1/*
2 * asm-ia64/rwsem.h: R/W semaphores for ia64
3 *
4 * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>
5 * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>
6 * Copyright (C) 2005 Christoph Lameter <clameter@sgi.com>
7 *
8 * Based on asm-i386/rwsem.h and other architecture implementation.
9 *
10 * The MSW of the count is the negated number of active writers and
11 * waiting lockers, and the LSW is the total number of active locks.
12 *
13 * The lock count is initialized to 0 (no active and no waiting lockers).
14 *
15 * When a writer subtracts WRITE_BIAS, it'll get 0xffffffff00000001 for
16 * the case of an uncontended lock. Readers increment by 1 and see a positive
17 * value when uncontended, negative if there are writers (and maybe) readers
18 * waiting (in which case it goes to sleep).
19 */
20
21#ifndef _ASM_IA64_RWSEM_H
22#define _ASM_IA64_RWSEM_H
23
24#include <linux/list.h>
25#include <linux/spinlock.h>
26
27#include <asm/intrinsics.h>
28
29/*
30 * the semaphore definition
31 */
32struct rw_semaphore {
33	signed long		count;
34	spinlock_t		wait_lock;
35	struct list_head	wait_list;
36};
37
38#define RWSEM_UNLOCKED_VALUE		__IA64_UL_CONST(0x0000000000000000)
39#define RWSEM_ACTIVE_BIAS		__IA64_UL_CONST(0x0000000000000001)
40#define RWSEM_ACTIVE_MASK		__IA64_UL_CONST(0x00000000ffffffff)
41#define RWSEM_WAITING_BIAS		-__IA64_UL_CONST(0x0000000100000000)
42#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
43#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
44
45#define __RWSEM_INITIALIZER(name) \
46	{ RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
47	  LIST_HEAD_INIT((name).wait_list) }
48
49#define DECLARE_RWSEM(name) \
50	struct rw_semaphore name = __RWSEM_INITIALIZER(name)
51
52extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
53extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
54extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem);
55extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
56
57static inline void
58init_rwsem (struct rw_semaphore *sem)
59{
60	sem->count = RWSEM_UNLOCKED_VALUE;
61	spin_lock_init(&sem->wait_lock);
62	INIT_LIST_HEAD(&sem->wait_list);
63}
64
65/*
66 * lock for reading
67 */
68static inline void
69__down_read (struct rw_semaphore *sem)
70{
71	long result = ia64_fetchadd8_acq((unsigned long *)&sem->count, 1);
72
73	if (result < 0)
74		rwsem_down_read_failed(sem);
75}
76
77/*
78 * lock for writing
79 */
80static inline void
81__down_write (struct rw_semaphore *sem)
82{
83	long old, new;
84
85	do {
86		old = sem->count;
87		new = old + RWSEM_ACTIVE_WRITE_BIAS;
88	} while (cmpxchg_acq(&sem->count, old, new) != old);
89
90	if (old != 0)
91		rwsem_down_write_failed(sem);
92}
93
94/*
95 * unlock after reading
96 */
97static inline void
98__up_read (struct rw_semaphore *sem)
99{
100	long result = ia64_fetchadd8_rel((unsigned long *)&sem->count, -1);
101
102	if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
103		rwsem_wake(sem);
104}
105
106/*
107 * unlock after writing
108 */
109static inline void
110__up_write (struct rw_semaphore *sem)
111{
112	long old, new;
113
114	do {
115		old = sem->count;
116		new = old - RWSEM_ACTIVE_WRITE_BIAS;
117	} while (cmpxchg_rel(&sem->count, old, new) != old);
118
119	if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
120		rwsem_wake(sem);
121}
122
123/*
124 * trylock for reading -- returns 1 if successful, 0 if contention
125 */
126static inline int
127__down_read_trylock (struct rw_semaphore *sem)
128{
129	long tmp;
130	while ((tmp = sem->count) >= 0) {
131		if (tmp == cmpxchg_acq(&sem->count, tmp, tmp+1)) {
132			return 1;
133		}
134	}
135	return 0;
136}
137
138/*
139 * trylock for writing -- returns 1 if successful, 0 if contention
140 */
141static inline int
142__down_write_trylock (struct rw_semaphore *sem)
143{
144	long tmp = cmpxchg_acq(&sem->count, RWSEM_UNLOCKED_VALUE,
145			      RWSEM_ACTIVE_WRITE_BIAS);
146	return tmp == RWSEM_UNLOCKED_VALUE;
147}
148
149/*
150 * downgrade write lock to read lock
151 */
152static inline void
153__downgrade_write (struct rw_semaphore *sem)
154{
155	long old, new;
156
157	do {
158		old = sem->count;
159		new = old - RWSEM_WAITING_BIAS;
160	} while (cmpxchg_rel(&sem->count, old, new) != old);
161
162	if (old < 0)
163		rwsem_downgrade_wake(sem);
164}
165
166/*
167 * Implement atomic add functionality.  These used to be "inline" functions, but GCC v3.1
168 * doesn't quite optimize this stuff right and ends up with bad calls to fetchandadd.
169 */
170#define rwsem_atomic_add(delta, sem)	atomic64_add(delta, (atomic64_t *)(&(sem)->count))
171#define rwsem_atomic_update(delta, sem)	atomic64_add_return(delta, (atomic64_t *)(&(sem)->count))
172
173static inline int rwsem_is_locked(struct rw_semaphore *sem)
174{
175	return (sem->count != 0);
176}
177
178#endif /* _ASM_IA64_RWSEM_H */
179