Input: elantech - report the middle button of the touchpad

In the past, no elantech was known with 3 touchpad mouse buttons.
Fujitsu H730 is the first known elantech with a middle button. This commit
enables this middle button. For backwards compatibility, the Fujitsu is
detected via DMI, and only for this one 3 buttons will be announced.

Reported-by: Stefan Valouch <stefan@valouch.com>
Signed-off-by: Ulrik De Bie <ulrik.debie-os@e2big.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/elantech.c

@@ -563,6 +563,7 @@ static void elantech_input_sync_v4(struct psmouse *psmouse)
 	} else {
 		input_report_key(dev, BTN_LEFT, packet[0] & 0x01);
 		input_report_key(dev, BTN_RIGHT, packet[0] & 0x02);
+		input_report_key(dev, BTN_MIDDLE, packet[0] & 0x04);
 	}
 
 	input_mt_report_pointer_emulation(dev, true);
@@ -1131,6 +1132,22 @@ static void elantech_set_buttonpad_prop(struct psmouse *psmouse)
 	}
 }
 
+/*
+ * Some hw_version 4 models do have a middle button
+ */
+static const struct dmi_system_id elantech_dmi_has_middle_button[] = {
+#if defined(CONFIG_DMI) && defined(CONFIG_X86)
+	{
+		/* Fujitsu H730 has a middle button */
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "FUJITSU"),
+			DMI_MATCH(DMI_PRODUCT_NAME, "CELSIUS H730"),
+		},
+	},
+#endif
+	{ }
+};
+
 /*
  * Set the appropriate event bits for the input subsystem
  */
@@ -1150,6 +1167,8 @@ static int elantech_set_input_params(struct psmouse *psmouse)
 	__clear_bit(EV_REL, dev->evbit);
 
 	__set_bit(BTN_LEFT, dev->keybit);
+	if (dmi_check_system(elantech_dmi_has_middle_button))
+		__set_bit(BTN_MIDDLE, dev->keybit);
 	__set_bit(BTN_RIGHT, dev->keybit);
 
 	__set_bit(BTN_TOUCH, dev->keybit);