Merge branch 'pm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Subsystem-Level Methods

-----------------------

The core methods to suspend and resume devices reside in struct dev_pm_ops

pointed to by the pm member of struct bus_type, struct device_type and

struct class.  They are mostly of interest to the people writing infrastructure

for buses, like PCI or USB, or device type and device class drivers.

pointed to by the ops member of struct dev_pm_domain, or by the pm member of

struct bus_type, struct device_type and struct class.  They are mostly of

interest to the people writing infrastructure for platforms and buses, like PCI

or USB, or device type and device class drivers.

Bus drivers implement these methods as appropriate for the hardware and the

drivers using it; PCI works differently from USB, and so on.  Not many people

/sys/devices/.../power/wakeup files

-----------------------------------

All devices in the driver model have two flags to control handling of wakeup

events (hardware signals that can force the device and/or system out of a low

power state).  These flags are initialized by bus or device driver code using

All device objects in the driver model contain fields that control the handling

of system wakeup events (hardware signals that can force the system out of a

sleep state).  These fields are initialized by bus or device driver code using

device_set_wakeup_capable() and device_set_wakeup_enable(), defined in

include/linux/pm_wakeup.h.

The "can_wakeup" flag just records whether the device (and its driver) can

The "power.can_wakeup" flag just records whether the device (and its driver) can

physically support wakeup events.  The device_set_wakeup_capable() routine

affects this flag.  The "should_wakeup" flag controls whether the device should

try to use its wakeup mechanism.  device_set_wakeup_enable() affects this flag;

for the most part drivers should not change its value.  The initial value of

should_wakeup is supposed to be false for the majority of devices; the major

exceptions are power buttons, keyboards, and Ethernet adapters whose WoL

(wake-on-LAN) feature has been set up with ethtool.  It should also default

to true for devices that don't generate wakeup requests on their own but merely

forward wakeup requests from one bus to another (like PCI bridges).

affects this flag.  The "power.wakeup" field is a pointer to an object of type

struct wakeup_source used for controlling whether or not the device should use

its system wakeup mechanism and for notifying the PM core of system wakeup

events signaled by the device.  This object is only present for wakeup-capable

devices (i.e. devices whose "can_wakeup" flags are set) and is created (or

removed) by device_set_wakeup_capable().

Whether or not a device is capable of issuing wakeup events is a hardware

matter, and the kernel is responsible for keeping track of it.  By contrast,

whether or not a wakeup-capable device should issue wakeup events is a policy

decision, and it is managed by user space through a sysfs attribute: the

power/wakeup file.  User space can write the strings "enabled" or "disabled" to

set or clear the "should_wakeup" flag, respectively.  This file is only present

for wakeup-capable devices (i.e. devices whose "can_wakeup" flags are set)

and is created (or removed) by device_set_wakeup_capable().  Reads from the

file will return the corresponding string.

The device_may_wakeup() routine returns true only if both flags are set.

"power/wakeup" file.  User space can write the strings "enabled" or "disabled"

to it to indicate whether or not, respectively, the device is supposed to signal

system wakeup.  This file is only present if the "power.wakeup" object exists

for the given device and is created (or removed) along with that object, by

device_set_wakeup_capable().  Reads from the file will return the corresponding

string.

The "power/wakeup" file is supposed to contain the "disabled" string initially

for the majority of devices; the major exceptions are power buttons, keyboards,

and Ethernet adapters whose WoL (wake-on-LAN) feature has been set up with

ethtool.  It should also default to "enabled" for devices that don't generate

wakeup requests on their own but merely forward wakeup requests from one bus to

another (like PCI Express ports).

The device_may_wakeup() routine returns true only if the "power.wakeup" object

exists and the corresponding "power/wakeup" file contains the string "enabled".

This information is used by subsystems, like the PCI bus type code, to see

whether or not to enable the devices' wakeup mechanisms.  If device wakeup

mechanisms are enabled or disabled directly by drivers, they also should use

device_may_wakeup() to decide what to do during a system sleep transition.

However for runtime power management, wakeup events should be enabled whenever

the device and driver both support them, regardless of the should_wakeup flag.

Device drivers, however, are not supposed to call device_set_wakeup_enable()

directly in any case.

It ought to be noted that system wakeup is conceptually different from "remote

wakeup" used by runtime power management, although it may be supported by the

same physical mechanism.  Remote wakeup is a feature allowing devices in

low-power states to trigger specific interrupts to signal conditions in which

they should be put into the full-power state.  Those interrupts may or may not

be used to signal system wakeup events, depending on the hardware design.  On

some systems it is impossible to trigger them from system sleep states.  In any

case, remote wakeup should always be enabled for runtime power management for

all devices and drivers that support it.

/sys/devices/.../power/control files

------------------------------------

support all these callbacks and not all drivers use all the callbacks.  The

various phases always run after tasks have been frozen and before they are

unfrozen.  Furthermore, the *_noirq phases run at a time when IRQ handlers have

been disabled (except for those marked with the IRQ_WAKEUP flag).

All phases use bus, type, or class callbacks (that is, methods defined in

dev->bus->pm, dev->type->pm, or dev->class->pm).  These callbacks are mutually

exclusive, so if the device type provides a struct dev_pm_ops object pointed to

by its pm field (i.e. both dev->type and dev->type->pm are defined), the

callbacks included in that object (i.e. dev->type->pm) will be used.  Otherwise,

if the class provides a struct dev_pm_ops object pointed to by its pm field

(i.e. both dev->class and dev->class->pm are defined), the PM core will use the

callbacks from that object (i.e. dev->class->pm).  Finally, if the pm fields of

both the device type and class objects are NULL (or those objects do not exist),

the callbacks provided by the bus (that is, the callbacks from dev->bus->pm)

will be used (this allows device types to override callbacks provided by bus

types or classes if necessary).

been disabled (except for those marked with the IRQF_NO_SUSPEND flag).

All phases use PM domain, bus, type, or class callbacks (that is, methods

defined in dev->pm_domain->ops, dev->bus->pm, dev->type->pm, or dev->class->pm).

These callbacks are regarded by the PM core as mutually exclusive.  Moreover,

PM domain callbacks always take precedence over bus, type and class callbacks,

while type callbacks take precedence over bus and class callbacks, and class

callbacks take precedence over bus callbacks.  To be precise, the following

rules are used to determine which callback to execute in the given phase:

    1.	If dev->pm_domain is present, the PM core will attempt to execute the

	callback included in dev->pm_domain->ops.  If that callback is not

	present, no action will be carried out for the given device.

    2.	Otherwise, if both dev->type and dev->type->pm are present, the callback

	included in dev->type->pm will be executed.

    3.	Otherwise, if both dev->class and dev->class->pm are present, the

	callback included in dev->class->pm will be executed.

    4.	Otherwise, if both dev->bus and dev->bus->pm are present, the callback

	included in dev->bus->pm will be executed.

This allows PM domains and device types to override callbacks provided by bus

types or device classes if necessary.

These callbacks may in turn invoke device- or driver-specific methods stored in

dev->driver->pm, but they don't have to.

	After the prepare callback method returns, no new children may be

	registered below the device.  The method may also prepare the device or

	driver in some way for the upcoming system power transition (for

	example, by allocating additional memory required for this purpose), but

	it should not put the device into a low-power state.

	driver in some way for the upcoming system power transition, but it

	should not put the device into a low-power state.

    2.	The suspend methods should quiesce the device to stop it from performing

	I/O.  They also may save the device registers and put it into the

};

The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks

are executed by the PM core for either the power domain, or the device type

(if the device power domain's struct dev_pm_ops does not exist), or the class

(if the device power domain's and type's struct dev_pm_ops object does not

exist), or the bus type (if the device power domain's, type's and class'

struct dev_pm_ops objects do not exist) of the given device, so the priority

order of callbacks from high to low is that power domain callbacks, device

type callbacks, class callbacks and bus type callbacks, and the high priority

one will take precedence over low priority one. The bus type, device type and

class callbacks are referred to as subsystem-level callbacks in what follows,

and generally speaking, the power domain callbacks are used for representing

power domains within a SoC.

are executed by the PM core for the device's subsystem that may be either of

the following:

  1. PM domain of the device, if the device's PM domain object, dev->pm_domain,

     is present.

  2. Device type of the device, if both dev->type and dev->type->pm are present.

  3. Device class of the device, if both dev->class and dev->class->pm are

     present.

  4. Bus type of the device, if both dev->bus and dev->bus->pm are present.

The PM core always checks which callback to use in the order given above, so the

priority order of callbacks from high to low is: PM domain, device type, class

and bus type.  Moreover, the high-priority one will always take precedence over

a low-priority one.  The PM domain, bus type, device type and class callbacks

are referred to as subsystem-level callbacks in what follows.

By default, the callbacks are always invoked in process context with interrupts

enabled.  However, subsystems can use the pm_runtime_irq_safe() helper function

to tell the PM core that a device's ->runtime_suspend() and ->runtime_resume()

callbacks should be invoked in atomic context with interrupts disabled.

This implies that these callback routines must not block or sleep, but it also

means that the synchronous helper functions listed at the end of Section 4 can

be used within an interrupt handler or in an atomic context.

to tell the PM core that their ->runtime_suspend(), ->runtime_resume() and

->runtime_idle() callbacks may be invoked in atomic context with interrupts

disabled for a given device.  This implies that the callback routines in

question must not block or sleep, but it also means that the synchronous helper

functions listed at the end of Section 4 may be used for that device within an

interrupt handler or generally in an atomic context.

The subsystem-level suspend callback is _entirely_ _responsible_ for handling

the suspend of the device as appropriate, which may, but need not include

	error = freeze_kernel_threads();

	if (error)

		goto Close;

		goto Cleanup;

	if (hibernation_test(TEST_FREEZER) ||

		hibernation_testmode(HIBERNATION_TESTPROC)) {

		 * successful freezer test.

		 */

		freezer_test_done = true;

		goto Close;

		goto Cleanup;

	}

	error = dpm_prepare(PMSG_FREEZE);

	if (error)

		goto Complete_devices;

	if (error) {

		dpm_complete(msg);

		goto Cleanup;

	}

	suspend_console();

	pm_restrict_gfp_mask();

		pm_restore_gfp_mask();

	resume_console();

 Complete_devices:

	dpm_complete(msg);

 Close:

 Recover_platform:

	platform_recover(platform_mode);

	goto Resume_devices;

 Cleanup:

	swsusp_free();

	goto Close;

}

/**