drivers/base/power/opp.c - kernel/panda - Git at Google

 /*
  * Generic OPP Interface
  *
  * Copyright (C) 2009-2010 Texas Instruments Incorporated.
  *	Nishanth Menon
  *	Romit Dasgupta
  *	Kevin Hilman
  *
  * 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/errno.h>
 #include <linux/err.h>
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/cpufreq.h>
 #include <linux/list.h>
 #include <linux/rculist.h>
 #include <linux/rcupdate.h>
 #include <linux/opp.h>

 /*
  * Internal data structure organization with the OPP layer library is as
  * follows:
  * dev_opp_list (root)
  *	|- device 1 (represents voltage domain 1)
  *	|	|- opp 1 (availability, freq, voltage)
  *	|	|- opp 2 ..
  *	...	...
  *	|	`- opp n ..
  *	|- device 2 (represents the next voltage domain)
  *	...
  *	`- device m (represents mth voltage domain)
  * device 1, 2.. are represented by dev_opp structure while each opp
  * is represented by the opp structure.
  */

 /**
  * struct opp - Generic OPP description structure
  * @node:	opp list node. The nodes are maintained throughout the lifetime
  *		of boot. It is expected only an optimal set of OPPs are
  *		added to the library by the SoC framework.
  *		RCU usage: opp list is traversed with RCU locks. node
  *		modification is possible realtime, hence the modifications
  *		are protected by the dev_opp_list_lock for integrity.
  *		IMPORTANT: the opp nodes should be maintained in increasing
  *		order.
  * @available:	true/false - marks if this OPP as available or not
  * @rate:	Frequency in hertz
  * @u_volt:	Nominal voltage in microvolts corresponding to this OPP
  * @dev_opp:	points back to the device_opp struct this opp belongs to
  *
  * This structure stores the OPP information for a given device.
  */
 struct opp {
 	struct list_head node;

 	bool available;
 	unsigned long rate;
 	unsigned long u_volt;

 	struct device_opp *dev_opp;
 };

 /**
  * struct device_opp - Device opp structure
  * @node:	list node - contains the devices with OPPs that
  *		have been registered. Nodes once added are not modified in this
  *		list.
  *		RCU usage: nodes are not modified in the list of device_opp,
  *		however addition is possible and is secured by dev_opp_list_lock
  * @dev:	device pointer
  * @head:	notifier head to notify the OPP availability changes.
  * @opp_list:	list of opps
  *
  * This is an internal data structure maintaining the link to opps attached to
  * a device. This structure is not meant to be shared to users as it is
  * meant for book keeping and private to OPP library
  */
 struct device_opp {
 	struct list_head node;

 	struct device *dev;
 	struct srcu_notifier_head head;
 	struct list_head opp_list;
 };

 /*
  * The root of the list of all devices. All device_opp structures branch off
  * from here, with each device_opp containing the list of opp it supports in
  * various states of availability.
  */
 static LIST_HEAD(dev_opp_list);
 /* Lock to allow exclusive modification to the device and opp lists */
 static DEFINE_MUTEX(dev_opp_list_lock);

 /**
  * find_device_opp() - find device_opp struct using device pointer
  * @dev:	device pointer used to lookup device OPPs
  *
  * Search list of device OPPs for one containing matching device. Does a RCU
  * reader operation to grab the pointer needed.
  *
  * Returns pointer to 'struct device_opp' if found, otherwise -ENODEV or
  * -EINVAL based on type of error.
  *
  * Locking: This function must be called under rcu_read_lock(). device_opp
  * is a RCU protected pointer. This means that device_opp is valid as long
  * as we are under RCU lock.
  */
 static struct device_opp *find_device_opp(struct device *dev)
 {
 	struct device_opp *tmp_dev_opp, *dev_opp = ERR_PTR(-ENODEV);

 	if (unlikely(IS_ERR_OR_NULL(dev))) {
 		pr_err("%s: Invalid parameters\n", __func__);
 		return ERR_PTR(-EINVAL);
 	}

 	list_for_each_entry_rcu(tmp_dev_opp, &dev_opp_list, node) {
 		if (tmp_dev_opp->dev == dev) {
 			dev_opp = tmp_dev_opp;
 			break;
 		}
 	}

 	return dev_opp;
 }

 /**
  * opp_get_voltage() - Gets the voltage corresponding to an available opp
  * @opp:	opp for which voltage has to be returned for
  *
  * Return voltage in micro volt corresponding to the opp, else
  * return 0
  *
  * Locking: This function must be called under rcu_read_lock(). opp is a rcu
  * protected pointer. This means that opp which could have been fetched by
  * opp_find_freq_{exact,ceil,floor} functions is valid as long as we are
  * under RCU lock. The pointer returned by the opp_find_freq family must be
  * used in the same section as the usage of this function with the pointer
  * prior to unlocking with rcu_read_unlock() to maintain the integrity of the
  * pointer.
  */
 unsigned long opp_get_voltage(struct opp *opp)
 {
 	struct opp *tmp_opp;
 	unsigned long v = 0;

 	tmp_opp = rcu_dereference(opp);
 	if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
 		pr_err("%s: Invalid parameters\n", __func__);
 	else
 		v = tmp_opp->u_volt;

 	return v;
 }

 /**
  * opp_get_freq() - Gets the frequency corresponding to an available opp
  * @opp:	opp for which frequency has to be returned for
  *
  * Return frequency in hertz corresponding to the opp, else
  * return 0
  *
  * Locking: This function must be called under rcu_read_lock(). opp is a rcu
  * protected pointer. This means that opp which could have been fetched by
  * opp_find_freq_{exact,ceil,floor} functions is valid as long as we are
  * under RCU lock. The pointer returned by the opp_find_freq family must be
  * used in the same section as the usage of this function with the pointer
  * prior to unlocking with rcu_read_unlock() to maintain the integrity of the
  * pointer.
  */
 unsigned long opp_get_freq(struct opp *opp)
 {
 	struct opp *tmp_opp;
 	unsigned long f = 0;

 	tmp_opp = rcu_dereference(opp);
 	if (unlikely(IS_ERR_OR_NULL(tmp_opp)) || !tmp_opp->available)
 		pr_err("%s: Invalid parameters\n", __func__);
 	else
 		f = tmp_opp->rate;

 	return f;
 }

 /**
  * opp_get_opp_count() - Get number of opps available in the opp list
  * @dev:	device for which we do this operation
  *
  * This function returns the number of available opps if there are any,
  * else returns 0 if none or the corresponding error value.
  *
  * Locking: This function must be called under rcu_read_lock(). This function
  * internally references two RCU protected structures: device_opp and opp which
  * are safe as long as we are under a common RCU locked section.
  */
 int opp_get_opp_count(struct device *dev)
 {
 	struct device_opp *dev_opp;
 	struct opp *temp_opp;
 	int count = 0;

 	dev_opp = find_device_opp(dev);
 	if (IS_ERR(dev_opp)) {
 		int r = PTR_ERR(dev_opp);
 		dev_err(dev, "%s: device OPP not found (%d)\n", __func__, r);
 		return r;
 	}

 	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
 		if (temp_opp->available)
 			count++;
 	}

 	return count;
 }

 /**
  * opp_find_freq_exact() - search for an exact frequency
  * @dev:		device for which we do this operation
  * @freq:		frequency to search for
  * @available:		true/false - match for available opp
  *
  * Searches for exact match in the opp list and returns pointer to the matching
  * opp if found, else returns ERR_PTR in case of error and should be handled
  * using IS_ERR.
  *
  * Note: available is a modifier for the search. if available=true, then the
  * match is for exact matching frequency and is available in the stored OPP
  * table. if false, the match is for exact frequency which is not available.
  *
  * This provides a mechanism to enable an opp which is not available currently
  * or the opposite as well.
  *
  * Locking: This function must be called under rcu_read_lock(). opp is a rcu
  * protected pointer. The reason for the same is that the opp pointer which is
  * returned will remain valid for use with opp_get_{voltage, freq} only while
  * under the locked area. The pointer returned must be used prior to unlocking
  * with rcu_read_unlock() to maintain the integrity of the pointer.
  */
 struct opp *opp_find_freq_exact(struct device *dev, unsigned long freq,
 				bool available)
 {
 	struct device_opp *dev_opp;
 	struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);

 	dev_opp = find_device_opp(dev);
 	if (IS_ERR(dev_opp)) {
 		int r = PTR_ERR(dev_opp);
 		dev_err(dev, "%s: device OPP not found (%d)\n", __func__, r);
 		return ERR_PTR(r);
 	}

 	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
 		if (temp_opp->available == available &&
 				temp_opp->rate == freq) {
 			opp = temp_opp;
 			break;
 		}
 	}

 	return opp;
 }

 /**
  * opp_find_freq_ceil() - Search for an rounded ceil freq
  * @dev:	device for which we do this operation
  * @freq:	Start frequency
  *
  * Search for the matching ceil *available* OPP from a starting freq
  * for a device.
  *
  * Returns matching *opp and refreshes *freq accordingly, else returns
  * ERR_PTR in case of error and should be handled using IS_ERR.
  *
  * Locking: This function must be called under rcu_read_lock(). opp is a rcu
  * protected pointer. The reason for the same is that the opp pointer which is
  * returned will remain valid for use with opp_get_{voltage, freq} only while
  * under the locked area. The pointer returned must be used prior to unlocking
  * with rcu_read_unlock() to maintain the integrity of the pointer.
  */
 struct opp *opp_find_freq_ceil(struct device *dev, unsigned long *freq)
 {
 	struct device_opp *dev_opp;
 	struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);

 	if (!dev || !freq) {
 		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
 		return ERR_PTR(-EINVAL);
 	}

 	dev_opp = find_device_opp(dev);
 	if (IS_ERR(dev_opp))
 		return opp;

 	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
 		if (temp_opp->available && temp_opp->rate >= *freq) {
 			opp = temp_opp;
 			*freq = opp->rate;
 			break;
 		}
 	}

 	return opp;
 }

 /**
  * opp_find_freq_floor() - Search for a rounded floor freq
  * @dev:	device for which we do this operation
  * @freq:	Start frequency
  *
  * Search for the matching floor *available* OPP from a starting freq
  * for a device.
  *
  * Returns matching *opp and refreshes *freq accordingly, else returns
  * ERR_PTR in case of error and should be handled using IS_ERR.
  *
  * Locking: This function must be called under rcu_read_lock(). opp is a rcu
  * protected pointer. The reason for the same is that the opp pointer which is
  * returned will remain valid for use with opp_get_{voltage, freq} only while
  * under the locked area. The pointer returned must be used prior to unlocking
  * with rcu_read_unlock() to maintain the integrity of the pointer.
  */
 struct opp *opp_find_freq_floor(struct device *dev, unsigned long *freq)
 {
 	struct device_opp *dev_opp;
 	struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);

 	if (!dev || !freq) {
 		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
 		return ERR_PTR(-EINVAL);
 	}

 	dev_opp = find_device_opp(dev);
 	if (IS_ERR(dev_opp))
 		return opp;

 	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
 		if (temp_opp->available) {
 			/* go to the next node, before choosing prev */
 			if (temp_opp->rate > *freq)
 				break;
 			else
 				opp = temp_opp;
 		}
 	}
 	if (!IS_ERR(opp))
 		*freq = opp->rate;

 	return opp;
 }

 /**
  * opp_add()  - Add an OPP table from a table definitions
  * @dev:	device for which we do this operation
  * @freq:	Frequency in Hz for this OPP
  * @u_volt:	Voltage in uVolts for this OPP
  *
  * This function adds an opp definition to the opp list and returns status.
  * The opp is made available by default and it can be controlled using
  * opp_enable/disable functions.
  *
  * Locking: The internal device_opp and opp structures are RCU protected.
  * Hence this function internally uses RCU updater strategy with mutex locks
  * to keep the integrity of the internal data structures. Callers should ensure
  * that this function is *NOT* called under RCU protection or in contexts where
  * mutex cannot be locked.
  */
 int opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
 {
 	struct device_opp *dev_opp = NULL;
 	struct opp *opp, *new_opp;
 	struct list_head *head;

 	/* allocate new OPP node */
 	new_opp = kzalloc(sizeof(struct opp), GFP_KERNEL);
 	if (!new_opp) {
 		dev_warn(dev, "%s: Unable to create new OPP node\n", __func__);
 		return -ENOMEM;
 	}

 	/* Hold our list modification lock here */
 	mutex_lock(&dev_opp_list_lock);

 	/* Check for existing list for 'dev' */
 	dev_opp = find_device_opp(dev);
 	if (IS_ERR(dev_opp)) {
 		/*
 		 * Allocate a new device OPP table. In the infrequent case
 		 * where a new device is needed to be added, we pay this
 		 * penalty.
 		 */
 		dev_opp = kzalloc(sizeof(struct device_opp), GFP_KERNEL);
 		if (!dev_opp) {
 			mutex_unlock(&dev_opp_list_lock);
 			kfree(new_opp);
 			dev_warn(dev,
 				"%s: Unable to create device OPP structure\n",
 				__func__);
 			return -ENOMEM;
 		}

 		dev_opp->dev = dev;
 		srcu_init_notifier_head(&dev_opp->head);
 		INIT_LIST_HEAD(&dev_opp->opp_list);

 		/* Secure the device list modification */
 		list_add_rcu(&dev_opp->node, &dev_opp_list);
 	}

 	/* populate the opp table */
 	new_opp->dev_opp = dev_opp;
 	new_opp->rate = freq;
 	new_opp->u_volt = u_volt;
 	new_opp->available = true;

 	/* Insert new OPP in order of increasing frequency */
 	head = &dev_opp->opp_list;
 	list_for_each_entry_rcu(opp, &dev_opp->opp_list, node) {
 		if (new_opp->rate < opp->rate)
 			break;
 		else
 			head = &opp->node;
 	}

 	list_add_rcu(&new_opp->node, head);
 	mutex_unlock(&dev_opp_list_lock);

 	/*
 	 * Notify the changes in the availability of the operable
 	 * frequency/voltage list.
 	 */
 	srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ADD, new_opp);
 	return 0;
 }

 /**
  * opp_set_availability() - helper to set the availability of an opp
  * @dev:		device for which we do this operation
  * @freq:		OPP frequency to modify availability
  * @availability_req:	availability status requested for this opp
  *
  * Set the availability of an OPP with an RCU operation, opp_{enable,disable}
  * share a common logic which is isolated here.
  *
  * Returns -EINVAL for bad pointers, -ENOMEM if no memory available for the
  * copy operation, returns 0 if no modifcation was done OR modification was
  * successful.
  *
  * Locking: The internal device_opp and opp structures are RCU protected.
  * Hence this function internally uses RCU updater strategy with mutex locks to
  * keep the integrity of the internal data structures. Callers should ensure
  * that this function is *NOT* called under RCU protection or in contexts where
  * mutex locking or synchronize_rcu() blocking calls cannot be used.
  */
 static int opp_set_availability(struct device *dev, unsigned long freq,
 		bool availability_req)
 {
 	struct device_opp *tmp_dev_opp, *dev_opp = ERR_PTR(-ENODEV);
 	struct opp *new_opp, *tmp_opp, *opp = ERR_PTR(-ENODEV);
 	int r = 0;

 	if (!dev)
 		return -EINVAL;

 	/* keep the node allocated */
 	new_opp = kmalloc(sizeof(struct opp), GFP_KERNEL);
 	if (!new_opp) {
 		pr_err("%s: Unable to create OPP\n", __func__);
 		return -ENOMEM;
 	}

 	mutex_lock(&dev_opp_list_lock);

 	/* Find the device_opp */
 	list_for_each_entry(tmp_dev_opp, &dev_opp_list, node) {
 		if (dev == tmp_dev_opp->dev) {
 			dev_opp = tmp_dev_opp;
 			break;
 		}
 	}
 	if (IS_ERR(dev_opp)) {
 		r = PTR_ERR(dev_opp);
 		pr_err("%s: Device OPP not found (%d)\n", __func__, r);
 		goto unlock;
 	}

 	/* Do we have the frequency? */
 	list_for_each_entry(tmp_opp, &dev_opp->opp_list, node) {
 		if (tmp_opp->rate == freq) {
 			opp = tmp_opp;
 			break;
 		}
 	}
 	if (IS_ERR(opp)) {
 		r = PTR_ERR(opp);
 		goto unlock;
 	}

 	/* Is update really needed? */
 	if (opp->available == availability_req)
 		goto unlock;
 	/* copy the old data over */
 	*new_opp = *opp;

 	/* plug in new node */
 	new_opp->available = availability_req;

 	list_replace_rcu(&opp->node, &new_opp->node);
 	mutex_unlock(&dev_opp_list_lock);
 	synchronize_rcu();

 	/* Notify the change of the OPP availability */
 	if (availability_req)
 		srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ENABLE,
 					 new_opp);
 	else
 		srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_DISABLE,
 					 new_opp);

 	/* clean up old opp */
 	new_opp = opp;
 	goto out;

 unlock:
 	mutex_unlock(&dev_opp_list_lock);
 out:
 	kfree(new_opp);
 	return r;
 }

 /**
  * opp_enable() - Enable a specific OPP
  * @dev:	device for which we do this operation
  * @freq:	OPP frequency to enable
  *
  * Enables a provided opp. If the operation is valid, this returns 0, else the
  * corresponding error value. It is meant to be used for users an OPP available
  * after being temporarily made unavailable with opp_disable.
  *
  * Locking: The internal device_opp and opp structures are RCU protected.
  * Hence this function indirectly uses RCU and mutex locks to keep the
  * integrity of the internal data structures. Callers should ensure that
  * this function is *NOT* called under RCU protection or in contexts where
  * mutex locking or synchronize_rcu() blocking calls cannot be used.
  */
 int opp_enable(struct device *dev, unsigned long freq)
 {
 	return opp_set_availability(dev, freq, true);
 }

 /**
  * opp_disable() - Disable a specific OPP
  * @dev:	device for which we do this operation
  * @freq:	OPP frequency to disable
  *
  * Disables a provided opp. If the operation is valid, this returns
  * 0, else the corresponding error value. It is meant to be a temporary
  * control by users to make this OPP not available until the circumstances are
  * right to make it available again (with a call to opp_enable).
  *
  * Locking: The internal device_opp and opp structures are RCU protected.
  * Hence this function indirectly uses RCU and mutex locks to keep the
  * integrity of the internal data structures. Callers should ensure that
  * this function is *NOT* called under RCU protection or in contexts where
  * mutex locking or synchronize_rcu() blocking calls cannot be used.
  */
 int opp_disable(struct device *dev, unsigned long freq)
 {
 	return opp_set_availability(dev, freq, false);
 }

 #ifdef CONFIG_CPU_FREQ
 /**
  * opp_init_cpufreq_table() - create a cpufreq table for a device
  * @dev:	device for which we do this operation
  * @table:	Cpufreq table returned back to caller
  *
  * Generate a cpufreq table for a provided device- this assumes that the
  * opp list is already initialized and ready for usage.
  *
  * This function allocates required memory for the cpufreq table. It is
  * expected that the caller does the required maintenance such as freeing
  * the table as required.
  *
  * Returns -EINVAL for bad pointers, -ENODEV if the device is not found, -ENOMEM
  * if no memory available for the operation (table is not populated), returns 0
  * if successful and table is populated.
  *
  * WARNING: It is  important for the callers to ensure refreshing their copy of
  * the table if any of the mentioned functions have been invoked in the interim.
  *
  * Locking: The internal device_opp and opp structures are RCU protected.
  * To simplify the logic, we pretend we are updater and hold relevant mutex here
  * Callers should ensure that this function is *NOT* called under RCU protection
  * or in contexts where mutex locking cannot be used.
  */
 int opp_init_cpufreq_table(struct device *dev,
 			    struct cpufreq_frequency_table **table)
 {
 	struct device_opp *dev_opp;
 	struct opp *opp;
 	struct cpufreq_frequency_table *freq_table;
 	int i = 0;

 	if (!dev)
 		return -EINVAL;

 	/* Pretend as if I am an updater */
 	mutex_lock(&dev_opp_list_lock);

 	dev_opp = find_device_opp(dev);
 	if (IS_ERR(dev_opp)) {
 		int r = PTR_ERR(dev_opp);
 		mutex_unlock(&dev_opp_list_lock);
 		dev_err(dev, "%s: Device OPP not found (%d)\n", __func__, r);
 		return r;
 	}

 	freq_table = kzalloc(sizeof(struct cpufreq_frequency_table) *
 			     (opp_get_opp_count(dev) + 1), GFP_KERNEL);
 	if (!freq_table) {
 		mutex_unlock(&dev_opp_list_lock);
 		dev_warn(dev, "%s: Unable to allocate frequency table\n",
 			__func__);
 		return -ENOMEM;
 	}

 	list_for_each_entry(opp, &dev_opp->opp_list, node) {
 		if (opp->available) {
 			freq_table[i].index = i;
 			freq_table[i].frequency = opp->rate / 1000;
 			i++;
 		}
 	}
 	mutex_unlock(&dev_opp_list_lock);

 	freq_table[i].index = i;
 	freq_table[i].frequency = CPUFREQ_TABLE_END;

 	*table = &freq_table[0];

 	return 0;
 }

 /**
  * opp_free_cpufreq_table() - free the cpufreq table
  * @dev:	device for which we do this operation
  * @table:	table to free
  *
  * Free up the table allocated by opp_init_cpufreq_table
  */
 void opp_free_cpufreq_table(struct device *dev,
 				struct cpufreq_frequency_table **table)
 {
 	if (!table)
 		return;

 	kfree(*table);
 	*table = NULL;
 }
 #endif		/* CONFIG_CPU_FREQ */

 /**
  * opp_get_notifier() - find notifier_head of the device with opp
  * @dev:	device pointer used to lookup device OPPs.
  */
 struct srcu_notifier_head *opp_get_notifier(struct device *dev)
 {
 	struct device_opp *dev_opp = find_device_opp(dev);

 	if (IS_ERR(dev_opp))
 		return ERR_CAST(dev_opp); /* matching type */

 	return &dev_opp->head;
 }
	/*
	* Generic OPP Interface
	*
	* Copyright (C) 2009-2010 Texas Instruments Incorporated.
	* Nishanth Menon
	* Romit Dasgupta
	* Kevin Hilman
	*
	* 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/errno.h>
	#include <linux/err.h>
	#include <linux/init.h>
	#include <linux/slab.h>
	#include <linux/cpufreq.h>
	#include <linux/list.h>
	#include <linux/rculist.h>
	#include <linux/rcupdate.h>
	#include <linux/opp.h>

	/*
	* Internal data structure organization with the OPP layer library is as
	* follows:
	* dev_opp_list (root)
	* \|- device 1 (represents voltage domain 1)
	* \| \|- opp 1 (availability, freq, voltage)
	* \| \|- opp 2 ..
	* ... ...
	* \| `- opp n ..
	* \|- device 2 (represents the next voltage domain)
	* ...
	* `- device m (represents mth voltage domain)
	* device 1, 2.. are represented by dev_opp structure while each opp
	* is represented by the opp structure.
	*/

	/**
	* struct opp - Generic OPP description structure
	* @node: opp list node. The nodes are maintained throughout the lifetime
	* of boot. It is expected only an optimal set of OPPs are
	* added to the library by the SoC framework.
	* RCU usage: opp list is traversed with RCU locks. node
	* modification is possible realtime, hence the modifications
	* are protected by the dev_opp_list_lock for integrity.
	* IMPORTANT: the opp nodes should be maintained in increasing
	* order.
	* @available: true/false - marks if this OPP as available or not
	* @rate: Frequency in hertz
	* @u_volt: Nominal voltage in microvolts corresponding to this OPP
	* @dev_opp: points back to the device_opp struct this opp belongs to
	*
	* This structure stores the OPP information for a given device.
	*/
	struct opp {
	struct list_head node;

	bool available;
	unsigned long rate;
	unsigned long u_volt;

	struct device_opp *dev_opp;
	};

	/**
	* struct device_opp - Device opp structure
	* @node: list node - contains the devices with OPPs that
	* have been registered. Nodes once added are not modified in this
	* list.
	* RCU usage: nodes are not modified in the list of device_opp,
	* however addition is possible and is secured by dev_opp_list_lock
	* @dev: device pointer
	* @head: notifier head to notify the OPP availability changes.
	* @opp_list: list of opps
	*
	* This is an internal data structure maintaining the link to opps attached to
	* a device. This structure is not meant to be shared to users as it is
	* meant for book keeping and private to OPP library
	*/
	struct device_opp {
	struct list_head node;

	struct device *dev;
	struct srcu_notifier_head head;
	struct list_head opp_list;
	};

	/*
	* The root of the list of all devices. All device_opp structures branch off
	* from here, with each device_opp containing the list of opp it supports in
	* various states of availability.
	*/
	static LIST_HEAD(dev_opp_list);
	/* Lock to allow exclusive modification to the device and opp lists */
	static DEFINE_MUTEX(dev_opp_list_lock);

	/**
	* find_device_opp() - find device_opp struct using device pointer
	* @dev: device pointer used to lookup device OPPs
	*
	* Search list of device OPPs for one containing matching device. Does a RCU
	* reader operation to grab the pointer needed.
	*
	* Returns pointer to 'struct device_opp' if found, otherwise -ENODEV or
	* -EINVAL based on type of error.
	*
	* Locking: This function must be called under rcu_read_lock(). device_opp
	* is a RCU protected pointer. This means that device_opp is valid as long
	* as we are under RCU lock.
	*/
	static struct device_opp find_device_opp(struct device dev)
	{
	struct device_opp tmp_dev_opp, dev_opp = ERR_PTR(-ENODEV);

	if (unlikely(IS_ERR_OR_NULL(dev))) {
	pr_err("%s: Invalid parameters\n", __func__);
	return ERR_PTR(-EINVAL);
	}

	list_for_each_entry_rcu(tmp_dev_opp, &dev_opp_list, node) {
	if (tmp_dev_opp->dev == dev) {
	dev_opp = tmp_dev_opp;
	break;
	}
	}

	return dev_opp;
	}

	/**
	* opp_get_voltage() - Gets the voltage corresponding to an available opp
	* @opp: opp for which voltage has to be returned for
	*
	* Return voltage in micro volt corresponding to the opp, else
	* return 0
	*
	* Locking: This function must be called under rcu_read_lock(). opp is a rcu
	* protected pointer. This means that opp which could have been fetched by
	* opp_find_freq_{exact,ceil,floor} functions is valid as long as we are
	* under RCU lock. The pointer returned by the opp_find_freq family must be
	* used in the same section as the usage of this function with the pointer
	* prior to unlocking with rcu_read_unlock() to maintain the integrity of the
	* pointer.
	*/
	unsigned long opp_get_voltage(struct opp *opp)
	{
	struct opp *tmp_opp;
	unsigned long v = 0;

	tmp_opp = rcu_dereference(opp);
	if (unlikely(IS_ERR_OR_NULL(tmp_opp)) \|\| !tmp_opp->available)
	pr_err("%s: Invalid parameters\n", __func__);
	else
	v = tmp_opp->u_volt;

	return v;
	}

	/**
	* opp_get_freq() - Gets the frequency corresponding to an available opp
	* @opp: opp for which frequency has to be returned for
	*
	* Return frequency in hertz corresponding to the opp, else
	* return 0
	*
	* Locking: This function must be called under rcu_read_lock(). opp is a rcu
	* protected pointer. This means that opp which could have been fetched by
	* opp_find_freq_{exact,ceil,floor} functions is valid as long as we are
	* under RCU lock. The pointer returned by the opp_find_freq family must be
	* used in the same section as the usage of this function with the pointer
	* prior to unlocking with rcu_read_unlock() to maintain the integrity of the
	* pointer.
	*/
	unsigned long opp_get_freq(struct opp *opp)
	{
	struct opp *tmp_opp;
	unsigned long f = 0;

	tmp_opp = rcu_dereference(opp);
	if (unlikely(IS_ERR_OR_NULL(tmp_opp)) \|\| !tmp_opp->available)
	pr_err("%s: Invalid parameters\n", __func__);
	else
	f = tmp_opp->rate;

	return f;
	}

	/**
	* opp_get_opp_count() - Get number of opps available in the opp list
	* @dev: device for which we do this operation
	*
	* This function returns the number of available opps if there are any,
	* else returns 0 if none or the corresponding error value.
	*
	* Locking: This function must be called under rcu_read_lock(). This function
	* internally references two RCU protected structures: device_opp and opp which
	* are safe as long as we are under a common RCU locked section.
	*/
	int opp_get_opp_count(struct device *dev)
	{
	struct device_opp *dev_opp;
	struct opp *temp_opp;
	int count = 0;

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp)) {
	int r = PTR_ERR(dev_opp);
	dev_err(dev, "%s: device OPP not found (%d)\n", __func__, r);
	return r;
	}

	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
	if (temp_opp->available)
	count++;
	}

	return count;
	}

	/**
	* opp_find_freq_exact() - search for an exact frequency
	* @dev: device for which we do this operation
	* @freq: frequency to search for
	* @available: true/false - match for available opp
	*
	* Searches for exact match in the opp list and returns pointer to the matching
	* opp if found, else returns ERR_PTR in case of error and should be handled
	* using IS_ERR.
	*
	* Note: available is a modifier for the search. if available=true, then the
	* match is for exact matching frequency and is available in the stored OPP
	* table. if false, the match is for exact frequency which is not available.
	*
	* This provides a mechanism to enable an opp which is not available currently
	* or the opposite as well.
	*
	* Locking: This function must be called under rcu_read_lock(). opp is a rcu
	* protected pointer. The reason for the same is that the opp pointer which is
	* returned will remain valid for use with opp_get_{voltage, freq} only while
	* under the locked area. The pointer returned must be used prior to unlocking
	* with rcu_read_unlock() to maintain the integrity of the pointer.
	*/
	struct opp opp_find_freq_exact(struct device dev, unsigned long freq,
	bool available)
	{
	struct device_opp *dev_opp;
	struct opp temp_opp, opp = ERR_PTR(-ENODEV);

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp)) {
	int r = PTR_ERR(dev_opp);
	dev_err(dev, "%s: device OPP not found (%d)\n", __func__, r);
	return ERR_PTR(r);
	}

	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
	if (temp_opp->available == available &&
	temp_opp->rate == freq) {
	opp = temp_opp;
	break;
	}
	}

	return opp;
	}

	/**
	* opp_find_freq_ceil() - Search for an rounded ceil freq
	* @dev: device for which we do this operation
	* @freq: Start frequency
	*
	* Search for the matching ceil available OPP from a starting freq
	* for a device.
	*
	* Returns matching opp and refreshes freq accordingly, else returns
	* ERR_PTR in case of error and should be handled using IS_ERR.
	*
	* Locking: This function must be called under rcu_read_lock(). opp is a rcu
	* protected pointer. The reason for the same is that the opp pointer which is
	* returned will remain valid for use with opp_get_{voltage, freq} only while
	* under the locked area. The pointer returned must be used prior to unlocking
	* with rcu_read_unlock() to maintain the integrity of the pointer.
	*/
	struct opp opp_find_freq_ceil(struct device dev, unsigned long *freq)
	{
	struct device_opp *dev_opp;
	struct opp temp_opp, opp = ERR_PTR(-ENODEV);

	if (!dev \|\| !freq) {
	dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
	return ERR_PTR(-EINVAL);
	}

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp))
	return opp;

	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
	if (temp_opp->available && temp_opp->rate >= *freq) {
	opp = temp_opp;
	*freq = opp->rate;
	break;
	}
	}

	return opp;
	}

	/**
	* opp_find_freq_floor() - Search for a rounded floor freq
	* @dev: device for which we do this operation
	* @freq: Start frequency
	*
	* Search for the matching floor available OPP from a starting freq
	* for a device.
	*
	* Returns matching opp and refreshes freq accordingly, else returns
	* ERR_PTR in case of error and should be handled using IS_ERR.
	*
	* Locking: This function must be called under rcu_read_lock(). opp is a rcu
	* protected pointer. The reason for the same is that the opp pointer which is
	* returned will remain valid for use with opp_get_{voltage, freq} only while
	* under the locked area. The pointer returned must be used prior to unlocking
	* with rcu_read_unlock() to maintain the integrity of the pointer.
	*/
	struct opp opp_find_freq_floor(struct device dev, unsigned long *freq)
	{
	struct device_opp *dev_opp;
	struct opp temp_opp, opp = ERR_PTR(-ENODEV);

	if (!dev \|\| !freq) {
	dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
	return ERR_PTR(-EINVAL);
	}

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp))
	return opp;

	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
	if (temp_opp->available) {
	/* go to the next node, before choosing prev */
	if (temp_opp->rate > *freq)
	break;
	else
	opp = temp_opp;
	}
	}
	if (!IS_ERR(opp))
	*freq = opp->rate;

	return opp;
	}

	/**
	* opp_add() - Add an OPP table from a table definitions
	* @dev: device for which we do this operation
	* @freq: Frequency in Hz for this OPP
	* @u_volt: Voltage in uVolts for this OPP
	*
	* This function adds an opp definition to the opp list and returns status.
	* The opp is made available by default and it can be controlled using
	* opp_enable/disable functions.
	*
	* Locking: The internal device_opp and opp structures are RCU protected.
	* Hence this function internally uses RCU updater strategy with mutex locks
	* to keep the integrity of the internal data structures. Callers should ensure
	* that this function is NOT called under RCU protection or in contexts where
	* mutex cannot be locked.
	*/
	int opp_add(struct device *dev, unsigned long freq, unsigned long u_volt)
	{
	struct device_opp *dev_opp = NULL;
	struct opp opp, new_opp;
	struct list_head *head;

	/* allocate new OPP node */
	new_opp = kzalloc(sizeof(struct opp), GFP_KERNEL);
	if (!new_opp) {
	dev_warn(dev, "%s: Unable to create new OPP node\n", __func__);
	return -ENOMEM;
	}

	/* Hold our list modification lock here */
	mutex_lock(&dev_opp_list_lock);

	/* Check for existing list for 'dev' */
	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp)) {
	/*
	* Allocate a new device OPP table. In the infrequent case
	* where a new device is needed to be added, we pay this
	* penalty.
	*/
	dev_opp = kzalloc(sizeof(struct device_opp), GFP_KERNEL);
	if (!dev_opp) {
	mutex_unlock(&dev_opp_list_lock);
	kfree(new_opp);
	dev_warn(dev,
	"%s: Unable to create device OPP structure\n",
	__func__);
	return -ENOMEM;
	}

	dev_opp->dev = dev;
	srcu_init_notifier_head(&dev_opp->head);
	INIT_LIST_HEAD(&dev_opp->opp_list);

	/* Secure the device list modification */
	list_add_rcu(&dev_opp->node, &dev_opp_list);
	}

	/* populate the opp table */
	new_opp->dev_opp = dev_opp;
	new_opp->rate = freq;
	new_opp->u_volt = u_volt;
	new_opp->available = true;

	/* Insert new OPP in order of increasing frequency */
	head = &dev_opp->opp_list;
	list_for_each_entry_rcu(opp, &dev_opp->opp_list, node) {
	if (new_opp->rate < opp->rate)
	break;
	else
	head = &opp->node;
	}

	list_add_rcu(&new_opp->node, head);
	mutex_unlock(&dev_opp_list_lock);

	/*
	* Notify the changes in the availability of the operable
	* frequency/voltage list.
	*/
	srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ADD, new_opp);
	return 0;
	}

	/**
	* opp_set_availability() - helper to set the availability of an opp
	* @dev: device for which we do this operation
	* @freq: OPP frequency to modify availability
	* @availability_req: availability status requested for this opp
	*
	* Set the availability of an OPP with an RCU operation, opp_{enable,disable}
	* share a common logic which is isolated here.
	*
	* Returns -EINVAL for bad pointers, -ENOMEM if no memory available for the
	* copy operation, returns 0 if no modifcation was done OR modification was
	* successful.
	*
	* Locking: The internal device_opp and opp structures are RCU protected.
	* Hence this function internally uses RCU updater strategy with mutex locks to
	* keep the integrity of the internal data structures. Callers should ensure
	* that this function is NOT called under RCU protection or in contexts where
	* mutex locking or synchronize_rcu() blocking calls cannot be used.
	*/
	static int opp_set_availability(struct device *dev, unsigned long freq,
	bool availability_req)
	{
	struct device_opp tmp_dev_opp, dev_opp = ERR_PTR(-ENODEV);
	struct opp new_opp, tmp_opp, *opp = ERR_PTR(-ENODEV);
	int r = 0;

	if (!dev)
	return -EINVAL;

	/* keep the node allocated */
	new_opp = kmalloc(sizeof(struct opp), GFP_KERNEL);
	if (!new_opp) {
	pr_err("%s: Unable to create OPP\n", __func__);
	return -ENOMEM;
	}

	mutex_lock(&dev_opp_list_lock);

	/* Find the device_opp */
	list_for_each_entry(tmp_dev_opp, &dev_opp_list, node) {
	if (dev == tmp_dev_opp->dev) {
	dev_opp = tmp_dev_opp;
	break;
	}
	}
	if (IS_ERR(dev_opp)) {
	r = PTR_ERR(dev_opp);
	pr_err("%s: Device OPP not found (%d)\n", __func__, r);
	goto unlock;
	}

	/* Do we have the frequency? */
	list_for_each_entry(tmp_opp, &dev_opp->opp_list, node) {
	if (tmp_opp->rate == freq) {
	opp = tmp_opp;
	break;
	}
	}
	if (IS_ERR(opp)) {
	r = PTR_ERR(opp);
	goto unlock;
	}

	/* Is update really needed? */
	if (opp->available == availability_req)
	goto unlock;
	/* copy the old data over */
	new_opp = opp;

	/* plug in new node */
	new_opp->available = availability_req;

	list_replace_rcu(&opp->node, &new_opp->node);
	mutex_unlock(&dev_opp_list_lock);
	synchronize_rcu();

	/* Notify the change of the OPP availability */
	if (availability_req)
	srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ENABLE,
	new_opp);
	else
	srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_DISABLE,
	new_opp);

	/* clean up old opp */
	new_opp = opp;
	goto out;

	unlock:
	mutex_unlock(&dev_opp_list_lock);
	out:
	kfree(new_opp);
	return r;
	}

	/**
	* opp_enable() - Enable a specific OPP
	* @dev: device for which we do this operation
	* @freq: OPP frequency to enable
	*
	* Enables a provided opp. If the operation is valid, this returns 0, else the
	* corresponding error value. It is meant to be used for users an OPP available
	* after being temporarily made unavailable with opp_disable.
	*
	* Locking: The internal device_opp and opp structures are RCU protected.
	* Hence this function indirectly uses RCU and mutex locks to keep the
	* integrity of the internal data structures. Callers should ensure that
	* this function is NOT called under RCU protection or in contexts where
	* mutex locking or synchronize_rcu() blocking calls cannot be used.
	*/
	int opp_enable(struct device *dev, unsigned long freq)
	{
	return opp_set_availability(dev, freq, true);
	}

	/**
	* opp_disable() - Disable a specific OPP
	* @dev: device for which we do this operation
	* @freq: OPP frequency to disable
	*
	* Disables a provided opp. If the operation is valid, this returns
	* 0, else the corresponding error value. It is meant to be a temporary
	* control by users to make this OPP not available until the circumstances are
	* right to make it available again (with a call to opp_enable).
	*
	* Locking: The internal device_opp and opp structures are RCU protected.
	* Hence this function indirectly uses RCU and mutex locks to keep the
	* integrity of the internal data structures. Callers should ensure that
	* this function is NOT called under RCU protection or in contexts where
	* mutex locking or synchronize_rcu() blocking calls cannot be used.
	*/
	int opp_disable(struct device *dev, unsigned long freq)
	{
	return opp_set_availability(dev, freq, false);
	}

	#ifdef CONFIG_CPU_FREQ
	/**
	* opp_init_cpufreq_table() - create a cpufreq table for a device
	* @dev: device for which we do this operation
	* @table: Cpufreq table returned back to caller
	*
	* Generate a cpufreq table for a provided device- this assumes that the
	* opp list is already initialized and ready for usage.
	*
	* This function allocates required memory for the cpufreq table. It is
	* expected that the caller does the required maintenance such as freeing
	* the table as required.
	*
	* Returns -EINVAL for bad pointers, -ENODEV if the device is not found, -ENOMEM
	* if no memory available for the operation (table is not populated), returns 0
	* if successful and table is populated.
	*
	* WARNING: It is important for the callers to ensure refreshing their copy of
	* the table if any of the mentioned functions have been invoked in the interim.
	*
	* Locking: The internal device_opp and opp structures are RCU protected.
	* To simplify the logic, we pretend we are updater and hold relevant mutex here
	* Callers should ensure that this function is NOT called under RCU protection
	* or in contexts where mutex locking cannot be used.
	*/
	int opp_init_cpufreq_table(struct device *dev,
	struct cpufreq_frequency_table **table)
	{
	struct device_opp *dev_opp;
	struct opp *opp;
	struct cpufreq_frequency_table *freq_table;
	int i = 0;

	if (!dev)
	return -EINVAL;

	/* Pretend as if I am an updater */
	mutex_lock(&dev_opp_list_lock);

	dev_opp = find_device_opp(dev);
	if (IS_ERR(dev_opp)) {
	int r = PTR_ERR(dev_opp);
	mutex_unlock(&dev_opp_list_lock);
	dev_err(dev, "%s: Device OPP not found (%d)\n", __func__, r);
	return r;
	}

	freq_table = kzalloc(sizeof(struct cpufreq_frequency_table) *
	(opp_get_opp_count(dev) + 1), GFP_KERNEL);
	if (!freq_table) {
	mutex_unlock(&dev_opp_list_lock);
	dev_warn(dev, "%s: Unable to allocate frequency table\n",
	__func__);
	return -ENOMEM;
	}

	list_for_each_entry(opp, &dev_opp->opp_list, node) {
	if (opp->available) {
	freq_table[i].index = i;
	freq_table[i].frequency = opp->rate / 1000;
	i++;
	}
	}
	mutex_unlock(&dev_opp_list_lock);

	freq_table[i].index = i;
	freq_table[i].frequency = CPUFREQ_TABLE_END;

	*table = &freq_table[0];

	return 0;
	}

	/**
	* opp_free_cpufreq_table() - free the cpufreq table
	* @dev: device for which we do this operation
	* @table: table to free
	*
	* Free up the table allocated by opp_init_cpufreq_table
	*/
	void opp_free_cpufreq_table(struct device *dev,
	struct cpufreq_frequency_table **table)
	{
	if (!table)
	return;

	kfree(*table);
	*table = NULL;
	}
	#endif /* CONFIG_CPU_FREQ */

	/**
	* opp_get_notifier() - find notifier_head of the device with opp
	* @dev: device pointer used to lookup device OPPs.
	*/
	struct srcu_notifier_head opp_get_notifier(struct device dev)
	{
	struct device_opp *dev_opp = find_device_opp(dev);

	if (IS_ERR(dev_opp))
	return ERR_CAST(dev_opp); /* matching type */

	return &dev_opp->head;
	}