[PATCH] cpuidle: cpu hotplug support

[Zhenzhong Duan <zhenzhong.duan@oracle.com>]

Currently cpuidle driver doesn't support cpu hotplug. When
cpus != maxcpus cpuidle_register() will fail to register all cpus
past the online ones and thus fail to register the idle driver.
This is because cpuidle_add_sysfs() will return with -ENODEV as a
consequence from get_cpu_device() return no device for a non-existing
CPU.

At least cpuidle-haltpoll and intel_idle are making their own custom
code to support cpu hotplug.

This patch ease the work if we need to write a cpuidle driver with cpu
hotplug support in the future.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
---
 drivers/cpuidle/cpuidle.c | 76 ++++++++++++++++++++++++++++++++---------------
 1 file changed, 52 insertions(+), 24 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 0895b98..3ce6d2d 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -558,6 +558,51 @@ static void __cpuidle_device_init(struct cpuidle_device *dev)
 	dev->next_hrtimer = 0;
 }
 
+static int cpuidle_cpu_online(unsigned int cpu)
+{
+	int ret;
+	struct cpuidle_device *device;
+	struct cpuidle_driver *drv;
+
+	device = &per_cpu(cpuidle_dev, cpu);
+	device->cpu = cpu;
+
+	drv = cpuidle_get_cpu_driver(device);
+	if (!drv || !cpumask_test_cpu(cpu, drv->cpumask))
+		return 0;
+
+#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
+	/*
+	 * On multiplatform for ARM, the coupled idle states could be
+	 * enabled in the kernel even if the cpuidle driver does not
+	 * use it. Note, coupled_cpus is a struct copy.
+	 */
+	if (coupled_cpus)
+		device->coupled_cpus = *coupled_cpus;
+#endif
+	ret = cpuidle_register_device(device);
+	if (ret)
+		pr_err("Failed to register cpuidle device for cpu%d\n", cpu);
+
+	return ret;
+}
+
+static int cpuidle_cpu_offline(unsigned int cpu)
+{
+	struct cpuidle_device *device;
+	struct cpuidle_driver *drv;
+
+	device = &per_cpu(cpuidle_dev, cpu);
+
+	drv = cpuidle_get_cpu_driver(device);
+	if (!drv || !cpumask_test_cpu(cpu, drv->cpumask))
+		return 0;
+
+	cpuidle_unregister_device(device);
+
+	return 0;
+}
+
 /**
  * __cpuidle_register_device - internal register function called before register
  * and enable routines
@@ -690,8 +735,8 @@ void cpuidle_unregister(struct cpuidle_driver *drv)
 int cpuidle_register(struct cpuidle_driver *drv,
 		     const struct cpumask *const coupled_cpus)
 {
-	int ret, cpu;
-	struct cpuidle_device *device;
+	int ret;
+	char cb_name[64];
 
 	ret = cpuidle_register_driver(drv);
 	if (ret) {
@@ -699,28 +744,11 @@ int cpuidle_register(struct cpuidle_driver *drv,
 		return ret;
 	}
 
-	for_each_cpu(cpu, drv->cpumask) {
-		device = &per_cpu(cpuidle_dev, cpu);
-		device->cpu = cpu;
-
-#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
-		/*
-		 * On multiplatform for ARM, the coupled idle states could be
-		 * enabled in the kernel even if the cpuidle driver does not
-		 * use it. Note, coupled_cpus is a struct copy.
-		 */
-		if (coupled_cpus)
-			device->coupled_cpus = *coupled_cpus;
-#endif
-		ret = cpuidle_register_device(device);
-		if (!ret)
-			continue;
-
-		pr_err("Failed to register cpuidle device for cpu%d\n", cpu);
-
-		cpuidle_unregister(drv);
-		break;
-	}
+	sprintf(cb_name, "cpuidle/%s:online", drv->name);
+	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, cb_name,
+				cpuidle_cpu_online, cpuidle_cpu_offline);
+	if (ret < 0)
+		cpuidle_unregister_driver(drv);
 
 	return ret;
 }
-- 
1.8.3.1