Lines Matching +full:simple +full:- +full:pm +full:- +full:bus

1 .. SPDX-License-Identifier: GPL-2.0
10 :Copyright: |copy| 2010-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
18 management (PM) code is also driver-specific. Most drivers will do very
22 This writeup gives an overview of how drivers interact with system-wide
25 background for the domain-specific work you'd do with any specific driver.
31 Drivers will use one or both of these models to put devices into low-power
36 Drivers can enter low-power states as part of entering system-wide
37 low-power states like "suspend" (also known as "suspend-to-RAM"), or
39 "suspend-to-disk").
41 This is something that device, bus, and class drivers collaborate on
42 by implementing various role-specific suspend and resume methods to
47 leave the low-power state. This feature may be enabled or disabled
51 whole system enter low-power states more often.
55 Devices may also be put into low-power states while the system is
59 devices have been suspended). Moreover, depending on the bus type the
60 device is on, it may be necessary to carry out some bus-specific
62 states at run time may require special handling during system-wide power
66 appropriate subsystem (bus type, device type or device class) driver and
67 the PM core are involved in runtime power management. As in the system
69 various role-specific suspend and resume methods, so that the hardware
72 There's not a lot to be said about those low-power states except that they are
73 very system-specific, and often device-specific. Also, that if enough devices
74 have been put into low-power states (at runtime), the effect may be very similar
75 to entering some system-wide low-power state (system sleep) ... and that
76 synergies exist, so that several drivers using runtime PM might put the system
81 drivers are no longer accepted. A given bus or platform may have different
85 network wake-on-LAN packets, keyboard or mouse activity, and media insertion
91 There are programming interfaces provided for subsystems (bus type, device type,
98 ----------------------------------
102 struct dev_pm_ops defined in :file:`include/linux/pm.h`. The roles of the
105 management while the remaining ones are used during system-wide power
116 Subsystem-Level Methods
117 -----------------------
121 struct dev_pm_domain, or by the :c:member:`pm` member of struct bus_type,
125 device drivers whose subsystems (PM domains, device types, device classes and
126 bus types) don't provide all power management methods.
128 Bus drivers implement these methods as appropriate for the hardware and the
130 write subsystem-level drivers; most driver code is a "device driver" that builds
131 on top of bus-specific framework code.
134 they are called in phases for every device, respecting the parent-child
139 -------------------------------------------
143 sleep state). These fields are initialized by bus or device driver code using
152 its system wakeup mechanism and for notifying the PM core of system wakeup
153 events signaled by the device. This object is only present for wakeup-capable
159 whether or not a wakeup-capable device should issue wakeup events is a policy
170 Ethernet adapters whose WoL (wake-on-LAN) feature has been set up with ethtool.
172 requests on their own but merely forward wakeup requests from one bus to another
178 like the PCI bus type code, to see whether or not to enable the devices' wakeup
187 low-power states to trigger specific interrupts to signal conditions in which
188 they should be put into the full-power state. Those interrupts may or may not
196 --------------------------------------------
200 by the bus type (or generally subsystem) code using :c:func:`pm_runtime_allow()`
207 runtime power-managed by its driver. Writing "on" calls
209 power if it was in a low-power state, and preventing the
210 device from being runtime power-managed. User space can check the current value
214 system-wide power transitions. In particular, the device can (and in the
215 majority of cases should and will) be put into a low-power state during a
216 system-wide transition to a sleep state even though its :c:member:`runtime_auto`
229 system-specific. Also, wakeup-enabled devices will usually stay partly
232 When the system leaves that low-power state, the device's driver is asked to
234 always go together, and both are multi-phase operations.
236 For simple drivers, suspend might quiesce the device using class code
241 More power-aware drivers might prepare the devices for triggering system wakeup
246 ------------------------
250 walked in a bottom-up order to suspend devices. A top-down order is
257 The policy is that the device hierarchy should match hardware bus topology.
258 [Or at least the control bus, for devices which use multiple busses.]
260 the device is suspending (i.e. has been chosen by the PM core as the next
267 ------------------------------
270 are used for suspend-to-idle, shallow (standby), and deep ("suspend-to-RAM")
271 sleep states and the hibernation state ("suspend-to-disk"). Each phase involves
279 All phases use PM domain, bus, type, class or driver callbacks (that is, methods
280 defined in ``dev->pm_domain->ops``, ``dev->bus->pm``, ``dev->type->pm``,
281 ``dev->class->pm`` or ``dev->driver->pm``). These callbacks are regarded by the
282 PM core as mutually exclusive. Moreover, PM domain callbacks always take
284 precedence over bus, class and driver callbacks. To be precise, the following
287 1. If ``dev->pm_domain`` is present, the PM core will choose the callback
288 provided by ``dev->pm_domain->ops`` for execution.
290 2. Otherwise, if both ``dev->type`` and ``dev->type->pm`` are present, the
291 callback provided by ``dev->type->pm`` will be chosen for execution.
293 3. Otherwise, if both ``dev->class`` and ``dev->class->pm`` are present,
294 the callback provided by ``dev->class->pm`` will be chosen for
297 4. Otherwise, if both ``dev->bus`` and ``dev->bus->pm`` are present, the
298 callback provided by ``dev->bus->pm`` will be chosen for execution.
300 This allows PM domains and device types to override callbacks provided by bus
303 The PM domain, type, class and bus callbacks may in turn invoke device- or
304 driver-specific methods stored in ``dev->driver->pm``, but they don't have to do
307 If the subsystem callback chosen for execution is not present, the PM core will
308 execute the corresponding method from the ``dev->driver->pm`` set instead if
313 -----------------------
319 devices from being registered; the PM core would never know that all the
321 registered at will. [By contrast, from the PM core's perspective,
323 suspend-related phases, during the ``prepare`` phase the device
324 hierarchy is traversed top-down.
326 After the ``->prepare`` callback method returns, no new children may be
329 should not put the device into a low-power state. Moreover, if the
330 device supports runtime power management, the ``->prepare`` callback
335 prepare callback can be used to indicate to the PM core that it may
336 safely leave the device in runtime suspend (if runtime-suspended
340 and all of them (including the device itself) are runtime-suspended, the
341 PM core will skip the ``suspend``, ``suspend_late`` and
344 the ``->complete`` callback will be the next one invoked after the
345 ``->prepare`` callback and is entirely responsible for putting the
348 Note that this direct-complete procedure applies even if the device is
349 disabled for runtime PM; only the runtime-PM status matters. It follows
350 that if a device has system-sleep callbacks but does not support runtime
351 PM, then its prepare callback must never return a positive value. This
352 is because all such devices are initially set to runtime-suspended with
353 runtime PM disabled.
360 these flags is set, the PM core will not apply the direct-complete
363 code (bus types, device types, PM domains, classes) that it should take
364 the return value of the ``->prepare`` callback provided by the driver
366 ``->prepare`` callback if the driver's one also has returned a positive
369 2. The ``->suspend`` methods should quiesce the device to stop it from
371 the appropriate low-power state, depending on the bus type the device is
375 ``->suspend`` methods provided by subsystems (bus types and PM domains
377 to the devices before their drivers' ``->suspend`` methods are called.
382 suspend in their ``->suspend`` methods). In fact, the PM core prevents
385 the ``->prepare`` callback (and calling :c:func:`pm_runtime_put` after
386 issuing the ``->complete`` callback).
395 the callback method is running. The ``->suspend_noirq`` methods should
397 and finally put the device into the appropriate low-power state.
400 callback. However, bus types allowing devices to share interrupt
407 (DMA, IRQs), saved enough state that they can re-initialize or restore previous
408 state (as needed by the hardware), and placed the device into a low-power state.
411 runtime PM may already have performed some or all of these steps.]
420 low-power state. Instead, the PM core will unwind its actions by resuming all
425 ----------------------
430 1. The ``->resume_noirq`` callback methods should perform any actions
433 the bus type permits devices to share interrupt vectors, like PCI, the
438 For example, the PCI bus type's ``->pm.resume_noirq()`` puts the device
439 into the full-power state (D0 in the PCI terminology) and restores the
441 device driver's ``->pm.resume_noirq()`` method to perform device-specific
444 2. The ``->resume_early`` methods should prepare devices for the execution
448 3. The ``->resume`` methods should bring the device back to its operating
453 For this reason, unlike the other resume-related phases, during the
454 ``complete`` phase the device hierarchy is traversed bottom-up.
457 soon as the ``->resume`` callbacks occur; it's not necessary to wait
460 Moreover, if the preceding ``->prepare`` callback returned a positive
462 whole system suspend and resume (its ``->suspend``, ``->suspend_late``,
463 ``->suspend_noirq``, ``->resume_noirq``,
464 ``->resume_early``, and ``->resume`` callbacks may have been
465 skipped). In that case, the ``->complete`` callback is entirely
469 the case, the ``->complete`` callback can consult the device's
471 ``->complete`` callback is being run then the direct-complete mechanism
479 However, the details here may again be platform-specific. For example,
490 system sleep entered was suspend-to-idle. For the other system sleep states
491 that may not be the case (and usually isn't for ACPI-defined system sleep
498 will notice and handle such removals are currently bus-specific, and often
501 These callbacks may return an error value, but the PM core will ignore such
507 --------------------
525 2. The ``->freeze`` methods should quiesce the device so that it doesn't
527 registers. However the device does not have to be put in a low-power
533 low-power state and should not be allowed to generate wakeup events.
537 a low-power state and should not be allowed to generate wakeup events.
561 before putting the system into the suspend-to-idle, shallow or deep sleep state,
572 The ``->poweroff``, ``->poweroff_late`` and ``->poweroff_noirq`` callbacks
573 should do essentially the same things as the ``->suspend``, ``->suspend_late``
574 and ``->suspend_noirq`` callbacks, respectively. A notable difference is
577 ``freeze_noirq`` phases. Also, on many machines the firmware will power-down
579 a low-power state.
583 -------------------
587 a system image to be loaded into memory and the pre-hibernation memory contents
591 pre-hibernation memory contents restored by the boot loader, in practice this
596 reads the system image, restores the pre-hibernation memory contents, and passes
614 Should the restoration of the pre-hibernation memory contents fail, the restore
618 pre-hibernation memory contents are restored successfully and control is passed
622 To achieve this, the image kernel must restore the devices' pre-hibernation
640 reset and completely re-initialized. In many cases this difference doesn't
641 matter, so the ``->resume[_early|_noirq]`` and ``->restore[_early|_norq]``
654 been thawed. Generally speaking, the PM notifiers are suitable for performing
658 For details refer to Documentation/driver-api/pm/notifiers.rst.
661 Device Low-Power (suspend) States
664 Device low-power states aren't standard. One device might only handle
670 gives one example: after the suspend sequence completes, a non-legacy
672 issues would be issued through the PME# bus signal. Plus, there are
673 several PCI-standard device states, some of which are optional.
675 In contrast, integrated system-on-chip processors often use IRQs as the
680 Some details here may be platform-specific. Systems may have devices that
683 its frame buffer might even be updated by a DSP or other non-Linux CPU while
688 another might require a hard shut down with re-initialization on resume.
698 cases it generally is not possible to put devices into low-power states
700 into a low-power state together at the same time by turning off the shared
701 power resource. Of course, they also need to be put into the full-power state
705 sub-domain of the parent domain.
709 struct dev_pm_domain, defined in :file:`include/linux/pm.h`, providing a set
710 of power management callbacks analogous to the subsystem-level and device driver
712 instead of the respective subsystem-level callbacks. Specifically, if a
713 device's :c:member:`pm_domain` pointer is not NULL, the ``->suspend()`` callback
715 (e.g. bus type's) ``->suspend()`` callback and analogously for all of the
718 by the device's subsystem (e.g. bus type).
723 support for power domains into subsystem-level callbacks, for example by
724 modifying the platform bus type. Other platforms need not implement it or take
727 Devices may be defined as IRQ-safe which indicates to the PM core that their
728 runtime PM callbacks may be invoked with disabled interrupts (see
730 IRQ-safe device belongs to a PM domain, the runtime PM of the domain will be
731 disallowed, unless the domain itself is defined as IRQ-safe. However, it
732 makes sense to define a PM domain as IRQ-safe only if all the devices in it
733 are IRQ-safe. Moreover, if an IRQ-safe domain has a parent domain, the runtime
734 PM of the parent is only allowed if the parent itself is IRQ-safe too with the
735 additional restriction that all child domains of an IRQ-safe parent must also
736 be IRQ-safe.
747 cases (like PCI) be partially constrained by the bus the device uses, and will
750 A system-wide power transition can be started while some devices are in low
751 power states due to runtime power management. The system sleep PM callbacks
753 necessary actions are subsystem-specific.
757 desirable to leave a suspended device in that state during a system-wide power
758 transition, but in other cases the device must be put back into the full-power
763 If it is necessary to resume a device from runtime suspend during a system-wide
765 :c:func:`pm_runtime_resume` from the ``->suspend`` callback (or the ``->freeze``
766 or ``->poweroff`` callback for transitions related to hibernation) of either the
767 device's driver or its subsystem (for example, a bus type or a PM domain).
769 from their ``->prepare`` and ``->suspend`` callbacks (or equivalent) *before*
770 invoking device drivers' ``->suspend`` callbacks (or equivalent).
775 ------------------------------------------
777 Some bus types and PM domains have a policy to resume all devices from runtime
778 suspend upfront in their ``->suspend`` callbacks, but that may not be really
779 necessary if the device's driver can cope with runtime-suspended devices.
784 Setting that flag causes the PM core and middle-layer code
785 (bus types, PM domains etc.) to skip the ``->suspend_late`` and
786 ``->suspend_noirq`` callbacks provided by the driver if the device remains in
787 runtime suspend throughout those phases of the system-wide suspend (and
791 be valid in general.] If the middle-layer system-wide PM callbacks are present
793 if not then the PM core skips them. The subsystem callback routines can
797 In addition, with ``DPM_FLAG_SMART_SUSPEND`` set, the driver's ``->thaw_noirq``
798 and ``->thaw_early`` callbacks are skipped in hibernation if the device remained
800 middle-layer callbacks are present for the device, they are responsible for
801 doing this, otherwise the PM core takes care of it.
805 --------------------------------------------
807 During system-wide resume from a sleep state it's easiest to put devices into
808 the full-power state, as explained in Documentation/power/runtime_pm.rst.
813 runtime suspend before the preceding system-wide suspend (or analogous)
817 indicate to the PM core and middle-layer code that they allow their "noirq" and
819 after system-wide PM transitions to the working state. Whether or not that is
821 suspend-resume cycle and on the type of the system transition under way.
832 the :c:member:`power.may_skip_resume` status bit set by the PM core during the
833 "suspend" phase of suspend-type transitions. If the driver or the middle layer
836 clear :c:member:`power.may_skip_resume` in its ``->suspend``, ``->suspend_late``
837 or ``->suspend_noirq`` callback. [Note that the drivers setting
839 their ``->suspend`` callback in case the other two are skipped.]
848 callbacks should be skipped and the device's runtime PM status will be set to
849 "suspended" by the PM core. Otherwise, if the device was runtime-suspended
850 during the preceding system-wide suspend transition and its
851 ``DPM_FLAG_SMART_SUSPEND`` is set, its runtime PM status will be set to
852 "active" by the PM core. [Hence, the drivers that do not set
853 ``DPM_FLAG_SMART_SUSPEND`` should not expect the runtime PM status of their
854 devices to be changed from "suspended" to "active" by the PM core during
855 system-wide resume-type transitions.]
859 callbacks are skipped, its system-wide "noirq" and "early" resume callbacks, if
860 present, are invoked as usual and the device's runtime PM status is set to
861 "active" by the PM core before enabling runtime PM for it. In that case, the
862 driver must be prepared to cope with the invocation of its system-wide resume
863 callbacks back-to-back with its ``->runtime_suspend`` one (without the
864 intervening ``->runtime_resume`` and system-wide suspend callbacks) and the
865 final state of the device must reflect the "active" runtime PM status in that
867 ``->suspend_late`` callback pointer points to the same function as its
868 ``->runtime_suspend`` one and its ``->resume_early`` callback pointer points to
869 the same function as the ``->runtime_resume`` one, while none of the other
870 system-wide suspend-resume callbacks of the driver are present, for example.]
873 system-wide "noirq" and "early" resume callbacks may be skipped while its "late"
876 needs to be able to cope with the invocation of its ``->runtime_resume``
877 callback back-to-back with its "late" and "noirq" suspend ones. [For instance,
880 functions for runtime PM and system-wide suspend/resume.]