drivers/usb/gadget/usbstring.c

   1 /*
   2  * Copyright (C) 2003 David Brownell
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU Lesser General Public License as published
   6  * by the Free Software Foundation; either version 2.1 of the License, or
   7  * (at your option) any later version.
   8  */
   9
  10 #include <linux/errno.h>
  11 #include <linux/kernel.h>
  12 #include <linux/list.h>
  13 #include <linux/string.h>
  14 #include <linux/device.h>
  15 #include <linux/init.h>
  16 #include <linux/nls.h>
  17
  18 #include <linux/usb/ch9.h>
  19 #include <linux/usb/gadget.h>
  20
  21
  22 /**
  23  * usb_gadget_get_string - fill out a string descriptor
  24  * @table: of c strings encoded using UTF-8
  25  * @id: string id, from low byte of wValue in get string descriptor
  26  * @buf: at least 256 bytes, must be 16-bit aligned
  27  *
  28  * Finds the UTF-8 string matching the ID, and converts it into a
  29  * string descriptor in utf16-le.
  30  * Returns length of descriptor (always even) or negative errno
  31  *
  32  * If your driver needs stings in multiple languages, you'll probably
  33  * "switch (wIndex) { ... }"  in your ep0 string descriptor logic,
  34  * using this routine after choosing which set of UTF-8 strings to use.
  35  * Note that US-ASCII is a strict subset of UTF-8; any string bytes with
  36  * the eighth bit set will be multibyte UTF-8 characters, not ISO-8859/1
  37  * characters (which are also widely used in C strings).
  38  */
  39 int
  40 usb_gadget_get_string (struct usb_gadget_strings *table, int id, u8 *buf)
  41 {
  42         struct usb_string       *s;
  43         int                     len;
  44
  45         /* descriptor 0 has the language id */
  46         if (id == 0) {
  47                 buf [0] = 4;
  48                 buf [1] = USB_DT_STRING;
  49                 buf [2] = (u8) table->language;
  50                 buf [3] = (u8) (table->language >> 8);
  51                 return 4;
  52         }
  53         for (s = table->strings; s && s->s; s++)
  54                 if (s->id == id)
  55                         break;
  56
  57         /* unrecognized: stall. */
  58         if (!s || !s->s)
  59                 return -EINVAL;
  60
  61         /* string descriptors have length, tag, then UTF16-LE text */
  62         len = min ((size_t) 126, strlen (s->s));
  63         len = utf8s_to_utf16s(s->s, len, UTF16_LITTLE_ENDIAN,
  64                         (wchar_t *) &buf[2], 126);
  65         if (len < 0)
  66                 return -EINVAL;
  67         buf [0] = (len + 1) * 2;
  68         buf [1] = USB_DT_STRING;
  69         return buf [0];
  70 }
  71