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/module.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         spinlock_t lock;
  33         char pad[L1_CACHE_BYTES];
  34 } atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp;
  35
  36 static inline 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
  45 long long atomic64_read(const atomic64_t *v)
  46 {
  47         unsigned long flags;
  48         spinlock_t *lock = lock_addr(v);
  49         long long val;
  50
  51         spin_lock_irqsave(lock, flags);
  52         val = v->counter;
  53         spin_unlock_irqrestore(lock, flags);
  54         return val;
  55 }
  56 EXPORT_SYMBOL(atomic64_read);
  57
  58 void atomic64_set(atomic64_t *v, long long i)
  59 {
  60         unsigned long flags;
  61         spinlock_t *lock = lock_addr(v);
  62
  63         spin_lock_irqsave(lock, flags);
  64         v->counter = i;
  65         spin_unlock_irqrestore(lock, flags);
  66 }
  67 EXPORT_SYMBOL(atomic64_set);
  68
  69 void atomic64_add(long long a, atomic64_t *v)
  70 {
  71         unsigned long flags;
  72         spinlock_t *lock = lock_addr(v);
  73
  74         spin_lock_irqsave(lock, flags);
  75         v->counter += a;
  76         spin_unlock_irqrestore(lock, flags);
  77 }
  78 EXPORT_SYMBOL(atomic64_add);
  79
  80 long long atomic64_add_return(long long a, atomic64_t *v)
  81 {
  82         unsigned long flags;
  83         spinlock_t *lock = lock_addr(v);
  84         long long val;
  85
  86         spin_lock_irqsave(lock, flags);
  87         val = v->counter += a;
  88         spin_unlock_irqrestore(lock, flags);
  89         return val;
  90 }
  91 EXPORT_SYMBOL(atomic64_add_return);
  92
  93 void atomic64_sub(long long a, atomic64_t *v)
  94 {
  95         unsigned long flags;
  96         spinlock_t *lock = lock_addr(v);
  97
  98         spin_lock_irqsave(lock, flags);
  99         v->counter -= a;
 100         spin_unlock_irqrestore(lock, flags);
 101 }
 102 EXPORT_SYMBOL(atomic64_sub);
 103
 104 long long atomic64_sub_return(long long a, atomic64_t *v)
 105 {
 106         unsigned long flags;
 107         spinlock_t *lock = lock_addr(v);
 108         long long val;
 109
 110         spin_lock_irqsave(lock, flags);
 111         val = v->counter -= a;
 112         spin_unlock_irqrestore(lock, flags);
 113         return val;
 114 }
 115 EXPORT_SYMBOL(atomic64_sub_return);
 116
 117 long long atomic64_dec_if_positive(atomic64_t *v)
 118 {
 119         unsigned long flags;
 120         spinlock_t *lock = lock_addr(v);
 121         long long val;
 122
 123         spin_lock_irqsave(lock, flags);
 124         val = v->counter - 1;
 125         if (val >= 0)
 126                 v->counter = val;
 127         spin_unlock_irqrestore(lock, flags);
 128         return val;
 129 }
 130 EXPORT_SYMBOL(atomic64_dec_if_positive);
 131
 132 long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
 133 {
 134         unsigned long flags;
 135         spinlock_t *lock = lock_addr(v);
 136         long long val;
 137
 138         spin_lock_irqsave(lock, flags);
 139         val = v->counter;
 140         if (val == o)
 141                 v->counter = n;
 142         spin_unlock_irqrestore(lock, flags);
 143         return val;
 144 }
 145 EXPORT_SYMBOL(atomic64_cmpxchg);
 146
 147 long long atomic64_xchg(atomic64_t *v, long long new)
 148 {
 149         unsigned long flags;
 150         spinlock_t *lock = lock_addr(v);
 151         long long val;
 152
 153         spin_lock_irqsave(lock, flags);
 154         val = v->counter;
 155         v->counter = new;
 156         spin_unlock_irqrestore(lock, flags);
 157         return val;
 158 }
 159 EXPORT_SYMBOL(atomic64_xchg);
 160
 161 int atomic64_add_unless(atomic64_t *v, long long a, long long u)
 162 {
 163         unsigned long flags;
 164         spinlock_t *lock = lock_addr(v);
 165         int ret = 0;
 166
 167         spin_lock_irqsave(lock, flags);
 168         if (v->counter != u) {
 169                 v->counter += a;
 170                 ret = 1;
 171         }
 172         spin_unlock_irqrestore(lock, flags);
 173         return ret;
 174 }
 175 EXPORT_SYMBOL(atomic64_add_unless);
 176
 177 static int init_atomic64_lock(void)
 178 {
 179         int i;
 180
 181         for (i = 0; i < NR_LOCKS; ++i)
 182                 spin_lock_init(&atomic64_lock[i].lock);
 183         return 0;
 184 }
 185
 186 pure_initcall(init_atomic64_lock);