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linux-next/arch/arm/common/mcpm_head.S
Will Deacon 40a5c0b415 ARM: mcpm: use -st dsb option prior to sev instructions 
In a similar manner to our spinlock implementation, mcpm uses sev to
wake up cores waiting on a lock when the lock is unlocked. In order to
ensure that the final write unlocking the lock is visible, a dsb
instruction is executed immediately prior to the sev.

This patch changes these dsbs to use the -st option, since we only
require that the store unlocking the lock is made visible.

Acked-by: Nicolas Pitre <nico@linaro.org>
Reviewed-by: Dave Martin <dave.martin@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
2013-08-12 12:25:45 +01:00

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/*
* arch/arm/common/mcpm_head.S -- kernel entry point for multi-cluster PM
*
* Created by: Nicolas Pitre, March 2012
* 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.
*
*
* Refer to Documentation/arm/cluster-pm-race-avoidance.txt
* for details of the synchronisation algorithms used here.
*/
#include <linux/linkage.h>
#include <asm/mcpm.h>
#include "vlock.h"
.if MCPM_SYNC_CLUSTER_CPUS
.error "cpus must be the first member of struct mcpm_sync_struct"
.endif
.macro pr_dbg string
#if defined(CONFIG_DEBUG_LL) && defined(DEBUG)
b 1901f
1902: .asciz "CPU"
1903: .asciz " cluster"
1904: .asciz ": \string"
.align
1901: adr r0, 1902b
bl printascii
mov r0, r9
bl printhex2
adr r0, 1903b
bl printascii
mov r0, r10
bl printhex2
adr r0, 1904b
bl printascii
#endif
.endm
.arm
.align
ENTRY(mcpm_entry_point)
THUMB( adr r12, BSYM(1f) )
THUMB( bx r12 )
THUMB( .thumb )
1:
mrc p15, 0, r0, c0, c0, 5 @ MPIDR
ubfx r9, r0, #0, #8 @ r9 = cpu
ubfx r10, r0, #8, #8 @ r10 = cluster
mov r3, #MAX_CPUS_PER_CLUSTER
mla r4, r3, r10, r9 @ r4 = canonical CPU index
cmp r4, #(MAX_CPUS_PER_CLUSTER * MAX_NR_CLUSTERS)
blo 2f
/* We didn't expect this CPU. Try to cheaply make it quiet. */
1: wfi
wfe
b 1b
2: pr_dbg "kernel mcpm_entry_point\n"
/*
* MMU is off so we need to get to various variables in a
* position independent way.
*/
adr r5, 3f
ldmia r5, {r6, r7, r8, r11}
add r6, r5, r6 @ r6 = mcpm_entry_vectors
ldr r7, [r5, r7] @ r7 = mcpm_power_up_setup_phys
add r8, r5, r8 @ r8 = mcpm_sync
add r11, r5, r11 @ r11 = first_man_locks
mov r0, #MCPM_SYNC_CLUSTER_SIZE
mla r8, r0, r10, r8 @ r8 = sync cluster base
@ Signal that this CPU is coming UP:
mov r0, #CPU_COMING_UP
mov r5, #MCPM_SYNC_CPU_SIZE
mla r5, r9, r5, r8 @ r5 = sync cpu address
strb r0, [r5]
@ At this point, the cluster cannot unexpectedly enter the GOING_DOWN
@ state, because there is at least one active CPU (this CPU).
mov r0, #VLOCK_SIZE
mla r11, r0, r10, r11 @ r11 = cluster first man lock
mov r0, r11
mov r1, r9 @ cpu
bl vlock_trylock @ implies DMB
cmp r0, #0 @ failed to get the lock?
bne mcpm_setup_wait @ wait for cluster setup if so
ldrb r0, [r8, #MCPM_SYNC_CLUSTER_CLUSTER]
cmp r0, #CLUSTER_UP @ cluster already up?
bne mcpm_setup @ if not, set up the cluster
@ Otherwise, release the first man lock and skip setup:
mov r0, r11
bl vlock_unlock
b mcpm_setup_complete
mcpm_setup:
@ Control dependency implies strb not observable before previous ldrb.
@ Signal that the cluster is being brought up:
mov r0, #INBOUND_COMING_UP
strb r0, [r8, #MCPM_SYNC_CLUSTER_INBOUND]
dmb
@ Any CPU trying to take the cluster into CLUSTER_GOING_DOWN from this
@ point onwards will observe INBOUND_COMING_UP and abort.
@ Wait for any previously-pending cluster teardown operations to abort
@ or complete:
mcpm_teardown_wait:
ldrb r0, [r8, #MCPM_SYNC_CLUSTER_CLUSTER]
cmp r0, #CLUSTER_GOING_DOWN
bne first_man_setup
wfe
b mcpm_teardown_wait
first_man_setup:
dmb
@ If the outbound gave up before teardown started, skip cluster setup:
cmp r0, #CLUSTER_UP
beq mcpm_setup_leave
@ power_up_setup is now responsible for setting up the cluster:
cmp r7, #0
mov r0, #1 @ second (cluster) affinity level
blxne r7 @ Call power_up_setup if defined
dmb
mov r0, #CLUSTER_UP
strb r0, [r8, #MCPM_SYNC_CLUSTER_CLUSTER]
dmb
mcpm_setup_leave:
@ Leave the cluster setup critical section:
mov r0, #INBOUND_NOT_COMING_UP
strb r0, [r8, #MCPM_SYNC_CLUSTER_INBOUND]
dsb st
sev
mov r0, r11
bl vlock_unlock @ implies DMB
b mcpm_setup_complete
@ In the contended case, non-first men wait here for cluster setup
@ to complete:
mcpm_setup_wait:
ldrb r0, [r8, #MCPM_SYNC_CLUSTER_CLUSTER]
cmp r0, #CLUSTER_UP
wfene
bne mcpm_setup_wait
dmb
mcpm_setup_complete:
@ If a platform-specific CPU setup hook is needed, it is
@ called from here.
cmp r7, #0
mov r0, #0 @ first (CPU) affinity level
blxne r7 @ Call power_up_setup if defined
dmb
@ Mark the CPU as up:
mov r0, #CPU_UP
strb r0, [r5]
@ Observability order of CPU_UP and opening of the gate does not matter.
mcpm_entry_gated:
ldr r5, [r6, r4, lsl #2] @ r5 = CPU entry vector
cmp r5, #0
wfeeq
beq mcpm_entry_gated
dmb
pr_dbg "released\n"
bx r5
.align 2
3: .word mcpm_entry_vectors - .
.word mcpm_power_up_setup_phys - 3b
.word mcpm_sync - 3b
.word first_man_locks - 3b
ENDPROC(mcpm_entry_point)
.bss
.align CACHE_WRITEBACK_ORDER
.type first_man_locks, #object
first_man_locks:
.space VLOCK_SIZE * MAX_NR_CLUSTERS
.align CACHE_WRITEBACK_ORDER
.type mcpm_entry_vectors, #object
ENTRY(mcpm_entry_vectors)
.space 4 * MAX_NR_CLUSTERS * MAX_CPUS_PER_CLUSTER
.type mcpm_power_up_setup_phys, #object
ENTRY(mcpm_power_up_setup_phys)
.space 4 @ set by mcpm_sync_init()
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