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usbdi_util.c revision 1.43
      1 /*	$NetBSD: usbdi_util.c,v 1.43 2005/04/12 13:10:14 itohy Exp $	*/
      2 
      3 /*
      4  * Copyright (c) 1998 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Lennart Augustsson (lennart (at) augustsson.net) at
      9  * Carlstedt Research & Technology.
     10  *
     11  * Redistribution and use in source and binary forms, with or without
     12  * modification, are permitted provided that the following conditions
     13  * are met:
     14  * 1. Redistributions of source code must retain the above copyright
     15  *    notice, this list of conditions and the following disclaimer.
     16  * 2. Redistributions in binary form must reproduce the above copyright
     17  *    notice, this list of conditions and the following disclaimer in the
     18  *    documentation and/or other materials provided with the distribution.
     19  * 3. All advertising materials mentioning features or use of this software
     20  *    must display the following acknowledgement:
     21  *        This product includes software developed by the NetBSD
     22  *        Foundation, Inc. and its contributors.
     23  * 4. Neither the name of The NetBSD Foundation nor the names of its
     24  *    contributors may be used to endorse or promote products derived
     25  *    from this software without specific prior written permission.
     26  *
     27  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     28  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     29  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     30  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     31  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     32  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     33  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     34  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     35  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     36  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     37  * POSSIBILITY OF SUCH DAMAGE.
     38  */
     39 
     40 #include <sys/cdefs.h>
     41 __KERNEL_RCSID(0, "$NetBSD: usbdi_util.c,v 1.43 2005/04/12 13:10:14 itohy Exp $");
     42 
     43 #include <sys/param.h>
     44 #include <sys/systm.h>
     45 #include <sys/kernel.h>
     46 #include <sys/malloc.h>
     47 #if defined(__NetBSD__) || defined(__OpenBSD__)
     48 #include <sys/proc.h>
     49 #include <sys/device.h>
     50 #elif defined(__FreeBSD__)
     51 #include <sys/bus.h>
     52 #endif
     53 
     54 #include <dev/usb/usb.h>
     55 #include <dev/usb/usbhid.h>
     56 
     57 #include <dev/usb/usbdi.h>
     58 #include <dev/usb/usbdi_util.h>
     59 
     60 #ifdef USB_DEBUG
     61 #define DPRINTF(x)	if (usbdebug) logprintf x
     62 #define DPRINTFN(n,x)	if (usbdebug>(n)) logprintf x
     63 extern int usbdebug;
     64 #else
     65 #define DPRINTF(x)
     66 #define DPRINTFN(n,x)
     67 #endif
     68 
     69 usbd_status
     70 usbd_get_desc(usbd_device_handle dev, int type, int index, int len, void *desc)
     71 {
     72 	usb_device_request_t req;
     73 
     74 	DPRINTFN(3,("usbd_get_desc: type=%d, index=%d, len=%d\n",
     75 		    type, index, len));
     76 
     77 	req.bmRequestType = UT_READ_DEVICE;
     78 	req.bRequest = UR_GET_DESCRIPTOR;
     79 	USETW2(req.wValue, type, index);
     80 	USETW(req.wIndex, 0);
     81 	USETW(req.wLength, len);
     82 	return (usbd_do_request(dev, &req, desc));
     83 }
     84 
     85 usbd_status
     86 usbd_get_config_desc(usbd_device_handle dev, int confidx,
     87 		     usb_config_descriptor_t *d)
     88 {
     89 	usbd_status err;
     90 
     91 	DPRINTFN(3,("usbd_get_config_desc: confidx=%d\n", confidx));
     92 	err = usbd_get_desc(dev, UDESC_CONFIG, confidx,
     93 			    USB_CONFIG_DESCRIPTOR_SIZE, d);
     94 	if (err)
     95 		return (err);
     96 	if (d->bDescriptorType != UDESC_CONFIG) {
     97 		DPRINTFN(-1,("usbd_get_config_desc: confidx=%d, bad desc "
     98 			     "len=%d type=%d\n",
     99 			     confidx, d->bLength, d->bDescriptorType));
    100 		return (USBD_INVAL);
    101 	}
    102 	return (USBD_NORMAL_COMPLETION);
    103 }
    104 
    105 usbd_status
    106 usbd_get_config_desc_full(usbd_device_handle dev, int conf, void *d, int size)
    107 {
    108 	DPRINTFN(3,("usbd_get_config_desc_full: conf=%d\n", conf));
    109 	return (usbd_get_desc(dev, UDESC_CONFIG, conf, size, d));
    110 }
    111 
    112 usbd_status
    113 usbd_get_device_desc(usbd_device_handle dev, usb_device_descriptor_t *d)
    114 {
    115 	DPRINTFN(3,("usbd_get_device_desc:\n"));
    116 	return (usbd_get_desc(dev, UDESC_DEVICE,
    117 			     0, USB_DEVICE_DESCRIPTOR_SIZE, d));
    118 }
    119 
    120 usbd_status
    121 usbd_get_device_status(usbd_device_handle dev, usb_status_t *st)
    122 {
    123 	usb_device_request_t req;
    124 
    125 	req.bmRequestType = UT_READ_DEVICE;
    126 	req.bRequest = UR_GET_STATUS;
    127 	USETW(req.wValue, 0);
    128 	USETW(req.wIndex, 0);
    129 	USETW(req.wLength, sizeof(usb_status_t));
    130 	return (usbd_do_request(dev, &req, st));
    131 }
    132 
    133 usbd_status
    134 usbd_get_hub_status(usbd_device_handle dev, usb_hub_status_t *st)
    135 {
    136 	usb_device_request_t req;
    137 
    138 	req.bmRequestType = UT_READ_CLASS_DEVICE;
    139 	req.bRequest = UR_GET_STATUS;
    140 	USETW(req.wValue, 0);
    141 	USETW(req.wIndex, 0);
    142 	USETW(req.wLength, sizeof(usb_hub_status_t));
    143 	return (usbd_do_request(dev, &req, st));
    144 }
    145 
    146 usbd_status
    147 usbd_set_address(usbd_device_handle dev, int addr)
    148 {
    149 	usb_device_request_t req;
    150 
    151 	req.bmRequestType = UT_WRITE_DEVICE;
    152 	req.bRequest = UR_SET_ADDRESS;
    153 	USETW(req.wValue, addr);
    154 	USETW(req.wIndex, 0);
    155 	USETW(req.wLength, 0);
    156 	return usbd_do_request(dev, &req, 0);
    157 }
    158 
    159 usbd_status
    160 usbd_get_port_status(usbd_device_handle dev, int port, usb_port_status_t *ps)
    161 {
    162 	usb_device_request_t req;
    163 
    164 	req.bmRequestType = UT_READ_CLASS_OTHER;
    165 	req.bRequest = UR_GET_STATUS;
    166 	USETW(req.wValue, 0);
    167 	USETW(req.wIndex, port);
    168 	USETW(req.wLength, sizeof *ps);
    169 	return (usbd_do_request(dev, &req, ps));
    170 }
    171 
    172 usbd_status
    173 usbd_clear_hub_feature(usbd_device_handle dev, int sel)
    174 {
    175 	usb_device_request_t req;
    176 
    177 	req.bmRequestType = UT_WRITE_CLASS_DEVICE;
    178 	req.bRequest = UR_CLEAR_FEATURE;
    179 	USETW(req.wValue, sel);
    180 	USETW(req.wIndex, 0);
    181 	USETW(req.wLength, 0);
    182 	return (usbd_do_request(dev, &req, 0));
    183 }
    184 
    185 usbd_status
    186 usbd_set_hub_feature(usbd_device_handle dev, int sel)
    187 {
    188 	usb_device_request_t req;
    189 
    190 	req.bmRequestType = UT_WRITE_CLASS_DEVICE;
    191 	req.bRequest = UR_SET_FEATURE;
    192 	USETW(req.wValue, sel);
    193 	USETW(req.wIndex, 0);
    194 	USETW(req.wLength, 0);
    195 	return (usbd_do_request(dev, &req, 0));
    196 }
    197 
    198 usbd_status
    199 usbd_clear_port_feature(usbd_device_handle dev, int port, int sel)
    200 {
    201 	usb_device_request_t req;
    202 
    203 	req.bmRequestType = UT_WRITE_CLASS_OTHER;
    204 	req.bRequest = UR_CLEAR_FEATURE;
    205 	USETW(req.wValue, sel);
    206 	USETW(req.wIndex, port);
    207 	USETW(req.wLength, 0);
    208 	return (usbd_do_request(dev, &req, 0));
    209 }
    210 
    211 usbd_status
    212 usbd_set_port_feature(usbd_device_handle dev, int port, int sel)
    213 {
    214 	usb_device_request_t req;
    215 
    216 	req.bmRequestType = UT_WRITE_CLASS_OTHER;
    217 	req.bRequest = UR_SET_FEATURE;
    218 	USETW(req.wValue, sel);
    219 	USETW(req.wIndex, port);
    220 	USETW(req.wLength, 0);
    221 	return (usbd_do_request(dev, &req, 0));
    222 }
    223 
    224 usbd_status
    225 usbd_get_protocol(usbd_interface_handle iface, u_int8_t *report)
    226 {
    227 	usb_interface_descriptor_t *id = usbd_get_interface_descriptor(iface);
    228 	usbd_device_handle dev;
    229 	usb_device_request_t req;
    230 
    231 	DPRINTFN(4, ("usbd_get_protocol: iface=%p, endpt=%d\n",
    232 		     iface, id->bInterfaceNumber));
    233 	if (id == NULL)
    234 		return (USBD_IOERROR);
    235 	usbd_interface2device_handle(iface, &dev);
    236 	req.bmRequestType = UT_READ_CLASS_INTERFACE;
    237 	req.bRequest = UR_GET_PROTOCOL;
    238 	USETW(req.wValue, 0);
    239 	USETW(req.wIndex, id->bInterfaceNumber);
    240 	USETW(req.wLength, 1);
    241 	return (usbd_do_request(dev, &req, report));
    242 }
    243 
    244 usbd_status
    245 usbd_set_protocol(usbd_interface_handle iface, int report)
    246 {
    247 	usb_interface_descriptor_t *id = usbd_get_interface_descriptor(iface);
    248 	usbd_device_handle dev;
    249 	usb_device_request_t req;
    250 
    251 	DPRINTFN(4, ("usbd_set_protocol: iface=%p, report=%d, endpt=%d\n",
    252 		     iface, report, id->bInterfaceNumber));
    253 	if (id == NULL)
    254 		return (USBD_IOERROR);
    255 	usbd_interface2device_handle(iface, &dev);
    256 	req.bmRequestType = UT_WRITE_CLASS_INTERFACE;
    257 	req.bRequest = UR_SET_PROTOCOL;
    258 	USETW(req.wValue, report);
    259 	USETW(req.wIndex, id->bInterfaceNumber);
    260 	USETW(req.wLength, 0);
    261 	return (usbd_do_request(dev, &req, 0));
    262 }
    263 
    264 usbd_status
    265 usbd_set_report(usbd_interface_handle iface, int type, int id, void *data,
    266 		int len)
    267 {
    268 	usb_interface_descriptor_t *ifd = usbd_get_interface_descriptor(iface);
    269 	usbd_device_handle dev;
    270 	usb_device_request_t req;
    271 
    272 	DPRINTFN(4, ("usbd_set_report: len=%d\n", len));
    273 	if (ifd == NULL)
    274 		return (USBD_IOERROR);
    275 	usbd_interface2device_handle(iface, &dev);
    276 	req.bmRequestType = UT_WRITE_CLASS_INTERFACE;
    277 	req.bRequest = UR_SET_REPORT;
    278 	USETW2(req.wValue, type, id);
    279 	USETW(req.wIndex, ifd->bInterfaceNumber);
    280 	USETW(req.wLength, len);
    281 	return (usbd_do_request(dev, &req, data));
    282 }
    283 
    284 usbd_status
    285 usbd_set_report_async(usbd_interface_handle iface, int type, int id, void *data,
    286 		      int len)
    287 {
    288 	usb_interface_descriptor_t *ifd = usbd_get_interface_descriptor(iface);
    289 	usbd_device_handle dev;
    290 	usb_device_request_t req;
    291 
    292 	DPRINTFN(4, ("usbd_set_report_async: len=%d\n", len));
    293 	if (ifd == NULL)
    294 		return (USBD_IOERROR);
    295 	usbd_interface2device_handle(iface, &dev);
    296 	req.bmRequestType = UT_WRITE_CLASS_INTERFACE;
    297 	req.bRequest = UR_SET_REPORT;
    298 	USETW2(req.wValue, type, id);
    299 	USETW(req.wIndex, ifd->bInterfaceNumber);
    300 	USETW(req.wLength, len);
    301 	return (usbd_do_request_async(dev, &req, data));
    302 }
    303 
    304 usbd_status
    305 usbd_get_report(usbd_interface_handle iface, int type, int id, void *data,
    306 		int len)
    307 {
    308 	usb_interface_descriptor_t *ifd = usbd_get_interface_descriptor(iface);
    309 	usbd_device_handle dev;
    310 	usb_device_request_t req;
    311 
    312 	DPRINTFN(4, ("usbd_get_report: len=%d\n", len));
    313 	if (ifd == NULL)
    314 		return (USBD_IOERROR);
    315 	usbd_interface2device_handle(iface, &dev);
    316 	req.bmRequestType = UT_READ_CLASS_INTERFACE;
    317 	req.bRequest = UR_GET_REPORT;
    318 	USETW2(req.wValue, type, id);
    319 	USETW(req.wIndex, ifd->bInterfaceNumber);
    320 	USETW(req.wLength, len);
    321 	return (usbd_do_request(dev, &req, data));
    322 }
    323 
    324 usbd_status
    325 usbd_set_idle(usbd_interface_handle iface, int duration, int id)
    326 {
    327 	usb_interface_descriptor_t *ifd = usbd_get_interface_descriptor(iface);
    328 	usbd_device_handle dev;
    329 	usb_device_request_t req;
    330 
    331 	DPRINTFN(4, ("usbd_set_idle: %d %d\n", duration, id));
    332 	if (ifd == NULL)
    333 		return (USBD_IOERROR);
    334 	usbd_interface2device_handle(iface, &dev);
    335 	req.bmRequestType = UT_WRITE_CLASS_INTERFACE;
    336 	req.bRequest = UR_SET_IDLE;
    337 	USETW2(req.wValue, duration, id);
    338 	USETW(req.wIndex, ifd->bInterfaceNumber);
    339 	USETW(req.wLength, 0);
    340 	return (usbd_do_request(dev, &req, 0));
    341 }
    342 
    343 usbd_status
    344 usbd_get_report_descriptor(usbd_device_handle dev, int ifcno,
    345 			   int size, void *d)
    346 {
    347 	usb_device_request_t req;
    348 
    349 	req.bmRequestType = UT_READ_INTERFACE;
    350 	req.bRequest = UR_GET_DESCRIPTOR;
    351 	USETW2(req.wValue, UDESC_REPORT, 0); /* report id should be 0 */
    352 	USETW(req.wIndex, ifcno);
    353 	USETW(req.wLength, size);
    354 	return (usbd_do_request(dev, &req, d));
    355 }
    356 
    357 usb_hid_descriptor_t *
    358 usbd_get_hid_descriptor(usbd_interface_handle ifc)
    359 {
    360 	usb_interface_descriptor_t *idesc = usbd_get_interface_descriptor(ifc);
    361 	usbd_device_handle dev;
    362 	usb_config_descriptor_t *cdesc;
    363 	usb_hid_descriptor_t *hd;
    364 	char *p, *end;
    365 
    366 	if (idesc == NULL)
    367 		return (NULL);
    368 	usbd_interface2device_handle(ifc, &dev);
    369 	cdesc = usbd_get_config_descriptor(dev);
    370 
    371 	p = (char *)idesc + idesc->bLength;
    372 	end = (char *)cdesc + UGETW(cdesc->wTotalLength);
    373 
    374 	for (; p < end; p += hd->bLength) {
    375 		hd = (usb_hid_descriptor_t *)p;
    376 		if (p + hd->bLength <= end && hd->bDescriptorType == UDESC_HID)
    377 			return (hd);
    378 		if (hd->bDescriptorType == UDESC_INTERFACE)
    379 			break;
    380 	}
    381 	return (NULL);
    382 }
    383 
    384 usbd_status
    385 usbd_read_report_desc(usbd_interface_handle ifc, void **descp, int *sizep,
    386 		       usb_malloc_type mem)
    387 {
    388 	usb_interface_descriptor_t *id;
    389 	usb_hid_descriptor_t *hid;
    390 	usbd_device_handle dev;
    391 	usbd_status err;
    392 
    393 	usbd_interface2device_handle(ifc, &dev);
    394 	id = usbd_get_interface_descriptor(ifc);
    395 	if (id == NULL)
    396 		return (USBD_INVAL);
    397 	hid = usbd_get_hid_descriptor(ifc);
    398 	if (hid == NULL)
    399 		return (USBD_IOERROR);
    400 	*sizep = UGETW(hid->descrs[0].wDescriptorLength);
    401 	*descp = malloc(*sizep, mem, M_NOWAIT);
    402 	if (*descp == NULL)
    403 		return (USBD_NOMEM);
    404 	err = usbd_get_report_descriptor(dev, id->bInterfaceNumber,
    405 					 *sizep, *descp);
    406 	if (err) {
    407 		free(*descp, mem);
    408 		*descp = NULL;
    409 		return (err);
    410 	}
    411 	return (USBD_NORMAL_COMPLETION);
    412 }
    413 
    414 usbd_status
    415 usbd_get_config(usbd_device_handle dev, u_int8_t *conf)
    416 {
    417 	usb_device_request_t req;
    418 
    419 	req.bmRequestType = UT_READ_DEVICE;
    420 	req.bRequest = UR_GET_CONFIG;
    421 	USETW(req.wValue, 0);
    422 	USETW(req.wIndex, 0);
    423 	USETW(req.wLength, 1);
    424 	return (usbd_do_request(dev, &req, conf));
    425 }
    426 
    427 Static void usbd_bulk_transfer_cb(usbd_xfer_handle xfer,
    428 				  usbd_private_handle priv, usbd_status status);
    429 Static void
    430 usbd_bulk_transfer_cb(usbd_xfer_handle xfer, usbd_private_handle priv,
    431 		      usbd_status status)
    432 {
    433 	wakeup(xfer);
    434 }
    435 
    436 usbd_status
    437 usbd_bulk_transfer(usbd_xfer_handle xfer, usbd_pipe_handle pipe,
    438 		   u_int16_t flags, u_int32_t timeout, void *buf,
    439 		   u_int32_t *size, char *lbl)
    440 {
    441 	usbd_status err;
    442 	int s, error;
    443 
    444 	usbd_setup_xfer(xfer, pipe, 0, buf, *size,
    445 			flags, timeout, usbd_bulk_transfer_cb);
    446 	DPRINTFN(1, ("usbd_bulk_transfer: start transfer %d bytes\n", *size));
    447 	s = splusb();		/* don't want callback until tsleep() */
    448 	err = usbd_transfer(xfer);
    449 	if (err != USBD_IN_PROGRESS) {
    450 		splx(s);
    451 		return (err);
    452 	}
    453 	error = tsleep((caddr_t)xfer, PZERO | PCATCH, lbl, 0);
    454 	splx(s);
    455 	if (error) {
    456 		DPRINTF(("usbd_bulk_transfer: tsleep=%d\n", error));
    457 		usbd_abort_pipe(pipe);
    458 		return (USBD_INTERRUPTED);
    459 	}
    460 	usbd_get_xfer_status(xfer, NULL, NULL, size, &err);
    461 	DPRINTFN(1,("usbd_bulk_transfer: transferred %d\n", *size));
    462 	if (err) {
    463 		DPRINTF(("usbd_bulk_transfer: error=%d\n", err));
    464 		usbd_clear_endpoint_stall(pipe);
    465 	}
    466 	return (err);
    467 }
    468 
    469 Static void usbd_intr_transfer_cb(usbd_xfer_handle xfer,
    470 				  usbd_private_handle priv, usbd_status status);
    471 Static void
    472 usbd_intr_transfer_cb(usbd_xfer_handle xfer, usbd_private_handle priv,
    473 		      usbd_status status)
    474 {
    475 	wakeup(xfer);
    476 }
    477 
    478 usbd_status
    479 usbd_intr_transfer(usbd_xfer_handle xfer, usbd_pipe_handle pipe,
    480 		   u_int16_t flags, u_int32_t timeout, void *buf,
    481 		   u_int32_t *size, char *lbl)
    482 {
    483 	usbd_status err;
    484 	int s, error;
    485 
    486 	usbd_setup_xfer(xfer, pipe, 0, buf, *size,
    487 			flags, timeout, usbd_intr_transfer_cb);
    488 	DPRINTFN(1, ("usbd_intr_transfer: start transfer %d bytes\n", *size));
    489 	s = splusb();		/* don't want callback until tsleep() */
    490 	err = usbd_transfer(xfer);
    491 	if (err != USBD_IN_PROGRESS) {
    492 		splx(s);
    493 		return (err);
    494 	}
    495 	error = tsleep(xfer, PZERO | PCATCH, lbl, 0);
    496 	splx(s);
    497 	if (error) {
    498 		DPRINTF(("usbd_intr_transfer: tsleep=%d\n", error));
    499 		usbd_abort_pipe(pipe);
    500 		return (USBD_INTERRUPTED);
    501 	}
    502 	usbd_get_xfer_status(xfer, NULL, NULL, size, &err);
    503 	DPRINTFN(1,("usbd_intr_transfer: transferred %d\n", *size));
    504 	if (err) {
    505 		DPRINTF(("usbd_intr_transfer: error=%d\n", err));
    506 		usbd_clear_endpoint_stall(pipe);
    507 	}
    508 	return (err);
    509 }
    510 
    511 void
    512 usb_detach_wait(device_ptr_t dv)
    513 {
    514 	DPRINTF(("usb_detach_wait: waiting for %s\n", USBDEVPTRNAME(dv)));
    515 	if (tsleep(dv, PZERO, "usbdet", hz * 60))
    516 		printf("usb_detach_wait: %s didn't detach\n",
    517 		        USBDEVPTRNAME(dv));
    518 	DPRINTF(("usb_detach_wait: %s done\n", USBDEVPTRNAME(dv)));
    519 }
    520 
    521 void
    522 usb_detach_wakeup(device_ptr_t dv)
    523 {
    524 	DPRINTF(("usb_detach_wakeup: for %s\n", USBDEVPTRNAME(dv)));
    525 	wakeup(dv);
    526 }
    527 
    528 const usb_descriptor_t *
    529 usb_find_desc(usbd_device_handle dev, int type, int subtype)
    530 {
    531 	usbd_desc_iter_t iter;
    532 	const usb_descriptor_t *desc;
    533 
    534 	usb_desc_iter_init(dev, &iter);
    535 	for (;;) {
    536 		desc = usb_desc_iter_next(&iter);
    537 		if (!desc || (desc->bDescriptorType == type &&
    538 			      (subtype == USBD_SUBTYPE_ANY ||
    539 			       subtype == desc->bDescriptorSubtype)))
    540 			break;
    541 	}
    542 	return desc;
    543 }
    544 
    545 /* same as usb_find_desc(), but searches only in the specified interface. */
    546 const usb_descriptor_t *
    547 usb_find_desc_if(usbd_device_handle dev, int type, int subtype,
    548 		 usb_interface_descriptor_t *id)
    549 {
    550 	usbd_desc_iter_t iter;
    551 	const usb_descriptor_t *desc;
    552 
    553 	usb_desc_iter_init(dev, &iter);
    554 
    555 	iter.cur = (void *)id;		/* start from the interface desc */
    556 	usb_desc_iter_next(&iter);	/* and skip it */
    557 
    558 	while ((desc = usb_desc_iter_next(&iter)) != NULL) {
    559 		if (desc->bDescriptorType == UDESC_INTERFACE) {
    560 			/* we ran into the next interface --- not found */
    561 			return NULL;
    562 		}
    563 		if (desc->bDescriptorType == type &&
    564 		    (subtype == USBD_SUBTYPE_ANY ||
    565 		     subtype == desc->bDescriptorSubtype))
    566 			break;
    567 	}
    568 	return desc;
    569 }
    570