drivers/usb/gadget/usbstring.c

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