/*
 * 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/device.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;

        /* keep the node allocated */
        new_opp = kmalloc(sizeof(struct opp), GFP_KERNEL);
        if (!new_opp) {
                dev_warn(dev, "%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);
                dev_warn(dev, "%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;

        /* 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;
}