spinlock_32.h

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/*
 * Copyright 2010 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 *
 * 32-bit SMP spinlocks.
 */

#ifndef _ASM_TILE_SPINLOCK_32_H
#define _ASM_TILE_SPINLOCK_32_H

#include <linux/atomic.h>
#include <asm/page.h>
#include <linux/compiler.h>

/*
 * We only use even ticket numbers so the '1' inserted by a tns is
 * an unambiguous "ticket is busy" flag.
 */
#define TICKET_QUANTUM 2


/*
 * SMP ticket spinlocks, allowing only a single CPU anywhere
 *
 * (the type definitions are in asm/spinlock_types.h)
 */
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
    /*
     * Note that even if a new ticket is in the process of being
     * acquired, so lock->next_ticket is 1, it's still reasonable
     * to claim the lock is held, since it will be momentarily
     * if not already.  There's no need to wait for a "valid"
     * lock->next_ticket to become available.
     */
    return lock->next_ticket != lock->current_ticket;
}

void arch_spin_lock(arch_spinlock_t *lock);

/* We cannot take an interrupt after getting a ticket, so don't enable them. */
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)

int arch_spin_trylock(arch_spinlock_t *lock);

static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
    /* For efficiency, overlap fetching the old ticket with the wmb(). */
    int old_ticket = lock->current_ticket;
    wmb();  /* guarantee anything modified under the lock is visible */
    lock->current_ticket = old_ticket + TICKET_QUANTUM;
}

void arch_spin_unlock_wait(arch_spinlock_t *lock);

/*
 * Read-write spinlocks, allowing multiple readers
 * but only one writer.
 *
 * We use a "tns/store-back" technique on a single word to manage
 * the lock state, looping around to retry if the tns returns 1.
 */

/* Internal layout of the word; do not use. */
#define _WR_NEXT_SHIFT  8
#define _WR_CURR_SHIFT  16
#define _WR_WIDTH       8
#define _RD_COUNT_SHIFT 24
#define _RD_COUNT_WIDTH 8

static inline int arch_read_can_lock(arch_rwlock_t *rwlock)
{
    return (rwlock->lock << _RD_COUNT_WIDTH) == 0;
}

static inline int arch_write_can_lock(arch_rwlock_t *rwlock)
{
    return rwlock->lock == 0;
}

void arch_read_lock(arch_rwlock_t *rwlock);

void arch_write_lock(arch_rwlock_t *rwlock);

int arch_read_trylock(arch_rwlock_t *rwlock);

int arch_write_trylock(arch_rwlock_t *rwlock);

void arch_read_unlock(arch_rwlock_t *rwlock);

void arch_write_unlock(arch_rwlock_t *rwlock);

#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)

#endif /* _ASM_TILE_SPINLOCK_32_H */