[PATCH 12/13] cpuidle: psci: Manage runtime PM in the idle path

[Ulf Hansson <ulf.hansson@xxxxxxxxxx>]

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.

To set the triggering point for when runtime PM reference counting should
be done, let's store the index of deepest idle state for the CPU in the per
CPU struct. Then use this index to compare the selected idle state index
when entering idle, as to understand whether runtime PM reference counting
is needed or not.

Note that, 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@xxxxxxxxxx>
---
 drivers/cpuidle/cpuidle-psci.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index 1510422c7a53..0919b40c1a85 100644
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/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>
@@ -25,6 +26,7 @@
 
 struct psci_cpuidle_data {
 	u32 *psci_states;
+	u32 rpm_state_id;
 	struct device *dev;
 };
 
@@ -50,14 +52,28 @@ static int psci_enter_idle_state(struct cpuidle_device *dev,
 				struct cpuidle_driver *drv, int idx)
 {
 	int ret;
-	u32 *states = __this_cpu_read(psci_cpuidle_data.psci_states);
-	u32 state = psci_get_domain_state();
+	struct psci_cpuidle_data *data = this_cpu_ptr(&psci_cpuidle_data);
+	u32 *states = data->psci_states;
+	struct device *pd_dev = data->dev;
+	bool runtime_pm = (pd_dev && data->rpm_state_id == idx);
+	u32 state;
 
+	/*
+	 * Do runtime PM if we are using the hierarchical CPU toplogy, but only
+	 * when cpuidle have selected the deepest idle state for the CPU.
+	 */
+	if (runtime_pm)
+		pm_runtime_put_sync_suspend(pd_dev);
+
+	state = psci_get_domain_state();
 	if (!state && idx)
 		state = states[idx - 1];
 
 	ret = __psci_enter_idle_state(idx, state);
 
+	if (runtime_pm)
+		pm_runtime_get_sync(pd_dev);
+
 	/* Clear the domain state to start fresh when back from idle. */
 	psci_set_domain_state(0);
 	return ret;
@@ -142,6 +158,7 @@ static int __init psci_dt_cpu_init_idle(struct device_node *cpu_node,
 	}
 
 	data->dev = dev;
+	data->rpm_state_id = state_nodes;
 
 	/* Idle states parsed correctly, store them in the per-cpu struct. */
 	data->psci_states = psci_states;
-- 
2.17.1