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	 */
 45	return lock->next_ticket != lock->current_ticket;
 46}
 47
 48void 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
 53int arch_spin_trylock(arch_spinlock_t *lock);
 54
 55static 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
 63void 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 */
 83static 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 */
 91static 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 */
 99void arch_read_lock(arch_rwlock_t *rwlock);
100
101/**
102 * arch_write_lock() - acquire a write lock.
103 */
104void arch_write_lock(arch_rwlock_t *rwlock);
105
106/**
107 * arch_read_trylock() - try to acquire a read lock.
108 */
109int arch_read_trylock(arch_rwlock_t *rwlock);
110
111/**
112 * arch_write_trylock() - try to acquire a write lock.
113 */
114int arch_write_trylock(arch_rwlock_t *rwlock);
115
116/**
117 * arch_read_unlock() - release a read lock.
118 */
119void arch_read_unlock(arch_rwlock_t *rwlock);
120
121/**
122 * arch_write_unlock() - release a write lock.
123 */
124void 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 */