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>

1 files changed, 95 insertions, 0 deletions

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index ca63a452393a..11bacc7220a1 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);
 }