spinlock_64.h
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/*
* Copyright 2011 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.
*
* 64-bit SMP ticket spinlocks, allowing only a single CPU anywhere
* (the type definitions are in asm/spinlock_types.h)
*/
#ifndef _ASM_TILE_SPINLOCK_64_H
#define _ASM_TILE_SPINLOCK_64_H
#include <linux/compiler.h>
/* Shifts and masks for the various fields in "lock". */
#define __ARCH_SPIN_CURRENT_SHIFT 17
#define __ARCH_SPIN_NEXT_MASK 0x7fff
#define __ARCH_SPIN_NEXT_OVERFLOW 0x8000
/*
* Return the "current" portion of a ticket lock value,
* i.e. the number that currently owns the lock.
*/
static inline u32 arch_spin_current(u32 val)
{
return val >> __ARCH_SPIN_CURRENT_SHIFT;
}
/*
* Return the "next" portion of a ticket lock value,
* i.e. the number that the next task to try to acquire the lock will get.
*/
static inline u32 arch_spin_next(u32 val)
{
return val & __ARCH_SPIN_NEXT_MASK;
}
/* The lock is locked if a task would have to wait to get it. */
static inline int arch_spin_is_locked(arch_spinlock_t *lock)
{
/* Use READ_ONCE() to ensure that calling this in a loop is OK. */
u32 val = READ_ONCE(lock->lock);
return arch_spin_current(val) != arch_spin_next(val);
}
/* Bump the current ticket so the next task owns the lock. */
static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
wmb(); /* guarantee anything modified under the lock is visible */
__insn_fetchadd4(&lock->lock, 1U << __ARCH_SPIN_CURRENT_SHIFT);
}
void arch_spin_unlock_wait(arch_spinlock_t *lock);
void arch_spin_lock_slow(arch_spinlock_t *lock, u32 val);
/* Grab the "next" ticket number and bump it atomically.
* If the current ticket is not ours, go to the slow path.
* We also take the slow path if the "next" value overflows.
*/
static inline void arch_spin_lock(arch_spinlock_t *lock)
{
u32 val = __insn_fetchadd4(&lock->lock, 1);
u32 ticket = val & (__ARCH_SPIN_NEXT_MASK | __ARCH_SPIN_NEXT_OVERFLOW);
if (unlikely(arch_spin_current(val) != ticket))
arch_spin_lock_slow(lock, ticket);
}
/* Try to get the lock, and return whether we succeeded. */
int arch_spin_trylock(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)
/*
* Read-write spinlocks, allowing multiple readers
* but only one writer.
*
* We use fetchadd() for readers, and fetchor() with the sign bit
* for writers.
*/
#define __WRITE_LOCK_BIT (1 << 31)
static inline int arch_write_val_locked(int val)
{
return val < 0; /* Optimize "val & __WRITE_LOCK_BIT". */
}
/**
* read_can_lock - would read_trylock() succeed?
* @lock: the rwlock in question.
*/
static inline int arch_read_can_lock(arch_rwlock_t *rw)
{
return !arch_write_val_locked(rw->lock);
}
/**
* write_can_lock - would write_trylock() succeed?
* @lock: the rwlock in question.
*/
static inline int arch_write_can_lock(arch_rwlock_t *rw)
{
return rw->lock == 0;
}
extern void __read_lock_failed(arch_rwlock_t *rw);
static inline void arch_read_lock(arch_rwlock_t *rw)
{
u32 val = __insn_fetchaddgez4(&rw->lock, 1);
if (unlikely(arch_write_val_locked(val)))
__read_lock_failed(rw);
}
extern void __write_lock_failed(arch_rwlock_t *rw, u32 val);
static inline void arch_write_lock(arch_rwlock_t *rw)
{
u32 val = __insn_fetchor4(&rw->lock, __WRITE_LOCK_BIT);
if (unlikely(val != 0))
__write_lock_failed(rw, val);
}
static inline void arch_read_unlock(arch_rwlock_t *rw)
{
__insn_mf();
__insn_fetchadd4(&rw->lock, -1);
}
static inline void arch_write_unlock(arch_rwlock_t *rw)
{
__insn_mf();
__insn_exch4(&rw->lock, 0); /* Avoid waiting in the write buffer. */
}
static inline int arch_read_trylock(arch_rwlock_t *rw)
{
return !arch_write_val_locked(__insn_fetchaddgez4(&rw->lock, 1));
}
static inline int arch_write_trylock(arch_rwlock_t *rw)
{
u32 val = __insn_fetchor4(&rw->lock, __WRITE_LOCK_BIT);
if (likely(val == 0))
return 1;
if (!arch_write_val_locked(val))
__insn_fetchand4(&rw->lock, ~__WRITE_LOCK_BIT);
return 0;
}
#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_64_H */