arch/ia64/include/asm/rwsem.h

   1 /*
   2  * R/W semaphores for ia64
   3  *
   4  * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>
   5  * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>
   6  * Copyright (C) 2005 Christoph Lameter <cl@linux.com>
   7  *
   8  * Based on asm-i386/rwsem.h and other architecture implementation.
   9  *
  10  * The MSW of the count is the negated number of active writers and
  11  * waiting lockers, and the LSW is the total number of active locks.
  12  *
  13  * The lock count is initialized to 0 (no active and no waiting lockers).
  14  *
  15  * When a writer subtracts WRITE_BIAS, it'll get 0xffffffff00000001 for
  16  * the case of an uncontended lock. Readers increment by 1 and see a positive
  17  * value when uncontended, negative if there are writers (and maybe) readers
  18  * waiting (in which case it goes to sleep).
  19  */
  20
  21 #ifndef _ASM_IA64_RWSEM_H
  22 #define _ASM_IA64_RWSEM_H
  23
  24 #ifndef _LINUX_RWSEM_H
  25 #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
  26 #endif
  27
  28 #include <asm/intrinsics.h>
  29
  30 #define RWSEM_UNLOCKED_VALUE            __IA64_UL_CONST(0x0000000000000000)
  31 #define RWSEM_ACTIVE_BIAS               (1L)
  32 #define RWSEM_ACTIVE_MASK               (0xffffffffL)
  33 #define RWSEM_WAITING_BIAS              (-0x100000000L)
  34 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  35 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  36
  37 /*
  38  * lock for reading
  39  */
  40 static inline void
  41 __down_read (struct rw_semaphore *sem)
  42 {
  43         long result = ia64_fetchadd8_acq((unsigned long *)&sem->count.counter, 1);
  44
  45         if (result < 0)
  46                 rwsem_down_read_failed(sem);
  47 }
  48
  49 /*
  50  * lock for writing
  51  */
  52 static inline long
  53 ___down_write (struct rw_semaphore *sem)
  54 {
  55         long old, new;
  56
  57         do {
  58                 old = atomic_long_read(&sem->count);
  59                 new = old + RWSEM_ACTIVE_WRITE_BIAS;
  60         } while (atomic_long_cmpxchg_acquire(&sem->count, old, new) != old);
  61
  62         return old;
  63 }
  64
  65 static inline void
  66 __down_write (struct rw_semaphore *sem)
  67 {
  68         if (___down_write(sem))
  69                 rwsem_down_write_failed(sem);
  70 }
  71
  72 static inline int
  73 __down_write_killable (struct rw_semaphore *sem)
  74 {
  75         if (___down_write(sem))
  76                 if (IS_ERR(rwsem_down_write_failed_killable(sem)))
  77                         return -EINTR;
  78
  79         return 0;
  80 }
  81
  82 /*
  83  * unlock after reading
  84  */
  85 static inline void
  86 __up_read (struct rw_semaphore *sem)
  87 {
  88         long result = ia64_fetchadd8_rel((unsigned long *)&sem->count.counter, -1);
  89
  90         if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
  91                 rwsem_wake(sem);
  92 }
  93
  94 /*
  95  * unlock after writing
  96  */
  97 static inline void
  98 __up_write (struct rw_semaphore *sem)
  99 {
 100         long old, new;
 101
 102         do {
 103                 old = atomic_long_read(&sem->count);
 104                 new = old - RWSEM_ACTIVE_WRITE_BIAS;
 105         } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
 106
 107         if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
 108                 rwsem_wake(sem);
 109 }
 110
 111 /*
 112  * trylock for reading -- returns 1 if successful, 0 if contention
 113  */
 114 static inline int
 115 __down_read_trylock (struct rw_semaphore *sem)
 116 {
 117         long tmp;
 118         while ((tmp = atomic_long_read(&sem->count)) >= 0) {
 119                 if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, tmp+1)) {
 120                         return 1;
 121                 }
 122         }
 123         return 0;
 124 }
 125
 126 /*
 127  * trylock for writing -- returns 1 if successful, 0 if contention
 128  */
 129 static inline int
 130 __down_write_trylock (struct rw_semaphore *sem)
 131 {
 132         long tmp = atomic_long_cmpxchg_acquire(&sem->count,
 133                         RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS);
 134         return tmp == RWSEM_UNLOCKED_VALUE;
 135 }
 136
 137 /*
 138  * downgrade write lock to read lock
 139  */
 140 static inline void
 141 __downgrade_write (struct rw_semaphore *sem)
 142 {
 143         long old, new;
 144
 145         do {
 146                 old = atomic_long_read(&sem->count);
 147                 new = old - RWSEM_WAITING_BIAS;
 148         } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
 149
 150         if (old < 0)
 151                 rwsem_downgrade_wake(sem);
 152 }
 153
 154 #endif /* _ASM_IA64_RWSEM_H */