aboutsummaryrefslogtreecommitdiff
path: root/drivers/usb/core/urb.c
blob: eebc070c3cc7fae1fa66bdb06d94da397d146fd5 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
#include <linux/module.h>
#include <linux/string.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/log2.h>
#include <linux/usb.h>
#include <linux/wait.h>
#include "hcd.h"

#define to_urb(d) container_of(d, struct urb, kref)

static DEFINE_SPINLOCK(usb_reject_lock);

static void urb_destroy(struct kref *kref)
{
	struct urb *urb = to_urb(kref);

	if (urb->transfer_flags & URB_FREE_BUFFER)
		kfree(urb->transfer_buffer);

	kfree(urb);
}

/**
 * usb_init_urb - initializes a urb so that it can be used by a USB driver
 * @urb: pointer to the urb to initialize
 *
 * Initializes a urb so that the USB subsystem can use it properly.
 *
 * If a urb is created with a call to usb_alloc_urb() it is not
 * necessary to call this function.  Only use this if you allocate the
 * space for a struct urb on your own.  If you call this function, be
 * careful when freeing the memory for your urb that it is no longer in
 * use by the USB core.
 *
 * Only use this function if you _really_ understand what you are doing.
 */
void usb_init_urb(struct urb *urb)
{
	if (urb) {
		memset(urb, 0, sizeof(*urb));
		kref_init(&urb->kref);
		INIT_LIST_HEAD(&urb->anchor_list);
	}
}
EXPORT_SYMBOL_GPL(usb_init_urb);

/**
 * usb_alloc_urb - creates a new urb for a USB driver to use
 * @iso_packets: number of iso packets for this urb
 * @mem_flags: the type of memory to allocate, see kmalloc() for a list of
 *	valid options for this.
 *
 * Creates an urb for the USB driver to use, initializes a few internal
 * structures, incrementes the usage counter, and returns a pointer to it.
 *
 * If no memory is available, NULL is returned.
 *
 * If the driver want to use this urb for interrupt, control, or bulk
 * endpoints, pass '0' as the number of iso packets.
 *
 * The driver must call usb_free_urb() when it is finished with the urb.
 */
struct urb *usb_alloc_urb(int iso_packets, gfp_t mem_flags)
{
	struct urb *urb;

	urb = kmalloc(sizeof(struct urb) +
		iso_packets * sizeof(struct usb_iso_packet_descriptor),
		mem_flags);
	if (!urb) {
		err("alloc_urb: kmalloc failed");
		return NULL;
	}
	usb_init_urb(urb);
	return urb;
}
EXPORT_SYMBOL_GPL(usb_alloc_urb);

/**
 * usb_free_urb - frees the memory used by a urb when all users of it are finished
 * @urb: pointer to the urb to free, may be NULL
 *
 * Must be called when a user of a urb is finished with it.  When the last user
 * of the urb calls this function, the memory of the urb is freed.
 *
 * Note: The transfer buffer associated with the urb is not freed, that must be
 * done elsewhere.
 */
void usb_free_urb(struct urb *urb)
{
	if (urb)
		kref_put(&urb->kref, urb_destroy);
}
EXPORT_SYMBOL_GPL(usb_free_urb);

/**
 * usb_get_urb - increments the reference count of the urb
 * @urb: pointer to the urb to modify, may be NULL
 *
 * This must be  called whenever a urb is transferred from a device driver to a
 * host controller driver.  This allows proper reference counting to happen
 * for urbs.
 *
 * A pointer to the urb with the incremented reference counter is returned.
 */
struct urb *usb_get_urb(struct urb *urb)
{
	if (urb)
		kref_get(&urb->kref);
	return urb;
}
EXPORT_SYMBOL_GPL(usb_get_urb);

/**
 * usb_anchor_urb - anchors an URB while it is processed
 * @urb: pointer to the urb to anchor
 * @anchor: pointer to the anchor
 *
 * This can be called to have access to URBs which are to be executed
 * without bothering to track them
 */
void usb_anchor_urb(struct urb *urb, struct usb_anchor *anchor)
{
	unsigned long flags;

	spin_lock_irqsave(&anchor->lock, flags);
	usb_get_urb(urb);
	list_add_tail(&urb->anchor_list, &anchor->urb_list);
	urb->anchor = anchor;

	if (unlikely(anchor->poisoned)) {
		spin_lock(&usb_reject_lock);
		urb->reject++;
		spin_unlock(&usb_reject_lock);
	}

	spin_unlock_irqrestore(&anchor->lock, flags);
}
EXPORT_SYMBOL_GPL(usb_anchor_urb);

/**
 * usb_unanchor_urb - unanchors an URB
 * @urb: pointer to the urb to anchor
 *
 * Call this to stop the system keeping track of this URB
 */
void usb_unanchor_urb(struct urb *urb)
{
	unsigned long flags;
	struct usb_anchor *anchor;

	if (!urb)
		return;

	anchor = urb->anchor;
	if (!anchor)
		return;

	spin_lock_irqsave(&anchor->lock, flags);
	if (unlikely(anchor != urb->anchor)) {
		/* we've lost the race to another thread */
		spin_unlock_irqrestore(&anchor->lock, flags);
		return;
	}
	urb->anchor = NULL;
	list_del(&urb->anchor_list);
	spin_unlock_irqrestore(&anchor->lock, flags);
	usb_put_urb(urb);
	if (list_empty(&anchor->urb_list))
		wake_up(&anchor->wait);
}
EXPORT_SYMBOL_GPL(usb_unanchor_urb);

/*-------------------------------------------------------------------*/

/**
 * usb_submit_urb - issue an asynchronous transfer request for an endpoint
 * @urb: pointer to the urb describing the request
 * @mem_flags: the type of memory to allocate, see kmalloc() for a list
 *	of valid options for this.
 *
 * This submits a transfer request, and transfers control of the URB
 * describing that request to the USB subsystem.  Request completion will
 * be indicated later, asynchronously, by calling the completion handler.
 * The three types of completion are success, error, and unlink
 * (a software-induced fault, also called "request cancellation").
 *
 * URBs may be submitted in interrupt context.
 *
 * The caller must have correctly initialized the URB before submitting
 * it.  Functions such as usb_fill_bulk_urb() and usb_fill_control_urb() are
 * available to ensure that most fields are correctly initialized, for
 * the particular kind of transfer, although they will not initialize
 * any transfer flags.
 *
 * Successful submissions return 0; otherwise this routine returns a
 * negative error number.  If the submission is successful, the complete()
 * callback from the URB will be called exactly once, when the USB core and
 * Host Controller Driver (HCD) are finished with the URB.  When the completion
 * function is called, control of the URB is returned to the device
 * driver which issued the request.  The completion handler may then
 * immediately free or reuse that URB.
 *
 * With few exceptions, USB device drivers should never access URB fields
 * provided by usbcore or the HCD until its complete() is called.
 * The exceptions relate to periodic transfer scheduling.  For both
 * interrupt and isochronous urbs, as part of successful URB submission
 * urb->interval is modified to reflect the actual transfer period used
 * (normally some power of two units).  And for isochronous urbs,
 * urb->start_frame is modified to reflect when the URB's transfers were
 * scheduled to start.  Not all isochronous transfer scheduling policies
 * will work, but most host controller drivers should easily handle ISO
 * queues going from now until 10-200 msec into the future.
 *
 * For control endpoints, the synchronous usb_control_msg() call is
 * often used (in non-interrupt context) instead of this call.
 * That is often used through convenience wrappers, for the requests
 * that are standardized in the USB 2.0 specification.  For bulk
 * endpoints, a synchronous usb_bulk_msg() call is available.
 *
 * Request Queuing:
 *
 * URBs may be submitted to endpoints before previous ones complete, to
 * minimize the impact of interrupt latencies and system overhead on data
 * throughput.  With that queuing policy, an endpoint's queue would never
 * be empty.  This is required for continuous isochronous data streams,
 * and may also be required for some kinds of interrupt transfers. Such
 * queuing also maximizes bandwidth utilization by letting USB controllers
 * start work on later requests before driver software has finished the
 * completion processing for earlier (successful) requests.
 *
 * As of Linux 2.6, all USB endpoint transfer queues support depths greater
 * than one.  This was previously a HCD-specific behavior, except for ISO
 * transfers.  Non-isochronous endpoint queues are inactive during cleanup
 * after faults (transfer errors or cancellation).
 *
 * Reserved Bandwidth Transfers:
 *
 * Periodic transfers (interrupt or isochronous) are performed repeatedly,
 * using the interval specified in the urb.  Submitting the first urb to
 * the endpoint reserves the bandwidth necessary to make those transfers.
 * If the USB subsystem can't allocate sufficient bandwidth to perform
 * the periodic request, submitting such a periodic request should fail.
 *
 * Device drivers must explicitly request that repetition, by ensuring that
 * some URB is always on the endpoint's queue (except possibly for short
 * periods during completion callacks).  When there is no longer an urb
 * queued, the endpoint's bandwidth reservation is canceled.  This means
 * drivers can use their completion handlers to ensure they keep bandwidth
 * they need, by reinitializing and resubmitting the just-completed urb
 * until the driver longer needs that periodic bandwidth.
 *
 * Memory Flags:
 *
 * The general rules for how to decide which mem_flags to use
 * are the same as for kmalloc.  There are four
 * different possible values; GFP_KERNEL, GFP_NOFS, GFP_NOIO and
 * GFP_ATOMIC.
 *
 * GFP_NOFS is not ever used, as it has not been implemented yet.
 *
 * GFP_ATOMIC is used when
 *   (a) you are inside a completion handler, an interrupt, bottom half,
 *       tasklet or timer, or
 *   (b) you are holding a spinlock or rwlock (does not apply to
 *       semaphores), or
 *   (c) current->state != TASK_RUNNING, this is the case only after
 *       you've changed it.
 *
 * GFP_NOIO is used in the block io path and error handling of storage
 * devices.
 *
 * All other situations use GFP_KERNEL.
 *
 * Some more specific rules for mem_flags can be inferred, such as
 *  (1) start_xmit, timeout, and receive methods of network drivers must
 *      use GFP_ATOMIC (they are called with a spinlock held);
 *  (2) queuecommand methods of scsi drivers must use GFP_ATOMIC (also
 *      called with a spinlock held);
 *  (3) If you use a kernel thread with a network driver you must use
 *      GFP_NOIO, unless (b) or (c) apply;
 *  (4) after you have done a down() you can use GFP_KERNEL, unless (b) or (c)
 *      apply or your are in a storage driver's block io path;
 *  (5) USB probe and disconnect can use GFP_KERNEL unless (b) or (c) apply; and
 *  (6) changing firmware on a running storage or net device uses
 *      GFP_NOIO, unless b) or c) apply
 *
 */
int usb_submit_urb(struct urb *urb, gfp_t mem_flags)
{
	int				xfertype, max;
	struct usb_device		*dev;
	struct usb_host_endpoint	*ep;
	int				is_out;

	if (!urb || urb->hcpriv || !urb->complete)
		return -EINVAL;
	dev = urb->dev;
	if ((!dev) || (dev->state < USB_STATE_DEFAULT))
		return -ENODEV;

	/* For now, get the endpoint from the pipe.  Eventually drivers
	 * will be required to set urb->ep directly and we will eliminate
	 * urb->pipe.
	 */
	ep = (usb_pipein(urb->pipe) ? dev->ep_in : dev->ep_out)
			[usb_pipeendpoint(urb->pipe)];
	if (!ep)
		return -ENOENT;

	urb->ep = ep;
	urb->status = -EINPROGRESS;
	urb->actual_length = 0;

	/* Lots of sanity checks, so HCDs can rely on clean data
	 * and don't need to duplicate tests
	 */
	xfertype = usb_endpoint_type(&ep->desc);
	if (xfertype == USB_ENDPOINT_XFER_CONTROL) {
		struct usb_ctrlrequest *setup =
				(struct usb_ctrlrequest *) urb->setup_packet;

		if (!setup)
			return -ENOEXEC;
		is_out = !(setup->bRequestType & USB_DIR_IN) ||
				!setup->wLength;
	} else {
		is_out = usb_endpoint_dir_out(&ep->desc);
	}

	/* Cache the direction for later use */
	urb->transfer_flags = (urb->transfer_flags & ~URB_DIR_MASK) |
			(is_out ? URB_DIR_OUT : URB_DIR_IN);

	if (xfertype != USB_ENDPOINT_XFER_CONTROL &&
			dev->state < USB_STATE_CONFIGURED)
		return -ENODEV;

	max = le16_to_cpu(ep->desc.wMaxPacketSize);
	if (max <= 0) {
		dev_dbg(&dev->dev,
			"bogus endpoint ep%d%s in %s (bad maxpacket %d)\n",
			usb_endpoint_num(&ep->desc), is_out ? "out" : "in",
			__func__, max);
		return -EMSGSIZE;
	}

	/* periodic transfers limit size per frame/uframe,
	 * but drivers only control those sizes for ISO.
	 * while we're checking, initialize return status.
	 */
	if (xfertype == USB_ENDPOINT_XFER_ISOC) {
		int	n, len;

		/* "high bandwidth" mode, 1-3 packets/uframe? */
		if (dev->speed == USB_SPEED_HIGH) {
			int	mult = 1 + ((max >> 11) & 0x03);
			max &= 0x07ff;
			max *= mult;
		}

		if (urb->number_of_packets <= 0)
			return -EINVAL;
		for (n = 0; n < urb->number_of_packets; n++) {
			len = urb->iso_frame_desc[n].length;
			if (len < 0 || len > max)
				return -EMSGSIZE;
			urb->iso_frame_desc[n].status = -EXDEV;
			urb->iso_frame_desc[n].actual_length = 0;
		}
	}

	/* the I/O buffer must be mapped/unmapped, except when length=0 */
	if (urb->transfer_buffer_length < 0)
		return -EMSGSIZE;

#ifdef DEBUG
	/* stuff that drivers shouldn't do, but which shouldn't
	 * cause problems in HCDs if they get it wrong.
	 */
	{
	unsigned int	orig_flags = urb->transfer_flags;
	unsigned int	allowed;

	/* enforce simple/standard policy */
	allowed = (URB_NO_TRANSFER_DMA_MAP | URB_NO_SETUP_DMA_MAP |
			URB_NO_INTERRUPT | URB_DIR_MASK | URB_FREE_BUFFER);
	switch (xfertype) {
	case USB_ENDPOINT_XFER_BULK:
		if (is_out)
			allowed |= URB_ZERO_PACKET;
		/* FALLTHROUGH */
	case USB_ENDPOINT_XFER_CONTROL:
		allowed |= URB_NO_FSBR;	/* only affects UHCI */
		/* FALLTHROUGH */
	default:			/* all non-iso endpoints */
		if (!is_out)
			allowed |= URB_SHORT_NOT_OK;
		break;
	case USB_ENDPOINT_XFER_ISOC:
		allowed |= URB_ISO_ASAP;
		break;
	}
	urb->transfer_flags &= allowed;

	/* fail if submitter gave bogus flags */
	if (urb->transfer_flags != orig_flags) {
		err("BOGUS urb flags, %x --> %x",
			orig_flags, urb->transfer_flags);
		return -EINVAL;
	}
	}
#endif
	/*
	 * Force periodic transfer intervals to be legal values that are
	 * a power of two (so HCDs don't need to).
	 *
	 * FIXME want bus->{intr,iso}_sched_horizon values here.  Each HC
	 * supports different values... this uses EHCI/UHCI defaults (and
	 * EHCI can use smaller non-default values).
	 */
	switch (xfertype) {
	case USB_ENDPOINT_XFER_ISOC:
	case USB_ENDPOINT_XFER_INT:
		/* too small? */
		if (urb->interval <= 0)
			return -EINVAL;
		/* too big? */
		switch (dev->speed) {
		case USB_SPEED_HIGH:	/* units are microframes */
			/* NOTE usb handles 2^15 */
			if (urb->interval > (1024 * 8))
				urb->interval = 1024 * 8;
			max = 1024 * 8;
			break;
		case USB_SPEED_FULL:	/* units are frames/msec */
		case USB_SPEED_LOW:
			if (xfertype == USB_ENDPOINT_XFER_INT) {
				if (urb->interval > 255)
					return -EINVAL;
				/* NOTE ohci only handles up to 32 */
				max = 128;
			} else {
				if (urb->interval > 1024)
					urb->interval = 1024;
				/* NOTE usb and ohci handle up to 2^15 */
				max = 1024;
			}
			break;
		default:
			return -EINVAL;
		}
		/* Round down to a power of 2, no more than max */
		urb->interval = min(max, 1 << ilog2(urb->interval));
	}

	return usb_hcd_submit_urb(urb, mem_flags);
}
EXPORT_SYMBOL_GPL(usb_submit_urb);

/*-------------------------------------------------------------------*/

/**
 * usb_unlink_urb - abort/cancel a transfer request for an endpoint
 * @urb: pointer to urb describing a previously submitted request,
 *	may be NULL
 *
 * This routine cancels an in-progress request.  URBs complete only once
 * per submission, and may be canceled only once per submission.
 * Successful cancellation means termination of @urb will be expedited
 * and the completion handler will be called with a status code
 * indicating that the request has been canceled (rather than any other
 * code).
 *
 * This request is always asynchronous.  Success is indicated by
 * returning -EINPROGRESS, at which time the URB will probably not yet
 * have been given back to the device driver.  When it is eventually
 * called, the completion function will see @urb->status == -ECONNRESET.
 * Failure is indicated by usb_unlink_urb() returning any other value.
 * Unlinking will fail when @urb is not currently "linked" (i.e., it was
 * never submitted, or it was unlinked before, or the hardware is already
 * finished with it), even if the completion handler has not yet run.
 *
 * Unlinking and Endpoint Queues:
 *
 * [The behaviors and guarantees described below do not apply to virtual
 * root hubs but only to endpoint queues for physical USB devices.]
 *
 * Host Controller Drivers (HCDs) place all the URBs for a particular
 * endpoint in a queue.  Normally the queue advances as the controller
 * hardware processes each request.  But when an URB terminates with an
 * error its queue generally stops (see below), at least until that URB's
 * completion routine returns.  It is guaranteed that a stopped queue
 * will not restart until all its unlinked URBs have been fully retired,
 * with their completion routines run, even if that's not until some time
 * after the original completion handler returns.  The same behavior and
 * guarantee apply when an URB terminates because it was unlinked.
 *
 * Bulk and interrupt endpoint queues are guaranteed to stop whenever an
 * URB terminates with any sort of error, including -ECONNRESET, -ENOENT,
 * and -EREMOTEIO.  Control endpoint queues behave the same way except
 * that they are not guaranteed to stop for -EREMOTEIO errors.  Queues
 * for isochronous endpoints are treated differently, because they must
 * advance at fixed rates.  Such queues do not stop when an URB
 * encounters an error or is unlinked.  An unlinked isochronous URB may
 * leave a gap in the stream of packets; it is undefined whether such
 * gaps can be filled in.
 *
 * Note that early termination of an URB because a short packet was
 * received will generate a -EREMOTEIO error if and only if the
 * URB_SHORT_NOT_OK flag is set.  By setting this flag, USB device
 * drivers can build deep queues for large or complex bulk transfers
 * and clean them up reliably after any sort of aborted transfer by
 * unlinking all pending URBs at the first fault.
 *
 * When a control URB terminates with an error other than -EREMOTEIO, it
 * is quite likely that the status stage of the transfer will not take
 * place.
 */
int usb_unlink_urb(struct urb *urb)
{
	if (!urb)
		return -EINVAL;
	if (!urb->dev)
		return -ENODEV;
	if (!urb->ep)
		return -EIDRM;
	return usb_hcd_unlink_urb(urb, -ECONNRESET);
}
EXPORT_SYMBOL_GPL(usb_unlink_urb);

/**
 * usb_kill_urb - cancel a transfer request and wait for it to finish
 * @urb: pointer to URB describing a previously submitted request,
 *	may be NULL
 *
 * This routine cancels an in-progress request.  It is guaranteed that
 * upon return all completion handlers will have finished and the URB
 * will be totally idle and available for reuse.  These features make
 * this an ideal way to stop I/O in a disconnect() callback or close()
 * function.  If the request has not already finished or been unlinked
 * the completion handler will see urb->status == -ENOENT.
 *
 * While the routine is running, attempts to resubmit the URB will fail
 * with error -EPERM.  Thus even if the URB's completion handler always
 * tries to resubmit, it will not succeed and the URB will become idle.
 *
 * This routine may not be used in an interrupt context (such as a bottom
 * half or a completion handler), or when holding a spinlock, or in other
 * situations where the caller can't schedule().
 */
void usb_kill_urb(struct urb *urb)
{
	might_sleep();
	if (!(urb && urb->dev && urb->ep))
		return;
	spin_lock_irq(&usb_reject_lock);
	++urb->reject;
	spin_unlock_irq(&usb_reject_lock);

	usb_hcd_unlink_urb(urb, -ENOENT);
	wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0);

	spin_lock_irq(&usb_reject_lock);
	--urb->reject;
	spin_unlock_irq(&usb_reject_lock);
}
EXPORT_SYMBOL_GPL(usb_kill_urb);

/**
 * usb_poison_urb - reliably kill a transfer and prevent further use of an URB
 * @urb: pointer to URB describing a previously submitted request,
 *	may be NULL
 *
 * This routine cancels an in-progress request.  It is guaranteed that
 * upon return all completion handlers will have finished and the URB
 * will be totally idle and cannot be reused.  These features make
 * this an ideal way to stop I/O in a disconnect() callback.
 * If the request has not already finished or been unlinked
 * the completion handler will see urb->status == -ENOENT.
 *
 * After and while the routine runs, attempts to resubmit the URB will fail
 * with error -EPERM.  Thus even if the URB's completion handler always
 * tries to resubmit, it will not succeed and the URB will become idle.
 *
 * This routine may not be used in an interrupt context (such as a bottom
 * half or a completion handler), or when holding a spinlock, or in other
 * situations where the caller can't schedule().
 */
void usb_poison_urb(struct urb *urb)
{
	might_sleep();
	if (!(urb && urb->dev && urb->ep))
		return;
	spin_lock_irq(&usb_reject_lock);
	++urb->reject;
	spin_unlock_irq(&usb_reject_lock);

	usb_hcd_unlink_urb(urb, -ENOENT);
	wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0);
}
EXPORT_SYMBOL_GPL(usb_poison_urb);

void usb_unpoison_urb(struct urb *urb)
{
	unsigned long flags;

	if (!urb)
		return;

	spin_lock_irqsave(&usb_reject_lock, flags);
	--urb->reject;
	spin_unlock_irqrestore(&usb_reject_lock, flags);
}
EXPORT_SYMBOL_GPL(usb_unpoison_urb);

/**
 * usb_kill_anchored_urbs - cancel transfer requests en masse
 * @anchor: anchor the requests are bound to
 *
 * this allows all outstanding URBs to be killed starting
 * from the back of the queue
 */
void usb_kill_anchored_urbs(struct usb_anchor *anchor)
{
	struct urb *victim;

	spin_lock_irq(&anchor->lock);
	while (!list_empty(&anchor->urb_list)) {
		victim = list_entry(anchor->urb_list.prev, struct urb,
				    anchor_list);
		/* we must make sure the URB isn't freed before we kill it*/
		usb_get_urb(victim);
		spin_unlock_irq(&anchor->lock);
		/* this will unanchor the URB */
		usb_kill_urb(victim);
		usb_put_urb(victim);
		spin_lock_irq(&anchor->lock);
	}
	spin_unlock_irq(&anchor->lock);
}
EXPORT_SYMBOL_GPL(usb_kill_anchored_urbs);


/**
 * usb_poison_anchored_urbs - cease all traffic from an anchor
 * @anchor: anchor the requests are bound to
 *
 * this allows all outstanding URBs to be poisoned starting
 * from the back of the queue. Newly added URBs will also be
 * poisoned
 */
void usb_poison_anchored_urbs(struct usb_anchor *anchor)
{
	struct urb *victim;

	spin_lock_irq(&anchor->lock);
	anchor->poisoned = 1;
	while (!list_empty(&anchor->urb_list)) {
		victim = list_entry(anchor->urb_list.prev, struct urb,
				    anchor_list);
		/* we must make sure the URB isn't freed before we kill it*/
		usb_get_urb(victim);
		spin_unlock_irq(&anchor->lock);
		/* this will unanchor the URB */
		usb_poison_urb(victim);
		usb_put_urb(victim);
		spin_lock_irq(&anchor->lock);
	}
	spin_unlock_irq(&anchor->lock);
}
EXPORT_SYMBOL_GPL(usb_poison_anchored_urbs);
/**
 * usb_unlink_anchored_urbs - asynchronously cancel transfer requests en masse
 * @anchor: anchor the requests are bound to
 *
 * this allows all outstanding URBs to be unlinked starting
 * from the back of the queue. This function is asynchronous.
 * The unlinking is just tiggered. It may happen after this
 * function has returned.
 */
void usb_unlink_anchored_urbs(struct usb_anchor *anchor)
{
	struct urb *victim;
	unsigned long flags;

	spin_lock_irqsave(&anchor->lock, flags);
	while (!list_empty(&anchor->urb_list)) {
		victim = list_entry(anchor->urb_list.prev, struct urb,
				    anchor_list);
		usb_get_urb(victim);
		spin_unlock_irqrestore(&anchor->lock, flags);
		/* this will unanchor the URB */
		usb_unlink_urb(victim);
		usb_put_urb(victim);
		spin_lock_irqsave(&anchor->lock, flags);
	}
	spin_unlock_irqrestore(&anchor->lock, flags);
}
EXPORT_SYMBOL_GPL(usb_unlink_anchored_urbs);

/**
 * usb_wait_anchor_empty_timeout - wait for an anchor to be unused
 * @anchor: the anchor you want to become unused
 * @timeout: how long you are willing to wait in milliseconds
 *
 * Call this is you want to be sure all an anchor's
 * URBs have finished
 */
int usb_wait_anchor_empty_timeout(struct usb_anchor *anchor,
				  unsigned int timeout)
{
	return wait_event_timeout(anchor->wait, list_empty(&anchor->urb_list),
				  msecs_to_jiffies(timeout));
}
EXPORT_SYMBOL_GPL(usb_wait_anchor_empty_timeout);