627ae54854
This avoid potential issues if callers were to loop on these routines without some kind of memory barrier. Currently there are no such users in-tree, but it seems better safe than sorry. Also, in the tilepro case we read "current" before "next", which gives us a slightly better guarantee that the lock was actually unlocked at least momentarily if we return claiming that it is not locked. None of the callers actually rely on this behavior, as far as I know, however. Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>
134 lines
3.5 KiB
C
134 lines
3.5 KiB
C
/*
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* Copyright 2010 Tilera Corporation. All Rights Reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for
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* more details.
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*
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* 32-bit SMP spinlocks.
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*/
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#ifndef _ASM_TILE_SPINLOCK_32_H
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#define _ASM_TILE_SPINLOCK_32_H
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#include <linux/atomic.h>
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#include <asm/page.h>
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#include <linux/compiler.h>
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/*
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* We only use even ticket numbers so the '1' inserted by a tns is
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* an unambiguous "ticket is busy" flag.
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*/
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#define TICKET_QUANTUM 2
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/*
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* SMP ticket spinlocks, allowing only a single CPU anywhere
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*
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* (the type definitions are in asm/spinlock_types.h)
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*/
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static inline int arch_spin_is_locked(arch_spinlock_t *lock)
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{
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/*
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* Note that even if a new ticket is in the process of being
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* acquired, so lock->next_ticket is 1, it's still reasonable
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* to claim the lock is held, since it will be momentarily
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* if not already. There's no need to wait for a "valid"
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* lock->next_ticket to become available.
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* Use READ_ONCE() to ensure that calling this in a loop is OK.
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*/
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int curr = READ_ONCE(lock->current_ticket);
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int next = READ_ONCE(lock->next_ticket);
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return next != curr;
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}
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void arch_spin_lock(arch_spinlock_t *lock);
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/* We cannot take an interrupt after getting a ticket, so don't enable them. */
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#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
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int arch_spin_trylock(arch_spinlock_t *lock);
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static inline void arch_spin_unlock(arch_spinlock_t *lock)
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{
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/* For efficiency, overlap fetching the old ticket with the wmb(). */
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int old_ticket = lock->current_ticket;
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wmb(); /* guarantee anything modified under the lock is visible */
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lock->current_ticket = old_ticket + TICKET_QUANTUM;
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}
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void arch_spin_unlock_wait(arch_spinlock_t *lock);
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/*
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* Read-write spinlocks, allowing multiple readers
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* but only one writer.
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*
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* We use a "tns/store-back" technique on a single word to manage
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* the lock state, looping around to retry if the tns returns 1.
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*/
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/* Internal layout of the word; do not use. */
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#define _WR_NEXT_SHIFT 8
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#define _WR_CURR_SHIFT 16
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#define _WR_WIDTH 8
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#define _RD_COUNT_SHIFT 24
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#define _RD_COUNT_WIDTH 8
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/**
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* arch_read_can_lock() - would read_trylock() succeed?
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*/
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static inline int arch_read_can_lock(arch_rwlock_t *rwlock)
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{
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return (rwlock->lock << _RD_COUNT_WIDTH) == 0;
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}
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/**
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* arch_write_can_lock() - would write_trylock() succeed?
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*/
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static inline int arch_write_can_lock(arch_rwlock_t *rwlock)
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{
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return rwlock->lock == 0;
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}
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/**
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* arch_read_lock() - acquire a read lock.
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*/
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void arch_read_lock(arch_rwlock_t *rwlock);
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/**
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* arch_write_lock() - acquire a write lock.
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*/
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void arch_write_lock(arch_rwlock_t *rwlock);
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/**
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* arch_read_trylock() - try to acquire a read lock.
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*/
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int arch_read_trylock(arch_rwlock_t *rwlock);
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/**
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* arch_write_trylock() - try to acquire a write lock.
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*/
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int arch_write_trylock(arch_rwlock_t *rwlock);
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/**
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* arch_read_unlock() - release a read lock.
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*/
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void arch_read_unlock(arch_rwlock_t *rwlock);
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/**
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* arch_write_unlock() - release a write lock.
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*/
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void arch_write_unlock(arch_rwlock_t *rwlock);
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#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
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#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
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#endif /* _ASM_TILE_SPINLOCK_32_H */
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