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          * Use READ_ONCE() to ensure that calling this in a loop is OK.
  45          */
  46         int curr = READ_ONCE(lock->current_ticket);
  47         int next = READ_ONCE(lock->next_ticket);
  48
  49         return next != curr;
  50 }
  51
  52 void arch_spin_lock(arch_spinlock_t *lock);
  53
  54 /* We cannot take an interrupt after getting a ticket, so don't enable them. */
  55 #define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
  56
  57 int arch_spin_trylock(arch_spinlock_t *lock);
  58
  59 static inline void arch_spin_unlock(arch_spinlock_t *lock)
  60 {
  61         /* For efficiency, overlap fetching the old ticket with the wmb(). */
  62         int old_ticket = lock->current_ticket;
  63         wmb();  /* guarantee anything modified under the lock is visible */
  64         lock->current_ticket = old_ticket + TICKET_QUANTUM;
  65 }
  66
  67 void arch_spin_unlock_wait(arch_spinlock_t *lock);
  68
  69 /*
  70  * Read-write spinlocks, allowing multiple readers
  71  * but only one writer.
  72  *
  73  * We use a "tns/store-back" technique on a single word to manage
  74  * the lock state, looping around to retry if the tns returns 1.
  75  */
  76
  77 /* Internal layout of the word; do not use. */
  78 #define _WR_NEXT_SHIFT  8
  79 #define _WR_CURR_SHIFT  16
  80 #define _WR_WIDTH       8
  81 #define _RD_COUNT_SHIFT 24
  82 #define _RD_COUNT_WIDTH 8
  83
  84 /**
  85  * arch_read_can_lock() - would read_trylock() succeed?
  86  */
  87 static inline int arch_read_can_lock(arch_rwlock_t *rwlock)
  88 {
  89         return (rwlock->lock << _RD_COUNT_WIDTH) == 0;
  90 }
  91
  92 /**
  93  * arch_write_can_lock() - would write_trylock() succeed?
  94  */
  95 static inline int arch_write_can_lock(arch_rwlock_t *rwlock)
  96 {
  97         return rwlock->lock == 0;
  98 }
  99
 100 /**
 101  * arch_read_lock() - acquire a read lock.
 102  */
 103 void arch_read_lock(arch_rwlock_t *rwlock);
 104
 105 /**
 106  * arch_write_lock() - acquire a write lock.
 107  */
 108 void arch_write_lock(arch_rwlock_t *rwlock);
 109
 110 /**
 111  * arch_read_trylock() - try to acquire a read lock.
 112  */
 113 int arch_read_trylock(arch_rwlock_t *rwlock);
 114
 115 /**
 116  * arch_write_trylock() - try to acquire a write lock.
 117  */
 118 int arch_write_trylock(arch_rwlock_t *rwlock);
 119
 120 /**
 121  * arch_read_unlock() - release a read lock.
 122  */
 123 void arch_read_unlock(arch_rwlock_t *rwlock);
 124
 125 /**
 126  * arch_write_unlock() - release a write lock.
 127  */
 128 void arch_write_unlock(arch_rwlock_t *rwlock);
 129
 130 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
 131 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
 132
 133 #endif /* _ASM_TILE_SPINLOCK_32_H */