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 */
130