1/* 2 * Copyright 2010 Tilera Corporation. All Rights Reserved. 3 * 4 * This program is free software; you can redistribute it and/or 5 * modify it under the terms of the GNU General Public License 6 * as published by the Free Software Foundation, version 2. 7 * 8 * This program is distributed in the hope that it will be useful, but 9 * WITHOUT ANY WARRANTY; without even the implied warranty of 10 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or 11 * NON INFRINGEMENT. See the GNU General Public License for 12 * more details. 13 * 14 * 32-bit SMP spinlocks. 15 */ 16 17#ifndef _ASM_TILE_SPINLOCK_32_H 18#define _ASM_TILE_SPINLOCK_32_H 19 20#include <asm/atomic.h> 21#include <asm/page.h> 22#include <asm/system.h> 23#include <linux/compiler.h> 24 25/* 26 * We only use even ticket numbers so the '1' inserted by a tns is 27 * an unambiguous "ticket is busy" flag. 28 */ 29#define TICKET_QUANTUM 2 30 31 32/* 33 * SMP ticket spinlocks, allowing only a single CPU anywhere 34 * 35 * (the type definitions are in asm/spinlock_types.h) 36 */ 37static inline int arch_spin_is_locked(arch_spinlock_t *lock) 38{ 39 /* 40 * Note that even if a new ticket is in the process of being 41 * acquired, so lock->next_ticket is 1, it's still reasonable 42 * to claim the lock is held, since it will be momentarily 43 * if not already. There's no need to wait for a "valid" 44 * lock->next_ticket to become available. 45 */ 46 return lock->next_ticket != lock->current_ticket; 47} 48 49void arch_spin_lock(arch_spinlock_t *lock); 50 51/* We cannot take an interrupt after getting a ticket, so don't enable them. */ 52#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock) 53 54int arch_spin_trylock(arch_spinlock_t *lock); 55 56static inline void arch_spin_unlock(arch_spinlock_t *lock) 57{ 58 /* For efficiency, overlap fetching the old ticket with the wmb(). */ 59 int old_ticket = lock->current_ticket; 60 wmb(); /* guarantee anything modified under the lock is visible */ 61 lock->current_ticket = old_ticket + TICKET_QUANTUM; 62} 63 64void arch_spin_unlock_wait(arch_spinlock_t *lock); 65 66/* 67 * Read-write spinlocks, allowing multiple readers 68 * but only one writer. 69 * 70 * We use a "tns/store-back" technique on a single word to manage 71 * the lock state, looping around to retry if the tns returns 1. 72 */ 73 74/* Internal layout of the word; do not use. */ 75#define _WR_NEXT_SHIFT 8 76#define _WR_CURR_SHIFT 16 77#define _WR_WIDTH 8 78#define _RD_COUNT_SHIFT 24 79#define _RD_COUNT_WIDTH 8 80 81/* Internal functions; do not use. */ 82void arch_read_lock_slow(arch_rwlock_t *, u32); 83int arch_read_trylock_slow(arch_rwlock_t *); 84void arch_read_unlock_slow(arch_rwlock_t *); 85void arch_write_lock_slow(arch_rwlock_t *, u32); 86void arch_write_unlock_slow(arch_rwlock_t *, u32); 87 88/** 89 * arch_read_can_lock() - would read_trylock() succeed? 90 */ 91static inline int arch_read_can_lock(arch_rwlock_t *rwlock) 92{ 93 return (rwlock->lock << _RD_COUNT_WIDTH) == 0; 94} 95 96/** 97 * arch_write_can_lock() - would write_trylock() succeed? 98 */ 99static inline int arch_write_can_lock(arch_rwlock_t *rwlock) 100{ 101 return rwlock->lock == 0; 102} 103 104/** 105 * arch_read_lock() - acquire a read lock. 106 */ 107static inline void arch_read_lock(arch_rwlock_t *rwlock) 108{ 109 u32 val = __insn_tns((int *)&rwlock->lock); 110 if (unlikely(val << _RD_COUNT_WIDTH)) { 111 arch_read_lock_slow(rwlock, val); 112 return; 113 } 114 rwlock->lock = val + (1 << _RD_COUNT_SHIFT); 115} 116 117/** 118 * arch_read_lock() - acquire a write lock. 119 */ 120static inline void arch_write_lock(arch_rwlock_t *rwlock) 121{ 122 u32 val = __insn_tns((int *)&rwlock->lock); 123 if (unlikely(val != 0)) { 124 arch_write_lock_slow(rwlock, val); 125 return; 126 } 127 rwlock->lock = 1 << _WR_NEXT_SHIFT; 128} 129 130/** 131 * arch_read_trylock() - try to acquire a read lock. 132 */ 133static inline int arch_read_trylock(arch_rwlock_t *rwlock) 134{ 135 int locked; 136 u32 val = __insn_tns((int *)&rwlock->lock); 137 if (unlikely(val & 1)) 138 return arch_read_trylock_slow(rwlock); 139 locked = (val << _RD_COUNT_WIDTH) == 0; 140 rwlock->lock = val + (locked << _RD_COUNT_SHIFT); 141 return locked; 142} 143 144/** 145 * arch_write_trylock() - try to acquire a write lock. 146 */ 147static inline int arch_write_trylock(arch_rwlock_t *rwlock) 148{ 149 u32 val = __insn_tns((int *)&rwlock->lock); 150 151 /* 152 * If a tns is in progress, or there's a waiting or active locker, 153 * or active readers, we can't take the lock, so give up. 154 */ 155 if (unlikely(val != 0)) { 156 if (!(val & 1)) 157 rwlock->lock = val; 158 return 0; 159 } 160 161 /* Set the "next" field to mark it locked. */ 162 rwlock->lock = 1 << _WR_NEXT_SHIFT; 163 return 1; 164} 165 166/** 167 * arch_read_unlock() - release a read lock. 168 */ 169static inline void arch_read_unlock(arch_rwlock_t *rwlock) 170{ 171 u32 val; 172 mb(); /* guarantee anything modified under the lock is visible */ 173 val = __insn_tns((int *)&rwlock->lock); 174 if (unlikely(val & 1)) { 175 arch_read_unlock_slow(rwlock); 176 return; 177 } 178 rwlock->lock = val - (1 << _RD_COUNT_SHIFT); 179} 180 181/** 182 * arch_write_unlock() - release a write lock. 183 */ 184static inline void arch_write_unlock(arch_rwlock_t *rwlock) 185{ 186 u32 val; 187 mb(); /* guarantee anything modified under the lock is visible */ 188 val = __insn_tns((int *)&rwlock->lock); 189 if (unlikely(val != (1 << _WR_NEXT_SHIFT))) { 190 arch_write_unlock_slow(rwlock, val); 191 return; 192 } 193 rwlock->lock = 0; 194} 195 196#define arch_read_lock_flags(lock, flags) arch_read_lock(lock) 197#define arch_write_lock_flags(lock, flags) arch_write_lock(lock) 198 199#endif /* _ASM_TILE_SPINLOCK_32_H */ 200