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 ATOMIC64_OP(and, &=)
 106 ATOMIC64_OP(or, |=)
 107 ATOMIC64_OP(xor, ^=)
 108
 109 #undef ATOMIC64_OPS
 110 #undef ATOMIC64_OP_RETURN
 111 #undef ATOMIC64_OP
 112
 113 long long atomic64_dec_if_positive(atomic64_t *v)
 114 {
 115         unsigned long flags;
 116         raw_spinlock_t *lock = lock_addr(v);
 117         long long val;
 118
 119         raw_spin_lock_irqsave(lock, flags);
 120         val = v->counter - 1;
 121         if (val >= 0)
 122                 v->counter = val;
 123         raw_spin_unlock_irqrestore(lock, flags);
 124         return val;
 125 }
 126 EXPORT_SYMBOL(atomic64_dec_if_positive);
 127
 128 long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
 129 {
 130         unsigned long flags;
 131         raw_spinlock_t *lock = lock_addr(v);
 132         long long val;
 133
 134         raw_spin_lock_irqsave(lock, flags);
 135         val = v->counter;
 136         if (val == o)
 137                 v->counter = n;
 138         raw_spin_unlock_irqrestore(lock, flags);
 139         return val;
 140 }
 141 EXPORT_SYMBOL(atomic64_cmpxchg);
 142
 143 long long atomic64_xchg(atomic64_t *v, long long new)
 144 {
 145         unsigned long flags;
 146         raw_spinlock_t *lock = lock_addr(v);
 147         long long val;
 148
 149         raw_spin_lock_irqsave(lock, flags);
 150         val = v->counter;
 151         v->counter = new;
 152         raw_spin_unlock_irqrestore(lock, flags);
 153         return val;
 154 }
 155 EXPORT_SYMBOL(atomic64_xchg);
 156
 157 int atomic64_add_unless(atomic64_t *v, long long a, long long u)
 158 {
 159         unsigned long flags;
 160         raw_spinlock_t *lock = lock_addr(v);
 161         int ret = 0;
 162
 163         raw_spin_lock_irqsave(lock, flags);
 164         if (v->counter != u) {
 165                 v->counter += a;
 166                 ret = 1;
 167         }
 168         raw_spin_unlock_irqrestore(lock, flags);
 169         return ret;
 170 }
 171 EXPORT_SYMBOL(atomic64_add_unless);