Merge tag 'pm-5.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm

Pull power management updates from Rafael Wysocki:
 "These are PM-runtime framework changes to use ktime instead of jiffies
  for accounting, new PM core flag to mark devices that don't need any
  form of power management, cpuidle updates including driver API
  documentation and a new governor, cpufreq updates including a new
  driver for Armada 8K, thermal cleanups and more, some energy-aware
  scheduling (EAS) enabling changes, new chips support in the intel_idle
  and RAPL drivers and assorted cleanups in some other places.

  Specifics:

   - Update the PM-runtime framework to use ktime instead of jiffies for
     accounting (Thara Gopinath, Vincent Guittot)

   - Optimize the autosuspend code in the PM-runtime framework somewhat
     (Ladislav Michl)

   - Add a PM core flag to mark devices that don't need any form of
     power management (Sudeep Holla)

   - Introduce driver API documentation for cpuidle and add a new
     cpuidle governor for tickless systems (Rafael Wysocki)

   - Add Jacobsville support to the intel_idle driver (Zhang Rui)

   - Clean up a cpuidle core header file and the cpuidle-dt and ACPI
     processor-idle drivers (Yangtao Li, Joseph Lo, Yazen Ghannam)

   - Add new cpufreq driver for Armada 8K (Gregory Clement)

   - Fix and clean up cpufreq core (Rafael Wysocki, Viresh Kumar, Amit
     Kucheria)

   - Add support for light-weight tear-down and bring-up of CPUs to the
     cpufreq core and use it in the cpufreq-dt driver (Viresh Kumar)

   - Fix cpu_cooling Kconfig dependencies, add support for CPU cooling
     auto-registration to the cpufreq core and use it in multiple
     cpufreq drivers (Amit Kucheria)

   - Fix some minor issues and do some cleanups in the davinci,
     e_powersaver, ap806, s5pv210, qcom and kryo cpufreq drivers
     (Bartosz Golaszewski, Gustavo Silva, Julia Lawall, Paweł Chmiel,
     Taniya Das, Viresh Kumar)

   - Add a Hisilicon CPPC quirk to the cppc_cpufreq driver (Xiongfeng
     Wang)

   - Clean up the intel_pstate and acpi-cpufreq drivers (Erwan Velu,
     Rafael Wysocki)

   - Clean up multiple cpufreq drivers (Yangtao Li)

   - Update cpufreq-related MAINTAINERS entries (Baruch Siach, Lukas
     Bulwahn)

   - Add support for exposing the Energy Model via debugfs and make
     multiple cpufreq drivers register an Energy Model to support
     energy-aware scheduling (Quentin Perret, Dietmar Eggemann, Matthias
     Kaehlcke)

   - Add Ice Lake mobile and Jacobsville support to the Intel RAPL
     power-capping driver (Gayatri Kammela, Zhang Rui)

   - Add a power estimation helper to the operating performance points
     (OPP) framework and clean up a core function in it (Quentin Perret,
     Viresh Kumar)

   - Make minor improvements in the generic power domains (genpd), OPP
     and system suspend frameworks and in the PM core (Aditya Pakki,
     Douglas Anderson, Greg Kroah-Hartman, Rafael Wysocki, Yangtao Li)"

* tag 'pm-5.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm: (80 commits)
  cpufreq: kryo: Release OPP tables on module removal
  cpufreq: ap806: add missing of_node_put after of_device_is_available
  cpufreq: acpi-cpufreq: Report if CPU doesn't support boost technologies
  cpufreq: Pass updated policy to driver ->setpolicy() callback
  cpufreq: Fix two debug messages in cpufreq_set_policy()
  cpufreq: Reorder and simplify cpufreq_update_policy()
  cpufreq: Add kerneldoc comments for two core functions
  PM / core: Add support to skip power management in device/driver model
  cpufreq: intel_pstate: Rework iowait boosting to be less aggressive
  cpufreq: intel_pstate: Eliminate intel_pstate_get_base_pstate()
  cpufreq: intel_pstate: Avoid redundant initialization of local vars
  powercap/intel_rapl: add Ice Lake mobile
  ACPI / processor: Set P_LVL{2,3} idle state descriptions
  cpufreq / cppc: Work around for Hisilicon CPPC cpufreq
  ACPI / CPPC: Add a helper to get desired performance
  cpufreq: davinci: move configuration to include/linux/platform_data
  cpufreq: speedstep: convert BUG() to BUG_ON()
  cpufreq: powernv: fix missing check of return value in init_powernv_pstates()
  cpufreq: longhaul: remove unneeded semicolon
  cpufreq: pcc-cpufreq: remove unneeded semicolon
  ..

5 files changed, 382 insertions, 76 deletions

diff --git a/Documentation/admin-guide/pm/cpuidle.rst b/Documentation/admin-guide/pm/cpuidle.rst
index 106379e2619f..9c58b35a81cb 100644
--- a/Documentation/admin-guide/pm/cpuidle.rst
+++ b/Documentation/admin-guide/pm/cpuidle.rst
@@ -155,14 +155,14 @@ governor uses that information depends on what algorithm is implemented by it
 and that is the primary reason for having more than one governor in the
 ``CPUIdle`` subsystem.
 
-There are two ``CPUIdle`` governors available, ``menu`` and ``ladder``.  Which
-of them is used depends on the configuration of the kernel and in particular on
-whether or not the scheduler tick can be `stopped by the idle
-loop <idle-cpus-and-tick_>`_.  It is possible to change the governor at run time
-if the ``cpuidle_sysfs_switch`` command line parameter has been passed to the
-kernel, but that is not safe in general, so it should not be done on production
-systems (that may change in the future, though).  The name of the ``CPUIdle``
-governor currently used by the kernel can be read from the
+There are three ``CPUIdle`` governors available, ``menu``, `TEO <teo-gov_>`_
+and ``ladder``.  Which of them is used by default depends on the configuration
+of the kernel and in particular on whether or not the scheduler tick can be
+`stopped by the idle loop <idle-cpus-and-tick_>`_.  It is possible to change the
+governor at run time if the ``cpuidle_sysfs_switch`` command line parameter has
+been passed to the kernel, but that is not safe in general, so it should not be
+done on production systems (that may change in the future, though).  The name of
+the ``CPUIdle`` governor currently used by the kernel can be read from the
 :file:`current_governor_ro` (or :file:`current_governor` if
 ``cpuidle_sysfs_switch`` is present in the kernel command line) file under
 :file:`/sys/devices/system/cpu/cpuidle/` in ``sysfs``.
@@ -256,6 +256,8 @@ the ``menu`` governor by default and if it is not tickless, the default
 ``CPUIdle`` governor on it will be ``ladder``.
 
 
+.. _menu-gov:
+
 The ``menu`` Governor
 =====================
 
@@ -333,6 +335,92 @@ that time, the governor may need to select a shallower state with a suitable
 target residency.
 
 
+.. _teo-gov:
+
+The Timer Events Oriented (TEO) Governor
+========================================
+
+The timer events oriented (TEO) governor is an alternative ``CPUIdle`` governor
+for tickless systems.  It follows the same basic strategy as the ``menu`` `one
+<menu-gov_>`_: it always tries to find the deepest idle state suitable for the
+given conditions.  However, it applies a different approach to that problem.
+
+First, it does not use sleep length correction factors, but instead it attempts
+to correlate the observed idle duration values with the available idle states
+and use that information to pick up the idle state that is most likely to
+"match" the upcoming CPU idle interval.   Second, it does not take the tasks
+that were running on the given CPU in the past and are waiting on some I/O
+operations to complete now at all (there is no guarantee that they will run on
+the same CPU when they become runnable again) and the pattern detection code in
+it avoids taking timer wakeups into account.  It also only uses idle duration
+values less than the current time till the closest timer (with the scheduler
+tick excluded) for that purpose.
+
+Like in the ``menu`` governor `case <menu-gov_>`_, the first step is to obtain
+the *sleep length*, which is the time until the closest timer event with the
+assumption that the scheduler tick will be stopped (that also is the upper bound
+on the time until the next CPU wakeup).  That value is then used to preselect an
+idle state on the basis of three metrics maintained for each idle state provided
+by the ``CPUIdle`` driver: ``hits``, ``misses`` and ``early_hits``.
+
+The ``hits`` and ``misses`` metrics measure the likelihood that a given idle
+state will "match" the observed (post-wakeup) idle duration if it "matches" the
+sleep length.  They both are subject to decay (after a CPU wakeup) every time
+the target residency of the idle state corresponding to them is less than or
+equal to the sleep length and the target residency of the next idle state is
+greater than the sleep length (that is, when the idle state corresponding to
+them "matches" the sleep length).  The ``hits`` metric is increased if the
+former condition is satisfied and the target residency of the given idle state
+is less than or equal to the observed idle duration and the target residency of
+the next idle state is greater than the observed idle duration at the same time
+(that is, it is increased when the given idle state "matches" both the sleep
+length and the observed idle duration).  In turn, the ``misses`` metric is
+increased when the given idle state "matches" the sleep length only and the
+observed idle duration is too short for its target residency.
+
+The ``early_hits`` metric measures the likelihood that a given idle state will
+"match" the observed (post-wakeup) idle duration if it does not "match" the
+sleep length.  It is subject to decay on every CPU wakeup and it is increased
+when the idle state corresponding to it "matches" the observed (post-wakeup)
+idle duration and the target residency of the next idle state is less than or
+equal to the sleep length (i.e. the idle state "matching" the sleep length is
+deeper than the given one).
+
+The governor walks the list of idle states provided by the ``CPUIdle`` driver
+and finds the last (deepest) one with the target residency less than or equal
+to the sleep length.  Then, the ``hits`` and ``misses`` metrics of that idle
+state are compared with each other and it is preselected if the ``hits`` one is
+greater (which means that that idle state is likely to "match" the observed idle
+duration after CPU wakeup).  If the ``misses`` one is greater, the governor
+preselects the shallower idle state with the maximum ``early_hits`` metric
+(or if there are multiple shallower idle states with equal ``early_hits``
+metric which also is the maximum, the shallowest of them will be preselected).
+[If there is a wakeup latency constraint coming from the `PM QoS framework
+<cpu-pm-qos_>`_ which is hit before reaching the deepest idle state with the
+target residency within the sleep length, the deepest idle state with the exit
+latency within the constraint is preselected without consulting the ``hits``,
+``misses`` and ``early_hits`` metrics.]
+
+Next, the governor takes several idle duration values observed most recently
+into consideration and if at least a half of them are greater than or equal to
+the target residency of the preselected idle state, that idle state becomes the
+final candidate to ask for.  Otherwise, the average of the most recent idle
+duration values below the target residency of the preselected idle state is
+computed and the governor walks the idle states shallower than the preselected
+one and finds the deepest of them with the target residency within that average.
+That idle state is then taken as the final candidate to ask for.
+
+Still, at this point the governor may need to refine the idle state selection if
+it has not decided to `stop the scheduler tick <idle-cpus-and-tick_>`_.  That
+generally happens if the target residency of the idle state selected so far is
+less than the tick period and the tick has not been stopped already (in a
+previous iteration of the idle loop).  Then, like in the ``menu`` governor
+`case <menu-gov_>`_, the sleep length used in the previous computations may not
+reflect the real time until the closest timer event and if it really is greater
+than that time, a shallower state with a suitable target residency may need to
+be selected.
+
+
 .. _idle-states-representation:
 
 Representation of Idle States
diff --git a/Documentation/cpuidle/driver.txt b/Documentation/cpuidle/driver.txt
deleted file mode 100644
index 1b0d81d92583..000000000000
--- a/Documentation/cpuidle/driver.txt
+++ /dev/null
@@ -1,37 +0,0 @@
-
-
-		Supporting multiple CPU idle levels in kernel
-
-				cpuidle drivers
-
-
-
-
-cpuidle driver hooks into the cpuidle infrastructure and handles the
-architecture/platform dependent part of CPU idle states. Driver
-provides the platform idle state detection capability and also
-has mechanisms in place to support actual entry-exit into CPU idle states.
-
-cpuidle driver initializes the cpuidle_device structure for each CPU device
-and registers with cpuidle using cpuidle_register_device.
-
-If all the idle states are the same, the wrapper function cpuidle_register
-could be used instead.
-
-It can also support the dynamic changes (like battery <-> AC), by using
-cpuidle_pause_and_lock, cpuidle_disable_device and cpuidle_enable_device,
-cpuidle_resume_and_unlock.
-
-Interfaces:
-extern int cpuidle_register(struct cpuidle_driver *drv,
-                            const struct cpumask *const coupled_cpus);
-extern int cpuidle_unregister(struct cpuidle_driver *drv);
-extern int cpuidle_register_driver(struct cpuidle_driver *drv);
-extern void cpuidle_unregister_driver(struct cpuidle_driver *drv);
-extern int cpuidle_register_device(struct cpuidle_device *dev);
-extern void cpuidle_unregister_device(struct cpuidle_device *dev);
-
-extern void cpuidle_pause_and_lock(void);
-extern void cpuidle_resume_and_unlock(void);
-extern int cpuidle_enable_device(struct cpuidle_device *dev);
-extern void cpuidle_disable_device(struct cpuidle_device *dev);
diff --git a/Documentation/cpuidle/governor.txt b/Documentation/cpuidle/governor.txt
deleted file mode 100644
index d9020f5e847b..000000000000
--- a/Documentation/cpuidle/governor.txt
+++ /dev/null
@@ -1,28 +0,0 @@
-
-
-
-		Supporting multiple CPU idle levels in kernel
-
-				cpuidle governors
-
-
-
-
-cpuidle governor is policy routine that decides what idle state to enter at
-any given time. cpuidle core uses different callbacks to the governor.
-
-* enable() to enable governor for a particular device
-* disable() to disable governor for a particular device
-* select() to select an idle state to enter
-* reflect() called after returning from the idle state, which can be used
-  by the governor for some record keeping.
-
-More than one governor can be registered at the same time and
-users can switch between drivers using /sysfs interface (when enabled).
-More than one governor part is supported for developers to easily experiment
-with different governors. By default, most optimal governor based on your
-kernel configuration and platform will be selected by cpuidle.
-
-Interfaces:
-extern int cpuidle_register_governor(struct cpuidle_governor *gov);
-struct cpuidle_governor
diff --git a/Documentation/driver-api/pm/cpuidle.rst b/Documentation/driver-api/pm/cpuidle.rst
new file mode 100644
index 000000000000..5842ab621a58
--- /dev/null
+++ b/Documentation/driver-api/pm/cpuidle.rst
@@ -0,0 +1,282 @@
+.. |struct cpuidle_governor| replace:: :c:type:`struct cpuidle_governor <cpuidle_governor>`
+.. |struct cpuidle_device| replace:: :c:type:`struct cpuidle_device <cpuidle_device>`
+.. |struct cpuidle_driver| replace:: :c:type:`struct cpuidle_driver <cpuidle_driver>`
+.. |struct cpuidle_state| replace:: :c:type:`struct cpuidle_state <cpuidle_state>`
+
+========================
+CPU Idle Time Management
+========================
+
+::
+
+ Copyright (c) 2019 Intel Corp., Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+
+
+CPU Idle Time Management Subsystem
+==================================
+
+Every time one of the logical CPUs in the system (the entities that appear to
+fetch and execute instructions: hardware threads, if present, or processor
+cores) is idle after an interrupt or equivalent wakeup event, which means that
+there are no tasks to run on it except for the special "idle" task associated
+with it, there is an opportunity to save energy for the processor that it
+belongs to.  That can be done by making the idle logical CPU stop fetching
+instructions from memory and putting some of the processor's functional units
+depended on by it into an idle state in which they will draw less power.
+
+However, there may be multiple different idle states that can be used in such a
+situation in principle, so it may be necessary to find the most suitable one
+(from the kernel perspective) and ask the processor to use (or "enter") that
+particular idle state.  That is the role of the CPU idle time management
+subsystem in the kernel, called ``CPUIdle``.
+
+The design of ``CPUIdle`` is modular and based on the code duplication avoidance
+principle, so the generic code that in principle need not depend on the hardware
+or platform design details in it is separate from the code that interacts with
+the hardware.  It generally is divided into three categories of functional
+units: *governors* responsible for selecting idle states to ask the processor
+to enter, *drivers* that pass the governors' decisions on to the hardware and
+the *core* providing a common framework for them.
+
+
+CPU Idle Time Governors
+=======================
+
+A CPU idle time (``CPUIdle``) governor is a bundle of policy code invoked when
+one of the logical CPUs in the system turns out to be idle.  Its role is to
+select an idle state to ask the processor to enter in order to save some energy.
+
+``CPUIdle`` governors are generic and each of them can be used on any hardware
+platform that the Linux kernel can run on.  For this reason, data structures
+operated on by them cannot depend on any hardware architecture or platform
+design details as well.
+
+The governor itself is represented by a |struct cpuidle_governor| object
+containing four callback pointers, :c:member:`enable`, :c:member:`disable`,
+:c:member:`select`, :c:member:`reflect`, a :c:member:`rating` field described
+below, and a name (string) used for identifying it.
+
+For the governor to be available at all, that object needs to be registered
+with the ``CPUIdle`` core by calling :c:func:`cpuidle_register_governor()` with
+a pointer to it passed as the argument.  If successful, that causes the core to
+add the governor to the global list of available governors and, if it is the
+only one in the list (that is, the list was empty before) or the value of its
+:c:member:`rating` field is greater than the value of that field for the
+governor currently in use, or the name of the new governor was passed to the
+kernel as the value of the ``cpuidle.governor=`` command line parameter, the new
+governor will be used from that point on (there can be only one ``CPUIdle``
+governor in use at a time).  Also, if ``cpuidle_sysfs_switch`` is passed to the
+kernel in the command line, user space can choose the ``CPUIdle`` governor to
+use at run time via ``sysfs``.
+
+Once registered, ``CPUIdle`` governors cannot be unregistered, so it is not
+practical to put them into loadable kernel modules.
+
+The interface between ``CPUIdle`` governors and the core consists of four
+callbacks:
+
+:c:member:`enable`
+	::
+
+	  int (*enable) (struct cpuidle_driver *drv, struct cpuidle_device *dev);
+
+	The role of this callback is to prepare the governor for handling the
+	(logical) CPU represented by the |struct cpuidle_device| object	pointed
+	to by the ``dev`` argument.  The |struct cpuidle_driver| object pointed
+	to by the ``drv`` argument represents the ``CPUIdle`` driver to be used
+	with that CPU (among other things, it should contain the list of
+	|struct cpuidle_state| objects representing idle states that the
+	processor holding the given CPU can be asked to enter).
+
+	It may fail, in which case it is expected to return a negative error
+	code, and that causes the kernel to run the architecture-specific
+	default code for idle CPUs on the CPU in question instead of ``CPUIdle``
+	until the ``->enable()`` governor callback is invoked for that CPU
+	again.
+
+:c:member:`disable`
+	::
+
+	  void (*disable) (struct cpuidle_driver *drv, struct cpuidle_device *dev);
+
+	Called to make the governor stop handling the (logical) CPU represented
+	by the |struct cpuidle_device| object pointed to by the ``dev``
+	argument.
+
+	It is expected to reverse any changes made by the ``->enable()``
+	callback when it was last invoked for the target CPU, free all memory
+	allocated by that callback and so on.
+
+:c:member:`select`
+	::
+
+	  int (*select) (struct cpuidle_driver *drv, struct cpuidle_device *dev,
+	                 bool *stop_tick);
+
+	Called to select an idle state for the processor holding the (logical)
+	CPU represented by the |struct cpuidle_device| object pointed to by the
+	``dev`` argument.
+
+	The list of idle states to take into consideration is represented by the
+	:c:member:`states` array of |struct cpuidle_state| objects held by the
+	|struct cpuidle_driver| object pointed to by the ``drv`` argument (which
+	represents the ``CPUIdle`` driver to be used with the CPU at hand).  The
+	value returned by this callback is interpreted as an index into that
+	array (unless it is a negative error code).
+
+	The ``stop_tick`` argument is used to indicate whether or not to stop
+	the scheduler tick before asking the processor to enter the selected
+	idle state.  When the ``bool`` variable pointed to by it (which is set
+	to ``true`` before invoking this callback) is cleared to ``false``, the
+	processor will be asked to enter the selected idle state without
+	stopping the scheduler tick on the given CPU (if the tick has been
+	stopped on that CPU already, however, it will not be restarted before
+	asking the processor to enter the idle state).
+
+	This callback is mandatory (i.e. the :c:member:`select` callback pointer
+	in |struct cpuidle_governor| must not be ``NULL`` for the registration
+	of the governor to succeed).
+
+:c:member:`reflect`
+	::
+
+	  void (*reflect) (struct cpuidle_device *dev, int index);
+
+	Called to allow the governor to evaluate the accuracy of the idle state
+	selection made by the ``->select()`` callback (when it was invoked last
+	time) and possibly use the result of that to improve the accuracy of
+	idle state selections in the future.
+
+In addition, ``CPUIdle`` governors are required to take power management
+quality of service (PM QoS) constraints on the processor wakeup latency into
+account when selecting idle states.  In order to obtain the current effective
+PM QoS wakeup latency constraint for a given CPU, a ``CPUIdle`` governor is
+expected to pass the number of the CPU to
+:c:func:`cpuidle_governor_latency_req()`.  Then, the governor's ``->select()``
+callback must not return the index of an indle state whose
+:c:member:`exit_latency` value is greater than the number returned by that
+function.
+
+
+CPU Idle Time Management Drivers
+================================
+
+CPU idle time management (``CPUIdle``) drivers provide an interface between the
+other parts of ``CPUIdle`` and the hardware.
+
+First of all, a ``CPUIdle`` driver has to populate the :c:member:`states` array
+of |struct cpuidle_state| objects included in the |struct cpuidle_driver| object
+representing it.  Going forward this array will represent the list of available
+idle states that the processor hardware can be asked to enter shared by all of
+the logical CPUs handled by the given driver.
+
+The entries in the :c:member:`states` array are expected to be sorted by the
+value of the :c:member:`target_residency` field in |struct cpuidle_state| in
+the ascending order (that is, index 0 should correspond to the idle state with
+the minimum value of :c:member:`target_residency`).  [Since the
+:c:member:`target_residency` value is expected to reflect the "depth" of the
+idle state represented by the |struct cpuidle_state| object holding it, this
+sorting order should be the same as the ascending sorting order by the idle
+state "depth".]
+
+Three fields in |struct cpuidle_state| are used by the existing ``CPUIdle``
+governors for computations related to idle state selection:
+
+:c:member:`target_residency`
+	Minimum time to spend in this idle state including the time needed to
+	enter it (which may be substantial) to save more energy than could
+	be saved by staying in a shallower idle state for the same amount of
+	time, in microseconds.
+
+:c:member:`exit_latency`
+	Maximum time it will take a CPU asking the processor to enter this idle
+	state to start executing the first instruction after a wakeup from it,
+	in microseconds.
+
+:c:member:`flags`
+	Flags representing idle state properties.  Currently, governors only use
+	the ``CPUIDLE_FLAG_POLLING`` flag which is set if the given object
+	does not represent a real idle state, but an interface to a software
+	"loop" that can be used in order to avoid asking the processor to enter
+	any idle state at all.  [There are other flags used by the ``CPUIdle``
+	core in special situations.]
+
+The :c:member:`enter` callback pointer in |struct cpuidle_state|, which must not
+be ``NULL``, points to the routine to execute in order to ask the processor to
+enter this particular idle state:
+
+::
+
+  void (*enter) (struct cpuidle_device *dev, struct cpuidle_driver *drv,
+                 int index);
+
+The first two arguments of it point to the |struct cpuidle_device| object
+representing the logical CPU running this callback and the
+|struct cpuidle_driver| object representing the driver itself, respectively,
+and the last one is an index of the |struct cpuidle_state| entry in the driver's
+:c:member:`states` array representing the idle state to ask the processor to
+enter.
+
+The analogous ``->enter_s2idle()`` callback in |struct cpuidle_state| is used
+only for implementing the suspend-to-idle system-wide power management feature.
+The difference between in and ``->enter()`` is that it must not re-enable
+interrupts at any point (even temporarily) or attempt to change the states of
+clock event devices, which the ``->enter()`` callback may do sometimes.
+
+Once the :c:member:`states` array has been populated, the number of valid
+entries in it has to be stored in the :c:member:`state_count` field of the
+|struct cpuidle_driver| object representing the driver.  Moreover, if any
+entries in the :c:member:`states` array represent "coupled" idle states (that
+is, idle states that can only be asked for if multiple related logical CPUs are
+idle), the :c:member:`safe_state_index` field in |struct cpuidle_driver| needs
+to be the index of an idle state that is not "coupled" (that is, one that can be
+asked for if only one logical CPU is idle).
+
+In addition to that, if the given ``CPUIdle`` driver is only going to handle a
+subset of logical CPUs in the system, the :c:member:`cpumask` field in its
+|struct cpuidle_driver| object must point to the set (mask) of CPUs that will be
+handled by it.
+
+A ``CPUIdle`` driver can only be used after it has been registered.  If there
+are no "coupled" idle state entries in the driver's :c:member:`states` array,
+that can be accomplished by passing the driver's |struct cpuidle_driver| object
+to :c:func:`cpuidle_register_driver()`.  Otherwise, :c:func:`cpuidle_register()`
+should be used for this purpose.
+
+However, it also is necessary to register |struct cpuidle_device| objects for
+all of the logical CPUs to be handled by the given ``CPUIdle`` driver with the
+help of :c:func:`cpuidle_register_device()` after the driver has been registered
+and :c:func:`cpuidle_register_driver()`, unlike :c:func:`cpuidle_register()`,
+does not do that automatically.  For this reason, the drivers that use
+:c:func:`cpuidle_register_driver()` to register themselves must also take care
+of registering the |struct cpuidle_device| objects as needed, so it is generally
+recommended to use :c:func:`cpuidle_register()` for ``CPUIdle`` driver
+registration in all cases.
+
+The registration of a |struct cpuidle_device| object causes the ``CPUIdle``
+``sysfs`` interface to be created and the governor's ``->enable()`` callback to
+be invoked for the logical CPU represented by it, so it must take place after
+registering the driver that will handle the CPU in question.
+
+``CPUIdle`` drivers and |struct cpuidle_device| objects can be unregistered
+when they are not necessary any more which allows some resources associated with
+them to be released.  Due to dependencies between them, all of the
+|struct cpuidle_device| objects representing CPUs handled by the given
+``CPUIdle`` driver must be unregistered, with the help of
+:c:func:`cpuidle_unregister_device()`, before calling
+:c:func:`cpuidle_unregister_driver()` to unregister the driver.  Alternatively,
+:c:func:`cpuidle_unregister()` can be called to unregister a ``CPUIdle`` driver
+along with all of the |struct cpuidle_device| objects representing CPUs handled
+by it.
+
+``CPUIdle`` drivers can respond to runtime system configuration changes that
+lead to modifications of the list of available processor idle states (which can
+happen, for example, when the system's power source is switched from AC to
+battery or the other way around).  Upon a notification of such a change,
+a ``CPUIdle`` driver is expected to call :c:func:`cpuidle_pause_and_lock()` to
+turn ``CPUIdle`` off temporarily and then :c:func:`cpuidle_disable_device()` for
+all of the |struct cpuidle_device| objects representing CPUs affected by that
+change.  Next, it can update its :c:member:`states` array in accordance with
+the new configuration of the system, call :c:func:`cpuidle_enable_device()` for
+all of the relevant |struct cpuidle_device| objects and invoke
+:c:func:`cpuidle_resume_and_unlock()` to allow ``CPUIdle`` to be used again.
diff --git a/Documentation/driver-api/pm/index.rst b/Documentation/driver-api/pm/index.rst
index 2f6d0e9cf6b7..56975c6bc789 100644
--- a/Documentation/driver-api/pm/index.rst
+++ b/Documentation/driver-api/pm/index.rst
@@ -1,9 +1,10 @@
-=======================
-Device Power Management
-=======================
+===============================
+CPU and Device Power Management
+===============================
 
 .. toctree::
 
+   cpuidle
    devices
    notifiers
    types