1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3 * R/W semaphores for ia64
4 *
5 * Copyright (C) 2003 Ken Chen <kenneth.w.chen@intel.com>
6 * Copyright (C) 2003 Asit Mallick <asit.k.mallick@intel.com>
7 * Copyright (C) 2005 Christoph Lameter <cl@linux.com>
8 *
9 * Based on asm-i386/rwsem.h and other architecture implementation.
10 *
11 * The MSW of the count is the negated number of active writers and
12 * waiting lockers, and the LSW is the total number of active locks.
13 *
14 * The lock count is initialized to 0 (no active and no waiting lockers).
15 *
16 * When a writer subtracts WRITE_BIAS, it'll get 0xffffffff00000001 for
17 * the case of an uncontended lock. Readers increment by 1 and see a positive
18 * value when uncontended, negative if there are writers (and maybe) readers
19 * waiting (in which case it goes to sleep).
20 */
21
22 #ifndef _ASM_IA64_RWSEM_H
23 #define _ASM_IA64_RWSEM_H
24
25 #ifndef _LINUX_RWSEM_H
26 #error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
27 #endif
28
29 #include <asm/intrinsics.h>
30
31 #define RWSEM_UNLOCKED_VALUE __IA64_UL_CONST(0x0000000000000000)
32 #define RWSEM_ACTIVE_BIAS (1L)
33 #define RWSEM_ACTIVE_MASK (0xffffffffL)
34 #define RWSEM_WAITING_BIAS (-0x100000000L)
35 #define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
36 #define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
37
38 /*
39 * lock for reading
40 */
41 static inline int
___down_read(struct rw_semaphore * sem)42 ___down_read (struct rw_semaphore *sem)
43 {
44 long result = ia64_fetchadd8_acq((unsigned long *)&sem->count.counter, 1);
45
46 return (result < 0);
47 }
48
49 static inline void
__down_read(struct rw_semaphore * sem)50 __down_read (struct rw_semaphore *sem)
51 {
52 if (___down_read(sem))
53 rwsem_down_read_failed(sem);
54 }
55
56 static inline int
__down_read_killable(struct rw_semaphore * sem)57 __down_read_killable (struct rw_semaphore *sem)
58 {
59 if (___down_read(sem))
60 if (IS_ERR(rwsem_down_read_failed_killable(sem)))
61 return -EINTR;
62
63 return 0;
64 }
65
66 /*
67 * lock for writing
68 */
69 static inline long
___down_write(struct rw_semaphore * sem)70 ___down_write (struct rw_semaphore *sem)
71 {
72 long old, new;
73
74 do {
75 old = atomic_long_read(&sem->count);
76 new = old + RWSEM_ACTIVE_WRITE_BIAS;
77 } while (atomic_long_cmpxchg_acquire(&sem->count, old, new) != old);
78
79 return old;
80 }
81
82 static inline void
__down_write(struct rw_semaphore * sem)83 __down_write (struct rw_semaphore *sem)
84 {
85 if (___down_write(sem))
86 rwsem_down_write_failed(sem);
87 }
88
89 static inline int
__down_write_killable(struct rw_semaphore * sem)90 __down_write_killable (struct rw_semaphore *sem)
91 {
92 if (___down_write(sem)) {
93 if (IS_ERR(rwsem_down_write_failed_killable(sem)))
94 return -EINTR;
95 }
96
97 return 0;
98 }
99
100 /*
101 * unlock after reading
102 */
103 static inline void
__up_read(struct rw_semaphore * sem)104 __up_read (struct rw_semaphore *sem)
105 {
106 long result = ia64_fetchadd8_rel((unsigned long *)&sem->count.counter, -1);
107
108 if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
109 rwsem_wake(sem);
110 }
111
112 /*
113 * unlock after writing
114 */
115 static inline void
__up_write(struct rw_semaphore * sem)116 __up_write (struct rw_semaphore *sem)
117 {
118 long old, new;
119
120 do {
121 old = atomic_long_read(&sem->count);
122 new = old - RWSEM_ACTIVE_WRITE_BIAS;
123 } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
124
125 if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
126 rwsem_wake(sem);
127 }
128
129 /*
130 * trylock for reading -- returns 1 if successful, 0 if contention
131 */
132 static inline int
__down_read_trylock(struct rw_semaphore * sem)133 __down_read_trylock (struct rw_semaphore *sem)
134 {
135 long tmp;
136 while ((tmp = atomic_long_read(&sem->count)) >= 0) {
137 if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, tmp+1)) {
138 return 1;
139 }
140 }
141 return 0;
142 }
143
144 /*
145 * trylock for writing -- returns 1 if successful, 0 if contention
146 */
147 static inline int
__down_write_trylock(struct rw_semaphore * sem)148 __down_write_trylock (struct rw_semaphore *sem)
149 {
150 long tmp = atomic_long_cmpxchg_acquire(&sem->count,
151 RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS);
152 return tmp == RWSEM_UNLOCKED_VALUE;
153 }
154
155 /*
156 * downgrade write lock to read lock
157 */
158 static inline void
__downgrade_write(struct rw_semaphore * sem)159 __downgrade_write (struct rw_semaphore *sem)
160 {
161 long old, new;
162
163 do {
164 old = atomic_long_read(&sem->count);
165 new = old - RWSEM_WAITING_BIAS;
166 } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
167
168 if (old < 0)
169 rwsem_downgrade_wake(sem);
170 }
171
172 #endif /* _ASM_IA64_RWSEM_H */
173
