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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. Wysockif71495f2014-05-16 02:47:37 +02005(C) 2014 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +02006
71. Introduction
8
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02009Support for runtime power management (runtime PM) of I/O devices is provided
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020010at the power management core (PM core) level by means of:
11
12* The power management workqueue pm_wq in which bus types and device drivers can
13 put their PM-related work items. It is strongly recommended that pm_wq be
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020014 used for queuing all work items related to runtime PM, because this allows
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020015 them to be synchronized with system-wide power transitions (suspend to RAM,
16 hibernation and resume from system sleep states). pm_wq is declared in
17 include/linux/pm_runtime.h and defined in kernel/power/main.c.
18
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020019* A number of runtime PM fields in the 'power' member of 'struct device' (which
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020020 is of the type 'struct dev_pm_info', defined in include/linux/pm.h) that can
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020021 be used for synchronizing runtime PM operations with one another.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020022
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020023* Three device runtime PM callbacks in 'struct dev_pm_ops' (defined in
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020024 include/linux/pm.h).
25
26* A set of helper functions defined in drivers/base/power/runtime.c that can be
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020027 used for carrying out runtime PM operations in such a way that the
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020028 synchronization between them is taken care of by the PM core. Bus types and
29 device drivers are encouraged to use these functions.
30
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020031The runtime PM callbacks present in 'struct dev_pm_ops', the device runtime PM
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020032fields of 'struct dev_pm_info' and the core helper functions provided for
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020033runtime PM are described below.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020034
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200352. Device Runtime PM Callbacks
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020036
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +020037There are three device runtime PM callbacks defined in 'struct dev_pm_ops':
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020038
39struct dev_pm_ops {
40 ...
41 int (*runtime_suspend)(struct device *dev);
42 int (*runtime_resume)(struct device *dev);
Rafael J. Wysockie1b19032009-12-03 21:04:08 +010043 int (*runtime_idle)(struct device *dev);
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020044 ...
45};
46
Ming Lei2fb242a2011-10-09 11:40:25 +080047The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks
Rafael J. Wysocki5841eb62011-11-23 21:18:39 +010048are executed by the PM core for the device's subsystem that may be either of
49the following:
50
51 1. PM domain of the device, if the device's PM domain object, dev->pm_domain,
52 is present.
53
54 2. Device type of the device, if both dev->type and dev->type->pm are present.
55
56 3. Device class of the device, if both dev->class and dev->class->pm are
57 present.
58
59 4. Bus type of the device, if both dev->bus and dev->bus->pm are present.
60
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010061If the subsystem chosen by applying the above rules doesn't provide the relevant
62callback, the PM core will invoke the corresponding driver callback stored in
63dev->driver->pm directly (if present).
64
Rafael J. Wysocki5841eb62011-11-23 21:18:39 +010065The PM core always checks which callback to use in the order given above, so the
66priority order of callbacks from high to low is: PM domain, device type, class
67and bus type. Moreover, the high-priority one will always take precedence over
68a low-priority one. The PM domain, bus type, device type and class callbacks
69are referred to as subsystem-level callbacks in what follows.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020070
Alan Sternc7b61de2010-12-01 00:14:42 +010071By default, the callbacks are always invoked in process context with interrupts
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010072enabled. However, the pm_runtime_irq_safe() helper function can be used to tell
73the PM core that it is safe to run the ->runtime_suspend(), ->runtime_resume()
74and ->runtime_idle() callbacks for the given device in atomic context with
75interrupts disabled. This implies that the callback routines in question must
76not block or sleep, but it also means that the synchronous helper functions
77listed at the end of Section 4 may be used for that device within an interrupt
78handler or generally in an atomic context.
Alan Sternc7b61de2010-12-01 00:14:42 +010079
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010080The subsystem-level suspend callback, if present, is _entirely_ _responsible_
81for handling the suspend of the device as appropriate, which may, but need not
82include executing the device driver's own ->runtime_suspend() callback (from the
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +010083PM core's point of view it is not necessary to implement a ->runtime_suspend()
84callback in a device driver as long as the subsystem-level suspend callback
85knows what to do to handle the device).
86
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010087 * Once the subsystem-level suspend callback (or the driver suspend callback,
88 if invoked directly) has completed successfully for the given device, the PM
89 core regards the device as suspended, which need not mean that it has been
90 put into a low power state. It is supposed to mean, however, that the
91 device will not process data and will not communicate with the CPU(s) and
92 RAM until the appropriate resume callback is executed for it. The runtime
93 PM status of a device after successful execution of the suspend callback is
94 'suspended'.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020095
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +010096 * If the suspend callback returns -EBUSY or -EAGAIN, the device's runtime PM
97 status remains 'active', which means that the device _must_ be fully
98 operational afterwards.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +020099
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100100 * 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
102 the helper functions described in Section 4 for the device until its status
103 is directly set to either'active', or 'suspended' (the PM core provides
104 special helper functions for this purpose).
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200105
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100106In particular, if the driver requires remote wakeup capability (i.e. hardware
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100107mechanism allowing the device to request a change of its power state, such as
108PCI PME) for proper functioning and device_run_wake() returns 'false' for the
109device, then ->runtime_suspend() should return -EBUSY. On the other hand, if
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100110device_run_wake() returns 'true' for the device and the device is put into a
111low-power state during the execution of the suspend callback, it is expected
112that remote wakeup will be enabled for the device. Generally, remote wakeup
113should be enabled for all input devices put into low-power states at run time.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200114
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100115The subsystem-level resume callback, if present, is _entirely_ _responsible_ for
116handling the resume of the device as appropriate, which may, but need not
117include executing the device driver's own ->runtime_resume() callback (from the
118PM core's point of view it is not necessary to implement a ->runtime_resume()
119callback in a device driver as long as the subsystem-level resume callback knows
120what to do to handle the device).
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200121
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100122 * Once the subsystem-level resume callback (or the driver resume callback, if
123 invoked directly) has completed successfully, the PM core regards the device
124 as fully operational, which means that the device _must_ be able to complete
125 I/O operations as needed. The runtime PM status of the device is then
126 'active'.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200127
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100128 * If the resume callback returns an error code, the PM core regards this as a
129 fatal error and will refuse to run the helper functions described in Section
130 4 for the device, until its status is directly set to either 'active', or
131 'suspended' (by means of special helper functions provided by the PM core
132 for this purpose).
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200133
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100134The idle callback (a subsystem-level one, if present, or the driver one) is
135executed by the PM core whenever the device appears to be idle, which is
136indicated to the PM core by two counters, the device's usage counter and the
137counter of 'active' children of the device.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200138
139 * If any of these counters is decreased using a helper function provided by
140 the PM core and it turns out to be equal to zero, the other counter is
141 checked. If that counter also is equal to zero, the PM core executes the
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100142 idle callback with the device as its argument.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200143
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100144The action performed by the idle callback is totally dependent on the subsystem
145(or driver) in question, but the expected and recommended action is to check
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100146if the device can be suspended (i.e. if all of the conditions necessary for
147suspending the device are satisfied) and to queue up a suspend request for the
Alan Stern43d51af2013-06-03 21:49:59 +0200148device in that case. If there is no idle callback, or if the callback returns
Ulf Hanssond66e6db2013-10-15 22:25:08 +02001490, then the PM core will attempt to carry out a runtime suspend of the device,
150also respecting devices configured for autosuspend. In essence this means a
151call to pm_runtime_autosuspend() (do note that drivers needs to update the
152device last busy mark, pm_runtime_mark_last_busy(), to control the delay under
153this circumstance). To prevent this (for example, if the callback routine has
154started a delayed suspend), the routine must return a non-zero value. Negative
155error return codes are ignored by the PM core.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200156
157The helper functions provided by the PM core, described in Section 4, guarantee
Rafael J. Wysocki35cd1332011-12-18 00:34:13 +0100158that the following constraints are met with respect to runtime PM callbacks for
159one device:
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200160
161(1) The callbacks are mutually exclusive (e.g. it is forbidden to execute
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
166 of the other callbacks is being executed for the same device).
167
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
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200170 ->runtime_suspend() for the devices the runtime PM status of which is
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200171 'active').
172
173(3) ->runtime_idle() and ->runtime_suspend() can only be executed for a device
174 the usage counter of which is equal to zero _and_ either the counter of
175 'active' children of which is equal to zero, or the 'power.ignore_children'
176 flag of which is set.
177
178(4) ->runtime_resume() can only be executed for 'suspended' devices (i.e. the
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200179 PM core will only execute ->runtime_resume() for the devices the runtime
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200180 PM status of which is 'suspended').
181
182Additionally, the helper functions provided by the PM core obey the following
183rules:
184
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.
187
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
190 device.
191
192 * If ->runtime_resume() is about to be executed or there's a pending request
193 to execute it, the other callbacks will not be executed for the same device.
194
195 * A request to execute ->runtime_resume() will cancel any pending or
Alan Stern15bcb91d2010-09-25 23:35:21 +0200196 scheduled requests to execute the other callbacks for the same device,
197 except for scheduled autosuspends.
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200198
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02001993. Runtime PM Device Fields
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200200
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200201The following device runtime PM fields are present in 'struct dev_pm_info', as
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200202defined in include/linux/pm.h:
203
204 struct timer_list suspend_timer;
Alan Stern15bcb91d2010-09-25 23:35:21 +0200205 - timer used for scheduling (delayed) suspend and autosuspend requests
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200206
207 unsigned long timer_expires;
208 - timer expiration time, in jiffies (if this is different from zero, the
209 timer is running and will expire at that time, otherwise the timer is not
210 running)
211
212 struct work_struct work;
213 - work structure used for queuing up requests (i.e. work items in pm_wq)
214
215 wait_queue_head_t wait_queue;
216 - wait queue used if any of the helper functions needs to wait for another
217 one to complete
218
219 spinlock_t lock;
220 - lock used for synchronisation
221
222 atomic_t usage_count;
223 - the usage counter of the device
224
225 atomic_t child_count;
226 - the count of 'active' children of the device
227
228 unsigned int ignore_children;
229 - if set, the value of child_count is ignored (but still updated)
230
231 unsigned int disable_depth;
Masanari Iida1f999d12014-11-08 17:54:51 +0900232 - used for disabling the helper functions (they work normally if this is
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200233 equal to zero); the initial value of it is 1 (i.e. runtime PM is
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200234 initially disabled for all devices)
235
Geert Uytterhoevene1a29762014-03-24 21:31:27 +0100236 int runtime_error;
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200237 - if set, there was a fatal error (one of the callbacks returned error code
Masanari Iida1f999d12014-11-08 17:54:51 +0900238 as described in Section 2), so the helper functions will not work until
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200239 this flag is cleared; this is the error code returned by the failing
240 callback
241
242 unsigned int idle_notification;
243 - if set, ->runtime_idle() is being executed
244
245 unsigned int request_pending;
246 - if set, there's a pending request (i.e. a work item queued up into pm_wq)
247
248 enum rpm_request request;
249 - type of request that's pending (valid if request_pending is set)
250
251 unsigned int deferred_resume;
252 - set if ->runtime_resume() is about to be run while ->runtime_suspend() is
253 being executed for that device and it is not practical to wait for the
254 suspend to complete; means "start a resume as soon as you've suspended"
255
Rafael J. Wysocki7a1a8eb2009-12-03 21:19:18 +0100256 unsigned int run_wake;
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200257 - set if the device is capable of generating runtime wake-up events
Rafael J. Wysocki7a1a8eb2009-12-03 21:19:18 +0100258
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200259 enum rpm_status runtime_status;
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200260 - the runtime PM status of the device; this field's initial value is
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200261 RPM_SUSPENDED, which means that each device is initially regarded by the
262 PM core as 'suspended', regardless of its real hardware status
263
Rafael J. Wysocki87d1b3e2010-03-06 21:28:17 +0100264 unsigned int runtime_auto;
265 - if set, indicates that the user space has allowed the device driver to
266 power manage the device at run time via the /sys/devices/.../power/control
267 interface; it may only be modified with the help of the pm_runtime_allow()
268 and pm_runtime_forbid() helper functions
269
Alan Stern7490e442010-09-25 23:35:15 +0200270 unsigned int no_callbacks;
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200271 - indicates that the device does not use the runtime PM callbacks (see
Alan Stern7490e442010-09-25 23:35:15 +0200272 Section 8); it may be modified only by the pm_runtime_no_callbacks()
273 helper function
274
Alan Sternc7b61de2010-12-01 00:14:42 +0100275 unsigned int irq_safe;
276 - indicates that the ->runtime_suspend() and ->runtime_resume() callbacks
277 will be invoked with the spinlock held and interrupts disabled
278
Alan Stern15bcb91d2010-09-25 23:35:21 +0200279 unsigned int use_autosuspend;
280 - indicates that the device's driver supports delayed autosuspend (see
281 Section 9); it may be modified only by the
282 pm_runtime{_dont}_use_autosuspend() helper functions
283
284 unsigned int timer_autosuspends;
285 - indicates that the PM core should attempt to carry out an autosuspend
286 when the timer expires rather than a normal suspend
287
288 int autosuspend_delay;
289 - the delay time (in milliseconds) to be used for autosuspend
290
291 unsigned long last_busy;
292 - the time (in jiffies) when the pm_runtime_mark_last_busy() helper
293 function was last called for this device; used in calculating inactivity
294 periods for autosuspend
295
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200296All of the above fields are members of the 'power' member of 'struct device'.
297
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02002984. Runtime PM Device Helper Functions
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200299
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200300The following runtime PM helper functions are defined in
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200301drivers/base/power/runtime.c and include/linux/pm_runtime.h:
302
303 void pm_runtime_init(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200304 - initialize the device runtime PM fields in 'struct dev_pm_info'
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200305
306 void pm_runtime_remove(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200307 - make sure that the runtime PM of the device will be disabled after
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200308 removing the device from device hierarchy
309
310 int pm_runtime_idle(struct device *dev);
Alan Stern43d51af2013-06-03 21:49:59 +0200311 - execute the subsystem-level idle callback for the device; returns an
312 error code on failure, where -EINPROGRESS means that ->runtime_idle() is
313 already being executed; if there is no callback or the callback returns 0
Ulf Hanssond66e6db2013-10-15 22:25:08 +0200314 then run pm_runtime_autosuspend(dev) and return its result
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200315
316 int pm_runtime_suspend(struct device *dev);
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100317 - execute the subsystem-level suspend callback for the device; returns 0 on
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200318 success, 1 if the device's runtime PM status was already 'suspended', or
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200319 error code on failure, where -EAGAIN or -EBUSY means it is safe to attempt
Rafael J. Wysocki632e2702011-07-01 22:29:15 +0200320 to suspend the device again in future and -EACCES means that
321 'power.disable_depth' is different from 0
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200322
Alan Stern15bcb91d2010-09-25 23:35:21 +0200323 int pm_runtime_autosuspend(struct device *dev);
324 - same as pm_runtime_suspend() except that the autosuspend delay is taken
325 into account; if pm_runtime_autosuspend_expiration() says the delay has
326 not yet expired then an autosuspend is scheduled for the appropriate time
327 and 0 is returned
328
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200329 int pm_runtime_resume(struct device *dev);
Thadeu Lima de Souza Cascardode8164f2010-01-17 19:22:28 -0200330 - execute the subsystem-level resume callback for the device; returns 0 on
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200331 success, 1 if the device's runtime PM status was already 'active' or
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200332 error code on failure, where -EAGAIN means it may be safe to attempt to
333 resume the device again in future, but 'power.runtime_error' should be
Rafael J. Wysocki632e2702011-07-01 22:29:15 +0200334 checked additionally, and -EACCES means that 'power.disable_depth' is
335 different from 0
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200336
337 int pm_request_idle(struct device *dev);
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100338 - submit a request to execute the subsystem-level idle callback for the
339 device (the request is represented by a work item in pm_wq); returns 0 on
340 success or error code if the request has not been queued up
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200341
Alan Stern15bcb91d2010-09-25 23:35:21 +0200342 int pm_request_autosuspend(struct device *dev);
343 - schedule the execution of the subsystem-level suspend callback for the
344 device when the autosuspend delay has expired; if the delay has already
345 expired then the work item is queued up immediately
346
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200347 int pm_schedule_suspend(struct device *dev, unsigned int delay);
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100348 - schedule the execution of the subsystem-level suspend callback for the
349 device in future, where 'delay' is the time to wait before queuing up a
350 suspend work item in pm_wq, in milliseconds (if 'delay' is zero, the work
351 item is queued up immediately); returns 0 on success, 1 if the device's PM
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200352 runtime status was already 'suspended', or error code if the request
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200353 hasn't been scheduled (or queued up if 'delay' is 0); if the execution of
354 ->runtime_suspend() is already scheduled and not yet expired, the new
355 value of 'delay' will be used as the time to wait
356
357 int pm_request_resume(struct device *dev);
Rafael J. Wysockia6ab7aa2009-12-22 20:43:17 +0100358 - submit a request to execute the subsystem-level resume callback for the
359 device (the request is represented by a work item in pm_wq); returns 0 on
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200360 success, 1 if the device's runtime PM status was already 'active', or
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200361 error code if the request hasn't been queued up
362
363 void pm_runtime_get_noresume(struct device *dev);
364 - increment the device's usage counter
365
366 int pm_runtime_get(struct device *dev);
367 - increment the device's usage counter, run pm_request_resume(dev) and
368 return its result
369
370 int pm_runtime_get_sync(struct device *dev);
371 - increment the device's usage counter, run pm_runtime_resume(dev) and
372 return its result
373
Rafael J. Wysockia436b6a2015-12-17 02:54:26 +0100374 int pm_runtime_get_if_in_use(struct device *dev);
375 - return -EINVAL if 'power.disable_depth' is nonzero; otherwise, if the
376 runtime PM status is RPM_ACTIVE and the runtime PM usage counter is
377 nonzero, increment the counter and return 1; otherwise return 0 without
378 changing the counter
379
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200380 void pm_runtime_put_noidle(struct device *dev);
381 - decrement the device's usage counter
382
383 int pm_runtime_put(struct device *dev);
Alan Stern15bcb91d2010-09-25 23:35:21 +0200384 - decrement the device's usage counter; if the result is 0 then run
385 pm_request_idle(dev) and return its result
386
387 int pm_runtime_put_autosuspend(struct device *dev);
388 - decrement the device's usage counter; if the result is 0 then run
389 pm_request_autosuspend(dev) and return its result
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200390
391 int pm_runtime_put_sync(struct device *dev);
Alan Stern15bcb91d2010-09-25 23:35:21 +0200392 - decrement the device's usage counter; if the result is 0 then run
393 pm_runtime_idle(dev) and return its result
394
Alan Sternc7b61de2010-12-01 00:14:42 +0100395 int pm_runtime_put_sync_suspend(struct device *dev);
396 - decrement the device's usage counter; if the result is 0 then run
397 pm_runtime_suspend(dev) and return its result
398
Alan Stern15bcb91d2010-09-25 23:35:21 +0200399 int pm_runtime_put_sync_autosuspend(struct device *dev);
400 - decrement the device's usage counter; if the result is 0 then run
401 pm_runtime_autosuspend(dev) and return its result
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200402
403 void pm_runtime_enable(struct device *dev);
Rafael J. Wysockie358bad2011-07-06 10:52:06 +0200404 - decrement the device's 'power.disable_depth' field; if that field is equal
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200405 to zero, the runtime PM helper functions can execute subsystem-level
Rafael J. Wysockie358bad2011-07-06 10:52:06 +0200406 callbacks described in Section 2 for the device
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200407
408 int pm_runtime_disable(struct device *dev);
Rafael J. Wysockie358bad2011-07-06 10:52:06 +0200409 - increment the device's 'power.disable_depth' field (if the value of that
410 field was previously zero, this prevents subsystem-level runtime PM
Geert Uytterhoeven91e63cc2014-03-24 21:31:28 +0100411 callbacks from being run for the device), make sure that all of the
412 pending runtime PM operations on the device are either completed or
413 canceled; returns 1 if there was a resume request pending and it was
414 necessary to execute the subsystem-level resume callback for the device
415 to satisfy that request, otherwise 0 is returned
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200416
Rafael J. Wysockie358bad2011-07-06 10:52:06 +0200417 int pm_runtime_barrier(struct device *dev);
418 - check if there's a resume request pending for the device and resume it
419 (synchronously) in that case, cancel any other pending runtime PM requests
420 regarding it and wait for all runtime PM operations on it in progress to
421 complete; returns 1 if there was a resume request pending and it was
422 necessary to execute the subsystem-level resume callback for the device to
423 satisfy that request, otherwise 0 is returned
424
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200425 void pm_suspend_ignore_children(struct device *dev, bool enable);
426 - set/unset the power.ignore_children flag of the device
427
428 int pm_runtime_set_active(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200429 - clear the device's 'power.runtime_error' flag, set the device's runtime
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200430 PM status to 'active' and update its parent's counter of 'active'
431 children as appropriate (it is only valid to use this function if
432 'power.runtime_error' is set or 'power.disable_depth' is greater than
433 zero); it will fail and return error code if the device has a parent
434 which is not active and the 'power.ignore_children' flag of which is unset
435
436 void pm_runtime_set_suspended(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200437 - clear the device's 'power.runtime_error' flag, set the device's runtime
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200438 PM status to 'suspended' and update its parent's counter of 'active'
439 children as appropriate (it is only valid to use this function if
440 'power.runtime_error' is set or 'power.disable_depth' is greater than
441 zero)
442
ShuoX Liufbadc582013-01-23 21:49:37 +0100443 bool pm_runtime_active(struct device *dev);
444 - return true if the device's runtime PM status is 'active' or its
445 'power.disable_depth' field is not equal to zero, or false otherwise
446
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100447 bool pm_runtime_suspended(struct device *dev);
Rafael J. Wysockif08f5a02010-12-16 17:11:58 +0100448 - return true if the device's runtime PM status is 'suspended' and its
449 'power.disable_depth' field is equal to zero, or false otherwise
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100450
Kevin Hilmanf3393b62011-07-12 11:17:09 +0200451 bool pm_runtime_status_suspended(struct device *dev);
452 - return true if the device's runtime PM status is 'suspended'
453
Rafael J. Wysocki87d1b3e2010-03-06 21:28:17 +0100454 void pm_runtime_allow(struct device *dev);
455 - set the power.runtime_auto flag for the device and decrease its usage
456 counter (used by the /sys/devices/.../power/control interface to
457 effectively allow the device to be power managed at run time)
458
459 void pm_runtime_forbid(struct device *dev);
460 - unset the power.runtime_auto flag for the device and increase its usage
461 counter (used by the /sys/devices/.../power/control interface to
462 effectively prevent the device from being power managed at run time)
463
Alan Stern7490e442010-09-25 23:35:15 +0200464 void pm_runtime_no_callbacks(struct device *dev);
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200465 - set the power.no_callbacks flag for the device and remove the runtime
Alan Stern7490e442010-09-25 23:35:15 +0200466 PM attributes from /sys/devices/.../power (or prevent them from being
467 added when the device is registered)
468
Alan Sternc7b61de2010-12-01 00:14:42 +0100469 void pm_runtime_irq_safe(struct device *dev);
470 - set the power.irq_safe flag for the device, causing the runtime-PM
Rafael J. Wysocki64584eb2011-08-25 15:31:05 +0200471 callbacks to be invoked with interrupts off
Alan Sternc7b61de2010-12-01 00:14:42 +0100472
Krzysztof Kozlowski3fb15812014-11-14 09:47:25 +0100473 bool pm_runtime_is_irq_safe(struct device *dev);
474 - return true if power.irq_safe flag was set for the device, causing
475 the runtime-PM callbacks to be invoked with interrupts off
476
Alan Stern15bcb91d2010-09-25 23:35:21 +0200477 void pm_runtime_mark_last_busy(struct device *dev);
478 - set the power.last_busy field to the current time
479
480 void pm_runtime_use_autosuspend(struct device *dev);
481 - set the power.use_autosuspend flag, enabling autosuspend delays
482
483 void pm_runtime_dont_use_autosuspend(struct device *dev);
484 - clear the power.use_autosuspend flag, disabling autosuspend delays
485
486 void pm_runtime_set_autosuspend_delay(struct device *dev, int delay);
487 - set the power.autosuspend_delay value to 'delay' (expressed in
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200488 milliseconds); if 'delay' is negative then runtime suspends are
Alan Stern15bcb91d2010-09-25 23:35:21 +0200489 prevented
490
491 unsigned long pm_runtime_autosuspend_expiration(struct device *dev);
492 - calculate the time when the current autosuspend delay period will expire,
493 based on power.last_busy and power.autosuspend_delay; if the delay time
494 is 1000 ms or larger then the expiration time is rounded up to the
495 nearest second; returns 0 if the delay period has already expired or
496 power.use_autosuspend isn't set, otherwise returns the expiration time
497 in jiffies
498
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200499It is safe to execute the following helper functions from interrupt context:
500
501pm_request_idle()
Alan Stern15bcb91d2010-09-25 23:35:21 +0200502pm_request_autosuspend()
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200503pm_schedule_suspend()
504pm_request_resume()
505pm_runtime_get_noresume()
506pm_runtime_get()
507pm_runtime_put_noidle()
508pm_runtime_put()
Alan Stern15bcb91d2010-09-25 23:35:21 +0200509pm_runtime_put_autosuspend()
510pm_runtime_enable()
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200511pm_suspend_ignore_children()
512pm_runtime_set_active()
513pm_runtime_set_suspended()
Alan Stern15bcb91d2010-09-25 23:35:21 +0200514pm_runtime_suspended()
515pm_runtime_mark_last_busy()
516pm_runtime_autosuspend_expiration()
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200517
Alan Sternc7b61de2010-12-01 00:14:42 +0100518If pm_runtime_irq_safe() has been called for a device then the following helper
519functions may also be used in interrupt context:
520
Ming Lei2e6ba512011-09-21 22:31:33 +0200521pm_runtime_idle()
Alan Sternc7b61de2010-12-01 00:14:42 +0100522pm_runtime_suspend()
523pm_runtime_autosuspend()
524pm_runtime_resume()
525pm_runtime_get_sync()
Kevin Hilman02b26772011-08-05 21:45:20 +0200526pm_runtime_put_sync()
Alan Sternc7b61de2010-12-01 00:14:42 +0100527pm_runtime_put_sync_suspend()
Colin Cross311aab72011-08-08 23:39:36 +0200528pm_runtime_put_sync_autosuspend()
Alan Sternc7b61de2010-12-01 00:14:42 +0100529
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02005305. Runtime PM Initialization, Device Probing and Removal
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200531
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200532Initially, the runtime PM is disabled for all devices, which means that the
Masanari Iida1f999d12014-11-08 17:54:51 +0900533majority of the runtime PM helper functions described in Section 4 will return
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200534-EAGAIN until pm_runtime_enable() is called for the device.
535
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200536In addition to that, the initial runtime PM status of all devices is
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200537'suspended', but it need not reflect the actual physical state of the device.
538Thus, if the device is initially active (i.e. it is able to process I/O), its
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200539runtime PM status must be changed to 'active', with the help of
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200540pm_runtime_set_active(), before pm_runtime_enable() is called for the device.
541
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200542However, if the device has a parent and the parent's runtime PM is enabled,
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200543calling pm_runtime_set_active() for the device will affect the parent, unless
544the parent's 'power.ignore_children' flag is set. Namely, in that case the
545parent won't be able to suspend at run time, using the PM core's helper
546functions, as long as the child's status is 'active', even if the child's
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200547runtime PM is still disabled (i.e. pm_runtime_enable() hasn't been called for
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200548the child yet or pm_runtime_disable() has been called for it). For this reason,
549once pm_runtime_set_active() has been called for the device, pm_runtime_enable()
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200550should be called for it too as soon as reasonably possible or its runtime PM
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200551status should be changed back to 'suspended' with the help of
552pm_runtime_set_suspended().
553
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200554If the default initial runtime PM status of the device (i.e. 'suspended')
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200555reflects the actual state of the device, its bus type's or its driver's
556->probe() callback will likely need to wake it up using one of the PM core's
557helper functions described in Section 4. In that case, pm_runtime_resume()
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200558should be used. Of course, for this purpose the device's runtime PM has to be
Rafael J. Wysocki5e928f72009-08-18 23:38:32 +0200559enabled earlier by calling pm_runtime_enable().
560
Ben Dooksf6a2fbb2015-04-17 01:14:15 +0100561Note, if the device may execute pm_runtime calls during the probe (such as
562if it is registers with a subsystem that may call back in) then the
563pm_runtime_get_sync() call paired with a pm_runtime_put() call will be
564appropriate to ensure that the device is not put back to sleep during the
565probe. This can happen with systems such as the network device layer.
566
Ulf Hanssonea309942013-11-08 06:13:51 +0100567It may be desirable to suspend the device once ->probe() has finished.
568Therefore the driver core uses the asyncronous pm_request_idle() to submit a
569request to execute the subsystem-level idle callback for the device at that
570time. A driver that makes use of the runtime autosuspend feature, may want to
571update the last busy mark before returning from ->probe().
Rafael J. Wysockif5da24d2011-07-02 14:27:11 +0200572
573Moreover, the driver core prevents runtime PM callbacks from racing with the bus
574notifier callback in __device_release_driver(), which is necessary, because the
575notifier is used by some subsystems to carry out operations affecting the
576runtime PM functionality. It does so by calling pm_runtime_get_sync() before
577driver_sysfs_remove() and the BUS_NOTIFY_UNBIND_DRIVER notifications. This
578resumes the device if it's in the suspended state and prevents it from
579being suspended again while those routines are being executed.
580
581To allow bus types and drivers to put devices into the suspended state by
582calling pm_runtime_suspend() from their ->remove() routines, the driver core
583executes pm_runtime_put_sync() after running the BUS_NOTIFY_UNBIND_DRIVER
584notifications in __device_release_driver(). This requires bus types and
585drivers to make their ->remove() callbacks avoid races with runtime PM directly,
586but also it allows of more flexibility in the handling of devices during the
587removal of their drivers.
Alan Sternf1212ae2009-12-22 20:43:40 +0100588
Krzysztof Kozlowski8fd29102016-04-03 12:23:07 +0900589Drivers in ->remove() callback should undo the runtime PM changes done
590in ->probe(). Usually this means calling pm_runtime_disable(),
591pm_runtime_dont_use_autosuspend() etc.
592
Rafael J. Wysocki87d1b3e2010-03-06 21:28:17 +0100593The user space can effectively disallow the driver of the device to power manage
594it at run time by changing the value of its /sys/devices/.../power/control
595attribute to "on", which causes pm_runtime_forbid() to be called. In principle,
596this mechanism may also be used by the driver to effectively turn off the
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200597runtime power management of the device until the user space turns it on.
598Namely, during the initialization the driver can make sure that the runtime PM
Rafael J. Wysocki87d1b3e2010-03-06 21:28:17 +0100599status of the device is 'active' and call pm_runtime_forbid(). It should be
600noted, however, that if the user space has already intentionally changed the
601value of /sys/devices/.../power/control to "auto" to allow the driver to power
602manage the device at run time, the driver may confuse it by using
603pm_runtime_forbid() this way.
604
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +02006056. Runtime PM and System Sleep
Alan Sternf1212ae2009-12-22 20:43:40 +0100606
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200607Runtime PM and system sleep (i.e., system suspend and hibernation, also known
Alan Sternf1212ae2009-12-22 20:43:40 +0100608as suspend-to-RAM and suspend-to-disk) interact with each other in a couple of
609ways. If a device is active when a system sleep starts, everything is
610straightforward. But what should happen if the device is already suspended?
611
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200612The device may have different wake-up settings for runtime PM and system sleep.
613For example, remote wake-up may be enabled for runtime suspend but disallowed
Alan Sternf1212ae2009-12-22 20:43:40 +0100614for system sleep (device_may_wakeup(dev) returns 'false'). When this happens,
615the subsystem-level system suspend callback is responsible for changing the
616device's wake-up setting (it may leave that to the device driver's system
617suspend routine). It may be necessary to resume the device and suspend it again
618in order to do so. The same is true if the driver uses different power levels
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200619or other settings for runtime suspend and system sleep.
Alan Sternf1212ae2009-12-22 20:43:40 +0100620
Rafael J. Wysocki455716e2011-07-01 22:29:05 +0200621During system resume, the simplest approach is to bring all devices back to full
622power, even if they had been suspended before the system suspend began. There
623are several reasons for this, including:
Alan Sternf1212ae2009-12-22 20:43:40 +0100624
625 * The device might need to switch power levels, wake-up settings, etc.
626
627 * Remote wake-up events might have been lost by the firmware.
628
629 * The device's children may need the device to be at full power in order
630 to resume themselves.
631
632 * The driver's idea of the device state may not agree with the device's
633 physical state. This can happen during resume from hibernation.
634
635 * The device might need to be reset.
636
637 * Even though the device was suspended, if its usage counter was > 0 then most
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200638 likely it would need a runtime resume in the near future anyway.
Alan Sternf1212ae2009-12-22 20:43:40 +0100639
Rafael J. Wysocki455716e2011-07-01 22:29:05 +0200640If the device had been suspended before the system suspend began and it's
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200641brought back to full power during resume, then its runtime PM status will have
Rafael J. Wysocki455716e2011-07-01 22:29:05 +0200642to be updated to reflect the actual post-system sleep status. The way to do
643this is:
Alan Sternf1212ae2009-12-22 20:43:40 +0100644
645 pm_runtime_disable(dev);
646 pm_runtime_set_active(dev);
647 pm_runtime_enable(dev);
648
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200649The PM core always increments the runtime usage counter before calling the
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200650->suspend() callback and decrements it after calling the ->resume() callback.
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200651Hence disabling runtime PM temporarily like this will not cause any runtime
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200652suspend attempts to be permanently lost. If the usage count goes to zero
653following the return of the ->resume() callback, the ->runtime_idle() callback
654will be invoked as usual.
655
Rafael J. Wysocki455716e2011-07-01 22:29:05 +0200656On some systems, however, system sleep is not entered through a global firmware
657or hardware operation. Instead, all hardware components are put into low-power
658states directly by the kernel in a coordinated way. Then, the system sleep
659state effectively follows from the states the hardware components end up in
660and the system is woken up from that state by a hardware interrupt or a similar
661mechanism entirely under the kernel's control. As a result, the kernel never
662gives control away and the states of all devices during resume are precisely
663known to it. If that is the case and none of the situations listed above takes
664place (in particular, if the system is not waking up from hibernation), it may
665be more efficient to leave the devices that had been suspended before the system
666suspend began in the suspended state.
667
Rafael J. Wysockif71495f2014-05-16 02:47:37 +0200668To this end, the PM core provides a mechanism allowing some coordination between
669different levels of device hierarchy. Namely, if a system suspend .prepare()
670callback returns a positive number for a device, that indicates to the PM core
671that the device appears to be runtime-suspended and its state is fine, so it
672may be left in runtime suspend provided that all of its descendants are also
673left in runtime suspend. If that happens, the PM core will not execute any
674system suspend and resume callbacks for all of those devices, except for the
675complete callback, which is then entirely responsible for handling the device
676as appropriate. This only applies to system suspend transitions that are not
677related to hibernation (see Documentation/power/devices.txt for more
678information).
679
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200680The PM core does its best to reduce the probability of race conditions between
681the runtime PM and system suspend/resume (and hibernation) callbacks by carrying
682out the following operations:
683
Rafael J. Wysocki4ec6a9c2014-05-16 13:05:59 +0200684 * During system suspend pm_runtime_get_noresume() is called for every device
685 right before executing the subsystem-level .prepare() callback for it and
686 pm_runtime_barrier() is called for every device right before executing the
687 subsystem-level .suspend() callback for it. In addition to that the PM core
688 calls __pm_runtime_disable() with 'false' as the second argument for every
689 device right before executing the subsystem-level .suspend_late() callback
690 for it.
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200691
Rafael J. Wysocki4ec6a9c2014-05-16 13:05:59 +0200692 * During system resume pm_runtime_enable() and pm_runtime_put() are called for
693 every device right after executing the subsystem-level .resume_early()
694 callback and right after executing the subsystem-level .complete() callback
Rafael J. Wysocki9f6d8f62012-12-22 23:59:01 +0100695 for it, respectively.
Rafael J. Wysocki1e2ef052011-07-06 10:51:58 +0200696
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +01006977. Generic subsystem callbacks
698
699Subsystems may wish to conserve code space by using the set of generic power
700management callbacks provided by the PM core, defined in
701driver/base/power/generic_ops.c:
702
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100703 int pm_generic_runtime_suspend(struct device *dev);
704 - invoke the ->runtime_suspend() callback provided by the driver of this
Geert Uytterhoeven39c29f32014-03-24 21:31:29 +0100705 device and return its result, or return 0 if not defined
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100706
707 int pm_generic_runtime_resume(struct device *dev);
708 - invoke the ->runtime_resume() callback provided by the driver of this
Geert Uytterhoeven39c29f32014-03-24 21:31:29 +0100709 device and return its result, or return 0 if not defined
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100710
711 int pm_generic_suspend(struct device *dev);
712 - if the device has not been suspended at run time, invoke the ->suspend()
713 callback provided by its driver and return its result, or return 0 if not
714 defined
715
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200716 int pm_generic_suspend_noirq(struct device *dev);
717 - if pm_runtime_suspended(dev) returns "false", invoke the ->suspend_noirq()
718 callback provided by the device's driver and return its result, or return
719 0 if not defined
720
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100721 int pm_generic_resume(struct device *dev);
722 - invoke the ->resume() callback provided by the driver of this device and,
723 if successful, change the device's runtime PM status to 'active'
724
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200725 int pm_generic_resume_noirq(struct device *dev);
726 - invoke the ->resume_noirq() callback provided by the driver of this device
727
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100728 int pm_generic_freeze(struct device *dev);
729 - if the device has not been suspended at run time, invoke the ->freeze()
730 callback provided by its driver and return its result, or return 0 if not
731 defined
732
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200733 int pm_generic_freeze_noirq(struct device *dev);
734 - if pm_runtime_suspended(dev) returns "false", invoke the ->freeze_noirq()
735 callback provided by the device's driver and return its result, or return
736 0 if not defined
737
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100738 int pm_generic_thaw(struct device *dev);
739 - if the device has not been suspended at run time, invoke the ->thaw()
740 callback provided by its driver and return its result, or return 0 if not
741 defined
742
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200743 int pm_generic_thaw_noirq(struct device *dev);
744 - if pm_runtime_suspended(dev) returns "false", invoke the ->thaw_noirq()
745 callback provided by the device's driver and return its result, or return
746 0 if not defined
747
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100748 int pm_generic_poweroff(struct device *dev);
749 - if the device has not been suspended at run time, invoke the ->poweroff()
750 callback provided by its driver and return its result, or return 0 if not
751 defined
752
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200753 int pm_generic_poweroff_noirq(struct device *dev);
754 - if pm_runtime_suspended(dev) returns "false", run the ->poweroff_noirq()
755 callback provided by the device's driver and return its result, or return
756 0 if not defined
757
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100758 int pm_generic_restore(struct device *dev);
759 - invoke the ->restore() callback provided by the driver of this device and,
760 if successful, change the device's runtime PM status to 'active'
761
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200762 int pm_generic_restore_noirq(struct device *dev);
763 - invoke the ->restore_noirq() callback provided by the device's driver
764
Geert Uytterhoevenfd6fe822014-03-24 21:31:30 +0100765These functions are the defaults used by the PM core, if a subsystem doesn't
766provide its own callbacks for ->runtime_idle(), ->runtime_suspend(),
Rafael J. Wysockie5291922011-07-01 22:12:59 +0200767->runtime_resume(), ->suspend(), ->suspend_noirq(), ->resume(),
768->resume_noirq(), ->freeze(), ->freeze_noirq(), ->thaw(), ->thaw_noirq(),
Geert Uytterhoevenfd6fe822014-03-24 21:31:30 +0100769->poweroff(), ->poweroff_noirq(), ->restore(), ->restore_noirq() in the
770subsystem-level dev_pm_ops structure.
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100771
772Device drivers that wish to use the same function as a system suspend, freeze,
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200773poweroff and runtime suspend callback, and similarly for system resume, thaw,
774restore, and runtime resume, can achieve this with the help of the
Rafael J. Wysockid690b2c2010-03-06 21:28:37 +0100775UNIVERSAL_DEV_PM_OPS macro defined in include/linux/pm.h (possibly setting its
776last argument to NULL).
Alan Stern7490e442010-09-25 23:35:15 +0200777
7788. "No-Callback" Devices
779
780Some "devices" are only logical sub-devices of their parent and cannot be
781power-managed on their own. (The prototype example is a USB interface. Entire
782USB devices can go into low-power mode or send wake-up requests, but neither is
783possible for individual interfaces.) The drivers for these devices have no
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200784need of runtime PM callbacks; if the callbacks did exist, ->runtime_suspend()
Alan Stern7490e442010-09-25 23:35:15 +0200785and ->runtime_resume() would always return 0 without doing anything else and
786->runtime_idle() would always call pm_runtime_suspend().
787
788Subsystems can tell the PM core about these devices by calling
789pm_runtime_no_callbacks(). This should be done after the device structure is
790initialized and before it is registered (although after device registration is
791also okay). The routine will set the device's power.no_callbacks flag and
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200792prevent the non-debugging runtime PM sysfs attributes from being created.
Alan Stern7490e442010-09-25 23:35:15 +0200793
794When power.no_callbacks is set, the PM core will not invoke the
795->runtime_idle(), ->runtime_suspend(), or ->runtime_resume() callbacks.
796Instead it will assume that suspends and resumes always succeed and that idle
797devices should be suspended.
798
799As a consequence, the PM core will never directly inform the device's subsystem
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200800or driver about runtime power changes. Instead, the driver for the device's
Alan Stern7490e442010-09-25 23:35:15 +0200801parent must take responsibility for telling the device's driver when the
802parent's power state changes.
Alan Stern15bcb91d2010-09-25 23:35:21 +0200803
8049. Autosuspend, or automatically-delayed suspends
805
806Changing a device's power state isn't free; it requires both time and energy.
807A device should be put in a low-power state only when there's some reason to
808think it will remain in that state for a substantial time. A common heuristic
809says that a device which hasn't been used for a while is liable to remain
810unused; following this advice, drivers should not allow devices to be suspended
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200811at runtime until they have been inactive for some minimum period. Even when
Alan Stern15bcb91d2010-09-25 23:35:21 +0200812the heuristic ends up being non-optimal, it will still prevent devices from
813"bouncing" too rapidly between low-power and full-power states.
814
815The term "autosuspend" is an historical remnant. It doesn't mean that the
816device is automatically suspended (the subsystem or driver still has to call
Rafael J. Wysocki62052ab2011-07-06 10:52:13 +0200817the appropriate PM routines); rather it means that runtime suspends will
Alan Stern15bcb91d2010-09-25 23:35:21 +0200818automatically be delayed until the desired period of inactivity has elapsed.
819
820Inactivity is determined based on the power.last_busy field. Drivers should
821call pm_runtime_mark_last_busy() to update this field after carrying out I/O,
822typically just before calling pm_runtime_put_autosuspend(). The desired length
823of the inactivity period is a matter of policy. Subsystems can set this length
824initially by calling pm_runtime_set_autosuspend_delay(), but after device
825registration the length should be controlled by user space, using the
826/sys/devices/.../power/autosuspend_delay_ms attribute.
827
828In order to use autosuspend, subsystems or drivers must call
829pm_runtime_use_autosuspend() (preferably before registering the device), and
830thereafter they should use the various *_autosuspend() helper functions instead
831of the non-autosuspend counterparts:
832
833 Instead of: pm_runtime_suspend use: pm_runtime_autosuspend;
834 Instead of: pm_schedule_suspend use: pm_request_autosuspend;
835 Instead of: pm_runtime_put use: pm_runtime_put_autosuspend;
836 Instead of: pm_runtime_put_sync use: pm_runtime_put_sync_autosuspend.
837
838Drivers may also continue to use the non-autosuspend helper functions; they
839will behave normally, not taking the autosuspend delay into account.
840Similarly, if the power.use_autosuspend field isn't set then the autosuspend
841helper functions will behave just like the non-autosuspend counterparts.
842
Alan Stern886486b2011-11-03 23:39:18 +0100843Under some circumstances a driver or subsystem may want to prevent a device
844from autosuspending immediately, even though the usage counter is zero and the
845autosuspend delay time has expired. If the ->runtime_suspend() callback
846returns -EAGAIN or -EBUSY, and if the next autosuspend delay expiration time is
847in the future (as it normally would be if the callback invoked
848pm_runtime_mark_last_busy()), the PM core will automatically reschedule the
849autosuspend. The ->runtime_suspend() callback can't do this rescheduling
850itself because no suspend requests of any kind are accepted while the device is
851suspending (i.e., while the callback is running).
852
Alan Stern15bcb91d2010-09-25 23:35:21 +0200853The implementation is well suited for asynchronous use in interrupt contexts.
854However such use inevitably involves races, because the PM core can't
855synchronize ->runtime_suspend() callbacks with the arrival of I/O requests.
856This synchronization must be handled by the driver, using its private lock.
857Here is a schematic pseudo-code example:
858
859 foo_read_or_write(struct foo_priv *foo, void *data)
860 {
861 lock(&foo->private_lock);
862 add_request_to_io_queue(foo, data);
863 if (foo->num_pending_requests++ == 0)
864 pm_runtime_get(&foo->dev);
865 if (!foo->is_suspended)
866 foo_process_next_request(foo);
867 unlock(&foo->private_lock);
868 }
869
870 foo_io_completion(struct foo_priv *foo, void *req)
871 {
872 lock(&foo->private_lock);
873 if (--foo->num_pending_requests == 0) {
874 pm_runtime_mark_last_busy(&foo->dev);
875 pm_runtime_put_autosuspend(&foo->dev);
876 } else {
877 foo_process_next_request(foo);
878 }
879 unlock(&foo->private_lock);
880 /* Send req result back to the user ... */
881 }
882
883 int foo_runtime_suspend(struct device *dev)
884 {
885 struct foo_priv foo = container_of(dev, ...);
886 int ret = 0;
887
888 lock(&foo->private_lock);
889 if (foo->num_pending_requests > 0) {
890 ret = -EBUSY;
891 } else {
892 /* ... suspend the device ... */
893 foo->is_suspended = 1;
894 }
895 unlock(&foo->private_lock);
896 return ret;
897 }
898
899 int foo_runtime_resume(struct device *dev)
900 {
901 struct foo_priv foo = container_of(dev, ...);
902
903 lock(&foo->private_lock);
904 /* ... resume the device ... */
905 foo->is_suspended = 0;
906 pm_runtime_mark_last_busy(&foo->dev);
907 if (foo->num_pending_requests > 0)
Geert Uytterhoevenfe982452014-03-24 21:31:31 +0100908 foo_process_next_request(foo);
Alan Stern15bcb91d2010-09-25 23:35:21 +0200909 unlock(&foo->private_lock);
910 return 0;
911 }
912
913The important point is that after foo_io_completion() asks for an autosuspend,
914the foo_runtime_suspend() callback may race with foo_read_or_write().
915Therefore foo_runtime_suspend() has to check whether there are any pending I/O
916requests (while holding the private lock) before allowing the suspend to
917proceed.
918
919In addition, the power.autosuspend_delay field can be changed by user space at
920any time. If a driver cares about this, it can call
921pm_runtime_autosuspend_expiration() from within the ->runtime_suspend()
922callback while holding its private lock. If the function returns a nonzero
923value then the delay has not yet expired and the callback should return
924-EAGAIN.