HID: wacom: generic: Avoid reporting a serial of '0' to userspace

The xf86-input-wacom driver does not treat '0' as a valid serial
number and will drop any input report which contains an
MSC_SERIAL = 0 event. The kernel driver already takes care to
avoid sending any MSC_SERIAL event if the value of serial[0] == 0
(which is the case for devices that don't actually report a
serial number), but this is not quite sufficient.
Only the lower 32 bits of the serial get reported to userspace,
so if this portion of the serial is zero then there can still
be problems.

This commit allows the driver to report either the lower 32 bits
if they are non-zero or the upper 32 bits otherwise.
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Tatsunosuke Tobita <tatsunosuke.tobita@wacom.com>
Fixes: f85c9dc6 ("HID: wacom: generic: Support tool ID and additional tool types")
CC: stable@vger.kernel.org # v4.10
Signed-off-by: Jiri Kosina <jkosina@suse.com>

drivers/hid/wacom_wac.c

@@ -2575,7 +2575,14 @@ static void wacom_wac_pen_report(struct hid_device *hdev,
 				wacom_wac->hid_data.tipswitch);
 		input_report_key(input, wacom_wac->tool[0], sense);
 		if (wacom_wac->serial[0]) {
-			input_event(input, EV_MSC, MSC_SERIAL, wacom_wac->serial[0]);
+			/*
+			 * xf86-input-wacom does not accept a serial number
+			 * of '0'. Report the low 32 bits if possible, but
+			 * if they are zero, report the upper ones instead.
+			 */
+			__u32 serial_lo = wacom_wac->serial[0] & 0xFFFFFFFFu;
+			__u32 serial_hi = wacom_wac->serial[0] >> 32;
+			input_event(input, EV_MSC, MSC_SERIAL, (int)(serial_lo ? serial_lo : serial_hi));
 			input_report_abs(input, ABS_MISC, sense ? id : 0);
 		}