arch/parisc/include/asm/spinlock.h

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