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ARM: mcpm_head.S: vlock-based first man election

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Instead of requiring the first man to be elected in advance (which
can be suboptimal in some situations), this patch uses a per-
cluster mutex to co-ordinate selection of the first man.

This should also make it more feasible to reuse this code path for
asynchronous cluster resume (as in CPUidle scenarios).

We must ensure that the vlock data doesn't share a cacheline with
anything else, or dirty cache eviction could corrupt it.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Dave Martin 2012-08-17 16:07:02 +01:00 committed by Nicolas Pitre
parent 9762f12d3e
commit 1ae98561b1
3 changed files with 38 additions and 6 deletions
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2
arch/arm/common/Makefile
View File

@ -11,4 +11,4 @@ obj-$(CONFIG_SHARP_PARAM) += sharpsl_param.o
obj-$(CONFIG_SHARP_SCOOP) += scoop.o
obj-$(CONFIG_PCI_HOST_ITE8152) += it8152.o
obj-$(CONFIG_ARM_TIMER_SP804) += timer-sp.o
obj-$(CONFIG_MCPM) += mcpm_head.o mcpm_entry.o
obj-$(CONFIG_MCPM) += mcpm_head.o mcpm_entry.o vlock.o

41
arch/arm/common/mcpm_head.S
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@ -16,6 +16,8 @@
#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
@ -69,10 +71,11 @@ ENTRY(mcpm_entry_point)
* position independent way.
*/
adr r5, 3f
ldmia r5, {r6, r7, r8}
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
@ -86,13 +89,22 @@ ENTRY(mcpm_entry_point)
@ At this point, the cluster cannot unexpectedly enter the GOING_DOWN
@ state, because there is at least one active CPU (this CPU).
@ Note: the following is racy as another CPU might be testing
@ the same flag at the same moment. That'll be fixed later.
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, skip setup:
@ Otherwise, release the first man lock and skip setup:
mov r0, r11
bl vlock_unlock
b mcpm_setup_complete
mcpm_setup:
@ -142,6 +154,19 @@ mcpm_setup_leave:
dsb
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.
@ -173,11 +198,17 @@ mcpm_entry_gated:
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 5
.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)

1
arch/arm/kernel/asm-offsets.c
View File

@ -150,6 +150,7 @@ int main(void)
DEFINE(DMA_TO_DEVICE, DMA_TO_DEVICE);
DEFINE(DMA_FROM_DEVICE, DMA_FROM_DEVICE);
BLANK();
DEFINE(CACHE_WRITEBACK_ORDER, __CACHE_WRITEBACK_ORDER);
DEFINE(CACHE_WRITEBACK_GRANULE, __CACHE_WRITEBACK_GRANULE);
BLANK();
#ifdef CONFIG_KVM_ARM_HOST