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         /*
  26          * This smp_mb() is technically superfluous, we only need the one
  27          * after the lock for providing the ACQUIRE semantics.
  28          * However doing the "right" thing was regressing hackbench
  29          * so keeping this, pending further investigation
  30          */
  31         smp_mb();
  32
  33         __asm__ __volatile__(
  34         "1:     ex  %0, [%1]            \n"
  35         "       breq  %0, %2, 1b        \n"
  36         : "+&r" (tmp)
  37         : "r"(&(lock->slock)), "ir"(__ARCH_SPIN_LOCK_LOCKED__)
  38         : "memory");
  39
  40         /*
  41          * ACQUIRE barrier to ensure load/store after taking the lock
  42          * don't "bleed-up" out of the critical section (leak-in is allowed)
  43          * http://www.spinics.net/lists/kernel/msg2010409.html
  44          *
  45          * ARCv2 only has load-load, store-store and all-all barrier
  46          * thus need the full all-all barrier
  47          */
  48         smp_mb();
  49 }
  50
  51 static inline int arch_spin_trylock(arch_spinlock_t *lock)
  52 {
  53         unsigned int tmp = __ARCH_SPIN_LOCK_LOCKED__;
  54
  55         smp_mb();
  56
  57         __asm__ __volatile__(
  58         "1:     ex  %0, [%1]            \n"
  59         : "+r" (tmp)
  60         : "r"(&(lock->slock))
  61         : "memory");
  62
  63         smp_mb();
  64
  65         return (tmp == __ARCH_SPIN_LOCK_UNLOCKED__);
  66 }
  67
  68 static inline void arch_spin_unlock(arch_spinlock_t *lock)
  69 {
  70         unsigned int tmp = __ARCH_SPIN_LOCK_UNLOCKED__;
  71
  72         /*
  73          * RELEASE barrier: given the instructions avail on ARCv2, full barrier
  74          * is the only option
  75          */
  76         smp_mb();
  77
  78         __asm__ __volatile__(
  79         "       ex  %0, [%1]            \n"
  80         : "+r" (tmp)
  81         : "r"(&(lock->slock))
  82         : "memory");
  83
  84         /*
  85          * superfluous, but keeping for now - see pairing version in
  86          * arch_spin_lock above
  87          */
  88         smp_mb();
  89 }
  90
  91 /*
  92  * Read-write spinlocks, allowing multiple readers but only one writer.
  93  *
  94  * The spinlock itself is contained in @counter and access to it is
  95  * serialized with @lock_mutex.
  96  *
  97  * Unfair locking as Writers could be starved indefinitely by Reader(s)
  98  */
  99
 100 /* Would read_trylock() succeed? */
 101 #define arch_read_can_lock(x)   ((x)->counter > 0)
 102
 103 /* Would write_trylock() succeed? */
 104 #define arch_write_can_lock(x)  ((x)->counter == __ARCH_RW_LOCK_UNLOCKED__)
 105
 106 /* 1 - lock taken successfully */
 107 static inline int arch_read_trylock(arch_rwlock_t *rw)
 108 {
 109         int ret = 0;
 110
 111         arch_spin_lock(&(rw->lock_mutex));
 112
 113         /*
 114          * zero means writer holds the lock exclusively, deny Reader.
 115          * Otherwise grant lock to first/subseq reader
 116          */
 117         if (rw->counter > 0) {
 118                 rw->counter--;
 119                 ret = 1;
 120         }
 121
 122         arch_spin_unlock(&(rw->lock_mutex));
 123
 124         smp_mb();
 125         return ret;
 126 }
 127
 128 /* 1 - lock taken successfully */
 129 static inline int arch_write_trylock(arch_rwlock_t *rw)
 130 {
 131         int ret = 0;
 132
 133         arch_spin_lock(&(rw->lock_mutex));
 134
 135         /*
 136          * If reader(s) hold lock (lock < __ARCH_RW_LOCK_UNLOCKED__),
 137          * deny writer. Otherwise if unlocked grant to writer
 138          * Hence the claim that Linux rwlocks are unfair to writers.
 139          * (can be starved for an indefinite time by readers).
 140          */
 141         if (rw->counter == __ARCH_RW_LOCK_UNLOCKED__) {
 142                 rw->counter = 0;
 143                 ret = 1;
 144         }
 145         arch_spin_unlock(&(rw->lock_mutex));
 146
 147         return ret;
 148 }
 149
 150 static inline void arch_read_lock(arch_rwlock_t *rw)
 151 {
 152         while (!arch_read_trylock(rw))
 153                 cpu_relax();
 154 }
 155
 156 static inline void arch_write_lock(arch_rwlock_t *rw)
 157 {
 158         while (!arch_write_trylock(rw))
 159                 cpu_relax();
 160 }
 161
 162 static inline void arch_read_unlock(arch_rwlock_t *rw)
 163 {
 164         arch_spin_lock(&(rw->lock_mutex));
 165         rw->counter++;
 166         arch_spin_unlock(&(rw->lock_mutex));
 167 }
 168
 169 static inline void arch_write_unlock(arch_rwlock_t *rw)
 170 {
 171         arch_spin_lock(&(rw->lock_mutex));
 172         rw->counter = __ARCH_RW_LOCK_UNLOCKED__;
 173         arch_spin_unlock(&(rw->lock_mutex));
 174 }
 175
 176 #define arch_read_lock_flags(lock, flags)       arch_read_lock(lock)
 177 #define arch_write_lock_flags(lock, flags)      arch_write_lock(lock)
 178
 179 #define arch_spin_relax(lock)   cpu_relax()
 180 #define arch_read_relax(lock)   cpu_relax()
 181 #define arch_write_relax(lock)  cpu_relax()
 182
 183 #endif /* __ASM_SPINLOCK_H */