+static int usb_get_string(struct usb_device *dev, unsigned short langid,
+ unsigned char index, void *buf, int size)
+{
+ int i;
+ int result;
+
+ for (i = 0; i < 3; ++i) {
+ /* retry on length 0 or stall; some devices are flakey */
+ result = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
+ USB_REQ_GET_DESCRIPTOR, USB_DIR_IN,
+ (USB_DT_STRING << 8) + index, langid, buf, size,
+ USB_CTRL_GET_TIMEOUT);
+ if (!(result == 0 || result == -EPIPE))
+ break;
+ }
+ return result;
+}
+
+static void usb_try_string_workarounds(unsigned char *buf, int *length)
+{
+ int newlength, oldlength = *length;
+
+ for (newlength = 2; newlength + 1 < oldlength; newlength += 2)
+ if (!isprint(buf[newlength]) || buf[newlength + 1])
+ break;
+
+ if (newlength > 2) {
+ buf[0] = newlength;
+ *length = newlength;
+ }
+}
+
+static int usb_string_sub(struct usb_device *dev, unsigned int langid,
+ unsigned int index, unsigned char *buf)
+{
+ int rc;
+
+ /* Try to read the string descriptor by asking for the maximum
+ * possible number of bytes */
+ rc = usb_get_string(dev, langid, index, buf, 255);
+
+ /* If that failed try to read the descriptor length, then
+ * ask for just that many bytes */
+ if (rc < 2) {
+ rc = usb_get_string(dev, langid, index, buf, 2);
+ if (rc == 2)
+ rc = usb_get_string(dev, langid, index, buf, buf[0]);
+ }
+
+ if (rc >= 2) {
+ if (!buf[0] && !buf[1])
+ usb_try_string_workarounds(buf, &rc);
+
+ /* There might be extra junk at the end of the descriptor */
+ if (buf[0] < rc)
+ rc = buf[0];
+
+ rc = rc - (rc & 1); /* force a multiple of two */
+ }
+
+ if (rc < 2)
+ rc = (rc < 0 ? rc : -EINVAL);
+
+ return rc;
+}
+
+/**
+ * usb_string - returns ISO 8859-1 version of a string descriptor
+ * @dev: the device whose string descriptor is being retrieved
+ * @index: the number of the descriptor
+ * @buf: where to put the string
+ * @size: how big is "buf"?
+ * Context: !in_interrupt ()
+ *
+ * This converts the UTF-16LE encoded strings returned by devices, from
+ * usb_get_string_descriptor(), to null-terminated ISO-8859-1 encoded ones
+ * that are more usable in most kernel contexts. Note that all characters
+ * in the chosen descriptor that can't be encoded using ISO-8859-1
+ * are converted to the question mark ("?") character, and this function
+ * chooses strings in the first language supported by the device.
+ *
+ * The ASCII (or, redundantly, "US-ASCII") character set is the seven-bit
+ * subset of ISO 8859-1. ISO-8859-1 is the eight-bit subset of Unicode,
+ * and is appropriate for use many uses of English and several other
+ * Western European languages. (But it doesn't include the "Euro" symbol.)
+ *
+ * This call is synchronous, and may not be used in an interrupt context.
+ *
+ * Returns length of the string (>= 0) or usb_control_msg status (< 0).
+ */
+int usb_string(struct usb_device *dev, int index, char *buf, size_t size)