Commit a3c98b8b authored by MyungJoo Ham's avatar MyungJoo Ham Committed by Rafael J. Wysocki

PM: Introduce devfreq: generic DVFS framework with device-specific OPPs

With OPPs, a device may have multiple operable frequency and voltage
sets. However, there can be multiple possible operable sets and a system
will need to choose one from them. In order to reduce the power
consumption (by reducing frequency and voltage) without affecting the
performance too much, a Dynamic Voltage and Frequency Scaling (DVFS)
scheme may be used.

This patch introduces the DVFS capability to non-CPU devices with OPPs.
DVFS is a techique whereby the frequency and supplied voltage of a
device is adjusted on-the-fly. DVFS usually sets the frequency as low
as possible with given conditions (such as QoS assurance) and adjusts
voltage according to the chosen frequency in order to reduce power
consumption and heat dissipation.

The generic DVFS for devices, devfreq, may appear quite similar with
/drivers/cpufreq.  However, cpufreq does not allow to have multiple
devices registered and is not suitable to have multiple heterogenous
devices with different (but simple) governors.

Normally, DVFS mechanism controls frequency based on the demand for
the device, and then, chooses voltage based on the chosen frequency.
devfreq also controls the frequency based on the governor's frequency
recommendation and let OPP pick up the pair of frequency and voltage
based on the recommended frequency. Then, the chosen OPP is passed to
device driver's "target" callback.

When PM QoS is going to be used with the devfreq device, the device
driver should enable OPPs that are appropriate with the current PM QoS
requests. In order to do so, the device driver may call opp_enable and
opp_disable at the notifier callback of PM QoS so that PM QoS's
update_target() call enables the appropriate OPPs. Note that at least
one of OPPs should be enabled at any time; be careful when there is a
Signed-off-by: default avatarMyungJoo Ham <>
Signed-off-by: default avatarKyungmin Park <>
Reviewed-by: default avatarMike Turquette <>
Acked-by: default avatarKevin Hilman <>
Signed-off-by: default avatarRafael J. Wysocki <>
parent 03ca370f
......@@ -130,4 +130,6 @@ source "drivers/iommu/Kconfig"
source "drivers/virt/Kconfig"
source "drivers/devfreq/Kconfig"
......@@ -127,3 +127,5 @@ obj-$(CONFIG_IOMMU_SUPPORT) += iommu/
# Virtualization drivers
obj-$(CONFIG_VIRT_DRIVERS) += virt/
obj-$(CONFIG_PM_DEVFREQ) += devfreq/
depends on ARCH_HAS_OPP
Denotes that the architecture supports DEVFREQ. If the architecture
supports multiple OPP entries per device and the frequency of the
devices with OPPs may be altered dynamically, the architecture
supports DEVFREQ.
menuconfig PM_DEVFREQ
bool "Generic Dynamic Voltage and Frequency Scaling (DVFS) support"
With OPP support, a device may have a list of frequencies and
voltages available. DEVFREQ, a generic DVFS framework can be
registered for a device with OPP support in order to let the
governor provided to DEVFREQ choose an operating frequency
based on the OPP's list and the policy given with DEVFREQ.
Each device may have its own governor and policy. DEVFREQ can
reevaluate the device state periodically and/or based on the
OPP list changes (each frequency/voltage pair in OPP may be
disabled or enabled).
Like some CPUs with CPUFREQ, a device may have multiple clocks.
However, because the clock frequencies of a single device are
determined by the single device's state, an instance of DEVFREQ
is attached to a single device and returns a "representative"
clock frequency from the OPP of the device, which is also attached
to a device by 1-to-1. The device registering DEVFREQ takes the
responsiblity to "interpret" the frequency listed in OPP and
to set its every clock accordingly with the "target" callback
given to DEVFREQ.
comment "DEVFREQ Drivers"
endif # PM_DEVFREQ
obj-$(CONFIG_PM_DEVFREQ) += devfreq.o
This diff is collapsed.
* governor.h - internal header for devfreq governors.
* 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.
* This header is for devfreq governors in drivers/devfreq/
#ifndef _GOVERNOR_H
#define _GOVERNOR_H
#include <linux/devfreq.h>
#define to_devfreq(DEV) container_of((DEV), struct devfreq, dev)
/* Caution: devfreq->lock must be locked before calling update_devfreq */
extern int update_devfreq(struct devfreq *devfreq);
#endif /* _GOVERNOR_H */
* 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_date;
* 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.
* @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);
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.
* 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;
#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);
extern int devfreq_register_opp_notifier(struct device *dev,
struct devfreq *devfreq);
extern int devfreq_unregister_opp_notifier(struct device *dev,
struct devfreq *devfreq);
#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)
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;
#endif /* CONFIG_PM_DEVFREQ */
#endif /* __LINUX_DEVFREQ_H__ */
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