ACPI / AC: recheck adapter status upon battery status changes

On HP Pavilion dv6-6179er there are no notifications when AC adapter
is plugged/unplugged.
However, when AC status is read (acpi_ac_get_state), and if AC status
has changed, AML code triggers the notification.

This patch solves the problem by re-reading AC adapter status upon
ACPI_BATTERY_NOTIFY_STATUS notification.
Signed-off-by: NAlexander Mezin <mezin.alexander@gmail.com>
Acked-by: NLan Tianyu <tianyu.lan@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/ac.c

@@ -33,6 +33,7 @@
 #include <linux/platform_device.h>
 #include <linux/power_supply.h>
 #include <linux/acpi.h>
+#include "battery.h"
 
 #define PREFIX "ACPI: "
 
@@ -57,6 +58,7 @@ struct acpi_ac {
 	struct power_supply charger;
 	struct platform_device *pdev;
 	unsigned long long state;
+	struct notifier_block battery_nb;
 };
 
 #define to_acpi_ac(x) container_of(x, struct acpi_ac, charger)
@@ -152,6 +154,26 @@ static void acpi_ac_notify_handler(acpi_handle handle, u32 event, void *data)
 	return;
 }
 
+static int acpi_ac_battery_notify(struct notifier_block *nb,
+				  unsigned long action, void *data)
+{
+	struct acpi_ac *ac = container_of(nb, struct acpi_ac, battery_nb);
+	struct acpi_bus_event *event = (struct acpi_bus_event *)data;
+
+	/*
+	 * On HP Pavilion dv6-6179er AC status notifications aren't triggered
+	 * when adapter is plugged/unplugged. However, battery status
+	 * notifcations are triggered when battery starts charging or
+	 * discharging. Re-reading AC status triggers lost AC notifications,
+	 * if AC status has changed.
+	 */
+	if (strcmp(event->device_class, ACPI_BATTERY_CLASS) == 0 &&
+	    event->type == ACPI_BATTERY_NOTIFY_STATUS)
+		acpi_ac_get_state(ac);
+
+	return NOTIFY_OK;
+}
+
 static int thinkpad_e530_quirk(const struct dmi_system_id *d)
 {
 	ac_sleep_before_get_state_ms = 1000;
@@ -215,6 +237,8 @@ static int acpi_ac_probe(struct platform_device *pdev)
 	       acpi_device_name(adev), acpi_device_bid(adev),
 	       ac->state ? "on-line" : "off-line");
 
+	ac->battery_nb.notifier_call = acpi_ac_battery_notify;
+	register_acpi_notifier(&ac->battery_nb);
 end:
 	if (result)
 		kfree(ac);
@@ -261,6 +285,7 @@ static int acpi_ac_remove(struct platform_device *pdev)
 	ac = platform_get_drvdata(pdev);
 	if (ac->charger.dev)
 		power_supply_unregister(&ac->charger);
+	unregister_acpi_notifier(&ac->battery_nb);
 
 	kfree(ac);