2 * Generic implementation of 64-bit atomics using spinlocks,
3 * useful on processors that don't have 64-bit atomic instructions.
5 * Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
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.
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>
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.
29 * Ensure each lock is in a separate cacheline.
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),
40 static inline raw_spinlock_t *lock_addr(const atomic64_t *v)
42 unsigned long addr = (unsigned long) v;
44 addr >>= L1_CACHE_SHIFT;
45 addr ^= (addr >> 8) ^ (addr >> 16);
46 return &atomic64_lock[addr & (NR_LOCKS - 1)].lock;
49 long long atomic64_read(const atomic64_t *v)
52 raw_spinlock_t *lock = lock_addr(v);
55 raw_spin_lock_irqsave(lock, flags);
57 raw_spin_unlock_irqrestore(lock, flags);
60 EXPORT_SYMBOL(atomic64_read);
62 void atomic64_set(atomic64_t *v, long long i)
65 raw_spinlock_t *lock = lock_addr(v);
67 raw_spin_lock_irqsave(lock, flags);
69 raw_spin_unlock_irqrestore(lock, flags);
71 EXPORT_SYMBOL(atomic64_set);
73 #define ATOMIC64_OP(op, c_op) \
74 void atomic64_##op(long long a, atomic64_t *v) \
76 unsigned long flags; \
77 raw_spinlock_t *lock = lock_addr(v); \
79 raw_spin_lock_irqsave(lock, flags); \
81 raw_spin_unlock_irqrestore(lock, flags); \
83 EXPORT_SYMBOL(atomic64_##op);
85 #define ATOMIC64_OP_RETURN(op, c_op) \
86 long long atomic64_##op##_return(long long a, atomic64_t *v) \
88 unsigned long flags; \
89 raw_spinlock_t *lock = lock_addr(v); \
92 raw_spin_lock_irqsave(lock, flags); \
93 val = (v->counter c_op a); \
94 raw_spin_unlock_irqrestore(lock, flags); \
97 EXPORT_SYMBOL(atomic64_##op##_return);
99 #define ATOMIC64_OPS(op, c_op) \
100 ATOMIC64_OP(op, c_op) \
101 ATOMIC64_OP_RETURN(op, c_op)
103 ATOMIC64_OPS(add, +=)
104 ATOMIC64_OPS(sub, -=)
107 #undef ATOMIC64_OP_RETURN
110 long long atomic64_dec_if_positive(atomic64_t *v)
113 raw_spinlock_t *lock = lock_addr(v);
116 raw_spin_lock_irqsave(lock, flags);
117 val = v->counter - 1;
120 raw_spin_unlock_irqrestore(lock, flags);
123 EXPORT_SYMBOL(atomic64_dec_if_positive);
125 long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
128 raw_spinlock_t *lock = lock_addr(v);
131 raw_spin_lock_irqsave(lock, flags);
135 raw_spin_unlock_irqrestore(lock, flags);
138 EXPORT_SYMBOL(atomic64_cmpxchg);
140 long long atomic64_xchg(atomic64_t *v, long long new)
143 raw_spinlock_t *lock = lock_addr(v);
146 raw_spin_lock_irqsave(lock, flags);
149 raw_spin_unlock_irqrestore(lock, flags);
152 EXPORT_SYMBOL(atomic64_xchg);
154 int atomic64_add_unless(atomic64_t *v, long long a, long long u)
157 raw_spinlock_t *lock = lock_addr(v);
160 raw_spin_lock_irqsave(lock, flags);
161 if (v->counter != u) {
165 raw_spin_unlock_irqrestore(lock, flags);
168 EXPORT_SYMBOL(atomic64_add_unless);