[V2] cpuidle: simplify multiple driver support

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index c3a93fe..fdc432f 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -466,7 +466,7 @@  void cpuidle_unregister(struct cpuidle_driver *drv)
 	int cpu;
 	struct cpuidle_device *device;
 
-	for_each_possible_cpu(cpu) {
+	for_each_cpu(cpu, drv->cpumask) {
 		device = &per_cpu(cpuidle_dev, cpu);
 		cpuidle_unregister_device(device);
 	}
@@ -498,7 +498,7 @@  int cpuidle_register(struct cpuidle_driver *drv,
 		return ret;
 	}
 
-	for_each_possible_cpu(cpu) {
+	for_each_cpu(cpu, drv->cpumask) {
 		device = &per_cpu(cpuidle_dev, cpu);
 		device->cpu = cpu;
 
diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
index 8dfaaae..0268346 100644
--- a/drivers/cpuidle/driver.c
+++ b/drivers/cpuidle/driver.c
@@ -18,206 +18,266 @@ 
 
 DEFINE_SPINLOCK(cpuidle_driver_lock);
 
-static void __cpuidle_set_cpu_driver(struct cpuidle_driver *drv, int cpu);
-static struct cpuidle_driver * __cpuidle_get_cpu_driver(int cpu);
+#ifdef CONFIG_CPU_IDLE_MULTIPLE_DRIVERS
 
-static void cpuidle_setup_broadcast_timer(void *arg)
+static DEFINE_PER_CPU(struct cpuidle_driver *, cpuidle_drivers);
+
+/**
+ * __cpuidle_get_cpu_driver: returns the cpuidle driver tied with the specified
+ * cpu.
+ *
+ * @cpu: an integer specifying the cpu number
+ *
+ * Returns a pointer to struct cpuidle_driver, NULL if no driver has been
+ * registered for this driver
+ */
+static struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
 {
-	int cpu = smp_processor_id();
-	clockevents_notify((long)(arg), &cpu);
+	return per_cpu(cpuidle_drivers, cpu);
 }
 
-static void __cpuidle_driver_init(struct cpuidle_driver *drv, int cpu)
+/**
+ * __cpuidle_set_driver: assign to the per cpu variable the driver pointer for
+ * each cpu the driver is assigned to with the cpumask.
+ *
+ * @drv: a pointer to a struct cpuidle_driver
+ *
+ * Returns 0 on success, < 0 otherwise
+ */
+static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
 {
-	int i;
+	int cpu;
 
-	drv->refcnt = 0;
+	for_each_cpu(cpu, drv->cpumask) {
 
-	for (i = drv->state_count - 1; i >= 0 ; i--) {
+		if (__cpuidle_get_cpu_driver(cpu))
+			return -EBUSY;
 
-		if (!(drv->states[i].flags & CPUIDLE_FLAG_TIMER_STOP))
-			continue;
-
-		drv->bctimer = 1;
-		on_each_cpu_mask(get_cpu_mask(cpu), cpuidle_setup_broadcast_timer,
-				 (void *)CLOCK_EVT_NOTIFY_BROADCAST_ON, 1);
-		break;
+		per_cpu(cpuidle_drivers, cpu) = drv;
 	}
+
+	return 0;
 }
 
-static int __cpuidle_register_driver(struct cpuidle_driver *drv, int cpu)
+/**
+ * __cpuidle_unset_driver: for each cpu the driver is handling, set the per cpu
+ * variable driver to NULL.
+ *
+ * @drv: a pointer to a struct cpuidle_driver
+ */
+static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
 {
-	if (!drv || !drv->state_count)
-		return -EINVAL;
-
-	if (cpuidle_disabled())
-		return -ENODEV;
-
-	if (__cpuidle_get_cpu_driver(cpu))
-		return -EBUSY;
+	int cpu;
 
-	__cpuidle_driver_init(drv, cpu);
+	for_each_cpu(cpu, drv->cpumask) {
 
-	__cpuidle_set_cpu_driver(drv, cpu);
+		if (drv != __cpuidle_get_cpu_driver(cpu))
+			continue;
 
-	return 0;
+		per_cpu(cpuidle_drivers, cpu) = NULL;
+	}
 }
 
-static void __cpuidle_unregister_driver(struct cpuidle_driver *drv, int cpu)
-{
-	if (drv != __cpuidle_get_cpu_driver(cpu))
-		return;
+#else
 
-	if (!WARN_ON(drv->refcnt > 0))
-		__cpuidle_set_cpu_driver(NULL, cpu);
+static struct cpuidle_driver *cpuidle_curr_driver;
 
-	if (drv->bctimer) {
-		drv->bctimer = 0;
-		on_each_cpu_mask(get_cpu_mask(cpu), cpuidle_setup_broadcast_timer,
-				 (void *)CLOCK_EVT_NOTIFY_BROADCAST_OFF, 1);
-	}
+/**
+ * __cpuidle_get_cpu_driver: returns the global cpuidle driver pointer.
+ *
+ * @cpu: an integer specifying the cpu number, this parameter is ignored
+ *
+ * Returns a pointer to a struct cpuidle_driver, NULL if no driver was
+ * previously registered
+ */
+static inline struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
+{
+	return cpuidle_curr_driver;
 }
 
-#ifdef CONFIG_CPU_IDLE_MULTIPLE_DRIVERS
+/**
+ * __cpuidle_set_driver: assign the cpuidle driver pointer to the global cpuidle
+ * driver variable.
+ *
+ * @drv: a pointer to a struct cpuidle_driver
+ *
+ * Returns 0 on success, < 0 otherwise
+ */
+static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
+{
+	if (cpuidle_curr_driver)
+		return -EBUSY;
 
-static DEFINE_PER_CPU(struct cpuidle_driver *, cpuidle_drivers);
+	cpuidle_curr_driver = drv;
 
-static void __cpuidle_set_cpu_driver(struct cpuidle_driver *drv, int cpu)
-{
-	per_cpu(cpuidle_drivers, cpu) = drv;
+	return 0;
 }
 
-static struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
+/**
+ * __cpuidle_unset_driver: reset the global cpuidle driver variable if the
+ * cpuidle driver pointer match it.
+ *
+ * @drv: a pointer to a struct cpuidle_driver
+ */
+static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
 {
-	return per_cpu(cpuidle_drivers, cpu);
+	if (drv == cpuidle_curr_driver)
+		cpuidle_curr_driver = NULL;
 }
 
-static void __cpuidle_unregister_all_cpu_driver(struct cpuidle_driver *drv)
+#endif
+
+/**
+ * cpuidle_setup_broadcast_timer: set the broadcast timer notification for the
+ * current cpu. This function is called per cpu context invoked by a smp cross
+ * call. It is not supposed to be called directly.
+ *
+ * @arg: a void pointer, actually used to match the smp cross call api but used
+ * as a long with two values:
+ * - CLOCK_EVT_NOTIFY_BROADCAST_ON
+ * - CLOCK_EVT_NOTIFY_BROADCAST_OFF
+ */
+static void cpuidle_setup_broadcast_timer(void *arg)
 {
-	int cpu;
-	for_each_present_cpu(cpu)
-		__cpuidle_unregister_driver(drv, cpu);
+	int cpu = smp_processor_id();
+	clockevents_notify((long)(arg), &cpu);
 }
 
-static int __cpuidle_register_all_cpu_driver(struct cpuidle_driver *drv)
+/**
+ * __cpuidle_driver_init: initialize the driver internal data.
+ *
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * Returns 0 on success, < 0 otherwise
+ */
+static int __cpuidle_driver_init(struct cpuidle_driver *drv)
 {
-	int ret = 0;
-	int i, cpu;
+	int i;
 
-	for_each_present_cpu(cpu) {
-		ret = __cpuidle_register_driver(drv, cpu);
-		if (ret)
-			break;
-	}
+	drv->refcnt = 0;
 
-	if (ret)
-		for_each_present_cpu(i) {
-			if (i == cpu)
-				break;
-			__cpuidle_unregister_driver(drv, i);
-		}
+	/*
+	 * we default here to all cpu possible because if the kernel
+	 * boots with some cpus offline and then we online one of them
+	 * the cpu notifier won't know which driver to assign
+	 */
+	if (!drv->cpumask)
+		drv->cpumask = (struct cpumask *)cpu_possible_mask;
+
+	/*
+	 * we look for the timer stop flag in the different states,
+	 * so know we have to setup the broadcast timer. The loop is
+	 * in reverse order, because usually the deeper state has this
+	 * flag set
+	 */
+	for (i = drv->state_count - 1; i >= 0 ; i--) {
 
+		if (!(drv->states[i].flags & CPUIDLE_FLAG_TIMER_STOP))
+			continue;
 
-	return ret;
+		drv->bctimer = 1;
+		break;
+	}
+
+	return 0;
 }
 
-int cpuidle_register_cpu_driver(struct cpuidle_driver *drv, int cpu)
+/**
+ * __cpuidle_register_driver: do some sanity checks, initializes the driver,
+ * assign the driver to the global cpuidle driver variable(s) and setup the
+ * broadcast timer if the cpuidle driver has some states which shutdown the
+ * local timer.
+ *
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * Returns 0 on success, < 0 otherwise
+ */
+static int __cpuidle_register_driver(struct cpuidle_driver *drv)
 {
 	int ret;
 
-	spin_lock(&cpuidle_driver_lock);
-	ret = __cpuidle_register_driver(drv, cpu);
-	spin_unlock(&cpuidle_driver_lock);
+	if (!drv || !drv->state_count)
+		return -EINVAL;
 
-	return ret;
-}
+	if (cpuidle_disabled())
+		return -ENODEV;
 
-void cpuidle_unregister_cpu_driver(struct cpuidle_driver *drv, int cpu)
-{
-	spin_lock(&cpuidle_driver_lock);
-	__cpuidle_unregister_driver(drv, cpu);
-	spin_unlock(&cpuidle_driver_lock);
-}
+	ret = __cpuidle_driver_init(drv);
+	if (ret)
+		return ret;
 
-/**
- * cpuidle_register_driver - registers a driver
- * @drv: the driver
- */
-int cpuidle_register_driver(struct cpuidle_driver *drv)
-{
-	int ret;
+	ret = __cpuidle_set_driver(drv);
+	if (ret)
+		return ret;
 
-	spin_lock(&cpuidle_driver_lock);
-	ret = __cpuidle_register_all_cpu_driver(drv);
-	spin_unlock(&cpuidle_driver_lock);
+	if (drv->bctimer)
+		on_each_cpu_mask(drv->cpumask, cpuidle_setup_broadcast_timer,
+				 (void *)CLOCK_EVT_NOTIFY_BROADCAST_ON, 1);
 
-	return ret;
+	return 0;
 }
-EXPORT_SYMBOL_GPL(cpuidle_register_driver);
 
 /**
- * cpuidle_unregister_driver - unregisters a driver
- * @drv: the driver
+ * __cpuidle_unregister_driver: checks the driver is no longer in use, reset the
+ * global cpuidle driver variable(s) and disable the timer broadcast
+ * notification mechanism if it was in use.
+ *
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
  */
-void cpuidle_unregister_driver(struct cpuidle_driver *drv)
+static void __cpuidle_unregister_driver(struct cpuidle_driver *drv)
 {
-	spin_lock(&cpuidle_driver_lock);
-	__cpuidle_unregister_all_cpu_driver(drv);
-	spin_unlock(&cpuidle_driver_lock);
-}
-EXPORT_SYMBOL_GPL(cpuidle_unregister_driver);
-
-#else
-
-static struct cpuidle_driver *cpuidle_curr_driver;
+	if (WARN_ON(drv->refcnt > 0))
+		return;
 
-static inline void __cpuidle_set_cpu_driver(struct cpuidle_driver *drv, int cpu)
-{
-	cpuidle_curr_driver = drv;
-}
+	if (drv->bctimer) {
+		drv->bctimer = 0;
+		on_each_cpu_mask(drv->cpumask, cpuidle_setup_broadcast_timer,
+				 (void *)CLOCK_EVT_NOTIFY_BROADCAST_OFF, 1);
+	}
 
-static inline struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
-{
-	return cpuidle_curr_driver;
+	__cpuidle_unset_driver(drv);
 }
 
 /**
- * cpuidle_register_driver - registers a driver
- * @drv: the driver
+ * cpuidle_register_driver: registers a driver by taking a lock to prevent
+ * multiple callers to [un]register a driver at the same time.
+ *
+ * @drv: a pointer to a valid struct cpuidle_driver
+ *
+ * Returns 0 on success, < 0 otherwise
  */
 int cpuidle_register_driver(struct cpuidle_driver *drv)
 {
-	int ret, cpu;
+	int ret;
 
-	cpu = get_cpu();
 	spin_lock(&cpuidle_driver_lock);
-	ret = __cpuidle_register_driver(drv, cpu);
+	ret = __cpuidle_register_driver(drv);
 	spin_unlock(&cpuidle_driver_lock);
-	put_cpu();
 
 	return ret;
 }
 EXPORT_SYMBOL_GPL(cpuidle_register_driver);
 
 /**
- * cpuidle_unregister_driver - unregisters a driver
- * @drv: the driver
+ * cpuidle_unregister_driver: unregisters a driver by taking a lock to prevent
+ * multiple callers to [un]register a driver at the same time. The specified
+ * driver must match the driver currently registered.
+ *
+ * @drv: a pointer to a valid struct cpuidle_driver
  */
 void cpuidle_unregister_driver(struct cpuidle_driver *drv)
 {
-	int cpu;
-
-	cpu = get_cpu();
 	spin_lock(&cpuidle_driver_lock);
-	__cpuidle_unregister_driver(drv, cpu);
+	__cpuidle_unregister_driver(drv);
 	spin_unlock(&cpuidle_driver_lock);
-	put_cpu();
 }
 EXPORT_SYMBOL_GPL(cpuidle_unregister_driver);
-#endif
 
 /**
- * cpuidle_get_driver - return the current driver
+ * cpuidle_get_driver: returns the driver tied with the current cpu.
+ *
+ * Returns a struct cpuidle_driver pointer, or NULL if no driver is registered
  */
 struct cpuidle_driver *cpuidle_get_driver(void)
 {
@@ -233,7 +293,12 @@  struct cpuidle_driver *cpuidle_get_driver(void)
 EXPORT_SYMBOL_GPL(cpuidle_get_driver);
 
 /**
- * cpuidle_get_cpu_driver - return the driver tied with a cpu
+ * cpuidle_get_cpu_driver: returns the driver registered with a cpu.
+ *
+ * @dev: a valid pointer to a struct cpuidle_device
+ *
+ * Returns a struct cpuidle_driver pointer, or NULL if no driver is registered
+ * for the specified cpu
  */
 struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev)
 {
@@ -244,6 +309,13 @@  struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev)
 }
 EXPORT_SYMBOL_GPL(cpuidle_get_cpu_driver);
 
+/**
+ * cpuidle_driver_ref: gets a refcount for the driver. Note this function takes
+ * a refcount for the driver assigned to the current cpu.
+ *
+ * Returns a struct cpuidle_driver pointer, or NULL if no driver is registered
+ * for the current cpu
+ */
 struct cpuidle_driver *cpuidle_driver_ref(void)
 {
 	struct cpuidle_driver *drv;
@@ -257,6 +329,10 @@  struct cpuidle_driver *cpuidle_driver_ref(void)
 	return drv;
 }
 
+/**
+ * cpuidle_driver_unref: puts down the refcount for the driver. Note this
+ * function decrement the refcount for the driver assigned to the current cpu.
+ */
 void cpuidle_driver_unref(void)
 {
 	struct cpuidle_driver *drv = cpuidle_get_driver();
diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 8f04062..63d78b1 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -101,16 +101,20 @@  static inline int cpuidle_get_last_residency(struct cpuidle_device *dev)
  ****************************/
 
 struct cpuidle_driver {
-	const char		*name;
-	struct module 		*owner;
-	int                     refcnt;
+	const char	     *name;
+	struct module 	     *owner;
+	int                  refcnt;
 
         /* used by the cpuidle framework to setup the broadcast timer */
-	unsigned int            bctimer:1;
+	unsigned int         bctimer:1;
+
 	/* states array must be ordered in decreasing power consumption */
-	struct cpuidle_state	states[CPUIDLE_STATE_MAX];
-	int			state_count;
-	int			safe_state_index;
+	struct cpuidle_state states[CPUIDLE_STATE_MAX];
+	int		     state_count;
+	int		     safe_state_index;
+
+	/* the driver handles the cpus in cpumask */
+	struct cpumask       *cpumask;
 };
 
 #ifdef CONFIG_CPU_IDLE
@@ -135,9 +139,6 @@  extern void cpuidle_disable_device(struct cpuidle_device *dev);
 extern int cpuidle_play_dead(void);
 
 extern struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev);
-extern int cpuidle_register_cpu_driver(struct cpuidle_driver *drv, int cpu);
-extern void cpuidle_unregister_cpu_driver(struct cpuidle_driver *drv, int cpu);
-
 #else
 static inline void disable_cpuidle(void) { }
 static inline int cpuidle_idle_call(void) { return -ENODEV; }