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); 68