thermal: add generic cpufreq cooling implementation

This patchset introduces a new generic cooling device based on cpufreq
that can be used on non-ACPI platforms.  As a proof of concept, we have
drivers for the following platforms using this mechanism now:

 * Samsung Exynos (Exynos4 and Exynos5) in the current patchset.
 * Freescale i.MX (git://git.linaro.org/people/amitdanielk/linux.git imx6q_thermal)

There is a small change in cpufreq cooling registration APIs, so a minor
change is needed for Freescale platforms.

Brief Description:

1) The generic cooling devices code is placed inside driver/thermal/*
   as placing inside acpi folder will need un-necessary enabling of acpi
   code.  This code is architecture independent.

2) This patchset adds generic cpu cooling low level implementation
   through frequency clipping.  In future, other cpu related cooling
   devices may be added here.  An ACPI version of this already exists
   (drivers/acpi/processor_thermal.c) .But this will be useful for
   platforms like ARM using the generic thermal interface along with the
   generic cpu cooling devices.  The cooling device registration API's
   return cooling device pointers which can be easily binded with the
   thermal zone trip points.  The important APIs exposed are,

   a) struct thermal_cooling_device *cpufreq_cooling_register(
        struct cpumask *clip_cpus)
   b) void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)

3) Samsung exynos platform thermal implementation is done using the
   generic cpu cooling APIs and the new trip type.  The temperature sensor
   driver present in the hwmon folder(registered as hwmon driver) is moved
   to thermal folder and registered as a thermal driver.

A simple data/control flow diagrams is shown below,

Core Linux thermal <----->  Exynos thermal interface <----- Temperature Sensor
          |                             |
         \|/                            |
  Cpufreq cooling device <---------------

TODO:
*Will send the DT enablement patches later after the driver is merged.

This patch:

Add support for generic cpu thermal cooling low level implementations
using frequency scaling up/down based on the registration parameters.
Different cpu related cooling devices can be registered by the user and
the binding of these cooling devices to the corresponding trip points can
be easily done as the registration APIs return the cooling device pointer.
The user of these APIs are responsible for passing clipping frequency .
The drivers can also register to recieve notification about any cooling
action called.

[akpm@linux-foundation.org: fix comment layout]
Signed-off-by: Amit Daniel Kachhap <amit.kachhap@linaro.org>
Cc: Guenter Roeck <guenter.roeck@ericsson.com>
Cc: SangWook Ju <sw.ju@samsung.com>
Cc: Durgadoss <durgadoss.r@intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Jean Delvare <khali@linux-fr.org>
Cc: Kyungmin Park <kmpark@infradead.org>
Cc: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

5 files changed, 552 insertions, 0 deletions

diff --git a/Documentation/thermal/cpu-cooling-api.txt b/Documentation/thermal/cpu-cooling-api.txt
new file mode 100644
index 000000000000..fca24c931ec8
--- /dev/null
+++ b/Documentation/thermal/cpu-cooling-api.txt
@@ -0,0 +1,32 @@
+CPU cooling APIs How To
+===================================
+
+Written by Amit Daniel Kachhap <amit.kachhap@linaro.org>
+
+Updated: 12 May 2012
+
+Copyright (c)  2012 Samsung Electronics Co., Ltd(http://www.samsung.com)
+
+0. Introduction
+
+The generic cpu cooling(freq clipping) provides registration/unregistration APIs
+to the caller. The binding of the cooling devices to the trip point is left for
+the user. The registration APIs returns the cooling device pointer.
+
+1. cpu cooling APIs
+
+1.1 cpufreq registration/unregistration APIs
+1.1.1 struct thermal_cooling_device *cpufreq_cooling_register(
+	struct cpumask *clip_cpus)
+
+    This interface function registers the cpufreq cooling device with the name
+    "thermal-cpufreq-%x". This api can support multiple instances of cpufreq
+    cooling devices.
+
+   clip_cpus: cpumask of cpus where the frequency constraints will happen.
+
+1.1.2 void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)
+
+    This interface function unregisters the "thermal-cpufreq-%x" cooling device.
+
+    cdev: Cooling device pointer which has to be unregistered.
diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
index 7dd8c34552e1..996003b3438a 100644
--- a/drivers/thermal/Kconfig
+++ b/drivers/thermal/Kconfig
@@ -19,6 +19,17 @@ config THERMAL_HWMON
 	depends on HWMON=y || HWMON=THERMAL
 	default y
 
+config CPU_THERMAL
+	bool "generic cpu cooling support"
+	depends on THERMAL && CPU_FREQ
+	help
+	  This implements the generic cpu cooling mechanism through frequency
+	  reduction, cpu hotplug and any other ways of reducing temperature. An
+	  ACPI version of this already exists(drivers/acpi/processor_thermal.c).
+	  This will be useful for platforms using the generic thermal interface
+	  and not the ACPI interface.
+	  If you want this support, you should say Y here.
+
 config SPEAR_THERMAL
 	bool "SPEAr thermal sensor driver"
 	depends on THERMAL
diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
index fd9369aeb96f..aae59ad57c42 100644
--- a/drivers/thermal/Makefile
+++ b/drivers/thermal/Makefile
@@ -3,5 +3,6 @@
 #
 
 obj-$(CONFIG_THERMAL)		+= thermal_sys.o
+obj-$(CONFIG_CPU_THERMAL)		+= cpu_cooling.o
 obj-$(CONFIG_SPEAR_THERMAL)		+= spear_thermal.o
 obj-$(CONFIG_RCAR_THERMAL)	+= rcar_thermal.o
diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
new file mode 100644
index 000000000000..99a5d7551b33
--- /dev/null
+++ b/drivers/thermal/cpu_cooling.c
@@ -0,0 +1,450 @@
+/*
+ *  linux/drivers/thermal/cpu_cooling.c
+ *
+ *  Copyright (C) 2012	Samsung Electronics Co., Ltd(http://www.samsung.com)
+ *  Copyright (C) 2012  Amit Daniel <amit.kachhap@linaro.org>
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; version 2 of the License.
+ *
+ *  This program is distributed in the hope that it will be useful, but
+ *  WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program; if not, write to the Free Software Foundation, Inc.,
+ *  59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/thermal.h>
+#include <linux/platform_device.h>
+#include <linux/cpufreq.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/cpu.h>
+#include <linux/cpu_cooling.h>
+
+/**
+ * struct cpufreq_cooling_device
+ * @id: unique integer value corresponding to each cpufreq_cooling_device
+ *	registered.
+ * @cool_dev: thermal_cooling_device pointer to keep track of the the
+ *	egistered cooling device.
+ * @cpufreq_state: integer value representing the current state of cpufreq
+ *	cooling	devices.
+ * @cpufreq_val: integer value representing the absolute value of the clipped
+ *	frequency.
+ * @allowed_cpus: all the cpus involved for this cpufreq_cooling_device.
+ * @node: list_head to link all cpufreq_cooling_device together.
+ *
+ * This structure is required for keeping information of each
+ * cpufreq_cooling_device registered as a list whose head is represented by
+ * cooling_cpufreq_list. In order to prevent corruption of this list a
+ * mutex lock cooling_cpufreq_lock is used.
+ */
+struct cpufreq_cooling_device {
+	int id;
+	struct thermal_cooling_device *cool_dev;
+	unsigned int cpufreq_state;
+	unsigned int cpufreq_val;
+	struct cpumask allowed_cpus;
+	struct list_head node;
+};
+static LIST_HEAD(cooling_cpufreq_list);
+static DEFINE_IDR(cpufreq_idr);
+
+static struct mutex cooling_cpufreq_lock;
+
+/* notify_table passes value to the CPUFREQ_ADJUST callback function. */
+#define NOTIFY_INVALID NULL
+struct cpufreq_cooling_device *notify_device;
+
+/**
+ * get_idr - function to get a unique id.
+ * @idr: struct idr * handle used to create a id.
+ * @id: int * value generated by this function.
+ */
+static int get_idr(struct idr *idr, int *id)
+{
+	int err;
+again:
+	if (unlikely(idr_pre_get(idr, GFP_KERNEL) == 0))
+		return -ENOMEM;
+
+	mutex_lock(&cooling_cpufreq_lock);
+	err = idr_get_new(idr, NULL, id);
+	mutex_unlock(&cooling_cpufreq_lock);
+
+	if (unlikely(err == -EAGAIN))
+		goto again;
+	else if (unlikely(err))
+		return err;
+
+	*id = *id & MAX_ID_MASK;
+	return 0;
+}
+
+/**
+ * release_idr - function to free the unique id.
+ * @idr: struct idr * handle used for creating the id.
+ * @id: int value representing the unique id.
+ */
+static void release_idr(struct idr *idr, int id)
+{
+	mutex_lock(&cooling_cpufreq_lock);
+	idr_remove(idr, id);
+	mutex_unlock(&cooling_cpufreq_lock);
+}
+
+/* Below code defines functions to be used for cpufreq as cooling device */
+
+/**
+ * is_cpufreq_valid - function to check if a cpu has frequency transition policy.
+ * @cpu: cpu for which check is needed.
+ */
+static int is_cpufreq_valid(int cpu)
+{
+	struct cpufreq_policy policy;
+	return !cpufreq_get_policy(&policy, cpu);
+}
+
+/**
+ * get_cpu_frequency - get the absolute value of frequency from level.
+ * @cpu: cpu for which frequency is fetched.
+ * @level: level of frequency of the CPU
+ *	e.g level=1 --> 1st MAX FREQ, LEVEL=2 ---> 2nd MAX FREQ, .... etc
+ */
+static unsigned int get_cpu_frequency(unsigned int cpu, unsigned long level)
+{
+	int ret = 0, i = 0;
+	unsigned long level_index;
+	bool descend = false;
+	struct cpufreq_frequency_table *table =
+					cpufreq_frequency_get_table(cpu);
+	if (!table)
+		return ret;
+
+	while (table[i].frequency != CPUFREQ_TABLE_END) {
+		if (table[i].frequency == CPUFREQ_ENTRY_INVALID)
+			continue;
+
+		/*check if table in ascending or descending order*/
+		if ((table[i + 1].frequency != CPUFREQ_TABLE_END) &&
+			(table[i + 1].frequency < table[i].frequency)
+			&& !descend) {
+			descend = true;
+		}
+
+		/*return if level matched and table in descending order*/
+		if (descend && i == level)
+			return table[i].frequency;
+		i++;
+	}
+	i--;
+
+	if (level > i || descend)
+		return ret;
+	level_index = i - level;
+
+	/*Scan the table in reverse order and match the level*/
+	while (i >= 0) {
+		if (table[i].frequency == CPUFREQ_ENTRY_INVALID)
+			continue;
+		/*return if level matched*/
+		if (i == level_index)
+			return table[i].frequency;
+		i--;
+	}
+	return ret;
+}
+
+/**
+ * cpufreq_apply_cooling - function to apply frequency clipping.
+ * @cpufreq_device: cpufreq_cooling_device pointer containing frequency
+ *	clipping data.
+ * @cooling_state: value of the cooling state.
+ */
+static int cpufreq_apply_cooling(struct cpufreq_cooling_device *cpufreq_device,
+				unsigned long cooling_state)
+{
+	unsigned int cpuid, clip_freq;
+	struct cpumask *maskPtr = &cpufreq_device->allowed_cpus;
+	unsigned int cpu = cpumask_any(maskPtr);
+
+
+	/* Check if the old cooling action is same as new cooling action */
+	if (cpufreq_device->cpufreq_state == cooling_state)
+		return 0;
+
+	clip_freq = get_cpu_frequency(cpu, cooling_state);
+	if (!clip_freq)
+		return -EINVAL;
+
+	cpufreq_device->cpufreq_state = cooling_state;
+	cpufreq_device->cpufreq_val = clip_freq;
+	notify_device = cpufreq_device;
+
+	for_each_cpu(cpuid, maskPtr) {
+		if (is_cpufreq_valid(cpuid))
+			cpufreq_update_policy(cpuid);
+	}
+
+	notify_device = NOTIFY_INVALID;
+
+	return 0;
+}
+
+/**
+ * cpufreq_thermal_notifier - notifier callback for cpufreq policy change.
+ * @nb:	struct notifier_block * with callback info.
+ * @event: value showing cpufreq event for which this function invoked.
+ * @data: callback-specific data
+ */
+static int cpufreq_thermal_notifier(struct notifier_block *nb,
+					unsigned long event, void *data)
+{
+	struct cpufreq_policy *policy = data;
+	unsigned long max_freq = 0;
+
+	if (event != CPUFREQ_ADJUST || notify_device == NOTIFY_INVALID)
+		return 0;
+
+	if (cpumask_test_cpu(policy->cpu, &notify_device->allowed_cpus))
+		max_freq = notify_device->cpufreq_val;
+
+	/* Never exceed user_policy.max*/
+	if (max_freq > policy->user_policy.max)
+		max_freq = policy->user_policy.max;
+
+	if (policy->max != max_freq)
+		cpufreq_verify_within_limits(policy, 0, max_freq);
+
+	return 0;
+}
+
+/*
+ * cpufreq cooling device callback functions are defined below
+ */
+
+/**
+ * cpufreq_get_max_state - callback function to get the max cooling state.
+ * @cdev: thermal cooling device pointer.
+ * @state: fill this variable with the max cooling state.
+ */
+static int cpufreq_get_max_state(struct thermal_cooling_device *cdev,
+				 unsigned long *state)
+{
+	int ret = -EINVAL, i = 0;
+	struct cpufreq_cooling_device *cpufreq_device;
+	struct cpumask *maskPtr;
+	unsigned int cpu;
+	struct cpufreq_frequency_table *table;
+
+	mutex_lock(&cooling_cpufreq_lock);
+	list_for_each_entry(cpufreq_device, &cooling_cpufreq_list, node) {
+		if (cpufreq_device && cpufreq_device->cool_dev == cdev)
+			break;
+	}
+	if (cpufreq_device == NULL)
+		goto return_get_max_state;
+
+	maskPtr = &cpufreq_device->allowed_cpus;
+	cpu = cpumask_any(maskPtr);
+	table = cpufreq_frequency_get_table(cpu);
+	if (!table) {
+		*state = 0;
+		ret = 0;
+		goto return_get_max_state;
+	}
+
+	while (table[i].frequency != CPUFREQ_TABLE_END) {
+		if (table[i].frequency == CPUFREQ_ENTRY_INVALID)
+			continue;
+		i++;
+	}
+	if (i > 0) {
+		*state = --i;
+		ret = 0;
+	}
+
+return_get_max_state:
+	mutex_unlock(&cooling_cpufreq_lock);
+	return ret;
+}
+
+/**
+ * cpufreq_get_cur_state - callback function to get the current cooling state.
+ * @cdev: thermal cooling device pointer.
+ * @state: fill this variable with the current cooling state.
+ */
+static int cpufreq_get_cur_state(struct thermal_cooling_device *cdev,
+				 unsigned long *state)
+{
+	int ret = -EINVAL;
+	struct cpufreq_cooling_device *cpufreq_device;
+
+	mutex_lock(&cooling_cpufreq_lock);
+	list_for_each_entry(cpufreq_device, &cooling_cpufreq_list, node) {
+		if (cpufreq_device && cpufreq_device->cool_dev == cdev) {
+			*state = cpufreq_device->cpufreq_state;
+			ret = 0;
+			break;
+		}
+	}
+	mutex_unlock(&cooling_cpufreq_lock);
+
+	return ret;
+}
+
+/**
+ * cpufreq_set_cur_state - callback function to set the current cooling state.
+ * @cdev: thermal cooling device pointer.
+ * @state: set this variable to the current cooling state.
+ */
+static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
+				 unsigned long state)
+{
+	int ret = -EINVAL;
+	struct cpufreq_cooling_device *cpufreq_device;
+
+	mutex_lock(&cooling_cpufreq_lock);
+	list_for_each_entry(cpufreq_device, &cooling_cpufreq_list, node) {
+		if (cpufreq_device && cpufreq_device->cool_dev == cdev) {
+			ret = 0;
+			break;
+		}
+	}
+	if (!ret)
+		ret = cpufreq_apply_cooling(cpufreq_device, state);
+
+	mutex_unlock(&cooling_cpufreq_lock);
+
+	return ret;
+}
+
+/* Bind cpufreq callbacks to thermal cooling device ops */
+static struct thermal_cooling_device_ops const cpufreq_cooling_ops = {
+	.get_max_state = cpufreq_get_max_state,
+	.get_cur_state = cpufreq_get_cur_state,
+	.set_cur_state = cpufreq_set_cur_state,
+};
+
+/* Notifier for cpufreq policy change */
+static struct notifier_block thermal_cpufreq_notifier_block = {
+	.notifier_call = cpufreq_thermal_notifier,
+};
+
+/**
+ * cpufreq_cooling_register - function to create cpufreq cooling device.
+ * @clip_cpus: cpumask of cpus where the frequency constraints will happen.
+ */
+struct thermal_cooling_device *cpufreq_cooling_register(
+	struct cpumask *clip_cpus)
+{
+	struct thermal_cooling_device *cool_dev;
+	struct cpufreq_cooling_device *cpufreq_dev = NULL;
+	unsigned int cpufreq_dev_count = 0, min = 0, max = 0;
+	char dev_name[THERMAL_NAME_LENGTH];
+	int ret = 0, id = 0, i;
+	struct cpufreq_policy policy;
+
+	list_for_each_entry(cpufreq_dev, &cooling_cpufreq_list, node)
+		cpufreq_dev_count++;
+
+	/*Verify that all the clip cpus have same freq_min, freq_max limit*/
+	for_each_cpu(i, clip_cpus) {
+		/*continue if cpufreq policy not found and not return error*/
+		if (!cpufreq_get_policy(&policy, i))
+			continue;
+		if (min == 0 && max == 0) {
+			min = policy.cpuinfo.min_freq;
+			max = policy.cpuinfo.max_freq;
+		} else {
+			if (min != policy.cpuinfo.min_freq ||
+				max != policy.cpuinfo.max_freq)
+				return ERR_PTR(-EINVAL);
+}
+	}
+	cpufreq_dev = kzalloc(sizeof(struct cpufreq_cooling_device),
+			GFP_KERNEL);
+	if (!cpufreq_dev)
+		return ERR_PTR(-ENOMEM);
+
+	cpumask_copy(&cpufreq_dev->allowed_cpus, clip_cpus);
+
+	if (cpufreq_dev_count == 0)
+		mutex_init(&cooling_cpufreq_lock);
+
+	ret = get_idr(&cpufreq_idr, &cpufreq_dev->id);
+	if (ret) {
+		kfree(cpufreq_dev);
+		return ERR_PTR(-EINVAL);
+	}
+
+	sprintf(dev_name, "thermal-cpufreq-%d", cpufreq_dev->id);
+
+	cool_dev = thermal_cooling_device_register(dev_name, cpufreq_dev,
+						&cpufreq_cooling_ops);
+	if (!cool_dev) {
+		release_idr(&cpufreq_idr, cpufreq_dev->id);
+		kfree(cpufreq_dev);
+		return ERR_PTR(-EINVAL);
+	}
+	cpufreq_dev->id = id;
+	cpufreq_dev->cool_dev = cool_dev;
+	cpufreq_dev->cpufreq_state = 0;
+	mutex_lock(&cooling_cpufreq_lock);
+	list_add_tail(&cpufreq_dev->node, &cooling_cpufreq_list);
+
+	/* Register the notifier for first cpufreq cooling device */
+	if (cpufreq_dev_count == 0)
+		cpufreq_register_notifier(&thermal_cpufreq_notifier_block,
+						CPUFREQ_POLICY_NOTIFIER);
+
+	mutex_unlock(&cooling_cpufreq_lock);
+	return cool_dev;
+}
+EXPORT_SYMBOL(cpufreq_cooling_register);
+
+/**
+ * cpufreq_cooling_unregister - function to remove cpufreq cooling device.
+ * @cdev: thermal cooling device pointer.
+ */
+void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)
+{
+	struct cpufreq_cooling_device *cpufreq_dev = NULL;
+	unsigned int cpufreq_dev_count = 0;
+
+	mutex_lock(&cooling_cpufreq_lock);
+	list_for_each_entry(cpufreq_dev, &cooling_cpufreq_list, node) {
+		if (cpufreq_dev && cpufreq_dev->cool_dev == cdev)
+			break;
+		cpufreq_dev_count++;
+	}
+
+	if (!cpufreq_dev || cpufreq_dev->cool_dev != cdev) {
+		mutex_unlock(&cooling_cpufreq_lock);
+		return;
+	}
+
+	list_del(&cpufreq_dev->node);
+
+	/* Unregister the notifier for the last cpufreq cooling device */
+	if (cpufreq_dev_count == 1) {
+		cpufreq_unregister_notifier(&thermal_cpufreq_notifier_block,
+					CPUFREQ_POLICY_NOTIFIER);
+	}
+	mutex_unlock(&cooling_cpufreq_lock);
+	thermal_cooling_device_unregister(cpufreq_dev->cool_dev);
+	release_idr(&cpufreq_idr, cpufreq_dev->id);
+	if (cpufreq_dev_count == 1)
+		mutex_destroy(&cooling_cpufreq_lock);
+	kfree(cpufreq_dev);
+}
+EXPORT_SYMBOL(cpufreq_cooling_unregister);
diff --git a/include/linux/cpu_cooling.h b/include/linux/cpu_cooling.h
new file mode 100644
index 000000000000..851530128e65
--- /dev/null
+++ b/include/linux/cpu_cooling.h
@@ -0,0 +1,58 @@
+/*
+ *  linux/include/linux/cpu_cooling.h
+ *
+ *  Copyright (C) 2012	Samsung Electronics Co., Ltd(http://www.samsung.com)
+ *  Copyright (C) 2012  Amit Daniel <amit.kachhap@linaro.org>
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; version 2 of the License.
+ *
+ *  This program is distributed in the hope that it will be useful, but
+ *  WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program; if not, write to the Free Software Foundation, Inc.,
+ *  59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ */
+
+#ifndef __CPU_COOLING_H__
+#define __CPU_COOLING_H__
+
+#include <linux/thermal.h>
+
+#define CPUFREQ_COOLING_START		0
+#define CPUFREQ_COOLING_STOP		1
+
+#ifdef CONFIG_CPU_THERMAL
+/**
+ * cpufreq_cooling_register - function to create cpufreq cooling device.
+ * @clip_cpus: cpumask of cpus where the frequency constraints will happen
+ */
+struct thermal_cooling_device *cpufreq_cooling_register(
+		struct cpumask *clip_cpus);
+
+/**
+ * cpufreq_cooling_unregister - function to remove cpufreq cooling device.
+ * @cdev: thermal cooling device pointer.
+ */
+void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev);
+#else /* !CONFIG_CPU_THERMAL */
+static inline struct thermal_cooling_device *cpufreq_cooling_register(
+	struct cpumask *clip_cpus)
+{
+	return NULL;
+}
+static inline void cpufreq_cooling_unregister(
+		struct thermal_cooling_device *cdev)
+{
+	return;
+}
+#endif	/* CONFIG_CPU_THERMAL */
+
+#endif /* __CPU_COOLING_H__ */