LXR linux/arch/tile/include/asm/spinlock

   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 */
  36static 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
  52void 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
  57int arch_spin_trylock(arch_spinlock_t *lock);
  58
  59static 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
  67void 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 */
  87static 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 */
  95static 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 */
 103void arch_read_lock(arch_rwlock_t *rwlock);
 104
 105/**
 106 * arch_write_lock() - acquire a write lock.
 107 */
 108void arch_write_lock(arch_rwlock_t *rwlock);
 109
 110/**
 111 * arch_read_trylock() - try to acquire a read lock.
 112 */
 113int arch_read_trylock(arch_rwlock_t *rwlock);
 114
 115/**
 116 * arch_write_trylock() - try to acquire a write lock.
 117 */
 118int arch_write_trylock(arch_rwlock_t *rwlock);
 119
 120/**
 121 * arch_read_unlock() - release a read lock.
 122 */
 123void arch_read_unlock(arch_rwlock_t *rwlock);
 124
 125/**
 126 * arch_write_unlock() - release a write lock.
 127 */
 128void 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 */
 134