6 * Copyright IBM Corp. 2002
7 * Author(s): Martin Schwidefsky (schwidefsky@de.ibm.com)
9 * Based on asm-alpha/semaphore.h and asm-i386/rwsem.h
14 * The MSW of the count is the negated number of active writers and waiting
15 * lockers, and the LSW is the total number of active locks
17 * The lock count is initialized to 0 (no active and no waiting lockers).
19 * When a writer subtracts WRITE_BIAS, it'll get 0xffff0001 for the case of an
20 * uncontended lock. This can be determined because XADD returns the old value.
21 * Readers increment by 1 and see a positive value when uncontended, negative
22 * if there are writers (and maybe) readers waiting (in which case it goes to
25 * The value of WAITING_BIAS supports up to 32766 waiting processes. This can
26 * be extended to 65534 by manually checking the whole MSW rather than relying
29 * The value of ACTIVE_BIAS supports up to 65535 active processes.
31 * This should be totally fair - if anything is waiting, a process that wants a
32 * lock will go to the back of the queue. When the currently active lock is
33 * released, if there's a writer at the front of the queue, then that and only
34 * that will be woken up; if there's a bunch of consequtive readers at the
35 * front, then they'll all be woken up, but no other readers will be.
38 #ifndef _LINUX_RWSEM_H
39 #error "please don't include asm/rwsem.h directly, use linux/rwsem.h instead"
42 #define RWSEM_UNLOCKED_VALUE 0x0000000000000000L
43 #define RWSEM_ACTIVE_BIAS 0x0000000000000001L
44 #define RWSEM_ACTIVE_MASK 0x00000000ffffffffL
45 #define RWSEM_WAITING_BIAS (-0x0000000100000000L)
46 #define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
47 #define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
52 static inline void __down_read(struct rw_semaphore
*sem
)
62 : "=&d" (old
), "=&d" (new), "=Q" (sem
->count
)
63 : "Q" (sem
->count
), "i" (RWSEM_ACTIVE_READ_BIAS
)
66 rwsem_down_read_failed(sem
);
70 * trylock for reading -- returns 1 if successful, 0 if contention
72 static inline int __down_read_trylock(struct rw_semaphore
*sem
)
84 : "=&d" (old
), "=&d" (new), "=Q" (sem
->count
)
85 : "Q" (sem
->count
), "i" (RWSEM_ACTIVE_READ_BIAS
)
87 return old
>= 0 ? 1 : 0;
93 static inline void __down_write_nested(struct rw_semaphore
*sem
, int subclass
)
95 signed long old
, new, tmp
;
97 tmp
= RWSEM_ACTIVE_WRITE_BIAS
;
104 : "=&d" (old
), "=&d" (new), "=Q" (sem
->count
)
105 : "Q" (sem
->count
), "m" (tmp
)
108 rwsem_down_write_failed(sem
);
111 static inline void __down_write(struct rw_semaphore
*sem
)
113 __down_write_nested(sem
, 0);
117 * trylock for writing -- returns 1 if successful, 0 if contention
119 static inline int __down_write_trylock(struct rw_semaphore
*sem
)
130 : "=&d" (old
), "=Q" (sem
->count
)
131 : "Q" (sem
->count
), "d" (RWSEM_ACTIVE_WRITE_BIAS
)
133 return (old
== RWSEM_UNLOCKED_VALUE
) ? 1 : 0;
137 * unlock after reading
139 static inline void __up_read(struct rw_semaphore
*sem
)
141 signed long old
, new;
149 : "=&d" (old
), "=&d" (new), "=Q" (sem
->count
)
150 : "Q" (sem
->count
), "i" (-RWSEM_ACTIVE_READ_BIAS
)
153 if ((new & RWSEM_ACTIVE_MASK
) == 0)
158 * unlock after writing
160 static inline void __up_write(struct rw_semaphore
*sem
)
162 signed long old
, new, tmp
;
164 tmp
= -RWSEM_ACTIVE_WRITE_BIAS
;
171 : "=&d" (old
), "=&d" (new), "=Q" (sem
->count
)
172 : "Q" (sem
->count
), "m" (tmp
)
175 if ((new & RWSEM_ACTIVE_MASK
) == 0)
180 * downgrade write lock to read lock
182 static inline void __downgrade_write(struct rw_semaphore
*sem
)
184 signed long old
, new, tmp
;
186 tmp
= -RWSEM_WAITING_BIAS
;
193 : "=&d" (old
), "=&d" (new), "=Q" (sem
->count
)
194 : "Q" (sem
->count
), "m" (tmp
)
197 rwsem_downgrade_wake(sem
);
201 * implement atomic add functionality
203 static inline void rwsem_atomic_add(long delta
, struct rw_semaphore
*sem
)
205 signed long old
, new;
213 : "=&d" (old
), "=&d" (new), "=Q" (sem
->count
)
214 : "Q" (sem
->count
), "d" (delta
)
219 * implement exchange and add functionality
221 static inline long rwsem_atomic_update(long delta
, struct rw_semaphore
*sem
)
223 signed long old
, new;
231 : "=&d" (old
), "=&d" (new), "=Q" (sem
->count
)
232 : "Q" (sem
->count
), "d" (delta
)
237 #endif /* _S390_RWSEM_H */