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/*
* Copyright (C) 2012 ARM Ltd.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* 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. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef __ASM_SPINLOCK_H
#define __ASM_SPINLOCK_H
#include <asm/spinlock_types.h>
#include <asm/processor.h>
/*
* Spinlock implementation.
*
* The old value is read exclusively and the new one, if unlocked, is written
* exclusively. In case of failure, the loop is restarted.
*
* The memory barriers are implicit with the load-acquire and store-release
* instructions.
*
* Unlocked value: 0
* Locked value: 1
*/
#define arch_spin_is_locked(x) ((x)->lock != 0)
#define arch_spin_unlock_wait(lock) \
do { while (arch_spin_is_locked(lock)) cpu_relax(); } while (0)
#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
static inline void arch_spin_lock(arch_spinlock_t *lock)
{
unsigned int tmp;
asm volatile(
" sevl\n"
"1: wfe\n"
"2: ldaxr %w0, [%1]\n"
" cbnz %w0, 1b\n"
" stxr %w0, %w2, [%1]\n"
" cbnz %w0, 2b\n"
: "=&r" (tmp)
: "r" (&lock->lock), "r" (1)
: "memory");
}
static inline int arch_spin_trylock(arch_spinlock_t *lock)
{
unsigned int tmp;
asm volatile(
" ldaxr %w0, [%1]\n"
" cbnz %w0, 1f\n"
" stxr %w0, %w2, [%1]\n"
"1:\n"
: "=&r" (tmp)
: "r" (&lock->lock), "r" (1)
: "memory");
return !tmp;
}
static inline void arch_spin_unlock(arch_spinlock_t *lock)
{
asm volatile(
" stlr %w1, [%0]\n"
: : "r" (&lock->lock), "r" (0) : "memory");
}
/*
* Write lock implementation.
*
* Write locks set bit 31. Unlocking, is done by writing 0 since the lock is
* exclusively held.
*
* The memory barriers are implicit with the load-acquire and store-release
* instructions.
*/
static inline void arch_write_lock(arch_rwlock_t *rw)
{
unsigned int tmp;
asm volatile(
" sevl\n"
"1: wfe\n"
"2: ldaxr %w0, [%1]\n"
" cbnz %w0, 1b\n"
" stxr %w0, %w2, [%1]\n"
" cbnz %w0, 2b\n"
: "=&r" (tmp)
: "r" (&rw->lock), "r" (0x80000000)
: "memory");
}
static inline int arch_write_trylock(arch_rwlock_t *rw)
{
unsigned int tmp;
asm volatile(
" ldaxr %w0, [%1]\n"
" cbnz %w0, 1f\n"
" stxr %w0, %w2, [%1]\n"
"1:\n"
: "=&r" (tmp)
: "r" (&rw->lock), "r" (0x80000000)
: "memory");
return !tmp;
}
static inline void arch_write_unlock(arch_rwlock_t *rw)
{
asm volatile(
" stlr %w1, [%0]\n"
: : "r" (&rw->lock), "r" (0) : "memory");
}
/* write_can_lock - would write_trylock() succeed? */
#define arch_write_can_lock(x) ((x)->lock == 0)
/*
* Read lock implementation.
*
* It exclusively loads the lock value, increments it and stores the new value
* back if positive and the CPU still exclusively owns the location. If the
* value is negative, the lock is already held.
*
* During unlocking there may be multiple active read locks but no write lock.
*
* The memory barriers are implicit with the load-acquire and store-release
* instructions.
*/
static inline void arch_read_lock(arch_rwlock_t *rw)
{
unsigned int tmp, tmp2;
asm volatile(
" sevl\n"
"1: wfe\n"
"2: ldaxr %w0, [%2]\n"
" add %w0, %w0, #1\n"
" tbnz %w0, #31, 1b\n"
" stxr %w1, %w0, [%2]\n"
" cbnz %w1, 2b\n"
: "=&r" (tmp), "=&r" (tmp2)
: "r" (&rw->lock)
: "memory");
}
static inline void arch_read_unlock(arch_rwlock_t *rw)
{
unsigned int tmp, tmp2;
asm volatile(
"1: ldxr %w0, [%2]\n"
" sub %w0, %w0, #1\n"
" stlxr %w1, %w0, [%2]\n"
" cbnz %w1, 1b\n"
: "=&r" (tmp), "=&r" (tmp2)
: "r" (&rw->lock)
: "memory");
}
static inline int arch_read_trylock(arch_rwlock_t *rw)
{
unsigned int tmp, tmp2 = 1;
asm volatile(
" ldaxr %w0, [%2]\n"
" add %w0, %w0, #1\n"
" tbnz %w0, #31, 1f\n"
" stxr %w1, %w0, [%2]\n"
"1:\n"
: "=&r" (tmp), "+r" (tmp2)
: "r" (&rw->lock)
: "memory");
return !tmp2;
}
/* read_can_lock - would read_trylock() succeed? */
#define arch_read_can_lock(x) ((x)->lock < 0x80000000)
#define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
#define arch_write_lock_flags(lock, flags) arch_write_lock(lock)
#define arch_spin_relax(lock) cpu_relax()
#define arch_read_relax(lock) cpu_relax()
#define arch_write_relax(lock) cpu_relax()
#endif /* __ASM_SPINLOCK_H */
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