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1 /*
2 * Generic implementation of 64-bit atomics using spinlocks,
3 * useful on processors that don't have 64-bit atomic instructions.
4 *
5 * Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; either version
10 * 2 of the License, or (at your option) any later version.
11 */
12 #include <linux/types.h>
13 #include <linux/cache.h>
14 #include <linux/spinlock.h>
15 #include <linux/init.h>
16 #include <linux/module.h>
17 #include <asm/atomic.h>
18
19 /*
20 * We use a hashed array of spinlocks to provide exclusive access
21 * to each atomic64_t variable. Since this is expected to used on
22 * systems with small numbers of CPUs (<= 4 or so), we use a
23 * relatively small array of 16 spinlocks to avoid wasting too much
24 * memory on the spinlock array.
25 */
26 #define NR_LOCKS 16
27
28 /*
29 * Ensure each lock is in a separate cacheline.
30 */
31 static union {
32 spinlock_t lock;
33 char pad[L1_CACHE_BYTES];
34 } atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp;
35
36 static inline spinlock_t *lock_addr(const atomic64_t *v)
37 {
38 unsigned long addr = (unsigned long) v;
39
40 addr >>= L1_CACHE_SHIFT;
41 addr ^= (addr >> 8) ^ (addr >> 16);
42 return &atomic64_lock[addr & (NR_LOCKS - 1)].lock;
43 }
44
45 long long atomic64_read(const atomic64_t *v)
46 {
47 unsigned long flags;
48 spinlock_t *lock = lock_addr(v);
49 long long val;
50
51 spin_lock_irqsave(lock, flags);
52 val = v->counter;
53 spin_unlock_irqrestore(lock, flags);
54 return val;
55 }
56 EXPORT_SYMBOL(atomic64_read);
57
58 void atomic64_set(atomic64_t *v, long long i)
59 {
60 unsigned long flags;
61 spinlock_t *lock = lock_addr(v);
62
63 spin_lock_irqsave(lock, flags);
64 v->counter = i;
65 spin_unlock_irqrestore(lock, flags);
66 }
67 EXPORT_SYMBOL(atomic64_set);
68
69 void atomic64_add(long long a, atomic64_t *v)
70 {
71 unsigned long flags;
72 spinlock_t *lock = lock_addr(v);
73
74 spin_lock_irqsave(lock, flags);
75 v->counter += a;
76 spin_unlock_irqrestore(lock, flags);
77 }
78 EXPORT_SYMBOL(atomic64_add);
79
80 long long atomic64_add_return(long long a, atomic64_t *v)
81 {
82 unsigned long flags;
83 spinlock_t *lock = lock_addr(v);
84 long long val;
85
86 spin_lock_irqsave(lock, flags);
87 val = v->counter += a;
88 spin_unlock_irqrestore(lock, flags);
89 return val;
90 }
91 EXPORT_SYMBOL(atomic64_add_return);
92
93 void atomic64_sub(long long a, atomic64_t *v)
94 {
95 unsigned long flags;
96 spinlock_t *lock = lock_addr(v);
97
98 spin_lock_irqsave(lock, flags);
99 v->counter -= a;
100 spin_unlock_irqrestore(lock, flags);
101 }
102 EXPORT_SYMBOL(atomic64_sub);
103
104 long long atomic64_sub_return(long long a, atomic64_t *v)
105 {
106 unsigned long flags;
107 spinlock_t *lock = lock_addr(v);
108 long long val;
109
110 spin_lock_irqsave(lock, flags);
111 val = v->counter -= a;
112 spin_unlock_irqrestore(lock, flags);
113 return val;
114 }
115 EXPORT_SYMBOL(atomic64_sub_return);
116
117 long long atomic64_dec_if_positive(atomic64_t *v)
118 {
119 unsigned long flags;
120 spinlock_t *lock = lock_addr(v);
121 long long val;
122
123 spin_lock_irqsave(lock, flags);
124 val = v->counter - 1;
125 if (val >= 0)
126 v->counter = val;
127 spin_unlock_irqrestore(lock, flags);
128 return val;
129 }
130 EXPORT_SYMBOL(atomic64_dec_if_positive);
131
132 long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
133 {
134 unsigned long flags;
135 spinlock_t *lock = lock_addr(v);
136 long long val;
137
138 spin_lock_irqsave(lock, flags);
139 val = v->counter;
140 if (val == o)
141 v->counter = n;
142 spin_unlock_irqrestore(lock, flags);
143 return val;
144 }
145 EXPORT_SYMBOL(atomic64_cmpxchg);
146
147 long long atomic64_xchg(atomic64_t *v, long long new)
148 {
149 unsigned long flags;
150 spinlock_t *lock = lock_addr(v);
151 long long val;
152
153 spin_lock_irqsave(lock, flags);
154 val = v->counter;
155 v->counter = new;
156 spin_unlock_irqrestore(lock, flags);
157 return val;
158 }
159 EXPORT_SYMBOL(atomic64_xchg);
160
161 int atomic64_add_unless(atomic64_t *v, long long a, long long u)
162 {
163 unsigned long flags;
164 spinlock_t *lock = lock_addr(v);
165 int ret = 0;
166
167 spin_lock_irqsave(lock, flags);
168 if (v->counter != u) {
169 v->counter += a;
170 ret = 1;
171 }
172 spin_unlock_irqrestore(lock, flags);
173 return ret;
174 }
175 EXPORT_SYMBOL(atomic64_add_unless);
176
177 static int init_atomic64_lock(void)
178 {
179 int i;
180
181 for (i = 0; i < NR_LOCKS; ++i)
182 spin_lock_init(&atomic64_lock[i].lock);
183 return 0;
184 }
185
186 pure_initcall(init_atomic64_lock);
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