HID: length resolution should be reported units/mm

Input ABI requires reporting resolution on main axes in units per
millimeter, not units per inch, so we need to convert accordingly.

Tested-by: Nikolai Kondrashov <spbnick@gmail.com>
Acked-by: Nikolai Kondrashov <spbnick@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-input.c

@@ -162,8 +162,8 @@ static int hidinput_setkeycode(struct input_dev *dev,
  *
  * as seen in the HID specification v1.11 6.2.2.7 Global Items.
  *
- * Only exponent 1 length units are processed. Centimeters are converted to
- * inches. Degrees are converted to radians.
+ * Only exponent 1 length units are processed. Centimeters and inches are
+ * converted to millimeters. Degrees are converted to radians.
  */
 static __s32 hidinput_calc_abs_res(const struct hid_field *field, __u16 code)
 {
@@ -184,13 +184,16 @@ static __s32 hidinput_calc_abs_res(const struct hid_field *field, __u16 code)
 	 */
 	if (code == ABS_X || code == ABS_Y || code == ABS_Z) {
 		if (field->unit == 0x11) {		/* If centimeters */
-			/* Convert to inches */
-			prev = logical_extents;
-			logical_extents *= 254;
-			if (logical_extents < prev)
+			/* Convert to millimeters */
+			unit_exponent += 1;
+		} else if (field->unit == 0x13) {	/* If inches */
+			/* Convert to millimeters */
+			prev = physical_extents;
+			physical_extents *= 254;
+			if (physical_extents < prev)
 				return 0;
-			unit_exponent += 2;
-		} else if (field->unit != 0x13) {	/* If not inches */
+			unit_exponent -= 1;
+		} else {
 			return 0;
 		}
 	} else if (code == ABS_RX || code == ABS_RY || code == ABS_RZ) {