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1da177e4 LT |
1 | /* |
2 | * Smp timebase synchronization for ppc. | |
3 | * | |
4 | * Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se) | |
5 | * | |
6 | */ | |
7 | ||
8 | #include <linux/config.h> | |
9 | #include <linux/kernel.h> | |
10 | #include <linux/sched.h> | |
11 | #include <linux/smp.h> | |
12 | #include <linux/unistd.h> | |
13 | #include <linux/init.h> | |
14 | #include <asm/atomic.h> | |
15 | #include <asm/smp.h> | |
16 | #include <asm/time.h> | |
17 | ||
18 | #define NUM_ITER 300 | |
19 | ||
20 | enum { | |
21 | kExit=0, kSetAndTest, kTest | |
22 | }; | |
23 | ||
24 | static struct { | |
8ad200d7 PM |
25 | volatile u64 tb; |
26 | volatile u64 mark; | |
1da177e4 LT |
27 | volatile int cmd; |
28 | volatile int handshake; | |
8ad200d7 | 29 | int filler[2]; |
1da177e4 LT |
30 | |
31 | volatile int ack; | |
32 | int filler2[7]; | |
33 | ||
34 | volatile int race_result; | |
35 | } *tbsync; | |
36 | ||
37 | static volatile int running; | |
38 | ||
8ad200d7 | 39 | static void __devinit enter_contest(u64 mark, long add) |
1da177e4 | 40 | { |
8ad200d7 | 41 | while (get_tb() < mark) |
1da177e4 LT |
42 | tbsync->race_result = add; |
43 | } | |
44 | ||
8ad200d7 | 45 | void __devinit smp_generic_take_timebase(void) |
1da177e4 LT |
46 | { |
47 | int cmd; | |
8ad200d7 | 48 | u64 tb; |
1da177e4 LT |
49 | |
50 | local_irq_disable(); | |
8ad200d7 PM |
51 | while (!running) |
52 | barrier(); | |
1da177e4 LT |
53 | rmb(); |
54 | ||
8ad200d7 | 55 | for (;;) { |
1da177e4 | 56 | tbsync->ack = 1; |
8ad200d7 PM |
57 | while (!tbsync->handshake) |
58 | barrier(); | |
1da177e4 LT |
59 | rmb(); |
60 | ||
61 | cmd = tbsync->cmd; | |
62 | tb = tbsync->tb; | |
8ad200d7 | 63 | mb(); |
1da177e4 | 64 | tbsync->ack = 0; |
8ad200d7 PM |
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); | |
1da177e4 LT |
73 | } |
74 | local_irq_enable(); | |
75 | } | |
76 | ||
8ad200d7 | 77 | static int __devinit start_contest(int cmd, long offset, int num) |
1da177e4 LT |
78 | { |
79 | int i, score=0; | |
8ad200d7 PM |
80 | u64 tb; |
81 | long mark; | |
1da177e4 LT |
82 | |
83 | tbsync->cmd = cmd; | |
84 | ||
85 | local_irq_disable(); | |
8ad200d7 PM |
86 | for (i = -3; i < num; ) { |
87 | tb = get_tb() + 400; | |
1da177e4 LT |
88 | tbsync->tb = tb + offset; |
89 | tbsync->mark = mark = tb + 400; | |
90 | ||
91 | wmb(); | |
92 | ||
93 | tbsync->handshake = 1; | |
8ad200d7 PM |
94 | while (tbsync->ack) |
95 | barrier(); | |
1da177e4 | 96 | |
8ad200d7 PM |
97 | while (get_tb() <= tb) |
98 | barrier(); | |
1da177e4 | 99 | tbsync->handshake = 0; |
8ad200d7 | 100 | enter_contest(mark, 1); |
1da177e4 | 101 | |
8ad200d7 PM |
102 | while (!tbsync->ack) |
103 | barrier(); | |
1da177e4 | 104 | |
8ad200d7 | 105 | if (i++ > 0) |
1da177e4 LT |
106 | score += tbsync->race_result; |
107 | } | |
108 | local_irq_enable(); | |
109 | return score; | |
110 | } | |
111 | ||
8ad200d7 | 112 | void __devinit smp_generic_give_timebase(void) |
1da177e4 LT |
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 | ||
8ad200d7 PM |
124 | while (!tbsync->ack) |
125 | barrier(); | |
1da177e4 LT |
126 | |
127 | printk("Got ack\n"); | |
128 | ||
129 | /* binary search */ | |
8ad200d7 PM |
130 | for (old = -1; old != offset ; offset = (min+max) / 2) { |
131 | score = start_contest(kSetAndTest, offset, NUM_ITER); | |
1da177e4 LT |
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 | } | |
8ad200d7 PM |
141 | score = start_contest(kSetAndTest, min, NUM_ITER); |
142 | score2 = start_contest(kSetAndTest, max, NUM_ITER); | |
1da177e4 | 143 | |
8ad200d7 PM |
144 | printk("Min %d (score %d), Max %d (score %d)\n", |
145 | min, score, max, score2); | |
146 | score = abs(score); | |
147 | score2 = abs(score2); | |
1da177e4 LT |
148 | offset = (score < score2) ? min : max; |
149 | ||
150 | /* guard against inaccurate mttb */ | |
8ad200d7 PM |
151 | for (i = 0; i < 10; i++) { |
152 | start_contest(kSetAndTest, offset, NUM_ITER/10); | |
1da177e4 | 153 | |
8ad200d7 | 154 | if ((score2 = start_contest(kTest, offset, NUM_ITER)) < 0) |
1da177e4 | 155 | score2 = -score2; |
8ad200d7 | 156 | if (score2 <= score || score2 < 20) |
1da177e4 LT |
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; | |
8ad200d7 PM |
165 | while (tbsync->ack) |
166 | barrier(); | |
1da177e4 | 167 | tbsync->handshake = 0; |
8ad200d7 | 168 | kfree(tbsync); |
1da177e4 LT |
169 | tbsync = NULL; |
170 | running = 0; | |
171 | } |