Paul Mackerras | 8ad200d | 2005-11-04 13:28:58 +1100 | [diff] [blame] | 1 | /* |
| 2 | * Smp timebase synchronization for ppc. |
| 3 | * |
| 4 | * Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se) |
| 5 | * |
| 6 | */ |
| 7 | |
Paul Mackerras | 8ad200d | 2005-11-04 13:28:58 +1100 | [diff] [blame] | 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 | |
| 38 | static void __devinit enter_contest(u64 mark, long add) |
| 39 | { |
| 40 | while (get_tb() < mark) |
| 41 | tbsync->race_result = add; |
| 42 | } |
| 43 | |
| 44 | void __devinit smp_generic_take_timebase(void) |
| 45 | { |
| 46 | int cmd; |
| 47 | u64 tb; |
Paul Mackerras | 467c378 | 2006-08-30 16:10:47 +1000 | [diff] [blame] | 48 | unsigned long flags; |
Paul Mackerras | 8ad200d | 2005-11-04 13:28:58 +1100 | [diff] [blame] | 49 | |
Paul Mackerras | 467c378 | 2006-08-30 16:10:47 +1000 | [diff] [blame] | 50 | local_irq_save(flags); |
Paul Mackerras | 8ad200d | 2005-11-04 13:28:58 +1100 | [diff] [blame] | 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 | } |
Paul Mackerras | 467c378 | 2006-08-30 16:10:47 +1000 | [diff] [blame] | 74 | local_irq_restore(flags); |
Paul Mackerras | 8ad200d | 2005-11-04 13:28:58 +1100 | [diff] [blame] | 75 | } |
| 76 | |
| 77 | static 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 | |
| 112 | void __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 | } |