LXR linux/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
  17#include <linux/usb/ch9.h>
  18#include <linux/usb/gadget.h>
  19
  20#include <asm/unaligned.h>
  21
  22
  23static int utf8_to_utf16le(const char *s, __le16 *cp, unsigned len)
  24{
  25        int     count = 0;
  26        u8      c;
  27        u16     uchar;
  28
  29        /* this insists on correct encodings, though not minimal ones.
  30         * BUT it currently rejects legit 4-byte UTF-8 code points,
  31         * which need surrogate pairs.  (Unicode 3.1 can use them.)
  32         */
  33        while (len != 0 && (c = (u8) *s++) != 0) {
  34                if (unlikely(c & 0x80)) {
  35                        // 2-byte sequence:
  36                        // 00000yyyyyxxxxxx = 110yyyyy 10xxxxxx
  37                        if ((c & 0xe0) == 0xc0) {
  38                                uchar = (c & 0x1f) << 6;
  39
  40                                c = (u8) *s++;
  41                                if ((c & 0xc0) != 0x80)
  42                                        goto fail;
  43                                c &= 0x3f;
  44                                uchar |= c;
  45
  46                        // 3-byte sequence (most CJKV characters):
  47                        // zzzzyyyyyyxxxxxx = 1110zzzz 10yyyyyy 10xxxxxx
  48                        } else if ((c & 0xf0) == 0xe0) {
  49                                uchar = (c & 0x0f) << 12;
  50
  51                                c = (u8) *s++;
  52                                if ((c & 0xc0) != 0x80)
  53                                        goto fail;
  54                                c &= 0x3f;
  55                                uchar |= c << 6;
  56
  57                                c = (u8) *s++;
  58                                if ((c & 0xc0) != 0x80)
  59                                        goto fail;
  60                                c &= 0x3f;
  61                                uchar |= c;
  62
  63                                /* no bogus surrogates */
  64                                if (0xd800 <= uchar && uchar <= 0xdfff)
  65                                        goto fail;
  66
  67                        // 4-byte sequence (surrogate pairs, currently rare):
  68                        // 11101110wwwwzzzzyy + 110111yyyyxxxxxx
  69                        //     = 11110uuu 10uuzzzz 10yyyyyy 10xxxxxx
  70                        // (uuuuu = wwww + 1)
  71                        // FIXME accept the surrogate code points (only)
  72
  73                        } else
  74                                goto fail;
  75                } else
  76                        uchar = c;
  77                put_unaligned_le16(uchar, cp++);
  78                count++;
  79                len--;
  80        }
  81        return count;
  82fail:
  83        return -1;
  84}
  85
  86
  87/**
  88 * usb_gadget_get_string - fill out a string descriptor 
  89 * @table: of c strings encoded using UTF-8
  90 * @id: string id, from low byte of wValue in get string descriptor
  91 * @buf: at least 256 bytes
  92 *
  93 * Finds the UTF-8 string matching the ID, and converts it into a
  94 * string descriptor in utf16-le.
  95 * Returns length of descriptor (always even) or negative errno
  96 *
  97 * If your driver needs stings in multiple languages, you'll probably
  98 * "switch (wIndex) { ... }"  in your ep0 string descriptor logic,
  99 * using this routine after choosing which set of UTF-8 strings to use.
 100 * Note that US-ASCII is a strict subset of UTF-8; any string bytes with
 101 * the eighth bit set will be multibyte UTF-8 characters, not ISO-8859/1
 102 * characters (which are also widely used in C strings).
 103 */
 104int
 105usb_gadget_get_string (struct usb_gadget_strings *table, int id, u8 *buf)
 106{
 107        struct usb_string       *s;
 108        int                     len;
 109
 110        /* descriptor 0 has the language id */
 111        if (id == 0) {
 112                buf [0] = 4;
 113                buf [1] = USB_DT_STRING;
 114                buf [2] = (u8) table->language;
 115                buf [3] = (u8) (table->language >> 8);
 116                return 4;
 117        }
 118        for (s = table->strings; s && s->s; s++)
 119                if (s->id == id)
 120                        break;
 121
 122        /* unrecognized: stall. */
 123        if (!s || !s->s)
 124                return -EINVAL;
 125
 126        /* string descriptors have length, tag, then UTF16-LE text */
 127        len = min ((size_t) 126, strlen (s->s));
 128        memset (buf + 2, 0, 2 * len);   /* zero all the bytes */
 129        len = utf8_to_utf16le(s->s, (__le16 *)&buf[2], len);
 130        if (len < 0)
 131                return -EINVAL;
 132        buf [0] = (len + 1) * 2;
 133        buf [1] = USB_DT_STRING;
 134        return buf [0];
 135}
 136
 137