1 // SPDX-License-Identifier: GPL-2.0
2 /* ELM327 based CAN interface driver (tty line discipline)
4 * This driver started as a derivative of linux/drivers/net/can/slcan.c
5 * and my thanks go to the original authors for their inspiration, even
6 * after almost none of their code is left.
8 * elmcan.c Author : Max Staudt <max-linux@enpas.org>
9 * slcan.c Author : Oliver Hartkopp <socketcan@hartkopp.net>
10 * slip.c Authors : Laurence Culhane <loz@holmes.demon.co.uk>
11 * Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
14 #define pr_fmt(fmt) "elmcan: " fmt
16 #include <linux/init.h>
17 #include <linux/module.h>
18 #include <linux/moduleparam.h>
20 #include <linux/atomic.h>
21 #include <linux/bitops.h>
22 #include <linux/ctype.h>
23 #include <linux/delay.h>
24 #include <linux/errno.h>
25 #include <linux/if_ether.h>
26 #include <linux/kernel.h>
27 #include <linux/list.h>
28 #include <linux/netdevice.h>
29 #include <linux/skbuff.h>
30 #include <linux/spinlock.h>
31 #include <linux/string.h>
32 #include <linux/tty.h>
33 #include <linux/tty_ldisc.h>
34 #include <linux/version.h>
35 #include <linux/workqueue.h>
37 #include <uapi/linux/tty.h>
39 #include <linux/can.h>
40 #include <linux/can/dev.h>
41 #include <linux/can/error.h>
42 #include <linux/can/led.h>
43 #include <linux/can/rx-offload.h>
45 /* Line discipline ID number.
46 * N_DEVELOPMENT will likely be defined from Linux 5.18 onwards:
47 * https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git/commit/?h=tty-next&id=c2faf737abfb10f88f2d2612d573e9edc3c42c37
50 #define N_DEVELOPMENT 29
53 /* Compatibility for Linux < 5.11 */
54 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,11,0)
58 #define ELM327_NAPI_WEIGHT 4
60 #define ELM327_SIZE_RXBUF 256
61 #define ELM327_SIZE_TXBUF 32
63 #define ELM327_CAN_CONFIG_SEND_SFF 0x8000
64 #define ELM327_CAN_CONFIG_VARIABLE_DLC 0x4000
65 #define ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF 0x2000
66 #define ELM327_CAN_CONFIG_BAUDRATE_MULT_8_7 0x1000
68 #define ELM327_DUMMY_CHAR 'y'
69 #define ELM327_DUMMY_STRING "y"
70 #define ELM327_READY_CHAR '>'
72 /* Bits in elm->cmds_todo */
73 enum ELM327_TX_DO_BITS {
74 ELM327_TX_DO_CAN_DATA = 0,
75 ELM327_TX_DO_CANID_11BIT,
76 ELM327_TX_DO_CANID_29BIT_LOW,
77 ELM327_TX_DO_CANID_29BIT_HIGH,
78 ELM327_TX_DO_CAN_CONFIG_PART2,
79 ELM327_TX_DO_CAN_CONFIG,
80 ELM327_TX_DO_RESPONSES,
81 ELM327_TX_DO_SILENT_MONITOR,
86 /* This must be the first member when using alloc_candev() */
89 struct can_rx_offload offload;
91 /* TTY and netdev devices that we're bridging */
92 struct tty_struct *tty;
93 struct net_device *dev;
95 /* Per-channel lock */
98 /* Keep track of how many things are using this struct.
99 * Once it reaches 0, we are in the process of cleaning up,
100 * and new operations will be cancelled immediately.
101 * Use atomic_t rather than refcount_t because we deliberately
102 * decrement to 0, and refcount_dec() spills a WARN_ONCE in
107 /* Stop the channel on hardware failure.
108 * Once this is true, nothing will be sent to the TTY.
113 struct work_struct tx_work; /* Flushes TTY TX buffer */
114 unsigned char *txbuf;
115 unsigned char *txhead; /* Pointer to next TX byte */
116 int txleft; /* Bytes left to TX */
119 unsigned char rxbuf[ELM327_SIZE_RXBUF];
124 ELM327_STATE_NOTINIT = 0,
125 ELM327_STATE_GETDUMMYCHAR,
126 ELM327_STATE_GETPROMPT,
127 ELM327_STATE_RECEIVING,
132 /* The CAN frame and config the ELM327 is sending/using,
133 * or will send/use after finishing all cmds_todo
135 struct can_frame can_frame_to_send;
136 unsigned short can_config;
137 unsigned long can_bitrate;
138 unsigned char can_bitrate_divisor;
139 int silent_monitoring;
141 /* Things we have yet to send */
142 char **next_init_cmd;
143 unsigned long cmds_todo;
146 /* A lock for all tty->disc_data handled by this ldisc.
147 * This is to prevent a case where tty->disc_data is set to NULL,
148 * yet someone is still trying to dereference it.
149 * Without this, we cannot do a clean shutdown.
151 static DEFINE_SPINLOCK(elmcan_discdata_lock);
153 static inline void elm327_hw_failure(struct elmcan *elm);
155 /* Assumes elm->lock taken. */
156 static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
163 memcpy(elm->txbuf, buf, len);
165 /* Order of next two lines is *very* important.
166 * When we are sending a little amount of data,
167 * the transfer may be completed inside the ops->write()
168 * routine, because it's running with interrupts enabled.
169 * In this case we *never* got WRITE_WAKEUP event,
170 * if we did not request it before write operation.
171 * 14 Oct 1994 Dmitry Gorodchanin.
173 set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
174 actual = elm->tty->ops->write(elm->tty, elm->txbuf, len);
177 "Failed to write to tty %s.\n",
179 elm327_hw_failure(elm);
183 elm->txleft = len - actual;
184 elm->txhead = elm->txbuf + actual;
187 /* Take the ELM327 out of almost any state and back into command mode.
188 * We send ELM327_DUMMY_CHAR which will either abort any running
189 * operation, or be echoed back to us in case we're already in command
192 * Assumes elm->lock taken.
194 static void elm327_kick_into_cmd_mode(struct elmcan *elm)
196 if (elm->state != ELM327_STATE_GETDUMMYCHAR &&
197 elm->state != ELM327_STATE_GETPROMPT) {
198 elm327_send(elm, ELM327_DUMMY_STRING, 1);
200 elm->state = ELM327_STATE_GETDUMMYCHAR;
204 /* Schedule a CAN frame and necessary config changes to be sent to the TTY.
206 * Assumes elm->lock taken.
208 static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
210 /* Schedule any necessary changes in ELM327's CAN configuration */
211 if (elm->can_frame_to_send.can_id != frame->can_id) {
212 /* Set the new CAN ID for transmission. */
213 if ((frame->can_id & CAN_EFF_FLAG)
214 ^ (elm->can_frame_to_send.can_id & CAN_EFF_FLAG)) {
215 elm->can_config = (frame->can_id & CAN_EFF_FLAG
217 : ELM327_CAN_CONFIG_SEND_SFF)
218 | ELM327_CAN_CONFIG_VARIABLE_DLC
219 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
220 | elm->can_bitrate_divisor;
222 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
225 if (frame->can_id & CAN_EFF_FLAG) {
226 clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
227 set_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
228 set_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
230 set_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
231 clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
232 clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
236 /* Schedule the CAN frame itself. */
237 elm->can_frame_to_send = *frame;
238 set_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo);
240 elm327_kick_into_cmd_mode(elm);
243 /* ELM327 initialization sequence.
245 * Assumes elm->lock taken.
247 static char *elm327_init_script[] = {
248 "AT WS\r", /* v1.0: Warm Start */
249 "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
250 "AT M0\r", /* v1.0: Memory Off */
251 "AT AL\r", /* v1.0: Allow Long messages */
252 "AT BI\r", /* v1.0: Bypass Initialization */
253 "AT CAF0\r", /* v1.0: CAN Auto Formatting Off */
254 "AT CFC0\r", /* v1.0: CAN Flow Control Off */
255 "AT CF 000\r", /* v1.0: Reset CAN ID Filter */
256 "AT CM 000\r", /* v1.0: Reset CAN ID Mask */
257 "AT E1\r", /* v1.0: Echo On */
258 "AT H1\r", /* v1.0: Headers On */
259 "AT L0\r", /* v1.0: Linefeeds Off */
260 "AT SH 7DF\r", /* v1.0: Set CAN sending ID to 0x7df */
261 "AT ST FF\r", /* v1.0: Set maximum Timeout for response after TX */
262 "AT AT0\r", /* v1.2: Adaptive Timing Off */
263 "AT D1\r", /* v1.3: Print DLC On */
264 "AT S1\r", /* v1.3: Spaces On */
265 "AT TP B\r", /* v1.0: Try Protocol B */
269 static void elm327_init(struct elmcan *elm)
271 elm->state = ELM327_STATE_NOTINIT;
272 elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
274 elm->drop_next_line = 0;
276 /* We can only set the bitrate as a fraction of 500000.
277 * The bit timing constants in elmcan_bittiming_const will
278 * limit the user to the right values.
280 elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
281 elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
282 | ELM327_CAN_CONFIG_VARIABLE_DLC
283 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
284 | elm->can_bitrate_divisor;
286 /* Configure ELM327 and then start monitoring */
287 elm->next_init_cmd = &elm327_init_script[0];
288 set_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
289 set_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
290 set_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo);
291 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
293 elm327_kick_into_cmd_mode(elm);
296 /* Assumes elm->lock taken. */
297 static void elm327_feed_frame_to_netdev(struct elmcan *elm,
300 if (!netif_running(elm->dev))
303 /* Queue for NAPI pickup.
304 * rx-offload will update stats and LEDs for us.
306 if (can_rx_offload_queue_tail(&elm->offload, skb))
307 elm->dev->stats.rx_fifo_errors++;
309 #if LINUX_VERSION_CODE >= KERNEL_VERSION(5,15,0)
311 can_rx_offload_irq_finish(&elm->offload);
315 /* Called when we're out of ideas and just want it all to end.
316 * Assumes elm->lock taken.
318 static inline void elm327_hw_failure(struct elmcan *elm)
320 struct can_frame *frame;
323 elm->hw_failure = true;
325 elm->can.can_stats.bus_off++;
326 netif_stop_queue(elm->dev);
327 elm->can.state = CAN_STATE_BUS_OFF;
328 can_bus_off(elm->dev);
330 netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
332 skb = alloc_can_err_skb(elm->dev, &frame);
336 frame->can_id |= CAN_ERR_BUSOFF;
337 elm327_feed_frame_to_netdev(elm, skb);
340 /* Compare a buffer to a fixed string */
341 static inline int _memstrcmp(const u8 *mem, const char *str)
343 return memcmp(mem, str, strlen(str));
346 /* Compare buffer to string length, then compare buffer to fixed string.
347 * This ensures two things:
348 * - It flags cases where the fixed string is only the start of the
349 * buffer, rather than exactly all of it.
350 * - It avoids byte comparisons in case the length doesn't match.
352 static inline int _len_memstrcmp(const u8 *mem, size_t mem_len, const char *str)
354 size_t str_len = strlen(str);
356 return (mem_len != str_len) || memcmp(mem, str, str_len);
359 /* Assumes elm->lock taken. */
360 static void elm327_parse_error(struct elmcan *elm, size_t len)
362 struct can_frame *frame;
365 skb = alloc_can_err_skb(elm->dev, &frame);
367 /* It's okay to return here:
368 * The outer parsing loop will drop this UART buffer.
372 /* Filter possible error messages based on length of RX'd line */
373 if (!_len_memstrcmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
375 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
376 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUFFER FULL")) {
377 /* This will only happen if the last data line was complete.
378 * Otherwise, elm327_parse_frame() will heuristically
379 * emit this kind of error frame instead.
381 frame->can_id |= CAN_ERR_CRTL;
382 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
383 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS ERROR")) {
384 frame->can_id |= CAN_ERR_BUSERROR;
385 } else if (!_len_memstrcmp(elm->rxbuf, len, "CAN ERROR")) {
386 frame->can_id |= CAN_ERR_PROT;
387 } else if (!_len_memstrcmp(elm->rxbuf, len, "<RX ERROR")) {
388 frame->can_id |= CAN_ERR_PROT;
389 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS BUSY")) {
390 frame->can_id |= CAN_ERR_PROT;
391 frame->data[2] = CAN_ERR_PROT_OVERLOAD;
392 } else if (!_len_memstrcmp(elm->rxbuf, len, "FB ERROR")) {
393 frame->can_id |= CAN_ERR_PROT;
394 frame->data[2] = CAN_ERR_PROT_TX;
395 } else if (len == 5 && !_memstrcmp(elm->rxbuf, "ERR")) {
396 /* ERR is followed by two digits, hence line length 5 */
397 netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
398 elm->rxbuf[3], elm->rxbuf[4]);
399 frame->can_id |= CAN_ERR_CRTL;
401 /* Something else has happened.
402 * Maybe garbage on the UART line.
403 * Emit a generic error frame.
407 elm327_feed_frame_to_netdev(elm, skb);
410 /* Parse CAN frames coming as ASCII from ELM327.
411 * They can be of various formats:
413 * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
414 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
416 * where D = DLC, PL = payload byte
418 * Instead of a payload, RTR indicates a remote request.
420 * We will use the spaces and line length to guess the format.
422 * Assumes elm->lock taken.
424 static int elm327_parse_frame(struct elmcan *elm, size_t len)
426 struct can_frame *frame;
432 skb = alloc_can_skb(elm->dev, &frame);
436 /* Find first non-hex and non-space character:
437 * - In the simplest case, there is none.
438 * - For RTR frames, 'R' is the first non-hex character.
439 * - An error message may replace the end of the data line.
441 for (hexlen = 0; hexlen <= len; hexlen++) {
442 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
443 elm->rxbuf[hexlen] != ' ') {
448 /* Sanity check whether the line is really a clean hexdump,
449 * or terminated by an error message, or contains garbage.
452 !isdigit(elm->rxbuf[hexlen]) &&
453 !isupper(elm->rxbuf[hexlen]) &&
454 '<' != elm->rxbuf[hexlen] &&
455 ' ' != elm->rxbuf[hexlen]) {
456 /* The line is likely garbled anyway, so bail.
457 * The main code will restart listening.
462 /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
463 * No out-of-bounds access:
464 * We use the fact that we can always read from elm->rxbuf.
466 if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
467 elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
468 elm->rxbuf[13] == ' ') {
469 frame->can_id = CAN_EFF_FLAG;
471 } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
475 /* This is not a well-formatted data line.
476 * Assume it's an error message.
481 if (hexlen < datastart) {
482 /* The line is too short to be a valid frame hex dump.
483 * Something interrupted the hex dump or it is invalid.
488 /* From here on all chars up to buf[hexlen] are hex or spaces,
489 * at well-defined offsets.
492 /* Read CAN data length */
493 frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
496 if (frame->can_id & CAN_EFF_FLAG) {
497 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
498 | (hex_to_bin(elm->rxbuf[1]) << 24)
499 | (hex_to_bin(elm->rxbuf[3]) << 20)
500 | (hex_to_bin(elm->rxbuf[4]) << 16)
501 | (hex_to_bin(elm->rxbuf[6]) << 12)
502 | (hex_to_bin(elm->rxbuf[7]) << 8)
503 | (hex_to_bin(elm->rxbuf[9]) << 4)
504 | (hex_to_bin(elm->rxbuf[10]) << 0);
506 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
507 | (hex_to_bin(elm->rxbuf[1]) << 4)
508 | (hex_to_bin(elm->rxbuf[2]) << 0);
511 /* Check for RTR frame */
512 if (elm->rxfill >= hexlen + 3 &&
513 !_memstrcmp(&elm->rxbuf[hexlen], "RTR")) {
514 frame->can_id |= CAN_RTR_FLAG;
517 /* Is the line long enough to hold the advertised payload?
518 * Note: RTR frames have a DLC, but no actual payload.
520 if (!(frame->can_id & CAN_RTR_FLAG) &&
521 (hexlen < frame->len * 3 + datastart)) {
523 * Probably the ELM327's RS232 TX buffer was full.
524 * Emit an error frame and exit.
526 frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
527 frame->len = CAN_ERR_DLC;
528 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
529 elm327_feed_frame_to_netdev(elm, skb);
531 /* Signal failure to parse.
532 * The line will be re-parsed as an error line, which will fail.
533 * However, this will correctly drop the state machine back into
539 /* Parse the data nibbles. */
540 for (i = 0; i < frame->len; i++) {
541 frame->data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
542 | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
545 /* Feed the frame to the network layer. */
546 elm327_feed_frame_to_netdev(elm, skb);
551 /* Assumes elm->lock taken. */
552 static void elm327_parse_line(struct elmcan *elm, size_t len)
554 /* Skip empty lines */
558 /* Skip echo lines */
559 if (elm->drop_next_line) {
560 elm->drop_next_line = 0;
562 } else if (!_memstrcmp(elm->rxbuf, "AT")) {
566 /* Regular parsing */
567 if (elm->state == ELM327_STATE_RECEIVING
568 && elm327_parse_frame(elm, len)) {
569 /* Parse an error line. */
570 elm327_parse_error(elm, len);
573 elm327_kick_into_cmd_mode(elm);
577 /* Assumes elm->lock taken. */
578 static void elm327_handle_prompt(struct elmcan *elm)
580 struct can_frame *frame = &elm->can_frame_to_send;
581 char local_txbuf[20];
583 if (!elm->cmds_todo) {
584 /* Enter CAN monitor mode */
585 elm327_send(elm, "ATMA\r", 5);
586 elm->state = ELM327_STATE_RECEIVING;
591 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
592 if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
593 strcpy(local_txbuf, *elm->next_init_cmd);
595 elm->next_init_cmd++;
596 if (!(*elm->next_init_cmd)) {
597 clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
601 } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
602 sprintf(local_txbuf, "ATCSM%i\r",
603 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
605 } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo)) {
606 sprintf(local_txbuf, "ATR%i\r",
607 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
609 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
610 sprintf(local_txbuf, "ATPC\r");
611 set_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);
613 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
614 sprintf(local_txbuf, "ATPB%04X\r",
617 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
618 sprintf(local_txbuf, "ATCP%02X\r",
619 (frame->can_id & CAN_EFF_MASK) >> 24);
621 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
622 sprintf(local_txbuf, "ATSH%06X\r",
623 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
625 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
626 sprintf(local_txbuf, "ATSH%03X\r",
627 frame->can_id & CAN_SFF_MASK);
629 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
630 if (frame->can_id & CAN_RTR_FLAG) {
631 /* Send an RTR frame. Their DLC is fixed.
632 * Some chips don't send them at all.
634 sprintf(local_txbuf, "ATRTR\r");
636 /* Send a regular CAN data frame */
639 for (i = 0; i < frame->len; i++) {
640 sprintf(&local_txbuf[2 * i], "%02X",
644 sprintf(&local_txbuf[2 * i], "\r");
647 elm->drop_next_line = 1;
648 elm->state = ELM327_STATE_RECEIVING;
651 elm327_send(elm, local_txbuf, strlen(local_txbuf));
654 static bool elm327_is_ready_char(char c)
656 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
657 * Probably bad hardware.
659 return (c & 0x3f) == ELM327_READY_CHAR;
662 /* Assumes elm->lock taken. */
663 static void elm327_drop_bytes(struct elmcan *elm, size_t i)
665 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
669 /* Assumes elm->lock taken. */
670 static void elm327_parse_rxbuf(struct elmcan *elm)
675 switch (elm->state) {
676 case ELM327_STATE_NOTINIT:
680 case ELM327_STATE_GETDUMMYCHAR:
682 /* Wait for 'y' or '>' */
683 for (i = 0; i < elm->rxfill; i++) {
684 if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
685 elm327_send(elm, "\r", 1);
686 elm->state = ELM327_STATE_GETPROMPT;
689 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
690 elm327_send(elm, ELM327_DUMMY_STRING, 1);
696 elm327_drop_bytes(elm, i);
701 case ELM327_STATE_GETPROMPT:
703 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
704 elm327_handle_prompt(elm);
709 case ELM327_STATE_RECEIVING:
710 /* Find <CR> delimiting feedback lines. */
712 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
717 if (len == ELM327_SIZE_RXBUF) {
718 /* Line exceeds buffer. It's probably all garbage.
719 * Did we even connect at the right baud rate?
722 "RX buffer overflow. Faulty ELM327 or UART?\n");
723 elm327_hw_failure(elm);
725 } else if (len == elm->rxfill) {
726 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
727 /* The ELM327's AT ST response timeout ran out,
728 * so we got a prompt.
729 * Clear RX buffer and restart listening.
733 elm327_handle_prompt(elm);
737 /* No <CR> found - we haven't received a full line yet.
738 * Wait for more data.
743 /* We have a full line to parse. */
744 elm327_parse_line(elm, len);
746 /* Remove parsed data from RX buffer. */
747 elm327_drop_bytes(elm, len + 1);
749 /* More data to parse? */
751 elm327_parse_rxbuf(elm);
755 /* Dummy needed to use can_rx_offload */
756 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
757 unsigned int n, u32 *timestamp,
760 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
762 return ERR_PTR(-ENOBUFS);
765 static int elmcan_netdev_open(struct net_device *dev)
767 struct elmcan *elm = netdev_priv(dev);
770 spin_lock_bh(&elm->lock);
771 if (elm->hw_failure) {
772 netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
773 spin_unlock_bh(&elm->lock);
778 spin_unlock_bh(&elm->lock);
782 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
783 err = open_candev(dev);
785 spin_unlock_bh(&elm->lock);
790 spin_unlock_bh(&elm->lock);
792 elm->offload.mailbox_read = elmcan_mailbox_read;
793 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
799 can_rx_offload_enable(&elm->offload);
801 can_led_event(dev, CAN_LED_EVENT_OPEN);
802 elm->can.state = CAN_STATE_ERROR_ACTIVE;
803 netif_start_queue(dev);
808 static int elmcan_netdev_close(struct net_device *dev)
810 struct elmcan *elm = netdev_priv(dev);
812 netif_stop_queue(dev);
814 spin_lock_bh(&elm->lock);
816 /* Interrupt whatever we're doing right now */
817 elm327_send(elm, ELM327_DUMMY_STRING, 1);
819 /* Clear the wakeup bit, as the netdev will be down and thus
820 * the wakeup handler won't clear it
822 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
824 spin_unlock_bh(&elm->lock);
826 flush_work(&elm->tx_work);
828 spin_unlock_bh(&elm->lock);
831 can_rx_offload_disable(&elm->offload);
832 elm->can.state = CAN_STATE_STOPPED;
833 can_rx_offload_del(&elm->offload);
835 can_led_event(dev, CAN_LED_EVENT_STOP);
840 /* Send a can_frame to a TTY. */
841 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
842 struct net_device *dev)
844 struct elmcan *elm = netdev_priv(dev);
845 struct can_frame *frame = (struct can_frame *)skb->data;
847 /* BHs are already disabled, so no spin_lock_bh().
848 * See Documentation/networking/netdevices.txt
850 spin_lock(&elm->lock);
852 /* We shouldn't get here after a hardware fault:
853 * can_bus_off() calls netif_carrier_off()
855 WARN_ON_ONCE(elm->hw_failure);
859 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
860 spin_unlock(&elm->lock);
864 netif_stop_queue(dev);
866 elm327_send_frame(elm, frame);
867 spin_unlock(&elm->lock);
869 dev->stats.tx_packets++;
870 dev->stats.tx_bytes += frame->len;
872 can_led_event(dev, CAN_LED_EVENT_TX);
879 static const struct net_device_ops elmcan_netdev_ops = {
880 .ndo_open = elmcan_netdev_open,
881 .ndo_stop = elmcan_netdev_close,
882 .ndo_start_xmit = elmcan_netdev_start_xmit,
883 .ndo_change_mtu = can_change_mtu,
886 /* Get a reference to our struct, taking into account locks/refcounts.
887 * This is to ensure ordering in case we are shutting down, and to ensure
888 * there is a refcount at all (otherwise tty->disc_data may be freed and
889 * before we increment the refcount).
890 * Use this for anything that can race against elmcan_ldisc_close().
892 static struct elmcan *get_elm(struct tty_struct *tty)
897 spin_lock_bh(&elmcan_discdata_lock);
898 elm = (struct elmcan *)tty->disc_data;
901 spin_unlock_bh(&elmcan_discdata_lock);
905 got_ref = atomic_inc_not_zero(&elm->refcount);
906 spin_unlock_bh(&elmcan_discdata_lock);
914 static void put_elm(struct elmcan *elm)
916 atomic_dec(&elm->refcount);
919 static bool elmcan_is_valid_rx_char(char c)
921 return (isdigit(c) ||
923 c == ELM327_DUMMY_CHAR ||
924 c == ELM327_READY_CHAR ||
935 /* Handle incoming ELM327 ASCII data.
936 * This will not be re-entered while running, but other ldisc
937 * functions may be called in parallel.
939 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
940 static void elmcan_ldisc_rx(struct tty_struct *tty,
941 const unsigned char *cp, char *fp, int count)
943 static void elmcan_ldisc_rx(struct tty_struct *tty,
944 const unsigned char *cp, const char *fp, int count)
947 struct elmcan *elm = get_elm(tty);
952 spin_lock_bh(&elm->lock);
957 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
959 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
961 elm327_hw_failure(elm);
966 /* Ignore NUL characters, which the PIC microcontroller may
967 * inadvertently insert due to a known hardware bug.
968 * See ELM327 documentation, which refers to a Microchip PIC
972 /* Check for stray characters on the UART line.
973 * Likely caused by bad hardware.
975 if (!elmcan_is_valid_rx_char(*cp)) {
977 "Received illegal character %02x.\n",
979 elm327_hw_failure(elm);
984 elm->rxbuf[elm->rxfill++] = *cp;
991 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
993 elm327_hw_failure(elm);
998 elm327_parse_rxbuf(elm);
1001 spin_unlock_bh(&elm->lock);
1005 /* Write out remaining transmit buffer.
1006 * Scheduled when TTY is writable.
1008 static void elmcan_ldisc_tx_worker(struct work_struct *work)
1010 /* No need to use get_elm() here, as we'll always flush workers
1011 * before destroying the elmcan object.
1013 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
1016 spin_lock_bh(&elm->lock);
1017 if (elm->hw_failure) {
1018 spin_unlock_bh(&elm->lock);
1022 if (!elm->tty || !netif_running(elm->dev)) {
1023 spin_unlock_bh(&elm->lock);
1027 if (elm->txleft <= 0) {
1028 /* Our TTY write buffer is empty:
1029 * Allow netdev to hand us another packet
1031 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1032 spin_unlock_bh(&elm->lock);
1033 netif_wake_queue(elm->dev);
1037 actual = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
1039 netdev_err(elm->dev,
1040 "Failed to write to tty %s.\n",
1042 elm327_hw_failure(elm);
1043 spin_unlock_bh(&elm->lock);
1047 elm->txleft -= actual;
1048 elm->txhead += actual;
1049 spin_unlock_bh(&elm->lock);
1052 /* Called by the driver when there's room for more data. */
1053 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1055 struct elmcan *elm = get_elm(tty);
1060 schedule_work(&elm->tx_work);
1065 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1066 * or 7/8 of that. Divisors are 1 to 64.
1067 * Currently we don't implement support for 7/8 rates.
1069 static const u32 elmcan_bitrate_const[64] = {
1070 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1071 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1072 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1073 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1074 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1075 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1076 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1077 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1080 /* Dummy needed to use bitrate_const */
1081 static int elmcan_do_set_bittiming(struct net_device *netdev)
1086 static int elmcan_ldisc_open(struct tty_struct *tty)
1088 struct net_device *dev;
1092 if (!capable(CAP_NET_ADMIN))
1095 if (!tty->ops->write)
1098 dev = alloc_candev(sizeof(struct elmcan), 0);
1101 elm = netdev_priv(dev);
1103 elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
1109 /* Configure TTY interface */
1110 tty->receive_room = 65536; /* We don't flow control */
1111 elm->txleft = 0; /* Clear TTY TX buffer */
1112 spin_lock_init(&elm->lock);
1113 atomic_set(&elm->refcount, 1);
1114 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1116 /* Configure CAN metadata */
1117 elm->can.state = CAN_STATE_STOPPED;
1118 elm->can.bitrate_const = elmcan_bitrate_const;
1119 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1120 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1121 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1123 /* Configure netdev interface */
1125 dev->netdev_ops = &elmcan_netdev_ops;
1127 /* Mark ldisc channel as alive */
1129 tty->disc_data = elm;
1131 devm_can_led_init(elm->dev);
1134 err = register_candev(elm->dev);
1138 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1144 free_candev(elm->dev);
1148 /* Close down an elmcan channel.
1149 * This means flushing out any pending queues, and then returning.
1150 * This call is serialized against other ldisc functions:
1151 * Once this is called, no other ldisc function of ours is entered.
1153 * We also use this function for a hangup event.
1155 static void elmcan_ldisc_close(struct tty_struct *tty)
1157 struct elmcan *elm = get_elm(tty);
1162 /* unregister_netdev() calls .ndo_stop() so we don't have to. */
1163 unregister_candev(elm->dev);
1165 /* Decrease the refcount twice, once for our own get_elm(),
1166 * and once to remove the count of 1 that we set in _open().
1167 * Once it reaches 0, we can safely destroy it.
1172 while (atomic_read(&elm->refcount) > 0)
1173 msleep_interruptible(10);
1175 /* At this point, all ldisc calls to us have become no-ops. */
1177 flush_work(&elm->tx_work);
1179 /* Mark channel as dead */
1180 spin_lock_bh(&elm->lock);
1181 tty->disc_data = NULL;
1183 spin_unlock_bh(&elm->lock);
1185 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1188 free_candev(elm->dev);
1191 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1192 static int elmcan_ldisc_hangup(struct tty_struct *tty)
1194 static void elmcan_ldisc_hangup(struct tty_struct *tty)
1197 elmcan_ldisc_close(tty);
1198 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1203 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1204 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1207 unsigned int cmd, unsigned long arg)
1209 struct elmcan *elm = get_elm(tty);
1217 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1218 if (copy_to_user((void __user *)arg, elm->dev->name, tmp)) {
1232 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1233 return tty_mode_ioctl(tty, file, cmd, arg);
1235 return tty_mode_ioctl(tty, cmd, arg);
1240 static struct tty_ldisc_ops elmcan_ldisc = {
1241 .owner = THIS_MODULE,
1243 .num = N_DEVELOPMENT,
1244 .receive_buf = elmcan_ldisc_rx,
1245 .write_wakeup = elmcan_ldisc_tx_wakeup,
1246 .open = elmcan_ldisc_open,
1247 .close = elmcan_ldisc_close,
1248 .hangup = elmcan_ldisc_hangup,
1249 .ioctl = elmcan_ldisc_ioctl,
1252 static int __init elmcan_init(void)
1256 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1257 status = tty_register_ldisc(N_DEVELOPMENT, &elmcan_ldisc);
1259 status = tty_register_ldisc(&elmcan_ldisc);
1262 pr_err("Can't register line discipline\n");
1267 static void __exit elmcan_exit(void)
1269 /* This will only be called when all channels have been closed by
1270 * userspace - tty_ldisc.c takes care of the module's refcount.
1272 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1275 status = tty_unregister_ldisc(N_DEVELOPMENT);
1277 pr_err("Can't unregister line discipline (error: %d)\n",
1280 tty_unregister_ldisc(&elmcan_ldisc);
1284 module_init(elmcan_init);
1285 module_exit(elmcan_exit);
1287 MODULE_ALIAS_LDISC(N_DEVELOPMENT);
1288 MODULE_DESCRIPTION("ELM327 based CAN interface");
1289 MODULE_LICENSE("GPL");
1290 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");