cpuidle: psci: Manage runtime PM in the idle path

In case we have succeeded to attach a CPU to its PM domain, let's deploy
runtime PM support for the corresponding attached device, to allow the CPU
to be powered-managed accordingly.

The triggering point for when runtime PM reference counting should be done,
has been selected to the deepest idle state for the CPU. However, from the
hierarchical point view, there may be good reasons to do runtime PM
reference counting even on shallower idle states, but at this point this
isn't supported, mainly due to limitations set by the generic PM domain.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>

drivers/cpuidle/cpuidle-psci.c

@@ -16,6 +16,7 @@
 #include <linux/of.h>
 #include <linux/of_device.h>
 #include <linux/psci.h>
+#include <linux/pm_runtime.h>
 #include <linux/slab.h>
 
 #include <asm/cpuidle.h>
@@ -51,14 +52,21 @@ static int psci_enter_domain_idle_state(struct cpuidle_device *dev,
 {
 	struct psci_cpuidle_data *data = this_cpu_ptr(&psci_cpuidle_data);
 	u32 *states = data->psci_states;
-	u32 state = psci_get_domain_state();
+	struct device *pd_dev = data->dev;
+	u32 state;
 	int ret;
 
+	/* Do runtime PM to manage a hierarchical CPU toplogy. */
+	pm_runtime_put_sync_suspend(pd_dev);
+
+	state = psci_get_domain_state();
 	if (!state)
 		state = states[idx];
 
 	ret = psci_enter_state(idx, state);
 
+	pm_runtime_get_sync(pd_dev);
+
 	/* Clear the domain state to start fresh when back from idle. */
 	psci_set_domain_state(0);
 	return ret;