Device Frequency Scaling¶

Introduction¶

This framework provides a standard kernel interface for Dynamic Voltage and Frequency Switching on arbitrary devices.

It exposes controls for adjusting frequency through sysfs files which are similar to the cpufreq subsystem.

Devices for which current usage can be measured can have their frequency automatically adjusted by governors.

API¶

Device drivers need to initialize a devfreq_profile and call the devfreq_add_device() function to create a devfreq instance.

struct devfreq_dev_status: Data given from devfreq user device to governors. Represents the performance statistics.

Definition

struct devfreq_dev_status {
  unsigned long total_time;
  unsigned long busy_time;
  unsigned long current_frequency;
  void *private_data;
};

Members

total_time: The total time represented by this instance of devfreq_dev_status
busy_time: The time that the device was working among the total_time.
current_frequency: The operating frequency.
private_data: An entry not specified by the devfreq framework. A device and a specific governor may have their own protocol with private_data. However, because this is governor-specific, a governor using this will be only compatible with devices aware of it.

struct devfreq_dev_profile: Devfreq’s user device profile

Definition

struct devfreq_dev_profile {
  unsigned long initial_freq;
  unsigned int polling_ms;
  int (*target)(struct device *dev, unsigned long *freq, u32 flags);
  int (*get_dev_status)(struct device *dev, struct devfreq_dev_status *stat);
  int (*get_cur_freq)(struct device *dev, unsigned long *freq);
  void (*exit)(struct device *dev);
  unsigned long *freq_table;
  unsigned int max_state;
};

Members

initial_freq: The operating frequency when devfreq_add_device() is called.
polling_ms: The polling interval in ms. 0 disables polling.
target: The device should set its operating frequency at freq or lowest-upper-than-freq value. If freq is higher than any operable frequency, set maximum. Before returning, target function should set freq at the current frequency. The “flags” parameter’s possible values are explained above with “DEVFREQ_FLAG_*” macros.
get_dev_status: The device should provide the current performance status to devfreq. Governors are recommended not to use this directly. Instead, governors are recommended to use devfreq_update_stats() along with devfreq.last_status.
get_cur_freq: The device should provide the current frequency at which it is operating.
exit: An optional callback that is called when devfreq is removing the devfreq object due to error or from devfreq_remove_device() call. If the user has registered devfreq->nb at a notifier-head, this is the time to unregister it.
freq_table: Optional list of frequencies to support statistics and freq_table must be generated in ascending order.
max_state: The size of freq_table.

struct devfreq_stats: Statistics of devfreq device behavior

Definition

struct devfreq_stats {
  unsigned int total_trans;
  unsigned int *trans_table;
  u64 *time_in_state;
  u64 last_update;
};

Members

total_trans: Number of devfreq transitions.
trans_table: Statistics of devfreq transitions.
time_in_state: Statistics of devfreq states.
last_update: The last time stats were updated.

struct devfreq: Device devfreq structure

Definition

struct devfreq {
  struct list_head node;
  struct mutex lock;
  struct device dev;
  struct devfreq_dev_profile *profile;
  const struct devfreq_governor *governor;
  char governor_name[DEVFREQ_NAME_LEN];
  struct notifier_block nb;
  struct delayed_work work;
  unsigned long previous_freq;
  struct devfreq_dev_status last_status;
  void *data;
  struct dev_pm_qos_request user_min_freq_req;
  struct dev_pm_qos_request user_max_freq_req;
  unsigned long scaling_min_freq;
  unsigned long scaling_max_freq;
  bool stop_polling;
  unsigned long suspend_freq;
  unsigned long resume_freq;
  atomic_t suspend_count;
  struct devfreq_stats stats;
  struct srcu_notifier_head transition_notifier_list;
  struct notifier_block nb_min;
  struct notifier_block nb_max;
};

Members

node: list node - contains the devices with devfreq that have been registered.
lock: a mutex to protect accessing devfreq.
dev: device registered by devfreq class. dev.parent is the device using devfreq.
profile: device-specific devfreq profile
governor: method how to choose frequency based on the usage.
governor_name: devfreq governor name for use with this devfreq
nb: notifier block used to notify devfreq object that it should reevaluate operable frequencies. Devfreq users may use devfreq.nb to the corresponding register notifier call chain.
work: delayed work for load monitoring.
previous_freq: previously configured frequency value.
last_status: devfreq user device info, performance statistics
data: Private data of the governor. The devfreq framework does not touch this.
user_min_freq_req: PM QoS minimum frequency request from user (via sysfs)
user_max_freq_req: PM QoS maximum frequency request from user (via sysfs)
scaling_min_freq: Limit minimum frequency requested by OPP interface
scaling_max_freq: Limit maximum frequency requested by OPP interface
stop_polling: devfreq polling status of a device.
suspend_freq: frequency of a device set during suspend phase.
resume_freq: frequency of a device set in resume phase.
suspend_count: suspend requests counter for a device.
stats: Statistics of devfreq device behavior
transition_notifier_list: list head of DEVFREQ_TRANSITION_NOTIFIER notifier
nb_min: Notifier block for DEV_PM_QOS_MIN_FREQUENCY
nb_max: Notifier block for DEV_PM_QOS_MAX_FREQUENCY

Description

This structure stores the devfreq information for a given device.

Note that when a governor accesses entries in struct devfreq in its functions except for the context of callbacks defined in struct devfreq_governor, the governor should protect its access with the struct mutex lock in struct devfreq. A governor may use this mutex to protect its own private data in void *data as well.

int update_devfreq(struct devfreq *devfreq)¶: Reevaluate the device and configure frequency

Parameters

struct devfreq * devfreq: the devfreq device

Note

devfreq->lock must be held

struct devfreq_simple_ondemand_data: void *data fed to struct devfreq and devfreq_add_device

Definition

struct devfreq_simple_ondemand_data {
  unsigned int upthreshold;
  unsigned int downdifferential;
};

Members

upthreshold: If the load is over this value, the frequency jumps. Specify 0 to use the default. Valid value = 0 to 100.
downdifferential: If the load is under upthreshold - downdifferential, the governor may consider slowing the frequency down. Specify 0 to use the default. Valid value = 0 to 100. downdifferential < upthreshold must hold.

Description

If the fed devfreq_simple_ondemand_data pointer is NULL to the governor, the governor uses the default values.

struct devfreq_passive_data: void *data fed to struct devfreq and devfreq_add_device

Definition

struct devfreq_passive_data {
  struct devfreq *parent;
  int (*get_target_freq)(struct devfreq *this, unsigned long *freq);
  struct devfreq *this;
  struct notifier_block nb;
};

Members

parent: the devfreq instance of parent device.
get_target_freq: Optional callback, Returns desired operating frequency for the device using passive governor. That is called when passive governor should decide the next frequency by using the new frequency of parent devfreq device using governors except for passive governor. If the devfreq device has the specific method to decide the next frequency, should use this callback.
this: the devfreq instance of own device.
nb: the notifier block for DEVFREQ_TRANSITION_NOTIFIER list

Description

The devfreq_passive_data have to set the devfreq instance of parent device with governors except for the passive governor. But, don’t need to initialize the ‘this’ and ‘nb’ field because the devfreq core will handle them.

struct devfreq_event_dev: the devfreq-event device

Definition

struct devfreq_event_dev {
  struct list_head node;
  struct device dev;
  struct mutex lock;
  u32 enable_count;
  const struct devfreq_event_desc *desc;
};

Members

node: Contain the devfreq-event device that have been registered.
dev: the device registered by devfreq-event class. dev.parent is the device using devfreq-event.
lock: a mutex to protect accessing devfreq-event.
enable_count: the number of enable function have been called.
desc: the description for devfreq-event device.

Description

This structure contains devfreq-event device information.

struct devfreq_event_data: the devfreq-event data

Definition

struct devfreq_event_data {
  unsigned long load_count;
  unsigned long total_count;
};

Members

load_count: load count of devfreq-event device for the given period.
total_count: total count of devfreq-event device for the given period. each count may represent a clock cycle, a time unit (ns/us/…), or anything the device driver wants. Generally, utilization is load_count / total_count.

Description

This structure contains the data of devfreq-event device for polling period.

struct devfreq_event_ops: the operations of devfreq-event device

Definition

struct devfreq_event_ops {
  int (*enable)(struct devfreq_event_dev *edev);
  int (*disable)(struct devfreq_event_dev *edev);
  int (*reset)(struct devfreq_event_dev *edev);
  int (*set_event)(struct devfreq_event_dev *edev);
  int (*get_event)(struct devfreq_event_dev *edev, struct devfreq_event_data *edata);
};

Members

enable: Enable the devfreq-event device.
disable: Disable the devfreq-event device.
reset: Reset all setting of the devfreq-event device.
set_event: Set the specific event type for the devfreq-event device.
get_event: Get the result of the devfreq-event devie with specific event type.

Description

This structure contains devfreq-event device operations which can be implemented by devfreq-event device drivers.

struct devfreq_event_desc: the descriptor of devfreq-event device

Definition

struct devfreq_event_desc {
  const char *name;
  u32 event_type;
  void *driver_data;
  const struct devfreq_event_ops *ops;
};

Members

name: the name of devfreq-event device.
event_type: the type of the event determined and used by driver
driver_data: the private data for devfreq-event driver.
ops: the operation to control devfreq-event device.

Description

Each devfreq-event device is described with a this structure. This structure contains the various data for devfreq-event device. The event_type describes what is going to be counted in the register. It might choose to count e.g. read requests, write data in bytes, etc. The full supported list of types is present in specyfic header in: include/dt-bindings/pmu/.

int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)¶: Update statistics of devfreq behavior

Parameters

struct devfreq * devfreq: the devfreq instance
unsigned long freq: the update target frequency

int update_devfreq(struct devfreq *devfreq): Reevaluate the device and configure frequency.

Parameters

struct devfreq * devfreq: the devfreq instance.

Note

Lock devfreq->lock before calling update_devfreq: This function is exported for governors.

void devfreq_monitor_start(struct devfreq *devfreq)¶: Start load monitoring of devfreq instance

Parameters

struct devfreq * devfreq: the devfreq instance.

Description

Helper function for starting devfreq device load monitoring. By default delayed work based monitoring is supported. Function to be called from governor in response to DEVFREQ_GOV_START event when device is added to devfreq framework.

void devfreq_monitor_stop(struct devfreq *devfreq)¶: Stop load monitoring of a devfreq instance

Parameters

struct devfreq * devfreq: the devfreq instance.

Description

Helper function to stop devfreq device load monitoring. Function to be called from governor in response to DEVFREQ_GOV_STOP event when device is removed from devfreq framework.

void devfreq_monitor_suspend(struct devfreq *devfreq)¶: Suspend load monitoring of a devfreq instance

Parameters

struct devfreq * devfreq: the devfreq instance.

Description

Helper function to suspend devfreq device load monitoring. Function to be called from governor in response to DEVFREQ_GOV_SUSPEND event or when polling interval is set to zero.

Note

Though this function is same as devfreq_monitor_stop(), intentionally kept separate to provide hooks for collecting transition statistics.

void devfreq_monitor_resume(struct devfreq *devfreq)¶: Resume load monitoring of a devfreq instance

Parameters

struct devfreq * devfreq: the devfreq instance.

Description

Helper function to resume devfreq device load monitoring. Function to be called from governor in response to DEVFREQ_GOV_RESUME event or when polling interval is set to non-zero.

void devfreq_update_interval(struct devfreq *devfreq, unsigned int *delay)¶: Update device devfreq monitoring interval

Parameters

struct devfreq * devfreq: the devfreq instance.
unsigned int * delay: new polling interval to be set.

Description

Helper function to set new load monitoring polling interval. Function to be called from governor in response to DEVFREQ_GOV_UPDATE_INTERVAL event.

struct devfreq *devfreq_add_device(struct device *dev, struct devfreq_dev_profile *profile, const char *governor_name, void *data)¶: Add devfreq feature to the device

Parameters

struct device * dev: the device to add devfreq feature.
struct devfreq_dev_profile * profile: device-specific profile to run devfreq.
const char * governor_name: name of the policy to choose frequency.
void * data: private data for the governor. The devfreq framework does not touch this value.

int devfreq_remove_device(struct devfreq *devfreq)¶: Remove devfreq feature from a device.

Parameters

struct devfreq * devfreq: the devfreq instance to be removed

Description

The opposite of devfreq_add_device().

struct devfreq *devm_devfreq_add_device(struct device *dev, struct devfreq_dev_profile *profile, const char *governor_name, void *data)¶: Resource-managed devfreq_add_device()

Parameters

struct device * dev: the device to add devfreq feature.
struct devfreq_dev_profile * profile: device-specific profile to run devfreq.
const char * governor_name: name of the policy to choose frequency.
void * data: private data for the governor. The devfreq framework does not touch this value.

Description

This function manages automatically the memory of devfreq device using device resource management and simplify the free operation for memory of devfreq device.

void devm_devfreq_remove_device(struct device *dev, struct devfreq *devfreq)¶: Resource-managed devfreq_remove_device()

Parameters

struct device * dev: the device from which to remove devfreq feature.
struct devfreq * devfreq: the devfreq instance to be removed

int devfreq_suspend_device(struct devfreq *devfreq)¶: Suspend devfreq of a device.

Parameters

struct devfreq * devfreq: the devfreq instance to be suspended

Description

This function is intended to be called by the pm callbacks (e.g., runtime_suspend, suspend) of the device driver that holds the devfreq.

int devfreq_resume_device(struct devfreq *devfreq)¶: Resume devfreq of a device.

Parameters

struct devfreq * devfreq: the devfreq instance to be resumed

Description

This function is intended to be called by the pm callbacks (e.g., runtime_resume, resume) of the device driver that holds the devfreq.

int devfreq_add_governor(struct devfreq_governor *governor)¶: Add devfreq governor

Parameters

struct devfreq_governor * governor: the devfreq governor to be added

int devfreq_remove_governor(struct devfreq_governor *governor)¶: Remove devfreq feature from a device.

Parameters

struct devfreq_governor * governor: the devfreq governor to be removed

struct dev_pm_opp *devfreq_recommended_opp(struct device *dev, unsigned long *freq, u32 flags)¶: Helper function to get proper OPP for the freq value given to target callback.

Parameters

struct device * dev: The devfreq user device. (parent of devfreq)
unsigned long * freq: The frequency given to target function
u32 flags: Flags handed from devfreq framework.

Description

The callers are required to call dev_pm_opp_put() for the returned OPP after use.

int devfreq_register_opp_notifier(struct device *dev, struct devfreq *devfreq)¶: Helper function to get devfreq notified for any changes in the OPP availability changes

Parameters

struct device * dev: The devfreq user device. (parent of devfreq)
struct devfreq * devfreq: The devfreq object.

int devfreq_unregister_opp_notifier(struct device *dev, struct devfreq *devfreq)¶: Helper function to stop getting devfreq notified for any changes in the OPP availability changes anymore.

Parameters

struct device * dev: The devfreq user device. (parent of devfreq)
struct devfreq * devfreq: The devfreq object.

Description

At exit() callback of devfreq_dev_profile, this must be included if devfreq_recommended_opp is used.

int devm_devfreq_register_opp_notifier(struct device *dev, struct devfreq *devfreq)¶: Resource-managed devfreq_register_opp_notifier()

Parameters

struct device * dev: The devfreq user device. (parent of devfreq)
struct devfreq * devfreq: The devfreq object.

void devm_devfreq_unregister_opp_notifier(struct device *dev, struct devfreq *devfreq)¶: Resource-managed devfreq_unregister_opp_notifier()

Parameters

struct device * dev: The devfreq user device. (parent of devfreq)
struct devfreq * devfreq: The devfreq object.

int devfreq_register_notifier(struct devfreq *devfreq, struct notifier_block *nb, unsigned int list)¶: Register a driver with devfreq

Parameters

struct devfreq * devfreq: The devfreq object.
struct notifier_block * nb: The notifier block to register.
unsigned int list: DEVFREQ_TRANSITION_NOTIFIER.

int devm_devfreq_register_notifier(struct device *dev, struct devfreq *devfreq, struct notifier_block *nb, unsigned int list)¶

Parameters

struct device * dev: The devfreq user device. (parent of devfreq)
struct devfreq * devfreq: The devfreq object.
struct notifier_block * nb: The notifier block to be unregistered.
unsigned int list: DEVFREQ_TRANSITION_NOTIFIER.

Description

Resource-managed devfreq_register_notifier()

void devm_devfreq_unregister_notifier(struct device *dev, struct devfreq *devfreq, struct notifier_block *nb, unsigned int list)¶

Parameters

struct device * dev: The devfreq user device. (parent of devfreq)
struct devfreq * devfreq: The devfreq object.
struct notifier_block * nb: The notifier block to be unregistered.
unsigned int list: DEVFREQ_TRANSITION_NOTIFIER.

Description

Resource-managed devfreq_unregister_notifier()

int devfreq_event_enable_edev(struct devfreq_event_dev *edev)¶: Enable the devfreq-event dev and increase the enable_count of devfreq-event dev.

Parameters

struct devfreq_event_dev * edev: the devfreq-event device

Description

Note that this function increase the enable_count and enable the devfreq-event device. The devfreq-event device should be enabled before using it by devfreq device.

int devfreq_event_disable_edev(struct devfreq_event_dev *edev)¶: Disable the devfreq-event dev and decrease the enable_count of the devfreq-event dev.

Parameters

struct devfreq_event_dev * edev: the devfreq-event device

Description

Note that this function decrease the enable_count and disable the devfreq-event device. After the devfreq-event device is disabled, devfreq device can’t use the devfreq-event device for get/set/reset operations.

bool devfreq_event_is_enabled(struct devfreq_event_dev *edev)¶: Check whether devfreq-event dev is enabled or not.

Parameters

struct devfreq_event_dev * edev: the devfreq-event device

Description

Note that this function check whether devfreq-event dev is enabled or not. If return true, the devfreq-event dev is enabeld. If return false, the devfreq-event dev is disabled.

int devfreq_event_set_event(struct devfreq_event_dev *edev)¶: Set event to devfreq-event dev to start.

Parameters

struct devfreq_event_dev * edev: the devfreq-event device

Description

Note that this function set the event to the devfreq-event device to start for getting the event data which could be various event type.

int devfreq_event_get_event(struct devfreq_event_dev *edev, struct devfreq_event_data *edata)¶: Get {load|total}_count from devfreq-event dev.

Parameters

struct devfreq_event_dev * edev: the devfreq-event device
struct devfreq_event_data * edata: the calculated data of devfreq-event device

Description

Note that this function get the calculated event data from devfreq-event dev after stoping the progress of whole sequence of devfreq-event dev.

int devfreq_event_reset_event(struct devfreq_event_dev *edev)¶: Reset all opeations of devfreq-event dev.

Parameters

struct devfreq_event_dev * edev: the devfreq-event device

Description

Note that this function stop all operations of devfreq-event dev and reset the current event data to make the devfreq-event device into initial state.

struct devfreq_event_dev *devfreq_event_get_edev_by_phandle(struct device *dev, int index)¶: Get the devfreq-event dev from devicetree.

Parameters

struct device * dev: the pointer to the given device
int index: the index into list of devfreq-event device

Description

Note that this function return the pointer of devfreq-event device.

int devfreq_event_get_edev_count(struct device *dev)¶: Get the count of devfreq-event dev

Parameters

struct device * dev: the pointer to the given device

Description

Note that this function return the count of devfreq-event devices.

struct devfreq_event_dev *devfreq_event_add_edev(struct device *dev, struct devfreq_event_desc *desc)¶: Add new devfreq-event device.

Parameters

struct device * dev: the device owning the devfreq-event device being created
struct devfreq_event_desc * desc: the devfreq-event device’s decriptor which include essential data for devfreq-event device.

Description

Note that this function add new devfreq-event device to devfreq-event class list and register the device of the devfreq-event device.

int devfreq_event_remove_edev(struct devfreq_event_dev *edev)¶: Remove the devfreq-event device registered.

Parameters

struct devfreq_event_dev * edev: the devfreq-event device

Description

Note that this function removes the registered devfreq-event device.

struct devfreq_event_dev *devm_devfreq_event_add_edev(struct device *dev, struct devfreq_event_desc *desc)¶: Resource-managed devfreq_event_add_edev()

Parameters

struct device * dev: the device owning the devfreq-event device being created
struct devfreq_event_desc * desc: the devfreq-event device’s decriptor which include essential data for devfreq-event device.

Description

Note that this function manages automatically the memory of devfreq-event device using device resource management and simplify the free operation for memory of devfreq-event device.

void devm_devfreq_event_remove_edev(struct device *dev, struct devfreq_event_dev *edev)¶: Resource-managed devfreq_event_remove_edev()

Parameters

struct device * dev: the device owning the devfreq-event device being created
struct devfreq_event_dev * edev: the devfreq-event device

Description

Note that this function manages automatically the memory of devfreq-event device using device resource management.

Device Frequency Scaling¶

Introduction¶

API¶

The Linux Kernel

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