blob: de59c6c31a5b81f1cc3f28ff12af611d4b558df5 [file] [log] [blame]
Paul Mackerras8ad200d2005-11-04 13:28:58 +11001/*
2 * Smp timebase synchronization for ppc.
3 *
4 * Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se)
5 *
6 */
7
Paul Mackerras8ad200d2005-11-04 13:28:58 +11008#include <linux/kernel.h>
9#include <linux/sched.h>
10#include <linux/smp.h>
11#include <linux/unistd.h>
12#include <linux/init.h>
13#include <asm/atomic.h>
14#include <asm/smp.h>
15#include <asm/time.h>
16
17#define NUM_ITER 300
18
19enum {
20 kExit=0, kSetAndTest, kTest
21};
22
23static struct {
24 volatile u64 tb;
25 volatile u64 mark;
26 volatile int cmd;
27 volatile int handshake;
28 int filler[2];
29
30 volatile int ack;
31 int filler2[7];
32
33 volatile int race_result;
34} *tbsync;
35
36static volatile int running;
37
38static void __devinit enter_contest(u64 mark, long add)
39{
40 while (get_tb() < mark)
41 tbsync->race_result = add;
42}
43
44void __devinit smp_generic_take_timebase(void)
45{
46 int cmd;
47 u64 tb;
Paul Mackerras467c3782006-08-30 16:10:47 +100048 unsigned long flags;
Paul Mackerras8ad200d2005-11-04 13:28:58 +110049
Paul Mackerras467c3782006-08-30 16:10:47 +100050 local_irq_save(flags);
Paul Mackerras8ad200d2005-11-04 13:28:58 +110051 while (!running)
52 barrier();
53 rmb();
54
55 for (;;) {
56 tbsync->ack = 1;
57 while (!tbsync->handshake)
58 barrier();
59 rmb();
60
61 cmd = tbsync->cmd;
62 tb = tbsync->tb;
63 mb();
64 tbsync->ack = 0;
65 if (cmd == kExit)
66 break;
67
68 while (tbsync->handshake)
69 barrier();
70 if (cmd == kSetAndTest)
71 set_tb(tb >> 32, tb & 0xfffffffful);
72 enter_contest(tbsync->mark, -1);
73 }
Paul Mackerras467c3782006-08-30 16:10:47 +100074 local_irq_restore(flags);
Paul Mackerras8ad200d2005-11-04 13:28:58 +110075}
76
77static int __devinit start_contest(int cmd, long offset, int num)
78{
79 int i, score=0;
80 u64 tb;
81 long mark;
82
83 tbsync->cmd = cmd;
84
85 local_irq_disable();
86 for (i = -3; i < num; ) {
87 tb = get_tb() + 400;
88 tbsync->tb = tb + offset;
89 tbsync->mark = mark = tb + 400;
90
91 wmb();
92
93 tbsync->handshake = 1;
94 while (tbsync->ack)
95 barrier();
96
97 while (get_tb() <= tb)
98 barrier();
99 tbsync->handshake = 0;
100 enter_contest(mark, 1);
101
102 while (!tbsync->ack)
103 barrier();
104
105 if (i++ > 0)
106 score += tbsync->race_result;
107 }
108 local_irq_enable();
109 return score;
110}
111
112void __devinit smp_generic_give_timebase(void)
113{
114 int i, score, score2, old, min=0, max=5000, offset=1000;
115
116 printk("Synchronizing timebase\n");
117
118 /* if this fails then this kernel won't work anyway... */
119 tbsync = kmalloc( sizeof(*tbsync), GFP_KERNEL );
120 memset( tbsync, 0, sizeof(*tbsync) );
121 mb();
122 running = 1;
123
124 while (!tbsync->ack)
125 barrier();
126
127 printk("Got ack\n");
128
129 /* binary search */
130 for (old = -1; old != offset ; offset = (min+max) / 2) {
131 score = start_contest(kSetAndTest, offset, NUM_ITER);
132
133 printk("score %d, offset %d\n", score, offset );
134
135 if( score > 0 )
136 max = offset;
137 else
138 min = offset;
139 old = offset;
140 }
141 score = start_contest(kSetAndTest, min, NUM_ITER);
142 score2 = start_contest(kSetAndTest, max, NUM_ITER);
143
144 printk("Min %d (score %d), Max %d (score %d)\n",
145 min, score, max, score2);
146 score = abs(score);
147 score2 = abs(score2);
148 offset = (score < score2) ? min : max;
149
150 /* guard against inaccurate mttb */
151 for (i = 0; i < 10; i++) {
152 start_contest(kSetAndTest, offset, NUM_ITER/10);
153
154 if ((score2 = start_contest(kTest, offset, NUM_ITER)) < 0)
155 score2 = -score2;
156 if (score2 <= score || score2 < 20)
157 break;
158 }
159 printk("Final offset: %d (%d/%d)\n", offset, score2, NUM_ITER );
160
161 /* exiting */
162 tbsync->cmd = kExit;
163 wmb();
164 tbsync->handshake = 1;
165 while (tbsync->ack)
166 barrier();
167 tbsync->handshake = 0;
168 kfree(tbsync);
169 tbsync = NULL;
170 running = 0;
171}