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/*
* Copyright 2010 Tilera Corporation. All Rights Reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
* NON INFRINGEMENT. See the GNU General Public License for
* more details.
*
* 32-bit SMP spinlocks.
*/
#ifndef _ASM_TILE_SPINLOCK_32_H
#define _ASM_TILE_SPINLOCK_32_H
#include <linux/atomic.h>
#include <asm/page.h>
#include <linux/compiler.h>
/*
* We only use even ticket numbers so the '1' inserted by a tns is
* an unambiguous "ticket is busy" flag.
*/
#define TICKET_QUANTUM 2
/*
* SMP ticket spinlocks, allowing only a single CPU anywhere
*
* (the type definitions are in asm/spinlock_types.h)
*/
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
/*
* Note that even if a new ticket is in the process of being
* acquired, so lock->next_ticket is 1, it's still reasonable
* to claim the lock is held, since it will be momentarily
* if not already. There's no need to wait for a "valid"
* lock->next_ticket to become available.
* Use READ_ONCE() to ensure that calling this in a loop is OK.
*/
int curr = READ_ONCE(lock->current_ticket);
int next = READ_ONCE(lock->next_ticket);
return next != curr;
}
void arch_spin_lock(arch_spinlock_t *lock);
/* We cannot take an interrupt after getting a ticket, so don't enable them. */
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
int arch_spin_trylock(arch_spinlock_t *lock);
static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
/* For efficiency, overlap fetching the old ticket with the wmb(). */
int old_ticket = lock->current_ticket;
wmb(); /* guarantee anything modified under the lock is visible */
lock->current_ticket = old_ticket + TICKET_QUANTUM;
}
/*
* Read-write spinlocks, allowing multiple readers
* but only one writer.
*
* We use a "tns/store-back" technique on a single word to manage
* the lock state, looping around to retry if the tns returns 1.
*/
/* Internal layout of the word; do not use. */
#define _WR_NEXT_SHIFT 8
#define _WR_CURR_SHIFT 16
#define _WR_WIDTH 8
#define _RD_COUNT_SHIFT 24
#define _RD_COUNT_WIDTH 8
/**
* arch_read_can_lock() - would read_trylock() succeed?
*/
static inline int arch_read_can_lock(arch_rwlock_t *rwlock)
{
return (rwlock->lock << _RD_COUNT_WIDTH) == 0;
}
/**
* arch_write_can_lock() - would write_trylock() succeed?
*/
static inline int arch_write_can_lock(arch_rwlock_t *rwlock)
{
return rwlock->lock == 0;
}
/**
* arch_read_lock() - acquire a read lock.
*/
void arch_read_lock(arch_rwlock_t *rwlock);
/**
* arch_write_lock() - acquire a write lock.
*/
void arch_write_lock(arch_rwlock_t *rwlock);
/**
* arch_read_trylock() - try to acquire a read lock.
*/
int arch_read_trylock(arch_rwlock_t *rwlock);
/**
* arch_write_trylock() - try to acquire a write lock.
*/
int arch_write_trylock(arch_rwlock_t *rwlock);
/**
* arch_read_unlock() - release a read lock.
*/
void arch_read_unlock(arch_rwlock_t *rwlock);
/**
* arch_write_unlock() - release a write lock.
*/
void arch_write_unlock(arch_rwlock_t *rwlock);
#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
#endif /* _ASM_TILE_SPINLOCK_32_H */
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