ACPI / Button: Avoid disabling wakeup unnecessarily on remove

If a button device had already been enabled to wake up the system
from sleep states before the button driver saw it, the driver
shouldn't disable the device's wakeup capability when being detached
from the device.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
index e643a09..12c28f4 100644
--- a/drivers/acpi/button.c
+++ b/drivers/acpi/button.c
@@ -98,6 +98,7 @@
 	struct input_dev *input;
 	char phys[32];			/* for input device */
 	unsigned long pushed;
+	bool wakeup_enabled;
 };
 
 static const struct file_operations acpi_button_info_fops = {
@@ -430,7 +431,10 @@
 		/* Button's GPE is run-wake GPE */
 		acpi_enable_gpe(device->wakeup.gpe_device,
 				device->wakeup.gpe_number);
-		device_set_wakeup_enable(&device->dev, true);
+		if (!device_may_wakeup(&device->dev)) {
+			device_set_wakeup_enable(&device->dev, true);
+			button->wakeup_enabled = true;
+		}
 	}
 
 	printk(KERN_INFO PREFIX "%s [%s]\n", name, acpi_device_bid(device));
@@ -452,7 +456,8 @@
 	if (device->wakeup.flags.valid) {
 		acpi_disable_gpe(device->wakeup.gpe_device,
 				device->wakeup.gpe_number);
-		device_set_wakeup_enable(&device->dev, false);
+		if (button->wakeup_enabled)
+			device_set_wakeup_enable(&device->dev, false);
 	}
 
 	acpi_button_remove_fs(device);