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/lockdep.h>
29 #include <linux/netdevice.h>
30 #include <linux/skbuff.h>
31 #include <linux/spinlock.h>
32 #include <linux/string.h>
33 #include <linux/tty.h>
34 #include <linux/tty_ldisc.h>
35 #include <linux/version.h>
36 #include <linux/workqueue.h>
38 #include <uapi/linux/tty.h>
40 #include <linux/can.h>
41 #include <linux/can/dev.h>
42 #include <linux/can/error.h>
43 #include <linux/can/led.h>
44 #include <linux/can/rx-offload.h>
46 /* Line discipline ID number.
47 * N_DEVELOPMENT will likely be defined from Linux 5.18 onwards:
48 * https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git/commit/?h=tty-next&id=c2faf737abfb10f88f2d2612d573e9edc3c42c37
51 #define N_DEVELOPMENT 29
54 /* Compatibility for Linux < 5.11 */
55 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,11,0)
59 #define ELM327_NAPI_WEIGHT 4
61 #define ELM327_SIZE_RXBUF 256
62 #define ELM327_SIZE_TXBUF 32
64 #define ELM327_CAN_CONFIG_SEND_SFF 0x8000
65 #define ELM327_CAN_CONFIG_VARIABLE_DLC 0x4000
66 #define ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF 0x2000
67 #define ELM327_CAN_CONFIG_BAUDRATE_MULT_8_7 0x1000
69 #define ELM327_DUMMY_CHAR 'y'
70 #define ELM327_DUMMY_STRING "y"
71 #define ELM327_READY_CHAR '>'
73 /* Bits in elm->cmds_todo */
74 enum ELM327_TX_DO_BITS {
75 ELM327_TX_DO_CAN_DATA = 0,
76 ELM327_TX_DO_CANID_11BIT,
77 ELM327_TX_DO_CANID_29BIT_LOW,
78 ELM327_TX_DO_CANID_29BIT_HIGH,
79 ELM327_TX_DO_CAN_CONFIG_PART2,
80 ELM327_TX_DO_CAN_CONFIG,
81 ELM327_TX_DO_RESPONSES,
82 ELM327_TX_DO_SILENT_MONITOR,
87 /* This must be the first member when using alloc_candev() */
90 struct can_rx_offload offload;
92 /* TTY and netdev devices that we're bridging */
93 struct tty_struct *tty;
94 struct net_device *dev;
96 /* Per-channel lock */
99 /* Stop the channel on hardware failure.
100 * Once this is true, nothing will be sent to the TTY.
105 struct work_struct tx_work; /* Flushes TTY TX buffer */
106 u8 *txbuf; /* Pointer to our TX buffer */
107 u8 *txhead; /* Pointer to next TX byte */
108 unsigned txleft; /* Bytes left to TX */
111 u8 rxbuf[ELM327_SIZE_RXBUF];
116 ELM327_STATE_NOTINIT = 0,
117 ELM327_STATE_GETDUMMYCHAR,
118 ELM327_STATE_GETPROMPT,
119 ELM327_STATE_RECEIVING,
124 /* The CAN frame and config the ELM327 is sending/using,
125 * or will send/use after finishing all cmds_todo
127 struct can_frame can_frame_to_send;
129 u8 can_bitrate_divisor;
131 /* Things we have yet to send */
132 char **next_init_cmd;
133 unsigned long cmds_todo;
136 static inline void elm327_hw_failure(struct elmcan *elm);
138 static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
142 lockdep_assert_held(elm->lock);
147 memcpy(elm->txbuf, buf, len);
149 written = elm->tty->ops->write(elm->tty, elm->txbuf, len);
152 "Failed to write to tty %s.\n",
154 elm327_hw_failure(elm);
158 elm->txleft = len - written;
159 elm->txhead = elm->txbuf + written;
162 netif_wake_queue(elm->dev);
164 set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
167 /* Take the ELM327 out of almost any state and back into command mode.
168 * We send ELM327_DUMMY_CHAR which will either abort any running
169 * operation, or be echoed back to us in case we're already in command
172 static void elm327_kick_into_cmd_mode(struct elmcan *elm)
174 lockdep_assert_held(elm->lock);
176 if (elm->state != ELM327_STATE_GETDUMMYCHAR &&
177 elm->state != ELM327_STATE_GETPROMPT) {
178 elm327_send(elm, ELM327_DUMMY_STRING, 1);
180 elm->state = ELM327_STATE_GETDUMMYCHAR;
184 /* Schedule a CAN frame and necessary config changes to be sent to the TTY. */
185 static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
187 lockdep_assert_held(elm->lock);
189 /* Schedule any necessary changes in ELM327's CAN configuration */
190 if (elm->can_frame_to_send.can_id != frame->can_id) {
191 /* Set the new CAN ID for transmission. */
192 if ((frame->can_id & CAN_EFF_FLAG) ^
193 (elm->can_frame_to_send.can_id & CAN_EFF_FLAG)) {
194 elm->can_config = (frame->can_id & CAN_EFF_FLAG
196 : ELM327_CAN_CONFIG_SEND_SFF)
197 | ELM327_CAN_CONFIG_VARIABLE_DLC
198 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
199 | elm->can_bitrate_divisor;
201 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
204 if (frame->can_id & CAN_EFF_FLAG) {
205 clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
206 set_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
207 set_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
209 set_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
210 clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
211 clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
215 /* Schedule the CAN frame itself. */
216 elm->can_frame_to_send = *frame;
217 set_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo);
219 elm327_kick_into_cmd_mode(elm);
222 /* ELM327 initialisation sequence. */
223 static char *elm327_init_script[] = {
224 "AT WS\r", /* v1.0: Warm Start */
225 "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
226 "AT M0\r", /* v1.0: Memory Off */
227 "AT AL\r", /* v1.0: Allow Long messages */
228 "AT BI\r", /* v1.0: Bypass Initialisation */
229 "AT CAF0\r", /* v1.0: CAN Auto Formatting Off */
230 "AT CFC0\r", /* v1.0: CAN Flow Control Off */
231 "AT CF 000\r", /* v1.0: Reset CAN ID Filter */
232 "AT CM 000\r", /* v1.0: Reset CAN ID Mask */
233 "AT E1\r", /* v1.0: Echo On */
234 "AT H1\r", /* v1.0: Headers On */
235 "AT L0\r", /* v1.0: Linefeeds Off */
236 "AT SH 7DF\r", /* v1.0: Set CAN sending ID to 0x7df */
237 "AT ST FF\r", /* v1.0: Set maximum Timeout for response after TX */
238 "AT AT0\r", /* v1.2: Adaptive Timing Off */
239 "AT D1\r", /* v1.3: Print DLC On */
240 "AT S1\r", /* v1.3: Spaces On */
241 "AT TP B\r", /* v1.0: Try Protocol B */
245 static void elm327_init(struct elmcan *elm)
247 lockdep_assert_held(elm->lock);
249 elm->state = ELM327_STATE_NOTINIT;
250 elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
252 elm->drop_next_line = 0;
254 /* We can only set the bitrate as a fraction of 500000.
255 * The bit timing constants in elmcan_bittiming_const will
256 * limit the user to the right values.
258 elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
259 elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
260 | ELM327_CAN_CONFIG_VARIABLE_DLC
261 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
262 | elm->can_bitrate_divisor;
264 /* Configure ELM327 and then start monitoring */
265 elm->next_init_cmd = &elm327_init_script[0];
266 set_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
267 set_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
268 set_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo);
269 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
271 elm327_kick_into_cmd_mode(elm);
274 static void elm327_feed_frame_to_netdev(struct elmcan *elm,
277 lockdep_assert_held(elm->lock);
279 if (!netif_running(elm->dev))
282 /* Queue for NAPI pickup.
283 * rx-offload will update stats and LEDs for us.
285 if (can_rx_offload_queue_tail(&elm->offload, skb))
286 elm->dev->stats.rx_fifo_errors++;
288 #if LINUX_VERSION_CODE >= KERNEL_VERSION(5,15,0)
290 can_rx_offload_irq_finish(&elm->offload);
294 /* Called when we're out of ideas and just want it all to end. */
295 static inline void elm327_hw_failure(struct elmcan *elm)
297 struct can_frame *frame;
300 lockdep_assert_held(elm->lock);
302 elm->hw_failure = true;
304 elm->can.can_stats.bus_off++;
305 netif_stop_queue(elm->dev);
306 elm->can.state = CAN_STATE_BUS_OFF;
307 can_bus_off(elm->dev);
309 netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
311 skb = alloc_can_err_skb(elm->dev, &frame);
315 frame->can_id |= CAN_ERR_BUSOFF;
316 elm327_feed_frame_to_netdev(elm, skb);
319 /* Compare a buffer to a fixed string */
320 static inline int _memstrcmp(const u8 *mem, const char *str)
322 return memcmp(mem, str, strlen(str));
325 /* Compare buffer to string length, then compare buffer to fixed string.
326 * This ensures two things:
327 * - It flags cases where the fixed string is only the start of the
328 * buffer, rather than exactly all of it.
329 * - It avoids byte comparisons in case the length doesn't match.
331 static inline int _len_memstrcmp(const u8 *mem, size_t mem_len, const char *str)
333 size_t str_len = strlen(str);
335 return (mem_len != str_len) || memcmp(mem, str, str_len);
338 static void elm327_parse_error(struct elmcan *elm, size_t len)
340 struct can_frame *frame;
343 lockdep_assert_held(elm->lock);
345 skb = alloc_can_err_skb(elm->dev, &frame);
347 /* It's okay to return here:
348 * The outer parsing loop will drop this UART buffer.
352 /* Filter possible error messages based on length of RX'd line */
353 if (!_len_memstrcmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
355 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
356 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUFFER FULL")) {
357 /* This will only happen if the last data line was complete.
358 * Otherwise, elm327_parse_frame() will heuristically
359 * emit this kind of error frame instead.
361 frame->can_id |= CAN_ERR_CRTL;
362 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
363 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS ERROR")) {
364 frame->can_id |= CAN_ERR_BUSERROR;
365 } else if (!_len_memstrcmp(elm->rxbuf, len, "CAN ERROR")) {
366 frame->can_id |= CAN_ERR_PROT;
367 } else if (!_len_memstrcmp(elm->rxbuf, len, "<RX ERROR")) {
368 frame->can_id |= CAN_ERR_PROT;
369 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS BUSY")) {
370 frame->can_id |= CAN_ERR_PROT;
371 frame->data[2] = CAN_ERR_PROT_OVERLOAD;
372 } else if (!_len_memstrcmp(elm->rxbuf, len, "FB ERROR")) {
373 frame->can_id |= CAN_ERR_PROT;
374 frame->data[2] = CAN_ERR_PROT_TX;
375 } else if (len == 5 && !_memstrcmp(elm->rxbuf, "ERR")) {
376 /* ERR is followed by two digits, hence line length 5 */
377 netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
378 elm->rxbuf[3], elm->rxbuf[4]);
379 frame->can_id |= CAN_ERR_CRTL;
381 /* Something else has happened.
382 * Maybe garbage on the UART line.
383 * Emit a generic error frame.
387 elm327_feed_frame_to_netdev(elm, skb);
390 /* Parse CAN frames coming as ASCII from ELM327.
391 * They can be of various formats:
393 * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
394 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
396 * where D = DLC, PL = payload byte
398 * Instead of a payload, RTR indicates a remote request.
400 * We will use the spaces and line length to guess the format.
402 static int elm327_parse_frame(struct elmcan *elm, size_t len)
404 struct can_frame *frame;
410 lockdep_assert_held(elm->lock);
412 skb = alloc_can_skb(elm->dev, &frame);
416 /* Find first non-hex and non-space character:
417 * - In the simplest case, there is none.
418 * - For RTR frames, 'R' is the first non-hex character.
419 * - An error message may replace the end of the data line.
421 for (hexlen = 0; hexlen <= len; hexlen++) {
422 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
423 elm->rxbuf[hexlen] != ' ') {
428 /* Sanity check whether the line is really a clean hexdump,
429 * or terminated by an error message, or contains garbage.
432 !isdigit(elm->rxbuf[hexlen]) &&
433 !isupper(elm->rxbuf[hexlen]) &&
434 '<' != elm->rxbuf[hexlen] &&
435 ' ' != elm->rxbuf[hexlen]) {
436 /* The line is likely garbled anyway, so bail.
437 * The main code will restart listening.
442 /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
443 * No out-of-bounds access:
444 * We use the fact that we can always read from elm->rxbuf.
446 if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
447 elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
448 elm->rxbuf[13] == ' ') {
449 frame->can_id = CAN_EFF_FLAG;
451 } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
454 /* This is not a well-formatted data line.
455 * Assume it's an error message.
460 if (hexlen < datastart) {
461 /* The line is too short to be a valid frame hex dump.
462 * Something interrupted the hex dump or it is invalid.
467 /* From here on all chars up to buf[hexlen] are hex or spaces,
468 * at well-defined offsets.
471 /* Read CAN data length */
472 frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
475 if (frame->can_id & CAN_EFF_FLAG) {
476 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
477 | (hex_to_bin(elm->rxbuf[1]) << 24)
478 | (hex_to_bin(elm->rxbuf[3]) << 20)
479 | (hex_to_bin(elm->rxbuf[4]) << 16)
480 | (hex_to_bin(elm->rxbuf[6]) << 12)
481 | (hex_to_bin(elm->rxbuf[7]) << 8)
482 | (hex_to_bin(elm->rxbuf[9]) << 4)
483 | (hex_to_bin(elm->rxbuf[10]) << 0);
485 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
486 | (hex_to_bin(elm->rxbuf[1]) << 4)
487 | (hex_to_bin(elm->rxbuf[2]) << 0);
490 /* Check for RTR frame */
491 if (elm->rxfill >= hexlen + 3 &&
492 !_memstrcmp(&elm->rxbuf[hexlen], "RTR")) {
493 frame->can_id |= CAN_RTR_FLAG;
496 /* Is the line long enough to hold the advertised payload?
497 * Note: RTR frames have a DLC, but no actual payload.
499 if (!(frame->can_id & CAN_RTR_FLAG) &&
500 (hexlen < frame->len * 3 + datastart)) {
502 * Probably the ELM327's RS232 TX buffer was full.
503 * Emit an error frame and exit.
505 frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
506 frame->len = CAN_ERR_DLC;
507 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
508 elm327_feed_frame_to_netdev(elm, skb);
510 /* Signal failure to parse.
511 * The line will be re-parsed as an error line, which will fail.
512 * However, this will correctly drop the state machine back into
518 /* Parse the data nibbles. */
519 for (i = 0; i < frame->len; i++) {
520 frame->data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
521 | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
524 /* Feed the frame to the network layer. */
525 elm327_feed_frame_to_netdev(elm, skb);
530 static void elm327_parse_line(struct elmcan *elm, size_t len)
532 lockdep_assert_held(elm->lock);
534 /* Skip empty lines */
538 /* Skip echo lines */
539 if (elm->drop_next_line) {
540 elm->drop_next_line = 0;
542 } else if (!_memstrcmp(elm->rxbuf, "AT")) {
546 /* Regular parsing */
547 if (elm->state == ELM327_STATE_RECEIVING
548 && elm327_parse_frame(elm, len)) {
549 /* Parse an error line. */
550 elm327_parse_error(elm, len);
553 elm327_kick_into_cmd_mode(elm);
557 static void elm327_handle_prompt(struct elmcan *elm)
559 struct can_frame *frame = &elm->can_frame_to_send;
560 char local_txbuf[20];
562 lockdep_assert_held(elm->lock);
564 if (!elm->cmds_todo) {
565 /* Enter CAN monitor mode */
566 elm327_send(elm, "ATMA\r", 5);
567 elm->state = ELM327_STATE_RECEIVING;
572 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
573 if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
574 strcpy(local_txbuf, *elm->next_init_cmd);
576 elm->next_init_cmd++;
577 if (!(*elm->next_init_cmd)) {
578 clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
582 } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
583 sprintf(local_txbuf, "ATCSM%i\r",
584 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
586 } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo)) {
587 sprintf(local_txbuf, "ATR%i\r",
588 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
590 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
591 sprintf(local_txbuf, "ATPC\r");
592 set_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);
594 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
595 sprintf(local_txbuf, "ATPB%04X\r",
598 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
599 sprintf(local_txbuf, "ATCP%02X\r",
600 (frame->can_id & CAN_EFF_MASK) >> 24);
602 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
603 sprintf(local_txbuf, "ATSH%06X\r",
604 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
606 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
607 sprintf(local_txbuf, "ATSH%03X\r",
608 frame->can_id & CAN_SFF_MASK);
610 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
611 if (frame->can_id & CAN_RTR_FLAG) {
612 /* Send an RTR frame. Their DLC is fixed.
613 * Some chips don't send them at all.
615 sprintf(local_txbuf, "ATRTR\r");
617 /* Send a regular CAN data frame */
620 for (i = 0; i < frame->len; i++) {
621 sprintf(&local_txbuf[2 * i], "%02X",
625 sprintf(&local_txbuf[2 * i], "\r");
628 elm->drop_next_line = 1;
629 elm->state = ELM327_STATE_RECEIVING;
632 elm327_send(elm, local_txbuf, strlen(local_txbuf));
635 static bool elm327_is_ready_char(char c)
637 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
638 * Probably bad hardware.
640 return (c & 0x3f) == ELM327_READY_CHAR;
643 static void elm327_drop_bytes(struct elmcan *elm, size_t i)
645 lockdep_assert_held(elm->lock);
647 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
651 static void elm327_parse_rxbuf(struct elmcan *elm)
656 lockdep_assert_held(elm->lock);
658 switch (elm->state) {
659 case ELM327_STATE_NOTINIT:
663 case ELM327_STATE_GETDUMMYCHAR:
665 /* Wait for 'y' or '>' */
666 for (i = 0; i < elm->rxfill; i++) {
667 if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
668 elm327_send(elm, "\r", 1);
669 elm->state = ELM327_STATE_GETPROMPT;
672 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
673 elm327_send(elm, ELM327_DUMMY_STRING, 1);
679 elm327_drop_bytes(elm, i);
684 case ELM327_STATE_GETPROMPT:
686 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
687 elm327_handle_prompt(elm);
692 case ELM327_STATE_RECEIVING:
693 /* Find <CR> delimiting feedback lines. */
695 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
700 if (len == ELM327_SIZE_RXBUF) {
701 /* Line exceeds buffer. It's probably all garbage.
702 * Did we even connect at the right baud rate?
705 "RX buffer overflow. Faulty ELM327 or UART?\n");
706 elm327_hw_failure(elm);
708 } else if (len == elm->rxfill) {
709 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
710 /* The ELM327's AT ST response timeout ran out,
711 * so we got a prompt.
712 * Clear RX buffer and restart listening.
716 elm327_handle_prompt(elm);
720 /* No <CR> found - we haven't received a full line yet.
721 * Wait for more data.
726 /* We have a full line to parse. */
727 elm327_parse_line(elm, len);
729 /* Remove parsed data from RX buffer. */
730 elm327_drop_bytes(elm, len + 1);
732 /* More data to parse? */
734 elm327_parse_rxbuf(elm);
738 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
739 /* Dummy needed to use can_rx_offload */
740 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
741 unsigned int n, u32 *timestamp,
744 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
746 return ERR_PTR(-ENOBUFS);
750 static int elmcan_netdev_open(struct net_device *dev)
752 struct elmcan *elm = netdev_priv(dev);
755 spin_lock_bh(&elm->lock);
756 if (elm->hw_failure) {
757 netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
758 spin_unlock_bh(&elm->lock);
763 spin_unlock_bh(&elm->lock);
767 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
768 err = open_candev(dev);
770 spin_unlock_bh(&elm->lock);
775 spin_unlock_bh(&elm->lock);
777 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
778 elm->offload.mailbox_read = elmcan_mailbox_read;
779 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
781 err = can_rx_offload_add_manual(dev, &elm->offload, ELM327_NAPI_WEIGHT);
788 can_rx_offload_enable(&elm->offload);
790 can_led_event(dev, CAN_LED_EVENT_OPEN);
791 elm->can.state = CAN_STATE_ERROR_ACTIVE;
792 netif_start_queue(dev);
797 static int elmcan_netdev_close(struct net_device *dev)
799 struct elmcan *elm = netdev_priv(dev);
801 netif_stop_queue(dev);
803 spin_lock_bh(&elm->lock);
805 /* Interrupt whatever we're doing right now */
806 elm327_send(elm, ELM327_DUMMY_STRING, 1);
808 /* Clear the wakeup bit, as the netdev will be down and thus
809 * the wakeup handler won't clear it
811 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
813 spin_unlock_bh(&elm->lock);
815 flush_work(&elm->tx_work);
817 spin_unlock_bh(&elm->lock);
820 can_rx_offload_disable(&elm->offload);
821 elm->can.state = CAN_STATE_STOPPED;
822 can_rx_offload_del(&elm->offload);
824 can_led_event(dev, CAN_LED_EVENT_STOP);
829 /* Send a can_frame to a TTY. */
830 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
831 struct net_device *dev)
833 struct elmcan *elm = netdev_priv(dev);
834 struct can_frame *frame = (struct can_frame *)skb->data;
836 if (can_dropped_invalid_skb(dev, skb))
839 /* BHs are already disabled, so no spin_lock_bh().
840 * See Documentation/networking/netdevices.txt
842 spin_lock(&elm->lock);
844 /* We shouldn't get here after a hardware fault:
845 * can_bus_off() calls netif_carrier_off()
847 WARN_ON_ONCE(elm->hw_failure);
851 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
852 spin_unlock(&elm->lock);
856 netif_stop_queue(dev);
858 elm327_send_frame(elm, frame);
859 spin_unlock(&elm->lock);
861 dev->stats.tx_packets++;
862 dev->stats.tx_bytes += frame->len;
864 can_led_event(dev, CAN_LED_EVENT_TX);
871 static const struct net_device_ops elmcan_netdev_ops = {
872 .ndo_open = elmcan_netdev_open,
873 .ndo_stop = elmcan_netdev_close,
874 .ndo_start_xmit = elmcan_netdev_start_xmit,
875 .ndo_change_mtu = can_change_mtu,
878 static bool elmcan_is_valid_rx_char(char c)
880 return (isdigit(c) ||
882 c == ELM327_DUMMY_CHAR ||
883 c == ELM327_READY_CHAR ||
894 /* Handle incoming ELM327 ASCII data.
895 * This will not be re-entered while running, but other ldisc
896 * functions may be called in parallel.
898 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
899 static void elmcan_ldisc_rx(struct tty_struct *tty,
900 const unsigned char *cp, char *fp, int count)
902 static void elmcan_ldisc_rx(struct tty_struct *tty,
903 const unsigned char *cp, const char *fp, int count)
906 struct elmcan *elm = (struct elmcan *)tty->disc_data;
908 spin_lock_bh(&elm->lock);
913 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
915 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
917 elm327_hw_failure(elm);
922 /* Ignore NUL characters, which the PIC microcontroller may
923 * inadvertently insert due to a known hardware bug.
924 * See ELM327 documentation, which refers to a Microchip PIC
928 /* Check for stray characters on the UART line.
929 * Likely caused by bad hardware.
931 if (!elmcan_is_valid_rx_char(*cp)) {
933 "Received illegal character %02x.\n",
935 elm327_hw_failure(elm);
940 elm->rxbuf[elm->rxfill++] = *cp;
947 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
949 elm327_hw_failure(elm);
954 elm327_parse_rxbuf(elm);
957 spin_unlock_bh(&elm->lock);
960 /* Write out remaining transmit buffer.
961 * Scheduled when TTY is writable.
963 static void elmcan_ldisc_tx_worker(struct work_struct *work)
965 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
971 spin_lock_bh(&elm->lock);
974 written = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
977 "Failed to write to tty %s.\n",
979 elm327_hw_failure(elm);
980 spin_unlock_bh(&elm->lock);
983 elm->txleft -= written;
984 elm->txhead += written;
989 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
990 spin_unlock_bh(&elm->lock);
991 netif_wake_queue(elm->dev);
993 spin_unlock_bh(&elm->lock);
997 /* Called by the driver when there's room for more data. */
998 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1000 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1002 schedule_work(&elm->tx_work);
1005 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1006 * or 7/8 of that. Divisors are 1 to 64.
1007 * Currently we don't implement support for 7/8 rates.
1009 static const u32 elmcan_bitrate_const[64] = {
1010 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1011 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1012 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1013 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1014 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1015 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1016 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1017 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1020 /* Dummy needed to use bitrate_const */
1021 static int elmcan_do_set_bittiming(struct net_device *netdev)
1026 static int elmcan_ldisc_open(struct tty_struct *tty)
1028 struct net_device *dev;
1032 if (!capable(CAP_NET_ADMIN))
1035 if (!tty->ops->write)
1038 dev = alloc_candev(sizeof(struct elmcan), 0);
1041 elm = netdev_priv(dev);
1043 elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
1049 /* Configure TTY interface */
1050 tty->receive_room = 65536; /* We don't flow control */
1051 elm->txleft = 0; /* Clear TTY TX buffer */
1052 spin_lock_init(&elm->lock);
1053 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1055 /* Configure CAN metadata */
1056 elm->can.bitrate_const = elmcan_bitrate_const;
1057 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1058 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1059 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1061 /* Configure netdev interface */
1063 dev->netdev_ops = &elmcan_netdev_ops;
1065 /* Mark ldisc channel as alive */
1067 tty->disc_data = elm;
1069 devm_can_led_init(elm->dev);
1072 err = register_candev(elm->dev);
1076 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1082 free_candev(elm->dev);
1086 /* Close down an elmcan channel.
1087 * This means flushing out any pending queues, and then returning.
1088 * This call is serialized against other ldisc functions:
1089 * Once this is called, no other ldisc function of ours is entered.
1091 * We also use this function for a hangup event.
1093 static void elmcan_ldisc_close(struct tty_struct *tty)
1095 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1097 /* unregister_netdev() calls .ndo_stop() so we don't have to. */
1098 unregister_candev(elm->dev);
1100 /* Ensure that our worker won't be rescheduled */
1101 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
1102 flush_work(&elm->tx_work);
1104 /* Mark channel as dead */
1105 spin_lock_bh(&elm->lock);
1106 tty->disc_data = NULL;
1108 spin_unlock_bh(&elm->lock);
1110 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1113 free_candev(elm->dev);
1116 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1117 static int elmcan_ldisc_hangup(struct tty_struct *tty)
1119 static void elmcan_ldisc_hangup(struct tty_struct *tty)
1122 elmcan_ldisc_close(tty);
1123 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1128 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1129 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1132 unsigned int cmd, unsigned long arg)
1134 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1139 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1140 if (copy_to_user((void __user *)arg, elm->dev->name, tmp))
1148 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1149 return tty_mode_ioctl(tty, file, cmd, arg);
1151 return tty_mode_ioctl(tty, cmd, arg);
1156 static struct tty_ldisc_ops elmcan_ldisc = {
1157 .owner = THIS_MODULE,
1159 .num = N_DEVELOPMENT,
1160 .receive_buf = elmcan_ldisc_rx,
1161 .write_wakeup = elmcan_ldisc_tx_wakeup,
1162 .open = elmcan_ldisc_open,
1163 .close = elmcan_ldisc_close,
1164 .hangup = elmcan_ldisc_hangup,
1165 .ioctl = elmcan_ldisc_ioctl,
1168 static int __init elmcan_init(void)
1172 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1173 status = tty_register_ldisc(N_DEVELOPMENT, &elmcan_ldisc);
1175 status = tty_register_ldisc(&elmcan_ldisc);
1178 pr_err("Can't register line discipline\n");
1183 static void __exit elmcan_exit(void)
1185 /* This will only be called when all channels have been closed by
1186 * userspace - tty_ldisc.c takes care of the module's refcount.
1188 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1191 status = tty_unregister_ldisc(N_DEVELOPMENT);
1193 pr_err("Can't unregister line discipline (error: %d)\n",
1196 tty_unregister_ldisc(&elmcan_ldisc);
1200 module_init(elmcan_init);
1201 module_exit(elmcan_exit);
1203 MODULE_ALIAS_LDISC(N_DEVELOPMENT);
1204 MODULE_DESCRIPTION("ELM327 based CAN interface");
1205 MODULE_LICENSE("GPL");
1206 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");