arch/tile/include/asm/spinlock_32.h

   1 /*
   2  * Copyright 2010 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  *
  14  * 32-bit SMP spinlocks.
  15  */
  16
  17 #ifndef _ASM_TILE_SPINLOCK_32_H
  18 #define _ASM_TILE_SPINLOCK_32_H
  19
  20 #include <asm/atomic.h>
  21 #include <asm/page.h>
  22 #include <asm/system.h>
  23 #include <linux/compiler.h>
  24
  25 /*
  26  * We only use even ticket numbers so the '1' inserted by a tns is
  27  * an unambiguous "ticket is busy" flag.
  28  */
  29 #define TICKET_QUANTUM 2
  30
  31
  32 /*
  33  * SMP ticket spinlocks, allowing only a single CPU anywhere
  34  *
  35  * (the type definitions are in asm/spinlock_types.h)
  36  */
  37 static inline int arch_spin_is_locked(arch_spinlock_t *lock)
  38 {
  39         /*
  40          * Note that even if a new ticket is in the process of being
  41          * acquired, so lock->next_ticket is 1, it's still reasonable
  42          * to claim the lock is held, since it will be momentarily
  43          * if not already.  There's no need to wait for a "valid"
  44          * lock->next_ticket to become available.
  45          */
  46         return lock->next_ticket != lock->current_ticket;
  47 }
  48
  49 void arch_spin_lock(arch_spinlock_t *lock);
  50
  51 /* We cannot take an interrupt after getting a ticket, so don't enable them. */
  52 #define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
  53
  54 int arch_spin_trylock(arch_spinlock_t *lock);
  55
  56 static inline void arch_spin_unlock(arch_spinlock_t *lock)
  57 {
  58         /* For efficiency, overlap fetching the old ticket with the wmb(). */
  59         int old_ticket = lock->current_ticket;
  60         wmb();  /* guarantee anything modified under the lock is visible */
  61         lock->current_ticket = old_ticket + TICKET_QUANTUM;
  62 }
  63
  64 void arch_spin_unlock_wait(arch_spinlock_t *lock);
  65
  66 /*
  67  * Read-write spinlocks, allowing multiple readers
  68  * but only one writer.
  69  *
  70  * We use a "tns/store-back" technique on a single word to manage
  71  * the lock state, looping around to retry if the tns returns 1.
  72  */
  73
  74 /* Internal layout of the word; do not use. */
  75 #define _WR_NEXT_SHIFT  8
  76 #define _WR_CURR_SHIFT  16
  77 #define _WR_WIDTH       8
  78 #define _RD_COUNT_SHIFT 24
  79 #define _RD_COUNT_WIDTH 8
  80
  81 /* Internal functions; do not use. */
  82 void arch_read_lock_slow(arch_rwlock_t *, u32);
  83 int arch_read_trylock_slow(arch_rwlock_t *);
  84 void arch_read_unlock_slow(arch_rwlock_t *);
  85 void arch_write_lock_slow(arch_rwlock_t *, u32);
  86 void arch_write_unlock_slow(arch_rwlock_t *, u32);
  87
  88 /**
  89  * arch_read_can_lock() - would read_trylock() succeed?
  90  */
  91 static inline int arch_read_can_lock(arch_rwlock_t *rwlock)
  92 {
  93         return (rwlock->lock << _RD_COUNT_WIDTH) == 0;
  94 }
  95
  96 /**
  97  * arch_write_can_lock() - would write_trylock() succeed?
  98  */
  99 static inline int arch_write_can_lock(arch_rwlock_t *rwlock)
 100 {
 101         return rwlock->lock == 0;
 102 }
 103
 104 /**
 105  * arch_read_lock() - acquire a read lock.
 106  */
 107 static inline void arch_read_lock(arch_rwlock_t *rwlock)
 108 {
 109         u32 val = __insn_tns((int *)&rwlock->lock);
 110         if (unlikely(val << _RD_COUNT_WIDTH)) {
 111                 arch_read_lock_slow(rwlock, val);
 112                 return;
 113         }
 114         rwlock->lock = val + (1 << _RD_COUNT_SHIFT);
 115 }
 116
 117 /**
 118  * arch_read_lock() - acquire a write lock.
 119  */
 120 static inline void arch_write_lock(arch_rwlock_t *rwlock)
 121 {
 122         u32 val = __insn_tns((int *)&rwlock->lock);
 123         if (unlikely(val != 0)) {
 124                 arch_write_lock_slow(rwlock, val);
 125                 return;
 126         }
 127         rwlock->lock = 1 << _WR_NEXT_SHIFT;
 128 }
 129
 130 /**
 131  * arch_read_trylock() - try to acquire a read lock.
 132  */
 133 static inline int arch_read_trylock(arch_rwlock_t *rwlock)
 134 {
 135         int locked;
 136         u32 val = __insn_tns((int *)&rwlock->lock);
 137         if (unlikely(val & 1)) {
 138                 return arch_read_trylock_slow(rwlock);
 139         }
 140         locked = (val << _RD_COUNT_WIDTH) == 0;
 141         rwlock->lock = val + (locked << _RD_COUNT_SHIFT);
 142         return locked;
 143 }
 144
 145 /**
 146  * arch_write_trylock() - try to acquire a write lock.
 147  */
 148 static inline int arch_write_trylock(arch_rwlock_t *rwlock)
 149 {
 150         u32 val = __insn_tns((int *)&rwlock->lock);
 151
 152         /*
 153          * If a tns is in progress, or there's a waiting or active locker,
 154          * or active readers, we can't take the lock, so give up.
 155          */
 156         if (unlikely(val != 0)) {
 157                 if (!(val & 1))
 158                         rwlock->lock = val;
 159                 return 0;
 160         }
 161
 162         /* Set the "next" field to mark it locked. */
 163         rwlock->lock = 1 << _WR_NEXT_SHIFT;
 164         return 1;
 165 }
 166
 167 /**
 168  * arch_read_unlock() - release a read lock.
 169  */
 170 static inline void arch_read_unlock(arch_rwlock_t *rwlock)
 171 {
 172         u32 val;
 173         mb();  /* guarantee anything modified under the lock is visible */
 174         val = __insn_tns((int *)&rwlock->lock);
 175         if (unlikely(val & 1)) {
 176                 arch_read_unlock_slow(rwlock);
 177                 return;
 178         }
 179         rwlock->lock = val - (1 << _RD_COUNT_SHIFT);
 180 }
 181
 182 /**
 183  * arch_write_unlock() - release a write lock.
 184  */
 185 static inline void arch_write_unlock(arch_rwlock_t *rwlock)
 186 {
 187         u32 val;
 188         mb();  /* guarantee anything modified under the lock is visible */
 189         val = __insn_tns((int *)&rwlock->lock);
 190         if (unlikely(val != (1 << _WR_NEXT_SHIFT))) {
 191                 arch_write_unlock_slow(rwlock, val);
 192                 return;
 193         }
 194         rwlock->lock = 0;
 195 }
 196
 197 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
 198 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
 199
 200 #endif /* _ASM_TILE_SPINLOCK_32_H */