summaryrefslogtreecommitdiff
path: root/drivers/net/can/can327.c
blob: 24af639610309dd2a3372151782b8c9a32306306 (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
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
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
// SPDX-License-Identifier: GPL-2.0
/* ELM327 based CAN interface driver (tty line discipline)
 *
 * This driver started as a derivative of linux/drivers/net/can/slcan.c
 * and my thanks go to the original authors for their inspiration.
 *
 * can327.c Author : Max Staudt <max-linux@enpas.org>
 * slcan.c Author  : Oliver Hartkopp <socketcan@hartkopp.net>
 * slip.c Authors  : Laurence Culhane <loz@holmes.demon.co.uk>
 *                   Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/init.h>
#include <linux/module.h>

#include <linux/bitops.h>
#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/lockdep.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/tty.h>
#include <linux/tty_ldisc.h>
#include <linux/workqueue.h>

#include <uapi/linux/tty.h>

#include <linux/can.h>
#include <linux/can/dev.h>
#include <linux/can/error.h>
#include <linux/can/rx-offload.h>

#define CAN327_NAPI_WEIGHT 4

#define CAN327_SIZE_TXBUF 32
#define CAN327_SIZE_RXBUF 1024

#define CAN327_CAN_CONFIG_SEND_SFF 0x8000
#define CAN327_CAN_CONFIG_VARIABLE_DLC 0x4000
#define CAN327_CAN_CONFIG_RECV_BOTH_SFF_EFF 0x2000
#define CAN327_CAN_CONFIG_BAUDRATE_MULT_8_7 0x1000

#define CAN327_DUMMY_CHAR 'y'
#define CAN327_DUMMY_STRING "y"
#define CAN327_READY_CHAR '>'

/* Bits in elm->cmds_todo */
enum can327_tx_do {
	CAN327_TX_DO_CAN_DATA = 0,
	CAN327_TX_DO_CANID_11BIT,
	CAN327_TX_DO_CANID_29BIT_LOW,
	CAN327_TX_DO_CANID_29BIT_HIGH,
	CAN327_TX_DO_CAN_CONFIG_PART2,
	CAN327_TX_DO_CAN_CONFIG,
	CAN327_TX_DO_RESPONSES,
	CAN327_TX_DO_SILENT_MONITOR,
	CAN327_TX_DO_INIT,
};

struct can327 {
	/* This must be the first member when using alloc_candev() */
	struct can_priv can;

	struct can_rx_offload offload;

	/* TTY buffers */
	u8 txbuf[CAN327_SIZE_TXBUF];
	u8 rxbuf[CAN327_SIZE_RXBUF];

	/* Per-channel lock */
	spinlock_t lock;

	/* TTY and netdev devices that we're bridging */
	struct tty_struct *tty;
	struct net_device *dev;

	/* TTY buffer accounting */
	struct work_struct tx_work;	/* Flushes TTY TX buffer */
	u8 *txhead;			/* Next TX byte */
	size_t txleft;			/* Bytes left to TX */
	int rxfill;			/* Bytes already RX'd in buffer */

	/* State machine */
	enum {
		CAN327_STATE_NOTINIT = 0,
		CAN327_STATE_GETDUMMYCHAR,
		CAN327_STATE_GETPROMPT,
		CAN327_STATE_RECEIVING,
	} state;

	/* Things we have yet to send */
	char **next_init_cmd;
	unsigned long cmds_todo;

	/* The CAN frame and config the ELM327 is sending/using,
	 * or will send/use after finishing all cmds_todo
	 */
	struct can_frame can_frame_to_send;
	u16 can_config;
	u8 can_bitrate_divisor;

	/* Parser state */
	bool drop_next_line;

	/* Stop the channel on UART side hardware failure, e.g. stray
	 * characters or neverending lines. This may be caused by bad
	 * UART wiring, a bad ELM327, a bad UART bridge...
	 * Once this is true, nothing will be sent to the TTY.
	 */
	bool uart_side_failure;
};

static inline void can327_uart_side_failure(struct can327 *elm);

static void can327_send(struct can327 *elm, const void *buf, size_t len)
{
	int written;

	lockdep_assert_held(&elm->lock);

	if (elm->uart_side_failure)
		return;

	memcpy(elm->txbuf, buf, len);

	/* Order of next two lines is *very* important.
	 * When we are sending a little amount of data,
	 * the transfer may be completed inside the ops->write()
	 * routine, because it's running with interrupts enabled.
	 * In this case we *never* got WRITE_WAKEUP event,
	 * if we did not request it before write operation.
	 *       14 Oct 1994  Dmitry Gorodchanin.
	 */
	set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
	written = elm->tty->ops->write(elm->tty, elm->txbuf, len);
	if (written < 0) {
		netdev_err(elm->dev, "Failed to write to tty %s.\n",
			   elm->tty->name);
		can327_uart_side_failure(elm);
		return;
	}

	elm->txleft = len - written;
	elm->txhead = elm->txbuf + written;
}

/* Take the ELM327 out of almost any state and back into command mode.
 * We send CAN327_DUMMY_CHAR which will either abort any running
 * operation, or be echoed back to us in case we're already in command
 * mode.
 */
static void can327_kick_into_cmd_mode(struct can327 *elm)
{
	lockdep_assert_held(&elm->lock);

	if (elm->state != CAN327_STATE_GETDUMMYCHAR &&
	    elm->state != CAN327_STATE_GETPROMPT) {
		can327_send(elm, CAN327_DUMMY_STRING, 1);

		elm->state = CAN327_STATE_GETDUMMYCHAR;
	}
}

/* Schedule a CAN frame and necessary config changes to be sent to the TTY. */
static void can327_send_frame(struct can327 *elm, struct can_frame *frame)
{
	lockdep_assert_held(&elm->lock);

	/* Schedule any necessary changes in ELM327's CAN configuration */
	if (elm->can_frame_to_send.can_id != frame->can_id) {
		/* Set the new CAN ID for transmission. */
		if ((frame->can_id ^ elm->can_frame_to_send.can_id)
		    & CAN_EFF_FLAG) {
			elm->can_config =
				(frame->can_id & CAN_EFF_FLAG ? 0 : CAN327_CAN_CONFIG_SEND_SFF) |
				CAN327_CAN_CONFIG_VARIABLE_DLC |
				CAN327_CAN_CONFIG_RECV_BOTH_SFF_EFF |
				elm->can_bitrate_divisor;

			set_bit(CAN327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
		}

		if (frame->can_id & CAN_EFF_FLAG) {
			clear_bit(CAN327_TX_DO_CANID_11BIT, &elm->cmds_todo);
			set_bit(CAN327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
			set_bit(CAN327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
		} else {
			set_bit(CAN327_TX_DO_CANID_11BIT, &elm->cmds_todo);
			clear_bit(CAN327_TX_DO_CANID_29BIT_LOW,
				  &elm->cmds_todo);
			clear_bit(CAN327_TX_DO_CANID_29BIT_HIGH,
				  &elm->cmds_todo);
		}
	}

	/* Schedule the CAN frame itself. */
	elm->can_frame_to_send = *frame;
	set_bit(CAN327_TX_DO_CAN_DATA, &elm->cmds_todo);

	can327_kick_into_cmd_mode(elm);
}

/* ELM327 initialisation sequence.
 * The line length is limited by the buffer in can327_handle_prompt().
 */
static char *can327_init_script[] = {
	"AT WS\r",        /* v1.0: Warm Start */
	"AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
	"AT M0\r",        /* v1.0: Memory Off */
	"AT AL\r",        /* v1.0: Allow Long messages */
	"AT BI\r",        /* v1.0: Bypass Initialisation */
	"AT CAF0\r",      /* v1.0: CAN Auto Formatting Off */
	"AT CFC0\r",      /* v1.0: CAN Flow Control Off */
	"AT CF 000\r",    /* v1.0: Reset CAN ID Filter */
	"AT CM 000\r",    /* v1.0: Reset CAN ID Mask */
	"AT E1\r",        /* v1.0: Echo On */
	"AT H1\r",        /* v1.0: Headers On */
	"AT L0\r",        /* v1.0: Linefeeds Off */
	"AT SH 7DF\r",    /* v1.0: Set CAN sending ID to 0x7df */
	"AT ST FF\r",     /* v1.0: Set maximum Timeout for response after TX */
	"AT AT0\r",       /* v1.2: Adaptive Timing Off */
	"AT D1\r",        /* v1.3: Print DLC On */
	"AT S1\r",        /* v1.3: Spaces On */
	"AT TP B\r",      /* v1.0: Try Protocol B */
	NULL
};

static void can327_init_device(struct can327 *elm)
{
	lockdep_assert_held(&elm->lock);

	elm->state = CAN327_STATE_NOTINIT;
	elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
	elm->rxfill = 0;
	elm->drop_next_line = 0;

	/* We can only set the bitrate as a fraction of 500000.
	 * The bitrates listed in can327_bitrate_const will
	 * limit the user to the right values.
	 */
	elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
	elm->can_config =
		CAN327_CAN_CONFIG_SEND_SFF | CAN327_CAN_CONFIG_VARIABLE_DLC |
		CAN327_CAN_CONFIG_RECV_BOTH_SFF_EFF | elm->can_bitrate_divisor;

	/* Configure ELM327 and then start monitoring */
	elm->next_init_cmd = &can327_init_script[0];
	set_bit(CAN327_TX_DO_INIT, &elm->cmds_todo);
	set_bit(CAN327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
	set_bit(CAN327_TX_DO_RESPONSES, &elm->cmds_todo);
	set_bit(CAN327_TX_DO_CAN_CONFIG, &elm->cmds_todo);

	can327_kick_into_cmd_mode(elm);
}

static void can327_feed_frame_to_netdev(struct can327 *elm, struct sk_buff *skb)
{
	lockdep_assert_held(&elm->lock);

	if (!netif_running(elm->dev)) {
		kfree_skb(skb);
		return;
	}

	/* Queue for NAPI pickup.
	 * rx-offload will update stats and LEDs for us.
	 */
	if (can_rx_offload_queue_tail(&elm->offload, skb))
		elm->dev->stats.rx_fifo_errors++;

	/* Wake NAPI */
	can_rx_offload_irq_finish(&elm->offload);
}

/* Called when we're out of ideas and just want it all to end. */
static inline void can327_uart_side_failure(struct can327 *elm)
{
	struct can_frame *frame;
	struct sk_buff *skb;

	lockdep_assert_held(&elm->lock);

	elm->uart_side_failure = true;

	clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);

	elm->can.can_stats.bus_off++;
	netif_stop_queue(elm->dev);
	elm->can.state = CAN_STATE_BUS_OFF;
	can_bus_off(elm->dev);

	netdev_err(elm->dev,
		   "ELM327 misbehaved. Blocking further communication.\n");

	skb = alloc_can_err_skb(elm->dev, &frame);
	if (!skb)
		return;

	frame->can_id |= CAN_ERR_BUSOFF;
	can327_feed_frame_to_netdev(elm, skb);
}

/* Compares a byte buffer (non-NUL terminated) to the payload part of
 * a string, and returns true iff the buffer (content *and* length) is
 * exactly that string, without the terminating NUL byte.
 *
 * Example: If reference is "BUS ERROR", then this returns true iff nbytes == 9
 *          and !memcmp(buf, "BUS ERROR", 9).
 *
 * The reason to use strings is so we can easily include them in the C
 * code, and to avoid hardcoding lengths.
 */
static inline bool can327_rxbuf_cmp(const u8 *buf, size_t nbytes,
				    const char *reference)
{
	size_t ref_len = strlen(reference);

	return (nbytes == ref_len) && !memcmp(buf, reference, ref_len);
}

static void can327_parse_error(struct can327 *elm, size_t len)
{
	struct can_frame *frame;
	struct sk_buff *skb;

	lockdep_assert_held(&elm->lock);

	skb = alloc_can_err_skb(elm->dev, &frame);
	if (!skb)
		/* It's okay to return here:
		 * The outer parsing loop will drop this UART buffer.
		 */
		return;

	/* Filter possible error messages based on length of RX'd line */
	if (can327_rxbuf_cmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
		netdev_err(elm->dev,
			   "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "BUFFER FULL")) {
		/* This will only happen if the last data line was complete.
		 * Otherwise, can327_parse_frame() will heuristically
		 * emit this kind of error frame instead.
		 */
		frame->can_id |= CAN_ERR_CRTL;
		frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "BUS ERROR")) {
		frame->can_id |= CAN_ERR_BUSERROR;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "CAN ERROR")) {
		frame->can_id |= CAN_ERR_PROT;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "<RX ERROR")) {
		frame->can_id |= CAN_ERR_PROT;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "BUS BUSY")) {
		frame->can_id |= CAN_ERR_PROT;
		frame->data[2] = CAN_ERR_PROT_OVERLOAD;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "FB ERROR")) {
		frame->can_id |= CAN_ERR_PROT;
		frame->data[2] = CAN_ERR_PROT_TX;
	} else if (len == 5 && !memcmp(elm->rxbuf, "ERR", 3)) {
		/* ERR is followed by two digits, hence line length 5 */
		netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
			   elm->rxbuf[3], elm->rxbuf[4]);
		frame->can_id |= CAN_ERR_CRTL;
	} else {
		/* Something else has happened.
		 * Maybe garbage on the UART line.
		 * Emit a generic error frame.
		 */
	}

	can327_feed_frame_to_netdev(elm, skb);
}

/* Parse CAN frames coming as ASCII from ELM327.
 * They can be of various formats:
 *
 * 29-bit ID (EFF):  12 34 56 78 D PL PL PL PL PL PL PL PL
 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
 *
 * where D = DLC, PL = payload byte
 *
 * Instead of a payload, RTR indicates a remote request.
 *
 * We will use the spaces and line length to guess the format.
 */
static int can327_parse_frame(struct can327 *elm, size_t len)
{
	struct can_frame *frame;
	struct sk_buff *skb;
	int hexlen;
	int datastart;
	int i;

	lockdep_assert_held(&elm->lock);

	skb = alloc_can_skb(elm->dev, &frame);
	if (!skb)
		return -ENOMEM;

	/* Find first non-hex and non-space character:
	 *  - In the simplest case, there is none.
	 *  - For RTR frames, 'R' is the first non-hex character.
	 *  - An error message may replace the end of the data line.
	 */
	for (hexlen = 0; hexlen <= len; hexlen++) {
		if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
		    elm->rxbuf[hexlen] != ' ') {
			break;
		}
	}

	/* Sanity check whether the line is really a clean hexdump,
	 * or terminated by an error message, or contains garbage.
	 */
	if (hexlen < len && !isdigit(elm->rxbuf[hexlen]) &&
	    !isupper(elm->rxbuf[hexlen]) && '<' != elm->rxbuf[hexlen] &&
	    ' ' != elm->rxbuf[hexlen]) {
		/* The line is likely garbled anyway, so bail.
		 * The main code will restart listening.
		 */
		kfree_skb(skb);
		return -ENODATA;
	}

	/* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
	 * No out-of-bounds access:
	 * We use the fact that we can always read from elm->rxbuf.
	 */
	if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
	    elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
	    elm->rxbuf[13] == ' ') {
		frame->can_id = CAN_EFF_FLAG;
		datastart = 14;
	} else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
		datastart = 6;
	} else {
		/* This is not a well-formatted data line.
		 * Assume it's an error message.
		 */
		kfree_skb(skb);
		return -ENODATA;
	}

	if (hexlen < datastart) {
		/* The line is too short to be a valid frame hex dump.
		 * Something interrupted the hex dump or it is invalid.
		 */
		kfree_skb(skb);
		return -ENODATA;
	}

	/* From here on all chars up to buf[hexlen] are hex or spaces,
	 * at well-defined offsets.
	 */

	/* Read CAN data length */
	frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);

	/* Read CAN ID */
	if (frame->can_id & CAN_EFF_FLAG) {
		frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28) |
				 (hex_to_bin(elm->rxbuf[1]) << 24) |
				 (hex_to_bin(elm->rxbuf[3]) << 20) |
				 (hex_to_bin(elm->rxbuf[4]) << 16) |
				 (hex_to_bin(elm->rxbuf[6]) << 12) |
				 (hex_to_bin(elm->rxbuf[7]) << 8) |
				 (hex_to_bin(elm->rxbuf[9]) << 4) |
				 (hex_to_bin(elm->rxbuf[10]) << 0);
	} else {
		frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8) |
				 (hex_to_bin(elm->rxbuf[1]) << 4) |
				 (hex_to_bin(elm->rxbuf[2]) << 0);
	}

	/* Check for RTR frame */
	if (elm->rxfill >= hexlen + 3 &&
	    !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) {
		frame->can_id |= CAN_RTR_FLAG;
	}

	/* Is the line long enough to hold the advertised payload?
	 * Note: RTR frames have a DLC, but no actual payload.
	 */
	if (!(frame->can_id & CAN_RTR_FLAG) &&
	    (hexlen < frame->len * 3 + datastart)) {
		/* Incomplete frame.
		 * Probably the ELM327's RS232 TX buffer was full.
		 * Emit an error frame and exit.
		 */
		frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
		frame->len = CAN_ERR_DLC;
		frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
		can327_feed_frame_to_netdev(elm, skb);

		/* Signal failure to parse.
		 * The line will be re-parsed as an error line, which will fail.
		 * However, this will correctly drop the state machine back into
		 * command mode.
		 */
		return -ENODATA;
	}

	/* Parse the data nibbles. */
	for (i = 0; i < frame->len; i++) {
		frame->data[i] =
			(hex_to_bin(elm->rxbuf[datastart + 3 * i]) << 4) |
			(hex_to_bin(elm->rxbuf[datastart + 3 * i + 1]));
	}

	/* Feed the frame to the network layer. */
	can327_feed_frame_to_netdev(elm, skb);

	return 0;
}

static void can327_parse_line(struct can327 *elm, size_t len)
{
	lockdep_assert_held(&elm->lock);

	/* Skip empty lines */
	if (!len)
		return;

	/* Skip echo lines */
	if (elm->drop_next_line) {
		elm->drop_next_line = 0;
		return;
	} else if (!memcmp(elm->rxbuf, "AT", 2)) {
		return;
	}

	/* Regular parsing */
	if (elm->state == CAN327_STATE_RECEIVING &&
	    can327_parse_frame(elm, len)) {
		/* Parse an error line. */
		can327_parse_error(elm, len);

		/* Start afresh. */
		can327_kick_into_cmd_mode(elm);
	}
}

static void can327_handle_prompt(struct can327 *elm)
{
	struct can_frame *frame = &elm->can_frame_to_send;
	/* Size this buffer for the largest ELM327 line we may generate,
	 * which is currently an 8 byte CAN frame's payload hexdump.
	 * Items in can327_init_script must fit here, too!
	 */
	char local_txbuf[sizeof("0102030405060708\r")];

	lockdep_assert_held(&elm->lock);

	if (!elm->cmds_todo) {
		/* Enter CAN monitor mode */
		can327_send(elm, "ATMA\r", 5);
		elm->state = CAN327_STATE_RECEIVING;

		/* We will be in the default state once this command is
		 * sent, so enable the TX packet queue.
		 */
		netif_wake_queue(elm->dev);

		return;
	}

	/* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
	if (test_bit(CAN327_TX_DO_INIT, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf), "%s",
			 *elm->next_init_cmd);

		elm->next_init_cmd++;
		if (!(*elm->next_init_cmd)) {
			clear_bit(CAN327_TX_DO_INIT, &elm->cmds_todo);
			/* Init finished. */
		}

	} else if (test_and_clear_bit(CAN327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATCSM%i\r",
			 !!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));

	} else if (test_and_clear_bit(CAN327_TX_DO_RESPONSES, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATR%i\r",
			 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));

	} else if (test_and_clear_bit(CAN327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATPC\r");
		set_bit(CAN327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);

	} else if (test_and_clear_bit(CAN327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATPB%04X\r",
			 elm->can_config);

	} else if (test_and_clear_bit(CAN327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATCP%02X\r",
			 (frame->can_id & CAN_EFF_MASK) >> 24);

	} else if (test_and_clear_bit(CAN327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATSH%06X\r",
			 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));

	} else if (test_and_clear_bit(CAN327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATSH%03X\r",
			 frame->can_id & CAN_SFF_MASK);

	} else if (test_and_clear_bit(CAN327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
		if (frame->can_id & CAN_RTR_FLAG) {
			/* Send an RTR frame. Their DLC is fixed.
			 * Some chips don't send them at all.
			 */
			snprintf(local_txbuf, sizeof(local_txbuf), "ATRTR\r");
		} else {
			/* Send a regular CAN data frame */
			int i;

			for (i = 0; i < frame->len; i++) {
				snprintf(&local_txbuf[2 * i],
					 sizeof(local_txbuf), "%02X",
					 frame->data[i]);
			}

			snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
				 "\r");
		}

		elm->drop_next_line = 1;
		elm->state = CAN327_STATE_RECEIVING;

		/* We will be in the default state once this command is
		 * sent, so enable the TX packet queue.
		 */
		netif_wake_queue(elm->dev);
	}

	can327_send(elm, local_txbuf, strlen(local_txbuf));
}

static bool can327_is_ready_char(char c)
{
	/* Bits 0xc0 are sometimes set (randomly), hence the mask.
	 * Probably bad hardware.
	 */
	return (c & 0x3f) == CAN327_READY_CHAR;
}

static void can327_drop_bytes(struct can327 *elm, size_t i)
{
	lockdep_assert_held(&elm->lock);

	memmove(&elm->rxbuf[0], &elm->rxbuf[i], CAN327_SIZE_RXBUF - i);
	elm->rxfill -= i;
}

static void can327_parse_rxbuf(struct can327 *elm, size_t first_new_char_idx)
{
	size_t len, pos;

	lockdep_assert_held(&elm->lock);

	switch (elm->state) {
	case CAN327_STATE_NOTINIT:
		elm->rxfill = 0;
		break;

	case CAN327_STATE_GETDUMMYCHAR:
		/* Wait for 'y' or '>' */
		for (pos = 0; pos < elm->rxfill; pos++) {
			if (elm->rxbuf[pos] == CAN327_DUMMY_CHAR) {
				can327_send(elm, "\r", 1);
				elm->state = CAN327_STATE_GETPROMPT;
				pos++;
				break;
			} else if (can327_is_ready_char(elm->rxbuf[pos])) {
				can327_send(elm, CAN327_DUMMY_STRING, 1);
				pos++;
				break;
			}
		}

		can327_drop_bytes(elm, pos);
		break;

	case CAN327_STATE_GETPROMPT:
		/* Wait for '>' */
		if (can327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
			can327_handle_prompt(elm);

		elm->rxfill = 0;
		break;

	case CAN327_STATE_RECEIVING:
		/* Find <CR> delimiting feedback lines. */
		len = first_new_char_idx;
		while (len < elm->rxfill && elm->rxbuf[len] != '\r')
			len++;

		if (len == CAN327_SIZE_RXBUF) {
			/* Assume the buffer ran full with garbage.
			 * Did we even connect at the right baud rate?
			 */
			netdev_err(elm->dev,
				   "RX buffer overflow. Faulty ELM327 or UART?\n");
			can327_uart_side_failure(elm);
		} else if (len == elm->rxfill) {
			if (can327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
				/* The ELM327's AT ST response timeout ran out,
				 * so we got a prompt.
				 * Clear RX buffer and restart listening.
				 */
				elm->rxfill = 0;

				can327_handle_prompt(elm);
			}

			/* No <CR> found - we haven't received a full line yet.
			 * Wait for more data.
			 */
		} else {
			/* We have a full line to parse. */
			can327_parse_line(elm, len);

			/* Remove parsed data from RX buffer. */
			can327_drop_bytes(elm, len + 1);

			/* More data to parse? */
			if (elm->rxfill)
				can327_parse_rxbuf(elm, 0);
		}
	}
}

static int can327_netdev_open(struct net_device *dev)
{
	struct can327 *elm = netdev_priv(dev);
	int err;

	spin_lock_bh(&elm->lock);

	if (!elm->tty) {
		spin_unlock_bh(&elm->lock);
		return -ENODEV;
	}

	if (elm->uart_side_failure)
		netdev_warn(elm->dev,
			    "Reopening netdev after a UART side fault has been detected.\n");

	/* Clear TTY buffers */
	elm->rxfill = 0;
	elm->txleft = 0;

	/* open_candev() checks for elm->can.bittiming.bitrate != 0 */
	err = open_candev(dev);
	if (err) {
		spin_unlock_bh(&elm->lock);
		return err;
	}

	can327_init_device(elm);
	spin_unlock_bh(&elm->lock);

	err = can_rx_offload_add_manual(dev, &elm->offload, CAN327_NAPI_WEIGHT);
	if (err) {
		close_candev(dev);
		return err;
	}

	can_rx_offload_enable(&elm->offload);

	elm->can.state = CAN_STATE_ERROR_ACTIVE;
	netif_start_queue(dev);

	return 0;
}

static int can327_netdev_close(struct net_device *dev)
{
	struct can327 *elm = netdev_priv(dev);

	/* Interrupt whatever the ELM327 is doing right now */
	spin_lock_bh(&elm->lock);
	can327_send(elm, CAN327_DUMMY_STRING, 1);
	spin_unlock_bh(&elm->lock);

	netif_stop_queue(dev);

	/* We don't flush the UART TX queue here, as we want final stop
	 * commands (like the above dummy char) to be flushed out.
	 */

	can_rx_offload_disable(&elm->offload);
	elm->can.state = CAN_STATE_STOPPED;
	can_rx_offload_del(&elm->offload);
	close_candev(dev);

	return 0;
}

/* Send a can_frame to a TTY. */
static netdev_tx_t can327_netdev_start_xmit(struct sk_buff *skb,
					    struct net_device *dev)
{
	struct can327 *elm = netdev_priv(dev);
	struct can_frame *frame = (struct can_frame *)skb->data;

	if (can_dev_dropped_skb(dev, skb))
		return NETDEV_TX_OK;

	/* We shouldn't get here after a hardware fault:
	 * can_bus_off() calls netif_carrier_off()
	 */
	if (elm->uart_side_failure) {
		WARN_ON_ONCE(elm->uart_side_failure);
		goto out;
	}

	netif_stop_queue(dev);

	/* BHs are already disabled, so no spin_lock_bh().
	 * See Documentation/networking/netdevices.rst
	 */
	spin_lock(&elm->lock);
	can327_send_frame(elm, frame);
	spin_unlock(&elm->lock);

	dev->stats.tx_packets++;
	dev->stats.tx_bytes += frame->can_id & CAN_RTR_FLAG ? 0 : frame->len;

	skb_tx_timestamp(skb);

out:
	kfree_skb(skb);
	return NETDEV_TX_OK;
}

static const struct net_device_ops can327_netdev_ops = {
	.ndo_open = can327_netdev_open,
	.ndo_stop = can327_netdev_close,
	.ndo_start_xmit = can327_netdev_start_xmit,
	.ndo_change_mtu = can_change_mtu,
};

static const struct ethtool_ops can327_ethtool_ops = {
	.get_ts_info = ethtool_op_get_ts_info,
};

static bool can327_is_valid_rx_char(u8 c)
{
	static const bool lut_char_is_valid['z'] = {
		['\r'] = true,
		[' '] = true,
		['.'] = true,
		['0'] = true, true, true, true, true,
		['5'] = true, true, true, true, true,
		['<'] = true,
		[CAN327_READY_CHAR] = true,
		['?'] = true,
		['A'] = true, true, true, true, true, true, true,
		['H'] = true, true, true, true, true, true, true,
		['O'] = true, true, true, true, true, true, true,
		['V'] = true, true, true, true, true,
		['a'] = true,
		['b'] = true,
		['v'] = true,
		[CAN327_DUMMY_CHAR] = true,
	};
	BUILD_BUG_ON(CAN327_DUMMY_CHAR >= 'z');

	return (c < ARRAY_SIZE(lut_char_is_valid) && lut_char_is_valid[c]);
}

/* Handle incoming ELM327 ASCII data.
 * This will not be re-entered while running, but other ldisc
 * functions may be called in parallel.
 */
static void can327_ldisc_rx(struct tty_struct *tty, const u8 *cp,
			    const u8 *fp, size_t count)
{
	struct can327 *elm = tty->disc_data;
	size_t first_new_char_idx;

	if (elm->uart_side_failure)
		return;

	spin_lock_bh(&elm->lock);

	/* Store old rxfill, so can327_parse_rxbuf() will have
	 * the option of skipping already checked characters.
	 */
	first_new_char_idx = elm->rxfill;

	while (count--) {
		if (elm->rxfill >= CAN327_SIZE_RXBUF) {
			netdev_err(elm->dev,
				   "Receive buffer overflowed. Bad chip or wiring? count = %zu",
				   count);
			goto uart_failure;
		}
		if (fp && *fp++) {
			netdev_err(elm->dev,
				   "Error in received character stream. Check your wiring.");
			goto uart_failure;
		}

		/* Ignore NUL characters, which the PIC microcontroller may
		 * inadvertently insert due to a known hardware bug.
		 * See ELM327 documentation, which refers to a Microchip PIC
		 * bug description.
		 */
		if (*cp) {
			/* Check for stray characters on the UART line.
			 * Likely caused by bad hardware.
			 */
			if (!can327_is_valid_rx_char(*cp)) {
				netdev_err(elm->dev,
					   "Received illegal character %02x.\n",
					   *cp);
				goto uart_failure;
			}

			elm->rxbuf[elm->rxfill++] = *cp;
		}

		cp++;
	}

	can327_parse_rxbuf(elm, first_new_char_idx);
	spin_unlock_bh(&elm->lock);

	return;
uart_failure:
	can327_uart_side_failure(elm);
	spin_unlock_bh(&elm->lock);
}

/* Write out remaining transmit buffer.
 * Scheduled when TTY is writable.
 */
static void can327_ldisc_tx_worker(struct work_struct *work)
{
	struct can327 *elm = container_of(work, struct can327, tx_work);
	ssize_t written;

	if (elm->uart_side_failure)
		return;

	spin_lock_bh(&elm->lock);

	if (elm->txleft) {
		written = elm->tty->ops->write(elm->tty, elm->txhead,
					       elm->txleft);
		if (written < 0) {
			netdev_err(elm->dev, "Failed to write to tty %s.\n",
				   elm->tty->name);
			can327_uart_side_failure(elm);

			spin_unlock_bh(&elm->lock);
			return;
		}

		elm->txleft -= written;
		elm->txhead += written;
	}

	if (!elm->txleft)
		clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);

	spin_unlock_bh(&elm->lock);
}

/* Called by the driver when there's room for more data. */
static void can327_ldisc_tx_wakeup(struct tty_struct *tty)
{
	struct can327 *elm = tty->disc_data;

	schedule_work(&elm->tx_work);
}

/* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
 * or 7/8 of that. Divisors are 1 to 64.
 * Currently we don't implement support for 7/8 rates.
 */
static const u32 can327_bitrate_const[] = {
	7812,  7936,  8064,  8196,   8333,   8474,   8620,   8771,
	8928,  9090,  9259,  9433,   9615,   9803,   10000,  10204,
	10416, 10638, 10869, 11111,  11363,  11627,  11904,  12195,
	12500, 12820, 13157, 13513,  13888,  14285,  14705,  15151,
	15625, 16129, 16666, 17241,  17857,  18518,  19230,  20000,
	20833, 21739, 22727, 23809,  25000,  26315,  27777,  29411,
	31250, 33333, 35714, 38461,  41666,  45454,  50000,  55555,
	62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
};

static int can327_ldisc_open(struct tty_struct *tty)
{
	struct net_device *dev;
	struct can327 *elm;
	int err;

	if (!capable(CAP_NET_ADMIN))
		return -EPERM;

	if (!tty->ops->write)
		return -EOPNOTSUPP;

	dev = alloc_candev(sizeof(struct can327), 0);
	if (!dev)
		return -ENFILE;
	elm = netdev_priv(dev);

	/* Configure TTY interface */
	tty->receive_room = 65536; /* We don't flow control */
	spin_lock_init(&elm->lock);
	INIT_WORK(&elm->tx_work, can327_ldisc_tx_worker);

	/* Configure CAN metadata */
	elm->can.bitrate_const = can327_bitrate_const;
	elm->can.bitrate_const_cnt = ARRAY_SIZE(can327_bitrate_const);
	elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;

	/* Configure netdev interface */
	elm->dev = dev;
	dev->netdev_ops = &can327_netdev_ops;
	dev->ethtool_ops = &can327_ethtool_ops;

	/* Mark ldisc channel as alive */
	elm->tty = tty;
	tty->disc_data = elm;

	/* Let 'er rip */
	err = register_candev(elm->dev);
	if (err) {
		free_candev(elm->dev);
		return err;
	}

	netdev_info(elm->dev, "can327 on %s.\n", tty->name);

	return 0;
}

/* Close down a can327 channel.
 * This means flushing out any pending queues, and then returning.
 * This call is serialized against other ldisc functions:
 * Once this is called, no other ldisc function of ours is entered.
 *
 * We also use this function for a hangup event.
 */
static void can327_ldisc_close(struct tty_struct *tty)
{
	struct can327 *elm = tty->disc_data;

	/* unregister_netdev() calls .ndo_stop() so we don't have to. */
	unregister_candev(elm->dev);

	/* Give UART one final chance to flush.
	 * No need to clear TTY_DO_WRITE_WAKEUP since .write_wakeup() is
	 * serialised against .close() and will not be called once we return.
	 */
	flush_work(&elm->tx_work);

	/* Mark channel as dead */
	spin_lock_bh(&elm->lock);
	tty->disc_data = NULL;
	elm->tty = NULL;
	spin_unlock_bh(&elm->lock);

	netdev_info(elm->dev, "can327 off %s.\n", tty->name);

	free_candev(elm->dev);
}

static int can327_ldisc_ioctl(struct tty_struct *tty, unsigned int cmd,
			      unsigned long arg)
{
	struct can327 *elm = tty->disc_data;
	unsigned int tmp;

	switch (cmd) {
	case SIOCGIFNAME:
		tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
		if (copy_to_user((void __user *)arg, elm->dev->name, tmp))
			return -EFAULT;
		return 0;

	case SIOCSIFHWADDR:
		return -EINVAL;

	default:
		return tty_mode_ioctl(tty, cmd, arg);
	}
}

static struct tty_ldisc_ops can327_ldisc = {
	.owner = THIS_MODULE,
	.name = KBUILD_MODNAME,
	.num = N_CAN327,
	.receive_buf = can327_ldisc_rx,
	.write_wakeup = can327_ldisc_tx_wakeup,
	.open = can327_ldisc_open,
	.close = can327_ldisc_close,
	.ioctl = can327_ldisc_ioctl,
};

static int __init can327_init(void)
{
	int status;

	status = tty_register_ldisc(&can327_ldisc);
	if (status)
		pr_err("Can't register line discipline\n");

	return status;
}

static void __exit can327_exit(void)
{
	/* This will only be called when all channels have been closed by
	 * userspace - tty_ldisc.c takes care of the module's refcount.
	 */
	tty_unregister_ldisc(&can327_ldisc);
}

module_init(can327_init);
module_exit(can327_exit);

MODULE_ALIAS_LDISC(N_CAN327);
MODULE_DESCRIPTION("ELM327 based CAN interface");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Max Staudt <max@enpas.org>");