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/export.h>
17 #include <linux/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 raw_spinlock_t lock;
33 char pad[L1_CACHE_BYTES];
34 } atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp = {
35 [0 ... (NR_LOCKS - 1)] = {
36 .lock = __RAW_SPIN_LOCK_UNLOCKED(atomic64_lock.lock),
37 },
38 };
39
lock_addr(const atomic64_t * v)40 static inline raw_spinlock_t *lock_addr(const atomic64_t *v)
41 {
42 unsigned long addr = (unsigned long) v;
43
44 addr >>= L1_CACHE_SHIFT;
45 addr ^= (addr >> 8) ^ (addr >> 16);
46 return &atomic64_lock[addr & (NR_LOCKS - 1)].lock;
47 }
48
atomic64_read(const atomic64_t * v)49 long long atomic64_read(const atomic64_t *v)
50 {
51 unsigned long flags;
52 raw_spinlock_t *lock = lock_addr(v);
53 long long val;
54
55 raw_spin_lock_irqsave(lock, flags);
56 val = v->counter;
57 raw_spin_unlock_irqrestore(lock, flags);
58 return val;
59 }
60 EXPORT_SYMBOL(atomic64_read);
61
atomic64_set(atomic64_t * v,long long i)62 void atomic64_set(atomic64_t *v, long long i)
63 {
64 unsigned long flags;
65 raw_spinlock_t *lock = lock_addr(v);
66
67 raw_spin_lock_irqsave(lock, flags);
68 v->counter = i;
69 raw_spin_unlock_irqrestore(lock, flags);
70 }
71 EXPORT_SYMBOL(atomic64_set);
72
atomic64_add(long long a,atomic64_t * v)73 void atomic64_add(long long a, atomic64_t *v)
74 {
75 unsigned long flags;
76 raw_spinlock_t *lock = lock_addr(v);
77
78 raw_spin_lock_irqsave(lock, flags);
79 v->counter += a;
80 raw_spin_unlock_irqrestore(lock, flags);
81 }
82 EXPORT_SYMBOL(atomic64_add);
83
atomic64_add_return(long long a,atomic64_t * v)84 long long atomic64_add_return(long long a, atomic64_t *v)
85 {
86 unsigned long flags;
87 raw_spinlock_t *lock = lock_addr(v);
88 long long val;
89
90 raw_spin_lock_irqsave(lock, flags);
91 val = v->counter += a;
92 raw_spin_unlock_irqrestore(lock, flags);
93 return val;
94 }
95 EXPORT_SYMBOL(atomic64_add_return);
96
atomic64_sub(long long a,atomic64_t * v)97 void atomic64_sub(long long a, atomic64_t *v)
98 {
99 unsigned long flags;
100 raw_spinlock_t *lock = lock_addr(v);
101
102 raw_spin_lock_irqsave(lock, flags);
103 v->counter -= a;
104 raw_spin_unlock_irqrestore(lock, flags);
105 }
106 EXPORT_SYMBOL(atomic64_sub);
107
atomic64_sub_return(long long a,atomic64_t * v)108 long long atomic64_sub_return(long long a, atomic64_t *v)
109 {
110 unsigned long flags;
111 raw_spinlock_t *lock = lock_addr(v);
112 long long val;
113
114 raw_spin_lock_irqsave(lock, flags);
115 val = v->counter -= a;
116 raw_spin_unlock_irqrestore(lock, flags);
117 return val;
118 }
119 EXPORT_SYMBOL(atomic64_sub_return);
120
atomic64_dec_if_positive(atomic64_t * v)121 long long atomic64_dec_if_positive(atomic64_t *v)
122 {
123 unsigned long flags;
124 raw_spinlock_t *lock = lock_addr(v);
125 long long val;
126
127 raw_spin_lock_irqsave(lock, flags);
128 val = v->counter - 1;
129 if (val >= 0)
130 v->counter = val;
131 raw_spin_unlock_irqrestore(lock, flags);
132 return val;
133 }
134 EXPORT_SYMBOL(atomic64_dec_if_positive);
135
atomic64_cmpxchg(atomic64_t * v,long long o,long long n)136 long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
137 {
138 unsigned long flags;
139 raw_spinlock_t *lock = lock_addr(v);
140 long long val;
141
142 raw_spin_lock_irqsave(lock, flags);
143 val = v->counter;
144 if (val == o)
145 v->counter = n;
146 raw_spin_unlock_irqrestore(lock, flags);
147 return val;
148 }
149 EXPORT_SYMBOL(atomic64_cmpxchg);
150
atomic64_xchg(atomic64_t * v,long long new)151 long long atomic64_xchg(atomic64_t *v, long long new)
152 {
153 unsigned long flags;
154 raw_spinlock_t *lock = lock_addr(v);
155 long long val;
156
157 raw_spin_lock_irqsave(lock, flags);
158 val = v->counter;
159 v->counter = new;
160 raw_spin_unlock_irqrestore(lock, flags);
161 return val;
162 }
163 EXPORT_SYMBOL(atomic64_xchg);
164
atomic64_add_unless(atomic64_t * v,long long a,long long u)165 int atomic64_add_unless(atomic64_t *v, long long a, long long u)
166 {
167 unsigned long flags;
168 raw_spinlock_t *lock = lock_addr(v);
169 int ret = 0;
170
171 raw_spin_lock_irqsave(lock, flags);
172 if (v->counter != u) {
173 v->counter += a;
174 ret = 1;
175 }
176 raw_spin_unlock_irqrestore(lock, flags);
177 return ret;
178 }
179 EXPORT_SYMBOL(atomic64_add_unless);
180