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62052ab1 | 1 | Runtime Power Management Framework for I/O Devices |
5e928f77 | 2 | |
9659cc06 | 3 | (C) 2009-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc. |
7490e442 | 4 | (C) 2010 Alan Stern <stern@rowland.harvard.edu> |
5e928f77 RW |
5 | |
6 | 1. Introduction | |
7 | ||
62052ab1 | 8 | Support for runtime power management (runtime PM) of I/O devices is provided |
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9 | at 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 | |
62052ab1 | 13 | used for queuing all work items related to runtime PM, because this allows |
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14 | 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 | ||
62052ab1 | 18 | * A number of runtime PM fields in the 'power' member of 'struct device' (which |
5e928f77 | 19 | is of the type 'struct dev_pm_info', defined in include/linux/pm.h) that can |
62052ab1 | 20 | be used for synchronizing runtime PM operations with one another. |
5e928f77 | 21 | |
62052ab1 | 22 | * Three device runtime PM callbacks in 'struct dev_pm_ops' (defined in |
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23 | include/linux/pm.h). |
24 | ||
25 | * A set of helper functions defined in drivers/base/power/runtime.c that can be | |
62052ab1 | 26 | used for carrying out runtime PM operations in such a way that the |
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27 | synchronization between them is taken care of by the PM core. Bus types and |
28 | device drivers are encouraged to use these functions. | |
29 | ||
62052ab1 | 30 | The runtime PM callbacks present in 'struct dev_pm_ops', the device runtime PM |
5e928f77 | 31 | fields of 'struct dev_pm_info' and the core helper functions provided for |
62052ab1 | 32 | runtime PM are described below. |
5e928f77 | 33 | |
62052ab1 | 34 | 2. Device Runtime PM Callbacks |
5e928f77 | 35 | |
62052ab1 | 36 | There are three device runtime PM callbacks defined in 'struct dev_pm_ops': |
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37 | |
38 | struct dev_pm_ops { | |
39 | ... | |
40 | int (*runtime_suspend)(struct device *dev); | |
41 | int (*runtime_resume)(struct device *dev); | |
e1b1903e | 42 | int (*runtime_idle)(struct device *dev); |
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43 | ... |
44 | }; | |
45 | ||
2fb242ad ML |
46 | The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks |
47 | are executed by the PM core for either the power domain, or the device type | |
48 | (if the device power domain's struct dev_pm_ops does not exist), or the class | |
49 | (if the device power domain's and type's struct dev_pm_ops object does not | |
50 | exist), or the bus type (if the device power domain's, type's and class' | |
51 | struct dev_pm_ops objects do not exist) of the given device, so the priority | |
52 | order of callbacks from high to low is that power domain callbacks, device | |
53 | type callbacks, class callbacks and bus type callbacks, and the high priority | |
54 | one will take precedence over low priority one. The bus type, device type and | |
55 | class callbacks are referred to as subsystem-level callbacks in what follows, | |
56 | and generally speaking, the power domain callbacks are used for representing | |
57 | power domains within a SoC. | |
a6ab7aa9 | 58 | |
c7b61de5 AS |
59 | By default, the callbacks are always invoked in process context with interrupts |
60 | enabled. However, subsystems can use the pm_runtime_irq_safe() helper function | |
61 | to tell the PM core that a device's ->runtime_suspend() and ->runtime_resume() | |
02b26774 KH |
62 | callbacks should be invoked in atomic context with interrupts disabled. |
63 | This implies that these callback routines must not block or sleep, but it also | |
64 | means that the synchronous helper functions listed at the end of Section 4 can | |
65 | be used within an interrupt handler or in an atomic context. | |
c7b61de5 | 66 | |
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67 | The subsystem-level suspend callback is _entirely_ _responsible_ for handling |
68 | the suspend of the device as appropriate, which may, but need not include | |
69 | executing the device driver's own ->runtime_suspend() callback (from the | |
5e928f77 | 70 | PM core's point of view it is not necessary to implement a ->runtime_suspend() |
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71 | callback in a device driver as long as the subsystem-level suspend callback |
72 | knows what to do to handle the device). | |
5e928f77 | 73 | |
a6ab7aa9 | 74 | * Once the subsystem-level suspend callback has completed successfully |
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75 | for given device, the PM core regards the device as suspended, which need |
76 | not mean that the device has been put into a low power state. It is | |
77 | supposed to mean, however, that the device will not process data and will | |
a6ab7aa9 | 78 | not communicate with the CPU(s) and RAM until the subsystem-level resume |
62052ab1 | 79 | callback is executed for it. The runtime PM status of a device after |
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80 | successful execution of the subsystem-level suspend callback is 'suspended'. |
81 | ||
82 | * If the subsystem-level suspend callback returns -EBUSY or -EAGAIN, | |
62052ab1 | 83 | the device's runtime PM status is 'active', which means that the device |
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84 | _must_ be fully operational afterwards. |
85 | ||
86 | * If the subsystem-level suspend callback returns an error code different | |
87 | from -EBUSY or -EAGAIN, the PM core regards this as a fatal error and will | |
88 | refuse to run the helper functions described in Section 4 for the device, | |
89 | until the status of it is directly set either to 'active', or to 'suspended' | |
90 | (the PM core provides special helper functions for this purpose). | |
91 | ||
92 | In particular, if the driver requires remote wake-up capability (i.e. hardware | |
93 | mechanism allowing the device to request a change of its power state, such as | |
94 | PCI PME) for proper functioning and device_run_wake() returns 'false' for the | |
95 | device, then ->runtime_suspend() should return -EBUSY. On the other hand, if | |
96 | device_run_wake() returns 'true' for the device and the device is put into a low | |
97 | power state during the execution of the subsystem-level suspend callback, it is | |
98 | expected that remote wake-up will be enabled for the device. Generally, remote | |
99 | wake-up should be enabled for all input devices put into a low power state at | |
100 | run time. | |
101 | ||
102 | The subsystem-level resume callback is _entirely_ _responsible_ for handling the | |
103 | resume of the device as appropriate, which may, but need not include executing | |
104 | the device driver's own ->runtime_resume() callback (from the PM core's point of | |
105 | view it is not necessary to implement a ->runtime_resume() callback in a device | |
106 | driver as long as the subsystem-level resume callback knows what to do to handle | |
107 | the device). | |
108 | ||
109 | * Once the subsystem-level resume callback has completed successfully, the PM | |
110 | core regards the device as fully operational, which means that the device | |
62052ab1 | 111 | _must_ be able to complete I/O operations as needed. The runtime PM status |
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112 | of the device is then 'active'. |
113 | ||
114 | * If the subsystem-level resume callback returns an error code, the PM core | |
115 | regards this as a fatal error and will refuse to run the helper functions | |
116 | described in Section 4 for the device, until its status is directly set | |
117 | either to 'active' or to 'suspended' (the PM core provides special helper | |
118 | functions for this purpose). | |
119 | ||
120 | The subsystem-level idle callback is executed by the PM core whenever the device | |
121 | appears to be idle, which is indicated to the PM core by two counters, the | |
122 | device's usage counter and the counter of 'active' children of the device. | |
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123 | |
124 | * If any of these counters is decreased using a helper function provided by | |
125 | the PM core and it turns out to be equal to zero, the other counter is | |
126 | checked. If that counter also is equal to zero, the PM core executes the | |
a6ab7aa9 | 127 | subsystem-level idle callback with the device as an argument. |
5e928f77 | 128 | |
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129 | The action performed by a subsystem-level idle callback is totally dependent on |
130 | the subsystem in question, but the expected and recommended action is to check | |
131 | if the device can be suspended (i.e. if all of the conditions necessary for | |
132 | suspending the device are satisfied) and to queue up a suspend request for the | |
133 | device in that case. The value returned by this callback is ignored by the PM | |
134 | core. | |
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135 | |
136 | The helper functions provided by the PM core, described in Section 4, guarantee | |
62052ab1 | 137 | that the following constraints are met with respect to the bus type's runtime |
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138 | PM callbacks: |
139 | ||
140 | (1) The callbacks are mutually exclusive (e.g. it is forbidden to execute | |
141 | ->runtime_suspend() in parallel with ->runtime_resume() or with another | |
142 | instance of ->runtime_suspend() for the same device) with the exception that | |
143 | ->runtime_suspend() or ->runtime_resume() can be executed in parallel with | |
144 | ->runtime_idle() (although ->runtime_idle() will not be started while any | |
145 | of the other callbacks is being executed for the same device). | |
146 | ||
147 | (2) ->runtime_idle() and ->runtime_suspend() can only be executed for 'active' | |
148 | devices (i.e. the PM core will only execute ->runtime_idle() or | |
62052ab1 | 149 | ->runtime_suspend() for the devices the runtime PM status of which is |
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150 | 'active'). |
151 | ||
152 | (3) ->runtime_idle() and ->runtime_suspend() can only be executed for a device | |
153 | the usage counter of which is equal to zero _and_ either the counter of | |
154 | 'active' children of which is equal to zero, or the 'power.ignore_children' | |
155 | flag of which is set. | |
156 | ||
157 | (4) ->runtime_resume() can only be executed for 'suspended' devices (i.e. the | |
62052ab1 | 158 | PM core will only execute ->runtime_resume() for the devices the runtime |
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159 | PM status of which is 'suspended'). |
160 | ||
161 | Additionally, the helper functions provided by the PM core obey the following | |
162 | rules: | |
163 | ||
164 | * If ->runtime_suspend() is about to be executed or there's a pending request | |
165 | to execute it, ->runtime_idle() will not be executed for the same device. | |
166 | ||
167 | * A request to execute or to schedule the execution of ->runtime_suspend() | |
168 | will cancel any pending requests to execute ->runtime_idle() for the same | |
169 | device. | |
170 | ||
171 | * If ->runtime_resume() is about to be executed or there's a pending request | |
172 | to execute it, the other callbacks will not be executed for the same device. | |
173 | ||
174 | * A request to execute ->runtime_resume() will cancel any pending or | |
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175 | scheduled requests to execute the other callbacks for the same device, |
176 | except for scheduled autosuspends. | |
5e928f77 | 177 | |
62052ab1 | 178 | 3. Runtime PM Device Fields |
5e928f77 | 179 | |
62052ab1 | 180 | The following device runtime PM fields are present in 'struct dev_pm_info', as |
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181 | defined in include/linux/pm.h: |
182 | ||
183 | struct timer_list suspend_timer; | |
15bcb91d | 184 | - timer used for scheduling (delayed) suspend and autosuspend requests |
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185 | |
186 | unsigned long timer_expires; | |
187 | - timer expiration time, in jiffies (if this is different from zero, the | |
188 | timer is running and will expire at that time, otherwise the timer is not | |
189 | running) | |
190 | ||
191 | struct work_struct work; | |
192 | - work structure used for queuing up requests (i.e. work items in pm_wq) | |
193 | ||
194 | wait_queue_head_t wait_queue; | |
195 | - wait queue used if any of the helper functions needs to wait for another | |
196 | one to complete | |
197 | ||
198 | spinlock_t lock; | |
199 | - lock used for synchronisation | |
200 | ||
201 | atomic_t usage_count; | |
202 | - the usage counter of the device | |
203 | ||
204 | atomic_t child_count; | |
205 | - the count of 'active' children of the device | |
206 | ||
207 | unsigned int ignore_children; | |
208 | - if set, the value of child_count is ignored (but still updated) | |
209 | ||
210 | unsigned int disable_depth; | |
211 | - used for disabling the helper funcions (they work normally if this is | |
62052ab1 | 212 | equal to zero); the initial value of it is 1 (i.e. runtime PM is |
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213 | initially disabled for all devices) |
214 | ||
215 | unsigned int runtime_error; | |
216 | - if set, there was a fatal error (one of the callbacks returned error code | |
217 | as described in Section 2), so the helper funtions will not work until | |
218 | this flag is cleared; this is the error code returned by the failing | |
219 | callback | |
220 | ||
221 | unsigned int idle_notification; | |
222 | - if set, ->runtime_idle() is being executed | |
223 | ||
224 | unsigned int request_pending; | |
225 | - if set, there's a pending request (i.e. a work item queued up into pm_wq) | |
226 | ||
227 | enum rpm_request request; | |
228 | - type of request that's pending (valid if request_pending is set) | |
229 | ||
230 | unsigned int deferred_resume; | |
231 | - set if ->runtime_resume() is about to be run while ->runtime_suspend() is | |
232 | being executed for that device and it is not practical to wait for the | |
233 | suspend to complete; means "start a resume as soon as you've suspended" | |
234 | ||
7a1a8eb5 | 235 | unsigned int run_wake; |
62052ab1 | 236 | - set if the device is capable of generating runtime wake-up events |
7a1a8eb5 | 237 | |
5e928f77 | 238 | enum rpm_status runtime_status; |
62052ab1 | 239 | - the runtime PM status of the device; this field's initial value is |
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240 | RPM_SUSPENDED, which means that each device is initially regarded by the |
241 | PM core as 'suspended', regardless of its real hardware status | |
242 | ||
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243 | unsigned int runtime_auto; |
244 | - if set, indicates that the user space has allowed the device driver to | |
245 | power manage the device at run time via the /sys/devices/.../power/control | |
246 | interface; it may only be modified with the help of the pm_runtime_allow() | |
247 | and pm_runtime_forbid() helper functions | |
248 | ||
7490e442 | 249 | unsigned int no_callbacks; |
62052ab1 | 250 | - indicates that the device does not use the runtime PM callbacks (see |
7490e442 AS |
251 | Section 8); it may be modified only by the pm_runtime_no_callbacks() |
252 | helper function | |
253 | ||
c7b61de5 AS |
254 | unsigned int irq_safe; |
255 | - indicates that the ->runtime_suspend() and ->runtime_resume() callbacks | |
256 | will be invoked with the spinlock held and interrupts disabled | |
257 | ||
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258 | unsigned int use_autosuspend; |
259 | - indicates that the device's driver supports delayed autosuspend (see | |
260 | Section 9); it may be modified only by the | |
261 | pm_runtime{_dont}_use_autosuspend() helper functions | |
262 | ||
263 | unsigned int timer_autosuspends; | |
264 | - indicates that the PM core should attempt to carry out an autosuspend | |
265 | when the timer expires rather than a normal suspend | |
266 | ||
267 | int autosuspend_delay; | |
268 | - the delay time (in milliseconds) to be used for autosuspend | |
269 | ||
270 | unsigned long last_busy; | |
271 | - the time (in jiffies) when the pm_runtime_mark_last_busy() helper | |
272 | function was last called for this device; used in calculating inactivity | |
273 | periods for autosuspend | |
274 | ||
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275 | All of the above fields are members of the 'power' member of 'struct device'. |
276 | ||
62052ab1 | 277 | 4. Runtime PM Device Helper Functions |
5e928f77 | 278 | |
62052ab1 | 279 | The following runtime PM helper functions are defined in |
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280 | drivers/base/power/runtime.c and include/linux/pm_runtime.h: |
281 | ||
282 | void pm_runtime_init(struct device *dev); | |
62052ab1 | 283 | - initialize the device runtime PM fields in 'struct dev_pm_info' |
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284 | |
285 | void pm_runtime_remove(struct device *dev); | |
62052ab1 | 286 | - make sure that the runtime PM of the device will be disabled after |
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287 | removing the device from device hierarchy |
288 | ||
289 | int pm_runtime_idle(struct device *dev); | |
a6ab7aa9 RW |
290 | - execute the subsystem-level idle callback for the device; returns 0 on |
291 | success or error code on failure, where -EINPROGRESS means that | |
292 | ->runtime_idle() is already being executed | |
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293 | |
294 | int pm_runtime_suspend(struct device *dev); | |
a6ab7aa9 | 295 | - execute the subsystem-level suspend callback for the device; returns 0 on |
62052ab1 | 296 | success, 1 if the device's runtime PM status was already 'suspended', or |
5e928f77 | 297 | error code on failure, where -EAGAIN or -EBUSY means it is safe to attempt |
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298 | to suspend the device again in future and -EACCES means that |
299 | 'power.disable_depth' is different from 0 | |
5e928f77 | 300 | |
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301 | int pm_runtime_autosuspend(struct device *dev); |
302 | - same as pm_runtime_suspend() except that the autosuspend delay is taken | |
303 | into account; if pm_runtime_autosuspend_expiration() says the delay has | |
304 | not yet expired then an autosuspend is scheduled for the appropriate time | |
305 | and 0 is returned | |
306 | ||
5e928f77 | 307 | int pm_runtime_resume(struct device *dev); |
de8164fb | 308 | - execute the subsystem-level resume callback for the device; returns 0 on |
62052ab1 | 309 | success, 1 if the device's runtime PM status was already 'active' or |
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310 | error code on failure, where -EAGAIN means it may be safe to attempt to |
311 | resume the device again in future, but 'power.runtime_error' should be | |
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312 | checked additionally, and -EACCES means that 'power.disable_depth' is |
313 | different from 0 | |
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314 | |
315 | int pm_request_idle(struct device *dev); | |
a6ab7aa9 RW |
316 | - submit a request to execute the subsystem-level idle callback for the |
317 | device (the request is represented by a work item in pm_wq); returns 0 on | |
318 | success or error code if the request has not been queued up | |
5e928f77 | 319 | |
15bcb91d AS |
320 | int pm_request_autosuspend(struct device *dev); |
321 | - schedule the execution of the subsystem-level suspend callback for the | |
322 | device when the autosuspend delay has expired; if the delay has already | |
323 | expired then the work item is queued up immediately | |
324 | ||
5e928f77 | 325 | int pm_schedule_suspend(struct device *dev, unsigned int delay); |
a6ab7aa9 RW |
326 | - schedule the execution of the subsystem-level suspend callback for the |
327 | device in future, where 'delay' is the time to wait before queuing up a | |
328 | suspend work item in pm_wq, in milliseconds (if 'delay' is zero, the work | |
329 | item is queued up immediately); returns 0 on success, 1 if the device's PM | |
62052ab1 | 330 | runtime status was already 'suspended', or error code if the request |
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331 | hasn't been scheduled (or queued up if 'delay' is 0); if the execution of |
332 | ->runtime_suspend() is already scheduled and not yet expired, the new | |
333 | value of 'delay' will be used as the time to wait | |
334 | ||
335 | int pm_request_resume(struct device *dev); | |
a6ab7aa9 RW |
336 | - submit a request to execute the subsystem-level resume callback for the |
337 | device (the request is represented by a work item in pm_wq); returns 0 on | |
62052ab1 | 338 | success, 1 if the device's runtime PM status was already 'active', or |
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339 | error code if the request hasn't been queued up |
340 | ||
341 | void pm_runtime_get_noresume(struct device *dev); | |
342 | - increment the device's usage counter | |
343 | ||
344 | int pm_runtime_get(struct device *dev); | |
345 | - increment the device's usage counter, run pm_request_resume(dev) and | |
346 | return its result | |
347 | ||
348 | int pm_runtime_get_sync(struct device *dev); | |
349 | - increment the device's usage counter, run pm_runtime_resume(dev) and | |
350 | return its result | |
351 | ||
352 | void pm_runtime_put_noidle(struct device *dev); | |
353 | - decrement the device's usage counter | |
354 | ||
355 | int pm_runtime_put(struct device *dev); | |
15bcb91d AS |
356 | - decrement the device's usage counter; if the result is 0 then run |
357 | pm_request_idle(dev) and return its result | |
358 | ||
359 | int pm_runtime_put_autosuspend(struct device *dev); | |
360 | - decrement the device's usage counter; if the result is 0 then run | |
361 | pm_request_autosuspend(dev) and return its result | |
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362 | |
363 | int pm_runtime_put_sync(struct device *dev); | |
15bcb91d AS |
364 | - decrement the device's usage counter; if the result is 0 then run |
365 | pm_runtime_idle(dev) and return its result | |
366 | ||
c7b61de5 AS |
367 | int pm_runtime_put_sync_suspend(struct device *dev); |
368 | - decrement the device's usage counter; if the result is 0 then run | |
369 | pm_runtime_suspend(dev) and return its result | |
370 | ||
15bcb91d AS |
371 | int pm_runtime_put_sync_autosuspend(struct device *dev); |
372 | - decrement the device's usage counter; if the result is 0 then run | |
373 | pm_runtime_autosuspend(dev) and return its result | |
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374 | |
375 | void pm_runtime_enable(struct device *dev); | |
e358bad7 | 376 | - decrement the device's 'power.disable_depth' field; if that field is equal |
62052ab1 | 377 | to zero, the runtime PM helper functions can execute subsystem-level |
e358bad7 | 378 | callbacks described in Section 2 for the device |
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379 | |
380 | int pm_runtime_disable(struct device *dev); | |
e358bad7 RW |
381 | - increment the device's 'power.disable_depth' field (if the value of that |
382 | field was previously zero, this prevents subsystem-level runtime PM | |
383 | callbacks from being run for the device), make sure that all of the pending | |
62052ab1 | 384 | runtime PM operations on the device are either completed or canceled; |
a6ab7aa9 RW |
385 | returns 1 if there was a resume request pending and it was necessary to |
386 | execute the subsystem-level resume callback for the device to satisfy that | |
387 | request, otherwise 0 is returned | |
5e928f77 | 388 | |
e358bad7 RW |
389 | int pm_runtime_barrier(struct device *dev); |
390 | - check if there's a resume request pending for the device and resume it | |
391 | (synchronously) in that case, cancel any other pending runtime PM requests | |
392 | regarding it and wait for all runtime PM operations on it in progress to | |
393 | complete; returns 1 if there was a resume request pending and it was | |
394 | necessary to execute the subsystem-level resume callback for the device to | |
395 | satisfy that request, otherwise 0 is returned | |
396 | ||
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397 | void pm_suspend_ignore_children(struct device *dev, bool enable); |
398 | - set/unset the power.ignore_children flag of the device | |
399 | ||
400 | int pm_runtime_set_active(struct device *dev); | |
62052ab1 | 401 | - clear the device's 'power.runtime_error' flag, set the device's runtime |
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402 | PM status to 'active' and update its parent's counter of 'active' |
403 | children as appropriate (it is only valid to use this function if | |
404 | 'power.runtime_error' is set or 'power.disable_depth' is greater than | |
405 | zero); it will fail and return error code if the device has a parent | |
406 | which is not active and the 'power.ignore_children' flag of which is unset | |
407 | ||
408 | void pm_runtime_set_suspended(struct device *dev); | |
62052ab1 | 409 | - clear the device's 'power.runtime_error' flag, set the device's runtime |
5e928f77 RW |
410 | PM status to 'suspended' and update its parent's counter of 'active' |
411 | children as appropriate (it is only valid to use this function if | |
412 | 'power.runtime_error' is set or 'power.disable_depth' is greater than | |
413 | zero) | |
414 | ||
d690b2cd | 415 | bool pm_runtime_suspended(struct device *dev); |
f08f5a0a RW |
416 | - return true if the device's runtime PM status is 'suspended' and its |
417 | 'power.disable_depth' field is equal to zero, or false otherwise | |
d690b2cd | 418 | |
f3393b62 KH |
419 | bool pm_runtime_status_suspended(struct device *dev); |
420 | - return true if the device's runtime PM status is 'suspended' | |
421 | ||
87d1b3e6 RW |
422 | void pm_runtime_allow(struct device *dev); |
423 | - set the power.runtime_auto flag for the device and decrease its usage | |
424 | counter (used by the /sys/devices/.../power/control interface to | |
425 | effectively allow the device to be power managed at run time) | |
426 | ||
427 | void pm_runtime_forbid(struct device *dev); | |
428 | - unset the power.runtime_auto flag for the device and increase its usage | |
429 | counter (used by the /sys/devices/.../power/control interface to | |
430 | effectively prevent the device from being power managed at run time) | |
431 | ||
7490e442 | 432 | void pm_runtime_no_callbacks(struct device *dev); |
62052ab1 | 433 | - set the power.no_callbacks flag for the device and remove the runtime |
7490e442 AS |
434 | PM attributes from /sys/devices/.../power (or prevent them from being |
435 | added when the device is registered) | |
436 | ||
c7b61de5 AS |
437 | void pm_runtime_irq_safe(struct device *dev); |
438 | - set the power.irq_safe flag for the device, causing the runtime-PM | |
64584eb9 | 439 | callbacks to be invoked with interrupts off |
c7b61de5 | 440 | |
15bcb91d AS |
441 | void pm_runtime_mark_last_busy(struct device *dev); |
442 | - set the power.last_busy field to the current time | |
443 | ||
444 | void pm_runtime_use_autosuspend(struct device *dev); | |
445 | - set the power.use_autosuspend flag, enabling autosuspend delays | |
446 | ||
447 | void pm_runtime_dont_use_autosuspend(struct device *dev); | |
448 | - clear the power.use_autosuspend flag, disabling autosuspend delays | |
449 | ||
450 | void pm_runtime_set_autosuspend_delay(struct device *dev, int delay); | |
451 | - set the power.autosuspend_delay value to 'delay' (expressed in | |
62052ab1 | 452 | milliseconds); if 'delay' is negative then runtime suspends are |
15bcb91d AS |
453 | prevented |
454 | ||
455 | unsigned long pm_runtime_autosuspend_expiration(struct device *dev); | |
456 | - calculate the time when the current autosuspend delay period will expire, | |
457 | based on power.last_busy and power.autosuspend_delay; if the delay time | |
458 | is 1000 ms or larger then the expiration time is rounded up to the | |
459 | nearest second; returns 0 if the delay period has already expired or | |
460 | power.use_autosuspend isn't set, otherwise returns the expiration time | |
461 | in jiffies | |
462 | ||
5e928f77 RW |
463 | It is safe to execute the following helper functions from interrupt context: |
464 | ||
465 | pm_request_idle() | |
15bcb91d | 466 | pm_request_autosuspend() |
5e928f77 RW |
467 | pm_schedule_suspend() |
468 | pm_request_resume() | |
469 | pm_runtime_get_noresume() | |
470 | pm_runtime_get() | |
471 | pm_runtime_put_noidle() | |
472 | pm_runtime_put() | |
15bcb91d AS |
473 | pm_runtime_put_autosuspend() |
474 | pm_runtime_enable() | |
5e928f77 RW |
475 | pm_suspend_ignore_children() |
476 | pm_runtime_set_active() | |
477 | pm_runtime_set_suspended() | |
15bcb91d AS |
478 | pm_runtime_suspended() |
479 | pm_runtime_mark_last_busy() | |
480 | pm_runtime_autosuspend_expiration() | |
5e928f77 | 481 | |
c7b61de5 AS |
482 | If pm_runtime_irq_safe() has been called for a device then the following helper |
483 | functions may also be used in interrupt context: | |
484 | ||
2e6ba515 | 485 | pm_runtime_idle() |
c7b61de5 AS |
486 | pm_runtime_suspend() |
487 | pm_runtime_autosuspend() | |
488 | pm_runtime_resume() | |
489 | pm_runtime_get_sync() | |
02b26774 | 490 | pm_runtime_put_sync() |
c7b61de5 | 491 | pm_runtime_put_sync_suspend() |
311aab73 | 492 | pm_runtime_put_sync_autosuspend() |
c7b61de5 | 493 | |
62052ab1 | 494 | 5. Runtime PM Initialization, Device Probing and Removal |
5e928f77 | 495 | |
62052ab1 RW |
496 | Initially, the runtime PM is disabled for all devices, which means that the |
497 | majority of the runtime PM helper funtions described in Section 4 will return | |
5e928f77 RW |
498 | -EAGAIN until pm_runtime_enable() is called for the device. |
499 | ||
62052ab1 | 500 | In addition to that, the initial runtime PM status of all devices is |
5e928f77 RW |
501 | 'suspended', but it need not reflect the actual physical state of the device. |
502 | Thus, if the device is initially active (i.e. it is able to process I/O), its | |
62052ab1 | 503 | runtime PM status must be changed to 'active', with the help of |
5e928f77 RW |
504 | pm_runtime_set_active(), before pm_runtime_enable() is called for the device. |
505 | ||
62052ab1 | 506 | However, if the device has a parent and the parent's runtime PM is enabled, |
5e928f77 RW |
507 | calling pm_runtime_set_active() for the device will affect the parent, unless |
508 | the parent's 'power.ignore_children' flag is set. Namely, in that case the | |
509 | parent won't be able to suspend at run time, using the PM core's helper | |
510 | functions, as long as the child's status is 'active', even if the child's | |
62052ab1 | 511 | runtime PM is still disabled (i.e. pm_runtime_enable() hasn't been called for |
5e928f77 RW |
512 | the child yet or pm_runtime_disable() has been called for it). For this reason, |
513 | once pm_runtime_set_active() has been called for the device, pm_runtime_enable() | |
62052ab1 | 514 | should be called for it too as soon as reasonably possible or its runtime PM |
5e928f77 RW |
515 | status should be changed back to 'suspended' with the help of |
516 | pm_runtime_set_suspended(). | |
517 | ||
62052ab1 | 518 | If the default initial runtime PM status of the device (i.e. 'suspended') |
5e928f77 RW |
519 | reflects the actual state of the device, its bus type's or its driver's |
520 | ->probe() callback will likely need to wake it up using one of the PM core's | |
521 | helper functions described in Section 4. In that case, pm_runtime_resume() | |
62052ab1 | 522 | should be used. Of course, for this purpose the device's runtime PM has to be |
5e928f77 RW |
523 | enabled earlier by calling pm_runtime_enable(). |
524 | ||
f5da24db | 525 | If the device bus type's or driver's ->probe() callback runs |
5e928f77 RW |
526 | pm_runtime_suspend() or pm_runtime_idle() or their asynchronous counterparts, |
527 | they will fail returning -EAGAIN, because the device's usage counter is | |
f5da24db RW |
528 | incremented by the driver core before executing ->probe(). Still, it may be |
529 | desirable to suspend the device as soon as ->probe() has finished, so the driver | |
530 | core uses pm_runtime_put_sync() to invoke the subsystem-level idle callback for | |
531 | the device at that time. | |
532 | ||
533 | Moreover, the driver core prevents runtime PM callbacks from racing with the bus | |
534 | notifier callback in __device_release_driver(), which is necessary, because the | |
535 | notifier is used by some subsystems to carry out operations affecting the | |
536 | runtime PM functionality. It does so by calling pm_runtime_get_sync() before | |
537 | driver_sysfs_remove() and the BUS_NOTIFY_UNBIND_DRIVER notifications. This | |
538 | resumes the device if it's in the suspended state and prevents it from | |
539 | being suspended again while those routines are being executed. | |
540 | ||
541 | To allow bus types and drivers to put devices into the suspended state by | |
542 | calling pm_runtime_suspend() from their ->remove() routines, the driver core | |
543 | executes pm_runtime_put_sync() after running the BUS_NOTIFY_UNBIND_DRIVER | |
544 | notifications in __device_release_driver(). This requires bus types and | |
545 | drivers to make their ->remove() callbacks avoid races with runtime PM directly, | |
546 | but also it allows of more flexibility in the handling of devices during the | |
547 | removal of their drivers. | |
f1212ae1 | 548 | |
87d1b3e6 RW |
549 | The user space can effectively disallow the driver of the device to power manage |
550 | it at run time by changing the value of its /sys/devices/.../power/control | |
551 | attribute to "on", which causes pm_runtime_forbid() to be called. In principle, | |
552 | this mechanism may also be used by the driver to effectively turn off the | |
62052ab1 RW |
553 | runtime power management of the device until the user space turns it on. |
554 | Namely, during the initialization the driver can make sure that the runtime PM | |
87d1b3e6 RW |
555 | status of the device is 'active' and call pm_runtime_forbid(). It should be |
556 | noted, however, that if the user space has already intentionally changed the | |
557 | value of /sys/devices/.../power/control to "auto" to allow the driver to power | |
558 | manage the device at run time, the driver may confuse it by using | |
559 | pm_runtime_forbid() this way. | |
560 | ||
62052ab1 | 561 | 6. Runtime PM and System Sleep |
f1212ae1 | 562 | |
62052ab1 | 563 | Runtime PM and system sleep (i.e., system suspend and hibernation, also known |
f1212ae1 AS |
564 | as suspend-to-RAM and suspend-to-disk) interact with each other in a couple of |
565 | ways. If a device is active when a system sleep starts, everything is | |
566 | straightforward. But what should happen if the device is already suspended? | |
567 | ||
62052ab1 RW |
568 | The device may have different wake-up settings for runtime PM and system sleep. |
569 | For example, remote wake-up may be enabled for runtime suspend but disallowed | |
f1212ae1 AS |
570 | for system sleep (device_may_wakeup(dev) returns 'false'). When this happens, |
571 | the subsystem-level system suspend callback is responsible for changing the | |
572 | device's wake-up setting (it may leave that to the device driver's system | |
573 | suspend routine). It may be necessary to resume the device and suspend it again | |
574 | in order to do so. The same is true if the driver uses different power levels | |
62052ab1 | 575 | or other settings for runtime suspend and system sleep. |
f1212ae1 | 576 | |
455716e9 RW |
577 | During system resume, the simplest approach is to bring all devices back to full |
578 | power, even if they had been suspended before the system suspend began. There | |
579 | are several reasons for this, including: | |
f1212ae1 AS |
580 | |
581 | * The device might need to switch power levels, wake-up settings, etc. | |
582 | ||
583 | * Remote wake-up events might have been lost by the firmware. | |
584 | ||
585 | * The device's children may need the device to be at full power in order | |
586 | to resume themselves. | |
587 | ||
588 | * The driver's idea of the device state may not agree with the device's | |
589 | physical state. This can happen during resume from hibernation. | |
590 | ||
591 | * The device might need to be reset. | |
592 | ||
593 | * Even though the device was suspended, if its usage counter was > 0 then most | |
62052ab1 | 594 | likely it would need a runtime resume in the near future anyway. |
f1212ae1 | 595 | |
455716e9 | 596 | If the device had been suspended before the system suspend began and it's |
62052ab1 | 597 | brought back to full power during resume, then its runtime PM status will have |
455716e9 RW |
598 | to be updated to reflect the actual post-system sleep status. The way to do |
599 | this is: | |
f1212ae1 AS |
600 | |
601 | pm_runtime_disable(dev); | |
602 | pm_runtime_set_active(dev); | |
603 | pm_runtime_enable(dev); | |
604 | ||
62052ab1 | 605 | The PM core always increments the runtime usage counter before calling the |
1e2ef05b | 606 | ->suspend() callback and decrements it after calling the ->resume() callback. |
62052ab1 | 607 | Hence disabling runtime PM temporarily like this will not cause any runtime |
1e2ef05b RW |
608 | suspend attempts to be permanently lost. If the usage count goes to zero |
609 | following the return of the ->resume() callback, the ->runtime_idle() callback | |
610 | will be invoked as usual. | |
611 | ||
455716e9 RW |
612 | On some systems, however, system sleep is not entered through a global firmware |
613 | or hardware operation. Instead, all hardware components are put into low-power | |
614 | states directly by the kernel in a coordinated way. Then, the system sleep | |
615 | state effectively follows from the states the hardware components end up in | |
616 | and the system is woken up from that state by a hardware interrupt or a similar | |
617 | mechanism entirely under the kernel's control. As a result, the kernel never | |
618 | gives control away and the states of all devices during resume are precisely | |
619 | known to it. If that is the case and none of the situations listed above takes | |
620 | place (in particular, if the system is not waking up from hibernation), it may | |
621 | be more efficient to leave the devices that had been suspended before the system | |
622 | suspend began in the suspended state. | |
623 | ||
1e2ef05b RW |
624 | The PM core does its best to reduce the probability of race conditions between |
625 | the runtime PM and system suspend/resume (and hibernation) callbacks by carrying | |
626 | out the following operations: | |
627 | ||
628 | * During system suspend it calls pm_runtime_get_noresume() and | |
629 | pm_runtime_barrier() for every device right before executing the | |
630 | subsystem-level .suspend() callback for it. In addition to that it calls | |
631 | pm_runtime_disable() for every device right after executing the | |
632 | subsystem-level .suspend() callback for it. | |
633 | ||
634 | * During system resume it calls pm_runtime_enable() and pm_runtime_put_sync() | |
635 | for every device right before and right after executing the subsystem-level | |
636 | .resume() callback for it, respectively. | |
637 | ||
d690b2cd RW |
638 | 7. Generic subsystem callbacks |
639 | ||
640 | Subsystems may wish to conserve code space by using the set of generic power | |
641 | management callbacks provided by the PM core, defined in | |
642 | driver/base/power/generic_ops.c: | |
643 | ||
644 | int pm_generic_runtime_idle(struct device *dev); | |
645 | - invoke the ->runtime_idle() callback provided by the driver of this | |
646 | device, if defined, and call pm_runtime_suspend() for this device if the | |
647 | return value is 0 or the callback is not defined | |
648 | ||
649 | int pm_generic_runtime_suspend(struct device *dev); | |
650 | - invoke the ->runtime_suspend() callback provided by the driver of this | |
651 | device and return its result, or return -EINVAL if not defined | |
652 | ||
653 | int pm_generic_runtime_resume(struct device *dev); | |
654 | - invoke the ->runtime_resume() callback provided by the driver of this | |
655 | device and return its result, or return -EINVAL if not defined | |
656 | ||
657 | int pm_generic_suspend(struct device *dev); | |
658 | - if the device has not been suspended at run time, invoke the ->suspend() | |
659 | callback provided by its driver and return its result, or return 0 if not | |
660 | defined | |
661 | ||
e5291928 RW |
662 | int pm_generic_suspend_noirq(struct device *dev); |
663 | - if pm_runtime_suspended(dev) returns "false", invoke the ->suspend_noirq() | |
664 | callback provided by the device's driver and return its result, or return | |
665 | 0 if not defined | |
666 | ||
d690b2cd RW |
667 | int pm_generic_resume(struct device *dev); |
668 | - invoke the ->resume() callback provided by the driver of this device and, | |
669 | if successful, change the device's runtime PM status to 'active' | |
670 | ||
e5291928 RW |
671 | int pm_generic_resume_noirq(struct device *dev); |
672 | - invoke the ->resume_noirq() callback provided by the driver of this device | |
673 | ||
d690b2cd RW |
674 | int pm_generic_freeze(struct device *dev); |
675 | - if the device has not been suspended at run time, invoke the ->freeze() | |
676 | callback provided by its driver and return its result, or return 0 if not | |
677 | defined | |
678 | ||
e5291928 RW |
679 | int pm_generic_freeze_noirq(struct device *dev); |
680 | - if pm_runtime_suspended(dev) returns "false", invoke the ->freeze_noirq() | |
681 | callback provided by the device's driver and return its result, or return | |
682 | 0 if not defined | |
683 | ||
d690b2cd RW |
684 | int pm_generic_thaw(struct device *dev); |
685 | - if the device has not been suspended at run time, invoke the ->thaw() | |
686 | callback provided by its driver and return its result, or return 0 if not | |
687 | defined | |
688 | ||
e5291928 RW |
689 | int pm_generic_thaw_noirq(struct device *dev); |
690 | - if pm_runtime_suspended(dev) returns "false", invoke the ->thaw_noirq() | |
691 | callback provided by the device's driver and return its result, or return | |
692 | 0 if not defined | |
693 | ||
d690b2cd RW |
694 | int pm_generic_poweroff(struct device *dev); |
695 | - if the device has not been suspended at run time, invoke the ->poweroff() | |
696 | callback provided by its driver and return its result, or return 0 if not | |
697 | defined | |
698 | ||
e5291928 RW |
699 | int pm_generic_poweroff_noirq(struct device *dev); |
700 | - if pm_runtime_suspended(dev) returns "false", run the ->poweroff_noirq() | |
701 | callback provided by the device's driver and return its result, or return | |
702 | 0 if not defined | |
703 | ||
d690b2cd RW |
704 | int pm_generic_restore(struct device *dev); |
705 | - invoke the ->restore() callback provided by the driver of this device and, | |
706 | if successful, change the device's runtime PM status to 'active' | |
707 | ||
e5291928 RW |
708 | int pm_generic_restore_noirq(struct device *dev); |
709 | - invoke the ->restore_noirq() callback provided by the device's driver | |
710 | ||
d690b2cd | 711 | These functions can be assigned to the ->runtime_idle(), ->runtime_suspend(), |
e5291928 RW |
712 | ->runtime_resume(), ->suspend(), ->suspend_noirq(), ->resume(), |
713 | ->resume_noirq(), ->freeze(), ->freeze_noirq(), ->thaw(), ->thaw_noirq(), | |
714 | ->poweroff(), ->poweroff_noirq(), ->restore(), ->restore_noirq() callback | |
715 | pointers in the subsystem-level dev_pm_ops structures. | |
d690b2cd RW |
716 | |
717 | If a subsystem wishes to use all of them at the same time, it can simply assign | |
718 | the GENERIC_SUBSYS_PM_OPS macro, defined in include/linux/pm.h, to its | |
719 | dev_pm_ops structure pointer. | |
720 | ||
721 | Device drivers that wish to use the same function as a system suspend, freeze, | |
62052ab1 RW |
722 | poweroff and runtime suspend callback, and similarly for system resume, thaw, |
723 | restore, and runtime resume, can achieve this with the help of the | |
d690b2cd RW |
724 | UNIVERSAL_DEV_PM_OPS macro defined in include/linux/pm.h (possibly setting its |
725 | last argument to NULL). | |
7490e442 AS |
726 | |
727 | 8. "No-Callback" Devices | |
728 | ||
729 | Some "devices" are only logical sub-devices of their parent and cannot be | |
730 | power-managed on their own. (The prototype example is a USB interface. Entire | |
731 | USB devices can go into low-power mode or send wake-up requests, but neither is | |
732 | possible for individual interfaces.) The drivers for these devices have no | |
62052ab1 | 733 | need of runtime PM callbacks; if the callbacks did exist, ->runtime_suspend() |
7490e442 AS |
734 | and ->runtime_resume() would always return 0 without doing anything else and |
735 | ->runtime_idle() would always call pm_runtime_suspend(). | |
736 | ||
737 | Subsystems can tell the PM core about these devices by calling | |
738 | pm_runtime_no_callbacks(). This should be done after the device structure is | |
739 | initialized and before it is registered (although after device registration is | |
740 | also okay). The routine will set the device's power.no_callbacks flag and | |
62052ab1 | 741 | prevent the non-debugging runtime PM sysfs attributes from being created. |
7490e442 AS |
742 | |
743 | When power.no_callbacks is set, the PM core will not invoke the | |
744 | ->runtime_idle(), ->runtime_suspend(), or ->runtime_resume() callbacks. | |
745 | Instead it will assume that suspends and resumes always succeed and that idle | |
746 | devices should be suspended. | |
747 | ||
748 | As a consequence, the PM core will never directly inform the device's subsystem | |
62052ab1 | 749 | or driver about runtime power changes. Instead, the driver for the device's |
7490e442 AS |
750 | parent must take responsibility for telling the device's driver when the |
751 | parent's power state changes. | |
15bcb91d AS |
752 | |
753 | 9. Autosuspend, or automatically-delayed suspends | |
754 | ||
755 | Changing a device's power state isn't free; it requires both time and energy. | |
756 | A device should be put in a low-power state only when there's some reason to | |
757 | think it will remain in that state for a substantial time. A common heuristic | |
758 | says that a device which hasn't been used for a while is liable to remain | |
759 | unused; following this advice, drivers should not allow devices to be suspended | |
62052ab1 | 760 | at runtime until they have been inactive for some minimum period. Even when |
15bcb91d AS |
761 | the heuristic ends up being non-optimal, it will still prevent devices from |
762 | "bouncing" too rapidly between low-power and full-power states. | |
763 | ||
764 | The term "autosuspend" is an historical remnant. It doesn't mean that the | |
765 | device is automatically suspended (the subsystem or driver still has to call | |
62052ab1 | 766 | the appropriate PM routines); rather it means that runtime suspends will |
15bcb91d AS |
767 | automatically be delayed until the desired period of inactivity has elapsed. |
768 | ||
769 | Inactivity is determined based on the power.last_busy field. Drivers should | |
770 | call pm_runtime_mark_last_busy() to update this field after carrying out I/O, | |
771 | typically just before calling pm_runtime_put_autosuspend(). The desired length | |
772 | of the inactivity period is a matter of policy. Subsystems can set this length | |
773 | initially by calling pm_runtime_set_autosuspend_delay(), but after device | |
774 | registration the length should be controlled by user space, using the | |
775 | /sys/devices/.../power/autosuspend_delay_ms attribute. | |
776 | ||
777 | In order to use autosuspend, subsystems or drivers must call | |
778 | pm_runtime_use_autosuspend() (preferably before registering the device), and | |
779 | thereafter they should use the various *_autosuspend() helper functions instead | |
780 | of the non-autosuspend counterparts: | |
781 | ||
782 | Instead of: pm_runtime_suspend use: pm_runtime_autosuspend; | |
783 | Instead of: pm_schedule_suspend use: pm_request_autosuspend; | |
784 | Instead of: pm_runtime_put use: pm_runtime_put_autosuspend; | |
785 | Instead of: pm_runtime_put_sync use: pm_runtime_put_sync_autosuspend. | |
786 | ||
787 | Drivers may also continue to use the non-autosuspend helper functions; they | |
788 | will behave normally, not taking the autosuspend delay into account. | |
789 | Similarly, if the power.use_autosuspend field isn't set then the autosuspend | |
790 | helper functions will behave just like the non-autosuspend counterparts. | |
791 | ||
792 | The implementation is well suited for asynchronous use in interrupt contexts. | |
793 | However such use inevitably involves races, because the PM core can't | |
794 | synchronize ->runtime_suspend() callbacks with the arrival of I/O requests. | |
795 | This synchronization must be handled by the driver, using its private lock. | |
796 | Here is a schematic pseudo-code example: | |
797 | ||
798 | foo_read_or_write(struct foo_priv *foo, void *data) | |
799 | { | |
800 | lock(&foo->private_lock); | |
801 | add_request_to_io_queue(foo, data); | |
802 | if (foo->num_pending_requests++ == 0) | |
803 | pm_runtime_get(&foo->dev); | |
804 | if (!foo->is_suspended) | |
805 | foo_process_next_request(foo); | |
806 | unlock(&foo->private_lock); | |
807 | } | |
808 | ||
809 | foo_io_completion(struct foo_priv *foo, void *req) | |
810 | { | |
811 | lock(&foo->private_lock); | |
812 | if (--foo->num_pending_requests == 0) { | |
813 | pm_runtime_mark_last_busy(&foo->dev); | |
814 | pm_runtime_put_autosuspend(&foo->dev); | |
815 | } else { | |
816 | foo_process_next_request(foo); | |
817 | } | |
818 | unlock(&foo->private_lock); | |
819 | /* Send req result back to the user ... */ | |
820 | } | |
821 | ||
822 | int foo_runtime_suspend(struct device *dev) | |
823 | { | |
824 | struct foo_priv foo = container_of(dev, ...); | |
825 | int ret = 0; | |
826 | ||
827 | lock(&foo->private_lock); | |
828 | if (foo->num_pending_requests > 0) { | |
829 | ret = -EBUSY; | |
830 | } else { | |
831 | /* ... suspend the device ... */ | |
832 | foo->is_suspended = 1; | |
833 | } | |
834 | unlock(&foo->private_lock); | |
835 | return ret; | |
836 | } | |
837 | ||
838 | int foo_runtime_resume(struct device *dev) | |
839 | { | |
840 | struct foo_priv foo = container_of(dev, ...); | |
841 | ||
842 | lock(&foo->private_lock); | |
843 | /* ... resume the device ... */ | |
844 | foo->is_suspended = 0; | |
845 | pm_runtime_mark_last_busy(&foo->dev); | |
846 | if (foo->num_pending_requests > 0) | |
847 | foo_process_requests(foo); | |
848 | unlock(&foo->private_lock); | |
849 | return 0; | |
850 | } | |
851 | ||
852 | The important point is that after foo_io_completion() asks for an autosuspend, | |
853 | the foo_runtime_suspend() callback may race with foo_read_or_write(). | |
854 | Therefore foo_runtime_suspend() has to check whether there are any pending I/O | |
855 | requests (while holding the private lock) before allowing the suspend to | |
856 | proceed. | |
857 | ||
858 | In addition, the power.autosuspend_delay field can be changed by user space at | |
859 | any time. If a driver cares about this, it can call | |
860 | pm_runtime_autosuspend_expiration() from within the ->runtime_suspend() | |
861 | callback while holding its private lock. If the function returns a nonzero | |
862 | value then the delay has not yet expired and the callback should return | |
863 | -EAGAIN. |