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
  29         if (err)
  30                 return err;
  31
  32         if (data) {
  33                 if (data->upthreshold)
  34                         dfso_upthreshold = data->upthreshold;
  35                 if (data->downdifferential)
  36                         dfso_downdifferential = data->downdifferential;
  37         }
  38         if (dfso_upthreshold > 100 ||
  39             dfso_upthreshold < dfso_downdifferential)
  40                 return -EINVAL;
  41
  42         /* Assume MAX if it is going to be divided by zero */
  43         if (stat.total_time == 0) {
  44                 *freq = UINT_MAX;
  45                 return 0;
  46         }
  47
  48         /* Prevent overflow */
  49         if (stat.busy_time >= (1 << 24) || stat.total_time >= (1 << 24)) {
  50                 stat.busy_time >>= 7;
  51                 stat.total_time >>= 7;
  52         }
  53
  54         /* Set MAX if it's busy enough */
  55         if (stat.busy_time * 100 >
  56             stat.total_time * dfso_upthreshold) {
  57                 *freq = UINT_MAX;
  58                 return 0;
  59         }
  60
  61         /* Set MAX if we do not know the initial frequency */
  62         if (stat.current_frequency == 0) {
  63                 *freq = UINT_MAX;
  64                 return 0;
  65         }
  66
  67         /* Keep the current frequency */
  68         if (stat.busy_time * 100 >
  69             stat.total_time * (dfso_upthreshold - dfso_downdifferential)) {
  70                 *freq = stat.current_frequency;
  71                 return 0;
  72         }
  73
  74         /* Set the desired frequency based on the load */
  75         a = stat.busy_time;
  76         a *= stat.current_frequency;
  77         b = div_u64(a, stat.total_time);
  78         b *= 100;
  79         b = div_u64(b, (dfso_upthreshold - dfso_downdifferential / 2));
  80         *freq = (unsigned long) b;
  81
  82         return 0;
  83 }
  84
  85 const struct devfreq_governor devfreq_simple_ondemand = {
  86         .name = "simple_ondemand",
  87         .get_target_freq = devfreq_simple_ondemand_func,
  88 };