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 */