arch/ia64/include/asm/rwsem.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * R/W semaphores for ia64
   4  *
   5  * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>
   6  * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>
   7  * Copyright (C) 2005 Christoph Lameter <cl@linux.com>
   8  *
   9  * Based on asm-i386/rwsem.h and other architecture implementation.
  10  *
  11  * The MSW of the count is the negated number of active writers and
  12  * waiting lockers, and the LSW is the total number of active locks.
  13  *
  14  * The lock count is initialized to 0 (no active and no waiting lockers).
  15  *
  16  * When a writer subtracts WRITE_BIAS, it'll get 0xffffffff00000001 for
  17  * the case of an uncontended lock. Readers increment by 1 and see a positive
  18  * value when uncontended, negative if there are writers (and maybe) readers
  19  * waiting (in which case it goes to sleep).
  20  */
  21
  22 #ifndef _ASM_IA64_RWSEM_H
  23 #define _ASM_IA64_RWSEM_H
  24
  25 #ifndef _LINUX_RWSEM_H
  26 #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
  27 #endif
  28
  29 #include <asm/intrinsics.h>
  30
  31 #define RWSEM_UNLOCKED_VALUE            __IA64_UL_CONST(0x0000000000000000)
  32 #define RWSEM_ACTIVE_BIAS               (1L)
  33 #define RWSEM_ACTIVE_MASK               (0xffffffffL)
  34 #define RWSEM_WAITING_BIAS              (-0x100000000L)
  35 #define RWSEM_ACTIVE_READ_BIAS          RWSEM_ACTIVE_BIAS
  36 #define RWSEM_ACTIVE_WRITE_BIAS         (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
  37
  38 /*
  39  * lock for reading
  40  */
  41 static inline void
  42 __down_read (struct rw_semaphore *sem)
  43 {
  44         long result = ia64_fetchadd8_acq((unsigned long *)&sem->count.counter, 1);
  45
  46         if (result < 0)
  47                 rwsem_down_read_failed(sem);
  48 }
  49
  50 /*
  51  * lock for writing
  52  */
  53 static inline long
  54 ___down_write (struct rw_semaphore *sem)
  55 {
  56         long old, new;
  57
  58         do {
  59                 old = atomic_long_read(&sem->count);
  60                 new = old + RWSEM_ACTIVE_WRITE_BIAS;
  61         } while (atomic_long_cmpxchg_acquire(&sem->count, old, new) != old);
  62
  63         return old;
  64 }
  65
  66 static inline void
  67 __down_write (struct rw_semaphore *sem)
  68 {
  69         if (___down_write(sem))
  70                 rwsem_down_write_failed(sem);
  71 }
  72
  73 static inline int
  74 __down_write_killable (struct rw_semaphore *sem)
  75 {
  76         if (___down_write(sem))
  77                 if (IS_ERR(rwsem_down_write_failed_killable(sem)))
  78                         return -EINTR;
  79
  80         return 0;
  81 }
  82
  83 /*
  84  * unlock after reading
  85  */
  86 static inline void
  87 __up_read (struct rw_semaphore *sem)
  88 {
  89         long result = ia64_fetchadd8_rel((unsigned long *)&sem->count.counter, -1);
  90
  91         if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
  92                 rwsem_wake(sem);
  93 }
  94
  95 /*
  96  * unlock after writing
  97  */
  98 static inline void
  99 __up_write (struct rw_semaphore *sem)
 100 {
 101         long old, new;
 102
 103         do {
 104                 old = atomic_long_read(&sem->count);
 105                 new = old - RWSEM_ACTIVE_WRITE_BIAS;
 106         } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
 107
 108         if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
 109                 rwsem_wake(sem);
 110 }
 111
 112 /*
 113  * trylock for reading -- returns 1 if successful, 0 if contention
 114  */
 115 static inline int
 116 __down_read_trylock (struct rw_semaphore *sem)
 117 {
 118         long tmp;
 119         while ((tmp = atomic_long_read(&sem->count)) >= 0) {
 120                 if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, tmp+1)) {
 121                         return 1;
 122                 }
 123         }
 124         return 0;
 125 }
 126
 127 /*
 128  * trylock for writing -- returns 1 if successful, 0 if contention
 129  */
 130 static inline int
 131 __down_write_trylock (struct rw_semaphore *sem)
 132 {
 133         long tmp = atomic_long_cmpxchg_acquire(&sem->count,
 134                         RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS);
 135         return tmp == RWSEM_UNLOCKED_VALUE;
 136 }
 137
 138 /*
 139  * downgrade write lock to read lock
 140  */
 141 static inline void
 142 __downgrade_write (struct rw_semaphore *sem)
 143 {
 144         long old, new;
 145
 146         do {
 147                 old = atomic_long_read(&sem->count);
 148                 new = old - RWSEM_WAITING_BIAS;
 149         } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
 150
 151         if (old < 0)
 152                 rwsem_downgrade_wake(sem);
 153 }
 154
 155 #endif /* _ASM_IA64_RWSEM_H */