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
usb_gadget_get_string(const struct usb_gadget_strings * table,int id,u8 * buf)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)USB_MAX_STRING_LEN, strlen(s->s));
59 	len = utf8s_to_utf16s(s->s, len, UTF16_LITTLE_ENDIAN,
60 			(wchar_t *) &buf[2], USB_MAX_STRING_LEN);
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);
68 
69 /**
70  * usb_validate_langid - validate usb language identifiers
71  * @langid: usb language identifier
72  *
73  * Returns true for valid language identifier, otherwise false.
74  */
usb_validate_langid(u16 langid)75 bool usb_validate_langid(u16 langid)
76 {
77 	u16 primary_lang = langid & 0x3ff;	/* bit [9:0] */
78 	u16 sub_lang = langid >> 10;		/* bit [15:10] */
79 
80 	switch (primary_lang) {
81 	case 0:
82 	case 0x62 ... 0xfe:
83 	case 0x100 ... 0x3ff:
84 		return false;
85 	}
86 	if (!sub_lang)
87 		return false;
88 
89 	return true;
90 }
91 EXPORT_SYMBOL_GPL(usb_validate_langid);
92