perf: arm64: 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 value 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).

(cherry-picked from angler kernel)
Bug: 30839193

Change-Id: I0775acc020b5aa8eb79150498e342263c4429d2d

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/pmu.h b/arch/arm64/include/asm/pmu.h
index c9816daf85e0..48c59086aed2 100644
--- a/arch/arm64/include/asm/pmu.h
+++ b/arch/arm64/include/asm/pmu.h
@@ -67,6 +67,8 @@ struct arm_pmu {
 	u64			max_period;
 	struct platform_device	*plat_device;
 	struct pmu_hw_events	*(*get_hw_events)(void);
+	struct notifier_block	hotplug_nb;
+	struct notifier_block	cpu_pm_nb;
 	int			(*check_event)(
 					 struct arm_pmu *armpmu,
 					 struct hw_perf_event *hwc);