108 lines
2.6 KiB
ArmAsm
108 lines
2.6 KiB
ArmAsm
/*
|
|
* vlock.S - simple voting lock implementation for ARM
|
|
*
|
|
* Created by: Dave Martin, 2012-08-16
|
|
* Copyright: (C) 2012-2013 Linaro Limited
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License version 2 as
|
|
* published by the Free Software Foundation.
|
|
*
|
|
* This program is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
*
|
|
* 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)
|