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 224
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_to_to_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;
93 u8 rxbuf[ELM327_SIZE_RXBUF];
94 u8 txbuf[ELM327_SIZE_TXBUF] ____cacheline_aligned;
96 /* TTY buffer accounting */
97 struct work_struct tx_work; /* Flushes TTY TX buffer */
98 u8 *txhead; /* Next TX byte */
99 unsigned txleft; /* Bytes left to TX */
100 int rxfill; /* Bytes already RX'd in buffer */
102 /* TTY and netdev devices that we're bridging */
103 struct tty_struct *tty;
104 struct net_device *dev;
106 /* Per-channel lock */
111 ELM327_STATE_NOTINIT = 0,
112 ELM327_STATE_GETDUMMYCHAR,
113 ELM327_STATE_GETPROMPT,
114 ELM327_STATE_RECEIVING,
117 /* Things we have yet to send */
118 char **next_init_cmd;
119 unsigned long cmds_todo;
121 /* The CAN frame and config the ELM327 is sending/using,
122 * or will send/use after finishing all cmds_todo
124 struct can_frame can_frame_to_send;
126 u8 can_bitrate_divisor;
131 /* Stop the channel on UART side hardware failure, e.g. stray
132 * characters or neverending lines. This may be caused by bad
133 * UART wiring, a bad ELM327, a bad UART bridge...
134 * Once this is true, nothing will be sent to the TTY.
136 bool uart_side_failure;
139 static inline void elm327_uart_side_failure(struct elmcan *elm);
141 static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
145 lockdep_assert_held(elm->lock);
147 if (elm->uart_side_failure)
150 memcpy(elm->txbuf, buf, len);
152 written = elm->tty->ops->write(elm->tty, elm->txbuf, len);
155 "Failed to write to tty %s.\n",
157 elm327_uart_side_failure(elm);
161 elm->txleft = len - written;
162 elm->txhead = elm->txbuf + written;
165 netif_wake_queue(elm->dev);
167 set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
170 /* Take the ELM327 out of almost any state and back into command mode.
171 * We send ELM327_DUMMY_CHAR which will either abort any running
172 * operation, or be echoed back to us in case we're already in command
175 static void elm327_kick_into_cmd_mode(struct elmcan *elm)
177 lockdep_assert_held(elm->lock);
179 if (elm->state != ELM327_STATE_GETDUMMYCHAR &&
180 elm->state != ELM327_STATE_GETPROMPT) {
181 elm327_send(elm, ELM327_DUMMY_STRING, 1);
183 elm->state = ELM327_STATE_GETDUMMYCHAR;
187 /* Schedule a CAN frame and necessary config changes to be sent to the TTY. */
188 static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
190 lockdep_assert_held(elm->lock);
192 /* Schedule any necessary changes in ELM327's CAN configuration */
193 if (elm->can_frame_to_send.can_id != frame->can_id) {
194 /* Set the new CAN ID for transmission. */
195 if ((frame->can_id & CAN_EFF_FLAG) ^
196 (elm->can_frame_to_send.can_id & CAN_EFF_FLAG)) {
197 elm->can_config = (frame->can_id & CAN_EFF_FLAG
199 : ELM327_CAN_CONFIG_SEND_SFF)
200 | ELM327_CAN_CONFIG_VARIABLE_DLC
201 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
202 | elm->can_bitrate_divisor;
204 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
207 if (frame->can_id & CAN_EFF_FLAG) {
208 clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
209 set_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
210 set_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
212 set_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
213 clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
214 clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
218 /* Schedule the CAN frame itself. */
219 elm->can_frame_to_send = *frame;
220 set_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo);
222 elm327_kick_into_cmd_mode(elm);
225 /* ELM327 initialisation sequence.
226 * The line length is limited by the buffer in elm327_handle_prompt().
228 static char *elm327_init_script[] = {
229 "AT WS\r", /* v1.0: Warm Start */
230 "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
231 "AT M0\r", /* v1.0: Memory Off */
232 "AT AL\r", /* v1.0: Allow Long messages */
233 "AT BI\r", /* v1.0: Bypass Initialisation */
234 "AT CAF0\r", /* v1.0: CAN Auto Formatting Off */
235 "AT CFC0\r", /* v1.0: CAN Flow Control Off */
236 "AT CF 000\r", /* v1.0: Reset CAN ID Filter */
237 "AT CM 000\r", /* v1.0: Reset CAN ID Mask */
238 "AT E1\r", /* v1.0: Echo On */
239 "AT H1\r", /* v1.0: Headers On */
240 "AT L0\r", /* v1.0: Linefeeds Off */
241 "AT SH 7DF\r", /* v1.0: Set CAN sending ID to 0x7df */
242 "AT ST FF\r", /* v1.0: Set maximum Timeout for response after TX */
243 "AT AT0\r", /* v1.2: Adaptive Timing Off */
244 "AT D1\r", /* v1.3: Print DLC On */
245 "AT S1\r", /* v1.3: Spaces On */
246 "AT TP B\r", /* v1.0: Try Protocol B */
250 static void elm327_init(struct elmcan *elm)
252 lockdep_assert_held(elm->lock);
254 elm->state = ELM327_STATE_NOTINIT;
255 elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
257 elm->drop_next_line = 0;
259 /* We can only set the bitrate as a fraction of 500000.
260 * The bit timing constants in elmcan_bittiming_const will
261 * limit the user to the right values.
263 elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
264 elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
265 | ELM327_CAN_CONFIG_VARIABLE_DLC
266 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
267 | elm->can_bitrate_divisor;
269 /* Configure ELM327 and then start monitoring */
270 elm->next_init_cmd = &elm327_init_script[0];
271 set_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
272 set_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
273 set_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo);
274 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
276 elm327_kick_into_cmd_mode(elm);
279 static void elm327_feed_frame_to_netdev(struct elmcan *elm,
282 lockdep_assert_held(elm->lock);
284 if (!netif_running(elm->dev))
287 /* Queue for NAPI pickup.
288 * rx-offload will update stats and LEDs for us.
290 if (can_rx_offload_queue_tail(&elm->offload, skb))
291 elm->dev->stats.rx_fifo_errors++;
293 #if LINUX_VERSION_CODE >= KERNEL_VERSION(5,15,0)
295 can_rx_offload_irq_finish(&elm->offload);
299 /* Called when we're out of ideas and just want it all to end. */
300 static inline void elm327_uart_side_failure(struct elmcan *elm)
302 struct can_frame *frame;
305 lockdep_assert_held(elm->lock);
307 elm->uart_side_failure = true;
309 elm->can.can_stats.bus_off++;
310 netif_stop_queue(elm->dev);
311 elm->can.state = CAN_STATE_BUS_OFF;
312 can_bus_off(elm->dev);
314 netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
316 skb = alloc_can_err_skb(elm->dev, &frame);
320 frame->can_id |= CAN_ERR_BUSOFF;
321 elm327_feed_frame_to_netdev(elm, skb);
324 /* Compare buffer to string length, then compare buffer to fixed string.
325 * This ensures two things:
326 * - It flags cases where the fixed string is only the start of the
327 * buffer, rather than exactly all of it.
328 * - It avoids byte comparisons in case the length doesn't match.
330 * strncmp() cannot be used here because it accepts the following wrong case:
331 * strncmp("CAN ER", "CAN ERROR", 6);
332 * This must fail, hence this helper function.
334 static inline int check_len_then_cmp(const u8 *mem, size_t mem_len, const char *str)
336 size_t str_len = strlen(str);
338 return (mem_len == str_len) && !memcmp(mem, str, str_len);
341 static void elm327_parse_error(struct elmcan *elm, size_t len)
343 struct can_frame *frame;
346 lockdep_assert_held(elm->lock);
348 skb = alloc_can_err_skb(elm->dev, &frame);
350 /* It's okay to return here:
351 * The outer parsing loop will drop this UART buffer.
355 /* Filter possible error messages based on length of RX'd line */
356 if (check_len_then_cmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
358 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
359 } else if (check_len_then_cmp(elm->rxbuf, len, "BUFFER FULL")) {
360 /* This will only happen if the last data line was complete.
361 * Otherwise, elm327_parse_frame() will heuristically
362 * emit this kind of error frame instead.
364 frame->can_id |= CAN_ERR_CRTL;
365 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
366 } else if (check_len_then_cmp(elm->rxbuf, len, "BUS ERROR")) {
367 frame->can_id |= CAN_ERR_BUSERROR;
368 } else if (check_len_then_cmp(elm->rxbuf, len, "CAN ERROR")) {
369 frame->can_id |= CAN_ERR_PROT;
370 } else if (check_len_then_cmp(elm->rxbuf, len, "<RX ERROR")) {
371 frame->can_id |= CAN_ERR_PROT;
372 } else if (check_len_then_cmp(elm->rxbuf, len, "BUS BUSY")) {
373 frame->can_id |= CAN_ERR_PROT;
374 frame->data[2] = CAN_ERR_PROT_OVERLOAD;
375 } else if (check_len_then_cmp(elm->rxbuf, len, "FB ERROR")) {
376 frame->can_id |= CAN_ERR_PROT;
377 frame->data[2] = CAN_ERR_PROT_TX;
378 } else if (len == 5 && !memcmp(elm->rxbuf, "ERR", 3)) {
379 /* ERR is followed by two digits, hence line length 5 */
380 netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
381 elm->rxbuf[3], elm->rxbuf[4]);
382 frame->can_id |= CAN_ERR_CRTL;
384 /* Something else has happened.
385 * Maybe garbage on the UART line.
386 * Emit a generic error frame.
390 elm327_feed_frame_to_netdev(elm, skb);
393 /* Parse CAN frames coming as ASCII from ELM327.
394 * They can be of various formats:
396 * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
397 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
399 * where D = DLC, PL = payload byte
401 * Instead of a payload, RTR indicates a remote request.
403 * We will use the spaces and line length to guess the format.
405 static int elm327_parse_frame(struct elmcan *elm, size_t len)
407 struct can_frame *frame;
413 lockdep_assert_held(elm->lock);
415 skb = alloc_can_skb(elm->dev, &frame);
419 /* Find first non-hex and non-space character:
420 * - In the simplest case, there is none.
421 * - For RTR frames, 'R' is the first non-hex character.
422 * - An error message may replace the end of the data line.
424 for (hexlen = 0; hexlen <= len; hexlen++) {
425 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
426 elm->rxbuf[hexlen] != ' ') {
431 /* Sanity check whether the line is really a clean hexdump,
432 * or terminated by an error message, or contains garbage.
435 !isdigit(elm->rxbuf[hexlen]) &&
436 !isupper(elm->rxbuf[hexlen]) &&
437 '<' != elm->rxbuf[hexlen] &&
438 ' ' != elm->rxbuf[hexlen]) {
439 /* The line is likely garbled anyway, so bail.
440 * The main code will restart listening.
445 /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
446 * No out-of-bounds access:
447 * We use the fact that we can always read from elm->rxbuf.
449 if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
450 elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
451 elm->rxbuf[13] == ' ') {
452 frame->can_id = CAN_EFF_FLAG;
454 } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
457 /* This is not a well-formatted data line.
458 * Assume it's an error message.
463 if (hexlen < datastart) {
464 /* The line is too short to be a valid frame hex dump.
465 * Something interrupted the hex dump or it is invalid.
470 /* From here on all chars up to buf[hexlen] are hex or spaces,
471 * at well-defined offsets.
474 /* Read CAN data length */
475 frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
478 if (frame->can_id & CAN_EFF_FLAG) {
479 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
480 | (hex_to_bin(elm->rxbuf[1]) << 24)
481 | (hex_to_bin(elm->rxbuf[3]) << 20)
482 | (hex_to_bin(elm->rxbuf[4]) << 16)
483 | (hex_to_bin(elm->rxbuf[6]) << 12)
484 | (hex_to_bin(elm->rxbuf[7]) << 8)
485 | (hex_to_bin(elm->rxbuf[9]) << 4)
486 | (hex_to_bin(elm->rxbuf[10]) << 0);
488 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
489 | (hex_to_bin(elm->rxbuf[1]) << 4)
490 | (hex_to_bin(elm->rxbuf[2]) << 0);
493 /* Check for RTR frame */
494 if (elm->rxfill >= hexlen + 3 &&
495 !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) {
496 frame->can_id |= CAN_RTR_FLAG;
499 /* Is the line long enough to hold the advertised payload?
500 * Note: RTR frames have a DLC, but no actual payload.
502 if (!(frame->can_id & CAN_RTR_FLAG) &&
503 (hexlen < frame->len * 3 + datastart)) {
505 * Probably the ELM327's RS232 TX buffer was full.
506 * Emit an error frame and exit.
508 frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
509 frame->len = CAN_ERR_DLC;
510 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
511 elm327_feed_frame_to_netdev(elm, skb);
513 /* Signal failure to parse.
514 * The line will be re-parsed as an error line, which will fail.
515 * However, this will correctly drop the state machine back into
521 /* Parse the data nibbles. */
522 for (i = 0; i < frame->len; i++) {
523 frame->data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
524 | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
527 /* Feed the frame to the network layer. */
528 elm327_feed_frame_to_netdev(elm, skb);
533 static void elm327_parse_line(struct elmcan *elm, size_t len)
535 lockdep_assert_held(elm->lock);
537 /* Skip empty lines */
541 /* Skip echo lines */
542 if (elm->drop_next_line) {
543 elm->drop_next_line = 0;
545 } else if (!memcmp(elm->rxbuf, "AT", 2)) {
549 /* Regular parsing */
550 if (elm->state == ELM327_STATE_RECEIVING
551 && elm327_parse_frame(elm, len)) {
552 /* Parse an error line. */
553 elm327_parse_error(elm, len);
556 elm327_kick_into_cmd_mode(elm);
560 static void elm327_handle_prompt(struct elmcan *elm)
562 struct can_frame *frame = &elm->can_frame_to_send;
563 /* Size this buffer for the largest ELM327 line we may generate,
564 * which is currently an 8 byte CAN frame's payload hexdump.
565 * Items in elm327_init_script must fit here, too!
567 char local_txbuf[sizeof("0102030405060708\r")];
569 lockdep_assert_held(elm->lock);
571 if (!elm->cmds_todo) {
572 /* Enter CAN monitor mode */
573 elm327_send(elm, "ATMA\r", 5);
574 elm->state = ELM327_STATE_RECEIVING;
579 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
580 if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
581 snprintf(local_txbuf, sizeof(local_txbuf),
583 *elm->next_init_cmd);
585 elm->next_init_cmd++;
586 if (!(*elm->next_init_cmd)) {
587 clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
591 } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
592 snprintf(local_txbuf, sizeof(local_txbuf),
594 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
596 } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo)) {
597 snprintf(local_txbuf, sizeof(local_txbuf),
599 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
601 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
602 snprintf(local_txbuf, sizeof(local_txbuf),
604 set_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);
606 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
607 snprintf(local_txbuf, sizeof(local_txbuf),
611 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
612 snprintf(local_txbuf, sizeof(local_txbuf),
614 (frame->can_id & CAN_EFF_MASK) >> 24);
616 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
617 snprintf(local_txbuf, sizeof(local_txbuf),
619 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
621 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
622 snprintf(local_txbuf, sizeof(local_txbuf),
624 frame->can_id & CAN_SFF_MASK);
626 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
627 if (frame->can_id & CAN_RTR_FLAG) {
628 /* Send an RTR frame. Their DLC is fixed.
629 * Some chips don't send them at all.
631 snprintf(local_txbuf, sizeof(local_txbuf),
634 /* Send a regular CAN data frame */
637 for (i = 0; i < frame->len; i++) {
638 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
643 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
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 static void elm327_drop_bytes(struct elmcan *elm, size_t i)
664 lockdep_assert_held(elm->lock);
666 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
670 static void elm327_parse_rxbuf(struct elmcan *elm)
675 lockdep_assert_held(elm->lock);
677 switch (elm->state) {
678 case ELM327_STATE_NOTINIT:
682 case ELM327_STATE_GETDUMMYCHAR:
684 /* Wait for 'y' or '>' */
685 for (i = 0; i < elm->rxfill; i++) {
686 if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
687 elm327_send(elm, "\r", 1);
688 elm->state = ELM327_STATE_GETPROMPT;
691 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
692 elm327_send(elm, ELM327_DUMMY_STRING, 1);
698 elm327_drop_bytes(elm, i);
703 case ELM327_STATE_GETPROMPT:
705 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
706 elm327_handle_prompt(elm);
711 case ELM327_STATE_RECEIVING:
712 /* Find <CR> delimiting feedback lines. */
714 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
719 if (len == ELM327_SIZE_RXBUF) {
720 /* Line exceeds buffer. It's probably all garbage.
721 * Did we even connect at the right baud rate?
724 "RX buffer overflow. Faulty ELM327 or UART?\n");
725 elm327_uart_side_failure(elm);
727 } else if (len == elm->rxfill) {
728 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
729 /* The ELM327's AT ST response timeout ran out,
730 * so we got a prompt.
731 * Clear RX buffer and restart listening.
735 elm327_handle_prompt(elm);
739 /* No <CR> found - we haven't received a full line yet.
740 * Wait for more data.
745 /* We have a full line to parse. */
746 elm327_parse_line(elm, len);
748 /* Remove parsed data from RX buffer. */
749 elm327_drop_bytes(elm, len + 1);
751 /* More data to parse? */
753 elm327_parse_rxbuf(elm);
757 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
758 /* Dummy needed to use can_rx_offload */
759 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
760 unsigned int n, u32 *timestamp,
763 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
765 return ERR_PTR(-ENOBUFS);
769 static int elmcan_netdev_open(struct net_device *dev)
771 struct elmcan *elm = netdev_priv(dev);
774 spin_lock_bh(&elm->lock);
777 spin_unlock_bh(&elm->lock);
781 if (elm->uart_side_failure)
782 netdev_warn(elm->dev, "Reopening netdev after a UART side fault has been detected.\n");
784 /* Clear TTY buffers */
788 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
789 err = open_candev(dev);
791 spin_unlock_bh(&elm->lock);
796 spin_unlock_bh(&elm->lock);
798 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
799 elm->offload.mailbox_read = elmcan_mailbox_read;
800 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
802 err = can_rx_offload_add_manual(dev, &elm->offload, ELM327_NAPI_WEIGHT);
809 can_rx_offload_enable(&elm->offload);
811 can_led_event(dev, CAN_LED_EVENT_OPEN);
812 elm->can.state = CAN_STATE_ERROR_ACTIVE;
813 netif_start_queue(dev);
818 static int elmcan_netdev_close(struct net_device *dev)
820 struct elmcan *elm = netdev_priv(dev);
822 /* Interrupt whatever the ELM327 is doing right now */
823 spin_lock_bh(&elm->lock);
824 elm327_send(elm, ELM327_DUMMY_STRING, 1);
825 spin_unlock_bh(&elm->lock);
827 /* Give UART one final chance to flush.
828 * This may netif_wake_queue(), so don't netif_stop_queue()
829 * before flushing the worker.
831 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
832 flush_work(&elm->tx_work);
834 netif_stop_queue(dev);
836 can_rx_offload_disable(&elm->offload);
837 elm->can.state = CAN_STATE_STOPPED;
838 can_rx_offload_del(&elm->offload);
840 can_led_event(dev, CAN_LED_EVENT_STOP);
845 /* Send a can_frame to a TTY. */
846 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
847 struct net_device *dev)
849 struct elmcan *elm = netdev_priv(dev);
850 struct can_frame *frame = (struct can_frame *)skb->data;
852 if (can_dropped_invalid_skb(dev, skb))
855 /* BHs are already disabled, so no spin_lock_bh().
856 * See Documentation/networking/netdevices.txt
858 spin_lock(&elm->lock);
860 /* We shouldn't get here after a hardware fault:
861 * can_bus_off() calls netif_carrier_off()
863 WARN_ON_ONCE(elm->uart_side_failure);
866 elm->uart_side_failure ||
867 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
868 spin_unlock(&elm->lock);
872 netif_stop_queue(dev);
874 elm327_send_frame(elm, frame);
875 spin_unlock(&elm->lock);
877 dev->stats.tx_packets++;
878 dev->stats.tx_bytes += frame->len;
880 can_led_event(dev, CAN_LED_EVENT_TX);
887 static const struct net_device_ops elmcan_netdev_ops = {
888 .ndo_open = elmcan_netdev_open,
889 .ndo_stop = elmcan_netdev_close,
890 .ndo_start_xmit = elmcan_netdev_start_xmit,
891 .ndo_change_mtu = can_change_mtu,
894 static bool elmcan_is_valid_rx_char(char c)
896 return (isdigit(c) ||
898 c == ELM327_DUMMY_CHAR ||
899 c == ELM327_READY_CHAR ||
910 /* Handle incoming ELM327 ASCII data.
911 * This will not be re-entered while running, but other ldisc
912 * functions may be called in parallel.
914 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
915 static void elmcan_ldisc_rx(struct tty_struct *tty,
916 const unsigned char *cp, char *fp, int count)
918 static void elmcan_ldisc_rx(struct tty_struct *tty,
919 const unsigned char *cp, const char *fp, int count)
922 struct elmcan *elm = (struct elmcan *)tty->disc_data;
924 spin_lock_bh(&elm->lock);
926 if (elm->uart_side_failure)
929 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
931 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
933 elm327_uart_side_failure(elm);
938 /* Ignore NUL characters, which the PIC microcontroller may
939 * inadvertently insert due to a known hardware bug.
940 * See ELM327 documentation, which refers to a Microchip PIC
944 /* Check for stray characters on the UART line.
945 * Likely caused by bad hardware.
947 if (!elmcan_is_valid_rx_char(*cp)) {
949 "Received illegal character %02x.\n",
951 elm327_uart_side_failure(elm);
956 elm->rxbuf[elm->rxfill++] = *cp;
963 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
965 elm327_uart_side_failure(elm);
970 elm327_parse_rxbuf(elm);
973 spin_unlock_bh(&elm->lock);
976 /* Write out remaining transmit buffer.
977 * Scheduled when TTY is writable.
979 static void elmcan_ldisc_tx_worker(struct work_struct *work)
981 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
984 if (elm->uart_side_failure)
987 spin_lock_bh(&elm->lock);
990 written = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
993 "Failed to write to tty %s.\n",
995 elm327_uart_side_failure(elm);
996 spin_unlock_bh(&elm->lock);
999 elm->txleft -= written;
1000 elm->txhead += written;
1005 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1006 spin_unlock_bh(&elm->lock);
1007 netif_wake_queue(elm->dev);
1009 spin_unlock_bh(&elm->lock);
1013 /* Called by the driver when there's room for more data. */
1014 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1016 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1018 schedule_work(&elm->tx_work);
1021 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1022 * or 7/8 of that. Divisors are 1 to 64.
1023 * Currently we don't implement support for 7/8 rates.
1025 static const u32 elmcan_bitrate_const[64] = {
1026 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1027 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1028 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1029 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1030 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1031 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1032 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1033 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1036 /* Dummy needed to use bitrate_const */
1037 static int elmcan_do_set_bittiming(struct net_device *netdev)
1042 static int elmcan_ldisc_open(struct tty_struct *tty)
1044 struct net_device *dev;
1048 if (!capable(CAP_NET_ADMIN))
1051 if (!tty->ops->write)
1054 dev = alloc_candev(sizeof(struct elmcan), 0);
1057 elm = netdev_priv(dev);
1059 /* Configure TTY interface */
1060 tty->receive_room = 65536; /* We don't flow control */
1061 spin_lock_init(&elm->lock);
1062 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1064 /* Configure CAN metadata */
1065 elm->can.bitrate_const = elmcan_bitrate_const;
1066 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1067 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1068 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1070 /* Configure netdev interface */
1072 dev->netdev_ops = &elmcan_netdev_ops;
1074 /* Mark ldisc channel as alive */
1076 tty->disc_data = elm;
1078 devm_can_led_init(elm->dev);
1081 err = register_candev(elm->dev);
1085 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1090 free_candev(elm->dev);
1094 /* Close down an elmcan channel.
1095 * This means flushing out any pending queues, and then returning.
1096 * This call is serialized against other ldisc functions:
1097 * Once this is called, no other ldisc function of ours is entered.
1099 * We also use this function for a hangup event.
1101 static void elmcan_ldisc_close(struct tty_struct *tty)
1103 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1105 /* unregister_netdev() calls .ndo_stop() so we don't have to.
1106 * Our .ndo_stop() also flushes the TTY write wakeup handler,
1107 * so we can safely set elm->tty = NULL after this.
1109 unregister_candev(elm->dev);
1111 /* Mark channel as dead */
1112 spin_lock_bh(&elm->lock);
1113 tty->disc_data = NULL;
1115 spin_unlock_bh(&elm->lock);
1117 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1119 free_candev(elm->dev);
1122 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1123 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1126 unsigned int cmd, unsigned long arg)
1128 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1133 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1134 if (copy_to_user((void __user *)arg, elm->dev->name, tmp))
1142 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1143 return tty_mode_ioctl(tty, file, cmd, arg);
1145 return tty_mode_ioctl(tty, cmd, arg);
1150 static struct tty_ldisc_ops elmcan_ldisc = {
1151 .owner = THIS_MODULE,
1153 .num = N_DEVELOPMENT,
1154 .receive_buf = elmcan_ldisc_rx,
1155 .write_wakeup = elmcan_ldisc_tx_wakeup,
1156 .open = elmcan_ldisc_open,
1157 .close = elmcan_ldisc_close,
1158 .ioctl = elmcan_ldisc_ioctl,
1161 static int __init elmcan_init(void)
1165 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1166 status = tty_register_ldisc(N_DEVELOPMENT, &elmcan_ldisc);
1168 status = tty_register_ldisc(&elmcan_ldisc);
1171 pr_err("Can't register line discipline\n");
1176 static void __exit elmcan_exit(void)
1178 /* This will only be called when all channels have been closed by
1179 * userspace - tty_ldisc.c takes care of the module's refcount.
1181 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1184 status = tty_unregister_ldisc(N_DEVELOPMENT);
1186 pr_err("Can't unregister line discipline (error: %d)\n",
1189 tty_unregister_ldisc(&elmcan_ldisc);
1193 module_init(elmcan_init);
1194 module_exit(elmcan_exit);
1196 MODULE_ALIAS_LDISC(N_DEVELOPMENT);
1197 MODULE_DESCRIPTION("ELM327 based CAN interface");
1198 MODULE_LICENSE("GPL");
1199 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");