Notify runtime PM when the CPU is going to be powered off in the idle
state. This allows for runtime PM suspend/resume of the CPU as well as
its PM domain.

Cc: Kevin Hilman <khilman@kernel.org>
Cc: Rafael J. Wysocki <redacted>
Signed-off-by: Lina Iyer <redacted>
---
 include/linux/cpuhotplug.h |  1 +
 kernel/cpu_pm.c            | 47 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 921acaa..448226a 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h

@@ -79,6 +79,7 @@ enum cpuhp_state {
        CPUHP_AP_OFFLINE,
        CPUHP_AP_SCHED_STARTING,
        CPUHP_AP_RCUTREE_DYING,
+       CPUHP_AP_CPU_PM_STARTING,
        CPUHP_AP_IRQ_GIC_STARTING,
        CPUHP_AP_IRQ_HIP04_STARTING,
        CPUHP_AP_IRQ_ARMADA_XP_STARTING,

diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c
index 009cc9a..db95ef3 100644
--- a/kernel/cpu_pm.c
+++ b/kernel/cpu_pm.c

@@ -16,9 +16,12 @@
  */

 #include <linux/kernel.h>
+#include <linux/cpu.h>
+#include <linux/cpuhotplug.h>
 #include <linux/cpu_pm.h>
 #include <linux/module.h>
 #include <linux/notifier.h>
+#include <linux/pm_runtime.h>
 #include <linux/spinlock.h>
 #include <linux/syscore_ops.h>

@@ -99,6 +102,7 @@ int cpu_pm_enter(void)
 {
        int nr_calls;
        int ret = 0;
+       struct device *dev = get_cpu_device(smp_processor_id());

        read_lock(&cpu_pm_notifier_lock);
        ret = cpu_pm_notify(CPU_PM_ENTER, -1, &nr_calls);

@@ -110,6 +114,10 @@ int cpu_pm_enter(void)
                cpu_pm_notify(CPU_PM_ENTER_FAILED, nr_calls - 1, NULL);
        read_unlock(&cpu_pm_notifier_lock);

+       /* Notify Runtime PM that we are suspending the CPU */
+       if (!ret && dev)
+               RCU_NONIDLE(pm_runtime_put_sync_suspend(dev));
+

        return ret;
 }
 EXPORT_SYMBOL_GPL(cpu_pm_enter);

@@ -129,6 +137,11 @@ EXPORT_SYMBOL_GPL(cpu_pm_enter);
 int cpu_pm_exit(void)
 {
        int ret;
+       struct device *dev = get_cpu_device(smp_processor_id());
+
+       /* Notify Runtime PM that we are resuming the CPU */
+       if (dev)
+               RCU_NONIDLE(pm_runtime_get_sync(dev));

        read_lock(&cpu_pm_notifier_lock);
        ret = cpu_pm_notify(CPU_PM_EXIT, -1, NULL);

@@ -200,6 +213,40 @@ int cpu_cluster_pm_exit(void)
 }
 EXPORT_SYMBOL_GPL(cpu_cluster_pm_exit);

+#ifdef CONFIG_HOTPLUG_CPU
+static int cpu_pm_cpu_dying(unsigned int cpu)
+{
+       struct device *dev = get_cpu_device(cpu);
+
+       if (dev)
+               pm_runtime_put_sync_suspend(dev);
+
+       return 0;
+}
+
+static int cpu_pm_cpu_starting(unsigned int cpu)
+{
+       struct device *dev = get_cpu_device(cpu);
+
+       if (dev)
+               pm_runtime_get_sync(dev);