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171 lines · 3.1 KiB

1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Smp timebase synchronization for ppc.
4 *
5 * Copyright (C) 2003 Samuel Rydh ([email protected])
6 *
7 */
8
9#include <linux/kernel.h>
10#include <linux/sched.h>
11#include <linux/smp.h>
12#include <linux/unistd.h>
13#include <linux/slab.h>
14#include <linux/atomic.h>
15#include <asm/smp.h>
16#include <asm/time.h>
17
18#define NUM_ITER 300
19
20enum {
21 kExit=0, kSetAndTest, kTest
22};
23
24static struct {
25 volatile u64 tb;
26 volatile u64 mark;
27 volatile int cmd;
28 volatile int handshake;
29 int filler[2];
30
31 volatile int ack;
32 int filler2[7];
33
34 volatile int race_result;
35} *tbsync;
36
37static volatile int running;
38
39static void enter_contest(u64 mark, long add)
40{
41 while (get_tb() < mark)
42 tbsync->race_result = add;
43}
44
45void smp_generic_take_timebase(void)
46{
47 int cmd;
48 u64 tb;
49 unsigned long flags;
50
51 local_irq_save(flags);
52 while (!running)
53 barrier();
54 rmb();
55
56 for (;;) {
57 tbsync->ack = 1;
58 while (!tbsync->handshake)
59 barrier();
60 rmb();
61
62 cmd = tbsync->cmd;
63 tb = tbsync->tb;
64 mb();
65 tbsync->ack = 0;
66 if (cmd == kExit)
67 break;
68
69 while (tbsync->handshake)
70 barrier();
71 if (cmd == kSetAndTest)
72 set_tb(tb >> 32, tb & 0xfffffffful);
73 enter_contest(tbsync->mark, -1);
74 }
75 local_irq_restore(flags);
76}
77
78static int start_contest(int cmd, long offset, int num)
79{
80 int i, score=0;
81 u64 tb;
82 u64 mark;
83
84 tbsync->cmd = cmd;
85
86 local_irq_disable();
87 for (i = -3; i < num; ) {
88 tb = get_tb() + 400;
89 tbsync->tb = tb + offset;
90 tbsync->mark = mark = tb + 400;
91
92 wmb();
93
94 tbsync->handshake = 1;
95 while (tbsync->ack)
96 barrier();
97
98 while (get_tb() <= tb)
99 barrier();
100 tbsync->handshake = 0;
101 enter_contest(mark, 1);
102
103 while (!tbsync->ack)
104 barrier();
105
106 if (i++ > 0)
107 score += tbsync->race_result;
108 }
109 local_irq_enable();
110 return score;
111}
112
113void smp_generic_give_timebase(void)
114{
115 int i, score, score2, old, min=0, max=5000, offset=1000;
116
117 pr_debug("Software timebase sync\n");
118
119 /* if this fails then this kernel won't work anyway... */
120 tbsync = kzalloc_obj(*tbsync);
121 mb();
122 running = 1;
123
124 while (!tbsync->ack)
125 barrier();
126
127 pr_debug("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 pr_debug("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 pr_debug("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 pr_debug("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}