1/*
  2 * 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 <cl@linux.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#ifndef _LINUX_RWSEM_H
 25#error "Please don't include <asm/rwsem.h> directly, use <linux/rwsem.h> instead."
 26#endif
 27
 28#include <asm/intrinsics.h>
 29
 30#define RWSEM_UNLOCKED_VALUE		__IA64_UL_CONST(0x0000000000000000)
 31#define RWSEM_ACTIVE_BIAS		(1L)
 32#define RWSEM_ACTIVE_MASK		(0xffffffffL)
 33#define RWSEM_WAITING_BIAS		(-0x100000000L)
 34#define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
 35#define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
 36
 37/*
 38 * lock for reading
 39 */
 40static inline void
 41__down_read (struct rw_semaphore *sem)
 42{
 43	long result = ia64_fetchadd8_acq((unsigned long *)&sem->count.counter, 1);
 44
 45	if (result < 0)
 46		rwsem_down_read_failed(sem);
 47}
 48
 49/*
 50 * lock for writing
 51 */
 52static inline long
 53___down_write (struct rw_semaphore *sem)
 54{
 55	long old, new;
 56
 57	do {
 58		old = atomic_long_read(&sem->count);
 59		new = old + RWSEM_ACTIVE_WRITE_BIAS;
 60	} while (atomic_long_cmpxchg_acquire(&sem->count, old, new) != old);
 61
 62	return old;
 63}
 64
 65static inline void
 66__down_write (struct rw_semaphore *sem)
 67{
 68	if (___down_write(sem))
 69		rwsem_down_write_failed(sem);
 70}
 71
 72static inline int
 73__down_write_killable (struct rw_semaphore *sem)
 74{
 75	if (___down_write(sem))
 76		if (IS_ERR(rwsem_down_write_failed_killable(sem)))
 77			return -EINTR;
 78
 79	return 0;
 80}
 81
 82/*
 83 * unlock after reading
 84 */
 85static inline void
 86__up_read (struct rw_semaphore *sem)
 87{
 88	long result = ia64_fetchadd8_rel((unsigned long *)&sem->count.counter, -1);
 89
 90	if (result < 0 && (--result & RWSEM_ACTIVE_MASK) == 0)
 91		rwsem_wake(sem);
 92}
 93
 94/*
 95 * unlock after writing
 96 */
 97static inline void
 98__up_write (struct rw_semaphore *sem)
 99{
100	long old, new;
101
102	do {
103		old = atomic_long_read(&sem->count);
104		new = old - RWSEM_ACTIVE_WRITE_BIAS;
105	} while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
106
107	if (new < 0 && (new & RWSEM_ACTIVE_MASK) == 0)
108		rwsem_wake(sem);
109}
110
111/*
112 * trylock for reading -- returns 1 if successful, 0 if contention
113 */
114static inline int
115__down_read_trylock (struct rw_semaphore *sem)
116{
117	long tmp;
118	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
119		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp, tmp+1)) {
120			return 1;
121		}
122	}
123	return 0;
124}
125
126/*
127 * trylock for writing -- returns 1 if successful, 0 if contention
128 */
129static inline int
130__down_write_trylock (struct rw_semaphore *sem)
131{
132	long tmp = atomic_long_cmpxchg_acquire(&sem->count,
133			RWSEM_UNLOCKED_VALUE, RWSEM_ACTIVE_WRITE_BIAS);
134	return tmp == RWSEM_UNLOCKED_VALUE;
135}
136
137/*
138 * downgrade write lock to read lock
139 */
140static inline void
141__downgrade_write (struct rw_semaphore *sem)
142{
143	long old, new;
144
145	do {
146		old = atomic_long_read(&sem->count);
147		new = old - RWSEM_WAITING_BIAS;
148	} while (atomic_long_cmpxchg_release(&sem->count, old, new) != old);
149
150	if (old < 0)
151		rwsem_downgrade_wake(sem);
152}
153
154#endif /* _ASM_IA64_RWSEM_H */