diff options
Diffstat (limited to 'Documentation/driver-api')
| -rw-r--r-- | Documentation/driver-api/80211/mac80211.rst | 3 | ||||
| -rw-r--r-- | Documentation/driver-api/component.rst | 17 | ||||
| -rw-r--r-- | Documentation/driver-api/device_link.rst | 87 | ||||
| -rw-r--r-- | Documentation/driver-api/dmaengine/client.rst | 7 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/board.rst | 1 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/driver.rst | 2 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/legacy.rst | 9 | ||||
| -rw-r--r-- | Documentation/driver-api/iio/buffers.rst | 2 | ||||
| -rw-r--r-- | Documentation/driver-api/iio/core.rst | 6 | ||||
| -rw-r--r-- | Documentation/driver-api/iio/hw-consumer.rst | 2 | ||||
| -rw-r--r-- | Documentation/driver-api/iio/triggers.rst | 2 | ||||
| -rw-r--r-- | Documentation/driver-api/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/driver-api/pinctl.rst | 9 | ||||
| -rw-r--r-- | Documentation/driver-api/pm/cpuidle.rst | 282 | ||||
| -rw-r--r-- | Documentation/driver-api/pm/index.rst | 7 |
15 files changed, 389 insertions, 48 deletions
diff --git a/Documentation/driver-api/80211/mac80211.rst b/Documentation/driver-api/80211/mac80211.rst index 85a8335e80b6..eab40bcf3987 100644 --- a/Documentation/driver-api/80211/mac80211.rst +++ b/Documentation/driver-api/80211/mac80211.rst @@ -126,6 +126,9 @@ functions/definitions :functions: ieee80211_rx_status .. kernel-doc:: include/net/mac80211.h + :functions: mac80211_rx_encoding_flags + +.. kernel-doc:: include/net/mac80211.h :functions: mac80211_rx_flags .. kernel-doc:: include/net/mac80211.h diff --git a/Documentation/driver-api/component.rst b/Documentation/driver-api/component.rst new file mode 100644 index 000000000000..2da4a8f20607 --- /dev/null +++ b/Documentation/driver-api/component.rst @@ -0,0 +1,17 @@ +====================================== +Component Helper for Aggregate Drivers +====================================== + +.. kernel-doc:: drivers/base/component.c + :doc: overview + + +API +=== + +.. kernel-doc:: include/linux/component.h + :internal: + +.. kernel-doc:: drivers/base/component.c + :export: + diff --git a/Documentation/driver-api/device_link.rst b/Documentation/driver-api/device_link.rst index d6763272e747..ae1e3d0394b0 100644 --- a/Documentation/driver-api/device_link.rst +++ b/Documentation/driver-api/device_link.rst @@ -1,6 +1,9 @@ .. |struct dev_pm_domain| replace:: :c:type:`struct dev_pm_domain <dev_pm_domain>` .. |struct generic_pm_domain| replace:: :c:type:`struct generic_pm_domain <generic_pm_domain>` + +.. _device_link: + ============ Device links ============ @@ -25,8 +28,8 @@ suspend/resume and shutdown ordering. Device links allow representation of such dependencies in the driver core. -In its standard form, a device link combines *both* dependency types: -It guarantees correct suspend/resume and shutdown ordering between a +In its standard or *managed* form, a device link combines *both* dependency +types: It guarantees correct suspend/resume and shutdown ordering between a "supplier" device and its "consumer" devices, and it guarantees driver presence on the supplier. The consumer devices are not probed before the supplier is bound to a driver, and they're unbound before the supplier @@ -59,18 +62,24 @@ device ``->probe`` callback or a boot-time PCI quirk. Another example for an inconsistent state would be a device link that represents a driver presence dependency, yet is added from the consumer's -``->probe`` callback while the supplier hasn't probed yet: Had the driver -core known about the device link earlier, it wouldn't have probed the +``->probe`` callback while the supplier hasn't started to probe yet: Had the +driver core known about the device link earlier, it wouldn't have probed the consumer in the first place. The onus is thus on the consumer to check presence of the supplier after adding the link, and defer probing on -non-presence. - -If a device link is added in the ``->probe`` callback of the supplier or -consumer driver, it is typically deleted in its ``->remove`` callback for -symmetry. That way, if the driver is compiled as a module, the device -link is added on module load and orderly deleted on unload. The same -restrictions that apply to device link addition (e.g. exclusion of a -parallel suspend/resume transition) apply equally to deletion. +non-presence. [Note that it is valid to create a link from the consumer's +``->probe`` callback while the supplier is still probing, but the consumer must +know that the supplier is functional already at the link creation time (that is +the case, for instance, if the consumer has just acquired some resources that +would not have been available had the supplier not been functional then).] + +If a device link with ``DL_FLAG_STATELESS`` set (i.e. a stateless device link) +is added in the ``->probe`` callback of the supplier or consumer driver, it is +typically deleted in its ``->remove`` callback for symmetry. That way, if the +driver is compiled as a module, the device link is added on module load and +orderly deleted on unload. The same restrictions that apply to device link +addition (e.g. exclusion of a parallel suspend/resume transition) apply equally +to deletion. Device links with ``DL_FLAG_STATELESS`` unset (i.e. managed +device links) are deleted automatically by the driver core. Several flags may be specified on device link addition, two of which have already been mentioned above: ``DL_FLAG_STATELESS`` to express that no @@ -80,25 +89,55 @@ integration is desired. Two other flags are specifically targeted at use cases where the device link is added from the consumer's ``->probe`` callback: ``DL_FLAG_RPM_ACTIVE`` -can be specified to runtime resume the supplier upon addition of the -device link. ``DL_FLAG_AUTOREMOVE_CONSUMER`` causes the device link to be -automatically purged when the consumer fails to probe or later unbinds. -This obviates the need to explicitly delete the link in the ``->remove`` -callback or in the error path of the ``->probe`` callback. +can be specified to runtime resume the supplier and prevent it from suspending +before the consumer is runtime suspended. ``DL_FLAG_AUTOREMOVE_CONSUMER`` +causes the device link to be automatically purged when the consumer fails to +probe or later unbinds. Similarly, when the device link is added from supplier's ``->probe`` callback, ``DL_FLAG_AUTOREMOVE_SUPPLIER`` causes the device link to be automatically purged when the supplier fails to probe or later unbinds. +If neither ``DL_FLAG_AUTOREMOVE_CONSUMER`` nor ``DL_FLAG_AUTOREMOVE_SUPPLIER`` +is set, ``DL_FLAG_AUTOPROBE_CONSUMER`` can be used to request the driver core +to probe for a driver for the consumer driver on the link automatically after +a driver has been bound to the supplier device. + +Note, however, that any combinations of ``DL_FLAG_AUTOREMOVE_CONSUMER``, +``DL_FLAG_AUTOREMOVE_SUPPLIER`` or ``DL_FLAG_AUTOPROBE_CONSUMER`` with +``DL_FLAG_STATELESS`` are invalid and cannot be used. + Limitations =========== -Driver authors should be aware that a driver presence dependency (i.e. when -``DL_FLAG_STATELESS`` is not specified on link addition) may cause probing of -the consumer to be deferred indefinitely. This can become a problem if the -consumer is required to probe before a certain initcall level is reached. -Worse, if the supplier driver is blacklisted or missing, the consumer will -never be probed. +Driver authors should be aware that a driver presence dependency for managed +device links (i.e. when ``DL_FLAG_STATELESS`` is not specified on link addition) +may cause probing of the consumer to be deferred indefinitely. This can become +a problem if the consumer is required to probe before a certain initcall level +is reached. Worse, if the supplier driver is blacklisted or missing, the +consumer will never be probed. + +Moreover, managed device links cannot be deleted directly. They are deleted +by the driver core when they are not necessary any more in accordance with the +``DL_FLAG_AUTOREMOVE_CONSUMER`` and ``DL_FLAG_AUTOREMOVE_SUPPLIER`` flags. +However, stateless device links (i.e. device links with ``DL_FLAG_STATELESS`` +set) are expected to be removed by whoever called :c:func:`device_link_add()` +to add them with the help of either :c:func:`device_link_del()` or +:c:func:`device_link_remove()`. + +Passing ``DL_FLAG_RPM_ACTIVE`` along with ``DL_FLAG_STATELESS`` to +:c:func:`device_link_add()` may cause the PM-runtime usage counter of the +supplier device to remain nonzero after a subsequent invocation of either +:c:func:`device_link_del()` or :c:func:`device_link_remove()` to remove the +device link returned by it. This happens if :c:func:`device_link_add()` is +called twice in a row for the same consumer-supplier pair without removing the +link between these calls, in which case allowing the PM-runtime usage counter +of the supplier to drop on an attempt to remove the link may cause it to be +suspended while the consumer is still PM-runtime-active and that has to be +avoided. [To work around this limitation it is sufficient to let the consumer +runtime suspend at least once, or call :c:func:`pm_runtime_set_suspended()` for +it with PM-runtime disabled, between the :c:func:`device_link_add()` and +:c:func:`device_link_del()` or :c:func:`device_link_remove()` calls.] Sometimes drivers depend on optional resources. They are able to operate in a degraded mode (reduced feature set or performance) when those resources @@ -282,4 +321,4 @@ API === .. kernel-doc:: drivers/base/core.c - :functions: device_link_add device_link_del + :functions: device_link_add device_link_del device_link_remove diff --git a/Documentation/driver-api/dmaengine/client.rst b/Documentation/driver-api/dmaengine/client.rst index fbbb2831f29f..d728e50105eb 100644 --- a/Documentation/driver-api/dmaengine/client.rst +++ b/Documentation/driver-api/dmaengine/client.rst @@ -168,6 +168,13 @@ The details of these operations are: dmaengine_submit() will not start the DMA operation, it merely adds it to the pending queue. For this, see step 5, dma_async_issue_pending. + .. note:: + + After calling ``dmaengine_submit()`` the submitted transfer descriptor + (``struct dma_async_tx_descriptor``) belongs to the DMA engine. + Consequentially, the client must consider invalid the pointer to that + descriptor. + 5. Issue pending DMA requests and wait for callback notification The transactions in the pending queue can be activated by calling the diff --git a/Documentation/driver-api/gpio/board.rst b/Documentation/driver-api/gpio/board.rst index a0f294e2e250..b37f3f7b8926 100644 --- a/Documentation/driver-api/gpio/board.rst +++ b/Documentation/driver-api/gpio/board.rst @@ -204,6 +204,7 @@ between a caller and a respective .get/set_multiple() callback of a GPIO chip. In order to qualify for fast bitmap processing, the array must meet the following requirements: + - pin hardware number of array member 0 must also be 0, - pin hardware numbers of consecutive array members which belong to the same chip as member 0 does must also match their array indexes. diff --git a/Documentation/driver-api/gpio/driver.rst b/Documentation/driver-api/gpio/driver.rst index a92d8837b62b..3043167fc557 100644 --- a/Documentation/driver-api/gpio/driver.rst +++ b/Documentation/driver-api/gpio/driver.rst @@ -135,7 +135,7 @@ This configuration is normally used as a way to achieve one of two things: - inverse wire-OR on an I/O line, for example a GPIO line, making it possible for any driving stage on the line to drive it low even if any other output to the same line is simultaneously driving it high. A special case of this - is driving the SCL and SCA lines of an I2C bus, which is by definition a + is driving the SCL and SDA lines of an I2C bus, which is by definition a wire-OR bus. Both usecases require that the line be equipped with a pull-up resistor. This diff --git a/Documentation/driver-api/gpio/legacy.rst b/Documentation/driver-api/gpio/legacy.rst index 5e9421e05f1d..9bc34ba697d9 100644 --- a/Documentation/driver-api/gpio/legacy.rst +++ b/Documentation/driver-api/gpio/legacy.rst @@ -690,11 +690,10 @@ and have the following read/write attributes: and if it has been configured to generate interrupts (see the description of "edge"), you can poll(2) on that file and poll(2) will return whenever the interrupt was triggered. If - you use poll(2), set the events POLLPRI and POLLERR. If you - use select(2), set the file descriptor in exceptfds. After - poll(2) returns, either lseek(2) to the beginning of the sysfs - file and read the new value or close the file and re-open it - to read the value. + you use poll(2), set the events POLLPRI. If you use select(2), + set the file descriptor in exceptfds. After poll(2) returns, + either lseek(2) to the beginning of the sysfs file and read the + new value or close the file and re-open it to read the value. "edge" ... reads as either "none", "rising", "falling", or "both". Write these strings to select the signal edge(s) diff --git a/Documentation/driver-api/iio/buffers.rst b/Documentation/driver-api/iio/buffers.rst index 02c99a6bee18..e9036ef9f8f4 100644 --- a/Documentation/driver-api/iio/buffers.rst +++ b/Documentation/driver-api/iio/buffers.rst @@ -26,7 +26,7 @@ IIO buffer setup ================ The meta information associated with a channel reading placed in a buffer is -called a scan element . The important bits configuring scan elements are +called a scan element. The important bits configuring scan elements are exposed to userspace applications via the :file:`/sys/bus/iio/iio:device{X}/scan_elements/*` directory. This file contains attributes of the following form: diff --git a/Documentation/driver-api/iio/core.rst b/Documentation/driver-api/iio/core.rst index 9a34ae03b679..b0bc0c028cc5 100644 --- a/Documentation/driver-api/iio/core.rst +++ b/Documentation/driver-api/iio/core.rst @@ -2,8 +2,8 @@ Core elements ============= -The Industrial I/O core offers a unified framework for writing drivers for -many different types of embedded sensors. a standard interface to user space +The Industrial I/O core offers both a unified framework for writing drivers for +many different types of embedded sensors and a standard interface to user space applications manipulating sensors. The implementation can be found under :file:`drivers/iio/industrialio-*` @@ -11,7 +11,7 @@ Industrial I/O Devices ---------------------- * struct :c:type:`iio_dev` - industrial I/O device -* :c:func:`iio_device_alloc()` - alocate an :c:type:`iio_dev` from a driver +* :c:func:`iio_device_alloc()` - allocate an :c:type:`iio_dev` from a driver * :c:func:`iio_device_free()` - free an :c:type:`iio_dev` from a driver * :c:func:`iio_device_register()` - register a device with the IIO subsystem * :c:func:`iio_device_unregister()` - unregister a device from the IIO diff --git a/Documentation/driver-api/iio/hw-consumer.rst b/Documentation/driver-api/iio/hw-consumer.rst index 8facce6a6733..e0fe0b98230e 100644 --- a/Documentation/driver-api/iio/hw-consumer.rst +++ b/Documentation/driver-api/iio/hw-consumer.rst @@ -1,7 +1,7 @@ =========== HW consumer =========== -An IIO device can be directly connected to another device in hardware. in this +An IIO device can be directly connected to another device in hardware. In this case the buffers between IIO provider and IIO consumer are handled by hardware. The Industrial I/O HW consumer offers a way to bond these IIO devices without software buffer for data. The implementation can be found under diff --git a/Documentation/driver-api/iio/triggers.rst b/Documentation/driver-api/iio/triggers.rst index f89d37e7dd82..5c2156de6284 100644 --- a/Documentation/driver-api/iio/triggers.rst +++ b/Documentation/driver-api/iio/triggers.rst @@ -38,7 +38,7 @@ There are two locations in sysfs related to triggers: * :file:`/sys/bus/iio/devices/iio:device{X}/trigger/*`, this directory is created once the device supports a triggered buffer. We can associate a - trigger with our device by writing the trigger's name in the + trigger with our device by writing the trigger's name in the :file:`current_trigger` file. IIO trigger setup diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index ab38ced66a44..c0b600ed9961 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -22,6 +22,7 @@ available subsections can be seen below. device_connection dma-buf device_link + component message-based sound frame-buffer diff --git a/Documentation/driver-api/pinctl.rst b/Documentation/driver-api/pinctl.rst index 6cb68d67fa75..2bb1bc484278 100644 --- a/Documentation/driver-api/pinctl.rst +++ b/Documentation/driver-api/pinctl.rst @@ -274,15 +274,6 @@ configuration in the pin controller ops like this:: .confops = &foo_pconf_ops, }; -Since some controllers have special logic for handling entire groups of pins -they can exploit the special whole-group pin control function. The -pin_config_group_set() callback is allowed to return the error code -EAGAIN, -for groups it does not want to handle, or if it just wants to do some -group-level handling and then fall through to iterate over all pins, in which -case each individual pin will be treated by separate pin_config_set() calls as -well. - - Interaction with the GPIO subsystem =================================== 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 |