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 <asm/atomic.h>
  17
  18 /*
  19  * We use a hashed array of spinlocks to provide exclusive access
  20  * to each atomic64_t variable.  Since this is expected to used on
  21  * systems with small numbers of CPUs (<= 4 or so), we use a
  22  * relatively small array of 16 spinlocks to avoid wasting too much
  23  * memory on the spinlock array.
  24  */
  25 #define NR_LOCKS        16
  26
  27 /*
  28  * Ensure each lock is in a separate cacheline.
  29  */
  30 static union {
  31         spinlock_t lock;
  32         char pad[L1_CACHE_BYTES];
  33 } atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp;
  34
  35 static inline spinlock_t *lock_addr(const atomic64_t *v)
  36 {
  37         unsigned long addr = (unsigned long) v;
  38
  39         addr >>= L1_CACHE_SHIFT;
  40         addr ^= (addr >> 8) ^ (addr >> 16);
  41         return &atomic64_lock[addr & (NR_LOCKS - 1)].lock;
  42 }
  43
  44 long long atomic64_read(const atomic64_t *v)
  45 {
  46         unsigned long flags;
  47         spinlock_t *lock = lock_addr(v);
  48         long long val;
  49
  50         spin_lock_irqsave(lock, flags);
  51         val = v->counter;
  52         spin_unlock_irqrestore(lock, flags);
  53         return val;
  54 }
  55
  56 void atomic64_set(atomic64_t *v, long long i)
  57 {
  58         unsigned long flags;
  59         spinlock_t *lock = lock_addr(v);
  60
  61         spin_lock_irqsave(lock, flags);
  62         v->counter = i;
  63         spin_unlock_irqrestore(lock, flags);
  64 }
  65
  66 void atomic64_add(long long a, atomic64_t *v)
  67 {
  68         unsigned long flags;
  69         spinlock_t *lock = lock_addr(v);
  70
  71         spin_lock_irqsave(lock, flags);
  72         v->counter += a;
  73         spin_unlock_irqrestore(lock, flags);
  74 }
  75
  76 long long atomic64_add_return(long long a, atomic64_t *v)
  77 {
  78         unsigned long flags;
  79         spinlock_t *lock = lock_addr(v);
  80         long long val;
  81
  82         spin_lock_irqsave(lock, flags);
  83         val = v->counter += a;
  84         spin_unlock_irqrestore(lock, flags);
  85         return val;
  86 }
  87
  88 void atomic64_sub(long long a, atomic64_t *v)
  89 {
  90         unsigned long flags;
  91         spinlock_t *lock = lock_addr(v);
  92
  93         spin_lock_irqsave(lock, flags);
  94         v->counter -= a;
  95         spin_unlock_irqrestore(lock, flags);
  96 }
  97
  98 long long atomic64_sub_return(long long a, atomic64_t *v)
  99 {
 100         unsigned long flags;
 101         spinlock_t *lock = lock_addr(v);
 102         long long val;
 103
 104         spin_lock_irqsave(lock, flags);
 105         val = v->counter -= a;
 106         spin_unlock_irqrestore(lock, flags);
 107         return val;
 108 }
 109
 110 long long atomic64_dec_if_positive(atomic64_t *v)
 111 {
 112         unsigned long flags;
 113         spinlock_t *lock = lock_addr(v);
 114         long long val;
 115
 116         spin_lock_irqsave(lock, flags);
 117         val = v->counter - 1;
 118         if (val >= 0)
 119                 v->counter = val;
 120         spin_unlock_irqrestore(lock, flags);
 121         return val;
 122 }
 123
 124 long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
 125 {
 126         unsigned long flags;
 127         spinlock_t *lock = lock_addr(v);
 128         long long val;
 129
 130         spin_lock_irqsave(lock, flags);
 131         val = v->counter;
 132         if (val == o)
 133                 v->counter = n;
 134         spin_unlock_irqrestore(lock, flags);
 135         return val;
 136 }
 137
 138 long long atomic64_xchg(atomic64_t *v, long long new)
 139 {
 140         unsigned long flags;
 141         spinlock_t *lock = lock_addr(v);
 142         long long val;
 143
 144         spin_lock_irqsave(lock, flags);
 145         val = v->counter;
 146         v->counter = new;
 147         spin_unlock_irqrestore(lock, flags);
 148         return val;
 149 }
 150
 151 int atomic64_add_unless(atomic64_t *v, long long a, long long u)
 152 {
 153         unsigned long flags;
 154         spinlock_t *lock = lock_addr(v);
 155         int ret = 1;
 156
 157         spin_lock_irqsave(lock, flags);
 158         if (v->counter != u) {
 159                 v->counter += a;
 160                 ret = 0;
 161         }
 162         spin_unlock_irqrestore(lock, flags);
 163         return ret;
 164 }
 165
 166 static int init_atomic64_lock(void)
 167 {
 168         int i;
 169
 170         for (i = 0; i < NR_LOCKS; ++i)
 171                 spin_lock_init(&atomic64_lock[i].lock);
 172         return 0;
 173 }
 174
 175 pure_initcall(init_atomic64_lock);