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ARM: 7358/1: perf: add PMU hotplug notifier 

When a CPU is taken out of reset, either cold booted or hotplugged in,
some of its PMU registers can contain UNKNOWN values.

This patch adds a hotplug notifier to ARM core perf code so that upon
CPU restart the PMU unit is reset and becomes ready to use again.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Lorenzo Pieralisi 2012-03-06 17:37:45 +01:00 committed by Russell King
parent 3f31ae1213
commit a0feb6db0f
1 changed files with 23 additions and 0 deletions
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23
arch/arm/kernel/perf_event.c
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@ -679,6 +679,28 @@ static void __init cpu_pmu_init(struct arm_pmu *armpmu)
armpmu->type = ARM_PMU_DEVICE_CPU;
}
/*
* PMU hardware loses all context when a CPU goes offline.
* When a CPU is hotplugged back in, since some hardware registers are
* UNKNOWN at reset, the PMU must be explicitly reset to avoid reading
* junk values out of them.
*/
static int __cpuinit pmu_cpu_notify(struct notifier_block *b,
unsigned long action, void *hcpu)
{
if ((action & ~CPU_TASKS_FROZEN) != CPU_STARTING)
return NOTIFY_DONE;
if (cpu_pmu && cpu_pmu->reset)
cpu_pmu->reset(NULL);
return NOTIFY_OK;
}
static struct notifier_block __cpuinitdata pmu_cpu_notifier = {
.notifier_call = pmu_cpu_notify,
};
/*
* CPU PMU identification and registration.
*/
@ -730,6 +752,7 @@ init_hw_perf_events(void)
pr_info("enabled with %s PMU driver, %d counters available\n",
cpu_pmu->name, cpu_pmu->num_events);
cpu_pmu_init(cpu_pmu);
register_cpu_notifier(&pmu_cpu_notifier);
armpmu_register(cpu_pmu, "cpu", PERF_TYPE_RAW);
} else {
pr_info("no hardware support available\n");