PM: sleep: Add kerneldoc comments to some functions

Add kerneldoc comments to pm_suspend_via_firmware(),
pm_resume_via_firmware() and pm_suspend_via_s2idle()
to explain what they do.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/suspend.h

@@ -227,11 +227,42 @@ static inline void pm_set_resume_via_firmware(void)
 	pm_suspend_global_flags |= PM_SUSPEND_FLAG_FW_RESUME;
 }
 
+/**
+ * pm_suspend_via_firmware - Check if platform firmware will suspend the system.
+ *
+ * To be called during system-wide power management transitions to sleep states
+ * or during the subsequent system-wide transitions back to the working state.
+ *
+ * Return 'true' if the platform firmware is going to be invoked at the end of
+ * the system-wide power management transition (to a sleep state) in progress in
+ * order to complete it, or if the platform firmware has been invoked in order
+ * to complete the last (or preceding) transition of the system to a sleep
+ * state.
+ *
+ * This matters if the caller needs or wants to carry out some special actions
+ * depending on whether or not control will be passed to the platform firmware
+ * subsequently (for example, the device may need to be reset before letting the
+ * platform firmware manipulate it, which is not necessary when the platform
+ * firmware is not going to be invoked) or when such special actions may have
+ * been carried out during the preceding transition of the system to a sleep
+ * state (as they may need to be taken into account).
+ */
 static inline bool pm_suspend_via_firmware(void)
 {
 	return !!(pm_suspend_global_flags & PM_SUSPEND_FLAG_FW_SUSPEND);
 }
 
+/**
+ * pm_resume_via_firmware - Check if platform firmware has woken up the system.
+ *
+ * To be called during system-wide power management transitions from sleep
+ * states.
+ *
+ * Return 'true' if the platform firmware has passed control to the kernel at
+ * the beginning of the system-wide power management transition in progress, so
+ * the event that woke up the system from sleep has been handled by the platform
+ * firmware.
+ */
 static inline bool pm_resume_via_firmware(void)
 {
 	return !!(pm_suspend_global_flags & PM_SUSPEND_FLAG_FW_RESUME);

kernel/power/suspend.c

@@ -62,6 +62,12 @@ static DECLARE_SWAIT_QUEUE_HEAD(s2idle_wait_head);
 enum s2idle_states __read_mostly s2idle_state;
 static DEFINE_RAW_SPINLOCK(s2idle_lock);
 
+/**
+ * pm_suspend_via_s2idle - Check if suspend-to-idle is the default suspend.
+ *
+ * Return 'true' if suspend-to-idle has been selected as the default system
+ * suspend method.
+ */
 bool pm_suspend_via_s2idle(void)
 {
 	return mem_sleep_current == PM_SUSPEND_TO_IDLE;