1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* |
3 | * Smp timebase synchronization for ppc. |
4 | * |
5 | * Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se) |
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 | |
20 | enum { |
21 | kExit=0, kSetAndTest, kTest |
22 | }; |
23 | |
24 | static 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 | |
37 | static volatile int running; |
38 | |
39 | static void enter_contest(u64 mark, long add) |
40 | { |
41 | while (get_tb() < mark) |
42 | tbsync->race_result = add; |
43 | } |
44 | |
45 | void 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(mark: tbsync->mark, add: -1); |
74 | } |
75 | local_irq_restore(flags); |
76 | } |
77 | |
78 | static 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, add: 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 | |
113 | void 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( size: sizeof(*tbsync), GFP_KERNEL ); |
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(cmd: 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(cmd: kSetAndTest, offset: min, NUM_ITER); |
142 | score2 = start_contest(cmd: kSetAndTest, offset: 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(cmd: kSetAndTest, offset, NUM_ITER/10); |
153 | |
154 | if ((score2 = start_contest(cmd: 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(objp: tbsync); |
169 | tbsync = NULL; |
170 | running = 0; |
171 | } |
172 | |