HID: asus: only support backlight when it's not driven by WMI

The Asus GL502VSK has the same 0B05:1837 keyboard as we've seen in
several Republic of Gamers laptops.

However, in this model, the keybard backlight control exposed by hid-asus
has no effect on the keyboard backlight. Instead, the keyboard
backlight is correctly driven by asus-wmi.

With two keyboard backlight devices available (and only the acer-wmi
one working), GNOME is picking the wrong one to drive in the UI.

Avoid this problem by not creating the backlight interface when we
detect a WMI-driven keyboard backlight.

We have also tested Asus GL702VMK which does have the hid-asus
backlight present, and it still works fine with this patch (WMI method
call returns UNSUPPORTED_METHOD).

A direct "depends on ASUS_WMI" is intentionally avoided so that HID_ASUS
users who have ASUS_WMI=n will not quietly lose their HID_ASUS driver on
a kernel upgrade.

Signed-off-by: Daniel Drake <drake@endlessm.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/hid/Kconfig

@@ -149,6 +149,7 @@ config HID_APPLEIR
 config HID_ASUS
 	tristate "Asus"
 	depends on LEDS_CLASS
+	depends on ASUS_WMI || ASUS_WMI=n
 	---help---
 	Support for Asus notebook built-in keyboard and touchpad via i2c, and
 	the Asus Republic of Gamers laptop keyboard special keys.

drivers/hid/hid-asus.c

@@ -29,6 +29,7 @@
 #include <linux/dmi.h>
 #include <linux/hid.h>
 #include <linux/module.h>
+#include <linux/platform_data/x86/asus-wmi.h>
 #include <linux/input/mt.h>
 #include <linux/usb.h> /* For to_usb_interface for T100 touchpad intf check */
 
@@ -349,6 +350,24 @@ static void asus_kbd_backlight_work(struct work_struct *work)
 		hid_err(led->hdev, "Asus failed to set keyboard backlight: %d\n", ret);
 }
 
+/* WMI-based keyboard backlight LED control (via asus-wmi driver) takes
+ * precedence. We only activate HID-based backlight control when the
+ * WMI control is not available.
+ */
+static bool asus_kbd_wmi_led_control_present(struct hid_device *hdev)
+{
+	u32 value;
+	int ret;
+
+	ret = asus_wmi_evaluate_method(ASUS_WMI_METHODID_DSTS2,
+				       ASUS_WMI_DEVID_KBD_BACKLIGHT, 0, &value);
+	hid_dbg(hdev, "WMI backlight check: rc %d value %x", ret, value);
+	if (ret)
+		return false;
+
+	return !!(value & ASUS_WMI_DSTS_PRESENCE_BIT);
+}
+
 static int asus_kbd_register_leds(struct hid_device *hdev)
 {
 	struct asus_drvdata *drvdata = hid_get_drvdata(hdev);
@@ -436,7 +455,9 @@ static int asus_input_configured(struct hid_device *hdev, struct hid_input *hi)
 
 	drvdata->input = input;
 
-	if (drvdata->enable_backlight && asus_kbd_register_leds(hdev))
+	if (drvdata->enable_backlight &&
+	    !asus_kbd_wmi_led_control_present(hdev) &&
+	    asus_kbd_register_leds(hdev))
 		hid_warn(hdev, "Failed to initialize backlight.\n");
 
 	return 0;