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Linux kernel mirror (for testing)
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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
67/*
68 * Read-write spinlocks, allowing multiple readers
69 * but only one writer.
70 *
71 * We use a "tns/store-back" technique on a single word to manage
72 * the lock state, looping around to retry if the tns returns 1.
73 */
74
75/* Internal layout of the word; do not use. */
76#define _WR_NEXT_SHIFT 8
77#define _WR_CURR_SHIFT 16
78#define _WR_WIDTH 8
79#define _RD_COUNT_SHIFT 24
80#define _RD_COUNT_WIDTH 8
81
82/**
83 * arch_read_can_lock() - would read_trylock() succeed?
84 */
85static inline int arch_read_can_lock(arch_rwlock_t *rwlock)
86{
87 return (rwlock->lock << _RD_COUNT_WIDTH) == 0;
88}
89
90/**
91 * arch_write_can_lock() - would write_trylock() succeed?
92 */
93static inline int arch_write_can_lock(arch_rwlock_t *rwlock)
94{
95 return rwlock->lock == 0;
96}
97
98/**
99 * arch_read_lock() - acquire a read lock.
100 */
101void arch_read_lock(arch_rwlock_t *rwlock);
102
103/**
104 * arch_write_lock() - acquire a write lock.
105 */
106void arch_write_lock(arch_rwlock_t *rwlock);
107
108/**
109 * arch_read_trylock() - try to acquire a read lock.
110 */
111int arch_read_trylock(arch_rwlock_t *rwlock);
112
113/**
114 * arch_write_trylock() - try to acquire a write lock.
115 */
116int arch_write_trylock(arch_rwlock_t *rwlock);
117
118/**
119 * arch_read_unlock() - release a read lock.
120 */
121void arch_read_unlock(arch_rwlock_t *rwlock);
122
123/**
124 * arch_write_unlock() - release a write lock.
125 */
126void arch_write_unlock(arch_rwlock_t *rwlock);
127
128#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
129#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
130
131#endif /* _ASM_TILE_SPINLOCK_32_H */