aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/uwb/i1480/i1480u-wlp/tx.c
blob: 3db3449dbda46962171f71acdf3ebca250a4d860 (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
/*
 * WUSB Wire Adapter: WLP interface
 * Deal with TX (massaging data to transmit, handling it)
 *
 * Copyright (C) 2005-2006 Intel Corporation
 * Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 *
 * Transmission engine. Get an skb, create from that a WLP transmit
 * context, add a WLP TX header (which we keep prefilled in the
 * device's instance), fill out the target-specific fields and
 * fire it.
 *
 * ROADMAP:
 *
 *   Entry points:
 *
 *     i1480u_tx_release(): called by i1480u_disconnect() to release
 *                          pending tx contexts.
 *
 *     i1480u_tx_cb(): callback for TX contexts (USB URBs)
 *       i1480u_tx_destroy():
 *
 *     i1480u_tx_timeout(): called for timeout handling from the
 *                          network stack.
 *
 *     i1480u_hard_start_xmit(): called for transmitting an skb from
 *                               the network stack. Will interact with WLP
 *                               substack to verify and prepare frame.
 *       i1480u_xmit_frame(): actual transmission on hardware
 *
 *         i1480u_tx_create()	    Creates TX context
 *            i1480u_tx_create_1()    For packets in 1 fragment
 *            i1480u_tx_create_n()    For packets in >1 fragments
 *
 * TODO:
 *
 * - FIXME: rewrite using usb_sg_*(), add asynch support to
 *          usb_sg_*(). It might not make too much sense as most of
 *          the times the MTU will be smaller than one page...
 */

#include "i1480u-wlp.h"

enum {
	/* This is only for Next and Last TX packets */
	i1480u_MAX_PL_SIZE = i1480u_MAX_FRG_SIZE
		- sizeof(struct untd_hdr_rst),
};

/* Free resources allocated to a i1480u tx context. */
static
void i1480u_tx_free(struct i1480u_tx *wtx)
{
	kfree(wtx->buf);
	if (wtx->skb)
		dev_kfree_skb_irq(wtx->skb);
	usb_free_urb(wtx->urb);
	kfree(wtx);
}

static
void i1480u_tx_destroy(struct i1480u *i1480u, struct i1480u_tx *wtx)
{
	unsigned long flags;
	spin_lock_irqsave(&i1480u->tx_list_lock, flags);	/* not active any more */
	list_del(&wtx->list_node);
	i1480u_tx_free(wtx);
	spin_unlock_irqrestore(&i1480u->tx_list_lock, flags);
}

static
void i1480u_tx_unlink_urbs(struct i1480u *i1480u)
{
	unsigned long flags;
	struct i1480u_tx *wtx, *next;

	spin_lock_irqsave(&i1480u->tx_list_lock, flags);
	list_for_each_entry_safe(wtx, next, &i1480u->tx_list, list_node) {
		usb_unlink_urb(wtx->urb);
	}
	spin_unlock_irqrestore(&i1480u->tx_list_lock, flags);
}


/*
 * Callback for a completed tx USB URB.
 *
 * TODO:
 *
 * - FIXME: recover errors more gracefully
 * - FIXME: handle NAKs (I dont think they come here) for flow ctl
 */
static
void i1480u_tx_cb(struct urb *urb)
{
	struct i1480u_tx *wtx = urb->context;
	struct i1480u *i1480u = wtx->i1480u;
	struct net_device *net_dev = i1480u->net_dev;
	struct device *dev = &i1480u->usb_iface->dev;
	unsigned long flags;

	switch (urb->status) {
	case 0:
		spin_lock_irqsave(&i1480u->lock, flags);
		net_dev->stats.tx_packets++;
		net_dev->stats.tx_bytes += urb->actual_length;
		spin_unlock_irqrestore(&i1480u->lock, flags);
		break;
	case -ECONNRESET:	/* Not an error, but a controlled situation; */
	case -ENOENT:		/* (we killed the URB)...so, no broadcast */
		dev_dbg(dev, "notif endp: reset/noent %d\n", urb->status);
		netif_stop_queue(net_dev);
		break;
	case -ESHUTDOWN:	/* going away! */
		dev_dbg(dev, "notif endp: down %d\n", urb->status);
		netif_stop_queue(net_dev);
		break;
	default:
		dev_err(dev, "TX: unknown URB status %d\n", urb->status);
		if (edc_inc(&i1480u->tx_errors, EDC_MAX_ERRORS,
					EDC_ERROR_TIMEFRAME)) {
			dev_err(dev, "TX: max acceptable errors exceeded."
					"Reset device.\n");
			netif_stop_queue(net_dev);
			i1480u_tx_unlink_urbs(i1480u);
			wlp_reset_all(&i1480u->wlp);
		}
		break;
	}
	i1480u_tx_destroy(i1480u, wtx);
	if (atomic_dec_return(&i1480u->tx_inflight.count)
	    <= i1480u->tx_inflight.threshold
	    && netif_queue_stopped(net_dev)
	    && i1480u->tx_inflight.threshold != 0) {
		netif_start_queue(net_dev);
		atomic_inc(&i1480u->tx_inflight.restart_count);
	}
	return;
}


/*
 * Given a buffer that doesn't fit in a single fragment, create an
 * scatter/gather structure for delivery to the USB pipe.
 *
 * Implements functionality of i1480u_tx_create().
 *
 * @wtx:	tx descriptor
 * @skb:	skb to send
 * @gfp_mask:	gfp allocation mask
 * @returns:    Pointer to @wtx if ok, NULL on error.
 *
 * Sorry, TOO LONG a function, but breaking it up is kind of hard
 *
 * This will break the buffer in chunks smaller than
 * i1480u_MAX_FRG_SIZE (including the header) and add proper headers
 * to each:
 *
 *   1st header           \
 *   i1480 tx header      |  fragment 1
 *   fragment data        /
 *   nxt header           \  fragment 2
 *   fragment data        /
 *   ..
 *   ..
 *   last header          \  fragment 3
 *   last fragment data   /
 *
 * This does not fill the i1480 TX header, it is left up to the
 * caller to do that; you can get it from @wtx->wlp_tx_hdr.
 *
 * This function consumes the skb unless there is an error.
 */
static
int i1480u_tx_create_n(struct i1480u_tx *wtx, struct sk_buff *skb,
		       gfp_t gfp_mask)
{
	int result;
	void *pl;
	size_t pl_size;

	void *pl_itr, *buf_itr;
	size_t pl_size_left, frgs, pl_size_1st, frg_pl_size = 0;
	struct untd_hdr_1st *untd_hdr_1st;
	struct wlp_tx_hdr *wlp_tx_hdr;
	struct untd_hdr_rst *untd_hdr_rst;

	wtx->skb = NULL;
	pl = skb->data;
	pl_itr = pl;
	pl_size = skb->len;
	pl_size_left = pl_size;	/* payload size */
	/* First fragment; fits as much as i1480u_MAX_FRG_SIZE minus
	 * the headers */
	pl_size_1st = i1480u_MAX_FRG_SIZE
		- sizeof(struct untd_hdr_1st) - sizeof(struct wlp_tx_hdr);
	BUG_ON(pl_size_1st > pl_size);
	pl_size_left -= pl_size_1st;
	/* The rest have an smaller header (no i1480 TX header). We
	 * need to break up the payload in blocks smaller than
	 * i1480u_MAX_PL_SIZE (payload excluding header). */
	frgs = (pl_size_left + i1480u_MAX_PL_SIZE - 1) / i1480u_MAX_PL_SIZE;
	/* Allocate space for the new buffer. In this new buffer we'll
	 * place the headers followed by the data fragment, headers,
	 * data fragments, etc..
	 */
	result = -ENOMEM;
	wtx->buf_size = sizeof(*untd_hdr_1st)
		+ sizeof(*wlp_tx_hdr)
		+ frgs * sizeof(*untd_hdr_rst)
		+ pl_size;
	wtx->buf = kmalloc(wtx->buf_size, gfp_mask);
	if (wtx->buf == NULL)
		goto error_buf_alloc;

	buf_itr = wtx->buf;		/* We got the space, let's fill it up */
	/* Fill 1st fragment */
	untd_hdr_1st = buf_itr;
	buf_itr += sizeof(*untd_hdr_1st);
	untd_hdr_set_type(&untd_hdr_1st->hdr, i1480u_PKT_FRAG_1ST);
	untd_hdr_set_rx_tx(&untd_hdr_1st->hdr, 0);
	untd_hdr_1st->hdr.len = cpu_to_le16(pl_size + sizeof(*wlp_tx_hdr));
	untd_hdr_1st->fragment_len =
		cpu_to_le16(pl_size_1st + sizeof(*wlp_tx_hdr));
	memset(untd_hdr_1st->padding, 0, sizeof(untd_hdr_1st->padding));
	/* Set up i1480 header info */
	wlp_tx_hdr = wtx->wlp_tx_hdr = buf_itr;
	buf_itr += sizeof(*wlp_tx_hdr);
	/* Copy the first fragment */
	memcpy(buf_itr, pl_itr, pl_size_1st);
	pl_itr += pl_size_1st;
	buf_itr += pl_size_1st;

	/* Now do each remaining fragment */
	result = -EINVAL;
	while (pl_size_left > 0) {
		if (buf_itr + sizeof(*untd_hdr_rst) - wtx->buf
		    > wtx->buf_size) {
			printk(KERN_ERR "BUG: no space for header\n");
			goto error_bug;
		}
		untd_hdr_rst = buf_itr;
		buf_itr += sizeof(*untd_hdr_rst);
		if (pl_size_left > i1480u_MAX_PL_SIZE) {
			frg_pl_size = i1480u_MAX_PL_SIZE;
			untd_hdr_set_type(&untd_hdr_rst->hdr, i1480u_PKT_FRAG_NXT);
		} else {
			frg_pl_size = pl_size_left;
			untd_hdr_set_type(&untd_hdr_rst->hdr, i1480u_PKT_FRAG_LST);
		}
		untd_hdr_set_rx_tx(&untd_hdr_rst->hdr, 0);
		untd_hdr_rst->hdr.len = cpu_to_le16(frg_pl_size);
		untd_hdr_rst->padding = 0;
		if (buf_itr + frg_pl_size - wtx->buf
		    > wtx->buf_size) {
			printk(KERN_ERR "BUG: no space for payload\n");
			goto error_bug;
		}
		memcpy(buf_itr, pl_itr, frg_pl_size);
		buf_itr += frg_pl_size;
		pl_itr += frg_pl_size;
		pl_size_left -= frg_pl_size;
	}
	dev_kfree_skb_irq(skb);
	return 0;

error_bug:
	printk(KERN_ERR
	       "BUG: skb %u bytes\n"
	       "BUG: frg_pl_size %zd i1480u_MAX_FRG_SIZE %u\n"
	       "BUG: buf_itr %zu buf_size %zu pl_size_left %zu\n",
	       skb->len,
	       frg_pl_size, i1480u_MAX_FRG_SIZE,
	       buf_itr - wtx->buf, wtx->buf_size, pl_size_left);

	kfree(wtx->buf);
error_buf_alloc:
	return result;
}


/*
 * Given a buffer that fits in a single fragment, fill out a @wtx
 * struct for transmitting it down the USB pipe.
 *
 * Uses the fact that we have space reserved in front of the skbuff
 * for hardware headers :]
 *
 * This does not fill the i1480 TX header, it is left up to the
 * caller to do that; you can get it from @wtx->wlp_tx_hdr.
 *
 * @pl:		pointer to payload data
 * @pl_size:    size of the payuload
 *
 * This function does not consume the @skb.
 */
static
int i1480u_tx_create_1(struct i1480u_tx *wtx, struct sk_buff *skb,
		       gfp_t gfp_mask)
{
	struct untd_hdr_cmp *untd_hdr_cmp;
	struct wlp_tx_hdr *wlp_tx_hdr;

	wtx->buf = NULL;
	wtx->skb = skb;
	BUG_ON(skb_headroom(skb) < sizeof(*wlp_tx_hdr));
	wlp_tx_hdr = (void *) __skb_push(skb, sizeof(*wlp_tx_hdr));
	wtx->wlp_tx_hdr = wlp_tx_hdr;
	BUG_ON(skb_headroom(skb) < sizeof(*untd_hdr_cmp));
	untd_hdr_cmp = (void *) __skb_push(skb, sizeof(*untd_hdr_cmp));

	untd_hdr_set_type(&untd_hdr_cmp->hdr, i1480u_PKT_FRAG_CMP);
	untd_hdr_set_rx_tx(&untd_hdr_cmp->hdr, 0);
	untd_hdr_cmp->hdr.len = cpu_to_le16(skb->len - sizeof(*untd_hdr_cmp));
	untd_hdr_cmp->padding = 0;
	return 0;
}


/*
 * Given a skb to transmit, massage it to become palatable for the TX pipe
 *
 * This will break the buffer in chunks smaller than
 * i1480u_MAX_FRG_SIZE and add proper headers to each.
 *
 *   1st header           \
 *   i1480 tx header      |  fragment 1
 *   fragment data        /
 *   nxt header           \  fragment 2
 *   fragment data        /
 *   ..
 *   ..
 *   last header          \  fragment 3
 *   last fragment data   /
 *
 * Each fragment will be always smaller or equal to i1480u_MAX_FRG_SIZE.
 *
 * If the first fragment is smaller than i1480u_MAX_FRG_SIZE, then the
 * following is composed:
 *
 *   complete header      \
 *   i1480 tx header      | single fragment
 *   packet data          /
 *
 * We were going to use s/g support, but because the interface is
 * synch and at the end there is plenty of overhead to do it, it
 * didn't seem that worth for data that is going to be smaller than
 * one page.
 */
static
struct i1480u_tx *i1480u_tx_create(struct i1480u *i1480u,
				   struct sk_buff *skb, gfp_t gfp_mask)
{
	int result;
	struct usb_endpoint_descriptor *epd;
	int usb_pipe;
	unsigned long flags;

	struct i1480u_tx *wtx;
	const size_t pl_max_size =
		i1480u_MAX_FRG_SIZE - sizeof(struct untd_hdr_cmp)
		- sizeof(struct wlp_tx_hdr);

	wtx = kmalloc(sizeof(*wtx), gfp_mask);
	if (wtx == NULL)
		goto error_wtx_alloc;
	wtx->urb = usb_alloc_urb(0, gfp_mask);
	if (wtx->urb == NULL)
		goto error_urb_alloc;
	epd = &i1480u->usb_iface->cur_altsetting->endpoint[2].desc;
	usb_pipe = usb_sndbulkpipe(i1480u->usb_dev, epd->bEndpointAddress);
	/* Fits in a single complete packet or need to split? */
	if (skb->len > pl_max_size) {
		result = i1480u_tx_create_n(wtx, skb, gfp_mask);
		if (result < 0)
			goto error_create;
		usb_fill_bulk_urb(wtx->urb, i1480u->usb_dev, usb_pipe,
				  wtx->buf, wtx->buf_size, i1480u_tx_cb, wtx);
	} else {
		result = i1480u_tx_create_1(wtx, skb, gfp_mask);
		if (result < 0)
			goto error_create;
		usb_fill_bulk_urb(wtx->urb, i1480u->usb_dev, usb_pipe,
				  skb->data, skb->len, i1480u_tx_cb, wtx);
	}
	spin_lock_irqsave(&i1480u->tx_list_lock, flags);
	list_add(&wtx->list_node, &i1480u->tx_list);
	spin_unlock_irqrestore(&i1480u->tx_list_lock, flags);
	return wtx;

error_create:
	kfree(wtx->urb);
error_urb_alloc:
	kfree(wtx);
error_wtx_alloc:
	return NULL;
}

/*
 * Actual fragmentation and transmission of frame
 *
 * @wlp:  WLP substack data structure
 * @skb:  To be transmitted
 * @dst:  Device address of destination
 * @returns: 0 on success, <0 on failure
 *
 * This function can also be called directly (not just from
 * hard_start_xmit), so we also check here if the interface is up before
 * taking sending anything.
 */
int i1480u_xmit_frame(struct wlp *wlp, struct sk_buff *skb,
		      struct uwb_dev_addr *dst)
{
	int result = -ENXIO;
	struct i1480u *i1480u = container_of(wlp, struct i1480u, wlp);
	struct device *dev = &i1480u->usb_iface->dev;
	struct net_device *net_dev = i1480u->net_dev;
	struct i1480u_tx *wtx;
	struct wlp_tx_hdr *wlp_tx_hdr;
	static unsigned char dev_bcast[2] = { 0xff, 0xff };

	BUG_ON(i1480u->wlp.rc == NULL);
	if ((net_dev->flags & IFF_UP) == 0)
		goto out;
	result = -EBUSY;
	if (atomic_read(&i1480u->tx_inflight.count) >= i1480u->tx_inflight.max) {
		netif_stop_queue(net_dev);
		goto error_max_inflight;
	}
	result = -ENOMEM;
	wtx = i1480u_tx_create(i1480u, skb, GFP_ATOMIC);
	if (unlikely(wtx == NULL)) {
		if (printk_ratelimit())
			dev_err(dev, "TX: no memory for WLP TX URB,"
				"dropping packet (in flight %d)\n",
				atomic_read(&i1480u->tx_inflight.count));
		netif_stop_queue(net_dev);
		goto error_wtx_alloc;
	}
	wtx->i1480u = i1480u;
	/* Fill out the i1480 header; @i1480u->def_tx_hdr read without
	 * locking. We do so because they are kind of orthogonal to
	 * each other (and thus not changed in an atomic batch).
	 * The ETH header is right after the WLP TX header. */
	wlp_tx_hdr = wtx->wlp_tx_hdr;
	*wlp_tx_hdr = i1480u->options.def_tx_hdr;
	wlp_tx_hdr->dstaddr = *dst;
	if (!memcmp(&wlp_tx_hdr->dstaddr, dev_bcast, sizeof(dev_bcast))
	    && (wlp_tx_hdr_delivery_id_type(wlp_tx_hdr) & WLP_DRP)) {
		/*Broadcast message directed to DRP host. Send as best effort
		 * on PCA. */
		wlp_tx_hdr_set_delivery_id_type(wlp_tx_hdr, i1480u->options.pca_base_priority);
	}

	result = usb_submit_urb(wtx->urb, GFP_ATOMIC);		/* Go baby */
	if (result < 0) {
		dev_err(dev, "TX: cannot submit URB: %d\n", result);
		/* We leave the freeing of skb to calling function */
		wtx->skb = NULL;
		goto error_tx_urb_submit;
	}
	atomic_inc(&i1480u->tx_inflight.count);
	net_dev->trans_start = jiffies;
	return result;

error_tx_urb_submit:
	i1480u_tx_destroy(i1480u, wtx);
error_wtx_alloc:
error_max_inflight:
out:
	return result;
}


/*
 * Transmit an skb  Called when an skbuf has to be transmitted
 *
 * The skb is first passed to WLP substack to ensure this is a valid
 * frame. If valid the device address of destination will be filled and
 * the WLP header prepended to the skb. If this step fails we fake sending
 * the frame, if we return an error the network stack will just keep trying.
 *
 * Broadcast frames inside a WSS needs to be treated special as multicast is
 * not supported. A broadcast frame is sent as unicast to each member of the
 * WSS - this is done by the WLP substack when it finds a broadcast frame.
 * So, we test if the WLP substack took over the skb and only transmit it
 * if it has not (been taken over).
 *
 * @net_dev->xmit_lock is held
 */
netdev_tx_t i1480u_hard_start_xmit(struct sk_buff *skb,
					 struct net_device *net_dev)
{
	int result;
	struct i1480u *i1480u = netdev_priv(net_dev);
	struct device *dev = &i1480u->usb_iface->dev;
	struct uwb_dev_addr dst;

	if ((net_dev->flags & IFF_UP) == 0)
		goto error;
	result = wlp_prepare_tx_frame(dev, &i1480u->wlp, skb, &dst);
	if (result < 0) {
		dev_err(dev, "WLP verification of TX frame failed (%d). "
			"Dropping packet.\n", result);
		goto error;
	} else if (result == 1) {
		/* trans_start time will be set when WLP actually transmits
		 * the frame */
		goto out;
	}
	result = i1480u_xmit_frame(&i1480u->wlp, skb, &dst);
	if (result < 0) {
		dev_err(dev, "Frame TX failed (%d).\n", result);
		goto error;
	}
	return NETDEV_TX_OK;
error:
	dev_kfree_skb_any(skb);
	net_dev->stats.tx_dropped++;
out:
	return NETDEV_TX_OK;
}


/*
 * Called when a pkt transmission doesn't complete in a reasonable period
 * Device reset may sleep - do it outside of interrupt context (delayed)
 */
void i1480u_tx_timeout(struct net_device *net_dev)
{
	struct i1480u *i1480u = netdev_priv(net_dev);

	wlp_reset_all(&i1480u->wlp);
}


void i1480u_tx_release(struct i1480u *i1480u)
{
	unsigned long flags;
	struct i1480u_tx *wtx, *next;
	int count = 0, empty;

	spin_lock_irqsave(&i1480u->tx_list_lock, flags);
	list_for_each_entry_safe(wtx, next, &i1480u->tx_list, list_node) {
		count++;
		usb_unlink_urb(wtx->urb);
	}
	spin_unlock_irqrestore(&i1480u->tx_list_lock, flags);
	count = count*10; /* i1480ut 200ms per unlinked urb (intervals of 20ms) */
	/*
	 * We don't like this sollution too much (dirty as it is), but
	 * it is cheaper than putting a refcount on each i1480u_tx and
	 * i1480uting for all of them to go away...
	 *
	 * Called when no more packets can be added to tx_list
	 * so can i1480ut for it to be empty.
	 */
	while (1) {
		spin_lock_irqsave(&i1480u->tx_list_lock, flags);
		empty = list_empty(&i1480u->tx_list);
		spin_unlock_irqrestore(&i1480u->tx_list_lock, flags);
		if (empty)
			break;
		count--;
		BUG_ON(count == 0);
		msleep(20);
	}
}