aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/net/hamradio/6pack.c
blob: 3e5d0b6b6516133039192fa5dfd1fdf88660d81b (plain) (blame)
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
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
/*
 * 6pack.c	This module implements the 6pack protocol for kernel-based
 *		devices like TTY. It interfaces between a raw TTY and the
 *		kernel's AX.25 protocol layers.
 *
 * Authors:	Andreas Könsgen <ajk@comnets.uni-bremen.de>
 *              Ralf Baechle DL5RB <ralf@linux-mips.org>
 *
 * Quite a lot of stuff "stolen" by Joerg Reuter from slip.c, written by
 *
 *		Laurence Culhane, <loz@holmes.demon.co.uk>
 *		Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
 */

#include <linux/module.h>
#include <asm/system.h>
#include <asm/uaccess.h>
#include <linux/bitops.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/tty.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/timer.h>
#include <linux/slab.h>
#include <net/ax25.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <linux/spinlock.h>
#include <linux/if_arp.h>
#include <linux/init.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/semaphore.h>
#include <linux/compat.h>
#include <asm/atomic.h>

#define SIXPACK_VERSION    "Revision: 0.3.0"

/* sixpack priority commands */
#define SIXP_SEOF		0x40	/* start and end of a 6pack frame */
#define SIXP_TX_URUN		0x48	/* transmit overrun */
#define SIXP_RX_ORUN		0x50	/* receive overrun */
#define SIXP_RX_BUF_OVL		0x58	/* receive buffer overflow */

#define SIXP_CHKSUM		0xFF	/* valid checksum of a 6pack frame */

/* masks to get certain bits out of the status bytes sent by the TNC */

#define SIXP_CMD_MASK		0xC0
#define SIXP_CHN_MASK		0x07
#define SIXP_PRIO_CMD_MASK	0x80
#define SIXP_STD_CMD_MASK	0x40
#define SIXP_PRIO_DATA_MASK	0x38
#define SIXP_TX_MASK		0x20
#define SIXP_RX_MASK		0x10
#define SIXP_RX_DCD_MASK	0x18
#define SIXP_LEDS_ON		0x78
#define SIXP_LEDS_OFF		0x60
#define SIXP_CON		0x08
#define SIXP_STA		0x10

#define SIXP_FOUND_TNC		0xe9
#define SIXP_CON_ON		0x68
#define SIXP_DCD_MASK		0x08
#define SIXP_DAMA_OFF		0

/* default level 2 parameters */
#define SIXP_TXDELAY			(HZ/4)	/* in 1 s */
#define SIXP_PERSIST			50	/* in 256ths */
#define SIXP_SLOTTIME			(HZ/10)	/* in 1 s */
#define SIXP_INIT_RESYNC_TIMEOUT	(3*HZ/2) /* in 1 s */
#define SIXP_RESYNC_TIMEOUT		5*HZ	/* in 1 s */

/* 6pack configuration. */
#define SIXP_NRUNIT			31      /* MAX number of 6pack channels */
#define SIXP_MTU			256	/* Default MTU */

enum sixpack_flags {
	SIXPF_ERROR,	/* Parity, etc. error	*/
};

struct sixpack {
	/* Various fields. */
	struct tty_struct	*tty;		/* ptr to TTY structure	*/
	struct net_device	*dev;		/* easy for intr handling  */

	/* These are pointers to the malloc()ed frame buffers. */
	unsigned char		*rbuff;		/* receiver buffer	*/
	int			rcount;         /* received chars counter  */
	unsigned char		*xbuff;		/* transmitter buffer	*/
	unsigned char		*xhead;         /* next byte to XMIT */
	int			xleft;          /* bytes left in XMIT queue  */

	unsigned char		raw_buf[4];
	unsigned char		cooked_buf[400];

	unsigned int		rx_count;
	unsigned int		rx_count_cooked;

	int			mtu;		/* Our mtu (to spot changes!) */
	int			buffsize;       /* Max buffers sizes */

	unsigned long		flags;		/* Flag values/ mode etc */
	unsigned char		mode;		/* 6pack mode */

	/* 6pack stuff */
	unsigned char		tx_delay;
	unsigned char		persistence;
	unsigned char		slottime;
	unsigned char		duplex;
	unsigned char		led_state;
	unsigned char		status;
	unsigned char		status1;
	unsigned char		status2;
	unsigned char		tx_enable;
	unsigned char		tnc_state;

	struct timer_list	tx_t;
	struct timer_list	resync_t;
	atomic_t		refcnt;
	struct semaphore	dead_sem;
	spinlock_t		lock;
};

#define AX25_6PACK_HEADER_LEN 0

static void sixpack_decode(struct sixpack *, unsigned char[], int);
static int encode_sixpack(unsigned char *, unsigned char *, int, unsigned char);

/*
 * Perform the persistence/slottime algorithm for CSMA access. If the
 * persistence check was successful, write the data to the serial driver.
 * Note that in case of DAMA operation, the data is not sent here.
 */

static void sp_xmit_on_air(unsigned long channel)
{
	struct sixpack *sp = (struct sixpack *) channel;
	int actual, when = sp->slottime;
	static unsigned char random;

	random = random * 17 + 41;

	if (((sp->status1 & SIXP_DCD_MASK) == 0) && (random < sp->persistence)) {
		sp->led_state = 0x70;
		sp->tty->ops->write(sp->tty, &sp->led_state, 1);
		sp->tx_enable = 1;
		actual = sp->tty->ops->write(sp->tty, sp->xbuff, sp->status2);
		sp->xleft -= actual;
		sp->xhead += actual;
		sp->led_state = 0x60;
		sp->tty->ops->write(sp->tty, &sp->led_state, 1);
		sp->status2 = 0;
	} else
		mod_timer(&sp->tx_t, jiffies + ((when + 1) * HZ) / 100);
}

/* ----> 6pack timer interrupt handler and friends. <---- */

/* Encapsulate one AX.25 frame and stuff into a TTY queue. */
static void sp_encaps(struct sixpack *sp, unsigned char *icp, int len)
{
	unsigned char *msg, *p = icp;
	int actual, count;

	if (len > sp->mtu) {	/* sp->mtu = AX25_MTU = max. PACLEN = 256 */
		msg = "oversized transmit packet!";
		goto out_drop;
	}

	if (len > sp->mtu) {	/* sp->mtu = AX25_MTU = max. PACLEN = 256 */
		msg = "oversized transmit packet!";
		goto out_drop;
	}

	if (p[0] > 5) {
		msg = "invalid KISS command";
		goto out_drop;
	}

	if ((p[0] != 0) && (len > 2)) {
		msg = "KISS control packet too long";
		goto out_drop;
	}

	if ((p[0] == 0) && (len < 15)) {
		msg = "bad AX.25 packet to transmit";
		goto out_drop;
	}

	count = encode_sixpack(p, sp->xbuff, len, sp->tx_delay);
	set_bit(TTY_DO_WRITE_WAKEUP, &sp->tty->flags);

	switch (p[0]) {
	case 1:	sp->tx_delay = p[1];
		return;
	case 2:	sp->persistence = p[1];
		return;
	case 3:	sp->slottime = p[1];
		return;
	case 4:	/* ignored */
		return;
	case 5:	sp->duplex = p[1];
		return;
	}

	if (p[0] != 0)
		return;

	/*
	 * In case of fullduplex or DAMA operation, we don't take care about the
	 * state of the DCD or of any timers, as the determination of the
	 * correct time to send is the job of the AX.25 layer. We send
	 * immediately after data has arrived.
	 */
	if (sp->duplex == 1) {
		sp->led_state = 0x70;
		sp->tty->ops->write(sp->tty, &sp->led_state, 1);
		sp->tx_enable = 1;
		actual = sp->tty->ops->write(sp->tty, sp->xbuff, count);
		sp->xleft = count - actual;
		sp->xhead = sp->xbuff + actual;
		sp->led_state = 0x60;
		sp->tty->ops->write(sp->tty, &sp->led_state, 1);
	} else {
		sp->xleft = count;
		sp->xhead = sp->xbuff;
		sp->status2 = count;
		sp_xmit_on_air((unsigned long)sp);
	}

	return;

out_drop:
	sp->dev->stats.tx_dropped++;
	netif_start_queue(sp->dev);
	if (net_ratelimit())
		printk(KERN_DEBUG "%s: %s - dropped.\n", sp->dev->name, msg);
}

/* Encapsulate an IP datagram and kick it into a TTY queue. */

static netdev_tx_t sp_xmit(struct sk_buff *skb, struct net_device *dev)
{
	struct sixpack *sp = netdev_priv(dev);

	spin_lock_bh(&sp->lock);
	/* We were not busy, so we are now... :-) */
	netif_stop_queue(dev);
	dev->stats.tx_bytes += skb->len;
	sp_encaps(sp, skb->data, skb->len);
	spin_unlock_bh(&sp->lock);

	dev_kfree_skb(skb);

	return NETDEV_TX_OK;
}

static int sp_open_dev(struct net_device *dev)
{
	struct sixpack *sp = netdev_priv(dev);

	if (sp->tty == NULL)
		return -ENODEV;
	return 0;
}

/* Close the low-level part of the 6pack channel. */
static int sp_close(struct net_device *dev)
{
	struct sixpack *sp = netdev_priv(dev);

	spin_lock_bh(&sp->lock);
	if (sp->tty) {
		/* TTY discipline is running. */
		clear_bit(TTY_DO_WRITE_WAKEUP, &sp->tty->flags);
	}
	netif_stop_queue(dev);
	spin_unlock_bh(&sp->lock);

	return 0;
}

/* Return the frame type ID */
static int sp_header(struct sk_buff *skb, struct net_device *dev,
		     unsigned short type, const void *daddr,
		     const void *saddr, unsigned len)
{
#ifdef CONFIG_INET
	if (type != ETH_P_AX25)
		return ax25_hard_header(skb, dev, type, daddr, saddr, len);
#endif
	return 0;
}

static int sp_set_mac_address(struct net_device *dev, void *addr)
{
	struct sockaddr_ax25 *sa = addr;

	netif_tx_lock_bh(dev);
	netif_addr_lock(dev);
	memcpy(dev->dev_addr, &sa->sax25_call, AX25_ADDR_LEN);
	netif_addr_unlock(dev);
	netif_tx_unlock_bh(dev);

	return 0;
}

static int sp_rebuild_header(struct sk_buff *skb)
{
#ifdef CONFIG_INET
	return ax25_rebuild_header(skb);
#else
	return 0;
#endif
}

static const struct header_ops sp_header_ops = {
	.create		= sp_header,
	.rebuild	= sp_rebuild_header,
};

static const struct net_device_ops sp_netdev_ops = {
	.ndo_open		= sp_open_dev,
	.ndo_stop		= sp_close,
	.ndo_start_xmit		= sp_xmit,
	.ndo_set_mac_address    = sp_set_mac_address,
};

static void sp_setup(struct net_device *dev)
{
	/* Finish setting up the DEVICE info. */
	dev->netdev_ops		= &sp_netdev_ops;
	dev->destructor		= free_netdev;
	dev->mtu		= SIXP_MTU;
	dev->hard_header_len	= AX25_MAX_HEADER_LEN;
	dev->header_ops 	= &sp_header_ops;

	dev->addr_len		= AX25_ADDR_LEN;
	dev->type		= ARPHRD_AX25;
	dev->tx_queue_len	= 10;

	/* Only activated in AX.25 mode */
	memcpy(dev->broadcast, &ax25_bcast, AX25_ADDR_LEN);
	memcpy(dev->dev_addr, &ax25_defaddr, AX25_ADDR_LEN);

	dev->flags		= 0;
}

/* Send one completely decapsulated IP datagram to the IP layer. */

/*
 * This is the routine that sends the received data to the kernel AX.25.
 * 'cmd' is the KISS command. For AX.25 data, it is zero.
 */

static void sp_bump(struct sixpack *sp, char cmd)
{
	struct sk_buff *skb;
	int count;
	unsigned char *ptr;

	count = sp->rcount + 1;

	sp->dev->stats.rx_bytes += count;

	if ((skb = dev_alloc_skb(count)) == NULL)
		goto out_mem;

	ptr = skb_put(skb, count);
	*ptr++ = cmd;	/* KISS command */

	memcpy(ptr, sp->cooked_buf + 1, count);
	skb->protocol = ax25_type_trans(skb, sp->dev);
	netif_rx(skb);
	sp->dev->stats.rx_packets++;

	return;

out_mem:
	sp->dev->stats.rx_dropped++;
}


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

/*
 * We have a potential race on dereferencing tty->disc_data, because the tty
 * layer provides no locking at all - thus one cpu could be running
 * sixpack_receive_buf while another calls sixpack_close, which zeroes
 * tty->disc_data and frees the memory that sixpack_receive_buf is using.  The
 * best way to fix this is to use a rwlock in the tty struct, but for now we
 * use a single global rwlock for all ttys in ppp line discipline.
 */
static DEFINE_RWLOCK(disc_data_lock);
                                                                                
static struct sixpack *sp_get(struct tty_struct *tty)
{
	struct sixpack *sp;

	read_lock(&disc_data_lock);
	sp = tty->disc_data;
	if (sp)
		atomic_inc(&sp->refcnt);
	read_unlock(&disc_data_lock);

	return sp;
}

static void sp_put(struct sixpack *sp)
{
	if (atomic_dec_and_test(&sp->refcnt))
		up(&sp->dead_sem);
}

/*
 * Called by the TTY driver when there's room for more data.  If we have
 * more packets to send, we send them here.
 */
static void sixpack_write_wakeup(struct tty_struct *tty)
{
	struct sixpack *sp = sp_get(tty);
	int actual;

	if (!sp)
		return;
	if (sp->xleft <= 0)  {
		/* Now serial buffer is almost free & we can start
		 * transmission of another packet */
		sp->dev->stats.tx_packets++;
		clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
		sp->tx_enable = 0;
		netif_wake_queue(sp->dev);
		goto out;
	}

	if (sp->tx_enable) {
		actual = tty->ops->write(tty, sp->xhead, sp->xleft);
		sp->xleft -= actual;
		sp->xhead += actual;
	}

out:
	sp_put(sp);
}

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

/*
 * Handle the 'receiver data ready' interrupt.
 * This function is called by the 'tty_io' module in the kernel when
 * a block of 6pack data has been received, which can now be decapsulated
 * and sent on to some IP layer for further processing.
 */
static void sixpack_receive_buf(struct tty_struct *tty,
	const unsigned char *cp, char *fp, int count)
{
	struct sixpack *sp;
	unsigned char buf[512];
	int count1;

	if (!count)
		return;

	sp = sp_get(tty);
	if (!sp)
		return;

	memcpy(buf, cp, count < sizeof(buf) ? count : sizeof(buf));

	/* Read the characters out of the buffer */

	count1 = count;
	while (count) {
		count--;
		if (fp && *fp++) {
			if (!test_and_set_bit(SIXPF_ERROR, &sp->flags))
				sp->dev->stats.rx_errors++;
			continue;
		}
	}
	sixpack_decode(sp, buf, count1);

	sp_put(sp);
	tty_unthrottle(tty);
}

/*
 * Try to resync the TNC. Called by the resync timer defined in
 * decode_prio_command
 */

#define TNC_UNINITIALIZED	0
#define TNC_UNSYNC_STARTUP	1
#define TNC_UNSYNCED		2
#define TNC_IN_SYNC		3

static void __tnc_set_sync_state(struct sixpack *sp, int new_tnc_state)
{
	char *msg;

	switch (new_tnc_state) {
	default:			/* gcc oh piece-o-crap ... */
	case TNC_UNSYNC_STARTUP:
		msg = "Synchronizing with TNC";
		break;
	case TNC_UNSYNCED:
		msg = "Lost synchronization with TNC\n";
		break;
	case TNC_IN_SYNC:
		msg = "Found TNC";
		break;
	}

	sp->tnc_state = new_tnc_state;
	printk(KERN_INFO "%s: %s\n", sp->dev->name, msg);
}

static inline void tnc_set_sync_state(struct sixpack *sp, int new_tnc_state)
{
	int old_tnc_state = sp->tnc_state;

	if (old_tnc_state != new_tnc_state)
		__tnc_set_sync_state(sp, new_tnc_state);
}

static void resync_tnc(unsigned long channel)
{
	struct sixpack *sp = (struct sixpack *) channel;
	static char resync_cmd = 0xe8;

	/* clear any data that might have been received */

	sp->rx_count = 0;
	sp->rx_count_cooked = 0;

	/* reset state machine */

	sp->status = 1;
	sp->status1 = 1;
	sp->status2 = 0;

	/* resync the TNC */

	sp->led_state = 0x60;
	sp->tty->ops->write(sp->tty, &sp->led_state, 1);
	sp->tty->ops->write(sp->tty, &resync_cmd, 1);


	/* Start resync timer again -- the TNC might be still absent */

	del_timer(&sp->resync_t);
	sp->resync_t.data	= (unsigned long) sp;
	sp->resync_t.function	= resync_tnc;
	sp->resync_t.expires	= jiffies + SIXP_RESYNC_TIMEOUT;
	add_timer(&sp->resync_t);
}

static inline int tnc_init(struct sixpack *sp)
{
	unsigned char inbyte = 0xe8;

	tnc_set_sync_state(sp, TNC_UNSYNC_STARTUP);

	sp->tty->ops->write(sp->tty, &inbyte, 1);

	del_timer(&sp->resync_t);
	sp->resync_t.data = (unsigned long) sp;
	sp->resync_t.function = resync_tnc;
	sp->resync_t.expires = jiffies + SIXP_RESYNC_TIMEOUT;
	add_timer(&sp->resync_t);

	return 0;
}

/*
 * Open the high-level part of the 6pack channel.
 * This function is called by the TTY module when the
 * 6pack line discipline is called for.  Because we are
 * sure the tty line exists, we only have to link it to
 * a free 6pcack channel...
 */
static int sixpack_open(struct tty_struct *tty)
{
	char *rbuff = NULL, *xbuff = NULL;
	struct net_device *dev;
	struct sixpack *sp;
	unsigned long len;
	int err = 0;

	if (!capable(CAP_NET_ADMIN))
		return -EPERM;
	if (tty->ops->write == NULL)
		return -EOPNOTSUPP;

	dev = alloc_netdev(sizeof(struct sixpack), "sp%d", sp_setup);
	if (!dev) {
		err = -ENOMEM;
		goto out;
	}

	sp = netdev_priv(dev);
	sp->dev = dev;

	spin_lock_init(&sp->lock);
	atomic_set(&sp->refcnt, 1);
	sema_init(&sp->dead_sem, 0);

	/* !!! length of the buffers. MTU is IP MTU, not PACLEN!  */

	len = dev->mtu * 2;

	rbuff = kmalloc(len + 4, GFP_KERNEL);
	xbuff = kmalloc(len + 4, GFP_KERNEL);

	if (rbuff == NULL || xbuff == NULL) {
		err = -ENOBUFS;
		goto out_free;
	}

	spin_lock_bh(&sp->lock);

	sp->tty = tty;

	sp->rbuff	= rbuff;
	sp->xbuff	= xbuff;

	sp->mtu		= AX25_MTU + 73;
	sp->buffsize	= len;
	sp->rcount	= 0;
	sp->rx_count	= 0;
	sp->rx_count_cooked = 0;
	sp->xleft	= 0;

	sp->flags	= 0;		/* Clear ESCAPE & ERROR flags */

	sp->duplex	= 0;
	sp->tx_delay    = SIXP_TXDELAY;
	sp->persistence = SIXP_PERSIST;
	sp->slottime    = SIXP_SLOTTIME;
	sp->led_state   = 0x60;
	sp->status      = 1;
	sp->status1     = 1;
	sp->status2     = 0;
	sp->tx_enable   = 0;

	netif_start_queue(dev);

	init_timer(&sp->tx_t);
	sp->tx_t.function = sp_xmit_on_air;
	sp->tx_t.data = (unsigned long) sp;

	init_timer(&sp->resync_t);

	spin_unlock_bh(&sp->lock);

	/* Done.  We have linked the TTY line to a channel. */
	tty->disc_data = sp;
	tty->receive_room = 65536;

	/* Now we're ready to register. */
	if (register_netdev(dev))
		goto out_free;

	tnc_init(sp);

	return 0;

out_free:
	kfree(xbuff);
	kfree(rbuff);

	if (dev)
		free_netdev(dev);

out:
	return err;
}


/*
 * Close down a 6pack channel.
 * This means flushing out any pending queues, and then restoring the
 * TTY line discipline to what it was before it got hooked to 6pack
 * (which usually is TTY again).
 */
static void sixpack_close(struct tty_struct *tty)
{
	struct sixpack *sp;

	write_lock(&disc_data_lock);
	sp = tty->disc_data;
	tty->disc_data = NULL;
	write_unlock(&disc_data_lock);
	if (!sp)
		return;

	/*
	 * We have now ensured that nobody can start using ap from now on, but
	 * we have to wait for all existing users to finish.
	 */
	if (!atomic_dec_and_test(&sp->refcnt))
		down(&sp->dead_sem);

	unregister_netdev(sp->dev);

	del_timer(&sp->tx_t);
	del_timer(&sp->resync_t);

	/* Free all 6pack frame buffers. */
	kfree(sp->rbuff);
	kfree(sp->xbuff);
}

/* Perform I/O control on an active 6pack channel. */
static int sixpack_ioctl(struct tty_struct *tty, struct file *file,
	unsigned int cmd, unsigned long arg)
{
	struct sixpack *sp = sp_get(tty);
	struct net_device *dev;
	unsigned int tmp, err;

	if (!sp)
		return -ENXIO;
	dev = sp->dev;

	switch(cmd) {
	case SIOCGIFNAME:
		err = copy_to_user((void __user *) arg, dev->name,
		                   strlen(dev->name) + 1) ? -EFAULT : 0;
		break;

	case SIOCGIFENCAP:
		err = put_user(0, (int __user *) arg);
		break;

	case SIOCSIFENCAP:
		if (get_user(tmp, (int __user *) arg)) {
			err = -EFAULT;
			break;
		}

		sp->mode = tmp;
		dev->addr_len        = AX25_ADDR_LEN;
		dev->hard_header_len = AX25_KISS_HEADER_LEN +
		                       AX25_MAX_HEADER_LEN + 3;
		dev->type            = ARPHRD_AX25;

		err = 0;
		break;

	 case SIOCSIFHWADDR: {
		char addr[AX25_ADDR_LEN];

		if (copy_from_user(&addr,
		                   (void __user *) arg, AX25_ADDR_LEN)) {
				err = -EFAULT;
				break;
			}

			netif_tx_lock_bh(dev);
			memcpy(dev->dev_addr, &addr, AX25_ADDR_LEN);
			netif_tx_unlock_bh(dev);

			err = 0;
			break;
		}

	default:
		err = tty_mode_ioctl(tty, file, cmd, arg);
	}

	sp_put(sp);

	return err;
}

#ifdef CONFIG_COMPAT
static long sixpack_compat_ioctl(struct tty_struct * tty, struct file * file,
				unsigned int cmd, unsigned long arg)
{
	switch (cmd) {
	case SIOCGIFNAME:
	case SIOCGIFENCAP:
	case SIOCSIFENCAP:
	case SIOCSIFHWADDR:
		return sixpack_ioctl(tty, file, cmd,
				(unsigned long)compat_ptr(arg));
	}

	return -ENOIOCTLCMD;
}
#endif

static struct tty_ldisc_ops sp_ldisc = {
	.owner		= THIS_MODULE,
	.magic		= TTY_LDISC_MAGIC,
	.name		= "6pack",
	.open		= sixpack_open,
	.close		= sixpack_close,
	.ioctl		= sixpack_ioctl,
#ifdef CONFIG_COMPAT
	.compat_ioctl	= sixpack_compat_ioctl,
#endif
	.receive_buf	= sixpack_receive_buf,
	.write_wakeup	= sixpack_write_wakeup,
};

/* Initialize 6pack control device -- register 6pack line discipline */

static const char msg_banner[]  __initdata = KERN_INFO \
	"AX.25: 6pack driver, " SIXPACK_VERSION "\n";
static const char msg_regfail[] __initdata = KERN_ERR  \
	"6pack: can't register line discipline (err = %d)\n";

static int __init sixpack_init_driver(void)
{
	int status;

	printk(msg_banner);

	/* Register the provided line protocol discipline */
	if ((status = tty_register_ldisc(N_6PACK, &sp_ldisc)) != 0)
		printk(msg_regfail, status);

	return status;
}

static const char msg_unregfail[] __exitdata = KERN_ERR \
	"6pack: can't unregister line discipline (err = %d)\n";

static void __exit sixpack_exit_driver(void)
{
	int ret;

	if ((ret = tty_unregister_ldisc(N_6PACK)))
		printk(msg_unregfail, ret);
}

/* encode an AX.25 packet into 6pack */

static int encode_sixpack(unsigned char *tx_buf, unsigned char *tx_buf_raw,
	int length, unsigned char tx_delay)
{
	int count = 0;
	unsigned char checksum = 0, buf[400];
	int raw_count = 0;

	tx_buf_raw[raw_count++] = SIXP_PRIO_CMD_MASK | SIXP_TX_MASK;
	tx_buf_raw[raw_count++] = SIXP_SEOF;

	buf[0] = tx_delay;
	for (count = 1; count < length; count++)
		buf[count] = tx_buf[count];

	for (count = 0; count < length; count++)
		checksum += buf[count];
	buf[length] = (unsigned char) 0xff - checksum;

	for (count = 0; count <= length; count++) {
		if ((count % 3) == 0) {
			tx_buf_raw[raw_count++] = (buf[count] & 0x3f);
			tx_buf_raw[raw_count] = ((buf[count] >> 2) & 0x30);
		} else if ((count % 3) == 1) {
			tx_buf_raw[raw_count++] |= (buf[count] & 0x0f);
			tx_buf_raw[raw_count] =	((buf[count] >> 2) & 0x3c);
		} else {
			tx_buf_raw[raw_count++] |= (buf[count] & 0x03);
			tx_buf_raw[raw_count++] = (buf[count] >> 2);
		}
	}
	if ((length % 3) != 2)
		raw_count++;
	tx_buf_raw[raw_count++] = SIXP_SEOF;
	return raw_count;
}

/* decode 4 sixpack-encoded bytes into 3 data bytes */

static void decode_data(struct sixpack *sp, unsigned char inbyte)
{
	unsigned char *buf;

	if (sp->rx_count != 3) {
		sp->raw_buf[sp->rx_count++] = inbyte;

		return;
	}

	buf = sp->raw_buf;
	sp->cooked_buf[sp->rx_count_cooked++] =
		buf[0] | ((buf[1] << 2) & 0xc0);
	sp->cooked_buf[sp->rx_count_cooked++] =
		(buf[1] & 0x0f) | ((buf[2] << 2) & 0xf0);
	sp->cooked_buf[sp->rx_count_cooked++] =
		(buf[2] & 0x03) | (inbyte << 2);
	sp->rx_count = 0;
}

/* identify and execute a 6pack priority command byte */

static void decode_prio_command(struct sixpack *sp, unsigned char cmd)
{
	unsigned char channel;
	int actual;

	channel = cmd & SIXP_CHN_MASK;
	if ((cmd & SIXP_PRIO_DATA_MASK) != 0) {     /* idle ? */

	/* RX and DCD flags can only be set in the same prio command,
	   if the DCD flag has been set without the RX flag in the previous
	   prio command. If DCD has not been set before, something in the
	   transmission has gone wrong. In this case, RX and DCD are
	   cleared in order to prevent the decode_data routine from
	   reading further data that might be corrupt. */

		if (((sp->status & SIXP_DCD_MASK) == 0) &&
			((cmd & SIXP_RX_DCD_MASK) == SIXP_RX_DCD_MASK)) {
				if (sp->status != 1)
					printk(KERN_DEBUG "6pack: protocol violation\n");
				else
					sp->status = 0;
				cmd &= ~SIXP_RX_DCD_MASK;
		}
		sp->status = cmd & SIXP_PRIO_DATA_MASK;
	} else { /* output watchdog char if idle */
		if ((sp->status2 != 0) && (sp->duplex == 1)) {
			sp->led_state = 0x70;
			sp->tty->ops->write(sp->tty, &sp->led_state, 1);
			sp->tx_enable = 1;
			actual = sp->tty->ops->write(sp->tty, sp->xbuff, sp->status2);
			sp->xleft -= actual;
			sp->xhead += actual;
			sp->led_state = 0x60;
			sp->status2 = 0;

		}
	}

	/* needed to trigger the TNC watchdog */
	sp->tty->ops->write(sp->tty, &sp->led_state, 1);

        /* if the state byte has been received, the TNC is present,
           so the resync timer can be reset. */

	if (sp->tnc_state == TNC_IN_SYNC) {
		del_timer(&sp->resync_t);
		sp->resync_t.data	= (unsigned long) sp;
		sp->resync_t.function	= resync_tnc;
		sp->resync_t.expires	= jiffies + SIXP_INIT_RESYNC_TIMEOUT;
		add_timer(&sp->resync_t);
	}

	sp->status1 = cmd & SIXP_PRIO_DATA_MASK;
}

/* identify and execute a standard 6pack command byte */

static void decode_std_command(struct sixpack *sp, unsigned char cmd)
{
	unsigned char checksum = 0, rest = 0, channel;
	short i;

	channel = cmd & SIXP_CHN_MASK;
	switch (cmd & SIXP_CMD_MASK) {     /* normal command */
	case SIXP_SEOF:
		if ((sp->rx_count == 0) && (sp->rx_count_cooked == 0)) {
			if ((sp->status & SIXP_RX_DCD_MASK) ==
				SIXP_RX_DCD_MASK) {
				sp->led_state = 0x68;
				sp->tty->ops->write(sp->tty, &sp->led_state, 1);
			}
		} else {
			sp->led_state = 0x60;
			/* fill trailing bytes with zeroes */
			sp->tty->ops->write(sp->tty, &sp->led_state, 1);
			rest = sp->rx_count;
			if (rest != 0)
				 for (i = rest; i <= 3; i++)
					decode_data(sp, 0);
			if (rest == 2)
				sp->rx_count_cooked -= 2;
			else if (rest == 3)
				sp->rx_count_cooked -= 1;
			for (i = 0; i < sp->rx_count_cooked; i++)
				checksum += sp->cooked_buf[i];
			if (checksum != SIXP_CHKSUM) {
				printk(KERN_DEBUG "6pack: bad checksum %2.2x\n", checksum);
			} else {
				sp->rcount = sp->rx_count_cooked-2;
				sp_bump(sp, 0);
			}
			sp->rx_count_cooked = 0;
		}
		break;
	case SIXP_TX_URUN: printk(KERN_DEBUG "6pack: TX underrun\n");
		break;
	case SIXP_RX_ORUN: printk(KERN_DEBUG "6pack: RX overrun\n");
		break;
	case SIXP_RX_BUF_OVL:
		printk(KERN_DEBUG "6pack: RX buffer overflow\n");
	}
}

/* decode a 6pack packet */

static void
sixpack_decode(struct sixpack *sp, unsigned char *pre_rbuff, int count)
{
	unsigned char inbyte;
	int count1;

	for (count1 = 0; count1 < count; count1++) {
		inbyte = pre_rbuff[count1];
		if (inbyte == SIXP_FOUND_TNC) {
			tnc_set_sync_state(sp, TNC_IN_SYNC);
			del_timer(&sp->resync_t);
		}
		if ((inbyte & SIXP_PRIO_CMD_MASK) != 0)
			decode_prio_command(sp, inbyte);
		else if ((inbyte & SIXP_STD_CMD_MASK) != 0)
			decode_std_command(sp, inbyte);
		else if ((sp->status & SIXP_RX_DCD_MASK) == SIXP_RX_DCD_MASK)
			decode_data(sp, inbyte);
	}
}

MODULE_AUTHOR("Ralf Baechle DO1GRB <ralf@linux-mips.org>");
MODULE_DESCRIPTION("6pack driver for AX.25");
MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_6PACK);

module_init(sixpack_init_driver);
module_exit(sixpack_exit_driver);