1 /*
2 * Smp timebase synchronization for ppc.
3 *
4 * Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se)
5 *
6 */
7
8 #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
19 enum {
20 kExit=0, kSetAndTest, kTest
21 };
22
23 static 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
36 static volatile int running;
37
enter_contest(u64 mark,long add)38 static void __devinit enter_contest(u64 mark, long add)
39 {
40 while (get_tb() < mark)
41 tbsync->race_result = add;
42 }
43
smp_generic_take_timebase(void)44 void __devinit smp_generic_take_timebase(void)
45 {
46 int cmd;
47 u64 tb;
48 unsigned long flags;
49
50 local_irq_save(flags);
51 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 }
74 local_irq_restore(flags);
75 }
76
start_contest(int cmd,long offset,int num)77 static int __devinit start_contest(int cmd, long offset, int num)
78 {
79 int i, score=0;
80 u64 tb;
81 u64 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
smp_generic_give_timebase(void)112 void __devinit smp_generic_give_timebase(void)
113 {
114 int i, score, score2, old, min=0, max=5000, offset=1000;
115
116 pr_debug("Software timebase sync\n");
117
118 /* if this fails then this kernel won't work anyway... */
119 tbsync = kzalloc( sizeof(*tbsync), GFP_KERNEL );
120 mb();
121 running = 1;
122
123 while (!tbsync->ack)
124 barrier();
125
126 pr_debug("Got ack\n");
127
128 /* binary search */
129 for (old = -1; old != offset ; offset = (min+max) / 2) {
130 score = start_contest(kSetAndTest, offset, NUM_ITER);
131
132 pr_debug("score %d, offset %d\n", score, offset );
133
134 if( score > 0 )
135 max = offset;
136 else
137 min = offset;
138 old = offset;
139 }
140 score = start_contest(kSetAndTest, min, NUM_ITER);
141 score2 = start_contest(kSetAndTest, max, NUM_ITER);
142
143 pr_debug("Min %d (score %d), Max %d (score %d)\n",
144 min, score, max, score2);
145 score = abs(score);
146 score2 = abs(score2);
147 offset = (score < score2) ? min : max;
148
149 /* guard against inaccurate mttb */
150 for (i = 0; i < 10; i++) {
151 start_contest(kSetAndTest, offset, NUM_ITER/10);
152
153 if ((score2 = start_contest(kTest, offset, NUM_ITER)) < 0)
154 score2 = -score2;
155 if (score2 <= score || score2 < 20)
156 break;
157 }
158 pr_debug("Final offset: %d (%d/%d)\n", offset, score2, NUM_ITER );
159
160 /* exiting */
161 tbsync->cmd = kExit;
162 wmb();
163 tbsync->handshake = 1;
164 while (tbsync->ack)
165 barrier();
166 tbsync->handshake = 0;
167 kfree(tbsync);
168 tbsync = NULL;
169 running = 0;
170 }
171