1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Generic implementation of 64-bit atomics using spinlocks,
4 * useful on processors that don't have 64-bit atomic instructions.
5 *
6 * Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
7 */
8#include <linux/types.h>
9#include <linux/cache.h>
10#include <linux/spinlock.h>
11#include <linux/init.h>
12#include <linux/export.h>
13#include <linux/atomic.h>
14
15/*
16 * We use a hashed array of spinlocks to provide exclusive access
17 * to each atomic64_t variable. Since this is expected to used on
18 * systems with small numbers of CPUs (<= 4 or so), we use a
19 * relatively small array of 16 spinlocks to avoid wasting too much
20 * memory on the spinlock array.
21 */
22#define NR_LOCKS 16
23
24/*
25 * Ensure each lock is in a separate cacheline.
26 */
27static union {
28 arch_spinlock_t lock;
29 char pad[L1_CACHE_BYTES];
30} atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp = {
31 [0 ... (NR_LOCKS - 1)] = {
32 .lock = __ARCH_SPIN_LOCK_UNLOCKED,
33 },
34};
35
36static inline arch_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
45s64 generic_atomic64_read(const atomic64_t *v)
46{
47 unsigned long flags;
48 arch_spinlock_t *lock = lock_addr(v);
49 s64 val;
50
51 local_irq_save(flags);
52 arch_spin_lock(lock);
53 val = v->counter;
54 arch_spin_unlock(lock);
55 local_irq_restore(flags);
56 return val;
57}
58EXPORT_SYMBOL(generic_atomic64_read);
59
60void generic_atomic64_set(atomic64_t *v, s64 i)
61{
62 unsigned long flags;
63 arch_spinlock_t *lock = lock_addr(v);
64
65 local_irq_save(flags);
66 arch_spin_lock(lock);
67 v->counter = i;
68 arch_spin_unlock(lock);
69 local_irq_restore(flags);
70}
71EXPORT_SYMBOL(generic_atomic64_set);
72
73#define ATOMIC64_OP(op, c_op) \
74void generic_atomic64_##op(s64 a, atomic64_t *v) \
75{ \
76 unsigned long flags; \
77 arch_spinlock_t *lock = lock_addr(v); \
78 \
79 local_irq_save(flags); \
80 arch_spin_lock(lock); \
81 v->counter c_op a; \
82 arch_spin_unlock(lock); \
83 local_irq_restore(flags); \
84} \
85EXPORT_SYMBOL(generic_atomic64_##op);
86
87#define ATOMIC64_OP_RETURN(op, c_op) \
88s64 generic_atomic64_##op##_return(s64 a, atomic64_t *v) \
89{ \
90 unsigned long flags; \
91 arch_spinlock_t *lock = lock_addr(v); \
92 s64 val; \
93 \
94 local_irq_save(flags); \
95 arch_spin_lock(lock); \
96 val = (v->counter c_op a); \
97 arch_spin_unlock(lock); \
98 local_irq_restore(flags); \
99 return val; \
100} \
101EXPORT_SYMBOL(generic_atomic64_##op##_return);
102
103#define ATOMIC64_FETCH_OP(op, c_op) \
104s64 generic_atomic64_fetch_##op(s64 a, atomic64_t *v) \
105{ \
106 unsigned long flags; \
107 arch_spinlock_t *lock = lock_addr(v); \
108 s64 val; \
109 \
110 local_irq_save(flags); \
111 arch_spin_lock(lock); \
112 val = v->counter; \
113 v->counter c_op a; \
114 arch_spin_unlock(lock); \
115 local_irq_restore(flags); \
116 return val; \
117} \
118EXPORT_SYMBOL(generic_atomic64_fetch_##op);
119
120#define ATOMIC64_OPS(op, c_op) \
121 ATOMIC64_OP(op, c_op) \
122 ATOMIC64_OP_RETURN(op, c_op) \
123 ATOMIC64_FETCH_OP(op, c_op)
124
125ATOMIC64_OPS(add, +=)
126ATOMIC64_OPS(sub, -=)
127
128#undef ATOMIC64_OPS
129#define ATOMIC64_OPS(op, c_op) \
130 ATOMIC64_OP(op, c_op) \
131 ATOMIC64_FETCH_OP(op, c_op)
132
133ATOMIC64_OPS(and, &=)
134ATOMIC64_OPS(or, |=)
135ATOMIC64_OPS(xor, ^=)
136
137#undef ATOMIC64_OPS
138#undef ATOMIC64_FETCH_OP
139#undef ATOMIC64_OP
140
141s64 generic_atomic64_dec_if_positive(atomic64_t *v)
142{
143 unsigned long flags;
144 arch_spinlock_t *lock = lock_addr(v);
145 s64 val;
146
147 local_irq_save(flags);
148 arch_spin_lock(lock);
149 val = v->counter - 1;
150 if (val >= 0)
151 v->counter = val;
152 arch_spin_unlock(lock);
153 local_irq_restore(flags);
154 return val;
155}
156EXPORT_SYMBOL(generic_atomic64_dec_if_positive);
157
158s64 generic_atomic64_cmpxchg(atomic64_t *v, s64 o, s64 n)
159{
160 unsigned long flags;
161 arch_spinlock_t *lock = lock_addr(v);
162 s64 val;
163
164 local_irq_save(flags);
165 arch_spin_lock(lock);
166 val = v->counter;
167 if (val == o)
168 v->counter = n;
169 arch_spin_unlock(lock);
170 local_irq_restore(flags);
171 return val;
172}
173EXPORT_SYMBOL(generic_atomic64_cmpxchg);
174
175s64 generic_atomic64_xchg(atomic64_t *v, s64 new)
176{
177 unsigned long flags;
178 arch_spinlock_t *lock = lock_addr(v);
179 s64 val;
180
181 local_irq_save(flags);
182 arch_spin_lock(lock);
183 val = v->counter;
184 v->counter = new;
185 arch_spin_unlock(lock);
186 local_irq_restore(flags);
187 return val;
188}
189EXPORT_SYMBOL(generic_atomic64_xchg);
190
191s64 generic_atomic64_fetch_add_unless(atomic64_t *v, s64 a, s64 u)
192{
193 unsigned long flags;
194 arch_spinlock_t *lock = lock_addr(v);
195 s64 val;
196
197 local_irq_save(flags);
198 arch_spin_lock(lock);
199 val = v->counter;
200 if (val != u)
201 v->counter += a;
202 arch_spin_unlock(lock);
203 local_irq_restore(flags);
204
205 return val;
206}
207EXPORT_SYMBOL(generic_atomic64_fetch_add_unless);
208

source code of linux/lib/atomic64.c