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 <linux/atomic.h>
  21 #include <asm/page.h>
  22 #include <linux/compiler.h>
  23
  24 /*
  25  * We only use even ticket numbers so the '1' inserted by a tns is
  26  * an unambiguous "ticket is busy" flag.
  27  */
  28 #define TICKET_QUANTUM 2
  29
  30
  31 /*
  32  * SMP ticket spinlocks, allowing only a single CPU anywhere
  33  *
  34  * (the type definitions are in asm/spinlock_types.h)
  35  */
  36 static inline int arch_spin_is_locked(arch_spinlock_t *lock)
  37 {
  38         /*
  39          * Note that even if a new ticket is in the process of being
  40          * acquired, so lock->next_ticket is 1, it's still reasonable
  41          * to claim the lock is held, since it will be momentarily
  42          * if not already.  There's no need to wait for a "valid"
  43          * lock->next_ticket to become available.
  44          */
  45         return lock->next_ticket != lock->current_ticket;
  46 }
  47
  48 void arch_spin_lock(arch_spinlock_t *lock);
  49
  50 /* We cannot take an interrupt after getting a ticket, so don't enable them. */
  51 #define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
  52
  53 int arch_spin_trylock(arch_spinlock_t *lock);
  54
  55 static inline void arch_spin_unlock(arch_spinlock_t *lock)
  56 {
  57         /* For efficiency, overlap fetching the old ticket with the wmb(). */
  58         int old_ticket = lock->current_ticket;
  59         wmb();  /* guarantee anything modified under the lock is visible */
  60         lock->current_ticket = old_ticket + TICKET_QUANTUM;
  61 }
  62
  63 void arch_spin_unlock_wait(arch_spinlock_t *lock);
  64
  65 /*
  66  * Read-write spinlocks, allowing multiple readers
  67  * but only one writer.
  68  *
  69  * We use a "tns/store-back" technique on a single word to manage
  70  * the lock state, looping around to retry if the tns returns 1.
  71  */
  72
  73 /* Internal layout of the word; do not use. */
  74 #define _WR_NEXT_SHIFT  8
  75 #define _WR_CURR_SHIFT  16
  76 #define _WR_WIDTH       8
  77 #define _RD_COUNT_SHIFT 24
  78 #define _RD_COUNT_WIDTH 8
  79
  80 /**
  81  * arch_read_can_lock() - would read_trylock() succeed?
  82  */
  83 static inline int arch_read_can_lock(arch_rwlock_t *rwlock)
  84 {
  85         return (rwlock->lock << _RD_COUNT_WIDTH) == 0;
  86 }
  87
  88 /**
  89  * arch_write_can_lock() - would write_trylock() succeed?
  90  */
  91 static inline int arch_write_can_lock(arch_rwlock_t *rwlock)
  92 {
  93         return rwlock->lock == 0;
  94 }
  95
  96 /**
  97  * arch_read_lock() - acquire a read lock.
  98  */
  99 void arch_read_lock(arch_rwlock_t *rwlock);
 100
 101 /**
 102  * arch_write_lock() - acquire a write lock.
 103  */
 104 void arch_write_lock(arch_rwlock_t *rwlock);
 105
 106 /**
 107  * arch_read_trylock() - try to acquire a read lock.
 108  */
 109 int arch_read_trylock(arch_rwlock_t *rwlock);
 110
 111 /**
 112  * arch_write_trylock() - try to acquire a write lock.
 113  */
 114 int arch_write_trylock(arch_rwlock_t *rwlock);
 115
 116 /**
 117  * arch_read_unlock() - release a read lock.
 118  */
 119 void arch_read_unlock(arch_rwlock_t *rwlock);
 120
 121 /**
 122  * arch_write_unlock() - release a write lock.
 123  */
 124 void arch_write_unlock(arch_rwlock_t *rwlock);
 125
 126 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
 127 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
 128
 129 #endif /* _ASM_TILE_SPINLOCK_32_H */