01 22:29:15 +0200333 checked additionally, and -EACCES means that 'power.disable_depth' is
334 different from 0
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200335
336 int pm_request_idle(struct device *dev);
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100337 - submit a request to execute the subsystem-level idle callback for the
338 device (the request is represented by a work item in pm_wq); returns 0 on
339 success or error code if the request has not been queued up
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200340
Alan Stern15bcb91d2010-09-25 23:35:21 +0200341 int pm_request_autosuspend(struct device *dev);
342 - schedule the execution of the subsystem-level suspend callback for the
343 device when the autosuspend delay has expired; if the delay has already
344 expired then the work item is queued up immediately
345
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200346 int pm_schedule_suspend(struct device *dev, unsigned int delay);
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100347 - schedule the execution of the subsystem-level suspend callback for the
348 device in future, where 'delay' is the time to wait before queuing up a
349 suspend work item in pm_wq, in milliseconds (if 'delay' is zero, the work
350 item is queued up immediately); returns 0 on success, 1 if the device's PM
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200351 runtime status was already 'suspended', or error code if the request
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200352 hasn't been scheduled (or queued up if 'delay' is 0); if the execution of
353 ->runtime_suspend() is already scheduled and not yet expired, the new
354 value of 'delay' will be used as the time to wait
355
356 int pm_request_resume(struct device *dev);
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100357 - submit a request to execute the subsystem-level resume callback for the
358 device (the request is represented by a work item in pm_wq); returns 0 on
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200359 success, 1 if the device's runtime PM status was already 'active', or
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200360 error code if the request hasn't been queued up
361
362 void pm_runtime_get_noresume(struct device *dev);
363 - increment the device's usage counter
364
365 int pm_runtime_get(struct device *dev);
366 - increment the device's usage counter, run pm_request_resume(dev) and
367 return its result
368
369 int pm_runtime_get_sync(struct device *dev);
370 - increment the device's usage counter, run pm_runtime_resume(dev) and
371 return its result
372
373 void pm_runtime_put_noidle(struct device *dev);
374 - decrement the device's usage counter
375
376 int pm_runtime_put(struct device *dev);
Alan Stern15bcb91d2010-09-25 23:35:21 +0200377 - decrement the device's usage counter; if the result is 0 then run
378 pm_request_idle(dev) and return its result
379
380 int pm_runtime_put_autosuspend(struct device *dev);
381 - decrement the device's usage counter; if the result is 0 then run
382 pm_request_autosuspend(dev) and return its result
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200383
384 int pm_runtime_put_sync(struct device *dev);
Alan Stern15bcb91d2010-09-25 23:35:21 +0200385 - decrement the device's usage counter; if the result is 0 then run
386 pm_runtime_idle(dev) and return its result
387
Alan Sternc7b61de2010-12-01 00:14:42 +0100388 int pm_runtime_put_sync_suspend(struct device *dev);
389 - decrement the device's usage counter; if the result is 0 then run
390 pm_runtime_suspend(dev) and return its result
391
Alan Stern15bcb91d2010-09-25 23:35:21 +0200392 int pm_runtime_put_sync_autosuspend(struct device *dev);
393 - decrement the device's usage counter; if the result is 0 then run
394 pm_runtime_autosuspend(dev) and return its result
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200395
396 void pm_runtime_enable(struct device *dev);
Rafael J. Wysockie358bad2011-07-06 10:52:06 +0200397 - decrement the device's 'power.disable_depth' field; if that field is equal
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200398 to zero, the runtime PM helper functions can execute subsystem-level
Rafael J. Wysockie358bad2011-07-06 10:52:06 +0200399 callbacks described in Section 2 for the device
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200400
401 int pm_runtime_disable(struct device *dev);
Rafael J. Wysockie358bad2011-07-06 10:52:06 +0200402 - increment the device's 'power.disable_depth' field (if the value of that
403 field was previously zero, this prevents subsystem-level runtime PM
Geert Uytterhoeven91e63cc2014-03-24 21:31:28 +0100404 callbacks from being run for the device), make sure that all of the
405 pending runtime PM operations on the device are either completed or
406 canceled; returns 1 if there was a resume request pending and it was
407 necessary to execute the subsystem-level resume callback for the device
408 to satisfy that request, otherwise 0 is returned
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200409
Rafael J. Wysockie358bad2011-07-06 10:52:06 +0200410 int pm_runtime_barrier(struct device *dev);
411 - check if there's a resume request pending for the device and resume it
412 (synchronously) in that case, cancel any other pending runtime PM requests
413 regarding it and wait for all runtime PM operations on it in progress to
414 complete; returns 1 if there was a resume request pending and it was
415 necessary to execute the subsystem-level resume callback for the device to
416 satisfy that request, otherwise 0 is returned
417
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200418 void pm_suspend_ignore_children(struct device *dev, bool enable);
419 - set/unset the power.ignore_children flag of the device
420
421 int pm_runtime_set_active(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200422 - clear the device's 'power.runtime_error' flag, set the device's runtime
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200423 PM status to 'active' and update its parent's counter of 'active'
424 children as appropriate (it is only valid to use this function if
425 'power.runtime_error' is set or 'power.disable_depth' is greater than
426 zero); it will fail and return error code if the device has a parent
427 which is not active and the 'power.ignore_children' flag of which is unset
428
429 void pm_runtime_set_suspended(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200430 - clear the device's 'power.runtime_error' flag, set the device's runtime
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200431 PM status to 'suspended' and update its parent's counter of 'active'
432 children as appropriate (it is only valid to use this function if
433 'power.runtime_error' is set or 'power.disable_depth' is greater than
434 zero)
435
ShuoX Liufbadc582013-01-23 21:49:37 +0100436 bool pm_runtime_active(struct device *dev);
437 - return true if the device's runtime PM status is 'active' or its
438 'power.disable_depth' field is not equal to zero, or false otherwise
439
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100440 bool pm_runtime_suspended(struct device *dev);
Rafael J. Wysockif08f5a02010-12-16 17:11:58 +0100441 - return true if the device's runtime PM status is 'suspended' and its
442 'power.disable_depth' field is equal to zero, or false otherwise
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100443
Kevin Hilmanf3393b62011-07-12 11:17:09 +0200444 bool pm_runtime_status_suspended(struct device *dev);
445 - return true if the device's runtime PM status is 'suspended'
446
Rafael J. Wysocki87d1b3e2010-03-06 21:28:17 +0100447 void pm_runtime_allow(struct device *dev);
448 - set the power.runtime_auto flag for the device and decrease its usage
449 counter (used by the /sys/devices/.../power/control interface to
450 effectively allow the device to be power managed at run time)
451
452 void pm_runtime_forbid(struct device *dev);
453 - unset the power.runtime_auto flag for the device and increase its usage
454 counter (used by the /sys/devices/.../power/control interface to
455 effectively prevent the device from being power managed at run time)
456
Alan Stern7490e442010-09-25 23:35:15 +0200457 void pm_runtime_no_callbacks(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200458 - set the power.no_callbacks flag for the device and remove the runtime
Alan Stern7490e442010-09-25 23:35:15 +0200459 PM attributes from /sys/devices/.../power (or prevent them from being
460 added when the device is registered)
461
Alan Sternc7b61de2010-12-01 00:14:42 +0100462 void pm_runtime_irq_safe(struct device *dev);
463 - set the power.irq_safe flag for the device, causing the runtime-PM
Rafael J. Wysocki64584eb2011-08-25 15:31:05 +0200464 callbacks to be invoked with interrupts off
Alan Sternc7b61de2010-12-01 00:14:42 +0100465
Alan Stern15bcb91d2010-09-25 23:35:21 +0200466 void pm_runtime_mark_last_busy(struct device *dev);
467 - set the power.last_busy field to the current time
468
469 void pm_runtime_use_autosuspend(struct device *dev);
470 - set the power.use_autosuspend flag, enabling autosuspend delays
471
472 void pm_runtime_dont_use_autosuspend(struct device *dev);
473 - clear the power.use_autosuspend flag, disabling autosuspend delays
474
475 void pm_runtime_set_autosuspend_delay(struct device *dev, int delay);
476 - set the power.autosuspend_delay value to 'delay' (expressed in
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200477 milliseconds); if 'delay' is negative then runtime suspends are
Alan Stern15bcb91d2010-09-25 23:35:21 +0200478 prevented
479
480 unsigned long pm_runtime_autosuspend_expiration(struct device *dev);
481 - calculate the time when the current autosuspend delay period will expire,
482 based on power.last_busy and power.autosuspend_delay; if the delay time
483 is 1000 ms or larger then the expiration time is rounded up to the
484 nearest second; returns 0 if the delay period has already expired or
485 power.use_autosuspend isn't set, otherwise returns the expiration time
486 in jiffies
487
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200488It is safe to execute the following helper functions from interrupt context:
489
490pm_request_idle()
Alan Stern15bcb91d2010-09-25 23:35:21 +0200491pm_request_autosuspend()
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200492pm_schedule_suspend()
493pm_request_resume()
494pm_runtime_get_noresume()
495pm_runtime_get()
496pm_runtime_put_noidle()
497pm_runtime_put()
Alan Stern15bcb91d2010-09-25 23:35:21 +0200498pm_runtime_put_autosuspend()
499pm_runtime_enable()
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200500pm_suspend_ignore_children()
501pm_runtime_set_active()
502pm_runtime_set_suspended()
Alan Stern15bcb91d2010-09-25 23:35:21 +0200503pm_runtime_suspended()
504pm_runtime_mark_last_busy()
505pm_runtime_autosuspend_expiration()
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200506
Alan Sternc7b61de2010-12-01 00:14:42 +0100507If pm_runtime_irq_safe() has been called for a device then the following helper
508functions may also be used in interrupt context:
509
Ming Lei2e6ba512011-09-21 22:31:33 +0200510pm_runtime_idle()
Alan Sternc7b61de2010-12-01 00:14:42 +0100511pm_runtime_suspend()
512pm_runtime_autosuspend()
513pm_runtime_resume()
514pm_runtime_get_sync()
Kevin Hilman02b26772011-08-05 21:45:20 +0200515pm_runtime_put_sync()
Alan Sternc7b61de2010-12-01 00:14:42 +0100516pm_runtime_put_sync_suspend()
Colin Cross311aab72011-08-08 23:39:36 +0200517pm_runtime_put_sync_autosuspend()
Alan Sternc7b61de2010-12-01 00:14:42 +0100518
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02005195. Runtime PM Initialization, Device Probing and Removal
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200520
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200521Initially, the runtime PM is disabled for all devices, which means that the
522majority of the runtime PM helper funtions described in Section 4 will return
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200523-EAGAIN until pm_runtime_enable() is called for the device.
524
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200525In addition to that, the initial runtime PM status of all devices is
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200526'suspended', but it need not reflect the actual physical state of the device.
527Thus, if the device is initially active (i.e. it is able to process I/O), its
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200528runtime PM status must be changed to 'active', with the help of
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200529pm_runtime_set_active(), before pm_runtime_enable() is called for the device.
530
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200531However, if the device has a parent and the parent's runtime PM is enabled,
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200532calling pm_runtime_set_active() for the device will affect the parent, unless
533the parent's 'power.ignore_children' flag is set. Namely, in that case the
534parent won't be able to suspend at run time, using the PM core's helper
535functions, as long as the child's status is 'active', even if the child's
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200536runtime PM is still disabled (i.e. pm_runtime_enable() hasn't been called for
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200537the child yet or pm_runtime_disable() has been called for it). For this reason,
538once pm_runtime_set_active() has been called for the device, pm_runtime_enable()
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200539should be called for it too as soon as reasonably possible or its runtime PM
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200540status should be changed back to 'suspended' with the help of
541pm_runtime_set_suspended().
542
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200543If the default initial runtime PM status of the device (i.e. 'suspended')
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200544reflects the actual state of the device, its bus type's or its driver's
545->probe() callback will likely need to wake it up using one of the PM core's
546helper functions described in Section 4. In that case, pm_runtime_resume()
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200547should be used. Of course, for this purpose the device's runtime PM has to be
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200548enabled earlier by calling pm_runtime_enable().
549
Ulf Hanssonea309942013-11-08 06:13:51 +0100550It may be desirable to suspend the device once ->probe() has finished.
551Therefore the driver core uses the asyncronous pm_request_idle() to submit a
552request to execute the subsystem-level idle callback for the device at that
553time. A driver that makes use of the runtime autosuspend feature, may want to
554update the last busy mark before returning from ->probe().
Rafael J. Wysockif5da24d2011-07-02 14:27:11 +0200555
556Moreover, the driver core prevents runtime PM callbacks from racing with the bus
557notifier callback in __device_release_driver(), which is necessary, because the
558notifier is used by some subsystems to carry out operations affecting the
559runtime PM functionality. It does so by calling pm_runtime_get_sync() before
560driver_sysfs_remove() and the BUS_NOTIFY_UNBIND_DRIVER notifications. This
561resumes the device if it's in the suspended state and prevents it from
562being suspended again while those routines are being executed.
563
564To allow bus types and drivers to put devices into the suspended state by
565calling pm_runtime_suspend() from their ->remove() routines, the driver core
566executes pm_runtime_put_sync() after running the BUS_NOTIFY_UNBIND_DRIVER
567notifications in __device_release_driver(). This requires bus types and
568drivers to make their ->remove() callbacks avoid races with runtime PM directly,
569but also it allows of more flexibility in the handling of devices during the
570removal of their drivers.
Alan Sternf1212ae2009-12-22 20:43:40 +0100571
Rafael J. Wysocki87d1b3e2010-03-06 21:28:17 +0100572The user space can effectively disallow the driver of the device to power manage
573it at run time by changing the value of its /sys/devices/.../power/control
574attribute to "on", which causes pm_runtime_forbid() to be called. In principle,
575this mechanism may also be used by the driver to effectively turn off the
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200576runtime power management of the device until the user space turns it on.
577Namely, during the initialization the driver can make sure that the runtime PM
Rafael J. Wysocki87d1b3e2010-03-06 21:28:17 +0100578status of the device is 'active' and call pm_runtime_forbid(). It should be
579noted, however, that if the user space has already intentionally changed the
580value of /sys/devices/.../power/control to "auto" to allow the driver to power
581manage the device at run time, the driver may confuse it by using
582pm_runtime_forbid() this way.
583
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02005846. Runtime PM and System Sleep
Alan Sternf1212ae2009-12-22 20:43:40 +0100585
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200586Runtime PM and system sleep (i.e., system suspend and hibernation, also known
Alan Sternf1212ae2009-12-22 20:43:40 +0100587as suspend-to-RAM and suspend-to-disk) interact with each other in a couple of
588ways. If a device is active when a system sleep starts, everything is
589straightforward. But what should happen if the device is already suspended?
590
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200591The device may have different wake-up settings for runtime PM and system sleep.
592For example, remote wake-up may be enabled for runtime suspend but disallowed
Alan Sternf1212ae2009-12-22 20:43:40 +0100593for system sleep (device_may_wakeup(dev) returns 'false'). When this happens,
594the subsystem-level system suspend callback is responsible for changing the
595device's wake-up setting (it may leave that to the device driver's system
596suspend routine). It may be necessary to resume the device and suspend it again
597in order to do so. The same is true if the driver uses different power levels
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200598or other settings for runtime suspend and system sleep.
Alan Sternf1212ae2009-12-22 20:43:40 +0100599
Rafael J. Wysocki455716e2011-07-01 22:29:05 +0200600During system resume, the simplest approach is to bring all devices back to full
601power, even if they had been suspended before the system suspend began. There
602are several reasons for this, including:
Alan Sternf1212ae2009-12-22 20:43:40 +0100603
604 * The device might need to switch power levels, wake-up settings, etc.
605
606 * Remote wake-up events might have been lost by the firmware.
607
608 * The device's children may need the device to be at full power in order
609 to resume themselves.
610
611 * The driver's idea of the device state may not agree with the device's
612 physical state. This can happen during resume from hibernation.
613
614 * The device might need to be reset.
615
616 * Even though the device was suspended, if its usage counter was > 0 then most
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200617 likely it would need a runtime resume in the near future anyway.
Alan Sternf1212ae2009-12-22 20:43:40 +0100618
Rafael J. Wysocki455716e2011-07-01 22:29:05 +0200619If the device had been suspended before the system suspend began and it's
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200620brought back to full power during resume, then its runtime PM status will have
Rafael J. Wysocki455716e2011-07-01 22:29:05 +0200621to be updated to reflect the actual post-system sleep status. The way to do
622this is:
Alan Sternf1212ae2009-12-22 20:43:40 +0100623
624 pm_runtime_disable(dev);
625 pm_runtime_set_active(dev);
626 pm_runtime_enable(dev);
627
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200628The PM core always increments the runtime usage counter before calling the
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200629->suspend() callback and decrements it after calling the ->resume() callback.
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200630Hence disabling runtime PM temporarily like this will not cause any runtime
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200631suspend attempts to be permanently lost. If the usage count goes to zero
632following the return of the ->resume() callback, the ->runtime_idle() callback
633will be invoked as usual.
634
Rafael J. Wysocki455716e2011-07-01 22:29:05 +0200635On some systems, however, system sleep is not entered through a global firmware
636or hardware operation. Instead, all hardware components are put into low-power
637states directly by the kernel in a coordinated way. Then, the system sleep
638state effectively follows from the states the hardware components end up in
639and the system is woken up from that state by a hardware interrupt or a similar
640mechanism entirely under the kernel's control. As a result, the kernel never
641gives control away and the states of all devices during resume are precisely
642known to it. If that is the case and none of the situations listed above takes
643place (in particular, if the system is not waking up from hibernation), it may
644be more efficient to leave the devices that had been suspended before the system
645suspend began in the suspended state.
646
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200647The PM core does its best to reduce the probability of race conditions between
648the runtime PM and system suspend/resume (and hibernation) callbacks by carrying
649out the following operations:
650
651 * During system suspend it calls pm_runtime_get_noresume() and
652 pm_runtime_barrier() for every device right before executing the
653 subsystem-level .suspend() callback for it. In addition to that it calls
Rafael J. Wysocki9f6d8f62012-12-22 23:59:01 +0100654 __pm_runtime_disable() with 'false' as the second argument for every device
655 right before executing the subsystem-level .suspend_late() callback for it.
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200656
Ulf Hanssonea309942013-11-08 06:13:51 +0100657 * During system resume it calls pm_runtime_enable() and pm_runtime_put()
Rafael J. Wysocki9f6d8f62012-12-22 23:59:01 +0100658 for every device right after executing the subsystem-level .resume_early()
659 callback and right after executing the subsystem-level .resume() callback
660 for it, respectively.
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200661
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +01006627. Generic subsystem callbacks
663
664Subsystems may wish to conserve code space by using the set of generic power
665management callbacks provided by the PM core, defined in
666driver/base/power/generic_ops.c:
667
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100668 int pm_generic_runtime_suspend(struct device *dev);
669 - invoke the ->runtime_suspend() callback provided by the driver of this
Geert Uytterhoeven39c29f32014-03-24 21:31:29 +0100670 device and return its result, or return 0 if not defined
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100671
672 int pm_generic_runtime_resume(struct device *dev);
673 - invoke the ->runtime_resume() callback provided by the driver of this
Geert Uytterhoeven39c29f32014-03-24 21:31:29 +0100674 device and return its result, or return 0 if not defined
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100675
676 int pm_generic_suspend(struct device *dev);
677 - if the device has not been suspended at run time, invoke the ->suspend()
678 callback provided by its driver and return its result, or return 0 if not
679 defined
680
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200681 int pm_generic_suspend_noirq(struct device *dev);
682 - if pm_runtime_suspended(dev) returns "false", invoke the ->suspend_noirq()
683 callback provided by the device's driver and return its result, or return
684 0 if not defined
685
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100686 int pm_generic_resume(struct device *dev);
687 - invoke the ->resume() callback provided by the driver of this device and,
688 if successful, change the device's runtime PM status to 'active'
689
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200690 int pm_generic_resume_noirq(struct device *dev);
691 - invoke the ->resume_noirq() callback provided by the driver of this device
692
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100693 int pm_generic_freeze(struct device *dev);
694 - if the device has not been suspended at run time, invoke the ->freeze()
695 callback provided by its driver and return its result, or return 0 if not
696 defined
697
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200698 int pm_generic_freeze_noirq(struct device *dev);
699 - if pm_runtime_suspended(dev) returns "false", invoke the ->freeze_noirq()
700 callback provided by the device's driver and return its result, or return
701 0 if not defined
702
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100703 int pm_generic_thaw(struct device *dev);
704 - if the device has not been suspended at run time, invoke the ->thaw()
705 callback provided by its driver and return its result, or return 0 if not
706 defined
707
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200708 int pm_generic_thaw_noirq(struct device *dev);
709 - if pm_runtime_suspended(dev) returns "false", invoke the ->thaw_noirq()
710 callback provided by the device's driver and return its result, or return
711 0 if not defined
712
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100713 int pm_generic_poweroff(struct device *dev);
714 - if the device has not been suspended at run time, invoke the ->poweroff()
715 callback provided by its driver and return its result, or return 0 if not
716 defined
717
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200718 int pm_generic_poweroff_noirq(struct device *dev);
719 - if pm_runtime_suspended(dev) returns "false", run the ->poweroff_noirq()
720 callback provided by the device's driver and return its result, or return
721 0 if not defined
722
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100723 int pm_generic_restore(struct device *dev);
724 - invoke the ->restore() callback provided by the driver of this device and,
725 if successful, change the device's runtime PM status to 'active'
726
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200727 int pm_generic_restore_noirq(struct device *dev);
728 - invoke the ->restore_noirq() callback provided by the device's driver
729
Geert Uytterhoevenfd6fe822014-03-24 21:31:30 +0100730These functions are the defaults used by the PM core, if a subsystem doesn't
731provide its own callbacks for ->runtime_idle(), ->runtime_suspend(),
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200732->runtime_resume(), ->suspend(), ->suspend_noirq(), ->resume(),
733->resume_noirq(), ->freeze(), ->freeze_noirq(), ->thaw(), ->thaw_noirq(),
Geert Uytterhoevenfd6fe822014-03-24 21:31:30 +0100734->poweroff(), ->poweroff_noirq(), ->restore(), ->restore_noirq() in the
735subsystem-level dev_pm_ops structure.
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100736
737Device drivers that wish to use the same function as a system suspend, freeze,
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200738poweroff and runtime suspend callback, and similarly for system resume, thaw,
739restore, and runtime resume, can achieve this with the help of the
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100740UNIVERSAL_DEV_PM_OPS macro defined in include/linux/pm.h (possibly setting its
741last argument to NULL).
Alan Stern7490e442010-09-25 23:35:15 +0200742
7438. "No-Callback" Devices
744
745Some "devices" are only logical sub-devices of their parent and cannot be
746power-managed on their own. (The prototype example is a USB interface. Entire
747USB devices can go into low-power mode or send wake-up requests, but neither is
748possible for individual interfaces.) The drivers for these devices have no
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200749need of runtime PM callbacks; if the callbacks did exist, ->runtime_suspend()
Alan Stern7490e442010-09-25 23:35:15 +0200750and ->runtime_resume() would always return 0 without doing anything else and
751->runtime_idle() would always call pm_runtime_suspend().
752
753Subsystems can tell the PM core about these devices by calling
754pm_runtime_no_callbacks(). This should be done after the device structure is
755initialized and before it is registered (although after device registration is
756also okay). The routine will set the device's power.no_callbacks flag and
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200757prevent the non-debugging runtime PM sysfs attributes from being created.
Alan Stern7490e442010-09-25 23:35:15 +0200758
759When power.no_callbacks is set, the PM core will not invoke the
760->runtime_idle(), ->runtime_suspend(), or ->runtime_resume() callbacks.
761Instead it will assume that suspends and resumes always succeed and that idle
762devices should be suspended.
763
764As a consequence, the PM core will never directly inform the device's subsystem
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200765or driver about runtime power changes. Instead, the driver for the device's
Alan Stern7490e442010-09-25 23:35:15 +0200766parent must take responsibility for telling the device's driver when the
767parent's power state changes.
Alan Stern15bcb91d2010-09-25 23:35:21 +0200768
7699. Autosuspend, or automatically-delayed suspends
770
771Changing a device's power state isn't free; it requires both time and energy.
772A device should be put in a low-power state only when there's some reason to
773think it will remain in that state for a substantial time. A common heuristic
774says that a device which hasn't been used for a while is liable to remain
775unused; following this advice, drivers should not allow devices to be suspended
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200776at runtime until they have been inactive for some minimum period. Even when
Alan Stern15bcb91d2010-09-25 23:35:21 +0200777the heuristic ends up being non-optimal, it will still prevent devices from
778"bouncing" too rapidly between low-power and full-power states.
779
780The term "autosuspend" is an historical remnant. It doesn't mean that the
781device is automatically suspended (the subsystem or driver still has to call
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200782the appropriate PM routines); rather it means that runtime suspends will
Alan Stern15bcb91d2010-09-25 23:35:21 +0200783automatically be delayed until the desired period of inactivity has elapsed.
784
785Inactivity is determined based on the power.last_busy field. Drivers should
786call pm_runtime_mark_last_busy() to update this field after carrying out I/O,
787typically just before calling pm_runtime_put_autosuspend(). The desired length
788of the inactivity period is a matter of policy. Subsystems can set this length
789initially by calling pm_runtime_set_autosuspend_delay(), but after device
790registration the length should be controlled by user space, using the
791/sys/devices/.../power/autosuspend_delay_ms attribute.
792
793In order to use autosuspend, subsystems or drivers must call
794pm_runtime_use_autosuspend() (preferably before registering the device), and
795thereafter they should use the various *_autosuspend() helper functions instead
796of the non-autosuspend counterparts:
797
798 Instead of: pm_runtime_suspend use: pm_runtime_autosuspend;
799 Instead of: pm_schedule_suspend use: pm_request_autosuspend;
800 Instead of: pm_runtime_put use: pm_runtime_put_autosuspend;
801 Instead of: pm_runtime_put_sync use: pm_runtime_put_sync_autosuspend.
802
803Drivers may also continue to use the non-autosuspend helper functions; they
804will behave normally, not taking the autosuspend delay into account.
805Similarly, if the power.use_autosuspend field isn't set then the autosuspend
806helper functions will behave just like the non-autosuspend counterparts.
807
Alan Stern886486b2011-11-03 23:39:18 +0100808Under some circumstances a driver or subsystem may want to prevent a device
809from autosuspending immediately, even though the usage counter is zero and the
810autosuspend delay time has expired. If the ->runtime_suspend() callback
811returns -EAGAIN or -EBUSY, and if the next autosuspend delay expiration time is
812in the future (as it normally would be if the callback invoked
813pm_runtime_mark_last_busy()), the PM core will automatically reschedule the
814autosuspend. The ->runtime_suspend() callback can't do this rescheduling
815itself because no suspend requests of any kind are accepted while the device is
816suspending (i.e., while the callback is running).
817
Alan Stern15bcb91d2010-09-25 23:35:21 +0200818The implementation is well suited for asynchronous use in interrupt contexts.
819However such use inevitably involves races, because the PM core can't
820synchronize ->runtime_suspend() callbacks with the arrival of I/O requests.
821This synchronization must be handled by the driver, using its private lock.
822Here is a schematic pseudo-code example:
823
824 foo_read_or_write(struct foo_priv *foo, void *data)
825 {
826 lock(&foo->private_lock);
827 add_request_to_io_queue(foo, data);
828 if (foo->num_pending_requests++ == 0)
829 pm_runtime_get(&foo->dev);
830 if (!foo->is_suspended)
831 foo_process_next_request(foo);
832 unlock(&foo->private_lock);
833 }
834
835 foo_io_completion(struct foo_priv *foo, void *req)
836 {
837 lock(&foo->private_lock);
838 if (--foo->num_pending_requests == 0) {
839 pm_runtime_mark_last_busy(&foo->dev);
840 pm_runtime_put_autosuspend(&foo->dev);
841 } else {
842 foo_process_next_request(foo);
843 }
844 unlock(&foo->private_lock);
845 /* Send req result back to the user ... */
846 }
847
848 int foo_runtime_suspend(struct device *dev)
849 {
850 struct foo_priv foo = container_of(dev, ...);
851 int ret = 0;
852
853 lock(&foo->private_lock);
854 if (foo->num_pending_requests > 0) {
855 ret = -EBUSY;
856 } else {
857 /* ... suspend the device ... */
858 foo->is_suspended = 1;
859 }
860 unlock(&foo->private_lock);
861 return ret;
862 }
863
864 int foo_runtime_resume(struct device *dev)
865 {
866 struct foo_priv foo = container_of(dev, ...);
867
868 lock(&foo->private_lock);
869 /* ... resume the device ... */
870 foo->is_suspended = 0;
871 pm_runtime_mark_last_busy(&foo->dev);
872 if (foo->num_pending_requests > 0)
Geert Uytterhoevenfe982452014-03-24 21:31:31 +0100873 foo_process_next_request(foo);
Alan Stern15bcb91d2010-09-25 23:35:21 +0200874 unlock(&foo->private_lock);
875 return 0;
876 }
877
878The important point is that after foo_io_completion() asks for an autosuspend,
879the foo_runtime_suspend() callback may race with foo_read_or_write().
880Therefore foo_runtime_suspend() has to check whether there are any pending I/O
881requests (while holding the private lock) before allowing the suspend to
882proceed.
883
884In addition, the power.autosuspend_delay field can be changed by user space at
885any time. If a driver cares about this, it can call
886pm_runtime_autosuspend_expiration() from within the ->runtime_suspend()
887callback while holding its private lock. If the function returns a nonzero
888value then the delay has not yet expired and the callback should return
889-EAGAIN.