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
  23 static 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) != 0xc0)
  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) != 0xc0)
  53                                         goto fail;
  54                                 c &= 0x3f;
  55                                 uchar |= c << 6;
  56
  57                                 c = (u8) *s++;
  58                                 if ((c & 0xc0) != 0xc0)
  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;
  82 fail:
  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  */
 104 int
 105 usb_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