xref: /freebsd/sys/dev/usb/usb_hid.c (revision 830940567b49bb0c08dfaed40418999e76616909)
1 /*	$NetBSD: hid.c,v 1.17 2001/11/13 06:24:53 lukem Exp $	*/
2 
3 
4 #include <sys/cdefs.h>
5 __FBSDID("$FreeBSD$");
6 /*-
7  * Copyright (c) 1998 The NetBSD Foundation, Inc.
8  * All rights reserved.
9  *
10  * This code is derived from software contributed to The NetBSD Foundation
11  * by Lennart Augustsson (lennart@augustsson.net) at
12  * Carlstedt Research & Technology.
13  *
14  * Redistribution and use in source and binary forms, with or without
15  * modification, are permitted provided that the following conditions
16  * are met:
17  * 1. Redistributions of source code must retain the above copyright
18  *    notice, this list of conditions and the following disclaimer.
19  * 2. Redistributions in binary form must reproduce the above copyright
20  *    notice, this list of conditions and the following disclaimer in the
21  *    documentation and/or other materials provided with the distribution.
22  * 3. All advertising materials mentioning features or use of this software
23  *    must display the following acknowledgement:
24  *        This product includes software developed by the NetBSD
25  *        Foundation, Inc. and its contributors.
26  * 4. Neither the name of The NetBSD Foundation nor the names of its
27  *    contributors may be used to endorse or promote products derived
28  *    from this software without specific prior written permission.
29  *
30  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
31  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
32  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
33  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
34  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
35  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
36  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
37  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
38  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
39  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
40  * POSSIBILITY OF SUCH DAMAGE.
41  */
42 
43 #include <sys/stdint.h>
44 #include <sys/stddef.h>
45 #include <sys/param.h>
46 #include <sys/queue.h>
47 #include <sys/types.h>
48 #include <sys/systm.h>
49 #include <sys/kernel.h>
50 #include <sys/bus.h>
51 #include <sys/linker_set.h>
52 #include <sys/module.h>
53 #include <sys/lock.h>
54 #include <sys/mutex.h>
55 #include <sys/condvar.h>
56 #include <sys/sysctl.h>
57 #include <sys/sx.h>
58 #include <sys/unistd.h>
59 #include <sys/callout.h>
60 #include <sys/malloc.h>
61 #include <sys/priv.h>
62 
63 #include <dev/usb/usb.h>
64 #include <dev/usb/usbdi.h>
65 #include <dev/usb/usbdi_util.h>
66 #include <dev/usb/usbhid.h>
67 
68 #define	USB_DEBUG_VAR usb_debug
69 
70 #include <dev/usb/usb_core.h>
71 #include <dev/usb/usb_debug.h>
72 #include <dev/usb/usb_process.h>
73 #include <dev/usb/usb_device.h>
74 #include <dev/usb/usb_request.h>
75 
76 static void hid_clear_local(struct hid_item *);
77 static uint8_t hid_get_byte(struct hid_data *s, const uint16_t wSize);
78 
79 #define	MAXUSAGE 64
80 #define	MAXPUSH 4
81 #define	MAXID 16
82 
83 struct hid_pos_data {
84 	int32_t rid;
85 	uint32_t pos;
86 };
87 
88 struct hid_data {
89 	const uint8_t *start;
90 	const uint8_t *end;
91 	const uint8_t *p;
92 	struct hid_item cur[MAXPUSH];
93 	struct hid_pos_data last_pos[MAXID];
94 	int32_t	usages_min[MAXUSAGE];
95 	int32_t	usages_max[MAXUSAGE];
96 	int32_t usage_last;	/* last seen usage */
97 	uint32_t loc_size;	/* last seen size */
98 	uint32_t loc_count;	/* last seen count */
99 	uint8_t	kindset;	/* we have 5 kinds so 8 bits are enough */
100 	uint8_t	pushlevel;	/* current pushlevel */
101 	uint8_t	ncount;		/* end usage item count */
102 	uint8_t icount;		/* current usage item count */
103 	uint8_t	nusage;		/* end "usages_min/max" index */
104 	uint8_t	iusage;		/* current "usages_min/max" index */
105 	uint8_t ousage;		/* current "usages_min/max" offset */
106 	uint8_t	susage;		/* usage set flags */
107 };
108 
109 /*------------------------------------------------------------------------*
110  *	hid_clear_local
111  *------------------------------------------------------------------------*/
112 static void
113 hid_clear_local(struct hid_item *c)
114 {
115 
116 	c->loc.count = 0;
117 	c->loc.size = 0;
118 	c->usage = 0;
119 	c->usage_minimum = 0;
120 	c->usage_maximum = 0;
121 	c->designator_index = 0;
122 	c->designator_minimum = 0;
123 	c->designator_maximum = 0;
124 	c->string_index = 0;
125 	c->string_minimum = 0;
126 	c->string_maximum = 0;
127 	c->set_delimiter = 0;
128 }
129 
130 static void
131 hid_switch_rid(struct hid_data *s, struct hid_item *c, int32_t next_rID)
132 {
133 	uint8_t i;
134 
135 	/* check for same report ID - optimise */
136 
137 	if (c->report_ID == next_rID)
138 		return;
139 
140 	/* save current position for current rID */
141 
142 	if (c->report_ID == 0) {
143 		i = 0;
144 	} else {
145 		for (i = 1; i != MAXID; i++) {
146 			if (s->last_pos[i].rid == c->report_ID)
147 				break;
148 			if (s->last_pos[i].rid == 0)
149 				break;
150 		}
151 	}
152 	if (i != MAXID) {
153 		s->last_pos[i].rid = c->report_ID;
154 		s->last_pos[i].pos = c->loc.pos;
155 	}
156 
157 	/* store next report ID */
158 
159 	c->report_ID = next_rID;
160 
161 	/* lookup last position for next rID */
162 
163 	if (next_rID == 0) {
164 		i = 0;
165 	} else {
166 		for (i = 1; i != MAXID; i++) {
167 			if (s->last_pos[i].rid == next_rID)
168 				break;
169 			if (s->last_pos[i].rid == 0)
170 				break;
171 		}
172 	}
173 	if (i != MAXID) {
174 		s->last_pos[i].rid = next_rID;
175 		c->loc.pos = s->last_pos[i].pos;
176 	} else {
177 		DPRINTF("Out of RID entries, position is set to zero!\n");
178 		c->loc.pos = 0;
179 	}
180 }
181 
182 /*------------------------------------------------------------------------*
183  *	hid_start_parse
184  *------------------------------------------------------------------------*/
185 struct hid_data *
186 hid_start_parse(const void *d, usb_size_t len, int kindset)
187 {
188 	struct hid_data *s;
189 
190 	if ((kindset-1) & kindset) {
191 		DPRINTFN(0, "Only one bit can be "
192 		    "set in the kindset\n");
193 		return (NULL);
194 	}
195 
196 	s = malloc(sizeof *s, M_TEMP, M_WAITOK | M_ZERO);
197 	s->start = s->p = d;
198 	s->end = ((const uint8_t *)d) + len;
199 	s->kindset = kindset;
200 	return (s);
201 }
202 
203 /*------------------------------------------------------------------------*
204  *	hid_end_parse
205  *------------------------------------------------------------------------*/
206 void
207 hid_end_parse(struct hid_data *s)
208 {
209 	if (s == NULL)
210 		return;
211 
212 	free(s, M_TEMP);
213 }
214 
215 /*------------------------------------------------------------------------*
216  *	get byte from HID descriptor
217  *------------------------------------------------------------------------*/
218 static uint8_t
219 hid_get_byte(struct hid_data *s, const uint16_t wSize)
220 {
221 	const uint8_t *ptr;
222 	uint8_t retval;
223 
224 	ptr = s->p;
225 
226 	/* check if end is reached */
227 	if (ptr == s->end)
228 		return (0);
229 
230 	/* read out a byte */
231 	retval = *ptr;
232 
233 	/* check if data pointer can be advanced by "wSize" bytes */
234 	if ((s->end - ptr) < wSize)
235 		ptr = s->end;
236 	else
237 		ptr += wSize;
238 
239 	/* update pointer */
240 	s->p = ptr;
241 
242 	return (retval);
243 }
244 
245 /*------------------------------------------------------------------------*
246  *	hid_get_item
247  *------------------------------------------------------------------------*/
248 int
249 hid_get_item(struct hid_data *s, struct hid_item *h)
250 {
251 	struct hid_item *c;
252 	unsigned int bTag, bType, bSize;
253 	uint32_t oldpos;
254 	int32_t mask;
255 	int32_t dval;
256 
257 	if (s == NULL)
258 		return (0);
259 
260 	c = &s->cur[s->pushlevel];
261 
262  top:
263 	/* check if there is an array of items */
264 	if (s->icount < s->ncount) {
265 		/* get current usage */
266 		if (s->iusage < s->nusage) {
267 			dval = s->usages_min[s->iusage] + s->ousage;
268 			c->usage = dval;
269 			s->usage_last = dval;
270 			if (dval == s->usages_max[s->iusage]) {
271 				s->iusage ++;
272 				s->ousage = 0;
273 			} else {
274 				s->ousage ++;
275 			}
276 		} else {
277 			DPRINTFN(1, "Using last usage\n");
278 			dval = s->usage_last;
279 		}
280 		s->icount ++;
281 		/*
282 		 * Only copy HID item, increment position and return
283 		 * if correct kindset!
284 		 */
285 		if (s->kindset & (1 << c->kind)) {
286 			*h = *c;
287 			DPRINTFN(1, "%u,%u,%u\n", h->loc.pos,
288 			    h->loc.size, h->loc.count);
289 			c->loc.pos += c->loc.size * c->loc.count;
290 			return (1);
291 		}
292 	}
293 
294 	/* reset state variables */
295 	s->icount = 0;
296 	s->ncount = 0;
297 	s->iusage = 0;
298 	s->nusage = 0;
299 	s->susage = 0;
300 	s->ousage = 0;
301 	hid_clear_local(c);
302 
303 	/* get next item */
304 	while (s->p != s->end) {
305 
306 		bSize = hid_get_byte(s, 1);
307 		if (bSize == 0xfe) {
308 			/* long item */
309 			bSize = hid_get_byte(s, 1);
310 			bSize |= hid_get_byte(s, 1) << 8;
311 			bTag = hid_get_byte(s, 1);
312 			bType = 0xff;	/* XXX what should it be */
313 		} else {
314 			/* short item */
315 			bTag = bSize >> 4;
316 			bType = (bSize >> 2) & 3;
317 			bSize &= 3;
318 			if (bSize == 3)
319 				bSize = 4;
320 		}
321 		switch (bSize) {
322 		case 0:
323 			dval = 0;
324 			mask = 0;
325 			break;
326 		case 1:
327 			dval = (int8_t)hid_get_byte(s, 1);
328 			mask = 0xFF;
329 			break;
330 		case 2:
331 			dval = hid_get_byte(s, 1);
332 			dval |= hid_get_byte(s, 1) << 8;
333 			dval = (int16_t)dval;
334 			mask = 0xFFFF;
335 			break;
336 		case 4:
337 			dval = hid_get_byte(s, 1);
338 			dval |= hid_get_byte(s, 1) << 8;
339 			dval |= hid_get_byte(s, 1) << 16;
340 			dval |= hid_get_byte(s, 1) << 24;
341 			mask = 0xFFFFFFFF;
342 			break;
343 		default:
344 			dval = hid_get_byte(s, bSize);
345 			DPRINTFN(0, "bad length %u (data=0x%02x)\n",
346 			    bSize, dval);
347 			continue;
348 		}
349 
350 		switch (bType) {
351 		case 0:		/* Main */
352 			switch (bTag) {
353 			case 8:	/* Input */
354 				c->kind = hid_input;
355 				c->flags = dval;
356 		ret:
357 				c->loc.count = s->loc_count;
358 				c->loc.size = s->loc_size;
359 
360 				if (c->flags & HIO_VARIABLE) {
361 					/* range check usage count */
362 					if (c->loc.count > 255) {
363 						DPRINTFN(0, "Number of "
364 						    "items truncated to 255\n");
365 						s->ncount = 255;
366 					} else
367 						s->ncount = c->loc.count;
368 
369 					/*
370 					 * The "top" loop will return
371 					 * one and one item:
372 					 */
373 					c->loc.count = 1;
374 				} else {
375 					s->ncount = 1;
376 				}
377 				goto top;
378 
379 			case 9:	/* Output */
380 				c->kind = hid_output;
381 				c->flags = dval;
382 				goto ret;
383 			case 10:	/* Collection */
384 				c->kind = hid_collection;
385 				c->collection = dval;
386 				c->collevel++;
387 				c->usage = s->usage_last;
388 				*h = *c;
389 				return (1);
390 			case 11:	/* Feature */
391 				c->kind = hid_feature;
392 				c->flags = dval;
393 				goto ret;
394 			case 12:	/* End collection */
395 				c->kind = hid_endcollection;
396 				if (c->collevel == 0) {
397 					DPRINTFN(0, "invalid end collection\n");
398 					return (0);
399 				}
400 				c->collevel--;
401 				*h = *c;
402 				return (1);
403 			default:
404 				DPRINTFN(0, "Main bTag=%d\n", bTag);
405 				break;
406 			}
407 			break;
408 		case 1:		/* Global */
409 			switch (bTag) {
410 			case 0:
411 				c->_usage_page = dval << 16;
412 				break;
413 			case 1:
414 				c->logical_minimum = dval;
415 				break;
416 			case 2:
417 				c->logical_maximum = dval;
418 				break;
419 			case 3:
420 				c->physical_minimum = dval;
421 				break;
422 			case 4:
423 				c->physical_maximum = dval;
424 				break;
425 			case 5:
426 				c->unit_exponent = dval;
427 				break;
428 			case 6:
429 				c->unit = dval;
430 				break;
431 			case 7:
432 				/* mask because value is unsigned */
433 				s->loc_size = dval & mask;
434 				break;
435 			case 8:
436 				hid_switch_rid(s, c, dval);
437 				break;
438 			case 9:
439 				/* mask because value is unsigned */
440 				s->loc_count = dval & mask;
441 				break;
442 			case 10:	/* Push */
443 				s->pushlevel ++;
444 				if (s->pushlevel < MAXPUSH) {
445 					s->cur[s->pushlevel] = *c;
446 					/* store size and count */
447 					c->loc.size = s->loc_size;
448 					c->loc.count = s->loc_count;
449 					/* update current item pointer */
450 					c = &s->cur[s->pushlevel];
451 				} else {
452 					DPRINTFN(0, "Cannot push "
453 					    "item @ %d!\n", s->pushlevel);
454 				}
455 				break;
456 			case 11:	/* Pop */
457 				s->pushlevel --;
458 				if (s->pushlevel < MAXPUSH) {
459 					/* preserve position */
460 					oldpos = c->loc.pos;
461 					c = &s->cur[s->pushlevel];
462 					/* restore size and count */
463 					s->loc_size = c->loc.size;
464 					s->loc_count = c->loc.count;
465 					/* set default item location */
466 					c->loc.pos = oldpos;
467 					c->loc.size = 0;
468 					c->loc.count = 0;
469 				} else {
470 					DPRINTFN(0, "Cannot pop "
471 					    "item @ %d!\n", s->pushlevel);
472 				}
473 				break;
474 			default:
475 				DPRINTFN(0, "Global bTag=%d\n", bTag);
476 				break;
477 			}
478 			break;
479 		case 2:		/* Local */
480 			switch (bTag) {
481 			case 0:
482 				if (bSize != 4)
483 					dval = (dval & mask) | c->_usage_page;
484 
485 				/* set last usage, in case of a collection */
486 				s->usage_last = dval;
487 
488 				if (s->nusage < MAXUSAGE) {
489 					s->usages_min[s->nusage] = dval;
490 					s->usages_max[s->nusage] = dval;
491 					s->nusage ++;
492 				} else {
493 					DPRINTFN(0, "max usage reached!\n");
494 				}
495 
496 				/* clear any pending usage sets */
497 				s->susage = 0;
498 				break;
499 			case 1:
500 				s->susage |= 1;
501 
502 				if (bSize != 4)
503 					dval = (dval & mask) | c->_usage_page;
504 				c->usage_minimum = dval;
505 
506 				goto check_set;
507 			case 2:
508 				s->susage |= 2;
509 
510 				if (bSize != 4)
511 					dval = (dval & mask) | c->_usage_page;
512 				c->usage_maximum = dval;
513 
514 			check_set:
515 				if (s->susage != 3)
516 					break;
517 
518 				/* sanity check */
519 				if ((s->nusage < MAXUSAGE) &&
520 				    (c->usage_minimum <= c->usage_maximum)) {
521 					/* add usage range */
522 					s->usages_min[s->nusage] =
523 					    c->usage_minimum;
524 					s->usages_max[s->nusage] =
525 					    c->usage_maximum;
526 					s->nusage ++;
527 				} else {
528 					DPRINTFN(0, "Usage set dropped!\n");
529 				}
530 				s->susage = 0;
531 				break;
532 			case 3:
533 				c->designator_index = dval;
534 				break;
535 			case 4:
536 				c->designator_minimum = dval;
537 				break;
538 			case 5:
539 				c->designator_maximum = dval;
540 				break;
541 			case 7:
542 				c->string_index = dval;
543 				break;
544 			case 8:
545 				c->string_minimum = dval;
546 				break;
547 			case 9:
548 				c->string_maximum = dval;
549 				break;
550 			case 10:
551 				c->set_delimiter = dval;
552 				break;
553 			default:
554 				DPRINTFN(0, "Local bTag=%d\n", bTag);
555 				break;
556 			}
557 			break;
558 		default:
559 			DPRINTFN(0, "default bType=%d\n", bType);
560 			break;
561 		}
562 	}
563 	return (0);
564 }
565 
566 /*------------------------------------------------------------------------*
567  *	hid_report_size
568  *------------------------------------------------------------------------*/
569 int
570 hid_report_size(const void *buf, usb_size_t len, enum hid_kind k, uint8_t *id)
571 {
572 	struct hid_data *d;
573 	struct hid_item h;
574 	uint32_t temp;
575 	uint32_t hpos;
576 	uint32_t lpos;
577 	uint8_t any_id;
578 
579 	any_id = 0;
580 	hpos = 0;
581 	lpos = 0xFFFFFFFF;
582 
583 	for (d = hid_start_parse(buf, len, 1 << k); hid_get_item(d, &h);) {
584 		if (h.kind == k) {
585 			/* check for ID-byte presense */
586 			if ((h.report_ID != 0) && !any_id) {
587 				if (id != NULL)
588 					*id = h.report_ID;
589 				any_id = 1;
590 			}
591 			/* compute minimum */
592 			if (lpos > h.loc.pos)
593 				lpos = h.loc.pos;
594 			/* compute end position */
595 			temp = h.loc.pos + (h.loc.size * h.loc.count);
596 			/* compute maximum */
597 			if (hpos < temp)
598 				hpos = temp;
599 		}
600 	}
601 	hid_end_parse(d);
602 
603 	/* safety check - can happen in case of currupt descriptors */
604 	if (lpos > hpos)
605 		temp = 0;
606 	else
607 		temp = hpos - lpos;
608 
609 	/* check for ID byte */
610 	if (any_id)
611 		temp += 8;
612 	else if (id != NULL)
613 		*id = 0;
614 
615 	/* return length in bytes rounded up */
616 	return ((temp + 7) / 8);
617 }
618 
619 /*------------------------------------------------------------------------*
620  *	hid_locate
621  *------------------------------------------------------------------------*/
622 int
623 hid_locate(const void *desc, usb_size_t size, uint32_t u, enum hid_kind k,
624     uint8_t index, struct hid_location *loc, uint32_t *flags, uint8_t *id)
625 {
626 	struct hid_data *d;
627 	struct hid_item h;
628 
629 	for (d = hid_start_parse(desc, size, 1 << k); hid_get_item(d, &h);) {
630 		if (h.kind == k && !(h.flags & HIO_CONST) && h.usage == u) {
631 			if (index--)
632 				continue;
633 			if (loc != NULL)
634 				*loc = h.loc;
635 			if (flags != NULL)
636 				*flags = h.flags;
637 			if (id != NULL)
638 				*id = h.report_ID;
639 			hid_end_parse(d);
640 			return (1);
641 		}
642 	}
643 	if (loc != NULL)
644 		loc->size = 0;
645 	if (flags != NULL)
646 		*flags = 0;
647 	if (id != NULL)
648 		*id = 0;
649 	hid_end_parse(d);
650 	return (0);
651 }
652 
653 /*------------------------------------------------------------------------*
654  *	hid_get_data
655  *------------------------------------------------------------------------*/
656 uint32_t
657 hid_get_data(const uint8_t *buf, usb_size_t len, struct hid_location *loc)
658 {
659 	uint32_t hpos = loc->pos;
660 	uint32_t hsize = loc->size;
661 	uint32_t data;
662 	uint32_t rpos;
663 	uint8_t n;
664 
665 	DPRINTFN(11, "hid_get_data: loc %d/%d\n", hpos, hsize);
666 
667 	/* Range check and limit */
668 	if (hsize == 0)
669 		return (0);
670 	if (hsize > 32)
671 		hsize = 32;
672 
673 	/* Get data in a safe way */
674 	data = 0;
675 	rpos = (hpos / 8);
676 	n = (hsize + 7) / 8;
677 	rpos += n;
678 	while (n--) {
679 		rpos--;
680 		if (rpos < len)
681 			data |= buf[rpos] << (8 * n);
682 	}
683 
684 	/* Correctly shift down data */
685 	data = (data >> (hpos % 8));
686 
687 	/* Mask and sign extend in one */
688 	n = 32 - hsize;
689 	data = ((int32_t)data << n) >> n;
690 
691 	DPRINTFN(11, "hid_get_data: loc %d/%d = %lu\n",
692 	    loc->pos, loc->size, (long)data);
693 	return (data);
694 }
695 
696 /*------------------------------------------------------------------------*
697  *	hid_is_collection
698  *------------------------------------------------------------------------*/
699 int
700 hid_is_collection(const void *desc, usb_size_t size, uint32_t usage)
701 {
702 	struct hid_data *hd;
703 	struct hid_item hi;
704 	int err;
705 
706 	hd = hid_start_parse(desc, size, hid_input);
707 	if (hd == NULL)
708 		return (0);
709 
710 	while ((err = hid_get_item(hd, &hi))) {
711 		 if (hi.kind == hid_collection &&
712 		     hi.usage == usage)
713 			break;
714 	}
715 	hid_end_parse(hd);
716 	return (err);
717 }
718 
719 /*------------------------------------------------------------------------*
720  *	hid_get_descriptor_from_usb
721  *
722  * This function will search for a HID descriptor between two USB
723  * interface descriptors.
724  *
725  * Return values:
726  * NULL: No more HID descriptors.
727  * Else: Pointer to HID descriptor.
728  *------------------------------------------------------------------------*/
729 struct usb_hid_descriptor *
730 hid_get_descriptor_from_usb(struct usb_config_descriptor *cd,
731     struct usb_interface_descriptor *id)
732 {
733 	struct usb_descriptor *desc = (void *)id;
734 
735 	if (desc == NULL) {
736 		return (NULL);
737 	}
738 	while ((desc = usb_desc_foreach(cd, desc))) {
739 		if ((desc->bDescriptorType == UDESC_HID) &&
740 		    (desc->bLength >= USB_HID_DESCRIPTOR_SIZE(0))) {
741 			return (void *)desc;
742 		}
743 		if (desc->bDescriptorType == UDESC_INTERFACE) {
744 			break;
745 		}
746 	}
747 	return (NULL);
748 }
749 
750 /*------------------------------------------------------------------------*
751  *	usbd_req_get_hid_desc
752  *
753  * This function will read out an USB report descriptor from the USB
754  * device.
755  *
756  * Return values:
757  * NULL: Failure.
758  * Else: Success. The pointer should eventually be passed to free().
759  *------------------------------------------------------------------------*/
760 usb_error_t
761 usbd_req_get_hid_desc(struct usb_device *udev, struct mtx *mtx,
762     void **descp, uint16_t *sizep,
763     struct malloc_type *mem, uint8_t iface_index)
764 {
765 	struct usb_interface *iface = usbd_get_iface(udev, iface_index);
766 	struct usb_hid_descriptor *hid;
767 	usb_error_t err;
768 
769 	if ((iface == NULL) || (iface->idesc == NULL)) {
770 		return (USB_ERR_INVAL);
771 	}
772 	hid = hid_get_descriptor_from_usb
773 	    (usbd_get_config_descriptor(udev), iface->idesc);
774 
775 	if (hid == NULL) {
776 		return (USB_ERR_IOERROR);
777 	}
778 	*sizep = UGETW(hid->descrs[0].wDescriptorLength);
779 	if (*sizep == 0) {
780 		return (USB_ERR_IOERROR);
781 	}
782 	if (mtx)
783 		mtx_unlock(mtx);
784 
785 	*descp = malloc(*sizep, mem, M_ZERO | M_WAITOK);
786 
787 	if (mtx)
788 		mtx_lock(mtx);
789 
790 	if (*descp == NULL) {
791 		return (USB_ERR_NOMEM);
792 	}
793 	err = usbd_req_get_report_descriptor
794 	    (udev, mtx, *descp, *sizep, iface_index);
795 
796 	if (err) {
797 		free(*descp, mem);
798 		*descp = NULL;
799 		return (err);
800 	}
801 	return (USB_ERR_NORMAL_COMPLETION);
802 }
803