governor_simpleondemand.c

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/*
 *  linux/drivers/devfreq/governor_simpleondemand.c
 *
 *  Copyright (C) 2011 Samsung Electronics
 *  MyungJoo Ham <[email protected]>
 *
 * 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/errno.h>
#include <linux/devfreq.h>
#include <linux/math64.h>

/* Default constants for DevFreq-Simple-Ondemand (DFSO) */
#define DFSO_UPTHRESHOLD    (90)
#define DFSO_DOWNDIFFERENCTIAL  (5)
static int devfreq_simple_ondemand_func(struct devfreq *df,
                    unsigned long *freq)
{
    struct devfreq_dev_status stat;
    int err = df->profile->get_dev_status(df->dev.parent, &stat);
    unsigned long long a, b;
    unsigned int dfso_upthreshold = DFSO_UPTHRESHOLD;
    unsigned int dfso_downdifferential = DFSO_DOWNDIFFERENCTIAL;
    struct devfreq_simple_ondemand_data *data = df->data;
    unsigned long max = (df->max_freq) ? df->max_freq : UINT_MAX;

    if (err)
        return err;

    if (data) {
        if (data->upthreshold)
            dfso_upthreshold = data->upthreshold;
        if (data->downdifferential)
            dfso_downdifferential = data->downdifferential;
    }
    if (dfso_upthreshold > 100 ||
        dfso_upthreshold < dfso_downdifferential)
        return -EINVAL;

    /* Assume MAX if it is going to be divided by zero */
    if (stat.total_time == 0) {
        *freq = max;
        return 0;
    }

    /* Prevent overflow */
    if (stat.busy_time >= (1 << 24) || stat.total_time >= (1 << 24)) {
        stat.busy_time >>= 7;
        stat.total_time >>= 7;
    }

    /* Set MAX if it's busy enough */
    if (stat.busy_time * 100 >
        stat.total_time * dfso_upthreshold) {
        *freq = max;
        return 0;
    }

    /* Set MAX if we do not know the initial frequency */
    if (stat.current_frequency == 0) {
        *freq = max;
        return 0;
    }

    /* Keep the current frequency */
    if (stat.busy_time * 100 >
        stat.total_time * (dfso_upthreshold - dfso_downdifferential)) {
        *freq = stat.current_frequency;
        return 0;
    }

    /* Set the desired frequency based on the load */
    a = stat.busy_time;
    a *= stat.current_frequency;
    b = div_u64(a, stat.total_time);
    b *= 100;
    b = div_u64(b, (dfso_upthreshold - dfso_downdifferential / 2));
    *freq = (unsigned long) b;

    if (df->min_freq && *freq < df->min_freq)
        *freq = df->min_freq;
    if (df->max_freq && *freq > df->max_freq)
        *freq = df->max_freq;

    return 0;
}

const struct devfreq_governor devfreq_simple_ondemand = {
    .name = "simple_ondemand",
    .get_target_freq = devfreq_simple_ondemand_func,
};