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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 | ||
1da177e4 LT |
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 { | |
8ad200d7 PM |
24 | volatile u64 tb; |
25 | volatile u64 mark; | |
1da177e4 LT |
26 | volatile int cmd; |
27 | volatile int handshake; | |
8ad200d7 | 28 | int filler[2]; |
1da177e4 LT |
29 | |
30 | volatile int ack; | |
31 | int filler2[7]; | |
32 | ||
33 | volatile int race_result; | |
34 | } *tbsync; | |
35 | ||
36 | static volatile int running; | |
37 | ||
8ad200d7 | 38 | static void __devinit enter_contest(u64 mark, long add) |
1da177e4 | 39 | { |
8ad200d7 | 40 | while (get_tb() < mark) |
1da177e4 LT |
41 | tbsync->race_result = add; |
42 | } | |
43 | ||
8ad200d7 | 44 | void __devinit smp_generic_take_timebase(void) |
1da177e4 LT |
45 | { |
46 | int cmd; | |
8ad200d7 | 47 | u64 tb; |
1da177e4 LT |
48 | |
49 | local_irq_disable(); | |
8ad200d7 PM |
50 | while (!running) |
51 | barrier(); | |
1da177e4 LT |
52 | rmb(); |
53 | ||
8ad200d7 | 54 | for (;;) { |
1da177e4 | 55 | tbsync->ack = 1; |
8ad200d7 PM |
56 | while (!tbsync->handshake) |
57 | barrier(); | |
1da177e4 LT |
58 | rmb(); |
59 | ||
60 | cmd = tbsync->cmd; | |
61 | tb = tbsync->tb; | |
8ad200d7 | 62 | mb(); |
1da177e4 | 63 | tbsync->ack = 0; |
8ad200d7 PM |
64 | if (cmd == kExit) |
65 | break; | |
66 | ||
67 | while (tbsync->handshake) | |
68 | barrier(); | |
69 | if (cmd == kSetAndTest) | |
70 | set_tb(tb >> 32, tb & 0xfffffffful); | |
71 | enter_contest(tbsync->mark, -1); | |
1da177e4 LT |
72 | } |
73 | local_irq_enable(); | |
74 | } | |
75 | ||
8ad200d7 | 76 | static int __devinit start_contest(int cmd, long offset, int num) |
1da177e4 LT |
77 | { |
78 | int i, score=0; | |
8ad200d7 PM |
79 | u64 tb; |
80 | long mark; | |
1da177e4 LT |
81 | |
82 | tbsync->cmd = cmd; | |
83 | ||
84 | local_irq_disable(); | |
8ad200d7 PM |
85 | for (i = -3; i < num; ) { |
86 | tb = get_tb() + 400; | |
1da177e4 LT |
87 | tbsync->tb = tb + offset; |
88 | tbsync->mark = mark = tb + 400; | |
89 | ||
90 | wmb(); | |
91 | ||
92 | tbsync->handshake = 1; | |
8ad200d7 PM |
93 | while (tbsync->ack) |
94 | barrier(); | |
1da177e4 | 95 | |
8ad200d7 PM |
96 | while (get_tb() <= tb) |
97 | barrier(); | |
1da177e4 | 98 | tbsync->handshake = 0; |
8ad200d7 | 99 | enter_contest(mark, 1); |
1da177e4 | 100 | |
8ad200d7 PM |
101 | while (!tbsync->ack) |
102 | barrier(); | |
1da177e4 | 103 | |
8ad200d7 | 104 | if (i++ > 0) |
1da177e4 LT |
105 | score += tbsync->race_result; |
106 | } | |
107 | local_irq_enable(); | |
108 | return score; | |
109 | } | |
110 | ||
8ad200d7 | 111 | void __devinit smp_generic_give_timebase(void) |
1da177e4 LT |
112 | { |
113 | int i, score, score2, old, min=0, max=5000, offset=1000; | |
114 | ||
115 | printk("Synchronizing timebase\n"); | |
116 | ||
117 | /* if this fails then this kernel won't work anyway... */ | |
118 | tbsync = kmalloc( sizeof(*tbsync), GFP_KERNEL ); | |
119 | memset( tbsync, 0, sizeof(*tbsync) ); | |
120 | mb(); | |
121 | running = 1; | |
122 | ||
8ad200d7 PM |
123 | while (!tbsync->ack) |
124 | barrier(); | |
1da177e4 LT |
125 | |
126 | printk("Got ack\n"); | |
127 | ||
128 | /* binary search */ | |
8ad200d7 PM |
129 | for (old = -1; old != offset ; offset = (min+max) / 2) { |
130 | score = start_contest(kSetAndTest, offset, NUM_ITER); | |
1da177e4 LT |
131 | |
132 | printk("score %d, offset %d\n", score, offset ); | |
133 | ||
134 | if( score > 0 ) | |
135 | max = offset; | |
136 | else | |
137 | min = offset; | |
138 | old = offset; | |
139 | } | |
8ad200d7 PM |
140 | score = start_contest(kSetAndTest, min, NUM_ITER); |
141 | score2 = start_contest(kSetAndTest, max, NUM_ITER); | |
1da177e4 | 142 | |
8ad200d7 PM |
143 | printk("Min %d (score %d), Max %d (score %d)\n", |
144 | min, score, max, score2); | |
145 | score = abs(score); | |
146 | score2 = abs(score2); | |
1da177e4 LT |
147 | offset = (score < score2) ? min : max; |
148 | ||
149 | /* guard against inaccurate mttb */ | |
8ad200d7 PM |
150 | for (i = 0; i < 10; i++) { |
151 | start_contest(kSetAndTest, offset, NUM_ITER/10); | |
1da177e4 | 152 | |
8ad200d7 | 153 | if ((score2 = start_contest(kTest, offset, NUM_ITER)) < 0) |
1da177e4 | 154 | score2 = -score2; |
8ad200d7 | 155 | if (score2 <= score || score2 < 20) |
1da177e4 LT |
156 | break; |
157 | } | |
158 | printk("Final offset: %d (%d/%d)\n", offset, score2, NUM_ITER ); | |
159 | ||
160 | /* exiting */ | |
161 | tbsync->cmd = kExit; | |
162 | wmb(); | |
163 | tbsync->handshake = 1; | |
8ad200d7 PM |
164 | while (tbsync->ack) |
165 | barrier(); | |
1da177e4 | 166 | tbsync->handshake = 0; |
8ad200d7 | 167 | kfree(tbsync); |
1da177e4 LT |
168 | tbsync = NULL; |
169 | running = 0; | |
170 | } |