1 files changed, 71 insertions, 0 deletions

diff --git a/drivers/input/tablet/wacom_sys.c b/drivers/input/tablet/wacom_sys.c
index 0d3219f29744..b44bba2a60c2 100644
--- a/drivers/input/tablet/wacom_sys.c
+++ b/drivers/input/tablet/wacom_sys.c
@@ -172,6 +172,76 @@ static void wacom_close(struct input_dev *dev)
 }
 
 /*
+ * Calculate the resolution of the X or Y axis, given appropriate HID data.
+ * This function is little more than hidinput_calc_abs_res stripped down.
+ */
+static int wacom_calc_hid_res(int logical_extents, int physical_extents,
+                              unsigned char unit, unsigned char exponent)
+{
+	int prev, unit_exponent;
+
+	/* Check if the extents are sane */
+	if (logical_extents <= 0 || physical_extents <= 0)
+		return 0;
+
+	/* Get signed value of nybble-sized twos-compliment exponent */
+	unit_exponent = exponent;
+	if (unit_exponent > 7)
+		unit_exponent -= 16;
+
+	/* Convert physical_extents to millimeters */
+	if (unit == 0x11) {		/* If centimeters */
+		unit_exponent += 1;
+	} else if (unit == 0x13) {	/* If inches */
+		prev = physical_extents;
+		physical_extents *= 254;
+		if (physical_extents < prev)
+			return 0;
+		unit_exponent -= 1;
+	} else {
+		return 0;
+	}
+
+	/* Apply negative unit exponent */
+	for (; unit_exponent < 0; unit_exponent++) {
+		prev = logical_extents;
+		logical_extents *= 10;
+		if (logical_extents < prev)
+			return 0;
+	}
+	/* Apply positive unit exponent */
+	for (; unit_exponent > 0; unit_exponent--) {
+		prev = physical_extents;
+		physical_extents *= 10;
+		if (physical_extents < prev)
+			return 0;
+	}
+
+	/* Calculate resolution */
+	return logical_extents / physical_extents;
+}
+
+/*
+ * The physical dimension specified by the HID descriptor is likely not in
+ * the "100th of a mm" units expected by wacom_calculate_touch_res. This
+ * function adjusts the value of [xy]_phy based on the unit and exponent
+ * provided by the HID descriptor. If an error occurs durring conversion
+ * (e.g. from the unit being left unspecified) [xy]_phy is not modified.
+ */
+static void wacom_fix_phy_from_hid(struct wacom_features *features)
+{
+	int xres = wacom_calc_hid_res(features->x_max, features->x_phy,
+					features->unit, features->unitExpo);
+	int yres = wacom_calc_hid_res(features->y_max, features->y_phy,
+					features->unit, features->unitExpo);
+
+	if (xres > 0 && yres > 0) {
+		features->x_phy = (100 * features->x_max) / xres;
+		features->y_phy = (100 * features->y_max) / yres;
+	}
+}
+
+/*
  * Static values for max X/Y and resolution of Pen interface is stored in
  * features. This mean physical size of active area can be computed.
  * This is useful to do when Pen and Touch have same active area of tablet.
@@ -531,6 +601,7 @@ static int wacom_retrieve_hid_descriptor(struct usb_interface *intf,
 	error = wacom_parse_hid(intf, hid_desc, features);
 	if (error)
 		goto out;
+	wacom_fix_phy_from_hid(features);
 
  out:
 	return error;