[PATCH v4 4/6] HID: wacom: add NULL input guards to wacom_intuos_bt_irq()

wacom_intuos_bt_irq() dereferences wacom->pen_input in every switch
branch, both directly for dev_warn/dev_dbg and indirectly through
wacom_intuos_bt_process_data() which calls input_sync(pen_input).
pad_input is also used in wacom_intuos_bt_process_data().

Both can be NULL when the corresponding setup_*_input_capabilities()
returns -ENODEV during a successful probe. For INTUOS4WL, pen and pad
are always expected together, so guard both at function entry.

Fixes: 2a6cdbdd4cc0 ("HID: wacom: Introduce new 'touch_input' device")
Signed-off-by: Jinmo Yang <redacted>
Co-Authored-By: Claude Opus 4.6 [off-list ref]
---
 drivers/hid/wacom_wac.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index c38fbec114e4..6e2e67abf80e 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c

@@ -1269,6 +1269,13 @@ static int wacom_intuos_bt_irq(struct wacom_wac *wacom, size_t len)
 	int i = 1;
 	unsigned power_raw, battery_capacity, bat_charging, ps_connected;
 
+	if (!wacom->pen_input || !wacom->pad_input) {
+		dev_warn_once(&container_of(wacom, struct wacom, wacom_wac)->hdev->dev,
+			      "%s: expected pen and pad input devices\n",
+			      __func__);
+		return 0;
+	}
+
 	switch (data[0]) {
 	case 0x04:
 		if (len < 32) {

-- 
2.53.0