7 files changed, 803 insertions, 0 deletions

diff --git a/drivers/Kconfig b/drivers/Kconfig
index 95b9e7eefadc..a1efd75070aa 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -130,4 +130,6 @@ source "drivers/iommu/Kconfig"
 
 source "drivers/virt/Kconfig"
 
+source "drivers/devfreq/Kconfig"
+
 endmenu
diff --git a/drivers/Makefile b/drivers/Makefile
index 7fa433a7030c..97c957b50819 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -127,3 +127,5 @@ obj-$(CONFIG_IOMMU_SUPPORT)	+= iommu/
 
 # Virtualization drivers
 obj-$(CONFIG_VIRT_DRIVERS)      += virt/
+
+obj-$(CONFIG_PM_DEVFREQ)        += devfreq/
diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
new file mode 100644
index 000000000000..1fb42de4f420
--- /dev/null
+++ b/drivers/devfreq/Kconfig
@@ -0,0 +1,39 @@
+config ARCH_HAS_DEVFREQ
+        bool
+        depends on ARCH_HAS_OPP
+        help
+          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"
+        depends on PM_OPP && ARCH_HAS_DEVFREQ
+        help
+          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.
+
+if PM_DEVFREQ
+
+comment "DEVFREQ Drivers"
+
+endif # PM_DEVFREQ
diff --git a/drivers/devfreq/Makefile b/drivers/devfreq/Makefile
new file mode 100644
index 000000000000..168934a12b38
--- /dev/null
+++ b/drivers/devfreq/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_PM_DEVFREQ)        += devfreq.o
diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
new file mode 100644
index 000000000000..f3100b19f798
--- /dev/null
+++ b/drivers/devfreq/devfreq.c
@@ -0,0 +1,532 @@
+/*
+ * devfreq: Generic Dynamic Voltage and Frequency Scaling (DVFS) Framework
+ *          for Non-CPU Devices.
+ *
+ * Copyright (C) 2011 Samsung Electronics
+ *      MyungJoo Ham <myungjoo.ham@samsung.com>
+ *
+ * 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.
+ */
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/opp.h>
+#include <linux/devfreq.h>
+#include <linux/workqueue.h>
+#include <linux/platform_device.h>
+#include <linux/list.h>
+#include <linux/printk.h>
+#include <linux/hrtimer.h>
+#include "governor.h"
+
+struct class *devfreq_class;
+
+/*
+ * devfreq_work periodically monitors every registered device.
+ * The minimum polling interval is one jiffy. The polling interval is
+ * determined by the minimum polling period among all polling devfreq
+ * devices. The resolution of polling interval is one jiffy.
+ */
+static bool polling;
+static struct workqueue_struct *devfreq_wq;
+static struct delayed_work devfreq_work;
+
+/* wait removing if this is to be removed */
+static struct devfreq *wait_remove_device;
+
+/* The list of all device-devfreq */
+static LIST_HEAD(devfreq_list);
+static DEFINE_MUTEX(devfreq_list_lock);
+
+/**
+ * find_device_devfreq() - find devfreq struct using device pointer
+ * @dev:        device pointer used to lookup device devfreq.
+ *
+ * Search the list of device devfreqs and return the matched device's
+ * devfreq info. devfreq_list_lock should be held by the caller.
+ */
+static struct devfreq *find_device_devfreq(struct device *dev)
+{
+        struct devfreq *tmp_devfreq;
+
+        if (unlikely(IS_ERR_OR_NULL(dev))) {
+                pr_err("DEVFREQ: %s: Invalid parameters\n", __func__);
+                return ERR_PTR(-EINVAL);
+        }
+        WARN(!mutex_is_locked(&devfreq_list_lock),
+             "devfreq_list_lock must be locked.");
+
+        list_for_each_entry(tmp_devfreq, &devfreq_list, node) {
+                if (tmp_devfreq->dev.parent == dev)
+                        return tmp_devfreq;
+        }
+
+        return ERR_PTR(-ENODEV);
+}
+
+/**
+ * update_devfreq() - Reevaluate the device and configure frequency.
+ * @devfreq:    the devfreq instance.
+ *
+ * Note: Lock devfreq->lock before calling update_devfreq
+ *       This function is exported for governors.
+ */
+int update_devfreq(struct devfreq *devfreq)
+{
+        unsigned long freq;
+        int err = 0;
+
+        if (!mutex_is_locked(&devfreq->lock)) {
+                WARN(true, "devfreq->lock must be locked by the caller.\n");
+                return -EINVAL;
+        }
+
+        /* Reevaluate the proper frequency */
+        err = devfreq->governor->get_target_freq(devfreq, &freq);
+        if (err)
+                return err;
+
+        err = devfreq->profile->target(devfreq->dev.parent, &freq);
+        if (err)
+                return err;
+
+        devfreq->previous_freq = freq;
+        return err;
+}
+
+/**
+ * devfreq_notifier_call() - Notify that the device frequency requirements
+ *                         has been changed out of devfreq framework.
+ * @nb          the notifier_block (supposed to be devfreq->nb)
+ * @type        not used
+ * @devp        not used
+ *
+ * Called by a notifier that uses devfreq->nb.
+ */
+static int devfreq_notifier_call(struct notifier_block *nb, unsigned long type,
+                                 void *devp)
+{
+        struct devfreq *devfreq = container_of(nb, struct devfreq, nb);
+        int ret;
+
+        mutex_lock(&devfreq->lock);
+        ret = update_devfreq(devfreq);
+        mutex_unlock(&devfreq->lock);
+
+        return ret;
+}
+
+/**
+ * _remove_devfreq() - Remove devfreq from the device.
+ * @devfreq:    the devfreq struct
+ * @skip:       skip calling device_unregister().
+ *
+ * Note that the caller should lock devfreq->lock before calling
+ * this. _remove_devfreq() will unlock it and free devfreq
+ * internally. devfreq_list_lock should be locked by the caller
+ * as well (not relased at return)
+ *
+ * Lock usage:
+ * devfreq->lock: locked before call.
+ *                unlocked at return (and freed)
+ * devfreq_list_lock: locked before call.
+ *                    kept locked at return.
+ *                    if devfreq is centrally polled.
+ *
+ * Freed memory:
+ * devfreq
+ */
+static void _remove_devfreq(struct devfreq *devfreq, bool skip)
+{
+        if (!mutex_is_locked(&devfreq->lock)) {
+                WARN(true, "devfreq->lock must be locked by the caller.\n");
+                return;
+        }
+        if (!devfreq->governor->no_central_polling &&
+            !mutex_is_locked(&devfreq_list_lock)) {
+                WARN(true, "devfreq_list_lock must be locked by the caller.\n");
+                return;
+        }
+
+        if (devfreq->being_removed)
+                return;
+
+        devfreq->being_removed = true;
+
+        if (devfreq->profile->exit)
+                devfreq->profile->exit(devfreq->dev.parent);
+
+        if (devfreq->governor->exit)
+                devfreq->governor->exit(devfreq);
+
+        if (!skip && get_device(&devfreq->dev)) {
+                device_unregister(&devfreq->dev);
+                put_device(&devfreq->dev);
+        }
+
+        if (!devfreq->governor->no_central_polling)
+                list_del(&devfreq->node);
+
+        mutex_unlock(&devfreq->lock);
+        mutex_destroy(&devfreq->lock);
+
+        kfree(devfreq);
+}
+
+/**
+ * devfreq_dev_release() - Callback for struct device to release the device.
+ * @dev:        the devfreq device
+ *
+ * This calls _remove_devfreq() if _remove_devfreq() is not called.
+ * Note that devfreq_dev_release() could be called by _remove_devfreq() as
+ * well as by others unregistering the device.
+ */
+static void devfreq_dev_release(struct device *dev)
+{
+        struct devfreq *devfreq = to_devfreq(dev);
+        bool central_polling = !devfreq->governor->no_central_polling;
+
+        /*
+         * If devfreq_dev_release() was called by device_unregister() of
+         * _remove_devfreq(), we cannot mutex_lock(&devfreq->lock) and
+         * being_removed is already set. This also partially checks the case
+         * where devfreq_dev_release() is called from a thread other than
+         * the one called _remove_devfreq(); however, this case is
+         * dealt completely with another following being_removed check.
+         *
+         * Because being_removed is never being
+         * unset, we do not need to worry about race conditions on
+         * being_removed.
+         */
+        if (devfreq->being_removed)
+                return;
+
+        if (central_polling)
+                mutex_lock(&devfreq_list_lock);
+
+        mutex_lock(&devfreq->lock);
+
+        /*
+         * Check being_removed flag again for the case where
+         * devfreq_dev_release() was called in a thread other than the one
+         * possibly called _remove_devfreq().
+         */
+        if (devfreq->being_removed) {
+                mutex_unlock(&devfreq->lock);
+                goto out;
+        }
+
+        /* devfreq->lock is unlocked and removed in _removed_devfreq() */
+        _remove_devfreq(devfreq, true);
+
+out:
+        if (central_polling)
+                mutex_unlock(&devfreq_list_lock);
+}
+
+/**
+ * devfreq_monitor() - Periodically poll devfreq objects.
+ * @work: the work struct used to run devfreq_monitor periodically.
+ *
+ */
+static void devfreq_monitor(struct work_struct *work)
+{
+        static unsigned long last_polled_at;
+        struct devfreq *devfreq, *tmp;
+        int error;
+        unsigned long jiffies_passed;
+        unsigned long next_jiffies = ULONG_MAX, now = jiffies;
+        struct device *dev;
+
+        /* Initially last_polled_at = 0, polling every device at bootup */
+        jiffies_passed = now - last_polled_at;
+        last_polled_at = now;
+        if (jiffies_passed == 0)
+                jiffies_passed = 1;
+
+        mutex_lock(&devfreq_list_lock);
+        list_for_each_entry_safe(devfreq, tmp, &devfreq_list, node) {
+                mutex_lock(&devfreq->lock);
+                dev = devfreq->dev.parent;
+
+                /* Do not remove tmp for a while */
+                wait_remove_device = tmp;
+
+                if (devfreq->governor->no_central_polling ||
+                    devfreq->next_polling == 0) {
+                        mutex_unlock(&devfreq->lock);
+                        continue;
+                }
+                mutex_unlock(&devfreq_list_lock);
+
+                /*
+                 * Reduce more next_polling if devfreq_wq took an extra
+                 * delay. (i.e., CPU has been idled.)
+                 */
+                if (devfreq->next_polling <= jiffies_passed) {
+                        error = update_devfreq(devfreq);
+
+                        /* Remove a devfreq with an error. */
+                        if (error && error != -EAGAIN) {
+
+                                dev_err(dev, "Due to update_devfreq error(%d), devfreq(%s) is removed from the device\n",
+                                        error, devfreq->governor->name);
+
+                                /*
+                                 * Unlock devfreq before locking the list
+                                 * in order to avoid deadlock with
+                                 * find_device_devfreq or others
+                                 */
+                                mutex_unlock(&devfreq->lock);
+                                mutex_lock(&devfreq_list_lock);
+                                /* Check if devfreq is already removed */
+                                if (IS_ERR(find_device_devfreq(dev)))
+                                        continue;
+                                mutex_lock(&devfreq->lock);
+                                /* This unlocks devfreq->lock and free it */
+                                _remove_devfreq(devfreq, false);
+                                continue;
+                        }
+                        devfreq->next_polling = devfreq->polling_jiffies;
+                } else {
+                        devfreq->next_polling -= jiffies_passed;
+                }
+
+                if (devfreq->next_polling)
+                        next_jiffies = (next_jiffies > devfreq->next_polling) ?
+                                        devfreq->next_polling : next_jiffies;
+
+                mutex_unlock(&devfreq->lock);
+                mutex_lock(&devfreq_list_lock);
+        }
+        wait_remove_device = NULL;
+        mutex_unlock(&devfreq_list_lock);
+
+        if (next_jiffies > 0 && next_jiffies < ULONG_MAX) {
+                polling = true;
+                queue_delayed_work(devfreq_wq, &devfreq_work, next_jiffies);
+        } else {
+                polling = false;
+        }
+}
+
+/**
+ * devfreq_add_device() - Add devfreq feature to the device
+ * @dev:        the device to add devfreq feature.
+ * @profile:    device-specific profile to run devfreq.
+ * @governor:   the policy to choose frequency.
+ * @data:       private data for the governor. The devfreq framework does not
+ *              touch this value.
+ */
+struct devfreq *devfreq_add_device(struct device *dev,
+                                   struct devfreq_dev_profile *profile,
+                                   const struct devfreq_governor *governor,
+                                   void *data)
+{
+        struct devfreq *devfreq;
+        int err = 0;
+
+        if (!dev || !profile || !governor) {
+                dev_err(dev, "%s: Invalid parameters.\n", __func__);
+                return ERR_PTR(-EINVAL);
+        }
+
+
+        if (!governor->no_central_polling) {
+                mutex_lock(&devfreq_list_lock);
+                devfreq = find_device_devfreq(dev);
+                mutex_unlock(&devfreq_list_lock);
+                if (!IS_ERR(devfreq)) {
+                        dev_err(dev, "%s: Unable to create devfreq for the device. It already has one.\n", __func__);
+                        err = -EINVAL;
+                        goto out;
+                }
+        }
+
+        devfreq = kzalloc(sizeof(struct devfreq), GFP_KERNEL);
+        if (!devfreq) {
+                dev_err(dev, "%s: Unable to create devfreq for the device\n",
+                        __func__);
+                err = -ENOMEM;
+                goto out;
+        }
+
+        mutex_init(&devfreq->lock);
+        mutex_lock(&devfreq->lock);
+        devfreq->dev.parent = dev;
+        devfreq->dev.class = devfreq_class;
+        devfreq->dev.release = devfreq_dev_release;
+        devfreq->profile = profile;
+        devfreq->governor = governor;
+        devfreq->previous_freq = profile->initial_freq;
+        devfreq->data = data;
+        devfreq->next_polling = devfreq->polling_jiffies
+                              = msecs_to_jiffies(devfreq->profile->polling_ms);
+        devfreq->nb.notifier_call = devfreq_notifier_call;
+
+        dev_set_name(&devfreq->dev, dev_name(dev));
+        err = device_register(&devfreq->dev);
+        if (err) {
+                put_device(&devfreq->dev);
+                goto err_dev;
+        }
+
+        if (governor->init)
+                err = governor->init(devfreq);
+        if (err)
+                goto err_init;
+
+        mutex_unlock(&devfreq->lock);
+
+        if (governor->no_central_polling)
+                goto out;
+
+        mutex_lock(&devfreq_list_lock);
+
+        list_add(&devfreq->node, &devfreq_list);
+
+        if (devfreq_wq && devfreq->next_polling && !polling) {
+                polling = true;
+                queue_delayed_work(devfreq_wq, &devfreq_work,
+                                   devfreq->next_polling);
+        }
+        mutex_unlock(&devfreq_list_lock);
+        goto out;
+err_init:
+        device_unregister(&devfreq->dev);
+err_dev:
+        mutex_unlock(&devfreq->lock);
+        kfree(devfreq);
+out:
+        if (err)
+                return ERR_PTR(err);
+        else
+                return devfreq;
+}
+
+/**
+ * devfreq_remove_device() - Remove devfreq feature from a device.
+ * @devfreq     the devfreq instance to be removed
+ */
+int devfreq_remove_device(struct devfreq *devfreq)
+{
+        if (!devfreq)
+                return -EINVAL;
+
+        if (!devfreq->governor->no_central_polling) {
+                mutex_lock(&devfreq_list_lock);
+                while (wait_remove_device == devfreq) {
+                        mutex_unlock(&devfreq_list_lock);
+                        schedule();
+                        mutex_lock(&devfreq_list_lock);
+                }
+        }
+
+        mutex_lock(&devfreq->lock);
+        _remove_devfreq(devfreq, false); /* it unlocks devfreq->lock */
+
+        if (!devfreq->governor->no_central_polling)
+                mutex_unlock(&devfreq_list_lock);
+
+        return 0;
+}
+
+/**
+ * devfreq_start_polling() - Initialize data structure for devfreq framework and
+ *                         start polling registered devfreq devices.
+ */
+static int __init devfreq_start_polling(void)
+{
+        mutex_lock(&devfreq_list_lock);
+        polling = false;
+        devfreq_wq = create_freezable_workqueue("devfreq_wq");
+        INIT_DELAYED_WORK_DEFERRABLE(&devfreq_work, devfreq_monitor);
+        mutex_unlock(&devfreq_list_lock);
+
+        devfreq_monitor(&devfreq_work.work);
+        return 0;
+}
+late_initcall(devfreq_start_polling);
+
+static int __init devfreq_init(void)
+{
+        devfreq_class = class_create(THIS_MODULE, "devfreq");
+        if (IS_ERR(devfreq_class)) {
+                pr_err("%s: couldn't create class\n", __FILE__);
+                return PTR_ERR(devfreq_class);
+        }
+        return 0;
+}
+subsys_initcall(devfreq_init);
+
+static void __exit devfreq_exit(void)
+{
+        class_destroy(devfreq_class);
+}
+module_exit(devfreq_exit);
+
+/*
+ * The followings are helper functions for devfreq user device drivers with
+ * OPP framework.
+ */
+
+/**
+ * devfreq_recommended_opp() - Helper function to get proper OPP for the
+ *                           freq value given to target callback.
+ * @dev         The devfreq user device. (parent of devfreq)
+ * @freq        The frequency given to target function
+ *
+ */
+struct opp *devfreq_recommended_opp(struct device *dev, unsigned long *freq)
+{
+        struct opp *opp = opp_find_freq_ceil(dev, freq);
+
+        if (opp == ERR_PTR(-ENODEV))
+                opp = opp_find_freq_floor(dev, freq);
+        return opp;
+}
+
+/**
+ * devfreq_register_opp_notifier() - Helper function to get devfreq notified
+ *                                 for any changes in the OPP availability
+ *                                 changes
+ * @dev         The devfreq user device. (parent of devfreq)
+ * @devfreq     The devfreq object.
+ */
+int devfreq_register_opp_notifier(struct device *dev, struct devfreq *devfreq)
+{
+        struct srcu_notifier_head *nh = opp_get_notifier(dev);
+
+        if (IS_ERR(nh))
+                return PTR_ERR(nh);
+        return srcu_notifier_chain_register(nh, &devfreq->nb);
+}
+
+/**
+ * devfreq_unregister_opp_notifier() - Helper function to stop getting devfreq
+ *                                   notified for any changes in the OPP
+ *                                   availability changes anymore.
+ * @dev         The devfreq user device. (parent of devfreq)
+ * @devfreq     The devfreq object.
+ *
+ * At exit() callback of devfreq_dev_profile, this must be included if
+ * devfreq_recommended_opp is used.
+ */
+int devfreq_unregister_opp_notifier(struct device *dev, struct devfreq *devfreq)
+{
+        struct srcu_notifier_head *nh = opp_get_notifier(dev);
+
+        if (IS_ERR(nh))
+                return PTR_ERR(nh);
+        return srcu_notifier_chain_unregister(nh, &devfreq->nb);
+}
+
+MODULE_AUTHOR("MyungJoo Ham <myungjoo.ham@samsung.com>");
+MODULE_DESCRIPTION("devfreq class support");
+MODULE_LICENSE("GPL");
diff --git a/drivers/devfreq/governor.h b/drivers/devfreq/governor.h
new file mode 100644
index 000000000000..ea7f13c58ded
--- /dev/null
+++ b/drivers/devfreq/governor.h
@@ -0,0 +1,24 @@
+/*
+ * governor.h - internal header for devfreq governors.
+ *
+ * Copyright (C) 2011 Samsung Electronics
+ *      MyungJoo Ham <myungjoo.ham@samsung.com>
+ *
+ * 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 */
diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
new file mode 100644
index 000000000000..b3be3d3cbaa7
--- /dev/null
+++ b/include/linux/devfreq.h
@@ -0,0 +1,203 @@
+/*
+ * devfreq: Generic Dynamic Voltage and Frequency Scaling (DVFS) Framework
+ *          for Non-CPU Devices.
+ *
+ * Copyright (C) 2011 Samsung Electronics
+ *      MyungJoo Ham <myungjoo.ham@samsung.com>
+ *
+ * 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>
+
+#define DEVFREQ_NAME_LEN 16
+
+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__ */