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);