HID: input: throttle battery uevents

The power_supply subsystem tends to emit uevent every time
power_supply_changed() is called, so we should call this API only when battery
strength reported by the device is actually different from the previous
readings, otherwise we'll drown the system in uevents.

Fixes: 581c4484 ("HID: input: map digitizer battery usage")
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-input.c

@@ -520,15 +520,21 @@ static void hidinput_cleanup_battery(struct hid_device *dev)
 
 static void hidinput_update_battery(struct hid_device *dev, int value)
 {
+	int capacity;
+
 	if (!dev->battery)
 		return;
 
 	if (value == 0 || value < dev->battery_min || value > dev->battery_max)
 		return;
 
-	dev->battery_capacity = hidinput_scale_battery_capacity(dev, value);
-	dev->battery_reported = true;
-	power_supply_changed(dev->battery);
+	capacity = hidinput_scale_battery_capacity(dev, value);
+
+	if (!dev->battery_reported || capacity != dev->battery_capacity) {
+		dev->battery_capacity = capacity;
+		dev->battery_reported = true;
+		power_supply_changed(dev->battery);
+	}
 }
 #else  /* !CONFIG_HID_BATTERY_STRENGTH */
 static int hidinput_setup_battery(struct hid_device *dev, unsigned report_type,