arch/tile/include/asm/spinlock_32.h

/*
 * 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.
	 * Use READ_ONCE() to ensure that calling this in a loop is OK.
	 */
	int curr = READ_ONCE(lock->current_ticket);
	int next = READ_ONCE(lock->next_ticket);

	return next != curr;
}

void arch_spin_lock(arch_spinlock_t *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;
}

/*
 * 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

/**
 * arch_read_lock() - acquire a read lock.
 */
void arch_read_lock(arch_rwlock_t *rwlock);

/**
 * arch_write_lock() - acquire a write lock.
 */
void arch_write_lock(arch_rwlock_t *rwlock);

/**
 * arch_read_trylock() - try to acquire a read lock.
 */
int arch_read_trylock(arch_rwlock_t *rwlock);

/**
 * arch_write_trylock() - try to acquire a write lock.
 */
int arch_write_trylock(arch_rwlock_t *rwlock);

/**
 * arch_read_unlock() - release a read lock.
 */
void arch_read_unlock(arch_rwlock_t *rwlock);

/**
 * arch_write_unlock() - release a write lock.
 */
void arch_write_unlock(arch_rwlock_t *rwlock);

#endif /* _ASM_TILE_SPINLOCK_32_H */