1/*
2 * Windfarm PowerMac thermal control. Generic PID helpers
3 *
4 * (c) Copyright 2005 Benjamin Herrenschmidt, IBM Corp.
5 *                    <benh@kernel.crashing.org>
6 *
7 * Released under the term of the GNU GPL v2.
8 */
9
10#include <linux/types.h>
11#include <linux/errno.h>
12#include <linux/kernel.h>
13#include <linux/string.h>
14#include <linux/module.h>
15
16#include "windfarm_pid.h"
17
18#undef DEBUG
19
20#ifdef DEBUG
21#define DBG(args...)	printk(args)
22#else
23#define DBG(args...)	do { } while(0)
24#endif
25
26void wf_pid_init(struct wf_pid_state *st, struct wf_pid_param *param)
27{
28	memset(st, 0, sizeof(struct wf_pid_state));
29	st->param = *param;
30	st->first = 1;
31}
32EXPORT_SYMBOL_GPL(wf_pid_init);
33
34s32 wf_pid_run(struct wf_pid_state *st, s32 new_sample)
35{
36	s64	error, integ, deriv;
37	s32	target;
38	int	i, hlen = st->param.history_len;
39
40	/* Calculate error term */
41	error = new_sample - st->param.itarget;
42
43	/* Get samples into our history buffer */
44	if (st->first) {
45		for (i = 0; i < hlen; i++) {
46			st->samples[i] = new_sample;
47			st->errors[i] = error;
48		}
49		st->first = 0;
50		st->index = 0;
51	} else {
52		st->index = (st->index + 1) % hlen;
53		st->samples[st->index] = new_sample;
54		st->errors[st->index] = error;
55	}
56
57	/* Calculate integral term */
58	for (i = 0, integ = 0; i < hlen; i++)
59		integ += st->errors[(st->index + hlen - i) % hlen];
60	integ *= st->param.interval;
61
62	/* Calculate derivative term */
63	deriv = st->errors[st->index] -
64		st->errors[(st->index + hlen - 1) % hlen];
65	deriv /= st->param.interval;
66
67	/* Calculate target */
68	target = (s32)((integ * (s64)st->param.gr + deriv * (s64)st->param.gd +
69		  error * (s64)st->param.gp) >> 36);
70	if (st->param.additive)
71		target += st->target;
72	target = max(target, st->param.min);
73	target = min(target, st->param.max);
74	st->target = target;
75
76	return st->target;
77}
78EXPORT_SYMBOL_GPL(wf_pid_run);
79
80void wf_cpu_pid_init(struct wf_cpu_pid_state *st,
81		     struct wf_cpu_pid_param *param)
82{
83	memset(st, 0, sizeof(struct wf_cpu_pid_state));
84	st->param = *param;
85	st->first = 1;
86}
87EXPORT_SYMBOL_GPL(wf_cpu_pid_init);
88
89s32 wf_cpu_pid_run(struct wf_cpu_pid_state *st, s32 new_power, s32 new_temp)
90{
91	s64	integ, deriv, prop;
92	s32	error, target, sval, adj;
93	int	i, hlen = st->param.history_len;
94
95	/* Calculate error term */
96	error = st->param.pmaxadj - new_power;
97
98	/* Get samples into our history buffer */
99	if (st->first) {
100		for (i = 0; i < hlen; i++) {
101			st->powers[i] = new_power;
102			st->errors[i] = error;
103		}
104		st->temps[0] = st->temps[1] = new_temp;
105		st->first = 0;
106		st->index = st->tindex = 0;
107	} else {
108		st->index = (st->index + 1) % hlen;
109		st->powers[st->index] = new_power;
110		st->errors[st->index] = error;
111		st->tindex = (st->tindex + 1) % 2;
112		st->temps[st->tindex] = new_temp;
113	}
114
115	/* Calculate integral term */
116	for (i = 0, integ = 0; i < hlen; i++)
117		integ += st->errors[(st->index + hlen - i) % hlen];
118	integ *= st->param.interval;
119	integ *= st->param.gr;
120	sval = st->param.tmax - (s32)(integ >> 20);
121	adj = min(st->param.ttarget, sval);
122
123	DBG("integ: %lx, sval: %lx, adj: %lx\n", integ, sval, adj);
124
125	/* Calculate derivative term */
126	deriv = st->temps[st->tindex] -
127		st->temps[(st->tindex + 2 - 1) % 2];
128	deriv /= st->param.interval;
129	deriv *= st->param.gd;
130
131	/* Calculate proportional term */
132	prop = st->last_delta = (new_temp - adj);
133	prop *= st->param.gp;
134
135	DBG("deriv: %lx, prop: %lx\n", deriv, prop);
136
137	/* Calculate target */
138	target = st->target + (s32)((deriv + prop) >> 36);
139	target = max(target, st->param.min);
140	target = min(target, st->param.max);
141	st->target = target;
142
143	return st->target;
144}
145EXPORT_SYMBOL_GPL(wf_cpu_pid_run);
146
147MODULE_AUTHOR("Benjamin Herrenschmidt <benh@kernel.crashing.org>");
148MODULE_DESCRIPTION("PID algorithm for PowerMacs thermal control");
149MODULE_LICENSE("GPL");
150