PM / devfreq: Add basic governors
[linux-2.6.git] / 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 };