1/* SPDX-License-Identifier: GPL-2.0-only */
  2/*
  3 * vlock.S - simple voting lock implementation for ARM
  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 in
  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 fit in a single word. */
 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, rscratch:req
 29	mov	\rscratch, #1
 30	strb	\rscratch, [\rbase, \rcpu]
 31	dmb
 32.endm
 33
 34.macro voting_end rbase:req, rcpu:req, rscratch:req
 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-Ordered or Device memory.
 44 * This implementation deliberately eliminates most of the barriers which
 45 * would be required for other memory types, and assumes that independent
 46 * writes to neighbouring locations within a cacheline do not interfere
 47 * with one another.
 48 */
 49
 50@ r0: lock structure base
 51@ r1: CPU ID (0-based index within cluster)
 52ENTRY(vlock_trylock)
 53	add	r1, r1, #VLOCK_VOTING_OFFSET
 54
 55	voting_begin	r0, r1, r2
 56
 57	ldrb	r2, [r0, #VLOCK_OWNER_OFFSET]	@ check whether lock is held
 58	cmp	r2, #VLOCK_OWNER_NONE
 59	bne	trylock_fail			@ fail if so
 60
 61	@ Control dependency implies strb not observable before previous ldrb.
 62
 63	strb	r1, [r0, #VLOCK_OWNER_OFFSET]	@ submit my vote
 64
 65	voting_end	r0, r1, r2		@ implies DMB
 66
 67	@ Wait for the current round of voting to finish:
 68
 69 MANY(	mov	r3, #VLOCK_VOTING_OFFSET			)
 700:
 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 + VLOCK_VOTING_SIZE	)
 78 MANY(	bne	0b						)
 79
 80	@ Check who won:
 81
 82	dmb
 83	ldrb	r2, [r0, #VLOCK_OWNER_OFFSET]
 84	eor	r0, r1, r2			@ zero if I won, else nonzero
 85	bx	lr
 86
 87trylock_fail:
 88	voting_end	r0, r1, r2
 89	mov	r0, #1				@ nonzero indicates that I lost
 90	bx	lr
 91ENDPROC(vlock_trylock)
 92
 93@ r0: lock structure base
 94ENTRY(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
101ENDPROC(vlock_unlock)

 1/* SPDX-License-Identifier: GPL-2.0-only */
 2/*
 3 * vlock.S - simple voting lock implementation for ARM
 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 in
 9 * Documentation/arm/vlocks.rst.
10 */
11
12#include <linux/linkage.h>
13#include "vlock.h"
 
 
14
15/* Select different code if voting flags  can fit in a single word. */
16#if VLOCK_VOTING_SIZE > 4
17#define FEW(x...)
18#define MANY(x...) x
19#else
20#define FEW(x...) x
21#define MANY(x...)
22#endif
23
24@ voting lock for first-man coordination
25
26.macro voting_begin rbase:req, rcpu:req, rscratch:req
27	mov	\rscratch, #1
28	strb	\rscratch, [\rbase, \rcpu]
29	dmb
30.endm
31
32.macro voting_end rbase:req, rcpu:req, rscratch:req
33	dmb
34	mov	\rscratch, #0
35	strb	\rscratch, [\rbase, \rcpu]
36	dsb	st
37	sev
38.endm
39
40/*
41 * The vlock structure must reside in Strongly-Ordered or Device memory.
42 * This implementation deliberately eliminates most of the barriers which
43 * would be required for other memory types, and assumes that independent
44 * writes to neighbouring locations within a cacheline do not interfere
45 * with one another.
46 */
47
48@ r0: lock structure base
49@ r1: CPU ID (0-based index within cluster)
50ENTRY(vlock_trylock)
51	add	r1, r1, #VLOCK_VOTING_OFFSET
52
53	voting_begin	r0, r1, r2
54
55	ldrb	r2, [r0, #VLOCK_OWNER_OFFSET]	@ check whether lock is held
56	cmp	r2, #VLOCK_OWNER_NONE
57	bne	trylock_fail			@ fail if so
58
59	@ Control dependency implies strb not observable before previous ldrb.
60
61	strb	r1, [r0, #VLOCK_OWNER_OFFSET]	@ submit my vote
62
63	voting_end	r0, r1, r2		@ implies DMB
64
65	@ Wait for the current round of voting to finish:
66
67 MANY(	mov	r3, #VLOCK_VOTING_OFFSET			)
680:
69 MANY(	ldr	r2, [r0, r3]					)
70 FEW(	ldr	r2, [r0, #VLOCK_VOTING_OFFSET]			)
71	cmp	r2, #0
72	wfene
73	bne	0b
74 MANY(	add	r3, r3, #4					)
75 MANY(	cmp	r3, #VLOCK_VOTING_OFFSET + VLOCK_VOTING_SIZE	)
76 MANY(	bne	0b						)
77
78	@ Check who won:
79
80	dmb
81	ldrb	r2, [r0, #VLOCK_OWNER_OFFSET]
82	eor	r0, r1, r2			@ zero if I won, else nonzero
83	bx	lr
84
85trylock_fail:
86	voting_end	r0, r1, r2
87	mov	r0, #1				@ nonzero indicates that I lost
88	bx	lr
89ENDPROC(vlock_trylock)
90
91@ r0: lock structure base
92ENTRY(vlock_unlock)
93	dmb
94	mov	r1, #VLOCK_OWNER_NONE
95	strb	r1, [r0, #VLOCK_OWNER_OFFSET]
96	dsb	st
97	sev
98	bx	lr
99ENDPROC(vlock_unlock)