Documentation/power/pci.rst

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
50 Devices supporting the native PCI PM usually can generate wakeup signals called
53 to put the device that sent it into the full-power state.  However, the PCI Bus
54 Power Management Interface Specification doesn't define any standard method of
62 the power state of a device, usually the platform also provides a method for
63 preparing the device to generate wakeup signals.  In that case, however, it
65 native PCI PM mechanism, because the method provided by the platform depends on
68 Thus in many situations both the native and the platform-based power management
72 --------------------------------
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
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
137 sufficiently active to generate a wakeup signal.
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
177 _PSx control method defined for the device.  In addition to that, if the device
178 is going to be put into a low-power state (D1-D3) and is supposed to generate
179 wakeup signals from that state, the _DSW (or _PSW, replaced with _DSW by ACPI
180 3.0) control method defined for it has to be executed before _PSx.  Power
187 system-wide transition into a sleep state or back into the working state.  ACPI
192 device's _SxD control method (where x is a number between 0 and 4 inclusive).
196 _SxW control method to obtain the number of that state.  It also is supposed to
197 use the device's _PRW control method to learn which power resources need to be
198 enabled for the device to be able to generate wakeup signals.
200 1.4. Wakeup Signaling
201 ---------------------
203 Wakeup signals generated by PCI devices, either as native PCI PMEs, or as
204 a result of the execution of the _DSW (or _PSW) ACPI control method before
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
210 sleeping, they should cause the system's core logic to trigger wakeup.
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
217 capable of signaling wakeup.  The information on the connections between GPEs
221 If a PCI device known to the system's ACPI BIOS signals wakeup, the GPE
223 bridges may also be triggered in response to a wakeup signal from one of the
229 the ACPI S1-S4 states), in which case system wakeup is started by its core logic
230 (the device that was the source of the signal causing the system wakeup to occur
232 wakeup GPEs.
239 a PCI device signaling wakeup).  The GPEs used for notifying the kernel of
243 Unfortunately, there is no standard way of handling wakeup signals sent by
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 --------------------------
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
347 The second function checks if the device can be prepared to signal wakeup with
349 the function updates the wakeup fields in struct device embedded in the
350 device's struct pci_dev and uses the firmware-provided method to prevent the
351 device from signaling wakeup.
355 during system-wide transitions to a sleep state and back to the working state.
358 ------------------------------------
363 Namely, it provides subsystem-level callbacks::
370 entire mechanics necessary for handling runtime wakeup signals from PCI devices
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
381 the device is prepared to generate wakeup signals and, finally, it is put into
382 the target low-power state.
384 The low-power state to put the device into is the lowest-power (highest number)
385 state from which it can signal wakeup.  The exact method of signaling wakeup is
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
393 not attempt to prepare the device for signaling wakeup or to put it into a
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
404 callback need not worry about the PCI-specific aspects of the device resume.
409 as a result of a wakeup signal from the device itself (this sometimes is
410 referred to as "remote wakeup").  Of course, for this purpose the wakeup signal
416 and pm_request_idle(), executes the device driver's pm->runtime_idle()
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
462 bridges are ignored by this routine).  Next, the device driver's pm->suspend()
480 returns success.  Otherwise the device driver's pm->suspend_noirq() callback is
484 saves them, prepares the device to signal wakeup (if necessary) and puts it into
485 a low-power state.
487 The low-power state to put the device into is the lowest-power (highest number)
488 state from which it can signal wakeup while the system is in the target sleep
490 signaling wakeup is system-dependent and determined by the PCI subsystem, which
491 is also responsible for preparing the device to signal wakeup from the system's
495 generally not expected to prepare devices for signaling wakeup or to put them
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
525 full-power state and their standard configuration registers have been restored
531 device driver's pm->resume_noirq() callback is executed, if defined, and its
540 returned.  Otherwise, the device's wakeup signaling mechanisms are blocked and
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
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
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
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
749 registers, to prepare it for system wakeup (if necessary), and to put it into a
750 low-power state, respectively.  Moreover, if the driver calls pci_save_state(),
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
786 In that cases the freeze() callback should not prepare the device system wakeup
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,
820 pci_set_power_state() to prepare the device for system wakeup and to put it
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.
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).
1071 zero for the device and it will never be runtime-suspended.  The simplest
1085 should let user space or some platform-specific code do that (user space can
1131 Documentation/driver-api/pm/devices.rst