[PATCH] drivers: perf: arm: implement CPU_PM notifier

When a CPU is suspended (either through suspend-to-RAM or CPUidle),
its PMU registers content can be lost, which means that counters
registers values that were initialized on power down entry have to be
reprogrammed on power-up to make sure the counters set-up is preserved
(ie on power-up registers take the reset values on Cold or Warm reset,
which can be architecturally UNKNOWN).

To guarantee seamless profiling conditions across a core power down
this patch adds a CPU PM notifier to ARM pmus, that upon CPU PM
entry/exit from low-power states saves/restores the pmu registers
set-up (by using the ARM perf API), so that the power-down/up cycle does
not affect the perf behaviour (apart from a black-out period between
power-up/down CPU PM notifications that is unavoidable).

Signed-off-by: Lorenzo Pieralisi <redacted>
Cc: Ashwin Chaugule <redacted>
Cc: Will Deacon <redacted>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: Sudeep Holla <redacted>
Cc: Daniel Lezcano <redacted>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
---
 drivers/perf/arm_pmu.c       | 95 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/perf/arm_pmu.h |  1 +
 2 files changed, 96 insertions(+)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 166637f..12317a9 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c

@@ -13,6 +13,7 @@

 #include <linux/bitmap.h>
 #include <linux/cpumask.h>
+#include <linux/cpu_pm.h>
 #include <linux/export.h>
 #include <linux/kernel.h>
 #include <linux/of_device.h>

@@ -710,6 +711,93 @@ static int cpu_pmu_notify(struct notifier_block *b, unsigned long action,
        return NOTIFY_OK;
 }

+#ifdef CONFIG_CPU_PM
+static void cpu_pm_pmu_setup(struct arm_pmu *armpmu, unsigned long cmd)
+{
+       struct pmu_hw_events *hw_events = this_cpu_ptr(armpmu->hw_events);
+       struct perf_event *event;
+       int idx;
+
+       for (idx = 0; idx < armpmu->num_events; idx++) {
+               /*
+                * If the counter is not used skip it, there is no
+                * need of stopping/restarting it.
+                */
+               if (!test_bit(idx, hw_events->used_mask))
+                       continue;
+
+               event = hw_events->events[idx];
+
+               switch (cmd) {
+               case CPU_PM_ENTER:
+                       /*
+                        * Stop and update the counter
+                        */
+                       armpmu_stop(event, PERF_EF_UPDATE);
+                       break;
+               case CPU_PM_EXIT:
+               case CPU_PM_ENTER_FAILED:
+                        /* Restore and enable the counter */
+                       armpmu_start(event, PERF_EF_RELOAD);
+                       break;
+               default:
+                       break;
+               }
+       }
+}
+
+static int cpu_pm_pmu_notify(struct notifier_block *b, unsigned long cmd,
+                            void *v)
+{
+       struct arm_pmu *armpmu = container_of(b, struct arm_pmu, cpu_pm_nb);
+       struct pmu_hw_events *hw_events = this_cpu_ptr(armpmu->hw_events);
+       int enabled = bitmap_weight(hw_events->used_mask, armpmu->num_events);
+
+       if (!cpumask_test_cpu(smp_processor_id(), &armpmu->supported_cpus))
+               return NOTIFY_DONE;
+
+       /*
+        * Always reset the PMU registers on power-up even if
+        * there are no events running.
+        */
+       if (cmd == CPU_PM_EXIT && armpmu->reset)
+               armpmu->reset(armpmu);

+
+       if (!enabled)
+               return NOTIFY_OK;
+
+       switch (cmd) {
+       case CPU_PM_ENTER:
+               armpmu->stop(armpmu);
+               cpu_pm_pmu_setup(armpmu, cmd);
+               break;
+       case CPU_PM_EXIT:
+               cpu_pm_pmu_setup(armpmu, cmd);
+       case CPU_PM_ENTER_FAILED:
+               armpmu->start(armpmu);
+               break;
+       default:
+               return NOTIFY_DONE;
+       }
+
+       return NOTIFY_OK;
+}
+
+static int cpu_pm_pmu_register(struct arm_pmu *cpu_pmu)
+{
+       cpu_pmu->cpu_pm_nb.notifier_call = cpu_pm_pmu_notify;
+       return cpu_pm_register_notifier(&cpu_pmu->cpu_pm_nb);
+}
+
+static void cpu_pm_pmu_unregister(struct arm_pmu *cpu_pmu)
+{
+       cpu_pm_unregister_notifier(&cpu_pmu->cpu_pm_nb);
+}
+#else
+static inline int cpu_pm_pmu_register(struct arm_pmu *cpu_pmu) { return 0; }
+static inline void cpu_pm_pmu_unregister(struct arm_pmu *cpu_pmu) { }
+#endif
+
 static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
 {
        int err;

@@ -725,6 +813,10 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
        if (err)
                goto out_hw_events;

+       err = cpu_pm_pmu_register(cpu_pmu);
+       if (err)
+               goto out_unregister;
+
        for_each_possible_cpu(cpu) {
                struct pmu_hw_events *events = per_cpu_ptr(cpu_hw_events, cpu);
                raw_spin_lock_init(&events->pmu_lock);

@@ -746,6 +838,8 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu)

        return 0;

+out_unregister:
+       unregister_cpu_notifier(&cpu_pmu->hotplug_nb);
 out_hw_events:
        free_percpu(cpu_hw_events);
        return err;

@@ -753,6 +847,7 @@ out_hw_events:

 static void cpu_pmu_destroy(struct arm_pmu *cpu_pmu)
 {
+       cpu_pm_pmu_unregister(cpu_pmu);
        unregister_cpu_notifier(&cpu_pmu->hotplug_nb);
        free_percpu(cpu_pmu->hw_events);
 }

diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 83b5e34..9ffa316 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h

@@ -107,6 +107,7 @@ struct arm_pmu {
        struct platform_device  *plat_device;
        struct pmu_hw_events    __percpu *hw_events;
        struct notifier_block   hotplug_nb;
+       struct notifier_block   cpu_pm_nb;
 };

 #define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))
--

2.5.1