[PATCH 1/2] cpuidle: add hotplug support to initialize the timer broadcast

[Daniel Lezcano <daniel.lezcano@linaro.org>]

Commit 89878baa73f0f1c679355006bd8632e5d78f96c2 introduced the flag
CPUIDLE_FLAG_TIMER_STOP where we specify a specific idle state stops the local
timer.

Commit a06df062a189a8d5588babb8bf0bb78672497798 introduced the initialization
of the timer broadcast framework depending of the flag presence.

If a system is booted with some cpus offline, by setting for example, maxcpus=1
in the kernel command line, and then they are set online, the timer broadcast
won't be setup automatically.

Fix this by adding the cpu hotplug notifier and enable/disable the timer
broadcast automatically. So no need to handle that at the arch specific driver
level like eg. intel_idle does.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
 drivers/cpuidle/driver.c |   48 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
index 3ac499d..e976994 100644
--- a/drivers/cpuidle/driver.c
+++ b/drivers/cpuidle/driver.c
@@ -10,6 +10,7 @@
 
 #include <linux/mutex.h>
 #include <linux/module.h>
+#include <linux/cpu.h>
 #include <linux/cpuidle.h>
 #include <linux/cpumask.h>
 #include <linux/clockchips.h>
@@ -147,6 +148,48 @@ static void cpuidle_setup_broadcast_timer(void *arg)
 }
 
 /**
+ * cpuidle_hotplug_notify: notifier callback when a cpu is onlined/offlined
+ * @n: the notifier block
+ * @action: an unsigned long giving the event related to the notification
+ * @hcpu: a void pointer but used as the cpu number which the event is related
+ *
+ * The kernel can boot with some cpus offline, we have to init the timer
+ * broadcast for these cpus when they are onlined. Also we have to disable
+ * the timer broadcast when the cpu is down.
+ *
+ * Returns NOTIFY_OK
+ */
+static int cpuidle_hotplug_notify(struct notifier_block *n,
+				  unsigned long action, void *hcpu)
+{
+	int cpu = (unsigned long)hcpu;
+	struct cpuidle_driver *drv;
+
+	drv = __cpuidle_get_cpu_driver(cpu);
+	if (!drv || !drv->bctimer)
+		goto out;
+
+	switch (action & 0xf) {
+	case CPU_ONLINE:
+		smp_call_function_single(cpu, cpuidle_setup_broadcast_timer,
+					 (void *)CLOCK_EVT_NOTIFY_BROADCAST_ON,
+					 1);
+		break;
+	case CPU_DEAD:
+		smp_call_function_single(cpu, cpuidle_setup_broadcast_timer,
+					 (void *)CLOCK_EVT_NOTIFY_BROADCAST_OFF,
+					 1);
+		break;
+	}
+out:
+	return NOTIFY_OK;
+}
+
+static struct notifier_block cpuidle_hotplug_notifier = {
+	.notifier_call = cpuidle_hotplug_notify,
+};
+
+/**
  * __cpuidle_driver_init - initialize the driver's internal data
  * @drv: a valid pointer to a struct cpuidle_driver
  *
@@ -262,6 +305,9 @@ int cpuidle_register_driver(struct cpuidle_driver *drv)
 	ret = __cpuidle_register_driver(drv);
 	spin_unlock(&cpuidle_driver_lock);
 
+	if (!ret)
+		ret = register_cpu_notifier(&cpuidle_hotplug_notifier);
+
 	return ret;
 }
 EXPORT_SYMBOL_GPL(cpuidle_register_driver);
@@ -276,6 +322,8 @@ EXPORT_SYMBOL_GPL(cpuidle_register_driver);
  */
 void cpuidle_unregister_driver(struct cpuidle_driver *drv)
 {
+	unregister_cpu_notifier(&cpuidle_hotplug_notifier);
+
 	spin_lock(&cpuidle_driver_lock);
 	__cpuidle_unregister_driver(drv);
 	spin_unlock(&cpuidle_driver_lock);
-- 
1.7.9.5