drivers/perf: arm_pmu: 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).

Cc: Will Deacon <will.deacon@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: Ashwin Chaugule <ashwin.chaugule@linaro.org>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

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);
@@ -746,13 +838,16 @@ 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;
 }
 
 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);
 }

include/linux/perf/arm_pmu.h

@@ -108,6 +108,7 @@ 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))