cpuidle: Comment the driver's framework code

Add kerneldoc (and other) comments to the cpuidle driver's framework
code.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpuidle/driver.c

@@ -22,11 +22,26 @@ DEFINE_SPINLOCK(cpuidle_driver_lock);
 
 static DEFINE_PER_CPU(struct cpuidle_driver *, cpuidle_drivers);
 
+/**
+ * __cpuidle_get_cpu_driver - return the cpuidle driver tied to a CPU.
+ * @cpu: the CPU handled by the driver
+ *
+ * Returns a pointer to struct cpuidle_driver or NULL if no driver has been
+ * registered for @cpu.
+ */
 static struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
 {
 	return per_cpu(cpuidle_drivers, cpu);
 }
 
+/**
+ * __cpuidle_unset_driver - unset per CPU driver variables.
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * For each CPU in the driver's CPU mask, unset the registered driver per CPU
+ * variable. If @drv is different from the registered driver, the corresponding
+ * variable is not cleared.
+ */
 static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
 {
 	int cpu;
@@ -40,6 +55,15 @@ static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
 	}
 }
 
+/**
+ * __cpuidle_set_driver - set per CPU driver variables the the given driver.
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * For each CPU in the driver's cpumask, unset the registered driver per CPU
+ * to @drv.
+ *
+ * Returns 0 on success, -EBUSY if the CPUs have driver(s) already.
+ */
 static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
 {
 	int cpu;
@@ -61,11 +85,24 @@ static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
 
 static struct cpuidle_driver *cpuidle_curr_driver;
 
+/**
+ * __cpuidle_get_cpu_driver - return the global cpuidle driver pointer.
+ * @cpu: ignored without the multiple driver support
+ *
+ * Return a pointer to a struct cpuidle_driver object or NULL if no driver was
+ * previously registered.
+ */
 static inline struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
 {
 	return cpuidle_curr_driver;
 }
 
+/**
+ * __cpuidle_set_driver - assign the global cpuidle driver variable.
+ * @drv: pointer to a struct cpuidle_driver object
+ *
+ * Returns 0 on success, -EBUSY if the driver is already registered.
+ */
 static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
 {
 	if (cpuidle_curr_driver)
@@ -76,6 +113,13 @@ static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
 	return 0;
 }
 
+/**
+ * __cpuidle_unset_driver - unset the global cpuidle driver variable.
+ * @drv: a pointer to a struct cpuidle_driver
+ *
+ * Reset the global cpuidle variable to NULL.  If @drv does not match the
+ * registered driver, do nothing.
+ */
 static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
 {
 	if (drv == cpuidle_curr_driver)
@@ -84,21 +128,49 @@ static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
 
 #endif
 
+/**
+ * cpuidle_setup_broadcast_timer - enable/disable the broadcast timer
+ * @arg: a void pointer used to match the SMP cross call API
+ *
+ * @arg is used as a value of type 'long' with on of the two values:
+ * - CLOCK_EVT_NOTIFY_BROADCAST_ON
+ * - CLOCK_EVT_NOTIFY_BROADCAST_OFF
+ *
+ * Set the broadcast timer notification for the current CPU.  This function
+ * is executed per CPU by an SMP cross call.  It not supposed to be called
+ * directly.
+ */
 static void cpuidle_setup_broadcast_timer(void *arg)
 {
 	int cpu = smp_processor_id();
 	clockevents_notify((long)(arg), &cpu);
 }
 
+/**
+ * __cpuidle_driver_init - initialize the driver's internal data
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * Returns 0 on success, a negative error code otherwise.
+ */
 static int __cpuidle_driver_init(struct cpuidle_driver *drv)
 {
 	int i;
 
 	drv->refcnt = 0;
 
+	/*
+	 * Use all possible CPUs as the default, because if the kernel boots
+	 * with some CPUs offline and then we online one of them, the CPU
+	 * notifier has to know which driver to assign.
+	 */
 	if (!drv->cpumask)
 		drv->cpumask = (struct cpumask *)cpu_possible_mask;
 
+	/*
+	 * Look for the timer stop flag in the different states, so that we know
+	 * if the broadcast timer has to be set up.  The loop is in the reverse
+	 * order, because usually on of the the deeper states has this flag set.
+	 */
 	for (i = drv->state_count - 1; i >= 0 ; i--) {
 
 		if (!(drv->states[i].flags & CPUIDLE_FLAG_TIMER_STOP))
@@ -111,6 +183,19 @@ static int __cpuidle_driver_init(struct cpuidle_driver *drv)
 	return 0;
 }
 
+/**
+ * __cpuidle_register_driver: register the driver
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * Do some sanity checks, initialize the driver, assign the driver to the
+ * global cpuidle driver variable(s) and set up the broadcast timer if the
+ * cpuidle driver has some states that shut down the local timer.
+ *
+ * Returns 0 on success, a negative error code otherwise:
+ *  * -EINVAL if the driver pointer is NULL or no idle states are available
+ *  * -ENODEV if the cpuidle framework is disabled
+ *  * -EBUSY if the driver is already assigned to the global variable(s)
+ */
 static int __cpuidle_register_driver(struct cpuidle_driver *drv)
 {
 	int ret;
@@ -137,8 +222,13 @@ static int __cpuidle_register_driver(struct cpuidle_driver *drv)
 }
 
 /**
- * cpuidle_unregister_driver - unregisters a driver
- * @drv: the driver
+ * __cpuidle_unregister_driver - unregister the driver
+ * @drv: a valid pointer to a struct cpuidle_driver
+ *
+ * Check if 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.
+ *
  */
 static void __cpuidle_unregister_driver(struct cpuidle_driver *drv)
 {
@@ -156,7 +246,13 @@ static void __cpuidle_unregister_driver(struct cpuidle_driver *drv)
 
 /**
  * cpuidle_register_driver - registers a driver
- * @drv: the driver
+ * @drv: a pointer to a valid struct cpuidle_driver
+ *
+ * Register the driver under a lock to prevent concurrent attempts to
+ * [un]register the driver from occuring at the same time.
+ *
+ * Returns 0 on success, a negative error code (returned by
+ * __cpuidle_register_driver()) otherwise.
  */
 int cpuidle_register_driver(struct cpuidle_driver *drv)
 {
@@ -172,7 +268,11 @@ EXPORT_SYMBOL_GPL(cpuidle_register_driver);
 
 /**
  * cpuidle_unregister_driver - unregisters a driver
- * @drv: the driver
+ * @drv: a pointer to a valid struct cpuidle_driver
+ *
+ * Unregisters the cpuidle driver under a lock to prevent concurrent attempts
+ * to [un]register the driver from occuring at the same time.  @drv has to
+ * match the currently registered driver.
  */
 void cpuidle_unregister_driver(struct cpuidle_driver *drv)
 {
@@ -183,7 +283,9 @@ void cpuidle_unregister_driver(struct cpuidle_driver *drv)
 EXPORT_SYMBOL_GPL(cpuidle_unregister_driver);
 
 /**
- * cpuidle_get_driver - return the current driver
+ * cpuidle_get_driver - return the driver tied to the current CPU.
+ *
+ * Returns a struct cpuidle_driver pointer, or NULL if no driver is registered.
  */
 struct cpuidle_driver *cpuidle_get_driver(void)
 {
@@ -199,7 +301,11 @@ 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 - return the driver registered for 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 CPU associated with @dev.
  */
 struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev)
 {
@@ -210,6 +316,14 @@ struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev)
 }
 EXPORT_SYMBOL_GPL(cpuidle_get_cpu_driver);
 
+/**
+ * cpuidle_driver_ref - get a reference to the driver.
+ *
+ * Increment the reference counter of the cpuidle driver associated with
+ * the current CPU.
+ *
+ * Returns a pointer to the driver, or NULL if the current CPU has no driver.
+ */
 struct cpuidle_driver *cpuidle_driver_ref(void)
 {
 	struct cpuidle_driver *drv;
@@ -223,6 +337,12 @@ struct cpuidle_driver *cpuidle_driver_ref(void)
 	return drv;
 }
 
+/**
+ * cpuidle_driver_unref - puts down the refcount for the driver
+ *
+ * Decrement the reference counter of the cpuidle driver associated with
+ * the current CPU.
+ */
 void cpuidle_driver_unref(void)
 {
 	struct cpuidle_driver *drv = cpuidle_get_driver();