Input: elantech - detect middle button based on firmware version

Looks like the new generation of Lenovo machine also need to
be added to the PnPID whitelist. This is definitively not going
to scale, as there is nothing that tells us currently if a
touchpad supports a true physical middle button.

Consider that all new touchpads that are not clickpads
(so matching ETP_NEW_IC_SMBUS_HOST_NOTIFY) are handling 3 physical
buttons.

Signed-off-by: Benjamin Tissoires <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/mouse/elantech.c

···
 	{ }
 };
 
-static const char * const middle_button_pnp_ids[] = {
-	"LEN2131", /* ThinkPad P52 w/ NFC */
-	"LEN2132", /* ThinkPad P52 */
-	"LEN2133", /* ThinkPad P72 w/ NFC */
-	"LEN2134", /* ThinkPad P72 */
-	"LEN0407",
-	"LEN0408",
-	NULL
-};
-
 /*
  * Set the appropriate event bits for the input subsystem
  */
···
 	__clear_bit(EV_REL, dev->evbit);
 
 	__set_bit(BTN_LEFT, dev->keybit);
-	if (dmi_check_system(elantech_dmi_has_middle_button) ||
-			psmouse_matches_pnp_id(psmouse, middle_button_pnp_ids))
+	if (info->has_middle_button)
 		__set_bit(BTN_MIDDLE, dev->keybit);
 	__set_bit(BTN_RIGHT, dev->keybit);
 
···
 		info->width = info->x_max / (traces - 1);
 		break;
 	}
+
+	/* check for the middle button: DMI matching or new v4 firmwares */
+	info->has_middle_button = dmi_check_system(elantech_dmi_has_middle_button) ||
+				  (ETP_NEW_IC_SMBUS_HOST_NOTIFY(info->fw_version) &&
+				   !elantech_is_buttonpad(info));
 
 	return 0;
 }

drivers/input/mouse/elantech.h

···
 	bool crc_enabled;
 	bool set_hw_resolution;
 	bool has_trackpoint;
+	bool has_middle_button;
 	int (*send_cmd)(struct psmouse *psmouse, unsigned char c,
 			unsigned char *param);
 };