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)
19static 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
91const struct devfreq_governor devfreq_simple_ondemand = {
92	.name = "simple_ondemand",
93	.get_target_freq = devfreq_simple_ondemand_func,
94};