Input: elantech - force resolution of 31 u/mm

All Elantech touchpads pre-v4 with dynamic resolution queries have a fixed
resolution of 800dpi -> 31.49 units/mm. Set this statically, so userspace
does not have to guess.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/elantech.c

@@ -1167,7 +1167,7 @@ static int elantech_set_input_params(struct psmouse *psmouse)
 	struct input_dev *dev = psmouse->dev;
 	struct elantech_data *etd = psmouse->private;
 	unsigned int x_min = 0, y_min = 0, x_max = 0, y_max = 0, width = 0;
-	unsigned int x_res = 0, y_res = 0;
+	unsigned int x_res = 31, y_res = 31;
 
 	if (elantech_set_range(psmouse, &x_min, &y_min, &x_max, &y_max, &width))
 		return -1;
@@ -1232,8 +1232,6 @@ static int elantech_set_input_params(struct psmouse *psmouse)
 		/* For X to recognize me as touchpad. */
 		input_set_abs_params(dev, ABS_X, x_min, x_max, 0, 0);
 		input_set_abs_params(dev, ABS_Y, y_min, y_max, 0, 0);
-		input_abs_set_res(dev, ABS_X, x_res);
-		input_abs_set_res(dev, ABS_Y, y_res);
 		/*
 		 * range of pressure and width is the same as v2,
 		 * report ABS_PRESSURE, ABS_TOOL_WIDTH for compatibility.
@@ -1246,8 +1244,6 @@ static int elantech_set_input_params(struct psmouse *psmouse)
 		input_mt_init_slots(dev, ETP_MAX_FINGERS, 0);
 		input_set_abs_params(dev, ABS_MT_POSITION_X, x_min, x_max, 0, 0);
 		input_set_abs_params(dev, ABS_MT_POSITION_Y, y_min, y_max, 0, 0);
-		input_abs_set_res(dev, ABS_MT_POSITION_X, x_res);
-		input_abs_set_res(dev, ABS_MT_POSITION_Y, y_res);
 		input_set_abs_params(dev, ABS_MT_PRESSURE, ETP_PMIN_V2,
 				     ETP_PMAX_V2, 0, 0);
 		/*
@@ -1259,6 +1255,13 @@ static int elantech_set_input_params(struct psmouse *psmouse)
 		break;
 	}
 
+	input_abs_set_res(dev, ABS_X, x_res);
+	input_abs_set_res(dev, ABS_Y, y_res);
+	if (etd->hw_version > 1) {
+		input_abs_set_res(dev, ABS_MT_POSITION_X, x_res);
+		input_abs_set_res(dev, ABS_MT_POSITION_Y, y_res);
+	}
+
 	etd->y_max = y_max;
 	etd->width = width;