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-rw-r--r--Documentation/power/00-INDEX2
-rw-r--r--Documentation/power/basic-pm-debugging.txt26
-rw-r--r--Documentation/power/devices.txt127
-rw-r--r--Documentation/power/freezing-of-tasks.txt8
-rw-r--r--Documentation/power/opp.txt2
-rw-r--r--Documentation/power/pm_qos_interface.txt92
-rw-r--r--Documentation/power/regulator/machine.txt19
-rw-r--r--Documentation/power/runtime_pm.txt272
-rw-r--r--Documentation/power/suspend-and-cpuhotplug.txt275
-rw-r--r--Documentation/power/userland-swsusp.txt3
10 files changed, 666 insertions, 160 deletions
diff --git a/Documentation/power/00-INDEX b/Documentation/power/00-INDEX
index 45e9d4a..a4d682f 100644
--- a/Documentation/power/00-INDEX
+++ b/Documentation/power/00-INDEX
@@ -26,6 +26,8 @@ s2ram.txt
- How to get suspend to ram working (and debug it when it isn't)
states.txt
- System power management states
+suspend-and-cpuhotplug.txt
+ - Explains the interaction between Suspend-to-RAM (S3) and CPU hotplug
swsusp-and-swap-files.txt
- Using swap files with software suspend (to disk)
swsusp-dmcrypt.txt
diff --git a/Documentation/power/basic-pm-debugging.txt b/Documentation/power/basic-pm-debugging.txt
index ddd7817..40a4c65 100644
--- a/Documentation/power/basic-pm-debugging.txt
+++ b/Documentation/power/basic-pm-debugging.txt
@@ -173,7 +173,7 @@ kernel messages using the serial console. This may provide you with some
information about the reasons of the suspend (resume) failure. Alternatively,
it may be possible to use a FireWire port for debugging with firescope
(ftp://ftp.firstfloor.org/pub/ak/firescope/). On x86 it is also possible to
-use the PM_TRACE mechanism documented in Documentation/s2ram.txt .
+use the PM_TRACE mechanism documented in Documentation/power/s2ram.txt .
2. Testing suspend to RAM (STR)
@@ -201,3 +201,27 @@ case, you may be able to search for failing drivers by following the procedure
analogous to the one described in section 1. If you find some failing drivers,
you will have to unload them every time before an STR transition (ie. before
you run s2ram), and please report the problems with them.
+
+There is a debugfs entry which shows the suspend to RAM statistics. Here is an
+example of its output.
+ # mount -t debugfs none /sys/kernel/debug
+ # cat /sys/kernel/debug/suspend_stats
+ success: 20
+ fail: 5
+ failed_freeze: 0
+ failed_prepare: 0
+ failed_suspend: 5
+ failed_suspend_noirq: 0
+ failed_resume: 0
+ failed_resume_noirq: 0
+ failures:
+ last_failed_dev: alarm
+ adc
+ last_failed_errno: -16
+ -16
+ last_failed_step: suspend
+ suspend
+Field success means the success number of suspend to RAM, and field fail means
+the failure number. Others are the failure number of different steps of suspend
+to RAM. suspend_stats just lists the last 2 failed devices, error number and
+failed step of suspend.
diff --git a/Documentation/power/devices.txt b/Documentation/power/devices.txt
index 64565aa..3139fb5 100644
--- a/Documentation/power/devices.txt
+++ b/Documentation/power/devices.txt
@@ -123,9 +123,10 @@ please refer directly to the source code for more information about it.
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
@@ -139,39 +140,57 @@ sequencing in the driver model tree.
/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.
+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
------------------------------------
@@ -247,20 +266,31 @@ for every device before the next phase begins. Not all busses or classes
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.
@@ -279,15 +309,10 @@ When the system goes into the standby or memory sleep state, the phases are:
time.) Unlike the other suspend-related phases, during the prepare
phase the device tree is traversed top-down.
- In addition to that, if device drivers need to allocate additional
- memory to be able to hadle device suspend correctly, that should be
- done in the prepare phase.
-
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
@@ -506,8 +531,8 @@ routines. Nevertheless, different callback pointers are used in case there is a
situation where it actually matters.
-Device Power Domains
---------------------
+Device Power Management Domains
+-------------------------------
Sometimes devices share reference clocks or other power resources. In those
cases it generally is not possible to put devices into low-power states
individually. Instead, a set of devices sharing a power resource can be put
@@ -516,8 +541,8 @@ power resource. Of course, they also need to be put into the full-power state
together, by turning the shared power resource on. A set of devices with this
property is often referred to as a power domain.
-Support for power domains is provided through the pwr_domain field of struct
-device. This field is a pointer to an object of type struct dev_power_domain,
+Support for power domains is provided through the pm_domain field of struct
+device. This field is a pointer to an object of type struct dev_pm_domain,
defined in include/linux/pm.h, providing a set of power management callbacks
analogous to the subsystem-level and device driver callbacks that are executed
for the given device during all power transitions, instead of the respective
@@ -604,7 +629,7 @@ state temporarily, for example so that its system wakeup capability can be
disabled. This all depends on the hardware and the design of the subsystem and
device driver in question.
-During system-wide resume from a sleep state it's best to put devices into the
-full-power state, as explained in Documentation/power/runtime_pm.txt. Refer to
-that document for more information regarding this particular issue as well as
+During system-wide resume from a sleep state it's easiest to put devices into
+the full-power state, as explained in Documentation/power/runtime_pm.txt. Refer
+to that document for more information regarding this particular issue as well as
for information on the device runtime power management framework in general.
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt
index 38b5724..316c2ba 100644
--- a/Documentation/power/freezing-of-tasks.txt
+++ b/Documentation/power/freezing-of-tasks.txt
@@ -22,12 +22,12 @@ try_to_freeze_tasks() that sets TIF_FREEZE for all of the freezable tasks and
either wakes them up, if they are kernel threads, or sends fake signals to them,
if they are user space processes. A task that has TIF_FREEZE set, should react
to it by calling the function called refrigerator() (defined in
-kernel/power/process.c), which sets the task's PF_FROZEN flag, changes its state
+kernel/freezer.c), which sets the task's PF_FROZEN flag, changes its state
to TASK_UNINTERRUPTIBLE and makes it loop until PF_FROZEN is cleared for it.
Then, we say that the task is 'frozen' and therefore the set of functions
handling this mechanism is referred to as 'the freezer' (these functions are
-defined in kernel/power/process.c and include/linux/freezer.h). User space
-processes are generally frozen before kernel threads.
+defined in kernel/power/process.c, kernel/freezer.c & include/linux/freezer.h).
+User space processes are generally frozen before kernel threads.
It is not recommended to call refrigerator() directly. Instead, it is
recommended to use the try_to_freeze() function (defined in
@@ -95,7 +95,7 @@ after the memory for the image has been freed, we don't want tasks to allocate
additional memory and we prevent them from doing that by freezing them earlier.
[Of course, this also means that device drivers should not allocate substantial
amounts of memory from their .suspend() callbacks before hibernation, but this
-is e separate issue.]
+is a separate issue.]
3. The third reason is to prevent user space processes and some kernel threads
from interfering with the suspending and resuming of devices. A user space
diff --git a/Documentation/power/opp.txt b/Documentation/power/opp.txt
index 5ae70a12..3035d00 100644
--- a/Documentation/power/opp.txt
+++ b/Documentation/power/opp.txt
@@ -321,6 +321,8 @@ opp_init_cpufreq_table - cpufreq framework typically is initialized with
addition to CONFIG_PM as power management feature is required to
dynamically scale voltage and frequency in a system.
+opp_free_cpufreq_table - Free up the table allocated by opp_init_cpufreq_table
+
7. Data Structures
==================
Typically an SoC contains multiple voltage domains which are variable. Each
diff --git a/Documentation/power/pm_qos_interface.txt b/Documentation/power/pm_qos_interface.txt
index bfed898..17e130a 100644
--- a/Documentation/power/pm_qos_interface.txt
+++ b/Documentation/power/pm_qos_interface.txt
@@ -4,14 +4,19 @@ This interface provides a kernel and user mode interface for registering
performance expectations by drivers, subsystems and user space applications on
one of the parameters.
-Currently we have {cpu_dma_latency, network_latency, network_throughput} as the
-initial set of pm_qos parameters.
+Two different PM QoS frameworks are available:
+1. PM QoS classes for cpu_dma_latency, network_latency, network_throughput.
+2. the per-device PM QoS framework provides the API to manage the per-device latency
+constraints.
Each parameters have defined units:
* latency: usec
* timeout: usec
* throughput: kbs (kilo bit / sec)
+
+1. PM QoS framework
+
The infrastructure exposes multiple misc device nodes one per implemented
parameter. The set of parameters implement is defined by pm_qos_power_init()
and pm_qos_params.h. This is done because having the available parameters
@@ -23,14 +28,18 @@ an aggregated target value. The aggregated target value is updated with
changes to the request list or elements of the list. Typically the
aggregated target value is simply the max or min of the request values held
in the parameter list elements.
+Note: the aggregated target value is implemented as an atomic variable so that
+reading the aggregated value does not require any locking mechanism.
+
From kernel mode the use of this interface is simple:
-handle = pm_qos_add_request(param_class, target_value):
-Will insert an element into the list for that identified PM_QOS class with the
+void pm_qos_add_request(handle, param_class, target_value):
+Will insert an element into the list for that identified PM QoS class with the
target value. Upon change to this list the new target is recomputed and any
registered notifiers are called only if the target value is now different.
-Clients of pm_qos need to save the returned handle.
+Clients of pm_qos need to save the returned handle for future use in other
+pm_qos API functions.
void pm_qos_update_request(handle, new_target_value):
Will update the list element pointed to by the handle with the new target value
@@ -42,6 +51,20 @@ Will remove the element. After removal it will update the aggregate target and
call the notification tree if the target was changed as a result of removing
the request.
+int pm_qos_request(param_class):
+Returns the aggregated value for a given PM QoS class.
+
+int pm_qos_request_active(handle):
+Returns if the request is still active, i.e. it has not been removed from a
+PM QoS class constraints list.
+
+int pm_qos_add_notifier(param_class, notifier):
+Adds a notification callback function to the PM QoS class. The callback is
+called when the aggregated value for the PM QoS class is changed.
+
+int pm_qos_remove_notifier(int param_class, notifier):
+Removes the notification callback function for the PM QoS class.
+
From user mode:
Only processes can register a pm_qos request. To provide for automatic
@@ -63,4 +86,63 @@ To remove the user mode request for a target value simply close the device
node.
+2. PM QoS per-device latency framework
+
+For each device a list of performance requests is maintained along with
+an aggregated target value. The aggregated target value is updated with
+changes to the request list or elements of the list. Typically the
+aggregated target value is simply the max or min of the request values held
+in the parameter list elements.
+Note: the aggregated target value is implemented as an atomic variable so that
+reading the aggregated value does not require any locking mechanism.
+
+
+From kernel mode the use of this interface is the following:
+
+int dev_pm_qos_add_request(device, handle, value):
+Will insert an element into the list for that identified device with the
+target value. Upon change to this list the new target is recomputed and any
+registered notifiers are called only if the target value is now different.
+Clients of dev_pm_qos need to save the handle for future use in other
+dev_pm_qos API functions.
+
+int dev_pm_qos_update_request(handle, new_value):
+Will update the list element pointed to by the handle with the new target value
+and recompute the new aggregated target, calling the notification trees if the
+target is changed.
+
+int dev_pm_qos_remove_request(handle):
+Will remove the element. After removal it will update the aggregate target and
+call the notification trees if the target was changed as a result of removing
+the request.
+
+s32 dev_pm_qos_read_value(device):
+Returns the aggregated value for a given device's constraints list.
+
+
+Notification mechanisms:
+The per-device PM QoS framework has 2 different and distinct notification trees:
+a per-device notification tree and a global notification tree.
+
+int dev_pm_qos_add_notifier(device, notifier):
+Adds a notification callback function for the device.
+The callback is called when the aggregated value of the device constraints list
+is changed.
+
+int dev_pm_qos_remove_notifier(device, notifier):
+Removes the notification callback function for the device.
+
+int dev_pm_qos_add_global_notifier(notifier):
+Adds a notification callback function in the global notification tree of the
+framework.
+The callback is called when the aggregated value for any device is changed.
+
+int dev_pm_qos_remove_global_notifier(notifier):
+Removes the notification callback function from the global notification tree
+of the framework.
+
+
+From user mode:
+No API for user space access to the per-device latency constraints is provided
+yet - still under discussion.
diff --git a/Documentation/power/regulator/machine.txt b/Documentation/power/regulator/machine.txt
index b42419b..ce63af0 100644
--- a/Documentation/power/regulator/machine.txt
+++ b/Documentation/power/regulator/machine.txt
@@ -16,7 +16,7 @@ initialisation code by creating a struct regulator_consumer_supply for
each regulator.
struct regulator_consumer_supply {
- struct device *dev; /* consumer */
+ const char *dev_name; /* consumer dev_name() */
const char *supply; /* consumer supply - e.g. "vcc" */
};
@@ -24,13 +24,13 @@ e.g. for the machine above
static struct regulator_consumer_supply regulator1_consumers[] = {
{
- .dev = &platform_consumerB_device.dev,
- .supply = "Vcc",
+ .dev_name = "dev_name(consumer B)",
+ .supply = "Vcc",
},};
static struct regulator_consumer_supply regulator2_consumers[] = {
{
- .dev = &platform_consumerA_device.dev,
+ .dev = "dev_name(consumer A"),
.supply = "Vcc",
},};
@@ -43,6 +43,7 @@ to their supply regulator :-
static struct regulator_init_data regulator1_data = {
.constraints = {
+ .name = "Regulator-1",
.min_uV = 3300000,
.max_uV = 3300000,
.valid_modes_mask = REGULATOR_MODE_NORMAL,
@@ -51,13 +52,19 @@ static struct regulator_init_data regulator1_data = {
.consumer_supplies = regulator1_consumers,
};
+The name field should be set to something that is usefully descriptive
+for the board for configuration of supplies for other regulators and
+for use in logging and other diagnostic output. Normally the name
+used for the supply rail in the schematic is a good choice. If no
+name is provided then the subsystem will choose one.
+
Regulator-1 supplies power to Regulator-2. This relationship must be registered
with the core so that Regulator-1 is also enabled when Consumer A enables its
supply (Regulator-2). The supply regulator is set by the supply_regulator
-field below:-
+field below and co:-
static struct regulator_init_data regulator2_data = {
- .supply_regulator = "regulator_name",
+ .supply_regulator = "Regulator-1",
.constraints = {
.min_uV = 1800000,
.max_uV = 2000000,
diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
index a6b3430..c2ae8bf 100644
--- a/Documentation/power/runtime_pm.txt
+++ b/Documentation/power/runtime_pm.txt
@@ -1,39 +1,39 @@
-Run-time Power Management Framework for I/O Devices
+Runtime Power Management Framework for I/O Devices
(C) 2009-2011 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
(C) 2010 Alan Stern <stern@rowland.harvard.edu>
1. Introduction
-Support for run-time power management (run-time PM) of I/O devices is provided
+Support for runtime power management (runtime PM) of I/O devices is provided
at the power management core (PM core) level by means of:
* The power management workqueue pm_wq in which bus types and device drivers can
put their PM-related work items. It is strongly recommended that pm_wq be
- used for queuing all work items related to run-time PM, because this allows
+ used for queuing all work items related to runtime PM, because this allows
them to be synchronized with system-wide power transitions (suspend to RAM,
hibernation and resume from system sleep states). pm_wq is declared in
include/linux/pm_runtime.h and defined in kernel/power/main.c.
-* A number of run-time PM fields in the 'power' member of 'struct device' (which
+* A number of runtime PM fields in the 'power' member of 'struct device' (which
is of the type 'struct dev_pm_info', defined in include/linux/pm.h) that can
- be used for synchronizing run-time PM operations with one another.
+ be used for synchronizing runtime PM operations with one another.
-* Three device run-time PM callbacks in 'struct dev_pm_ops' (defined in
+* Three device runtime PM callbacks in 'struct dev_pm_ops' (defined in
include/linux/pm.h).
* A set of helper functions defined in drivers/base/power/runtime.c that can be
- used for carrying out run-time PM operations in such a way that the
+ used for carrying out runtime PM operations in such a way that the
synchronization between them is taken care of by the PM core. Bus types and
device drivers are encouraged to use these functions.
-The run-time PM callbacks present in 'struct dev_pm_ops', the device run-time PM
+The runtime PM callbacks present in 'struct dev_pm_ops', the device runtime PM
fields of 'struct dev_pm_info' and the core helper functions provided for
-run-time PM are described below.
+runtime PM are described below.
-2. Device Run-time PM Callbacks
+2. Device Runtime PM Callbacks
-There are three device run-time PM callbacks defined in 'struct dev_pm_ops':
+There are three device runtime PM callbacks defined in 'struct dev_pm_ops':
struct dev_pm_ops {
...
@@ -43,22 +43,34 @@ struct dev_pm_ops {
...
};
-The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks are
-executed by the PM core for either the device type, or the class (if the device
-type's struct dev_pm_ops object does not exist), or the bus type (if the
-device type's and class' struct dev_pm_ops objects do not exist) of the given
-device (this allows device types to override callbacks provided by bus types or
-classes if necessary). The bus type, device type and class callbacks are
-referred to as subsystem-level callbacks in what follows.
+The ->runtime_suspend(), ->runtime_resume() and ->runtime_idle() callbacks
+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
-(->runtime_idle() is still invoked the default way). 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
@@ -72,11 +84,11 @@ knows what to do to handle the device).
not mean that the device has been put into a low power state. It is
supposed to mean, however, that the device will not process data and will
not communicate with the CPU(s) and RAM until the subsystem-level resume
- callback is executed for it. The run-time PM status of a device after
+ callback is executed for it. The runtime PM status of a device after
successful execution of the subsystem-level suspend callback is 'suspended'.
* If the subsystem-level suspend callback returns -EBUSY or -EAGAIN,
- the device's run-time PM status is 'active', which means that the device
+ the device's runtime PM status is 'active', which means that the device
_must_ be fully operational afterwards.
* If the subsystem-level suspend callback returns an error code different
@@ -104,7 +116,7 @@ the device).
* Once the subsystem-level resume callback has completed successfully, the PM
core regards the device as fully operational, which means that the device
- _must_ be able to complete I/O operations as needed. The run-time PM status
+ _must_ be able to complete I/O operations as needed. The runtime PM status
of the device is then 'active'.
* If the subsystem-level resume callback returns an error code, the PM core
@@ -130,7 +142,7 @@ device in that case. The value returned by this callback is ignored by the PM
core.
The helper functions provided by the PM core, described in Section 4, guarantee
-that the following constraints are met with respect to the bus type's run-time
+that the following constraints are met with respect to the bus type's runtime
PM callbacks:
(1) The callbacks are mutually exclusive (e.g. it is forbidden to execute
@@ -142,7 +154,7 @@ PM callbacks:
(2) ->runtime_idle() and ->runtime_suspend() can only be executed for 'active'
devices (i.e. the PM core will only execute ->runtime_idle() or
- ->runtime_suspend() for the devices the run-time PM status of which is
+ ->runtime_suspend() for the devices the runtime PM status of which is
'active').
(3) ->runtime_idle() and ->runtime_suspend() can only be executed for a device
@@ -151,7 +163,7 @@ PM callbacks:
flag of which is set.
(4) ->runtime_resume() can only be executed for 'suspended' devices (i.e. the
- PM core will only execute ->runtime_resume() for the devices the run-time
+ PM core will only execute ->runtime_resume() for the devices the runtime
PM status of which is 'suspended').
Additionally, the helper functions provided by the PM core obey the following
@@ -171,9 +183,9 @@ rules:
scheduled requests to execute the other callbacks for the same device,
except for scheduled autosuspends.
-3. Run-time PM Device Fields
+3. Runtime PM Device Fields
-The following device run-time PM fields are present in 'struct dev_pm_info', as
+The following device runtime PM fields are present in 'struct dev_pm_info', as
defined in include/linux/pm.h:
struct timer_list suspend_timer;
@@ -205,7 +217,7 @@ defined in include/linux/pm.h:
unsigned int disable_depth;
- used for disabling the helper funcions (they work normally if this is
- equal to zero); the initial value of it is 1 (i.e. run-time PM is
+ equal to zero); the initial value of it is 1 (i.e. runtime PM is
initially disabled for all devices)
unsigned int runtime_error;
@@ -229,10 +241,10 @@ defined in include/linux/pm.h:
suspend to complete; means "start a resume as soon as you've suspended"
unsigned int run_wake;
- - set if the device is capable of generating run-time wake-up events
+ - set if the device is capable of generating runtime wake-up events
enum rpm_status runtime_status;
- - the run-time PM status of the device; this field's initial value is
+ - the runtime PM status of the device; this field's initial value is
RPM_SUSPENDED, which means that each device is initially regarded by the
PM core as 'suspended', regardless of its real hardware status
@@ -243,7 +255,7 @@ defined in include/linux/pm.h:
and pm_runtime_forbid() helper functions
unsigned int no_callbacks;
- - indicates that the device does not use the run-time PM callbacks (see
+ - indicates that the device does not use the runtime PM callbacks (see
Section 8); it may be modified only by the pm_runtime_no_callbacks()
helper function
@@ -270,16 +282,16 @@ defined in include/linux/pm.h:
All of the above fields are members of the 'power' member of 'struct device'.
-4. Run-time PM Device Helper Functions
+4. Runtime PM Device Helper Functions
-The following run-time PM helper functions are defined in
+The following runtime PM helper functions are defined in
drivers/base/power/runtime.c and include/linux/pm_runtime.h:
void pm_runtime_init(struct device *dev);
- - initialize the device run-time PM fields in 'struct dev_pm_info'
+ - initialize the device runtime PM fields in 'struct dev_pm_info'
void pm_runtime_remove(struct device *dev);
- - make sure that the run-time PM of the device will be disabled after
+ - make sure that the runtime PM of the device will be disabled after
removing the device from device hierarchy
int pm_runtime_idle(struct device *dev);
@@ -289,9 +301,10 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
int pm_runtime_suspend(struct device *dev);
- execute the subsystem-level suspend callback for the device; returns 0 on
- success, 1 if the device's run-time PM status was already 'suspended', or
+ success, 1 if the device's runtime PM status was already 'suspended', or
error code on failure, where -EAGAIN or -EBUSY means it is safe to attempt
- to suspend the device again in future
+ to suspend the device again in future and -EACCES means that
+ 'power.disable_depth' is different from 0
int pm_runtime_autosuspend(struct device *dev);
- same as pm_runtime_suspend() except that the autosuspend delay is taken
@@ -301,10 +314,11 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
int pm_runtime_resume(struct device *dev);
- execute the subsystem-level resume callback for the device; returns 0 on
- success, 1 if the device's run-time PM status was already 'active' or
+ success, 1 if the device's runtime PM status was already 'active' or
error code on failure, where -EAGAIN means it may be safe to attempt to
resume the device again in future, but 'power.runtime_error' should be
- checked additionally
+ checked additionally, and -EACCES means that 'power.disable_depth' is
+ different from 0
int pm_request_idle(struct device *dev);
- submit a request to execute the subsystem-level idle callback for the
@@ -321,7 +335,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
device in future, where 'delay' is the time to wait before queuing up a
suspend work item in pm_wq, in milliseconds (if 'delay' is zero, the work
item is queued up immediately); returns 0 on success, 1 if the device's PM
- run-time status was already 'suspended', or error code if the request
+ runtime status was already 'suspended', or error code if the request
hasn't been scheduled (or queued up if 'delay' is 0); if the execution of
->runtime_suspend() is already scheduled and not yet expired, the new
value of 'delay' will be used as the time to wait
@@ -329,7 +343,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
int pm_request_resume(struct device *dev);
- submit a request to execute the subsystem-level resume callback for the
device (the request is represented by a work item in pm_wq); returns 0 on
- success, 1 if the device's run-time PM status was already 'active', or
+ success, 1 if the device's runtime PM status was already 'active', or
error code if the request hasn't been queued up
void pm_runtime_get_noresume(struct device *dev);
@@ -367,22 +381,32 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
pm_runtime_autosuspend(dev) and return its result
void pm_runtime_enable(struct device *dev);
- - enable the run-time PM helper functions to run the device bus type's
- run-time PM callbacks described in Section 2
+ - decrement the device's 'power.disable_depth' field; if that field is equal
+ to zero, the runtime PM helper functions can execute subsystem-level
+ callbacks described in Section 2 for the device
int pm_runtime_disable(struct device *dev);
- - prevent the run-time PM helper functions from running subsystem-level
- run-time PM callbacks for the device, make sure that all of the pending
- run-time PM operations on the device are either completed or canceled;
+ - increment the device's 'power.disable_depth' field (if the value of that
+ field was previously zero, this prevents subsystem-level runtime PM
+ callbacks from being run for the device), make sure that all of the pending
+ runtime PM operations on the device are either completed or canceled;
returns 1 if there was a resume request pending and it was necessary to
execute the subsystem-level resume callback for the device to satisfy that
request, otherwise 0 is returned
+ int pm_runtime_barrier(struct device *dev);
+ - check if there's a resume request pending for the device and resume it
+ (synchronously) in that case, cancel any other pending runtime PM requests
+ regarding it and wait for all runtime PM operations on it in progress to
+ complete; returns 1 if there was a resume request pending and it was
+ necessary to execute the subsystem-level resume callback for the device to
+ satisfy that request, otherwise 0 is returned
+
void pm_suspend_ignore_children(struct device *dev, bool enable);
- set/unset the power.ignore_children flag of the device
int pm_runtime_set_active(struct device *dev);
- - clear the device's 'power.runtime_error' flag, set the device's run-time
+ - clear the device's 'power.runtime_error' flag, set the device's runtime
PM status to 'active' and update its parent's counter of 'active'
children as appropriate (it is only valid to use this function if
'power.runtime_error' is set or 'power.disable_depth' is greater than
@@ -390,7 +414,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
which is not active and the 'power.ignore_children' flag of which is unset
void pm_runtime_set_suspended(struct device *dev);
- - clear the device's 'power.runtime_error' flag, set the device's run-time
+ - clear the device's 'power.runtime_error' flag, set the device's runtime
PM status to 'suspended' and update its parent's counter of 'active'
children as appropriate (it is only valid to use this function if
'power.runtime_error' is set or 'power.disable_depth' is greater than
@@ -400,6 +424,9 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
- return true if the device's runtime PM status is 'suspended' and its
'power.disable_depth' field is equal to zero, or false otherwise
+ bool pm_runtime_status_suspended(struct device *dev);
+ - return true if the device's runtime PM status is 'suspended'
+
void pm_runtime_allow(struct device *dev);
- set the power.runtime_auto flag for the device and decrease its usage
counter (used by the /sys/devices/.../power/control interface to
@@ -411,14 +438,13 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
effectively prevent the device from being power managed at run time)
void pm_runtime_no_callbacks(struct device *dev);
- - set the power.no_callbacks flag for the device and remove the run-time
+ - set the power.no_callbacks flag for the device and remove the runtime
PM attributes from /sys/devices/.../power (or prevent them from being
added when the device is registered)
void pm_runtime_irq_safe(struct device *dev);
- set the power.irq_safe flag for the device, causing the runtime-PM
- suspend and resume callbacks (but not the idle callback) to be invoked
- with interrupts disabled
+ callbacks to be invoked with interrupts off
void pm_runtime_mark_last_busy(struct device *dev);
- set the power.last_busy field to the current time
@@ -431,7 +457,7 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
void pm_runtime_set_autosuspend_delay(struct device *dev, int delay);
- set the power.autosuspend_delay value to 'delay' (expressed in
- milliseconds); if 'delay' is negative then run-time suspends are
+ milliseconds); if 'delay' is negative then runtime suspends are
prevented
unsigned long pm_runtime_autosuspend_expiration(struct device *dev);
@@ -464,42 +490,44 @@ pm_runtime_autosuspend_expiration()
If pm_runtime_irq_safe() has been called for a device then the following helper
functions may also be used in interrupt context:
+pm_runtime_idle()
pm_runtime_suspend()
pm_runtime_autosuspend()
pm_runtime_resume()
pm_runtime_get_sync()
+pm_runtime_put_sync()
pm_runtime_put_sync_suspend()
pm_runtime_put_sync_autosuspend()
-5. Run-time PM Initialization, Device Probing and Removal
+5. Runtime PM Initialization, Device Probing and Removal
-Initially, the run-time PM is disabled for all devices, which means that the
-majority of the run-time PM helper funtions described in Section 4 will return
+Initially, the runtime PM is disabled for all devices, which means that the
+majority of the runtime PM helper funtions described in Section 4 will return
-EAGAIN until pm_runtime_enable() is called for the device.
-In addition to that, the initial run-time PM status of all devices is
+In addition to that, the initial runtime PM status of all devices is
'suspended', but it need not reflect the actual physical state of the device.
Thus, if the device is initially active (i.e. it is able to process I/O), its
-run-time PM status must be changed to 'active', with the help of
+runtime PM status must be changed to 'active', with the help of
pm_runtime_set_active(), before pm_runtime_enable() is called for the device.
-However, if the device has a parent and the parent's run-time PM is enabled,
+However, if the device has a parent and the parent's runtime PM is enabled,
calling pm_runtime_set_active() for the device will affect the parent, unless
the parent's 'power.ignore_children' flag is set. Namely, in that case the
parent won't be able to suspend at run time, using the PM core's helper
functions, as long as the child's status is 'active', even if the child's
-run-time PM is still disabled (i.e. pm_runtime_enable() hasn't been called for
+runtime PM is still disabled (i.e. pm_runtime_enable() hasn't been called for
the child yet or pm_runtime_disable() has been called for it). For this reason,
once pm_runtime_set_active() has been called for the device, pm_runtime_enable()
-should be called for it too as soon as reasonably possible or its run-time PM
+should be called for it too as soon as reasonably possible or its runtime PM
status should be changed back to 'suspended' with the help of
pm_runtime_set_suspended().
-If the default initial run-time PM status of the device (i.e. 'suspended')
+If the default initial runtime PM status of the device (i.e. 'suspended')
reflects the actual state of the device, its bus type's or its driver's
->probe() callback will likely need to wake it up using one of the PM core's
helper functions described in Section 4. In that case, pm_runtime_resume()
-should be used. Of course, for this purpose the device's run-time PM has to be
+should be used. Of course, for this purpose the device's runtime PM has to be
enabled earlier by calling pm_runtime_enable().
If the device bus type's or driver's ->probe() callback runs
@@ -530,33 +558,33 @@ The user space can effectively disallow the driver of the device to power manage
it at run time by changing the value of its /sys/devices/.../power/control
attribute to "on", which causes pm_runtime_forbid() to be called. In principle,
this mechanism may also be used by the driver to effectively turn off the
-run-time power management of the device until the user space turns it on.
-Namely, during the initialization the driver can make sure that the run-time PM
+runtime power management of the device until the user space turns it on.
+Namely, during the initialization the driver can make sure that the runtime PM
status of the device is 'active' and call pm_runtime_forbid(). It should be
noted, however, that if the user space has already intentionally changed the
value of /sys/devices/.../power/control to "auto" to allow the driver to power
manage the device at run time, the driver may confuse it by using
pm_runtime_forbid() this way.
-6. Run-time PM and System Sleep
+6. Runtime PM and System Sleep
-Run-time PM and system sleep (i.e., system suspend and hibernation, also known
+Runtime PM and system sleep (i.e., system suspend and hibernation, also known
as suspend-to-RAM and suspend-to-disk) interact with each other in a couple of
ways. If a device is active when a system sleep starts, everything is
straightforward. But what should happen if the device is already suspended?
-The device may have different wake-up settings for run-time PM and system sleep.
-For example, remote wake-up may be enabled for run-time suspend but disallowed
+The device may have different wake-up settings for runtime PM and system sleep.
+For example, remote wake-up may be enabled for runtime suspend but disallowed
for system sleep (device_may_wakeup(dev) returns 'false'). When this happens,
the subsystem-level system suspend callback is responsible for changing the
device's wake-up setting (it may leave that to the device driver's system
suspend routine). It may be necessary to resume the device and suspend it again
in order to do so. The same is true if the driver uses different power levels
-or other settings for run-time suspend and system sleep.
+or other settings for runtime suspend and system sleep.
-During system resume, devices generally should be brought back to full power,
-even if they were suspended before the system sleep began. There are several
-reasons for this, including:
+During system resume, the simplest approach is to bring all devices back to full
+power, even if they had been suspended before the system suspend began. There
+are several reasons for this, including:
* The device might need to switch power levels, wake-up settings, etc.
@@ -571,18 +599,50 @@ reasons for this, including:
* The device might need to be reset.
* Even though the device was suspended, if its usage counter was > 0 then most
- likely it would need a run-time resume in the near future anyway.
-
- * Always going back to full power is simplest.
+ likely it would need a runtime resume in the near future anyway.
-If the device was suspended before the sleep began, then its run-time PM status
-will have to be updated to reflect the actual post-system sleep status. The way
-to do this is:
+If the device had been suspended before the system suspend began and it's
+brought back to full power during resume, then its runtime PM status will have
+to be updated to reflect the actual post-system sleep status. The way to do
+this is:
pm_runtime_disable(dev);
pm_runtime_set_active(dev);
pm_runtime_enable(dev);
+The PM core always increments the runtime usage counter before calling the
+->suspend() callback and decrements it after calling the ->resume() callback.
+Hence disabling runtime PM temporarily like this will not cause any runtime
+suspend attempts to be permanently lost. If the usage count goes to zero
+following the return of the ->resume() callback, the ->runtime_idle() callback
+will be invoked as usual.
+
+On some systems, however, system sleep is not entered through a global firmware
+or hardware operation. Instead, all hardware components are put into low-power
+states directly by the kernel in a coordinated way. Then, the system sleep
+state effectively follows from the states the hardware components end up in
+and the system is woken up from that state by a hardware interrupt or a similar
+mechanism entirely under the kernel's control. As a result, the kernel never
+gives control away and the states of all devices during resume are precisely
+known to it. If that is the case and none of the situations listed above takes
+place (in particular, if the system is not waking up from hibernation), it may
+be more efficient to leave the devices that had been suspended before the system
+suspend began in the suspended state.
+
+The PM core does its best to reduce the probability of race conditions between
+the runtime PM and system suspend/resume (and hibernation) callbacks by carrying
+out the following operations:
+
+ * During system suspend it calls pm_runtime_get_noresume() and
+ pm_runtime_barrier() for every device right before executing the
+ subsystem-level .suspend() callback for it. In addition to that it calls
+ pm_runtime_disable() for every device right after executing the
+ subsystem-level .suspend() callback for it.
+
+ * During system resume it calls pm_runtime_enable() and pm_runtime_put_sync()
+ for every device right before and right after executing the subsystem-level
+ .resume() callback for it, respectively.
+
7. Generic subsystem callbacks
Subsystems may wish to conserve code space by using the set of generic power
@@ -607,40 +667,68 @@ driver/base/power/generic_ops.c:
callback provided by its driver and return its result, or return 0 if not
defined
+ int pm_generic_suspend_noirq(struct device *dev);
+ - if pm_runtime_suspended(dev) returns "false", invoke the ->suspend_noirq()
+ callback provided by the device's driver and return its result, or return
+ 0 if not defined
+
int pm_generic_resume(struct device *dev);
- invoke the ->resume() callback provided by the driver of this device and,
if successful, change the device's runtime PM status to 'active'
+ int pm_generic_resume_noirq(struct device *dev);
+ - invoke the ->resume_noirq() callback provided by the driver of this device
+
int pm_generic_freeze(struct device *dev);
- if the device has not been suspended at run time, invoke the ->freeze()
callback provided by its driver and return its result, or return 0 if not
defined
+ int pm_generic_freeze_noirq(struct device *dev);
+ - if pm_runtime_suspended(dev) returns "false", invoke the ->freeze_noirq()
+ callback provided by the device's driver and return its result, or return
+ 0 if not defined
+
int pm_generic_thaw(struct device *dev);
- if the device has not been suspended at run time, invoke the ->thaw()
callback provided by its driver and return its result, or return 0 if not
defined
+ int pm_generic_thaw_noirq(struct device *dev);
+ - if pm_runtime_suspended(dev) returns "false", invoke the ->thaw_noirq()
+ callback provided by the device's driver and return its result, or return
+ 0 if not defined
+
int pm_generic_poweroff(struct device *dev);
- if the device has not been suspended at run time, invoke the ->poweroff()
callback provided by its driver and return its result, or return 0 if not
defined
+ int pm_generic_poweroff_noirq(struct device *dev);
+ - if pm_runtime_suspended(dev) returns "false", run the ->poweroff_noirq()
+ callback provided by the device's driver and return its result, or return
+ 0 if not defined
+
int pm_generic_restore(struct device *dev);
- invoke the ->restore() callback provided by the driver of this device and,
if successful, change the device's runtime PM status to 'active'
+ int pm_generic_restore_noirq(struct device *dev);
+ - invoke the ->restore_noirq() callback provided by the device's driver
+
These functions can be assigned to the ->runtime_idle(), ->runtime_suspend(),
-->runtime_resume(), ->suspend(), ->resume(), ->freeze(), ->thaw(), ->poweroff(),
-or ->restore() callback pointers in the subsystem-level dev_pm_ops structures.
+->runtime_resume(), ->suspend(), ->suspend_noirq(), ->resume(),
+->resume_noirq(), ->freeze(), ->freeze_noirq(), ->thaw(), ->thaw_noirq(),
+->poweroff(), ->poweroff_noirq(), ->restore(), ->restore_noirq() callback
+pointers in the subsystem-level dev_pm_ops structures.
If a subsystem wishes to use all of them at the same time, it can simply assign
the GENERIC_SUBSYS_PM_OPS macro, defined in include/linux/pm.h, to its
dev_pm_ops structure pointer.
Device drivers that wish to use the same function as a system suspend, freeze,
-poweroff and run-time suspend callback, and similarly for system resume, thaw,
-restore, and run-time resume, can achieve this with the help of the
+poweroff and runtime suspend callback, and similarly for system resume, thaw,
+restore, and runtime resume, can achieve this with the help of the
UNIVERSAL_DEV_PM_OPS macro defined in include/linux/pm.h (possibly setting its
last argument to NULL).
@@ -650,7 +738,7 @@ Some "devices" are only logical sub-devices of their parent and cannot be
power-managed on their own. (The prototype example is a USB interface. Entire
USB devices can go into low-power mode or send wake-up requests, but neither is
possible for individual interfaces.) The drivers for these devices have no
-need of run-time PM callbacks; if the callbacks did exist, ->runtime_suspend()
+need of runtime PM callbacks; if the callbacks did exist, ->runtime_suspend()
and ->runtime_resume() would always return 0 without doing anything else and
->runtime_idle() would always call pm_runtime_suspend().
@@ -658,7 +746,7 @@ Subsystems can tell the PM core about these devices by calling
pm_runtime_no_callbacks(). This should be done after the device structure is
initialized and before it is registered (although after device registration is
also okay). The routine will set the device's power.no_callbacks flag and
-prevent the non-debugging run-time PM sysfs attributes from being created.
+prevent the non-debugging runtime PM sysfs attributes from being created.
When power.no_callbacks is set, the PM core will not invoke the
->runtime_idle(), ->runtime_suspend(), or ->runtime_resume() callbacks.
@@ -666,7 +754,7 @@ Instead it will assume that suspends and resumes always succeed and that idle
devices should be suspended.
As a consequence, the PM core will never directly inform the device's subsystem
-or driver about run-time power changes. Instead, the driver for the device's
+or driver about runtime power changes. Instead, the driver for the device's
parent must take responsibility for telling the device's driver when the
parent's power state changes.
@@ -677,13 +765,13 @@ A device should be put in a low-power state only when there's some reason to
think it will remain in that state for a substantial time. A common heuristic
says that a device which hasn't been used for a while is liable to remain
unused; following this advice, drivers should not allow devices to be suspended
-at run-time until they have been inactive for some minimum period. Even when
+at runtime until they have been inactive for some minimum period. Even when
the heuristic ends up being non-optimal, it will still prevent devices from
"bouncing" too rapidly between low-power and full-power states.
The term "autosuspend" is an historical remnant. It doesn't mean that the
device is automatically suspended (the subsystem or driver still has to call
-the appropriate PM routines); rather it means that run-time suspends will
+the appropriate PM routines); rather it means that runtime suspends will
automatically be delayed until the desired period of inactivity has elapsed.
Inactivity is determined based on the power.last_busy field. Drivers should
diff --git a/Documentation/power/suspend-and-cpuhotplug.txt b/Documentation/power/suspend-and-cpuhotplug.txt
new file mode 100644
index 0000000..f28f9a6
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+++ b/Documentation/power/suspend-and-cpuhotplug.txt
@@ -0,0 +1,275 @@
+Interaction of Suspend code (S3) with the CPU hotplug infrastructure
+
+ (C) 2011 Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
+
+
+I. How does the regular CPU hotplug code differ from how the Suspend-to-RAM
+ infrastructure uses it internally? And where do they share common code?
+
+Well, a picture is worth a thousand words... So ASCII art follows :-)
+
+[This depicts the current design in the kernel, and focusses only on the
+interactions involving the freezer and CPU hotplug and also tries to explain
+the locking involved. It outlines the notifications involved as well.
+But please note that here, only the call paths are illustrated, with the aim
+of describing where they take different paths and where they share code.
+What happens when regular CPU hotplug and Suspend-to-RAM race with each other
+is not depicted here.]
+
+On a high level, the suspend-resume cycle goes like this:
+
+|Freeze| -> |Disable nonboot| -> |Do suspend| -> |Enable nonboot| -> |Thaw |
+|tasks | | cpus | | | | cpus | |tasks|
+
+
+More details follow:
+
+ Suspend call path
+ -----------------
+
+ Write 'mem' to
+ /sys/power/state
+ syfs file
+ |
+ v
+ Acquire pm_mutex lock
+ |
+ v
+ Send PM_SUSPEND_PREPARE
+ notifications
+ |
+ v
+ Freeze tasks
+ |
+ |
+ v
+ disable_nonboot_cpus()
+ /* start */
+ |
+ v
+ Acquire cpu_add_remove_lock
+ |
+ v
+ Iterate over CURRENTLY
+ online CPUs
+ |
+ |
+ | ----------
+ v | L
+ ======> _cpu_down() |
+ | [This takes cpuhotplug.lock |
+ Common | before taking down the CPU |
+ code | and releases it when done] | O
+ | While it is at it, notifications |
+ | are sent when notable events occur, |
+ ======> by running all registered callbacks. |
+ | | O
+ | |
+ | |
+ v |
+ Note down these cpus in | P
+ frozen_cpus mask ----------
+ |
+ v
+ Disable regular cpu hotplug
+ by setting cpu_hotplug_disabled=1
+ |
+ v
+ Release cpu_add_remove_lock
+ |
+ v
+ /* disable_nonboot_cpus() complete */
+ |
+ v
+ Do suspend
+
+
+
+Resuming back is likewise, with the counterparts being (in the order of
+execution during resume):
+* enable_nonboot_cpus() which involves:
+ | Acquire cpu_add_remove_lock
+ | Reset cpu_hotplug_disabled to 0, thereby enabling regular cpu hotplug
+ | Call _cpu_up() [for all those cpus in the frozen_cpus mask, in a loop]
+ | Release cpu_add_remove_lock
+ v
+
+* thaw tasks
+* send PM_POST_SUSPEND notifications
+* Release pm_mutex lock.
+
+
+It is to be noted here that the pm_mutex lock is acquired at the very
+beginning, when we are just starting out to suspend, and then released only
+after the entire cycle is complete (i.e., suspend + resume).
+
+
+
+ Regular CPU hotplug call path
+ -----------------------------
+
+ Write 0 (or 1) to
+ /sys/devices/system/cpu/cpu*/online
+ sysfs file
+ |
+ |
+ v
+ cpu_down()
+ |
+ v
+ Acquire cpu_add_remove_lock
+ |
+ v
+ If cpu_hotplug_disabled is 1
+ return gracefully
+ |
+ |
+ v
+ ======> _cpu_down()
+ | [This takes cpuhotplug.lock
+ Common | before taking down the CPU
+ code | and releases it when done]
+ | While it is at it, notifications
+ | are sent when notable events occur,
+ ======> by running all registered callbacks.
+ |
+ |
+ v
+ Release cpu_add_remove_lock
+ [That's it!, for
+ regular CPU hotplug]
+
+
+
+So, as can be seen from the two diagrams (the parts marked as "Common code"),
+regular CPU hotplug and the suspend code path converge at the _cpu_down() and
+_cpu_up() functions. They differ in the arguments passed to these functions,
+in that during regular CPU hotplug, 0 is passed for the 'tasks_frozen'
+argument. But during suspend, since the tasks are already frozen by the time
+the non-boot CPUs are offlined or onlined, the _cpu_*() functions are called
+with the 'tasks_frozen' argument set to 1.
+[See below for some known issues regarding this.]
+
+
+Important files and functions/entry points:
+------------------------------------------
+
+kernel/power/process.c : freeze_processes(), thaw_processes()
+kernel/power/suspend.c : suspend_prepare(), suspend_enter(), suspend_finish()
+kernel/cpu.c: cpu_[up|down](), _cpu_[up|down](), [disable|enable]_nonboot_cpus()
+
+
+
+II. What are the issues involved in CPU hotplug?
+ -------------------------------------------
+
+There are some interesting situations involving CPU hotplug and microcode
+update on the CPUs, as discussed below:
+
+[Please bear in mind that the kernel requests the microcode images from
+userspace, using the request_firmware() function defined in
+drivers/base/firmware_class.c]
+
+
+a. When all the CPUs are identical:
+
+ This is the most common situation and it is quite straightforward: we want
+ to apply the same microcode revision to each of the CPUs.
+ To give an example of x86, the collect_cpu_info() function defined in
+ arch/x86/kernel/microcode_core.c helps in discovering the type of the CPU
+ and thereby in applying the correct microcode revision to it.
+ But note that the kernel does not maintain a common microcode image for the
+ all CPUs, in order to handle case 'b' described below.
+
+
+b. When some of the CPUs are different than the rest:
+
+ In this case since we probably need to apply different microcode revisions
+ to different CPUs, the kernel maintains a copy of the correct microcode
+ image for each CPU (after appropriate CPU type/model discovery using
+ functions such as collect_cpu_info()).
+
+
+c. When a CPU is physically hot-unplugged and a new (and possibly different
+ type of) CPU is hot-plugged into the system:
+
+ In the current design of the kernel, whenever a CPU is taken offline during
+ a regular CPU hotplug operation, upon receiving the CPU_DEAD notification
+ (which is sent by the CPU hotplug code), the microcode update driver's
+ callback for that event reacts by freeing the kernel's copy of the
+ microcode image for that CPU.
+
+ Hence, when a new CPU is brought online, since the kernel finds that it
+ doesn't have the microcode image, it does the CPU type/model discovery
+ afresh and then requests the userspace for the appropriate microcode image
+ for that CPU, which is subsequently applied.
+
+ For example, in x86, the mc_cpu_callback() function (which is the microcode
+ update driver's callback registered for CPU hotplug events) calls
+ microcode_update_cpu() which would call microcode_init_cpu() in this case,
+ instead of microcode_resume_cpu() when it finds that the kernel doesn't
+ have a valid microcode image. This ensures that the CPU type/model
+ discovery is performed and the right microcode is applied to the CPU after
+ getting it from userspace.
+
+
+d. Handling microcode update during suspend/hibernate:
+
+ Strictly speaking, during a CPU hotplug operation which does not involve
+ physically removing or inserting CPUs, the CPUs are not actually powered
+ off during a CPU offline. They are just put to the lowest C-states possible.
+ Hence, in such a case, it is not really necessary to re-apply microcode
+ when the CPUs are brought back online, since they wouldn't have lost the
+ image during the CPU offline operation.
+
+ This is the usual scenario encountered during a resume after a suspend.
+ However, in the case of hibernation, since all the CPUs are completely
+ powered off, during restore it becomes necessary to apply the microcode
+ images to all the CPUs.
+
+ [Note that we don't expect someone to physically pull out nodes and insert
+ nodes with a different type of CPUs in-between a suspend-resume or a
+ hibernate/restore cycle.]
+
+ In the current design of the kernel however, during a CPU offline operation
+ as part of the suspend/hibernate cycle (the CPU_DEAD_FROZEN notification),
+ the existing copy of microcode image in the kernel is not freed up.
+ And during the CPU online operations (during resume/restore), since the
+ kernel finds that it already has copies of the microcode images for all the
+ CPUs, it just applies them to the CPUs, avoiding any re-discovery of CPU
+ type/model and the need for validating whether the microcode revisions are
+ right for the CPUs or not (due to the above assumption that physical CPU
+ hotplug will not be done in-between suspend/resume or hibernate/restore
+ cycles).
+
+
+III. Are there any known problems when regular CPU hotplug and suspend race
+ with each other?
+
+Yes, they are listed below:
+
+1. When invoking regular CPU hotplug, the 'tasks_frozen' argument passed to
+ the _cpu_down() and _cpu_up() functions is *always* 0.
+ This might not reflect the true current state of the system, since the
+ tasks could have been frozen by an out-of-band event such as a suspend
+ operation in progress. Hence, it will lead to wrong notifications being
+ sent during the cpu online/offline events (eg, CPU_ONLINE notification
+ instead of CPU_ONLINE_FROZEN) which in turn will lead to execution of
+ inappropriate code by the callbacks registered for such CPU hotplug events.
+
+2. If a regular CPU hotplug stress test happens to race with the freezer due
+ to a suspend operation in progress at the same time, then we could hit the
+ situation described below:
+
+ * A regular cpu online operation continues its journey from userspace
+ into the kernel, since the freezing has not yet begun.
+ * Then freezer gets to work and freezes userspace.
+ * If cpu online has not yet completed the microcode update stuff by now,
+ it will now start waiting on the frozen userspace in the
+ TASK_UNINTERRUPTIBLE state, in order to get the microcode image.
+ * Now the freezer continues and tries to freeze the remaining tasks. But
+ due to this wait mentioned above, the freezer won't be able to freeze
+ the cpu online hotplug task and hence freezing of tasks fails.
+
+ As a result of this task freezing failure, the suspend operation gets
+ aborted.
diff --git a/Documentation/power/userland-swsusp.txt b/Documentation/power/userland-swsusp.txt
index 1101bee..0e87082 100644
--- a/Documentation/power/userland-swsusp.txt
+++ b/Documentation/power/userland-swsusp.txt
@@ -77,7 +77,8 @@ SNAPSHOT_SET_SWAP_AREA - set the resume partition and the offset (in <PAGE_SIZE>
resume_swap_area, as defined in kernel/power/suspend_ioctls.h,
containing the resume device specification and the offset); for swap
partitions the offset is always 0, but it is different from zero for
- swap files (see Documentation/swsusp-and-swap-files.txt for details).
+ swap files (see Documentation/power/swsusp-and-swap-files.txt for
+ details).
SNAPSHOT_PLATFORM_SUPPORT - enable/disable the hibernation platform support,
depending on the argument value (enable, if the argument is nonzero)