[mirror_ubuntu-jammy-kernel.git] / arch / arm / common / vlock.S

/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * vlock.S - simple voting lock implementation for ARM
 *
 * Created by:	Dave Martin, 2012-08-16
 * Copyright:	(C) 2012-2013  Linaro Limited
 *
 * This algorithm is described in more detail in
 * Documentation/arm/vlocks.txt.
 */

#include <linux/linkage.h>
#include "vlock.h"

/* Select different code if voting flags  can fit in a single word. */
#if VLOCK_VOTING_SIZE > 4
#define FEW(x...)
#define MANY(x...) x
#else
#define FEW(x...) x
#define MANY(x...)
#endif

@ voting lock for first-man coordination

.macro voting_begin rbase:req, rcpu:req, rscratch:req
	mov	\rscratch, #1
	strb	\rscratch, [\rbase, \rcpu]
	dmb
.endm

.macro voting_end rbase:req, rcpu:req, rscratch:req
	dmb
	mov	\rscratch, #0
	strb	\rscratch, [\rbase, \rcpu]
	dsb	st
	sev
.endm

/*
 * The vlock structure must reside in Strongly-Ordered or Device memory.
 * This implementation deliberately eliminates most of the barriers which
 * would be required for other memory types, and assumes that independent
 * writes to neighbouring locations within a cacheline do not interfere
 * with one another.
 */

@ r0: lock structure base
@ r1: CPU ID (0-based index within cluster)
ENTRY(vlock_trylock)
	add	r1, r1, #VLOCK_VOTING_OFFSET

	voting_begin	r0, r1, r2

	ldrb	r2, [r0, #VLOCK_OWNER_OFFSET]	@ check whether lock is held
	cmp	r2, #VLOCK_OWNER_NONE
	bne	trylock_fail			@ fail if so

	@ Control dependency implies strb not observable before previous ldrb.

	strb	r1, [r0, #VLOCK_OWNER_OFFSET]	@ submit my vote

	voting_end	r0, r1, r2		@ implies DMB

	@ Wait for the current round of voting to finish:

 MANY(	mov	r3, #VLOCK_VOTING_OFFSET			)
0:
 MANY(	ldr	r2, [r0, r3]					)
 FEW(	ldr	r2, [r0, #VLOCK_VOTING_OFFSET]			)
	cmp	r2, #0
	wfene
	bne	0b
 MANY(	add	r3, r3, #4					)
 MANY(	cmp	r3, #VLOCK_VOTING_OFFSET + VLOCK_VOTING_SIZE	)
 MANY(	bne	0b						)

	@ Check who won:

	dmb
	ldrb	r2, [r0, #VLOCK_OWNER_OFFSET]
	eor	r0, r1, r2			@ zero if I won, else nonzero
	bx	lr

trylock_fail:
	voting_end	r0, r1, r2
	mov	r0, #1				@ nonzero indicates that I lost
	bx	lr
ENDPROC(vlock_trylock)

@ r0: lock structure base
ENTRY(vlock_unlock)
	dmb
	mov	r1, #VLOCK_OWNER_NONE
	strb	r1, [r0, #VLOCK_OWNER_OFFSET]
	dsb	st
	sev
	bx	lr
ENDPROC(vlock_unlock)
Commit	Line	Data
1802d0be	1	/* SPDX-License-Identifier: GPL-2.0-only */
9762f12d DM	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	*
9762f12d DM	8	* This algorithm is described in more detail in
	9	* Documentation/arm/vlocks.txt.
	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]
40a5c0b4	36	dsb st
9762f12d DM	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)
	50	ENTRY(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 )
	68	0:
	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
	85	trylock_fail:
	86	voting_end r0, r1, r2
	87	mov r0, #1 @ nonzero indicates that I lost
	88	bx lr
	89	ENDPROC(vlock_trylock)
	90
	91	@ r0: lock structure base
	92	ENTRY(vlock_unlock)
	93	dmb
	94	mov r1, #VLOCK_OWNER_NONE
	95	strb r1, [r0, #VLOCK_OWNER_OFFSET]
40a5c0b4	96	dsb st
9762f12d DM	97	sev
	98	bx lr
	99	ENDPROC(vlock_unlock)