HID: input: calculate resolution for pressure

Assume that if the pressure is given in newtons it should be normalized
to grams. If the pressure has no unit do not calculate resolution.

Signed-off-by: Angela Czubak <aczubak@google.com>
Co-developed-by: Jonathan Denose <jdenose@google.com>
Signed-off-by: Jonathan Denose <jdenose@google.com>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

Author: Angela Czubak

drivers/hid/hid-input.c

@@ -303,6 +303,19 @@ __s32 hidinput_calc_abs_res(const struct hid_field *field, __u16 code)
 		}
 		break;
 
+	case ABS_PRESSURE:
+	case ABS_MT_PRESSURE:
+		if (field->unit == HID_UNIT_NEWTON) {
+			/* Convert to grams, 1 newton is 101.97 grams */
+			prev = physical_extents;
+			physical_extents *= 10197;
+			if (physical_extents < prev)
+				return 0;
+			unit_exponent -= 2;
+		} else if (field->unit != HID_UNIT_GRAM) {
+			return 0;
+		}
+		break;
 	default:
 		return 0;
 	}