drivers/devfreq/governor_simpleondemand.c

   1 /*
   2  *  linux/drivers/devfreq/governor_simpleondemand.c
   3  *
   4  *  Copyright (C) 2011 Samsung Electronics
   5  *      MyungJoo Ham <myungjoo.ham@samsung.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/errno.h>
  13 #include <linux/devfreq.h>
  14 #include <linux/math64.h>
  15
  16 /* Default constants for DevFreq-Simple-Ondemand (DFSO) */
  17 #define DFSO_UPTHRESHOLD        (90)
  18 #define DFSO_DOWNDIFFERENCTIAL  (5)
  19 static int devfreq_simple_ondemand_func(struct devfreq *df,
  20                                         unsigned long *freq)
  21 {
  22         struct devfreq_dev_status stat;
  23         int err = df->profile->get_dev_status(df->dev.parent, &stat);
  24         unsigned long long a, b;
  25         unsigned int dfso_upthreshold = DFSO_UPTHRESHOLD;
  26         unsigned int dfso_downdifferential = DFSO_DOWNDIFFERENCTIAL;
  27         struct devfreq_simple_ondemand_data *data = df->data;
  28         unsigned long max = (df->max_freq) ? df->max_freq : UINT_MAX;
  29
  30         if (err)
  31                 return err;
  32
  33         if (data) {
  34                 if (data->upthreshold)
  35                         dfso_upthreshold = data->upthreshold;
  36                 if (data->downdifferential)
  37                         dfso_downdifferential = data->downdifferential;
  38         }
  39         if (dfso_upthreshold > 100 ||
  40             dfso_upthreshold < dfso_downdifferential)
  41                 return -EINVAL;
  42
  43         /* Assume MAX if it is going to be divided by zero */
  44         if (stat.total_time == 0) {
  45                 *freq = max;
  46                 return 0;
  47         }
  48
  49         /* Prevent overflow */
  50         if (stat.busy_time >= (1 << 24) || stat.total_time >= (1 << 24)) {
  51                 stat.busy_time >>= 7;
  52                 stat.total_time >>= 7;
  53         }
  54
  55         /* Set MAX if it's busy enough */
  56         if (stat.busy_time * 100 >
  57             stat.total_time * dfso_upthreshold) {
  58                 *freq = max;
  59                 return 0;
  60         }
  61
  62         /* Set MAX if we do not know the initial frequency */
  63         if (stat.current_frequency == 0) {
  64                 *freq = max;
  65                 return 0;
  66         }
  67
  68         /* Keep the current frequency */
  69         if (stat.busy_time * 100 >
  70             stat.total_time * (dfso_upthreshold - dfso_downdifferential)) {
  71                 *freq = stat.current_frequency;
  72                 return 0;
  73         }
  74
  75         /* Set the desired frequency based on the load */
  76         a = stat.busy_time;
  77         a *= stat.current_frequency;
  78         b = div_u64(a, stat.total_time);
  79         b *= 100;
  80         b = div_u64(b, (dfso_upthreshold - dfso_downdifferential / 2));
  81         *freq = (unsigned long) b;
  82
  83         if (df->min_freq && *freq < df->min_freq)
  84                 *freq = df->min_freq;
  85         if (df->max_freq && *freq > df->max_freq)
  86                 *freq = df->max_freq;
  87
  88         return 0;
  89 }
  90
  91 const struct devfreq_governor devfreq_simple_ondemand = {
  92         .name = "simple_ondemand",
  93         .get_target_freq = devfreq_simple_ondemand_func,
  94 };