PCI: Tolerate hierarchies with no Root Port
[linux-2.6-block.git] / lib / atomic64.c
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
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
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
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
73 #define ATOMIC64_OP(op, c_op)                                           \
74 void 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 }                                                                       \
83 EXPORT_SYMBOL(atomic64_##op);
84
85 #define ATOMIC64_OP_RETURN(op, c_op)                                    \
86 long 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 }                                                                       \
97 EXPORT_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
103 ATOMIC64_OPS(add, +=)
104 ATOMIC64_OPS(sub, -=)
105
106 #undef ATOMIC64_OPS
107 #undef ATOMIC64_OP_RETURN
108 #undef ATOMIC64_OP
109
110 long 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 }
123 EXPORT_SYMBOL(atomic64_dec_if_positive);
124
125 long 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 }
138 EXPORT_SYMBOL(atomic64_cmpxchg);
139
140 long 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 }
152 EXPORT_SYMBOL(atomic64_xchg);
153
154 int 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 }
168 EXPORT_SYMBOL(atomic64_add_unless);