1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
/*
* 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 ARM_ARCH_AT_LEAST(8, 1)
/*
* When compiled for ARMv8.1 or later, choose spin locks based on Compare and
* Swap instruction.
*/
# define USE_CAS 1
/*
* Lock contenders using CAS, upon failing to acquire the lock, wait with the
* monitor in open state. Therefore, a normal store upon unlocking won't
* generate an SEV. Use explicit SEV instruction with CAS unlock.
*/
# define COND_SEV() sev
#else
# define USE_CAS 0
/*
* Lock contenders using exclusive pairs, upon failing to acquire the lock, wait
* with the monitor in exclusive state. A normal store upon unlocking will
* implicitly generate an envent; so, no explicit SEV with unlock is required.
*/
# define COND_SEV()
#endif
#if USE_CAS
/*
* Acquire lock using Compare and Swap instruction.
*
* Compare for 0 with acquire semantics, and swap 1. Wait until CAS returns
* 0.
*
* void spin_lock(spinlock_t *lock);
*/
func spin_lock
mov w2, #1
sevl
1:
wfe
mov w1, wzr
casa w1, w2, [x0]
cbnz w1, 1b
ret
endfunc spin_lock
#else /* !USE_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_CAS */
/*
* Release lock previously acquired by spin_lock.
*
* Unconditionally write 0, and conditionally generate an event.
*
* void spin_unlock(spinlock_t *lock);
*/
func spin_unlock
stlr wzr, [x0]
COND_SEV()
ret
endfunc spin_unlock