5 * include/asm-s390x/rwsem.h
8 * Copyright (C) 2002 IBM Deutschland Entwicklung GmbH, IBM Corporation
9 * Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
11 * Based on asm-alpha/semaphore.h and asm-i386/rwsem.h
16 * The MSW of the count is the negated number of active writers and waiting
17 * lockers, and the LSW is the total number of active locks
19 * The lock count is initialized to 0 (no active and no waiting lockers).
21 * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
22 * uncontended lock. This can be determined because XADD returns the old value.
23 * Readers increment by 1 and see a positive value when uncontended, negative
24 * if there are writers (and maybe) readers waiting (in which case it goes to
27 * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
28 * be extended to 65534 by manually checking the whole MSW rather than relying
31 * The value of ACTIVE_BIAS supports up to 65535 active processes.
33 * This should be totally fair - if anything is waiting, a process that wants a
34 * lock will go to the back of the queue. When the currently active lock is
35 * released, if there's a writer at the front of the queue, then that and only
36 * that will be woken up; if there's a bunch of consequtive readers at the
37 * front, then they'll all be woken up, but no other readers will be.
40 #ifndef _LINUX_RWSEM_H
41 #error please dont include asm/rwsem.h directly, use linux/rwsem.h instead
46 #include <linux/list.h>
47 #include <linux/spinlock.h>
51 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
52 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
53 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
56 * the semaphore definition
61 struct list_head wait_list;
64 #define RWSEM_UNLOCKED_VALUE 0x0000000000000000L
65 #define RWSEM_ACTIVE_BIAS 0x0000000000000001L
66 #define RWSEM_ACTIVE_MASK 0x00000000ffffffffL
67 #define RWSEM_WAITING_BIAS (-0x0000000100000000L)
68 #define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
69 #define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
74 #define __RWSEM_INITIALIZER(name) \
75 { RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, LIST_HEAD_INIT((name).wait_list) }
77 #define DECLARE_RWSEM(name) \
78 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
80 static inline void init_rwsem(struct rw_semaphore *sem)
82 sem->count = RWSEM_UNLOCKED_VALUE;
83 spin_lock_init(&sem->wait_lock);
84 INIT_LIST_HEAD(&sem->wait_list);
90 static inline void __down_read(struct rw_semaphore *sem)
100 : "=&d" (old), "=&d" (new)
101 : "a" (&sem->count), "i" (RWSEM_ACTIVE_READ_BIAS)
104 rwsem_down_read_failed(sem);
108 * trylock for reading -- returns 1 if successful, 0 if contention
110 static inline int __down_read_trylock(struct rw_semaphore *sem)
112 signed long old, new;
114 __asm__ __volatile__(
122 : "=&d" (old), "=&d" (new)
123 : "a" (&sem->count), "i" (RWSEM_ACTIVE_READ_BIAS)
125 return old >= 0 ? 1 : 0;
131 static inline void __down_write(struct rw_semaphore *sem)
133 signed long old, new, tmp;
135 tmp = RWSEM_ACTIVE_WRITE_BIAS;
136 __asm__ __volatile__(
142 : "=&d" (old), "=&d" (new)
143 : "a" (&sem->count), "m" (tmp)
146 rwsem_down_write_failed(sem);
150 * trylock for writing -- returns 1 if successful, 0 if contention
152 static inline int __down_write_trylock(struct rw_semaphore *sem)
156 __asm__ __volatile__(
164 : "a" (&sem->count), "d" (RWSEM_ACTIVE_WRITE_BIAS)
166 return (old == RWSEM_UNLOCKED_VALUE) ? 1 : 0;
170 * unlock after reading
172 static inline void __up_read(struct rw_semaphore *sem)
174 signed long old, new;
176 __asm__ __volatile__(
182 : "=&d" (old), "=&d" (new)
183 : "a" (&sem->count), "i" (-RWSEM_ACTIVE_READ_BIAS)
191 * unlock after writing
193 static inline void __up_write(struct rw_semaphore *sem)
195 signed long old, new, tmp;
197 tmp = -RWSEM_ACTIVE_WRITE_BIAS;
198 __asm__ __volatile__(
204 : "=&d" (old), "=&d" (new)
205 : "a" (&sem->count), "m" (tmp)
213 * implement atomic add functionality
215 static inline void rwsem_atomic_add(long delta, struct rw_semaphore *sem)
217 signed long old, new;
219 __asm__ __volatile__(
225 : "=&d" (old), "=&d" (new)
226 : "a" (&sem->count), "d" (delta)
231 * implement exchange and add functionality
233 static inline long rwsem_atomic_update(long delta, struct rw_semaphore *sem)
235 signed long old, new;
237 __asm__ __volatile__(
243 : "=&d" (old), "=&d" (new)
244 : "a" (&sem->count), "d" (delta)
249 #endif /* __KERNEL__ */
250 #endif /* _S390X_RWSEM_H */