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governor.c

/*
 * governor.c - governor support
 *
 * (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
 *               Shaohua Li <shaohua.li@intel.com>
 *               Adam Belay <abelay@novell.com>
 *
 * This code is licenced under the GPL.
 */

#include <linux/mutex.h>
#include <linux/module.h>
#include <linux/cpuidle.h>

#include "cpuidle.h"

LIST_HEAD(cpuidle_governors);
struct cpuidle_governor *cpuidle_curr_governor;

/**
 * __cpuidle_find_governor - finds a governor of the specified name
 * @str: the name
 *
 * Must be called with cpuidle_lock aquired.
 */
static struct cpuidle_governor * __cpuidle_find_governor(const char *str)
{
      struct cpuidle_governor *gov;

      list_for_each_entry(gov, &cpuidle_governors, governor_list)
            if (!strnicmp(str, gov->name, CPUIDLE_NAME_LEN))
                  return gov;

      return NULL;
}

/**
 * cpuidle_switch_governor - changes the governor
 * @gov: the new target governor
 *
 * NOTE: "gov" can be NULL to specify disabled
 * Must be called with cpuidle_lock aquired.
 */
int cpuidle_switch_governor(struct cpuidle_governor *gov)
{
      struct cpuidle_device *dev;

      if (gov == cpuidle_curr_governor)
            return 0;

      cpuidle_uninstall_idle_handler();

      if (cpuidle_curr_governor) {
            list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
                  cpuidle_disable_device(dev);
            module_put(cpuidle_curr_governor->owner);
      }

      cpuidle_curr_governor = gov;

      if (gov) {
            if (!try_module_get(cpuidle_curr_governor->owner))
                  return -EINVAL;
            list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
                  cpuidle_enable_device(dev);
            cpuidle_install_idle_handler();
            printk(KERN_INFO "cpuidle: using governor %s\n", gov->name);
      }

      return 0;
}

/**
 * cpuidle_register_governor - registers a governor
 * @gov: the governor
 */
int cpuidle_register_governor(struct cpuidle_governor *gov)
{
      int ret = -EEXIST;

      if (!gov || !gov->select)
            return -EINVAL;

      mutex_lock(&cpuidle_lock);
      if (__cpuidle_find_governor(gov->name) == NULL) {
            ret = 0;
            list_add_tail(&gov->governor_list, &cpuidle_governors);
            if (!cpuidle_curr_governor ||
                cpuidle_curr_governor->rating < gov->rating)
                  cpuidle_switch_governor(gov);
      }
      mutex_unlock(&cpuidle_lock);

      return ret;
}

/**
 * cpuidle_replace_governor - find a replacement governor
 * @exclude_rating: the rating that will be skipped while looking for
 * new governor.
 */
static struct cpuidle_governor *cpuidle_replace_governor(int exclude_rating)
{
      struct cpuidle_governor *gov;
      struct cpuidle_governor *ret_gov = NULL;
      unsigned int max_rating = 0;

      list_for_each_entry(gov, &cpuidle_governors, governor_list) {
            if (gov->rating == exclude_rating)
                  continue;
            if (gov->rating > max_rating) {
                  max_rating = gov->rating;
                  ret_gov = gov;
            }
      }

      return ret_gov;
}

/**
 * cpuidle_unregister_governor - unregisters a governor
 * @gov: the governor
 */
void cpuidle_unregister_governor(struct cpuidle_governor *gov)
{
      if (!gov)
            return;

      mutex_lock(&cpuidle_lock);
      if (gov == cpuidle_curr_governor) {
            struct cpuidle_governor *new_gov;
            new_gov = cpuidle_replace_governor(gov->rating);
            cpuidle_switch_governor(new_gov);
      }
      list_del(&gov->governor_list);
      mutex_unlock(&cpuidle_lock);
}


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