Input: atmel_mxt_ts - add check for incorrect firmware file format

Atmel supplies firmware files in ASCII HEX format (.enc) which must be
converted before they can be loaded by kernel driver. Try to detect
the error and print a friendly error message rather than feeding junk
to the bootloader.
Signed-off-by: NNick Dyer <nick.dyer@itdev.co.uk>
Acked-by: NBenson Leung <bleung@chromium.org>
Acked-by: NYufeng Shen <miletus@chromium.org>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/atmel_mxt_ts.c

@@ -1185,6 +1185,30 @@ static ssize_t mxt_object_show(struct device *dev,
 	return error ?: count;
 }
 
+static int mxt_check_firmware_format(struct device *dev,
+				     const struct firmware *fw)
+{
+	unsigned int pos = 0;
+	char c;
+
+	while (pos < fw->size) {
+		c = *(fw->data + pos);
+
+		if (c < '0' || (c > '9' && c < 'A') || c > 'F')
+			return 0;
+
+		pos++;
+	}
+
+	/*
+	 * To convert file try:
+	 * xxd -r -p mXTXXX__APP_VX-X-XX.enc > maxtouch.fw
+	 */
+	dev_err(dev, "Aborting: firmware file must be in binary format\n");
+
+	return -EINVAL;
+}
+
 static int mxt_load_fw(struct device *dev, const char *fn)
 {
 	struct mxt_data *data = dev_get_drvdata(dev);
@@ -1201,6 +1225,11 @@ static int mxt_load_fw(struct device *dev, const char *fn)
 		return ret;
 	}
 
+	/* Check for incorrect enc file */
+	ret = mxt_check_firmware_format(dev, fw);
+	if (ret)
+		goto release_firmware;
+
 	ret = mxt_lookup_bootloader_address(data);
 	if (ret)
 		goto release_firmware;