1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /*
3 * vlock.S - simple voting lock implementation
4 *
5 * Created by: Dave Martin, 2012-08-16
6 * Copyright: (C) 2012-2013 Linaro Limited
7 *
8 * This algorithm is described in more detail
9 * Documentation/arch/arm/vlocks.rst.
10 */
11
12 #include <linux/linkage.h>
13 #include "vlock.h"
14
15 .arch armv7-a
16
17 /* Select different code if voting flags can
18 #if VLOCK_VOTING_SIZE > 4
19 #define FEW(x...)
20 #define MANY(x...) x
21 #else
22 #define FEW(x...) x
23 #define MANY(x...)
24 #endif
25
26 @ voting lock for first-man coordination
27
28 .macro voting_begin rbase:req, rcpu:req, rscra
29 mov \rscratch, #1
30 strb \rscratch, [\rbase, \rcpu]
31 dmb
32 .endm
33
34 .macro voting_end rbase:req, rcpu:req, rscratc
35 dmb
36 mov \rscratch, #0
37 strb \rscratch, [\rbase, \rcpu]
38 dsb st
39 sev
40 .endm
41
42 /*
43 * The vlock structure must reside in Strongly
44 * This implementation deliberately eliminates
45 * would be required for other memory types, a
46 * writes to neighbouring locations within a c
47 * with one another.
48 */
49
50 @ r0: lock structure base
51 @ r1: CPU ID (0-based index within cluster)
52 ENTRY(vlock_trylock)
53 add r1, r1, #VLOCK_VOTING_OFFSET
54
55 voting_begin r0, r1, r2
56
57 ldrb r2, [r0, #VLOCK_OWNER_OFFSET]
58 cmp r2, #VLOCK_OWNER_NONE
59 bne trylock_fail
60
61 @ Control dependency implies strb not
62
63 strb r1, [r0, #VLOCK_OWNER_OFFSET]
64
65 voting_end r0, r1, r2
66
67 @ Wait for the current round of voting
68
69 MANY( mov r3, #VLOCK_VOTING_OFFSET
70 0:
71 MANY( ldr r2, [r0, r3]
72 FEW( ldr r2, [r0, #VLOCK_VOTING_OFFSET]
73 cmp r2, #0
74 wfene
75 bne 0b
76 MANY( add r3, r3, #4
77 MANY( cmp r3, #VLOCK_VOTING_OFFSET + VLO
78 MANY( bne 0b
79
80 @ Check who won:
81
82 dmb
83 ldrb r2, [r0, #VLOCK_OWNER_OFFSET]
84 eor r0, r1, r2
85 bx lr
86
87 trylock_fail:
88 voting_end r0, r1, r2
89 mov r0, #1
90 bx lr
91 ENDPROC(vlock_trylock)
92
93 @ r0: lock structure base
94 ENTRY(vlock_unlock)
95 dmb
96 mov r1, #VLOCK_OWNER_NONE
97 strb r1, [r0, #VLOCK_OWNER_OFFSET]
98 dsb st
99 sev
100 bx lr
101 ENDPROC(vlock_unlock)
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