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/*
* Copyright (c) 2013-2019, ARM Limited and Contributors. All rights reserved.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
#include <asm_macros.S>
.globl spin_lock
.globl spin_unlock
#if USE_SPINLOCK_CAS
#if !ARM_ARCH_AT_LEAST(8, 1)
#error USE_SPINLOCK_CAS option requires at least an ARMv8.1 platform
#endif
/*
* When compiled for ARMv8.1 or later, choose spin locks based on Compare and
* Swap instruction.
*/
/*
* Acquire lock using Compare and Swap instruction.
*
* Compare for 0 with acquire semantics, and swap 1. If failed to acquire, use
* load exclusive semantics to monitor the address and enter WFE.
*
* void spin_lock(spinlock_t *lock);
*/
func spin_lock
mov w2, #1
1: mov w1, wzr
2: casa w1, w2, [x0]
cbz w1, 3f
ldxr w1, [x0]
cbz w1, 2b
wfe
b 1b
3:
ret
endfunc spin_lock
#else /* !USE_SPINLOCK_CAS */
/*
* Acquire lock using load-/store-exclusive instruction pair.
*
* void spin_lock(spinlock_t *lock);
*/
func spin_lock
mov w2, #1
sevl
l1: wfe
l2: ldaxr w1, [x0]
cbnz w1, l1
stxr w1, w2, [x0]
cbnz w1, l2
ret
endfunc spin_lock
#endif /* USE_SPINLOCK_CAS */
/*
* Release lock previously acquired by spin_lock.
*
* Use store-release to unconditionally clear the spinlock variable.
* Store operation generates an event to all cores waiting in WFE
* when address is monitored by the global monitor.
*
* void spin_unlock(spinlock_t *lock);
*/
func spin_unlock
stlr wzr, [x0]
ret
endfunc spin_unlock
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