arch/parisc/include/asm/spinlock.h

   1 #ifndef __ASM_SPINLOCK_H
   2 #define __ASM_SPINLOCK_H
   3
   4 #include <asm/barrier.h>
   5 #include <asm/ldcw.h>
   6 #include <asm/processor.h>
   7 #include <asm/spinlock_types.h>
   8
   9 static inline int arch_spin_is_locked(arch_spinlock_t *x)
  10 {
  11         volatile unsigned int *a = __ldcw_align(x);
  12         return *a == 0;
  13 }
  14
  15 #define arch_spin_lock(lock) arch_spin_lock_flags(lock, 0)
  16
  17 static inline void arch_spin_unlock_wait(arch_spinlock_t *x)
  18 {
  19         volatile unsigned int *a = __ldcw_align(x);
  20
  21         smp_cond_load_acquire(a, VAL);
  22 }
  23
  24 static inline void arch_spin_lock_flags(arch_spinlock_t *x,
  25                                          unsigned long flags)
  26 {
  27         volatile unsigned int *a;
  28
  29         mb();
  30         a = __ldcw_align(x);
  31         while (__ldcw(a) == 0)
  32                 while (*a == 0)
  33                         if (flags & PSW_SM_I) {
  34                                 local_irq_enable();
  35                                 cpu_relax();
  36                                 local_irq_disable();
  37                         } else
  38                                 cpu_relax();
  39         mb();
  40 }
  41
  42 static inline void arch_spin_unlock(arch_spinlock_t *x)
  43 {
  44         volatile unsigned int *a;
  45         mb();
  46         a = __ldcw_align(x);
  47         *a = 1;
  48         mb();
  49 }
  50
  51 static inline int arch_spin_trylock(arch_spinlock_t *x)
  52 {
  53         volatile unsigned int *a;
  54         int ret;
  55
  56         mb();
  57         a = __ldcw_align(x);
  58         ret = __ldcw(a) != 0;
  59         mb();
  60
  61         return ret;
  62 }
  63
  64 /*
  65  * Read-write spinlocks, allowing multiple readers but only one writer.
  66  * Linux rwlocks are unfair to writers; they can be starved for an indefinite
  67  * time by readers.  With care, they can also be taken in interrupt context.
  68  *
  69  * In the PA-RISC implementation, we have a spinlock and a counter.
  70  * Readers use the lock to serialise their access to the counter (which
  71  * records how many readers currently hold the lock).
  72  * Writers hold the spinlock, preventing any readers or other writers from
  73  * grabbing the rwlock.
  74  */
  75
  76 /* Note that we have to ensure interrupts are disabled in case we're
  77  * interrupted by some other code that wants to grab the same read lock */
  78 static  __inline__ void arch_read_lock(arch_rwlock_t *rw)
  79 {
  80         unsigned long flags;
  81         local_irq_save(flags);
  82         arch_spin_lock_flags(&rw->lock, flags);
  83         rw->counter++;
  84         arch_spin_unlock(&rw->lock);
  85         local_irq_restore(flags);
  86 }
  87
  88 /* Note that we have to ensure interrupts are disabled in case we're
  89  * interrupted by some other code that wants to grab the same read lock */
  90 static  __inline__ void arch_read_unlock(arch_rwlock_t *rw)
  91 {
  92         unsigned long flags;
  93         local_irq_save(flags);
  94         arch_spin_lock_flags(&rw->lock, flags);
  95         rw->counter--;
  96         arch_spin_unlock(&rw->lock);
  97         local_irq_restore(flags);
  98 }
  99
 100 /* Note that we have to ensure interrupts are disabled in case we're
 101  * interrupted by some other code that wants to grab the same read lock */
 102 static __inline__ int arch_read_trylock(arch_rwlock_t *rw)
 103 {
 104         unsigned long flags;
 105  retry:
 106         local_irq_save(flags);
 107         if (arch_spin_trylock(&rw->lock)) {
 108                 rw->counter++;
 109                 arch_spin_unlock(&rw->lock);
 110                 local_irq_restore(flags);
 111                 return 1;
 112         }
 113
 114         local_irq_restore(flags);
 115         /* If write-locked, we fail to acquire the lock */
 116         if (rw->counter < 0)
 117                 return 0;
 118
 119         /* Wait until we have a realistic chance at the lock */
 120         while (arch_spin_is_locked(&rw->lock) && rw->counter >= 0)
 121                 cpu_relax();
 122
 123         goto retry;
 124 }
 125
 126 /* Note that we have to ensure interrupts are disabled in case we're
 127  * interrupted by some other code that wants to read_trylock() this lock */
 128 static __inline__ void arch_write_lock(arch_rwlock_t *rw)
 129 {
 130         unsigned long flags;
 131 retry:
 132         local_irq_save(flags);
 133         arch_spin_lock_flags(&rw->lock, flags);
 134
 135         if (rw->counter != 0) {
 136                 arch_spin_unlock(&rw->lock);
 137                 local_irq_restore(flags);
 138
 139                 while (rw->counter != 0)
 140                         cpu_relax();
 141
 142                 goto retry;
 143         }
 144
 145         rw->counter = -1; /* mark as write-locked */
 146         mb();
 147         local_irq_restore(flags);
 148 }
 149
 150 static __inline__ void arch_write_unlock(arch_rwlock_t *rw)
 151 {
 152         rw->counter = 0;
 153         arch_spin_unlock(&rw->lock);
 154 }
 155
 156 /* Note that we have to ensure interrupts are disabled in case we're
 157  * interrupted by some other code that wants to read_trylock() this lock */
 158 static __inline__ int arch_write_trylock(arch_rwlock_t *rw)
 159 {
 160         unsigned long flags;
 161         int result = 0;
 162
 163         local_irq_save(flags);
 164         if (arch_spin_trylock(&rw->lock)) {
 165                 if (rw->counter == 0) {
 166                         rw->counter = -1;
 167                         result = 1;
 168                 } else {
 169                         /* Read-locked.  Oh well. */
 170                         arch_spin_unlock(&rw->lock);
 171                 }
 172         }
 173         local_irq_restore(flags);
 174
 175         return result;
 176 }
 177
 178 /*
 179  * read_can_lock - would read_trylock() succeed?
 180  * @lock: the rwlock in question.
 181  */
 182 static __inline__ int arch_read_can_lock(arch_rwlock_t *rw)
 183 {
 184         return rw->counter >= 0;
 185 }
 186
 187 /*
 188  * write_can_lock - would write_trylock() succeed?
 189  * @lock: the rwlock in question.
 190  */
 191 static __inline__ int arch_write_can_lock(arch_rwlock_t *rw)
 192 {
 193         return !rw->counter;
 194 }
 195
 196 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
 197 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
 198
 199 #endif /* __ASM_SPINLOCK_H */