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13 power management refer to Documentation/driver-api/pm/devices.rst and
27 1.1. Native and Platform-Based Power Management
28 -----------------------------------------------
31 devices into states in which they draw less power (low-power states) at the
34 Usually, a device is put into a low-power state when it is underutilized or
36 again, it has to be put back into the "fully functional" state (full-power
41 PCI devices may be put into low-power states in two ways, by using the device
46 specific value into one of its standard configuration registers. The second
53 to put the device that sent it into the full-power state. However, the PCI Bus
68 Thus in many situations both the native and the platform-based power management
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81 Spec, it has an 8 byte power management capability field in its PCI
85 The PCI PM Spec defines 4 operating states for devices (D0-D3) and for buses
86 (B0-B3). The higher the number, the less power is drawn by the device or bus
88 the device or bus to return to the full-power state (D0 or B0, respectively).
101 Note that every PCI device can be in the full-power state (D0) or in D3cold,
107 supported low-power states (except for D3cold). While in D1-D3hot the
110 its I/O and memory spaces are then disabled. This allows the device to be
112 forth between D0 and the supported low-power states (except for D3cold) and the
115 +----------------------------+
117 +----------------------------+
119 +----------------------------+
121 +----------------------------+
123 +----------------------------+
125 +----------------------------+
129 a full power-on reset sequence and the power-on defaults are restored to the
133 while in any power state (D0-D3), but they are not required to be capable
140 ---------------------------------
143 system-specific. However, if the system in question is compliant with the
145 majority of x86-based systems, it is supposed to implement device power
150 putting a device into a low-power state. These control methods are encoded
151 using special byte-code language called the ACPI Machine Language (AML) and
156 on the system design in a system-specific fashion.
167 D0-D3 states (although the difference between D3hot and D3cold is not taken
178 is going to be put into a low-power state (D1-D3) and is supposed to generate
187 system-wide transition into a sleep state or back into the working state. ACPI
201 ---------------------
205 putting the device into a low-power state, have to be caught and handled as
208 put the devices generating them into the full-power state and take care of the
212 On ACPI-based systems wakeup signals sent by conventional PCI devices are
213 converted into ACPI General-Purpose Events (GPEs) which are hardware signals
229 the ACPI S1-S4 states), in which case system wakeup is started by its core logic
244 conventional PCI devices on systems that are not ACPI-based, but there is one
247 root ports. For conventional PCI devices native PMEs are out-of-band, so they
250 they are in-band messages that have to pass through the PCI Express hierarchy,
261 In principle the native PCI Express PME signaling may also be used on ACPI-based
273 --------------------------------------
323 unsigned int d3hot_delay; /* D3hot->D0 transition time in ms */
331 --------------------------
339 and if that's the case the offset of its power management capability structure
341 pci_dev object. Next, the function checks which PCI low-power states are
342 supported by the device and from which low-power states the device can generate
350 device's struct pci_dev and uses the firmware-provided method to prevent the
355 during system-wide transitions to a sleep state and back to the working state.
358 ------------------------------------
363 Namely, it provides subsystem-level callbacks::
371 in low-power states, which at the time of this writing works for both the native
372 PCI Express PME signaling and the ACPI GPE-based wakeup signaling described in
375 First, a PCI device is put into a low-power state, or suspended, with the help
378 driver has to provide a pm->runtime_suspend() callback (see below), which is
382 the target low-power state.
384 The low-power state to put the device into is the lowest-power (highest number)
386 system-dependent and is determined by the PCI subsystem on the basis of the
388 device for signaling wakeup and put it into the selected low-power state, the
392 It is expected that the device driver's pm->runtime_suspend() callback will
394 low-power state. The driver ought to leave these tasks to the PCI subsystem
400 driver provides a pm->runtime_resume() callback (see below). However, before
402 back into the full-power state, prevents it from signaling wakeup while in that
403 state and restores its standard configuration registers. Thus the driver's
404 callback need not worry about the PCI-specific aspects of the device resume.
416 and pm_request_idle(), executes the device driver's pm->runtime_idle()
423 suspended, so it lets the device's driver decide by running its
424 pm->runtime_idle() callback.
426 2.4. System-Wide Power Transitions
427 ----------------------------------
428 There are a few different types of system-wide power transitions, described in
429 Documentation/driver-api/pm/devices.rst. Each of them requires devices to be
430 handled in a specific way and the PM core executes subsystem-level power
432 each phase involves executing the same subsystem-level callback for every device
440 be preserved, such as one of the ACPI sleep states S1-S3, the phases are:
452 driver's pm->prepare() callback if defined (i.e. if the driver's struct
457 suspend callback is executed, if present, and its result is returned. Next, if
462 bridges are ignored by this routine). Next, the device driver's pm->suspend()
463 callback is executed, if defined, and its result is returned if it fails.
476 late suspend routine is called and its result is returned (the standard
480 returns success. Otherwise the device driver's pm->suspend_noirq() callback is
481 executed, if present, and its result is returned if it fails. Next, if the
485 a low-power state.
487 The low-power state to put the device into is the lowest-power (highest number)
490 signaling wakeup is system-dependent and determined by the PCI subsystem, which
496 into low-power states. However, if one of the driver's suspend callbacks
497 (pm->suspend() or pm->suspend_noirq()) saves the device's standard configuration
499 to signal wakeup and put into a low-power state by the driver (the driver is
509 S1-S3, into the working state (ACPI S0), the phases are:
520 The pci_pm_resume_noirq() routine first puts the device into the full-power
521 state, restores its standard configuration registers and applies early resume
525 full-power state and their standard configuration registers have been restored
530 early resume callback is executed and its result is returned. Otherwise, the
531 device driver's pm->resume_noirq() callback is executed, if defined, and its
539 Section 3), the driver's legacy resume callback is executed and its result is
541 its driver's pm->resume() callback is executed, if defined (the callback's
549 The pci_pm_complete() routine only executes the device driver's pm->complete()
576 the device driver's pm->freeze() callback, if defined, instead of pm->suspend(),
577 and it doesn't apply the suspend-related hardware quirks. It is executed
582 pci_pm_suspend_noirq(), but it calls the device driver's pm->freeze_noirq()
583 routine instead of pm->suspend_noirq(). It also doesn't attempt to prepare the
584 device for signaling wakeup and put it into a low-power state. Still, it saves
604 It puts the device into the full power state and restores its standard
605 configuration registers. It also executes the device driver's pm->thaw_noirq()
606 callback, if defined, instead of pm->resume_noirq().
609 driver's pm->thaw() callback instead of pm->resume(). It is executed
616 enter the target sleep state (ACPI S4 for ACPI-based systems). This is done in
623 The PCI subsystem-level callbacks they correspond to::
636 pre-hibernation memory contents to be restored before the pre-hibernation system
639 As described in Documentation/driver-api/pm/devices.rst, the hibernation image
642 boot kernel has loaded the image, it needs to replace its own code and data with
653 Should the restoration of the pre-hibernation memory contents fail, the boot
658 If the pre-hibernation memory contents are restored successfully, which is the
661 it must restore the devices' pre-hibernation functionality, which is done much
675 respectively, but they execute the device driver's pm->restore_noirq() and
676 pm->restore() callbacks, if available.
686 -------------------------------
694 dev_pm_ops structure described in Documentation/driver-api/pm/devices.rst, and
705 its struct pci_driver object. Once that has happened, the "legacy" PM callbacks
718 (when a hibernation image is about to be created), during power-off after
731 in Documentation/driver-api/pm/notifiers.rst).
740 low-power state by the PCI subsystem. It is not required (in fact it even is
743 put it into a low-power state. All of these operations can very well be taken
750 low-power state, respectively. Moreover, if the driver calls pci_save_state(),
752 pci_set_power_state() for its device, so the driver is then responsible for
756 can be invoked to handle an interrupt from the device, so all suspend-related
775 The freeze() callback is hibernation-specific and is executed in two situations,
783 the driver takes the responsibility for putting the device into a low-power
787 or put it into a low-power state. Still, either it or freeze_noirq() should
793 The freeze_noirq() callback is hibernation-specific. It is executed during
810 The poweroff() callback is hibernation-specific. It is executed when the system
818 into a low-power state itself instead of allowing the PCI subsystem to do that,
821 into a low-power state, respectively, but it need not save the device's standard
827 The poweroff_noirq() callback is hibernation-specific. It is executed after
841 PM core has enabled the non-boot CPUs. The driver's interrupt handler will not
858 This callback is responsible for restoring the pre-suspend configuration of the
865 The thaw_noirq() callback is hibernation-specific. It is executed after a
866 system image has been created and the non-boot CPUs have been enabled by the PM
869 after enabling the non-boot CPUs). The driver's interrupt handler will not be
880 The thaw() callback is hibernation-specific. It is executed after thaw_noirq()
884 This callback is responsible for restoring the pre-freeze configuration of
890 The restore_noirq() callback is hibernation-specific. It is executed in the
892 the image kernel and the non-boot CPUs have been enabled by the image kernel's
898 suspend-resume cycle.
906 The restore() callback is hibernation-specific. It is executed after
922 - during system resume, after resume() callbacks have been executed for all
924 - during hibernation, before saving the system image, after thaw() callbacks
926 - during system restore, when the system is going back to its pre-hibernation
941 device is about to be suspended (i.e. quiesced and put into a low-power state)
945 put into a low-power state, but it must allow the PCI subsystem to perform all
946 of the PCI-specific actions necessary for suspending the device.
953 (i.e. put into the full-power state and programmed to process I/O normally) at
957 device after it has been put into the full-power state by the PCI subsystem.
1008 direct-complete mechanism allowing device suspend/resume callbacks to be skipped
1014 value from pci_pm_prepare() only if the ->prepare callback provided by the
1016 out from using the direct-complete mechanism dynamically (whereas setting
1017 DPM_FLAG_NO_DIRECT_COMPLETE means permanent opt-out).
1022 to avoid resuming the device from runtime suspend unless there are PCI-specific
1025 suspend during the "late" phase of the system-wide transition under way.
1027 pci_pm_restore_noirq(), its runtime PM status will be changed to "active" (as it
1030 Setting the DPM_FLAG_MAY_SKIP_RESUME flag means that the driver allows its
1032 in suspend after a system-wide transition into the working state. This flag is
1042 ------------------------------------
1058 device should really be suspended and return -EAGAIN if that is not the case).
1069 to decrement the device's runtime PM usage counter in its probe callback
1071 zero for the device and it will never be runtime-suspended. The simplest
1076 from its probe routine to make runtime PM work for the device.
1085 should let user space or some platform-specific code do that (user space can
1092 if it has decremented the counter in its probe callback, it must run
1093 pm_runtime_get_noresume() in its remove callback. [Since the core carries
1131 Documentation/driver-api/pm/devices.rst