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Commit a0feb6db authored by Lorenzo Pieralisi's avatar Lorenzo Pieralisi Committed by Russell King
Browse files

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: default avatarLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 3f31ae12

arch/arm/kernel/perf_event.c

+23 −0
Original line number Diff line number Diff line
@@ -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");