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* devfreq: Generic Dynamic Voltage and Frequency Scaling (DVFS) Framework
* for Non-CPU Devices.
* Copyright (C) 2011 Samsung Electronics
* MyungJoo Ham <>
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
#ifndef __LINUX_DEVFREQ_H__
#define __LINUX_DEVFREQ_H__
#include <linux/device.h>
#include <linux/notifier.h>
#include <linux/opp.h>
struct devfreq;
* struct devfreq_dev_status - Data given from devfreq user device to
* governors. Represents the performance
* statistics.
* @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_status {
/* both since the last measure */
unsigned long total_time;
unsigned long busy_time;
unsigned long current_frequency;
void *private_data;
* The resulting frequency should be at most this. (this bound is the
* least upper bound; thus, the resulting freq should be lower or same)
* If the flag is not set, the resulting frequency should be at most the
* bound (greatest lower bound)
* struct devfreq_dev_profile - Devfreq's user device profile
* @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, which is used by governors.
* @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.
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);
void (*exit)(struct device *dev);
* struct devfreq_governor - Devfreq policy governor
* @name Governor's name
* @get_target_freq Returns desired operating frequency for the device.
* Basically, get_target_freq will run
* devfreq_dev_profile.get_dev_status() to get the
* status of the device (load = busy_time / total_time).
* If no_central_polling is set, this callback is called
* only with update_devfreq() notified by OPP.
* @init Called when the devfreq is being attached to a device
* @exit Called when the devfreq is being removed from a
* device. Governor should stop any internal routines
* before return because related data may be
* freed after exit().
* @no_central_polling Do not use devfreq's central polling mechanism.
* When this is set, devfreq will not call
* get_target_freq with devfreq_monitor(). However,
* devfreq will call get_target_freq with
* devfreq_update() notified by OPP framework.
* Note that the callbacks are called with devfreq->lock locked by devfreq.
struct devfreq_governor {
const char name[DEVFREQ_NAME_LEN];
int (*get_target_freq)(struct devfreq *this, unsigned long *freq);
int (*init)(struct devfreq *this);
void (*exit)(struct devfreq *this);
const bool no_central_polling;
* struct devfreq - Device devfreq structure
* @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.
* @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.
* @polling_jiffies interval in jiffies.
* @previous_freq previously configured frequency value.
* @next_polling the number of remaining jiffies to poll with
* "devfreq_monitor" executions to reevaluate
* frequency/voltage of the device. Set by
* profile's polling_ms interval.
* @data Private data of the governor. The devfreq framework does not
* touch this.
* @being_removed a flag to mark that this object is being removed in
* order to prevent trying to remove the object multiple times.
* @min_freq Limit minimum frequency requested by user (0: none)
* @max_freq Limit maximum frequency requested by user (0: none)
* This structure stores the devfreq information for a give 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.
struct devfreq {
struct list_head node;
struct mutex lock;
struct device dev;
struct devfreq_dev_profile *profile;
const struct devfreq_governor *governor;
struct notifier_block nb;
unsigned long polling_jiffies;
unsigned long previous_freq;
unsigned int next_polling;
void *data; /* private data for governors */
bool being_removed;
unsigned long min_freq;
unsigned long max_freq;
#if defined(CONFIG_PM_DEVFREQ)
extern struct devfreq *devfreq_add_device(struct device *dev,
struct devfreq_dev_profile *profile,
const struct devfreq_governor *governor,
void *data);
extern int devfreq_remove_device(struct devfreq *devfreq);
/* Helper functions for devfreq user device driver with OPP. */
extern struct opp *devfreq_recommended_opp(struct device *dev,
unsigned long *freq, u32 flags);
extern int devfreq_register_opp_notifier(struct device *dev,
struct devfreq *devfreq);
extern int devfreq_unregister_opp_notifier(struct device *dev,
struct devfreq *devfreq);
extern const struct devfreq_governor devfreq_powersave;
extern const struct devfreq_governor devfreq_performance;
extern const struct devfreq_governor devfreq_userspace;
extern const struct devfreq_governor devfreq_simple_ondemand;
* struct devfreq_simple_ondemand_data - void *data fed to struct devfreq
* and devfreq_add_device
* @ 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.
* If the fed devfreq_simple_ondemand_data pointer is NULL to the governor,
* the governor uses the default values.
struct devfreq_simple_ondemand_data {
unsigned int upthreshold;
unsigned int downdifferential;
#else /* !CONFIG_PM_DEVFREQ */
static struct devfreq *devfreq_add_device(struct device *dev,
struct devfreq_dev_profile *profile,
struct devfreq_governor *governor,
void *data)
return NULL;
static int devfreq_remove_device(struct devfreq *devfreq)
return 0;
static struct opp *devfreq_recommended_opp(struct device *dev,
unsigned long *freq, u32 flags)
return -EINVAL;
static int devfreq_register_opp_notifier(struct device *dev,
struct devfreq *devfreq)
return -EINVAL;
static int devfreq_unregister_opp_notifier(struct device *dev,
struct devfreq *devfreq)
return -EINVAL;
#define devfreq_powersave NULL
#define devfreq_performance NULL
#define devfreq_userspace NULL
#define devfreq_simple_ondemand NULL
#endif /* CONFIG_PM_DEVFREQ */
#endif /* __LINUX_DEVFREQ_H__ */