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.
7 * elmcan.c Author : Max Staudt <max-linux@enpas.org>
8 * slcan.c Author : Oliver Hartkopp <socketcan@hartkopp.net>
9 * slip.c Authors : Laurence Culhane <loz@holmes.demon.co.uk>
10 * Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
13 #define pr_fmt(fmt) "elmcan: " fmt
15 #include <linux/init.h>
16 #include <linux/module.h>
17 #include <linux/moduleparam.h>
19 #include <linux/atomic.h>
20 #include <linux/bitops.h>
21 #include <linux/ctype.h>
22 #include <linux/delay.h>
23 #include <linux/errno.h>
24 #include <linux/if_ether.h>
25 #include <linux/kernel.h>
26 #include <linux/list.h>
27 #include <linux/lockdep.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 * Starting with Linux v5.18-rc1, N_DEVELOPMENT is defined as 29:
47 * https://github.com/torvalds/linux/commit/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 224
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_to_to_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;
92 u8 rxbuf[ELM327_SIZE_RXBUF];
93 u8 txbuf[ELM327_SIZE_TXBUF] ____cacheline_aligned;
95 /* TTY buffer accounting */
96 struct work_struct tx_work; /* Flushes TTY TX buffer */
97 u8 *txhead; /* Next TX byte */
98 unsigned txleft; /* Bytes left to TX */
99 int rxfill; /* Bytes already RX'd in buffer */
101 /* TTY and netdev devices that we're bridging */
102 struct tty_struct *tty;
103 struct net_device *dev;
105 /* Per-channel lock */
110 ELM327_STATE_NOTINIT = 0,
111 ELM327_STATE_GETDUMMYCHAR,
112 ELM327_STATE_GETPROMPT,
113 ELM327_STATE_RECEIVING,
116 /* Things we have yet to send */
117 char **next_init_cmd;
118 unsigned long cmds_todo;
120 /* The CAN frame and config the ELM327 is sending/using,
121 * or will send/use after finishing all cmds_todo
123 struct can_frame can_frame_to_send;
125 u8 can_bitrate_divisor;
130 /* Stop the channel on UART side hardware failure, e.g. stray
131 * characters or neverending lines. This may be caused by bad
132 * UART wiring, a bad ELM327, a bad UART bridge...
133 * Once this is true, nothing will be sent to the TTY.
135 bool uart_side_failure;
138 static inline void elm327_uart_side_failure(struct elmcan *elm);
140 static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
144 lockdep_assert_held(&elm->lock);
146 if (elm->uart_side_failure)
149 memcpy(elm->txbuf, buf, len);
151 written = elm->tty->ops->write(elm->tty, elm->txbuf, len);
154 "Failed to write to tty %s.\n",
156 elm327_uart_side_failure(elm);
160 elm->txleft = len - written;
161 elm->txhead = elm->txbuf + written;
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 * The line length is limited by the buffer in elm327_handle_prompt().
225 static char *elm327_init_script[] = {
226 "AT WS\r", /* v1.0: Warm Start */
227 "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
228 "AT M0\r", /* v1.0: Memory Off */
229 "AT AL\r", /* v1.0: Allow Long messages */
230 "AT BI\r", /* v1.0: Bypass Initialisation */
231 "AT CAF0\r", /* v1.0: CAN Auto Formatting Off */
232 "AT CFC0\r", /* v1.0: CAN Flow Control Off */
233 "AT CF 000\r", /* v1.0: Reset CAN ID Filter */
234 "AT CM 000\r", /* v1.0: Reset CAN ID Mask */
235 "AT E1\r", /* v1.0: Echo On */
236 "AT H1\r", /* v1.0: Headers On */
237 "AT L0\r", /* v1.0: Linefeeds Off */
238 "AT SH 7DF\r", /* v1.0: Set CAN sending ID to 0x7df */
239 "AT ST FF\r", /* v1.0: Set maximum Timeout for response after TX */
240 "AT AT0\r", /* v1.2: Adaptive Timing Off */
241 "AT D1\r", /* v1.3: Print DLC On */
242 "AT S1\r", /* v1.3: Spaces On */
243 "AT TP B\r", /* v1.0: Try Protocol B */
247 static void elm327_init(struct elmcan *elm)
249 lockdep_assert_held(&elm->lock);
251 elm->state = ELM327_STATE_NOTINIT;
252 elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
254 elm->drop_next_line = 0;
256 /* We can only set the bitrate as a fraction of 500000.
257 * The bit timing constants in elmcan_bittiming_const will
258 * limit the user to the right values.
260 elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
261 elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
262 | ELM327_CAN_CONFIG_VARIABLE_DLC
263 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
264 | elm->can_bitrate_divisor;
266 /* Configure ELM327 and then start monitoring */
267 elm->next_init_cmd = &elm327_init_script[0];
268 set_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
269 set_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
270 set_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo);
271 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
273 elm327_kick_into_cmd_mode(elm);
276 static void elm327_feed_frame_to_netdev(struct elmcan *elm,
279 lockdep_assert_held(&elm->lock);
281 if (!netif_running(elm->dev))
284 /* Queue for NAPI pickup.
285 * rx-offload will update stats and LEDs for us.
287 if (can_rx_offload_queue_tail(&elm->offload, skb))
288 elm->dev->stats.rx_fifo_errors++;
290 #if LINUX_VERSION_CODE >= KERNEL_VERSION(5,15,0)
292 can_rx_offload_irq_finish(&elm->offload);
296 /* Called when we're out of ideas and just want it all to end. */
297 static inline void elm327_uart_side_failure(struct elmcan *elm)
299 struct can_frame *frame;
302 lockdep_assert_held(&elm->lock);
304 elm->uart_side_failure = true;
306 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
308 elm->can.can_stats.bus_off++;
309 netif_stop_queue(elm->dev);
310 elm->can.state = CAN_STATE_BUS_OFF;
311 can_bus_off(elm->dev);
313 netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
315 skb = alloc_can_err_skb(elm->dev, &frame);
319 frame->can_id |= CAN_ERR_BUSOFF;
320 elm327_feed_frame_to_netdev(elm, skb);
323 /* Compare buffer to string length, then compare buffer to fixed string.
324 * This ensures two things:
325 * - It flags cases where the fixed string is only the start of the
326 * buffer, rather than exactly all of it.
327 * - It avoids byte comparisons in case the length doesn't match.
329 * strncmp() cannot be used here because it accepts the following wrong case:
330 * strncmp("CAN ER", "CAN ERROR", 6);
331 * This must fail, hence this helper function.
333 static inline int check_len_then_cmp(const u8 *mem, size_t mem_len, const char *str)
335 size_t str_len = strlen(str);
337 return (mem_len == str_len) && !memcmp(mem, str, str_len);
340 static void elm327_parse_error(struct elmcan *elm, size_t len)
342 struct can_frame *frame;
345 lockdep_assert_held(&elm->lock);
347 skb = alloc_can_err_skb(elm->dev, &frame);
349 /* It's okay to return here:
350 * The outer parsing loop will drop this UART buffer.
354 /* Filter possible error messages based on length of RX'd line */
355 if (check_len_then_cmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
357 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
358 } else if (check_len_then_cmp(elm->rxbuf, len, "BUFFER FULL")) {
359 /* This will only happen if the last data line was complete.
360 * Otherwise, elm327_parse_frame() will heuristically
361 * emit this kind of error frame instead.
363 frame->can_id |= CAN_ERR_CRTL;
364 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
365 } else if (check_len_then_cmp(elm->rxbuf, len, "BUS ERROR")) {
366 frame->can_id |= CAN_ERR_BUSERROR;
367 } else if (check_len_then_cmp(elm->rxbuf, len, "CAN ERROR")) {
368 frame->can_id |= CAN_ERR_PROT;
369 } else if (check_len_then_cmp(elm->rxbuf, len, "<RX ERROR")) {
370 frame->can_id |= CAN_ERR_PROT;
371 } else if (check_len_then_cmp(elm->rxbuf, len, "BUS BUSY")) {
372 frame->can_id |= CAN_ERR_PROT;
373 frame->data[2] = CAN_ERR_PROT_OVERLOAD;
374 } else if (check_len_then_cmp(elm->rxbuf, len, "FB ERROR")) {
375 frame->can_id |= CAN_ERR_PROT;
376 frame->data[2] = CAN_ERR_PROT_TX;
377 } else if (len == 5 && !memcmp(elm->rxbuf, "ERR", 3)) {
378 /* ERR is followed by two digits, hence line length 5 */
379 netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
380 elm->rxbuf[3], elm->rxbuf[4]);
381 frame->can_id |= CAN_ERR_CRTL;
383 /* Something else has happened.
384 * Maybe garbage on the UART line.
385 * Emit a generic error frame.
389 elm327_feed_frame_to_netdev(elm, skb);
392 /* Parse CAN frames coming as ASCII from ELM327.
393 * They can be of various formats:
395 * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
396 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
398 * where D = DLC, PL = payload byte
400 * Instead of a payload, RTR indicates a remote request.
402 * We will use the spaces and line length to guess the format.
404 static int elm327_parse_frame(struct elmcan *elm, size_t len)
406 struct can_frame *frame;
412 lockdep_assert_held(&elm->lock);
414 skb = alloc_can_skb(elm->dev, &frame);
418 /* Find first non-hex and non-space character:
419 * - In the simplest case, there is none.
420 * - For RTR frames, 'R' is the first non-hex character.
421 * - An error message may replace the end of the data line.
423 for (hexlen = 0; hexlen <= len; hexlen++) {
424 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
425 elm->rxbuf[hexlen] != ' ') {
430 /* Sanity check whether the line is really a clean hexdump,
431 * or terminated by an error message, or contains garbage.
434 !isdigit(elm->rxbuf[hexlen]) &&
435 !isupper(elm->rxbuf[hexlen]) &&
436 '<' != elm->rxbuf[hexlen] &&
437 ' ' != elm->rxbuf[hexlen]) {
438 /* The line is likely garbled anyway, so bail.
439 * The main code will restart listening.
444 /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
445 * No out-of-bounds access:
446 * We use the fact that we can always read from elm->rxbuf.
448 if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
449 elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
450 elm->rxbuf[13] == ' ') {
451 frame->can_id = CAN_EFF_FLAG;
453 } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
456 /* This is not a well-formatted data line.
457 * Assume it's an error message.
462 if (hexlen < datastart) {
463 /* The line is too short to be a valid frame hex dump.
464 * Something interrupted the hex dump or it is invalid.
469 /* From here on all chars up to buf[hexlen] are hex or spaces,
470 * at well-defined offsets.
473 /* Read CAN data length */
474 frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
477 if (frame->can_id & CAN_EFF_FLAG) {
478 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
479 | (hex_to_bin(elm->rxbuf[1]) << 24)
480 | (hex_to_bin(elm->rxbuf[3]) << 20)
481 | (hex_to_bin(elm->rxbuf[4]) << 16)
482 | (hex_to_bin(elm->rxbuf[6]) << 12)
483 | (hex_to_bin(elm->rxbuf[7]) << 8)
484 | (hex_to_bin(elm->rxbuf[9]) << 4)
485 | (hex_to_bin(elm->rxbuf[10]) << 0);
487 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
488 | (hex_to_bin(elm->rxbuf[1]) << 4)
489 | (hex_to_bin(elm->rxbuf[2]) << 0);
492 /* Check for RTR frame */
493 if (elm->rxfill >= hexlen + 3 &&
494 !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) {
495 frame->can_id |= CAN_RTR_FLAG;
498 /* Is the line long enough to hold the advertised payload?
499 * Note: RTR frames have a DLC, but no actual payload.
501 if (!(frame->can_id & CAN_RTR_FLAG) &&
502 (hexlen < frame->len * 3 + datastart)) {
504 * Probably the ELM327's RS232 TX buffer was full.
505 * Emit an error frame and exit.
507 frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
508 frame->len = CAN_ERR_DLC;
509 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
510 elm327_feed_frame_to_netdev(elm, skb);
512 /* Signal failure to parse.
513 * The line will be re-parsed as an error line, which will fail.
514 * However, this will correctly drop the state machine back into
520 /* Parse the data nibbles. */
521 for (i = 0; i < frame->len; i++) {
522 frame->data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
523 | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
526 /* Feed the frame to the network layer. */
527 elm327_feed_frame_to_netdev(elm, skb);
532 static void elm327_parse_line(struct elmcan *elm, size_t len)
534 lockdep_assert_held(&elm->lock);
536 /* Skip empty lines */
540 /* Skip echo lines */
541 if (elm->drop_next_line) {
542 elm->drop_next_line = 0;
544 } else if (!memcmp(elm->rxbuf, "AT", 2)) {
548 /* Regular parsing */
549 if (elm->state == ELM327_STATE_RECEIVING &&
550 elm327_parse_frame(elm, len)) {
551 /* Parse an error line. */
552 elm327_parse_error(elm, len);
555 elm327_kick_into_cmd_mode(elm);
559 static void elm327_handle_prompt(struct elmcan *elm)
561 struct can_frame *frame = &elm->can_frame_to_send;
562 /* Size this buffer for the largest ELM327 line we may generate,
563 * which is currently an 8 byte CAN frame's payload hexdump.
564 * Items in elm327_init_script must fit here, too!
566 char local_txbuf[sizeof("0102030405060708\r")];
568 lockdep_assert_held(&elm->lock);
570 if (!elm->cmds_todo) {
571 /* Enter CAN monitor mode */
572 elm327_send(elm, "ATMA\r", 5);
573 elm->state = ELM327_STATE_RECEIVING;
575 /* We will be in the default state once this command is
576 * send, so enable the TX packet queue.
578 netif_wake_queue(elm->dev);
583 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
584 if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
585 snprintf(local_txbuf, sizeof(local_txbuf),
587 *elm->next_init_cmd);
589 elm->next_init_cmd++;
590 if (!(*elm->next_init_cmd)) {
591 clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
595 } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
596 snprintf(local_txbuf, sizeof(local_txbuf),
598 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
600 } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo)) {
601 snprintf(local_txbuf, sizeof(local_txbuf),
603 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
605 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
606 snprintf(local_txbuf, sizeof(local_txbuf),
608 set_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);
610 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
611 snprintf(local_txbuf, sizeof(local_txbuf),
615 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
616 snprintf(local_txbuf, sizeof(local_txbuf),
618 (frame->can_id & CAN_EFF_MASK) >> 24);
620 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
621 snprintf(local_txbuf, sizeof(local_txbuf),
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 snprintf(local_txbuf, sizeof(local_txbuf),
628 frame->can_id & CAN_SFF_MASK);
630 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
631 if (frame->can_id & CAN_RTR_FLAG) {
632 /* Send an RTR frame. Their DLC is fixed.
633 * Some chips don't send them at all.
635 snprintf(local_txbuf, sizeof(local_txbuf),
638 /* Send a regular CAN data frame */
641 for (i = 0; i < frame->len; i++) {
642 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
647 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
651 elm->drop_next_line = 1;
652 elm->state = ELM327_STATE_RECEIVING;
654 /* We will be in the default state once this command is
655 * send, so enable the TX packet queue.
657 netif_wake_queue(elm->dev);
660 elm327_send(elm, local_txbuf, strlen(local_txbuf));
663 static bool elm327_is_ready_char(char c)
665 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
666 * Probably bad hardware.
668 return (c & 0x3f) == ELM327_READY_CHAR;
671 static void elm327_drop_bytes(struct elmcan *elm, size_t i)
673 lockdep_assert_held(&elm->lock);
675 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
679 static void elm327_parse_rxbuf(struct elmcan *elm)
684 lockdep_assert_held(&elm->lock);
686 switch (elm->state) {
687 case ELM327_STATE_NOTINIT:
691 case ELM327_STATE_GETDUMMYCHAR:
693 /* Wait for 'y' or '>' */
694 for (i = 0; i < elm->rxfill; i++) {
695 if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
696 elm327_send(elm, "\r", 1);
697 elm->state = ELM327_STATE_GETPROMPT;
700 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
701 elm327_send(elm, ELM327_DUMMY_STRING, 1);
707 elm327_drop_bytes(elm, i);
712 case ELM327_STATE_GETPROMPT:
714 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
715 elm327_handle_prompt(elm);
720 case ELM327_STATE_RECEIVING:
721 /* Find <CR> delimiting feedback lines. */
723 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
728 if (len == ELM327_SIZE_RXBUF) {
729 /* Line exceeds buffer. It's probably all garbage.
730 * Did we even connect at the right baud rate?
733 "RX buffer overflow. Faulty ELM327 or UART?\n");
734 elm327_uart_side_failure(elm);
736 } else if (len == elm->rxfill) {
737 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
738 /* The ELM327's AT ST response timeout ran out,
739 * so we got a prompt.
740 * Clear RX buffer and restart listening.
744 elm327_handle_prompt(elm);
748 /* No <CR> found - we haven't received a full line yet.
749 * Wait for more data.
754 /* We have a full line to parse. */
755 elm327_parse_line(elm, len);
757 /* Remove parsed data from RX buffer. */
758 elm327_drop_bytes(elm, len + 1);
760 /* More data to parse? */
762 elm327_parse_rxbuf(elm);
766 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
767 /* Dummy needed to use can_rx_offload */
768 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
769 unsigned int n, u32 *timestamp,
772 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
774 return ERR_PTR(-ENOBUFS);
778 static int elmcan_netdev_open(struct net_device *dev)
780 struct elmcan *elm = netdev_priv(dev);
783 spin_lock_bh(&elm->lock);
786 spin_unlock_bh(&elm->lock);
790 if (elm->uart_side_failure)
791 netdev_warn(elm->dev, "Reopening netdev after a UART side fault has been detected.\n");
793 /* Clear TTY buffers */
797 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
798 err = open_candev(dev);
800 spin_unlock_bh(&elm->lock);
805 spin_unlock_bh(&elm->lock);
807 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
808 elm->offload.mailbox_read = elmcan_mailbox_read;
809 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
811 err = can_rx_offload_add_manual(dev, &elm->offload, ELM327_NAPI_WEIGHT);
818 can_rx_offload_enable(&elm->offload);
820 can_led_event(dev, CAN_LED_EVENT_OPEN);
821 elm->can.state = CAN_STATE_ERROR_ACTIVE;
822 netif_start_queue(dev);
827 static int elmcan_netdev_close(struct net_device *dev)
829 struct elmcan *elm = netdev_priv(dev);
831 /* Interrupt whatever the ELM327 is doing right now */
832 spin_lock_bh(&elm->lock);
833 elm327_send(elm, ELM327_DUMMY_STRING, 1);
834 spin_unlock_bh(&elm->lock);
836 netif_stop_queue(dev);
838 /* Give UART one final chance to flush. */
839 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
840 flush_work(&elm->tx_work);
842 can_rx_offload_disable(&elm->offload);
843 elm->can.state = CAN_STATE_STOPPED;
844 can_rx_offload_del(&elm->offload);
846 can_led_event(dev, CAN_LED_EVENT_STOP);
851 /* Send a can_frame to a TTY. */
852 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
853 struct net_device *dev)
855 struct elmcan *elm = netdev_priv(dev);
856 struct can_frame *frame = (struct can_frame *)skb->data;
858 if (can_dropped_invalid_skb(dev, skb))
861 /* BHs are already disabled, so no spin_lock_bh().
862 * See Documentation/networking/netdevices.txt
864 spin_lock(&elm->lock);
866 /* We shouldn't get here after a hardware fault:
867 * can_bus_off() calls netif_carrier_off()
869 WARN_ON_ONCE(elm->uart_side_failure);
872 elm->uart_side_failure ||
873 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
874 spin_unlock(&elm->lock);
878 netif_stop_queue(dev);
880 elm327_send_frame(elm, frame);
881 spin_unlock(&elm->lock);
883 dev->stats.tx_packets++;
884 dev->stats.tx_bytes += frame->len;
886 can_led_event(dev, CAN_LED_EVENT_TX);
893 static const struct net_device_ops elmcan_netdev_ops = {
894 .ndo_open = elmcan_netdev_open,
895 .ndo_stop = elmcan_netdev_close,
896 .ndo_start_xmit = elmcan_netdev_start_xmit,
897 .ndo_change_mtu = can_change_mtu,
900 static bool elmcan_is_valid_rx_char(char c)
902 return (isdigit(c) ||
904 c == ELM327_DUMMY_CHAR ||
905 c == ELM327_READY_CHAR ||
916 /* Handle incoming ELM327 ASCII data.
917 * This will not be re-entered while running, but other ldisc
918 * functions may be called in parallel.
920 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
921 static void elmcan_ldisc_rx(struct tty_struct *tty,
922 const unsigned char *cp, char *fp, int count)
924 static void elmcan_ldisc_rx(struct tty_struct *tty,
925 const unsigned char *cp, const char *fp, int count)
928 struct elmcan *elm = (struct elmcan *)tty->disc_data;
930 spin_lock_bh(&elm->lock);
932 if (elm->uart_side_failure)
935 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
937 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
939 elm327_uart_side_failure(elm);
944 /* Ignore NUL characters, which the PIC microcontroller may
945 * inadvertently insert due to a known hardware bug.
946 * See ELM327 documentation, which refers to a Microchip PIC
950 /* Check for stray characters on the UART line.
951 * Likely caused by bad hardware.
953 if (!elmcan_is_valid_rx_char(*cp)) {
955 "Received illegal character %02x.\n",
957 elm327_uart_side_failure(elm);
962 elm->rxbuf[elm->rxfill++] = *cp;
969 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
971 elm327_uart_side_failure(elm);
976 elm327_parse_rxbuf(elm);
979 spin_unlock_bh(&elm->lock);
982 /* Write out remaining transmit buffer.
983 * Scheduled when TTY is writable.
985 static void elmcan_ldisc_tx_worker(struct work_struct *work)
987 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
990 if (elm->uart_side_failure)
993 spin_lock_bh(&elm->lock);
996 written = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
999 "Failed to write to tty %s.\n",
1001 elm327_uart_side_failure(elm);
1002 spin_unlock_bh(&elm->lock);
1006 elm->txleft -= written;
1007 elm->txhead += written;
1011 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1012 spin_unlock_bh(&elm->lock);
1014 spin_unlock_bh(&elm->lock);
1018 /* Called by the driver when there's room for more data. */
1019 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1021 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1023 schedule_work(&elm->tx_work);
1026 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1027 * or 7/8 of that. Divisors are 1 to 64.
1028 * Currently we don't implement support for 7/8 rates.
1030 static const u32 elmcan_bitrate_const[64] = {
1031 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1032 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1033 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1034 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1035 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1036 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1037 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1038 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1041 /* Dummy needed to use bitrate_const */
1042 static int elmcan_do_set_bittiming(struct net_device *netdev)
1047 static int elmcan_ldisc_open(struct tty_struct *tty)
1049 struct net_device *dev;
1053 if (!capable(CAP_NET_ADMIN))
1056 if (!tty->ops->write)
1059 dev = alloc_candev(sizeof(struct elmcan), 0);
1062 elm = netdev_priv(dev);
1064 /* Configure TTY interface */
1065 tty->receive_room = 65536; /* We don't flow control */
1066 spin_lock_init(&elm->lock);
1067 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1069 /* Configure CAN metadata */
1070 elm->can.bitrate_const = elmcan_bitrate_const;
1071 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1072 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1073 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1075 /* Configure netdev interface */
1077 dev->netdev_ops = &elmcan_netdev_ops;
1079 /* Mark ldisc channel as alive */
1081 tty->disc_data = elm;
1083 devm_can_led_init(elm->dev);
1086 err = register_candev(elm->dev);
1090 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1095 free_candev(elm->dev);
1099 /* Close down an elmcan channel.
1100 * This means flushing out any pending queues, and then returning.
1101 * This call is serialized against other ldisc functions:
1102 * Once this is called, no other ldisc function of ours is entered.
1104 * We also use this function for a hangup event.
1106 static void elmcan_ldisc_close(struct tty_struct *tty)
1108 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1110 /* unregister_netdev() calls .ndo_stop() so we don't have to.
1111 * Our .ndo_stop() also flushes the TTY write wakeup handler,
1112 * so we can safely set elm->tty = NULL after this.
1114 unregister_candev(elm->dev);
1116 /* Mark channel as dead */
1117 spin_lock_bh(&elm->lock);
1118 tty->disc_data = NULL;
1120 spin_unlock_bh(&elm->lock);
1122 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1124 free_candev(elm->dev);
1127 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1128 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1131 unsigned int cmd, unsigned long arg)
1133 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1138 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1139 if (copy_to_user((void __user *)arg, elm->dev->name, tmp))
1147 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1148 return tty_mode_ioctl(tty, file, cmd, arg);
1150 return tty_mode_ioctl(tty, cmd, arg);
1155 static struct tty_ldisc_ops elmcan_ldisc = {
1156 .owner = THIS_MODULE,
1158 .num = N_DEVELOPMENT,
1159 .receive_buf = elmcan_ldisc_rx,
1160 .write_wakeup = elmcan_ldisc_tx_wakeup,
1161 .open = elmcan_ldisc_open,
1162 .close = elmcan_ldisc_close,
1163 .ioctl = elmcan_ldisc_ioctl,
1166 static int __init elmcan_init(void)
1170 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1171 status = tty_register_ldisc(N_DEVELOPMENT, &elmcan_ldisc);
1173 status = tty_register_ldisc(&elmcan_ldisc);
1176 pr_err("Can't register line discipline\n");
1181 static void __exit elmcan_exit(void)
1183 /* This will only be called when all channels have been closed by
1184 * userspace - tty_ldisc.c takes care of the module's refcount.
1186 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1189 status = tty_unregister_ldisc(N_DEVELOPMENT);
1191 pr_err("Can't unregister line discipline (error: %d)\n",
1194 tty_unregister_ldisc(&elmcan_ldisc);
1198 module_init(elmcan_init);
1199 module_exit(elmcan_exit);
1201 MODULE_ALIAS_LDISC(N_DEVELOPMENT);
1202 MODULE_DESCRIPTION("ELM327 based CAN interface");
1203 MODULE_LICENSE("GPL");
1204 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");