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 void
__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 if (result < 0)
47 rwsem_down_read_failed(sem);
48 }
49
50 /*
51 * lock for writing
52 */
53 static inline long
___down_write(struct rw_semaphore * sem)54 ___down_write (struct rw_semaphore *sem)
55 {
56 long old, new;
57
58 do {
59 old = atomic_long_read(&sem->count);
60 new = old + RWSEM_ACTIVE_WRITE_BIAS;
61 } while (atomic_long_cmpxchg_acquire(&sem->count, old, new) != old);
62
63 return old;
64 }
65
66 static inline void
__down_write(struct rw_semaphore * sem)67 __down_write (struct rw_semaphore *sem)
68 {
69 if (___down_write(sem))
70 rwsem_down_write_failed(sem);
71 }
72
73 static inline int
__down_write_killable(struct rw_semaphore * sem)74 __down_write_killable (struct rw_semaphore *sem)
75 {
76 if (___down_write(sem))
77 if (IS_ERR(rwsem_down_write_failed_killable(sem)))
78 return -EINTR;
79
80 return 0;
81 }
82
83 /*
84 * unlock after reading
85 */
86 static inline void
__up_read(struct rw_semaphore * sem)87 __up_read (struct rw_semaphore *sem)
88 {
89 long result = ia64_fetchadd8_rel((unsigned long *)&sem->count.counter, -1);
90
91 if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
92 rwsem_wake(sem);
93 }
94
95 /*
96 * unlock after writing
97 */
98 static inline void
__up_write(struct rw_semaphore * sem)99 __up_write (struct rw_semaphore *sem)
100 {
101 long old, new;
102
103 do {
104 old = atomic_long_read(&sem->count);
105 new = old - RWSEM_ACTIVE_WRITE_BIAS;
106 } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
107
108 if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
109 rwsem_wake(sem);
110 }
111
112 /*
113 * trylock for reading -- returns 1 if successful, 0 if contention
114 */
115 static inline int
__down_read_trylock(struct rw_semaphore * sem)116 __down_read_trylock (struct rw_semaphore *sem)
117 {
118 long tmp;
119 while ((tmp = atomic_long_read(&sem->count)) >= 0) {
120 if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, tmp+1)) {
121 return 1;
122 }
123 }
124 return 0;
125 }
126
127 /*
128 * trylock for writing -- returns 1 if successful, 0 if contention
129 */
130 static inline int
__down_write_trylock(struct rw_semaphore * sem)131 __down_write_trylock (struct rw_semaphore *sem)
132 {
133 long tmp = atomic_long_cmpxchg_acquire(&sem->count,
134 RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS);
135 return tmp == RWSEM_UNLOCKED_VALUE;
136 }
137
138 /*
139 * downgrade write lock to read lock
140 */
141 static inline void
__downgrade_write(struct rw_semaphore * sem)142 __downgrade_write (struct rw_semaphore *sem)
143 {
144 long old, new;
145
146 do {
147 old = atomic_long_read(&sem->count);
148 new = old - RWSEM_WAITING_BIAS;
149 } while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
150
151 if (old < 0)
152 rwsem_downgrade_wake(sem);
153 }
154
155 #endif /* _ASM_IA64_RWSEM_H */
156