diff options
Diffstat (limited to 'Documentation/power')
-rw-r--r-- | Documentation/power/runtime_pm.txt | 130 |
1 files changed, 65 insertions, 65 deletions
diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt index ca15bbbe1891..40e47c75f064 100644 --- a/Documentation/power/runtime_pm.txt +++ b/Documentation/power/runtime_pm.txt | |||
@@ -1,39 +1,39 @@ | |||
1 | Run-time Power Management Framework for I/O Devices | 1 | Runtime Power Management Framework for I/O Devices |
2 | 2 | ||
3 | (C) 2009-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc. | 3 | (C) 2009-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc. |
4 | (C) 2010 Alan Stern <stern@rowland.harvard.edu> | 4 | (C) 2010 Alan Stern <stern@rowland.harvard.edu> |
5 | 5 | ||
6 | 1. Introduction | 6 | 1. Introduction |
7 | 7 | ||
8 | Support for run-time power management (run-time PM) of I/O devices is provided | 8 | Support for runtime power management (runtime PM) of I/O devices is provided |
9 | at the power management core (PM core) level by means of: | 9 | at the power management core (PM core) level by means of: |
10 | 10 | ||
11 | * The power management workqueue pm_wq in which bus types and device drivers can | 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 | 12 | put their PM-related work items. It is strongly recommended that pm_wq be |
13 | used for queuing all work items related to run-time PM, because this allows | 13 | used for queuing all work items related to runtime PM, because this allows |
14 | them to be synchronized with system-wide power transitions (suspend to RAM, | 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 | 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. | 16 | include/linux/pm_runtime.h and defined in kernel/power/main.c. |
17 | 17 | ||
18 | * A number of run-time PM fields in the 'power' member of 'struct device' (which | 18 | * A number of runtime PM fields in the 'power' member of 'struct device' (which |
19 | is of the type 'struct dev_pm_info', defined in include/linux/pm.h) that can | 19 | is of the type 'struct dev_pm_info', defined in include/linux/pm.h) that can |
20 | be used for synchronizing run-time PM operations with one another. | 20 | be used for synchronizing runtime PM operations with one another. |
21 | 21 | ||
22 | * Three device run-time PM callbacks in 'struct dev_pm_ops' (defined in | 22 | * Three device runtime PM callbacks in 'struct dev_pm_ops' (defined in |
23 | include/linux/pm.h). | 23 | include/linux/pm.h). |
24 | 24 | ||
25 | * A set of helper functions defined in drivers/base/power/runtime.c that can be | 25 | * A set of helper functions defined in drivers/base/power/runtime.c that can be |
26 | used for carrying out run-time PM operations in such a way that the | 26 | used for carrying out runtime PM operations in such a way that the |
27 | synchronization between them is taken care of by the PM core. Bus types and | 27 | synchronization between them is taken care of by the PM core. Bus types and |
28 | device drivers are encouraged to use these functions. | 28 | device drivers are encouraged to use these functions. |
29 | 29 | ||
30 | The run-time PM callbacks present in 'struct dev_pm_ops', the device run-time PM | 30 | The runtime PM callbacks present in 'struct dev_pm_ops', the device runtime PM |
31 | fields of 'struct dev_pm_info' and the core helper functions provided for | 31 | fields of 'struct dev_pm_info' and the core helper functions provided for |
32 | run-time PM are described below. | 32 | runtime PM are described below. |
33 | 33 | ||
34 | 2. Device Run-time PM Callbacks | 34 | 2. Device Runtime PM Callbacks |
35 | 35 | ||
36 | There are three device run-time PM callbacks defined in 'struct dev_pm_ops': | 36 | There are three device runtime PM callbacks defined in 'struct dev_pm_ops': |
37 | 37 | ||
38 | struct dev_pm_ops { | 38 | struct dev_pm_ops { |
39 | ... | 39 | ... |
@@ -72,11 +72,11 @@ knows what to do to handle the device). | |||
72 | not mean that the device has been put into a low power state. It is | 72 | not mean that the device has been put into a low power state. It is |
73 | supposed to mean, however, that the device will not process data and will | 73 | supposed to mean, however, that the device will not process data and will |
74 | not communicate with the CPU(s) and RAM until the subsystem-level resume | 74 | not communicate with the CPU(s) and RAM until the subsystem-level resume |
75 | callback is executed for it. The run-time PM status of a device after | 75 | callback is executed for it. The runtime PM status of a device after |
76 | successful execution of the subsystem-level suspend callback is 'suspended'. | 76 | successful execution of the subsystem-level suspend callback is 'suspended'. |
77 | 77 | ||
78 | * If the subsystem-level suspend callback returns -EBUSY or -EAGAIN, | 78 | * If the subsystem-level suspend callback returns -EBUSY or -EAGAIN, |
79 | the device's run-time PM status is 'active', which means that the device | 79 | the device's runtime PM status is 'active', which means that the device |
80 | _must_ be fully operational afterwards. | 80 | _must_ be fully operational afterwards. |
81 | 81 | ||
82 | * If the subsystem-level suspend callback returns an error code different | 82 | * If the subsystem-level suspend callback returns an error code different |
@@ -104,7 +104,7 @@ the device). | |||
104 | 104 | ||
105 | * Once the subsystem-level resume callback has completed successfully, the PM | 105 | * Once the subsystem-level resume callback has completed successfully, the PM |
106 | core regards the device as fully operational, which means that the device | 106 | core regards the device as fully operational, which means that the device |
107 | _must_ be able to complete I/O operations as needed. The run-time PM status | 107 | _must_ be able to complete I/O operations as needed. The runtime PM status |
108 | of the device is then 'active'. | 108 | of the device is then 'active'. |
109 | 109 | ||
110 | * If the subsystem-level resume callback returns an error code, the PM core | 110 | * If the subsystem-level resume callback returns an error code, the PM core |
@@ -130,7 +130,7 @@ device in that case. The value returned by this callback is ignored by the PM | |||
130 | core. | 130 | core. |
131 | 131 | ||
132 | The helper functions provided by the PM core, described in Section 4, guarantee | 132 | The helper functions provided by the PM core, described in Section 4, guarantee |
133 | that the following constraints are met with respect to the bus type's run-time | 133 | that the following constraints are met with respect to the bus type's runtime |
134 | PM callbacks: | 134 | PM callbacks: |
135 | 135 | ||
136 | (1) The callbacks are mutually exclusive (e.g. it is forbidden to execute | 136 | (1) The callbacks are mutually exclusive (e.g. it is forbidden to execute |
@@ -142,7 +142,7 @@ PM callbacks: | |||
142 | 142 | ||
143 | (2) ->runtime_idle() and ->runtime_suspend() can only be executed for 'active' | 143 | (2) ->runtime_idle() and ->runtime_suspend() can only be executed for 'active' |
144 | devices (i.e. the PM core will only execute ->runtime_idle() or | 144 | devices (i.e. the PM core will only execute ->runtime_idle() or |
145 | ->runtime_suspend() for the devices the run-time PM status of which is | 145 | ->runtime_suspend() for the devices the runtime PM status of which is |
146 | 'active'). | 146 | 'active'). |
147 | 147 | ||
148 | (3) ->runtime_idle() and ->runtime_suspend() can only be executed for a device | 148 | (3) ->runtime_idle() and ->runtime_suspend() can only be executed for a device |
@@ -151,7 +151,7 @@ PM callbacks: | |||
151 | flag of which is set. | 151 | flag of which is set. |
152 | 152 | ||
153 | (4) ->runtime_resume() can only be executed for 'suspended' devices (i.e. the | 153 | (4) ->runtime_resume() can only be executed for 'suspended' devices (i.e. the |
154 | PM core will only execute ->runtime_resume() for the devices the run-time | 154 | PM core will only execute ->runtime_resume() for the devices the runtime |
155 | PM status of which is 'suspended'). | 155 | PM status of which is 'suspended'). |
156 | 156 | ||
157 | Additionally, the helper functions provided by the PM core obey the following | 157 | Additionally, the helper functions provided by the PM core obey the following |
@@ -171,9 +171,9 @@ rules: | |||
171 | scheduled requests to execute the other callbacks for the same device, | 171 | scheduled requests to execute the other callbacks for the same device, |
172 | except for scheduled autosuspends. | 172 | except for scheduled autosuspends. |
173 | 173 | ||
174 | 3. Run-time PM Device Fields | 174 | 3. Runtime PM Device Fields |
175 | 175 | ||
176 | The following device run-time PM fields are present in 'struct dev_pm_info', as | 176 | The following device runtime PM fields are present in 'struct dev_pm_info', as |
177 | defined in include/linux/pm.h: | 177 | defined in include/linux/pm.h: |
178 | 178 | ||
179 | struct timer_list suspend_timer; | 179 | struct timer_list suspend_timer; |
@@ -205,7 +205,7 @@ defined in include/linux/pm.h: | |||
205 | 205 | ||
206 | unsigned int disable_depth; | 206 | unsigned int disable_depth; |
207 | - used for disabling the helper funcions (they work normally if this is | 207 | - used for disabling the helper funcions (they work normally if this is |
208 | equal to zero); the initial value of it is 1 (i.e. run-time PM is | 208 | equal to zero); the initial value of it is 1 (i.e. runtime PM is |
209 | initially disabled for all devices) | 209 | initially disabled for all devices) |
210 | 210 | ||
211 | unsigned int runtime_error; | 211 | unsigned int runtime_error; |
@@ -229,10 +229,10 @@ defined in include/linux/pm.h: | |||
229 | suspend to complete; means "start a resume as soon as you've suspended" | 229 | suspend to complete; means "start a resume as soon as you've suspended" |
230 | 230 | ||
231 | unsigned int run_wake; | 231 | unsigned int run_wake; |
232 | - set if the device is capable of generating run-time wake-up events | 232 | - set if the device is capable of generating runtime wake-up events |
233 | 233 | ||
234 | enum rpm_status runtime_status; | 234 | enum rpm_status runtime_status; |
235 | - the run-time PM status of the device; this field's initial value is | 235 | - the runtime PM status of the device; this field's initial value is |
236 | RPM_SUSPENDED, which means that each device is initially regarded by the | 236 | RPM_SUSPENDED, which means that each device is initially regarded by the |
237 | PM core as 'suspended', regardless of its real hardware status | 237 | PM core as 'suspended', regardless of its real hardware status |
238 | 238 | ||
@@ -243,7 +243,7 @@ defined in include/linux/pm.h: | |||
243 | and pm_runtime_forbid() helper functions | 243 | and pm_runtime_forbid() helper functions |
244 | 244 | ||
245 | unsigned int no_callbacks; | 245 | unsigned int no_callbacks; |
246 | - indicates that the device does not use the run-time PM callbacks (see | 246 | - indicates that the device does not use the runtime PM callbacks (see |
247 | Section 8); it may be modified only by the pm_runtime_no_callbacks() | 247 | Section 8); it may be modified only by the pm_runtime_no_callbacks() |
248 | helper function | 248 | helper function |
249 | 249 | ||
@@ -270,16 +270,16 @@ defined in include/linux/pm.h: | |||
270 | 270 | ||
271 | All of the above fields are members of the 'power' member of 'struct device'. | 271 | All of the above fields are members of the 'power' member of 'struct device'. |
272 | 272 | ||
273 | 4. Run-time PM Device Helper Functions | 273 | 4. Runtime PM Device Helper Functions |
274 | 274 | ||
275 | The following run-time PM helper functions are defined in | 275 | The following runtime PM helper functions are defined in |
276 | drivers/base/power/runtime.c and include/linux/pm_runtime.h: | 276 | drivers/base/power/runtime.c and include/linux/pm_runtime.h: |
277 | 277 | ||
278 | void pm_runtime_init(struct device *dev); | 278 | void pm_runtime_init(struct device *dev); |
279 | - initialize the device run-time PM fields in 'struct dev_pm_info' | 279 | - initialize the device runtime PM fields in 'struct dev_pm_info' |
280 | 280 | ||
281 | void pm_runtime_remove(struct device *dev); | 281 | void pm_runtime_remove(struct device *dev); |
282 | - make sure that the run-time PM of the device will be disabled after | 282 | - make sure that the runtime PM of the device will be disabled after |
283 | removing the device from device hierarchy | 283 | removing the device from device hierarchy |
284 | 284 | ||
285 | int pm_runtime_idle(struct device *dev); | 285 | int pm_runtime_idle(struct device *dev); |
@@ -289,7 +289,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: | |||
289 | 289 | ||
290 | int pm_runtime_suspend(struct device *dev); | 290 | int pm_runtime_suspend(struct device *dev); |
291 | - execute the subsystem-level suspend callback for the device; returns 0 on | 291 | - execute the subsystem-level suspend callback for the device; returns 0 on |
292 | success, 1 if the device's run-time PM status was already 'suspended', or | 292 | success, 1 if the device's runtime PM status was already 'suspended', or |
293 | error code on failure, where -EAGAIN or -EBUSY means it is safe to attempt | 293 | error code on failure, where -EAGAIN or -EBUSY means it is safe to attempt |
294 | to suspend the device again in future and -EACCES means that | 294 | to suspend the device again in future and -EACCES means that |
295 | 'power.disable_depth' is different from 0 | 295 | 'power.disable_depth' is different from 0 |
@@ -302,7 +302,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: | |||
302 | 302 | ||
303 | int pm_runtime_resume(struct device *dev); | 303 | int pm_runtime_resume(struct device *dev); |
304 | - execute the subsystem-level resume callback for the device; returns 0 on | 304 | - execute the subsystem-level resume callback for the device; returns 0 on |
305 | success, 1 if the device's run-time PM status was already 'active' or | 305 | success, 1 if the device's runtime PM status was already 'active' or |
306 | error code on failure, where -EAGAIN means it may be safe to attempt to | 306 | error code on failure, where -EAGAIN means it may be safe to attempt to |
307 | resume the device again in future, but 'power.runtime_error' should be | 307 | resume the device again in future, but 'power.runtime_error' should be |
308 | checked additionally, and -EACCES means that 'power.disable_depth' is | 308 | checked additionally, and -EACCES means that 'power.disable_depth' is |
@@ -323,7 +323,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: | |||
323 | device in future, where 'delay' is the time to wait before queuing up a | 323 | device in future, where 'delay' is the time to wait before queuing up a |
324 | suspend work item in pm_wq, in milliseconds (if 'delay' is zero, the work | 324 | suspend work item in pm_wq, in milliseconds (if 'delay' is zero, the work |
325 | item is queued up immediately); returns 0 on success, 1 if the device's PM | 325 | item is queued up immediately); returns 0 on success, 1 if the device's PM |
326 | run-time status was already 'suspended', or error code if the request | 326 | runtime status was already 'suspended', or error code if the request |
327 | hasn't been scheduled (or queued up if 'delay' is 0); if the execution of | 327 | hasn't been scheduled (or queued up if 'delay' is 0); if the execution of |
328 | ->runtime_suspend() is already scheduled and not yet expired, the new | 328 | ->runtime_suspend() is already scheduled and not yet expired, the new |
329 | value of 'delay' will be used as the time to wait | 329 | value of 'delay' will be used as the time to wait |
@@ -331,7 +331,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: | |||
331 | int pm_request_resume(struct device *dev); | 331 | int pm_request_resume(struct device *dev); |
332 | - submit a request to execute the subsystem-level resume callback for the | 332 | - submit a request to execute the subsystem-level resume callback for the |
333 | device (the request is represented by a work item in pm_wq); returns 0 on | 333 | device (the request is represented by a work item in pm_wq); returns 0 on |
334 | success, 1 if the device's run-time PM status was already 'active', or | 334 | success, 1 if the device's runtime PM status was already 'active', or |
335 | error code if the request hasn't been queued up | 335 | error code if the request hasn't been queued up |
336 | 336 | ||
337 | void pm_runtime_get_noresume(struct device *dev); | 337 | void pm_runtime_get_noresume(struct device *dev); |
@@ -370,14 +370,14 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: | |||
370 | 370 | ||
371 | void pm_runtime_enable(struct device *dev); | 371 | void pm_runtime_enable(struct device *dev); |
372 | - decrement the device's 'power.disable_depth' field; if that field is equal | 372 | - decrement the device's 'power.disable_depth' field; if that field is equal |
373 | to zero, the run-time PM helper functions can execute subsystem-level | 373 | to zero, the runtime PM helper functions can execute subsystem-level |
374 | callbacks described in Section 2 for the device | 374 | callbacks described in Section 2 for the device |
375 | 375 | ||
376 | int pm_runtime_disable(struct device *dev); | 376 | int pm_runtime_disable(struct device *dev); |
377 | - increment the device's 'power.disable_depth' field (if the value of that | 377 | - increment the device's 'power.disable_depth' field (if the value of that |
378 | field was previously zero, this prevents subsystem-level runtime PM | 378 | field was previously zero, this prevents subsystem-level runtime PM |
379 | callbacks from being run for the device), make sure that all of the pending | 379 | callbacks from being run for the device), make sure that all of the pending |
380 | run-time PM operations on the device are either completed or canceled; | 380 | runtime PM operations on the device are either completed or canceled; |
381 | returns 1 if there was a resume request pending and it was necessary to | 381 | returns 1 if there was a resume request pending and it was necessary to |
382 | execute the subsystem-level resume callback for the device to satisfy that | 382 | execute the subsystem-level resume callback for the device to satisfy that |
383 | request, otherwise 0 is returned | 383 | request, otherwise 0 is returned |
@@ -394,7 +394,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: | |||
394 | - set/unset the power.ignore_children flag of the device | 394 | - set/unset the power.ignore_children flag of the device |
395 | 395 | ||
396 | int pm_runtime_set_active(struct device *dev); | 396 | int pm_runtime_set_active(struct device *dev); |
397 | - clear the device's 'power.runtime_error' flag, set the device's run-time | 397 | - clear the device's 'power.runtime_error' flag, set the device's runtime |
398 | PM status to 'active' and update its parent's counter of 'active' | 398 | PM status to 'active' and update its parent's counter of 'active' |
399 | children as appropriate (it is only valid to use this function if | 399 | children as appropriate (it is only valid to use this function if |
400 | 'power.runtime_error' is set or 'power.disable_depth' is greater than | 400 | 'power.runtime_error' is set or 'power.disable_depth' is greater than |
@@ -402,7 +402,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: | |||
402 | which is not active and the 'power.ignore_children' flag of which is unset | 402 | which is not active and the 'power.ignore_children' flag of which is unset |
403 | 403 | ||
404 | void pm_runtime_set_suspended(struct device *dev); | 404 | void pm_runtime_set_suspended(struct device *dev); |
405 | - clear the device's 'power.runtime_error' flag, set the device's run-time | 405 | - clear the device's 'power.runtime_error' flag, set the device's runtime |
406 | PM status to 'suspended' and update its parent's counter of 'active' | 406 | PM status to 'suspended' and update its parent's counter of 'active' |
407 | children as appropriate (it is only valid to use this function if | 407 | children as appropriate (it is only valid to use this function if |
408 | 'power.runtime_error' is set or 'power.disable_depth' is greater than | 408 | 'power.runtime_error' is set or 'power.disable_depth' is greater than |
@@ -423,7 +423,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: | |||
423 | effectively prevent the device from being power managed at run time) | 423 | effectively prevent the device from being power managed at run time) |
424 | 424 | ||
425 | void pm_runtime_no_callbacks(struct device *dev); | 425 | void pm_runtime_no_callbacks(struct device *dev); |
426 | - set the power.no_callbacks flag for the device and remove the run-time | 426 | - set the power.no_callbacks flag for the device and remove the runtime |
427 | PM attributes from /sys/devices/.../power (or prevent them from being | 427 | PM attributes from /sys/devices/.../power (or prevent them from being |
428 | added when the device is registered) | 428 | added when the device is registered) |
429 | 429 | ||
@@ -443,7 +443,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: | |||
443 | 443 | ||
444 | void pm_runtime_set_autosuspend_delay(struct device *dev, int delay); | 444 | void pm_runtime_set_autosuspend_delay(struct device *dev, int delay); |
445 | - set the power.autosuspend_delay value to 'delay' (expressed in | 445 | - set the power.autosuspend_delay value to 'delay' (expressed in |
446 | milliseconds); if 'delay' is negative then run-time suspends are | 446 | milliseconds); if 'delay' is negative then runtime suspends are |
447 | prevented | 447 | prevented |
448 | 448 | ||
449 | unsigned long pm_runtime_autosuspend_expiration(struct device *dev); | 449 | unsigned long pm_runtime_autosuspend_expiration(struct device *dev); |
@@ -482,35 +482,35 @@ pm_runtime_resume() | |||
482 | pm_runtime_get_sync() | 482 | pm_runtime_get_sync() |
483 | pm_runtime_put_sync_suspend() | 483 | pm_runtime_put_sync_suspend() |
484 | 484 | ||
485 | 5. Run-time PM Initialization, Device Probing and Removal | 485 | 5. Runtime PM Initialization, Device Probing and Removal |
486 | 486 | ||
487 | Initially, the run-time PM is disabled for all devices, which means that the | 487 | Initially, the runtime PM is disabled for all devices, which means that the |
488 | majority of the run-time PM helper funtions described in Section 4 will return | 488 | majority of the runtime PM helper funtions described in Section 4 will return |
489 | -EAGAIN until pm_runtime_enable() is called for the device. | 489 | -EAGAIN until pm_runtime_enable() is called for the device. |
490 | 490 | ||
491 | In addition to that, the initial run-time PM status of all devices is | 491 | In addition to that, the initial runtime PM status of all devices is |
492 | 'suspended', but it need not reflect the actual physical state of the device. | 492 | 'suspended', but it need not reflect the actual physical state of the device. |
493 | Thus, if the device is initially active (i.e. it is able to process I/O), its | 493 | Thus, if the device is initially active (i.e. it is able to process I/O), its |
494 | run-time PM status must be changed to 'active', with the help of | 494 | runtime PM status must be changed to 'active', with the help of |
495 | pm_runtime_set_active(), before pm_runtime_enable() is called for the device. | 495 | pm_runtime_set_active(), before pm_runtime_enable() is called for the device. |
496 | 496 | ||
497 | However, if the device has a parent and the parent's run-time PM is enabled, | 497 | However, if the device has a parent and the parent's runtime PM is enabled, |
498 | calling pm_runtime_set_active() for the device will affect the parent, unless | 498 | calling pm_runtime_set_active() for the device will affect the parent, unless |
499 | the parent's 'power.ignore_children' flag is set. Namely, in that case the | 499 | the parent's 'power.ignore_children' flag is set. Namely, in that case the |
500 | parent won't be able to suspend at run time, using the PM core's helper | 500 | parent won't be able to suspend at run time, using the PM core's helper |
501 | functions, as long as the child's status is 'active', even if the child's | 501 | functions, as long as the child's status is 'active', even if the child's |
502 | run-time PM is still disabled (i.e. pm_runtime_enable() hasn't been called for | 502 | runtime PM is still disabled (i.e. pm_runtime_enable() hasn't been called for |
503 | the child yet or pm_runtime_disable() has been called for it). For this reason, | 503 | the child yet or pm_runtime_disable() has been called for it). For this reason, |
504 | once pm_runtime_set_active() has been called for the device, pm_runtime_enable() | 504 | once pm_runtime_set_active() has been called for the device, pm_runtime_enable() |
505 | should be called for it too as soon as reasonably possible or its run-time PM | 505 | should be called for it too as soon as reasonably possible or its runtime PM |
506 | status should be changed back to 'suspended' with the help of | 506 | status should be changed back to 'suspended' with the help of |
507 | pm_runtime_set_suspended(). | 507 | pm_runtime_set_suspended(). |
508 | 508 | ||
509 | If the default initial run-time PM status of the device (i.e. 'suspended') | 509 | If the default initial runtime PM status of the device (i.e. 'suspended') |
510 | reflects the actual state of the device, its bus type's or its driver's | 510 | reflects the actual state of the device, its bus type's or its driver's |
511 | ->probe() callback will likely need to wake it up using one of the PM core's | 511 | ->probe() callback will likely need to wake it up using one of the PM core's |
512 | helper functions described in Section 4. In that case, pm_runtime_resume() | 512 | helper functions described in Section 4. In that case, pm_runtime_resume() |
513 | should be used. Of course, for this purpose the device's run-time PM has to be | 513 | should be used. Of course, for this purpose the device's runtime PM has to be |
514 | enabled earlier by calling pm_runtime_enable(). | 514 | enabled earlier by calling pm_runtime_enable(). |
515 | 515 | ||
516 | If the device bus type's or driver's ->probe() callback runs | 516 | If the device bus type's or driver's ->probe() callback runs |
@@ -541,29 +541,29 @@ The user space can effectively disallow the driver of the device to power manage | |||
541 | it at run time by changing the value of its /sys/devices/.../power/control | 541 | it at run time by changing the value of its /sys/devices/.../power/control |
542 | attribute to "on", which causes pm_runtime_forbid() to be called. In principle, | 542 | attribute to "on", which causes pm_runtime_forbid() to be called. In principle, |
543 | this mechanism may also be used by the driver to effectively turn off the | 543 | this mechanism may also be used by the driver to effectively turn off the |
544 | run-time power management of the device until the user space turns it on. | 544 | runtime power management of the device until the user space turns it on. |
545 | Namely, during the initialization the driver can make sure that the run-time PM | 545 | Namely, during the initialization the driver can make sure that the runtime PM |
546 | status of the device is 'active' and call pm_runtime_forbid(). It should be | 546 | status of the device is 'active' and call pm_runtime_forbid(). It should be |
547 | noted, however, that if the user space has already intentionally changed the | 547 | noted, however, that if the user space has already intentionally changed the |
548 | value of /sys/devices/.../power/control to "auto" to allow the driver to power | 548 | value of /sys/devices/.../power/control to "auto" to allow the driver to power |
549 | manage the device at run time, the driver may confuse it by using | 549 | manage the device at run time, the driver may confuse it by using |
550 | pm_runtime_forbid() this way. | 550 | pm_runtime_forbid() this way. |
551 | 551 | ||
552 | 6. Run-time PM and System Sleep | 552 | 6. Runtime PM and System Sleep |
553 | 553 | ||
554 | Run-time PM and system sleep (i.e., system suspend and hibernation, also known | 554 | Runtime PM and system sleep (i.e., system suspend and hibernation, also known |
555 | as suspend-to-RAM and suspend-to-disk) interact with each other in a couple of | 555 | as suspend-to-RAM and suspend-to-disk) interact with each other in a couple of |
556 | ways. If a device is active when a system sleep starts, everything is | 556 | ways. If a device is active when a system sleep starts, everything is |
557 | straightforward. But what should happen if the device is already suspended? | 557 | straightforward. But what should happen if the device is already suspended? |
558 | 558 | ||
559 | The device may have different wake-up settings for run-time PM and system sleep. | 559 | The device may have different wake-up settings for runtime PM and system sleep. |
560 | For example, remote wake-up may be enabled for run-time suspend but disallowed | 560 | For example, remote wake-up may be enabled for runtime suspend but disallowed |
561 | for system sleep (device_may_wakeup(dev) returns 'false'). When this happens, | 561 | for system sleep (device_may_wakeup(dev) returns 'false'). When this happens, |
562 | the subsystem-level system suspend callback is responsible for changing the | 562 | the subsystem-level system suspend callback is responsible for changing the |
563 | device's wake-up setting (it may leave that to the device driver's system | 563 | device's wake-up setting (it may leave that to the device driver's system |
564 | suspend routine). It may be necessary to resume the device and suspend it again | 564 | suspend routine). It may be necessary to resume the device and suspend it again |
565 | in order to do so. The same is true if the driver uses different power levels | 565 | in order to do so. The same is true if the driver uses different power levels |
566 | or other settings for run-time suspend and system sleep. | 566 | or other settings for runtime suspend and system sleep. |
567 | 567 | ||
568 | During system resume, the simplest approach is to bring all devices back to full | 568 | During system resume, the simplest approach is to bring all devices back to full |
569 | power, even if they had been suspended before the system suspend began. There | 569 | power, even if they had been suspended before the system suspend began. There |
@@ -582,10 +582,10 @@ are several reasons for this, including: | |||
582 | * The device might need to be reset. | 582 | * The device might need to be reset. |
583 | 583 | ||
584 | * Even though the device was suspended, if its usage counter was > 0 then most | 584 | * Even though the device was suspended, if its usage counter was > 0 then most |
585 | likely it would need a run-time resume in the near future anyway. | 585 | likely it would need a runtime resume in the near future anyway. |
586 | 586 | ||
587 | If the device had been suspended before the system suspend began and it's | 587 | If the device had been suspended before the system suspend began and it's |
588 | brought back to full power during resume, then its run-time PM status will have | 588 | brought back to full power during resume, then its runtime PM status will have |
589 | to be updated to reflect the actual post-system sleep status. The way to do | 589 | to be updated to reflect the actual post-system sleep status. The way to do |
590 | this is: | 590 | this is: |
591 | 591 | ||
@@ -593,9 +593,9 @@ this is: | |||
593 | pm_runtime_set_active(dev); | 593 | pm_runtime_set_active(dev); |
594 | pm_runtime_enable(dev); | 594 | pm_runtime_enable(dev); |
595 | 595 | ||
596 | The PM core always increments the run-time usage counter before calling the | 596 | The PM core always increments the runtime usage counter before calling the |
597 | ->suspend() callback and decrements it after calling the ->resume() callback. | 597 | ->suspend() callback and decrements it after calling the ->resume() callback. |
598 | Hence disabling run-time PM temporarily like this will not cause any runtime | 598 | Hence disabling runtime PM temporarily like this will not cause any runtime |
599 | suspend attempts to be permanently lost. If the usage count goes to zero | 599 | suspend attempts to be permanently lost. If the usage count goes to zero |
600 | following the return of the ->resume() callback, the ->runtime_idle() callback | 600 | following the return of the ->resume() callback, the ->runtime_idle() callback |
601 | will be invoked as usual. | 601 | will be invoked as usual. |
@@ -710,8 +710,8 @@ the GENERIC_SUBSYS_PM_OPS macro, defined in include/linux/pm.h, to its | |||
710 | dev_pm_ops structure pointer. | 710 | dev_pm_ops structure pointer. |
711 | 711 | ||
712 | Device drivers that wish to use the same function as a system suspend, freeze, | 712 | Device drivers that wish to use the same function as a system suspend, freeze, |
713 | poweroff and run-time suspend callback, and similarly for system resume, thaw, | 713 | poweroff and runtime suspend callback, and similarly for system resume, thaw, |
714 | restore, and run-time resume, can achieve this with the help of the | 714 | restore, and runtime resume, can achieve this with the help of the |
715 | UNIVERSAL_DEV_PM_OPS macro defined in include/linux/pm.h (possibly setting its | 715 | UNIVERSAL_DEV_PM_OPS macro defined in include/linux/pm.h (possibly setting its |
716 | last argument to NULL). | 716 | last argument to NULL). |
717 | 717 | ||
@@ -721,7 +721,7 @@ Some "devices" are only logical sub-devices of their parent and cannot be | |||
721 | power-managed on their own. (The prototype example is a USB interface. Entire | 721 | power-managed on their own. (The prototype example is a USB interface. Entire |
722 | USB devices can go into low-power mode or send wake-up requests, but neither is | 722 | USB devices can go into low-power mode or send wake-up requests, but neither is |
723 | possible for individual interfaces.) The drivers for these devices have no | 723 | possible for individual interfaces.) The drivers for these devices have no |
724 | need of run-time PM callbacks; if the callbacks did exist, ->runtime_suspend() | 724 | need of runtime PM callbacks; if the callbacks did exist, ->runtime_suspend() |
725 | and ->runtime_resume() would always return 0 without doing anything else and | 725 | and ->runtime_resume() would always return 0 without doing anything else and |
726 | ->runtime_idle() would always call pm_runtime_suspend(). | 726 | ->runtime_idle() would always call pm_runtime_suspend(). |
727 | 727 | ||
@@ -729,7 +729,7 @@ Subsystems can tell the PM core about these devices by calling | |||
729 | pm_runtime_no_callbacks(). This should be done after the device structure is | 729 | pm_runtime_no_callbacks(). This should be done after the device structure is |
730 | initialized and before it is registered (although after device registration is | 730 | initialized and before it is registered (although after device registration is |
731 | also okay). The routine will set the device's power.no_callbacks flag and | 731 | also okay). The routine will set the device's power.no_callbacks flag and |
732 | prevent the non-debugging run-time PM sysfs attributes from being created. | 732 | prevent the non-debugging runtime PM sysfs attributes from being created. |
733 | 733 | ||
734 | When power.no_callbacks is set, the PM core will not invoke the | 734 | When power.no_callbacks is set, the PM core will not invoke the |
735 | ->runtime_idle(), ->runtime_suspend(), or ->runtime_resume() callbacks. | 735 | ->runtime_idle(), ->runtime_suspend(), or ->runtime_resume() callbacks. |
@@ -737,7 +737,7 @@ Instead it will assume that suspends and resumes always succeed and that idle | |||
737 | devices should be suspended. | 737 | devices should be suspended. |
738 | 738 | ||
739 | As a consequence, the PM core will never directly inform the device's subsystem | 739 | As a consequence, the PM core will never directly inform the device's subsystem |
740 | or driver about run-time power changes. Instead, the driver for the device's | 740 | or driver about runtime power changes. Instead, the driver for the device's |
741 | parent must take responsibility for telling the device's driver when the | 741 | parent must take responsibility for telling the device's driver when the |
742 | parent's power state changes. | 742 | parent's power state changes. |
743 | 743 | ||
@@ -748,13 +748,13 @@ A device should be put in a low-power state only when there's some reason to | |||
748 | think it will remain in that state for a substantial time. A common heuristic | 748 | think it will remain in that state for a substantial time. A common heuristic |
749 | says that a device which hasn't been used for a while is liable to remain | 749 | says that a device which hasn't been used for a while is liable to remain |
750 | unused; following this advice, drivers should not allow devices to be suspended | 750 | unused; following this advice, drivers should not allow devices to be suspended |
751 | at run-time until they have been inactive for some minimum period. Even when | 751 | at runtime until they have been inactive for some minimum period. Even when |
752 | the heuristic ends up being non-optimal, it will still prevent devices from | 752 | the heuristic ends up being non-optimal, it will still prevent devices from |
753 | "bouncing" too rapidly between low-power and full-power states. | 753 | "bouncing" too rapidly between low-power and full-power states. |
754 | 754 | ||
755 | The term "autosuspend" is an historical remnant. It doesn't mean that the | 755 | The term "autosuspend" is an historical remnant. It doesn't mean that the |
756 | device is automatically suspended (the subsystem or driver still has to call | 756 | device is automatically suspended (the subsystem or driver still has to call |
757 | the appropriate PM routines); rather it means that run-time suspends will | 757 | the appropriate PM routines); rather it means that runtime suspends will |
758 | automatically be delayed until the desired period of inactivity has elapsed. | 758 | automatically be delayed until the desired period of inactivity has elapsed. |
759 | 759 | ||
760 | Inactivity is determined based on the power.last_busy field. Drivers should | 760 | Inactivity is determined based on the power.last_busy field. Drivers should |