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 */
31static 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
40static 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
49long 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}
60EXPORT_SYMBOL(atomic64_read);
61
62void 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}
71EXPORT_SYMBOL(atomic64_set);
72
73#define ATOMIC64_OP(op, c_op)						\
74void atomic64_##op(long long a, atomic64_t *v)				\
75{									\
76	unsigned long flags;						\
77	raw_spinlock_t *lock = lock_addr(v);				\
78									\
79	raw_spin_lock_irqsave(lock, flags);				\
80	v->counter c_op a;						\
81	raw_spin_unlock_irqrestore(lock, flags);			\
82}									\
83EXPORT_SYMBOL(atomic64_##op);
84
85#define ATOMIC64_OP_RETURN(op, c_op)					\
86long long atomic64_##op##_return(long long a, atomic64_t *v)		\
87{									\
88	unsigned long flags;						\
89	raw_spinlock_t *lock = lock_addr(v);				\
90	long long val;							\
91									\
92	raw_spin_lock_irqsave(lock, flags);				\
93	val = (v->counter c_op a);					\
94	raw_spin_unlock_irqrestore(lock, flags);			\
95	return val;							\
96}									\
97EXPORT_SYMBOL(atomic64_##op##_return);
98
99#define ATOMIC64_OPS(op, c_op)						\
100	ATOMIC64_OP(op, c_op)						\
101	ATOMIC64_OP_RETURN(op, c_op)
102
103ATOMIC64_OPS(add, +=)
104ATOMIC64_OPS(sub, -=)
105
106#undef ATOMIC64_OPS
107#undef ATOMIC64_OP_RETURN
108#undef ATOMIC64_OP
109
110long long atomic64_dec_if_positive(atomic64_t *v)
111{
112	unsigned long flags;
113	raw_spinlock_t *lock = lock_addr(v);
114	long long val;
115
116	raw_spin_lock_irqsave(lock, flags);
117	val = v->counter - 1;
118	if (val >= 0)
119		v->counter = val;
120	raw_spin_unlock_irqrestore(lock, flags);
121	return val;
122}
123EXPORT_SYMBOL(atomic64_dec_if_positive);
124
125long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
126{
127	unsigned long flags;
128	raw_spinlock_t *lock = lock_addr(v);
129	long long val;
130
131	raw_spin_lock_irqsave(lock, flags);
132	val = v->counter;
133	if (val == o)
134		v->counter = n;
135	raw_spin_unlock_irqrestore(lock, flags);
136	return val;
137}
138EXPORT_SYMBOL(atomic64_cmpxchg);
139
140long long atomic64_xchg(atomic64_t *v, long long new)
141{
142	unsigned long flags;
143	raw_spinlock_t *lock = lock_addr(v);
144	long long val;
145
146	raw_spin_lock_irqsave(lock, flags);
147	val = v->counter;
148	v->counter = new;
149	raw_spin_unlock_irqrestore(lock, flags);
150	return val;
151}
152EXPORT_SYMBOL(atomic64_xchg);
153
154int atomic64_add_unless(atomic64_t *v, long long a, long long u)
155{
156	unsigned long flags;
157	raw_spinlock_t *lock = lock_addr(v);
158	int ret = 0;
159
160	raw_spin_lock_irqsave(lock, flags);
161	if (v->counter != u) {
162		v->counter += a;
163		ret = 1;
164	}
165	raw_spin_unlock_irqrestore(lock, flags);
166	return ret;
167}
168EXPORT_SYMBOL(atomic64_add_unless);
169