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-rw-r--r--lib/locks/exclusive/aarch64/spinlock.S75
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diff --git a/lib/locks/exclusive/aarch64/spinlock.S b/lib/locks/exclusive/aarch64/spinlock.S
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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