[PATCH] cpuidle: psci: Support CPU hotplug for the hierarchical model

[Ulf Hansson <ulf.hansson@linaro.org>]

When the hierarchical CPU topology is used and when a CPU is put offline,
that CPU prevents its PM domain from being powered off, which is because
genpd observes the corresponding attached device as being active from a
runtime PM point of view. Furthermore, any potential master PM domains are
also prevented from being powered off.

To address this limitation, let's add add a new CPU hotplug state
(CPUHP_AP_CPU_PM_STARTING) and register up/down callbacks for it, which
allows us to deal with runtime PM accordingly.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
---

Lorenzo, Sudeep, Rafael, Daniel,

Note that, this patch is based upon a recently posted series [1] and the intent
is to queue it on top. I can fold it into the series and resend it all, if that
makes it easier for people. Just tell me what you prefer.

Kind regards
Uffe

[1]
https://patchwork.kernel.org/cover/11263735/

---
 drivers/cpuidle/cpuidle-psci.c | 45 +++++++++++++++++++++++++++++++++-
 include/linux/cpuhotplug.h     |  1 +
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index 835c7c3aa118..46b481c524cc 100644
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c
@@ -8,6 +8,7 @@
 
 #define pr_fmt(fmt) "CPUidle PSCI: " fmt
 
+#include <linux/cpuhotplug.h>
 #include <linux/cpuidle.h>
 #include <linux/cpumask.h>
 #include <linux/cpu_pm.h>
@@ -31,6 +32,7 @@ struct psci_cpuidle_data {
 
 static DEFINE_PER_CPU_READ_MOSTLY(struct psci_cpuidle_data, psci_cpuidle_data);
 static DEFINE_PER_CPU(u32, domain_state);
+static bool psci_cpuidle_use_cpuhp;
 
 void psci_set_domain_state(u32 state)
 {
@@ -72,6 +74,44 @@ static int psci_enter_domain_idle_state(struct cpuidle_device *dev,
 	return ret;
 }
 
+static int psci_idle_cpuhp_up(unsigned int cpu)
+{
+	struct device *pd_dev = __this_cpu_read(psci_cpuidle_data.dev);
+
+	if (pd_dev)
+		pm_runtime_get_sync(pd_dev);
+
+	return 0;
+}
+
+static int psci_idle_cpuhp_down(unsigned int cpu)
+{
+	struct device *pd_dev = __this_cpu_read(psci_cpuidle_data.dev);
+
+	if (pd_dev) {
+		pm_runtime_put_sync(pd_dev);
+		/* Clear domain state to start fresh at next online. */
+		psci_set_domain_state(0);
+	}
+
+	return 0;
+}
+
+static void psci_idle_init_cpuhp(void)
+{
+	int err;
+
+	if (!psci_cpuidle_use_cpuhp)
+		return;
+
+	err = cpuhp_setup_state_nocalls(CPUHP_AP_CPU_PM_STARTING,
+					"cpuidle/psci:online",
+					psci_idle_cpuhp_up,
+					psci_idle_cpuhp_down);
+	if (err)
+		pr_warn("Failed %d while setup cpuhp state\n", err);
+}
+
 static int psci_enter_idle_state(struct cpuidle_device *dev,
 				struct cpuidle_driver *drv, int idx)
 {
@@ -161,9 +201,11 @@ static int __init psci_dt_cpu_init_idle(struct cpuidle_driver *drv,
 	}
 
 	/* Manage the deepest state via a dedicated enter-function. */
-	if (dev)
+	if (dev) {
 		drv->states[state_count - 1].enter =
 			psci_enter_domain_idle_state;
+		psci_cpuidle_use_cpuhp = true;
+	}
 
 	data->dev = dev;
 
@@ -285,6 +327,7 @@ static int __init psci_idle_init(void)
 			goto out_fail;
 	}
 
+	psci_idle_init_cpuhp();
 	return 0;
 
 out_fail:
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index e51ee772b9f5..01f04ed6ad92 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -95,6 +95,7 @@ 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,
-- 
2.17.1