/*
 *  linux/drivers/cpufreq/cpufreq_dynamic.c
 *
 * 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.
 *
 * *** Experimental! ***
 *
 * TODO: 
 *       - Handle more than CPU 0.
 *       - Put in a better stepping mechanism.
 *       - Step downwards slower than stepping upwards. (I think this would
 *          work more efficiently than as it is now.)
 *       - Documenting in Documentation/cpufreq
 *       - Documentation that is NOT crappy in this file.
 *       - Proper debug printing.
 *
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/cpufreq.h>
#include <linux/init.h>
#include <linux/timer.h>
#include <linux/times.h>
#include <asm/timex.h>

#include <linux/kernel_stat.h>

/* How many times/second to poll */
#define POLL_FREQUENCY 10

/* Wait HZ/POLL_FREQUENCY jiffies in between polling. */
#define SLEEP_JIFFIES HZ/POLL_FREQUENCY

/* Minimum and maximum idle thresholds, in percent */
#define MIN_IDLE 20
#define MAX_IDLE 80

/* Internal definitions for temporary frequency table. Ug-ly. */
#define FREQ_MAX 0
#define FREQ_MIN -1

/** Should be a list, from FREQ_MAX to FREQ_MIN of CPU speeds in KHz. 
 * e.g. { FREQ_MAX,1500000,1000000,500000,FREQ_MIN }
 */
static const int32_t cpufreq_dynamic_freqs[] = {
	FREQ_MAX, \
/**
 * FIXME: Find better way to find frequencies to switch to.
 *
 * These values work on my non-mobile P4 2 GHz, but 
 * would probably just waste CPU cycles on most other
 * CPUs. (I.e. these values would probably be invalid.)
 *
 *	1500000, \
 *	1000000, \
 *	500000, \
 *	250000, \ */
	FREQ_MIN \
};

/* Kernel Timer for this module. (Timers are awesome!) */
struct timer_list cpufreq_dynamic_timer;
unsigned long prev_idle; // CPU idle time, in jiffies.
unsigned long percent_idle; // Idle percentage. 
uint8_t	cpufreq_dynamic_cur_freq_id; // What ID from the stupid table we're at.


/**
 * Timer callback
 */
static void cpufreq_governor_dynamic_callback(unsigned long t) {
	percent_idle = POLL_FREQUENCY * 100 * (kstat_cpu(0).cpustat.idle - prev_idle) / HZ;
	prev_idle = kstat_cpu(0).cpustat.idle;

	if ((percent_idle > MAX_IDLE) || (percent_idle < MIN_IDLE)) { cpufreq_governor(0,CPUFREQ_GOV_LIMITS); }

	cpufreq_dynamic_timer.expires = jiffies + SLEEP_JIFFIES;
	add_timer(&cpufreq_dynamic_timer);
}

/**
 * The governor itself.
 * 
 * DOCUMENT ME!
 */
static int cpufreq_governor_dynamic(struct cpufreq_policy *policy,
					unsigned int event)
{
	switch (event) {
	case CPUFREQ_GOV_START:
		cpufreq_dynamic_timer.expires = jiffies + SLEEP_JIFFIES;
		cpufreq_dynamic_timer.function = cpufreq_governor_dynamic_callback;
		cpufreq_dynamic_cur_freq_id = 0;
		prev_idle = kstat_cpu(0).cpustat.idle;
		init_timer(&cpufreq_dynamic_timer);
		add_timer(&cpufreq_dynamic_timer);
	case CPUFREQ_GOV_LIMITS:
		if (percent_idle > MAX_IDLE) {
			if (cpufreq_dynamic_freqs[cpufreq_dynamic_cur_freq_id] != FREQ_MIN) {
				if (cpufreq_dynamic_freqs[++cpufreq_dynamic_cur_freq_id] == FREQ_MIN) {
					__cpufreq_driver_target(policy,policy->min,CPUFREQ_RELATION_L);
				} else {
					//printk("cpufreq_dynamic: Attempting to downgrade frequency: %i KHz\n",cpufreq_dynamic_freqs[cpufreq_dynamic_cur_freq_id]);
					__cpufreq_driver_target(policy,cpufreq_dynamic_freqs[cpufreq_dynamic_cur_freq_id],CPUFREQ_RELATION_L);
				}
			}
		} else if (percent_idle < MIN_IDLE) {
			if (cpufreq_dynamic_freqs[cpufreq_dynamic_cur_freq_id] != FREQ_MAX) {
				if (cpufreq_dynamic_freqs[--cpufreq_dynamic_cur_freq_id] == FREQ_MAX) {
					__cpufreq_driver_target(policy,policy->max,CPUFREQ_RELATION_L);
				} else {
					//printk("cpufreq_dynamic: Attempting to upgrade frequency: %i KHz\n",cpufreq_dynamic_freqs[cpufreq_dynamic_cur_freq_id]);
					__cpufreq_driver_target(policy,cpufreq_dynamic_freqs[cpufreq_dynamic_cur_freq_id],CPUFREQ_RELATION_L);
				}
			}
		}
		break;
	case CPUFREQ_GOV_STOP:
		del_timer(&cpufreq_dynamic_timer);
		break;
	default:
		break;
	}
	return 0;
}
                                                            
static struct cpufreq_governor cpufreq_gov_dynamic = {
	.name		= "dynamic",
	.governor	= cpufreq_governor_dynamic,
	.owner		= THIS_MODULE,
};
EXPORT_SYMBOL(cpufreq_gov_dynamic);


static int __init cpufreq_gov_dynamic_init(void)
{
	return cpufreq_register_governor(&cpufreq_gov_dynamic);
}


static void __exit cpufreq_gov_dynamic_exit(void)
{
	cpufreq_unregister_governor(&cpufreq_gov_dynamic);
}


MODULE_AUTHOR("Jonathan Anderson <janderson@janderson.ca");
MODULE_DESCRIPTION("Dynamic CPUfreq policy governor");
MODULE_LICENSE("GPL");

module_init(cpufreq_gov_dynamic_init);
module_exit(cpufreq_gov_dynamic_exit);