HID: wiimote: Parse calibration data of balance boards

The raw pressure-data that is reported by balance-boards is pretty useless
unless calibration data is applied. Therefore, we read the full
calibration data on extension initialization and apply it to every
reported data.
Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Florian Echtler <floe@butterbrot.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-wiimote-ext.c

@@ -28,6 +28,7 @@ struct wiimote_ext {
 	bool mp_plugged;
 	bool motionp;
 	__u8 ext_type;
+	__u16 calib[4][3];
 };
 
 enum wiiext_type {
@@ -127,6 +128,7 @@ static bool motionp_read(struct wiimote_ext *ext)
 static __u8 ext_read(struct wiimote_ext *ext)
 {
 	ssize_t ret;
+	__u8 buf[24], i, j, offs = 0;
 	__u8 rmem[2], wmem;
 	__u8 type = WIIEXT_NONE;
 
@@ -156,6 +158,26 @@ static __u8 ext_read(struct wiimote_ext *ext)
 			type = WIIEXT_BALANCE_BOARD;
 	}
 
+	/* get balance board calibration data */
+	if (type == WIIEXT_BALANCE_BOARD) {
+		ret = wiimote_cmd_read(ext->wdata, 0xa40024, buf, 12);
+		ret += wiimote_cmd_read(ext->wdata, 0xa40024 + 12,
+					buf + 12, 12);
+
+		if (ret != 24) {
+			type = WIIEXT_NONE;
+		} else {
+			for (i = 0; i < 3; i++) {
+				for (j = 0; j < 4; j++) {
+					ext->calib[j][i] = buf[offs];
+					ext->calib[j][i] <<= 8;
+					ext->calib[j][i] |= buf[offs + 1];
+					offs += 2;
+				}
+			}
+		}
+	}
+
 	wiimote_cmd_release(ext->wdata);
 
 	return type;
@@ -514,7 +536,8 @@ static void handler_classic(struct wiimote_ext *ext, const __u8 *payload)
 
 static void handler_balance_board(struct wiimote_ext *ext, const __u8 *payload)
 {
-	__s32 val[4];
+	__s32 val[4], tmp;
+	unsigned int i;
 
 	/*   Byte |  8  7  6  5  4  3  2  1  |
 	 *   -----+--------------------------+
@@ -553,6 +576,20 @@ static void handler_balance_board(struct wiimote_ext *ext, const __u8 *payload)
 	val[3] <<= 8;
 	val[3] |= payload[7];
 
+	/* apply calibration data */
+	for (i = 0; i < 4; i++) {
+		if (val[i] < ext->calib[i][1]) {
+			tmp = val[i] - ext->calib[i][0];
+			tmp *= 1700;
+			tmp /= ext->calib[i][1] - ext->calib[i][0];
+		} else {
+			tmp = val[i] - ext->calib[i][1];
+			tmp *= 1700;
+			tmp /= ext->calib[i][2] - ext->calib[i][1] + 1700;
+		}
+		val[i] = tmp;
+	}
+
 	input_report_abs(ext->input, ABS_HAT0X, val[0]);
 	input_report_abs(ext->input, ABS_HAT0Y, val[1]);
 	input_report_abs(ext->input, ABS_HAT1X, val[2]);