1/* SPDX-License-Identifier: GPL-2.0-or-later */
  2/*
  3 * Queue read/write lock
  4 *
  5 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P.
  6 *
  7 * Authors: Waiman Long <waiman.long@hp.com>
  8 */
  9#ifndef __ASM_GENERIC_QRWLOCK_H
 10#define __ASM_GENERIC_QRWLOCK_H
 11
 12#include <linux/atomic.h>
 13#include <asm/barrier.h>
 14#include <asm/processor.h>
 15
 16#include <asm-generic/qrwlock_types.h>
 17
 18/*
 19 * Writer states & reader shift and bias.
 20 */
 21#define	_QW_WAITING	0x100		/* A writer is waiting	   */
 22#define	_QW_LOCKED	0x0ff		/* A writer holds the lock */
 23#define	_QW_WMASK	0x1ff		/* Writer mask		   */
 24#define	_QR_SHIFT	9		/* Reader count shift	   */
 25#define _QR_BIAS	(1U << _QR_SHIFT)
 26
 27/*
 28 * External function declarations
 29 */
 30extern void queued_read_lock_slowpath(struct qrwlock *lock);
 31extern void queued_write_lock_slowpath(struct qrwlock *lock);
 32
 33/**
 34 * queued_read_trylock - try to acquire read lock of a queue rwlock
 35 * @lock : Pointer to queue rwlock structure
 36 * Return: 1 if lock acquired, 0 if failed
 37 */
 38static inline int queued_read_trylock(struct qrwlock *lock)
 39{
 40	u32 cnts;
 41
 42	cnts = atomic_read(&lock->cnts);
 43	if (likely(!(cnts & _QW_WMASK))) {
 44		cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
 45		if (likely(!(cnts & _QW_WMASK)))
 46			return 1;
 47		atomic_sub(_QR_BIAS, &lock->cnts);
 48	}
 49	return 0;
 50}
 51
 52/**
 53 * queued_write_trylock - try to acquire write lock of a queue rwlock
 54 * @lock : Pointer to queue rwlock structure
 55 * Return: 1 if lock acquired, 0 if failed
 56 */
 57static inline int queued_write_trylock(struct qrwlock *lock)
 58{
 59	u32 cnts;
 60
 61	cnts = atomic_read(&lock->cnts);
 62	if (unlikely(cnts))
 63		return 0;
 64
 65	return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts,
 66				_QW_LOCKED));
 67}
 68/**
 69 * queued_read_lock - acquire read lock of a queue rwlock
 70 * @lock: Pointer to queue rwlock structure
 71 */
 72static inline void queued_read_lock(struct qrwlock *lock)
 73{
 74	u32 cnts;
 75
 76	cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts);
 77	if (likely(!(cnts & _QW_WMASK)))
 78		return;
 79
 80	/* The slowpath will decrement the reader count, if necessary. */
 81	queued_read_lock_slowpath(lock);
 82}
 83
 84/**
 85 * queued_write_lock - acquire write lock of a queue rwlock
 86 * @lock : Pointer to queue rwlock structure
 87 */
 88static inline void queued_write_lock(struct qrwlock *lock)
 89{
 90	u32 cnts = 0;
 91	/* Optimize for the unfair lock case where the fair flag is 0. */
 92	if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED)))
 93		return;
 94
 95	queued_write_lock_slowpath(lock);
 96}
 97
 98/**
 99 * queued_read_unlock - release read lock of a queue rwlock
100 * @lock : Pointer to queue rwlock structure
101 */
102static inline void queued_read_unlock(struct qrwlock *lock)
103{
104	/*
105	 * Atomically decrement the reader count
106	 */
107	(void)atomic_sub_return_release(_QR_BIAS, &lock->cnts);
108}
109
110/**
111 * queued_write_unlock - release write lock of a queue rwlock
112 * @lock : Pointer to queue rwlock structure
113 */
114static inline void queued_write_unlock(struct qrwlock *lock)
115{
116	smp_store_release(&lock->wlocked, 0);
117}
118
119/*
120 * Remapping rwlock architecture specific functions to the corresponding
121 * queue rwlock functions.
122 */
123#define arch_read_lock(l)	queued_read_lock(l)
124#define arch_write_lock(l)	queued_write_lock(l)
125#define arch_read_trylock(l)	queued_read_trylock(l)
126#define arch_write_trylock(l)	queued_write_trylock(l)
127#define arch_read_unlock(l)	queued_read_unlock(l)
128#define arch_write_unlock(l)	queued_write_unlock(l)
129
130#endif /* __ASM_GENERIC_QRWLOCK_H */