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 */ 30 extern void queued_read_lock_slowpath(struct qrwlock *lock); 31 extern 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 */ 38 static 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 */ 57 static 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 */ 72 static 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 */ 88 static 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 */ 102 static 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 */ 114 static 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 */ 131