arch/arc/include/asm/spinlock.h

   1 /*
   2  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  */
   8
   9 #ifndef __ASM_SPINLOCK_H
  10 #define __ASM_SPINLOCK_H
  11
  12 #include <asm/spinlock_types.h>
  13 #include <asm/processor.h>
  14 #include <asm/barrier.h>
  15
  16 #define arch_spin_is_locked(x)  ((x)->slock != __ARCH_SPIN_LOCK_UNLOCKED__)
  17 #define arch_spin_lock_flags(lock, flags)       arch_spin_lock(lock)
  18 #define arch_spin_unlock_wait(x) \
  19         do { while (arch_spin_is_locked(x)) cpu_relax(); } while (0)
  20
  21 static inline void arch_spin_lock(arch_spinlock_t *lock)
  22 {
  23         unsigned int tmp = __ARCH_SPIN_LOCK_LOCKED__;
  24
  25         __asm__ __volatile__(
  26         "1:     ex  %0, [%1]            \n"
  27         "       breq  %0, %2, 1b        \n"
  28         : "+&r" (tmp)
  29         : "r"(&(lock->slock)), "ir"(__ARCH_SPIN_LOCK_LOCKED__)
  30         : "memory");
  31 }
  32
  33 static inline int arch_spin_trylock(arch_spinlock_t *lock)
  34 {
  35         unsigned int tmp = __ARCH_SPIN_LOCK_LOCKED__;
  36
  37         __asm__ __volatile__(
  38         "1:     ex  %0, [%1]            \n"
  39         : "+r" (tmp)
  40         : "r"(&(lock->slock))
  41         : "memory");
  42
  43         return (tmp == __ARCH_SPIN_LOCK_UNLOCKED__);
  44 }
  45
  46 static inline void arch_spin_unlock(arch_spinlock_t *lock)
  47 {
  48         unsigned int tmp = __ARCH_SPIN_LOCK_UNLOCKED__;
  49
  50         __asm__ __volatile__(
  51         "       ex  %0, [%1]            \n"
  52         : "+r" (tmp)
  53         : "r"(&(lock->slock))
  54         : "memory");
  55
  56         smp_mb();
  57 }
  58
  59 /*
  60  * Read-write spinlocks, allowing multiple readers but only one writer.
  61  *
  62  * The spinlock itself is contained in @counter and access to it is
  63  * serialized with @lock_mutex.
  64  *
  65  * Unfair locking as Writers could be starved indefinitely by Reader(s)
  66  */
  67
  68 /* Would read_trylock() succeed? */
  69 #define arch_read_can_lock(x)   ((x)->counter > 0)
  70
  71 /* Would write_trylock() succeed? */
  72 #define arch_write_can_lock(x)  ((x)->counter == __ARCH_RW_LOCK_UNLOCKED__)
  73
  74 /* 1 - lock taken successfully */
  75 static inline int arch_read_trylock(arch_rwlock_t *rw)
  76 {
  77         int ret = 0;
  78
  79         arch_spin_lock(&(rw->lock_mutex));
  80
  81         /*
  82          * zero means writer holds the lock exclusively, deny Reader.
  83          * Otherwise grant lock to first/subseq reader
  84          */
  85         if (rw->counter > 0) {
  86                 rw->counter--;
  87                 ret = 1;
  88         }
  89
  90         arch_spin_unlock(&(rw->lock_mutex));
  91
  92         smp_mb();
  93         return ret;
  94 }
  95
  96 /* 1 - lock taken successfully */
  97 static inline int arch_write_trylock(arch_rwlock_t *rw)
  98 {
  99         int ret = 0;
 100
 101         arch_spin_lock(&(rw->lock_mutex));
 102
 103         /*
 104          * If reader(s) hold lock (lock < __ARCH_RW_LOCK_UNLOCKED__),
 105          * deny writer. Otherwise if unlocked grant to writer
 106          * Hence the claim that Linux rwlocks are unfair to writers.
 107          * (can be starved for an indefinite time by readers).
 108          */
 109         if (rw->counter == __ARCH_RW_LOCK_UNLOCKED__) {
 110                 rw->counter = 0;
 111                 ret = 1;
 112         }
 113         arch_spin_unlock(&(rw->lock_mutex));
 114
 115         return ret;
 116 }
 117
 118 static inline void arch_read_lock(arch_rwlock_t *rw)
 119 {
 120         while (!arch_read_trylock(rw))
 121                 cpu_relax();
 122 }
 123
 124 static inline void arch_write_lock(arch_rwlock_t *rw)
 125 {
 126         while (!arch_write_trylock(rw))
 127                 cpu_relax();
 128 }
 129
 130 static inline void arch_read_unlock(arch_rwlock_t *rw)
 131 {
 132         arch_spin_lock(&(rw->lock_mutex));
 133         rw->counter++;
 134         arch_spin_unlock(&(rw->lock_mutex));
 135 }
 136
 137 static inline void arch_write_unlock(arch_rwlock_t *rw)
 138 {
 139         arch_spin_lock(&(rw->lock_mutex));
 140         rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
 141         arch_spin_unlock(&(rw->lock_mutex));
 142 }
 143
 144 #define arch_read_lock_flags(lock, flags)       arch_read_lock(lock)
 145 #define arch_write_lock_flags(lock, flags)      arch_write_lock(lock)
 146
 147 #define arch_spin_relax(lock)   cpu_relax()
 148 #define arch_read_relax(lock)   cpu_relax()
 149 #define arch_write_relax(lock)  cpu_relax()
 150
 151 #endif /* __ASM_SPINLOCK_H */