platform/x86: asus-wmi: don't allow eGPU switching if eGPU not connected

Check the ASUS_WMI_DEVID_EGPU_CONNECTED method for eGPU connection
before allowing the ASUS_WMI_DEVID_EGPU method to run.

Signed-off-by: Luke D. Jones <luke@ljones.dev>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230630053552.976579-6-luke@ljones.dev
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/asus-wmi.c

@@ -693,6 +693,15 @@ static ssize_t egpu_enable_store(struct device *dev,
 	if (enable > 1)
 		return -EINVAL;
 
+	err = asus_wmi_get_devstate_simple(asus, ASUS_WMI_DEVID_EGPU_CONNECTED);
+	if (err < 0)
+		return err;
+	if (err < 1) {
+		err = -ENODEV;
+		pr_warn("Failed to set egpu disable: %d\n", err);
+		return err;
+	}
+
 	err = asus_wmi_set_devstate(ASUS_WMI_DEVID_EGPU, enable, &result);
 	if (err) {
 		pr_warn("Failed to set egpu disable: %d\n", err);