From a0feb6db0fe03326d7d2c7a4615ce3289615c023 Mon Sep 17 00:00:00 2001 From: Lorenzo Pieralisi Date: Tue, 6 Mar 2012 17:37:45 +0100 Subject: [PATCH] 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 Signed-off-by: Will Deacon Signed-off-by: Russell King --- arch/arm/kernel/perf_event.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c index 56173ae1644..b2abfa18f13 100644 --- a/arch/arm/kernel/perf_event.c +++ b/arch/arm/kernel/perf_event.c @@ -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"); -- 2.20.1