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 */
 41static inline int
 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
 49static inline void
 50__down_read (struct rw_semaphore *sem)
 51{
 52	if (___down_read(sem))
 53		rwsem_down_read_failed(sem);
 54}
 55
 56static inline int
 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 */
 69static inline long
 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
 82static inline void
 83__down_write (struct rw_semaphore *sem)
 84{
 85	if (___down_write(sem))
 86		rwsem_down_write_failed(sem);
 87}
 88
 89static inline int
 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 */
103static inline void
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 */
115static inline void
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 */
132static inline int
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 */
147static inline int
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 */
158static inline void
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 */