summaryrefslogtreecommitdiff
path: root/net/nfc/hci/llc_shdlc.c
blob: 0eb4ddc056e789219bf09665a591246eac1b88bf (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
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
// SPDX-License-Identifier: GPL-2.0-only
/*
 * shdlc Link Layer Control
 *
 * Copyright (C) 2012  Intel Corporation. All rights reserved.
 */

#define pr_fmt(fmt) "shdlc: %s: " fmt, __func__

#include <linux/types.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/slab.h>
#include <linux/skbuff.h>

#include "llc.h"

enum shdlc_state {
	SHDLC_DISCONNECTED = 0,
	SHDLC_CONNECTING = 1,
	SHDLC_NEGOTIATING = 2,
	SHDLC_HALF_CONNECTED = 3,
	SHDLC_CONNECTED = 4
};

struct llc_shdlc {
	struct nfc_hci_dev *hdev;
	xmit_to_drv_t xmit_to_drv;
	rcv_to_hci_t rcv_to_hci;

	struct mutex state_mutex;
	enum shdlc_state state;
	int hard_fault;

	wait_queue_head_t *connect_wq;
	int connect_tries;
	int connect_result;
	struct timer_list connect_timer;/* aka T3 in spec 10.6.1 */

	u8 w;				/* window size */
	bool srej_support;

	struct timer_list t1_timer;	/* send ack timeout */
	bool t1_active;

	struct timer_list t2_timer;	/* guard/retransmit timeout */
	bool t2_active;

	int ns;				/* next seq num for send */
	int nr;				/* next expected seq num for receive */
	int dnr;			/* oldest sent unacked seq num */

	struct sk_buff_head rcv_q;

	struct sk_buff_head send_q;
	bool rnr;			/* other side is not ready to receive */

	struct sk_buff_head ack_pending_q;

	struct work_struct sm_work;

	int tx_headroom;
	int tx_tailroom;

	llc_failure_t llc_failure;
};

#define SHDLC_LLC_HEAD_ROOM	2

#define SHDLC_MAX_WINDOW	4
#define SHDLC_SREJ_SUPPORT	false

#define SHDLC_CONTROL_HEAD_MASK	0xe0
#define SHDLC_CONTROL_HEAD_I	0x80
#define SHDLC_CONTROL_HEAD_I2	0xa0
#define SHDLC_CONTROL_HEAD_S	0xc0
#define SHDLC_CONTROL_HEAD_U	0xe0

#define SHDLC_CONTROL_NS_MASK	0x38
#define SHDLC_CONTROL_NR_MASK	0x07
#define SHDLC_CONTROL_TYPE_MASK	0x18

#define SHDLC_CONTROL_M_MASK	0x1f

enum sframe_type {
	S_FRAME_RR = 0x00,
	S_FRAME_REJ = 0x01,
	S_FRAME_RNR = 0x02,
	S_FRAME_SREJ = 0x03
};

enum uframe_modifier {
	U_FRAME_UA = 0x06,
	U_FRAME_RSET = 0x19
};

#define SHDLC_CONNECT_VALUE_MS	5
#define SHDLC_T1_VALUE_MS(w)	((5 * w) / 4)
#define SHDLC_T2_VALUE_MS	300

#define SHDLC_DUMP_SKB(info, skb)				  \
do {								  \
	pr_debug("%s:\n", info);				  \
	print_hex_dump(KERN_DEBUG, "shdlc: ", DUMP_PREFIX_OFFSET, \
		       16, 1, skb->data, skb->len, 0);		  \
} while (0)

/* checks x < y <= z modulo 8 */
static bool llc_shdlc_x_lt_y_lteq_z(int x, int y, int z)
{
	if (x < z)
		return ((x < y) && (y <= z)) ? true : false;
	else
		return ((y > x) || (y <= z)) ? true : false;
}

/* checks x <= y < z modulo 8 */
static bool llc_shdlc_x_lteq_y_lt_z(int x, int y, int z)
{
	if (x <= z)
		return ((x <= y) && (y < z)) ? true : false;
	else			/* x > z -> z+8 > x */
		return ((y >= x) || (y < z)) ? true : false;
}

static struct sk_buff *llc_shdlc_alloc_skb(struct llc_shdlc *shdlc,
					   int payload_len)
{
	struct sk_buff *skb;

	skb = alloc_skb(shdlc->tx_headroom + SHDLC_LLC_HEAD_ROOM +
			shdlc->tx_tailroom + payload_len, GFP_KERNEL);
	if (skb)
		skb_reserve(skb, shdlc->tx_headroom + SHDLC_LLC_HEAD_ROOM);

	return skb;
}

/* immediately sends an S frame. */
static int llc_shdlc_send_s_frame(struct llc_shdlc *shdlc,
				  enum sframe_type sframe_type, int nr)
{
	int r;
	struct sk_buff *skb;

	pr_debug("sframe_type=%d nr=%d\n", sframe_type, nr);

	skb = llc_shdlc_alloc_skb(shdlc, 0);
	if (skb == NULL)
		return -ENOMEM;

	*(u8 *)skb_push(skb, 1) = SHDLC_CONTROL_HEAD_S | (sframe_type << 3) | nr;

	r = shdlc->xmit_to_drv(shdlc->hdev, skb);

	kfree_skb(skb);

	return r;
}

/* immediately sends an U frame. skb may contain optional payload */
static int llc_shdlc_send_u_frame(struct llc_shdlc *shdlc,
				  struct sk_buff *skb,
				  enum uframe_modifier uframe_modifier)
{
	int r;

	pr_debug("uframe_modifier=%d\n", uframe_modifier);

	*(u8 *)skb_push(skb, 1) = SHDLC_CONTROL_HEAD_U | uframe_modifier;

	r = shdlc->xmit_to_drv(shdlc->hdev, skb);

	kfree_skb(skb);

	return r;
}

/*
 * Free ack_pending frames until y_nr - 1, and reset t2 according to
 * the remaining oldest ack_pending frame sent time
 */
static void llc_shdlc_reset_t2(struct llc_shdlc *shdlc, int y_nr)
{
	struct sk_buff *skb;
	int dnr = shdlc->dnr;	/* MUST initially be < y_nr */

	pr_debug("release ack pending up to frame %d excluded\n", y_nr);

	while (dnr != y_nr) {
		pr_debug("release ack pending frame %d\n", dnr);

		skb = skb_dequeue(&shdlc->ack_pending_q);
		kfree_skb(skb);

		dnr = (dnr + 1) % 8;
	}

	if (skb_queue_empty(&shdlc->ack_pending_q)) {
		if (shdlc->t2_active) {
			del_timer_sync(&shdlc->t2_timer);
			shdlc->t2_active = false;

			pr_debug
			    ("All sent frames acked. Stopped T2(retransmit)\n");
		}
	} else {
		skb = skb_peek(&shdlc->ack_pending_q);

		mod_timer(&shdlc->t2_timer, *(unsigned long *)skb->cb +
			  msecs_to_jiffies(SHDLC_T2_VALUE_MS));
		shdlc->t2_active = true;

		pr_debug
		    ("Start T2(retransmit) for remaining unacked sent frames\n");
	}
}

/*
 * Receive validated frames from lower layer. skb contains HCI payload only.
 * Handle according to algorithm at spec:10.8.2
 */
static void llc_shdlc_rcv_i_frame(struct llc_shdlc *shdlc,
				  struct sk_buff *skb, int ns, int nr)
{
	int x_ns = ns;
	int y_nr = nr;

	pr_debug("recvd I-frame %d, remote waiting frame %d\n", ns, nr);

	if (shdlc->state != SHDLC_CONNECTED)
		goto exit;

	if (x_ns != shdlc->nr) {
		llc_shdlc_send_s_frame(shdlc, S_FRAME_REJ, shdlc->nr);
		goto exit;
	}

	if (shdlc->t1_active == false) {
		shdlc->t1_active = true;
		mod_timer(&shdlc->t1_timer, jiffies +
			  msecs_to_jiffies(SHDLC_T1_VALUE_MS(shdlc->w)));
		pr_debug("(re)Start T1(send ack)\n");
	}

	if (skb->len) {
		shdlc->rcv_to_hci(shdlc->hdev, skb);
		skb = NULL;
	}

	shdlc->nr = (shdlc->nr + 1) % 8;

	if (llc_shdlc_x_lt_y_lteq_z(shdlc->dnr, y_nr, shdlc->ns)) {
		llc_shdlc_reset_t2(shdlc, y_nr);

		shdlc->dnr = y_nr;
	}

exit:
	kfree_skb(skb);
}

static void llc_shdlc_rcv_ack(struct llc_shdlc *shdlc, int y_nr)
{
	pr_debug("remote acked up to frame %d excluded\n", y_nr);

	if (llc_shdlc_x_lt_y_lteq_z(shdlc->dnr, y_nr, shdlc->ns)) {
		llc_shdlc_reset_t2(shdlc, y_nr);
		shdlc->dnr = y_nr;
	}
}

static void llc_shdlc_requeue_ack_pending(struct llc_shdlc *shdlc)
{
	struct sk_buff *skb;

	pr_debug("ns reset to %d\n", shdlc->dnr);

	while ((skb = skb_dequeue_tail(&shdlc->ack_pending_q))) {
		skb_pull(skb, 1);	/* remove control field */
		skb_queue_head(&shdlc->send_q, skb);
	}
	shdlc->ns = shdlc->dnr;
}

static void llc_shdlc_rcv_rej(struct llc_shdlc *shdlc, int y_nr)
{
	struct sk_buff *skb;

	pr_debug("remote asks retransmission from frame %d\n", y_nr);

	if (llc_shdlc_x_lteq_y_lt_z(shdlc->dnr, y_nr, shdlc->ns)) {
		if (shdlc->t2_active) {
			del_timer_sync(&shdlc->t2_timer);
			shdlc->t2_active = false;
			pr_debug("Stopped T2(retransmit)\n");
		}

		if (shdlc->dnr != y_nr) {
			while ((shdlc->dnr = ((shdlc->dnr + 1) % 8)) != y_nr) {
				skb = skb_dequeue(&shdlc->ack_pending_q);
				kfree_skb(skb);
			}
		}

		llc_shdlc_requeue_ack_pending(shdlc);
	}
}

/* See spec RR:10.8.3 REJ:10.8.4 */
static void llc_shdlc_rcv_s_frame(struct llc_shdlc *shdlc,
				  enum sframe_type s_frame_type, int nr)
{
	struct sk_buff *skb;

	if (shdlc->state != SHDLC_CONNECTED)
		return;

	switch (s_frame_type) {
	case S_FRAME_RR:
		llc_shdlc_rcv_ack(shdlc, nr);
		if (shdlc->rnr == true) {	/* see SHDLC 10.7.7 */
			shdlc->rnr = false;
			if (shdlc->send_q.qlen == 0) {
				skb = llc_shdlc_alloc_skb(shdlc, 0);
				if (skb)
					skb_queue_tail(&shdlc->send_q, skb);
			}
		}
		break;
	case S_FRAME_REJ:
		llc_shdlc_rcv_rej(shdlc, nr);
		break;
	case S_FRAME_RNR:
		llc_shdlc_rcv_ack(shdlc, nr);
		shdlc->rnr = true;
		break;
	default:
		break;
	}
}

static void llc_shdlc_connect_complete(struct llc_shdlc *shdlc, int r)
{
	pr_debug("result=%d\n", r);

	del_timer_sync(&shdlc->connect_timer);

	if (r == 0) {
		shdlc->ns = 0;
		shdlc->nr = 0;
		shdlc->dnr = 0;

		shdlc->state = SHDLC_HALF_CONNECTED;
	} else {
		shdlc->state = SHDLC_DISCONNECTED;
	}

	shdlc->connect_result = r;

	wake_up(shdlc->connect_wq);
}

static int llc_shdlc_connect_initiate(struct llc_shdlc *shdlc)
{
	struct sk_buff *skb;

	pr_debug("\n");

	skb = llc_shdlc_alloc_skb(shdlc, 2);
	if (skb == NULL)
		return -ENOMEM;

	skb_put_u8(skb, SHDLC_MAX_WINDOW);
	skb_put_u8(skb, SHDLC_SREJ_SUPPORT ? 1 : 0);

	return llc_shdlc_send_u_frame(shdlc, skb, U_FRAME_RSET);
}

static int llc_shdlc_connect_send_ua(struct llc_shdlc *shdlc)
{
	struct sk_buff *skb;

	pr_debug("\n");

	skb = llc_shdlc_alloc_skb(shdlc, 0);
	if (skb == NULL)
		return -ENOMEM;

	return llc_shdlc_send_u_frame(shdlc, skb, U_FRAME_UA);
}

static void llc_shdlc_rcv_u_frame(struct llc_shdlc *shdlc,
				  struct sk_buff *skb,
				  enum uframe_modifier u_frame_modifier)
{
	u8 w = SHDLC_MAX_WINDOW;
	bool srej_support = SHDLC_SREJ_SUPPORT;
	int r;

	pr_debug("u_frame_modifier=%d\n", u_frame_modifier);

	switch (u_frame_modifier) {
	case U_FRAME_RSET:
		switch (shdlc->state) {
		case SHDLC_NEGOTIATING:
		case SHDLC_CONNECTING:
			/*
			 * We sent RSET, but chip wants to negociate or we
			 * got RSET before we managed to send out our.
			 */
			if (skb->len > 0)
				w = skb->data[0];

			if (skb->len > 1)
				srej_support = skb->data[1] & 0x01 ? true :
					       false;

			if ((w <= SHDLC_MAX_WINDOW) &&
			    (SHDLC_SREJ_SUPPORT || (srej_support == false))) {
				shdlc->w = w;
				shdlc->srej_support = srej_support;
				r = llc_shdlc_connect_send_ua(shdlc);
				llc_shdlc_connect_complete(shdlc, r);
			}
			break;
		case SHDLC_HALF_CONNECTED:
			/*
			 * Chip resent RSET due to its timeout - Ignote it
			 * as we already sent UA.
			 */
			break;
		case SHDLC_CONNECTED:
			/*
			 * Chip wants to reset link. This is unexpected and
			 * unsupported.
			 */
			shdlc->hard_fault = -ECONNRESET;
			break;
		default:
			break;
		}
		break;
	case U_FRAME_UA:
		if ((shdlc->state == SHDLC_CONNECTING &&
		     shdlc->connect_tries > 0) ||
		    (shdlc->state == SHDLC_NEGOTIATING)) {
			llc_shdlc_connect_complete(shdlc, 0);
			shdlc->state = SHDLC_CONNECTED;
		}
		break;
	default:
		break;
	}

	kfree_skb(skb);
}

static void llc_shdlc_handle_rcv_queue(struct llc_shdlc *shdlc)
{
	struct sk_buff *skb;
	u8 control;
	int nr;
	int ns;
	enum sframe_type s_frame_type;
	enum uframe_modifier u_frame_modifier;

	if (shdlc->rcv_q.qlen)
		pr_debug("rcvQlen=%d\n", shdlc->rcv_q.qlen);

	while ((skb = skb_dequeue(&shdlc->rcv_q)) != NULL) {
		control = skb->data[0];
		skb_pull(skb, 1);
		switch (control & SHDLC_CONTROL_HEAD_MASK) {
		case SHDLC_CONTROL_HEAD_I:
		case SHDLC_CONTROL_HEAD_I2:
			if (shdlc->state == SHDLC_HALF_CONNECTED)
				shdlc->state = SHDLC_CONNECTED;

			ns = (control & SHDLC_CONTROL_NS_MASK) >> 3;
			nr = control & SHDLC_CONTROL_NR_MASK;
			llc_shdlc_rcv_i_frame(shdlc, skb, ns, nr);
			break;
		case SHDLC_CONTROL_HEAD_S:
			if (shdlc->state == SHDLC_HALF_CONNECTED)
				shdlc->state = SHDLC_CONNECTED;

			s_frame_type = (control & SHDLC_CONTROL_TYPE_MASK) >> 3;
			nr = control & SHDLC_CONTROL_NR_MASK;
			llc_shdlc_rcv_s_frame(shdlc, s_frame_type, nr);
			kfree_skb(skb);
			break;
		case SHDLC_CONTROL_HEAD_U:
			u_frame_modifier = control & SHDLC_CONTROL_M_MASK;
			llc_shdlc_rcv_u_frame(shdlc, skb, u_frame_modifier);
			break;
		default:
			pr_err("UNKNOWN Control=%d\n", control);
			kfree_skb(skb);
			break;
		}
	}
}

static int llc_shdlc_w_used(int ns, int dnr)
{
	int unack_count;

	if (dnr <= ns)
		unack_count = ns - dnr;
	else
		unack_count = 8 - dnr + ns;

	return unack_count;
}

/* Send frames according to algorithm at spec:10.8.1 */
static void llc_shdlc_handle_send_queue(struct llc_shdlc *shdlc)
{
	struct sk_buff *skb;
	int r;
	unsigned long time_sent;

	if (shdlc->send_q.qlen)
		pr_debug
		    ("sendQlen=%d ns=%d dnr=%d rnr=%s w_room=%d unackQlen=%d\n",
		     shdlc->send_q.qlen, shdlc->ns, shdlc->dnr,
		     shdlc->rnr == false ? "false" : "true",
		     shdlc->w - llc_shdlc_w_used(shdlc->ns, shdlc->dnr),
		     shdlc->ack_pending_q.qlen);

	while (shdlc->send_q.qlen && shdlc->ack_pending_q.qlen < shdlc->w &&
	       (shdlc->rnr == false)) {

		if (shdlc->t1_active) {
			del_timer_sync(&shdlc->t1_timer);
			shdlc->t1_active = false;
			pr_debug("Stopped T1(send ack)\n");
		}

		skb = skb_dequeue(&shdlc->send_q);

		*(u8 *)skb_push(skb, 1) = SHDLC_CONTROL_HEAD_I | (shdlc->ns << 3) |
					shdlc->nr;

		pr_debug("Sending I-Frame %d, waiting to rcv %d\n", shdlc->ns,
			 shdlc->nr);
		SHDLC_DUMP_SKB("shdlc frame written", skb);

		r = shdlc->xmit_to_drv(shdlc->hdev, skb);
		if (r < 0) {
			shdlc->hard_fault = r;
			break;
		}

		shdlc->ns = (shdlc->ns + 1) % 8;

		time_sent = jiffies;
		*(unsigned long *)skb->cb = time_sent;

		skb_queue_tail(&shdlc->ack_pending_q, skb);

		if (shdlc->t2_active == false) {
			shdlc->t2_active = true;
			mod_timer(&shdlc->t2_timer, time_sent +
				  msecs_to_jiffies(SHDLC_T2_VALUE_MS));
			pr_debug("Started T2 (retransmit)\n");
		}
	}
}

static void llc_shdlc_connect_timeout(struct timer_list *t)
{
	struct llc_shdlc *shdlc = from_timer(shdlc, t, connect_timer);

	pr_debug("\n");

	schedule_work(&shdlc->sm_work);
}

static void llc_shdlc_t1_timeout(struct timer_list *t)
{
	struct llc_shdlc *shdlc = from_timer(shdlc, t, t1_timer);

	pr_debug("SoftIRQ: need to send ack\n");

	schedule_work(&shdlc->sm_work);
}

static void llc_shdlc_t2_timeout(struct timer_list *t)
{
	struct llc_shdlc *shdlc = from_timer(shdlc, t, t2_timer);

	pr_debug("SoftIRQ: need to retransmit\n");

	schedule_work(&shdlc->sm_work);
}

static void llc_shdlc_sm_work(struct work_struct *work)
{
	struct llc_shdlc *shdlc = container_of(work, struct llc_shdlc, sm_work);
	int r;

	pr_debug("\n");

	mutex_lock(&shdlc->state_mutex);

	switch (shdlc->state) {
	case SHDLC_DISCONNECTED:
		skb_queue_purge(&shdlc->rcv_q);
		skb_queue_purge(&shdlc->send_q);
		skb_queue_purge(&shdlc->ack_pending_q);
		break;
	case SHDLC_CONNECTING:
		if (shdlc->hard_fault) {
			llc_shdlc_connect_complete(shdlc, shdlc->hard_fault);
			break;
		}

		if (shdlc->connect_tries++ < 5)
			r = llc_shdlc_connect_initiate(shdlc);
		else
			r = -ETIME;
		if (r < 0) {
			llc_shdlc_connect_complete(shdlc, r);
		} else {
			mod_timer(&shdlc->connect_timer, jiffies +
				  msecs_to_jiffies(SHDLC_CONNECT_VALUE_MS));

			shdlc->state = SHDLC_NEGOTIATING;
		}
		break;
	case SHDLC_NEGOTIATING:
		if (timer_pending(&shdlc->connect_timer) == 0) {
			shdlc->state = SHDLC_CONNECTING;
			schedule_work(&shdlc->sm_work);
		}

		llc_shdlc_handle_rcv_queue(shdlc);

		if (shdlc->hard_fault) {
			llc_shdlc_connect_complete(shdlc, shdlc->hard_fault);
			break;
		}
		break;
	case SHDLC_HALF_CONNECTED:
	case SHDLC_CONNECTED:
		llc_shdlc_handle_rcv_queue(shdlc);
		llc_shdlc_handle_send_queue(shdlc);

		if (shdlc->t1_active && timer_pending(&shdlc->t1_timer) == 0) {
			pr_debug
			    ("Handle T1(send ack) elapsed (T1 now inactive)\n");

			shdlc->t1_active = false;
			r = llc_shdlc_send_s_frame(shdlc, S_FRAME_RR,
						   shdlc->nr);
			if (r < 0)
				shdlc->hard_fault = r;
		}

		if (shdlc->t2_active && timer_pending(&shdlc->t2_timer) == 0) {
			pr_debug
			    ("Handle T2(retransmit) elapsed (T2 inactive)\n");

			shdlc->t2_active = false;

			llc_shdlc_requeue_ack_pending(shdlc);
			llc_shdlc_handle_send_queue(shdlc);
		}

		if (shdlc->hard_fault)
			shdlc->llc_failure(shdlc->hdev, shdlc->hard_fault);
		break;
	default:
		break;
	}
	mutex_unlock(&shdlc->state_mutex);
}

/*
 * Called from syscall context to establish shdlc link. Sleeps until
 * link is ready or failure.
 */
static int llc_shdlc_connect(struct llc_shdlc *shdlc)
{
	DECLARE_WAIT_QUEUE_HEAD_ONSTACK(connect_wq);

	pr_debug("\n");

	mutex_lock(&shdlc->state_mutex);

	shdlc->state = SHDLC_CONNECTING;
	shdlc->connect_wq = &connect_wq;
	shdlc->connect_tries = 0;
	shdlc->connect_result = 1;

	mutex_unlock(&shdlc->state_mutex);

	schedule_work(&shdlc->sm_work);

	wait_event(connect_wq, shdlc->connect_result != 1);

	return shdlc->connect_result;
}

static void llc_shdlc_disconnect(struct llc_shdlc *shdlc)
{
	pr_debug("\n");

	mutex_lock(&shdlc->state_mutex);

	shdlc->state = SHDLC_DISCONNECTED;

	mutex_unlock(&shdlc->state_mutex);

	schedule_work(&shdlc->sm_work);
}

/*
 * Receive an incoming shdlc frame. Frame has already been crc-validated.
 * skb contains only LLC header and payload.
 * If skb == NULL, it is a notification that the link below is dead.
 */
static void llc_shdlc_recv_frame(struct llc_shdlc *shdlc, struct sk_buff *skb)
{
	if (skb == NULL) {
		pr_err("NULL Frame -> link is dead\n");
		shdlc->hard_fault = -EREMOTEIO;
	} else {
		SHDLC_DUMP_SKB("incoming frame", skb);
		skb_queue_tail(&shdlc->rcv_q, skb);
	}

	schedule_work(&shdlc->sm_work);
}

static void *llc_shdlc_init(struct nfc_hci_dev *hdev, xmit_to_drv_t xmit_to_drv,
			    rcv_to_hci_t rcv_to_hci, int tx_headroom,
			    int tx_tailroom, int *rx_headroom, int *rx_tailroom,
			    llc_failure_t llc_failure)
{
	struct llc_shdlc *shdlc;

	*rx_headroom = SHDLC_LLC_HEAD_ROOM;
	*rx_tailroom = 0;

	shdlc = kzalloc(sizeof(struct llc_shdlc), GFP_KERNEL);
	if (shdlc == NULL)
		return NULL;

	mutex_init(&shdlc->state_mutex);
	shdlc->state = SHDLC_DISCONNECTED;

	timer_setup(&shdlc->connect_timer, llc_shdlc_connect_timeout, 0);
	timer_setup(&shdlc->t1_timer, llc_shdlc_t1_timeout, 0);
	timer_setup(&shdlc->t2_timer, llc_shdlc_t2_timeout, 0);

	shdlc->w = SHDLC_MAX_WINDOW;
	shdlc->srej_support = SHDLC_SREJ_SUPPORT;

	skb_queue_head_init(&shdlc->rcv_q);
	skb_queue_head_init(&shdlc->send_q);
	skb_queue_head_init(&shdlc->ack_pending_q);

	INIT_WORK(&shdlc->sm_work, llc_shdlc_sm_work);

	shdlc->hdev = hdev;
	shdlc->xmit_to_drv = xmit_to_drv;
	shdlc->rcv_to_hci = rcv_to_hci;
	shdlc->tx_headroom = tx_headroom;
	shdlc->tx_tailroom = tx_tailroom;
	shdlc->llc_failure = llc_failure;

	return shdlc;
}

static void llc_shdlc_deinit(struct nfc_llc *llc)
{
	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);

	skb_queue_purge(&shdlc->rcv_q);
	skb_queue_purge(&shdlc->send_q);
	skb_queue_purge(&shdlc->ack_pending_q);

	kfree(shdlc);
}

static int llc_shdlc_start(struct nfc_llc *llc)
{
	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);

	return llc_shdlc_connect(shdlc);
}

static int llc_shdlc_stop(struct nfc_llc *llc)
{
	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);

	llc_shdlc_disconnect(shdlc);

	return 0;
}

static void llc_shdlc_rcv_from_drv(struct nfc_llc *llc, struct sk_buff *skb)
{
	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);

	llc_shdlc_recv_frame(shdlc, skb);
}

static int llc_shdlc_xmit_from_hci(struct nfc_llc *llc, struct sk_buff *skb)
{
	struct llc_shdlc *shdlc = nfc_llc_get_data(llc);

	skb_queue_tail(&shdlc->send_q, skb);

	schedule_work(&shdlc->sm_work);

	return 0;
}

static struct nfc_llc_ops llc_shdlc_ops = {
	.init = llc_shdlc_init,
	.deinit = llc_shdlc_deinit,
	.start = llc_shdlc_start,
	.stop = llc_shdlc_stop,
	.rcv_from_drv = llc_shdlc_rcv_from_drv,
	.xmit_from_hci = llc_shdlc_xmit_from_hci,
};

int nfc_llc_shdlc_register(void)
{
	return nfc_llc_register(LLC_SHDLC_NAME, &llc_shdlc_ops);
}