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 UART side hardware failure, e.g. stray
100 * characters or neverending lines. This may be caused by bad
101 * UART wiring, a bad ELM327, a bad UART bridge...
102 * Once this is true, nothing will be sent to the TTY.
104 bool uart_side_failure;
107 struct work_struct tx_work; /* Flushes TTY TX buffer */
108 u8 *txbuf; /* Pointer to our TX buffer */
109 u8 *txhead; /* Pointer to next TX byte */
110 unsigned txleft; /* Bytes left to TX */
113 u8 rxbuf[ELM327_SIZE_RXBUF];
118 ELM327_STATE_NOTINIT = 0,
119 ELM327_STATE_GETDUMMYCHAR,
120 ELM327_STATE_GETPROMPT,
121 ELM327_STATE_RECEIVING,
126 /* The CAN frame and config the ELM327 is sending/using,
127 * or will send/use after finishing all cmds_todo
129 struct can_frame can_frame_to_send;
131 u8 can_bitrate_divisor;
133 /* Things we have yet to send */
134 char **next_init_cmd;
135 unsigned long cmds_todo;
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 netif_wake_queue(elm->dev);
166 set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
169 /* Take the ELM327 out of almost any state and back into command mode.
170 * We send ELM327_DUMMY_CHAR which will either abort any running
171 * operation, or be echoed back to us in case we're already in command
174 static void elm327_kick_into_cmd_mode(struct elmcan *elm)
176 lockdep_assert_held(elm->lock);
178 if (elm->state != ELM327_STATE_GETDUMMYCHAR &&
179 elm->state != ELM327_STATE_GETPROMPT) {
180 elm327_send(elm, ELM327_DUMMY_STRING, 1);
182 elm->state = ELM327_STATE_GETDUMMYCHAR;
186 /* Schedule a CAN frame and necessary config changes to be sent to the TTY. */
187 static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
189 lockdep_assert_held(elm->lock);
191 /* Schedule any necessary changes in ELM327's CAN configuration */
192 if (elm->can_frame_to_send.can_id != frame->can_id) {
193 /* Set the new CAN ID for transmission. */
194 if ((frame->can_id & CAN_EFF_FLAG) ^
195 (elm->can_frame_to_send.can_id & CAN_EFF_FLAG)) {
196 elm->can_config = (frame->can_id & CAN_EFF_FLAG
198 : ELM327_CAN_CONFIG_SEND_SFF)
199 | ELM327_CAN_CONFIG_VARIABLE_DLC
200 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
201 | elm->can_bitrate_divisor;
203 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
206 if (frame->can_id & CAN_EFF_FLAG) {
207 clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
208 set_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
209 set_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
211 set_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
212 clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
213 clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
217 /* Schedule the CAN frame itself. */
218 elm->can_frame_to_send = *frame;
219 set_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo);
221 elm327_kick_into_cmd_mode(elm);
224 /* ELM327 initialisation sequence.
225 * The line length is limited by the buffer in elm327_handle_prompt().
227 static char *elm327_init_script[] = {
228 "AT WS\r", /* v1.0: Warm Start */
229 "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
230 "AT M0\r", /* v1.0: Memory Off */
231 "AT AL\r", /* v1.0: Allow Long messages */
232 "AT BI\r", /* v1.0: Bypass Initialisation */
233 "AT CAF0\r", /* v1.0: CAN Auto Formatting Off */
234 "AT CFC0\r", /* v1.0: CAN Flow Control Off */
235 "AT CF 000\r", /* v1.0: Reset CAN ID Filter */
236 "AT CM 000\r", /* v1.0: Reset CAN ID Mask */
237 "AT E1\r", /* v1.0: Echo On */
238 "AT H1\r", /* v1.0: Headers On */
239 "AT L0\r", /* v1.0: Linefeeds Off */
240 "AT SH 7DF\r", /* v1.0: Set CAN sending ID to 0x7df */
241 "AT ST FF\r", /* v1.0: Set maximum Timeout for response after TX */
242 "AT AT0\r", /* v1.2: Adaptive Timing Off */
243 "AT D1\r", /* v1.3: Print DLC On */
244 "AT S1\r", /* v1.3: Spaces On */
245 "AT TP B\r", /* v1.0: Try Protocol B */
249 static void elm327_init(struct elmcan *elm)
251 lockdep_assert_held(elm->lock);
253 elm->state = ELM327_STATE_NOTINIT;
254 elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
256 elm->drop_next_line = 0;
258 /* We can only set the bitrate as a fraction of 500000.
259 * The bit timing constants in elmcan_bittiming_const will
260 * limit the user to the right values.
262 elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
263 elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
264 | ELM327_CAN_CONFIG_VARIABLE_DLC
265 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
266 | elm->can_bitrate_divisor;
268 /* Configure ELM327 and then start monitoring */
269 elm->next_init_cmd = &elm327_init_script[0];
270 set_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
271 set_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
272 set_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo);
273 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
275 elm327_kick_into_cmd_mode(elm);
278 static void elm327_feed_frame_to_netdev(struct elmcan *elm,
281 lockdep_assert_held(elm->lock);
283 if (!netif_running(elm->dev))
286 /* Queue for NAPI pickup.
287 * rx-offload will update stats and LEDs for us.
289 if (can_rx_offload_queue_tail(&elm->offload, skb))
290 elm->dev->stats.rx_fifo_errors++;
292 #if LINUX_VERSION_CODE >= KERNEL_VERSION(5,15,0)
294 can_rx_offload_irq_finish(&elm->offload);
298 /* Called when we're out of ideas and just want it all to end. */
299 static inline void elm327_uart_side_failure(struct elmcan *elm)
301 struct can_frame *frame;
304 lockdep_assert_held(elm->lock);
306 elm->uart_side_failure = true;
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;
578 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
579 if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
580 snprintf(local_txbuf, sizeof(local_txbuf),
582 *elm->next_init_cmd);
584 elm->next_init_cmd++;
585 if (!(*elm->next_init_cmd)) {
586 clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
590 } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
591 snprintf(local_txbuf, sizeof(local_txbuf),
593 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
595 } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &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_CAN_CONFIG, &elm->cmds_todo)) {
601 snprintf(local_txbuf, sizeof(local_txbuf),
603 set_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);
605 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
606 snprintf(local_txbuf, sizeof(local_txbuf),
610 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
611 snprintf(local_txbuf, sizeof(local_txbuf),
613 (frame->can_id & CAN_EFF_MASK) >> 24);
615 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
616 snprintf(local_txbuf, sizeof(local_txbuf),
618 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
620 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
621 snprintf(local_txbuf, sizeof(local_txbuf),
623 frame->can_id & CAN_SFF_MASK);
625 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
626 if (frame->can_id & CAN_RTR_FLAG) {
627 /* Send an RTR frame. Their DLC is fixed.
628 * Some chips don't send them at all.
630 snprintf(local_txbuf, sizeof(local_txbuf),
633 /* Send a regular CAN data frame */
636 for (i = 0; i < frame->len; i++) {
637 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
642 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
646 elm->drop_next_line = 1;
647 elm->state = ELM327_STATE_RECEIVING;
650 elm327_send(elm, local_txbuf, strlen(local_txbuf));
653 static bool elm327_is_ready_char(char c)
655 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
656 * Probably bad hardware.
658 return (c & 0x3f) == ELM327_READY_CHAR;
661 static void elm327_drop_bytes(struct elmcan *elm, size_t i)
663 lockdep_assert_held(elm->lock);
665 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
669 static void elm327_parse_rxbuf(struct elmcan *elm)
674 lockdep_assert_held(elm->lock);
676 switch (elm->state) {
677 case ELM327_STATE_NOTINIT:
681 case ELM327_STATE_GETDUMMYCHAR:
683 /* Wait for 'y' or '>' */
684 for (i = 0; i < elm->rxfill; i++) {
685 if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
686 elm327_send(elm, "\r", 1);
687 elm->state = ELM327_STATE_GETPROMPT;
690 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
691 elm327_send(elm, ELM327_DUMMY_STRING, 1);
697 elm327_drop_bytes(elm, i);
702 case ELM327_STATE_GETPROMPT:
704 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
705 elm327_handle_prompt(elm);
710 case ELM327_STATE_RECEIVING:
711 /* Find <CR> delimiting feedback lines. */
713 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
718 if (len == ELM327_SIZE_RXBUF) {
719 /* Line exceeds buffer. It's probably all garbage.
720 * Did we even connect at the right baud rate?
723 "RX buffer overflow. Faulty ELM327 or UART?\n");
724 elm327_uart_side_failure(elm);
726 } else if (len == elm->rxfill) {
727 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
728 /* The ELM327's AT ST response timeout ran out,
729 * so we got a prompt.
730 * Clear RX buffer and restart listening.
734 elm327_handle_prompt(elm);
738 /* No <CR> found - we haven't received a full line yet.
739 * Wait for more data.
744 /* We have a full line to parse. */
745 elm327_parse_line(elm, len);
747 /* Remove parsed data from RX buffer. */
748 elm327_drop_bytes(elm, len + 1);
750 /* More data to parse? */
752 elm327_parse_rxbuf(elm);
756 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
757 /* Dummy needed to use can_rx_offload */
758 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
759 unsigned int n, u32 *timestamp,
762 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
764 return ERR_PTR(-ENOBUFS);
768 static int elmcan_netdev_open(struct net_device *dev)
770 struct elmcan *elm = netdev_priv(dev);
773 spin_lock_bh(&elm->lock);
774 if (elm->uart_side_failure) {
775 netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
776 spin_unlock_bh(&elm->lock);
781 spin_unlock_bh(&elm->lock);
785 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
786 err = open_candev(dev);
788 spin_unlock_bh(&elm->lock);
793 spin_unlock_bh(&elm->lock);
795 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
796 elm->offload.mailbox_read = elmcan_mailbox_read;
797 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
799 err = can_rx_offload_add_manual(dev, &elm->offload, ELM327_NAPI_WEIGHT);
806 can_rx_offload_enable(&elm->offload);
808 can_led_event(dev, CAN_LED_EVENT_OPEN);
809 elm->can.state = CAN_STATE_ERROR_ACTIVE;
810 netif_start_queue(dev);
815 static int elmcan_netdev_close(struct net_device *dev)
817 struct elmcan *elm = netdev_priv(dev);
819 netif_stop_queue(dev);
821 spin_lock_bh(&elm->lock);
823 /* Interrupt whatever we're doing right now */
824 elm327_send(elm, ELM327_DUMMY_STRING, 1);
826 /* Clear the wakeup bit, as the netdev will be down and thus
827 * the wakeup handler won't clear it
829 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
831 spin_unlock_bh(&elm->lock);
833 flush_work(&elm->tx_work);
835 spin_unlock_bh(&elm->lock);
838 can_rx_offload_disable(&elm->offload);
839 elm->can.state = CAN_STATE_STOPPED;
840 can_rx_offload_del(&elm->offload);
842 can_led_event(dev, CAN_LED_EVENT_STOP);
847 /* Send a can_frame to a TTY. */
848 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
849 struct net_device *dev)
851 struct elmcan *elm = netdev_priv(dev);
852 struct can_frame *frame = (struct can_frame *)skb->data;
854 if (can_dropped_invalid_skb(dev, skb))
857 /* BHs are already disabled, so no spin_lock_bh().
858 * See Documentation/networking/netdevices.txt
860 spin_lock(&elm->lock);
862 /* We shouldn't get here after a hardware fault:
863 * can_bus_off() calls netif_carrier_off()
865 WARN_ON_ONCE(elm->uart_side_failure);
868 elm->uart_side_failure ||
869 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
870 spin_unlock(&elm->lock);
874 netif_stop_queue(dev);
876 elm327_send_frame(elm, frame);
877 spin_unlock(&elm->lock);
879 dev->stats.tx_packets++;
880 dev->stats.tx_bytes += frame->len;
882 can_led_event(dev, CAN_LED_EVENT_TX);
889 static const struct net_device_ops elmcan_netdev_ops = {
890 .ndo_open = elmcan_netdev_open,
891 .ndo_stop = elmcan_netdev_close,
892 .ndo_start_xmit = elmcan_netdev_start_xmit,
893 .ndo_change_mtu = can_change_mtu,
896 static bool elmcan_is_valid_rx_char(char c)
898 return (isdigit(c) ||
900 c == ELM327_DUMMY_CHAR ||
901 c == ELM327_READY_CHAR ||
912 /* Handle incoming ELM327 ASCII data.
913 * This will not be re-entered while running, but other ldisc
914 * functions may be called in parallel.
916 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
917 static void elmcan_ldisc_rx(struct tty_struct *tty,
918 const unsigned char *cp, char *fp, int count)
920 static void elmcan_ldisc_rx(struct tty_struct *tty,
921 const unsigned char *cp, const char *fp, int count)
924 struct elmcan *elm = (struct elmcan *)tty->disc_data;
926 spin_lock_bh(&elm->lock);
928 if (elm->uart_side_failure)
931 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
933 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
935 elm327_uart_side_failure(elm);
940 /* Ignore NUL characters, which the PIC microcontroller may
941 * inadvertently insert due to a known hardware bug.
942 * See ELM327 documentation, which refers to a Microchip PIC
946 /* Check for stray characters on the UART line.
947 * Likely caused by bad hardware.
949 if (!elmcan_is_valid_rx_char(*cp)) {
951 "Received illegal character %02x.\n",
953 elm327_uart_side_failure(elm);
958 elm->rxbuf[elm->rxfill++] = *cp;
965 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
967 elm327_uart_side_failure(elm);
972 elm327_parse_rxbuf(elm);
975 spin_unlock_bh(&elm->lock);
978 /* Write out remaining transmit buffer.
979 * Scheduled when TTY is writable.
981 static void elmcan_ldisc_tx_worker(struct work_struct *work)
983 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
986 if (elm->uart_side_failure)
989 spin_lock_bh(&elm->lock);
992 written = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
995 "Failed to write to tty %s.\n",
997 elm327_uart_side_failure(elm);
998 spin_unlock_bh(&elm->lock);
1001 elm->txleft -= written;
1002 elm->txhead += written;
1007 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1008 spin_unlock_bh(&elm->lock);
1009 netif_wake_queue(elm->dev);
1011 spin_unlock_bh(&elm->lock);
1015 /* Called by the driver when there's room for more data. */
1016 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1018 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1020 schedule_work(&elm->tx_work);
1023 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1024 * or 7/8 of that. Divisors are 1 to 64.
1025 * Currently we don't implement support for 7/8 rates.
1027 static const u32 elmcan_bitrate_const[64] = {
1028 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1029 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1030 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1031 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1032 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1033 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1034 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1035 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1038 /* Dummy needed to use bitrate_const */
1039 static int elmcan_do_set_bittiming(struct net_device *netdev)
1044 static int elmcan_ldisc_open(struct tty_struct *tty)
1046 struct net_device *dev;
1050 if (!capable(CAP_NET_ADMIN))
1053 if (!tty->ops->write)
1056 dev = alloc_candev(sizeof(struct elmcan), 0);
1059 elm = netdev_priv(dev);
1061 elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
1067 /* Configure TTY interface */
1068 tty->receive_room = 65536; /* We don't flow control */
1069 elm->txleft = 0; /* Clear TTY TX buffer */
1070 spin_lock_init(&elm->lock);
1071 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1073 /* Configure CAN metadata */
1074 elm->can.bitrate_const = elmcan_bitrate_const;
1075 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1076 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1077 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1079 /* Configure netdev interface */
1081 dev->netdev_ops = &elmcan_netdev_ops;
1083 /* Mark ldisc channel as alive */
1085 tty->disc_data = elm;
1087 devm_can_led_init(elm->dev);
1090 err = register_candev(elm->dev);
1094 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1100 free_candev(elm->dev);
1104 /* Close down an elmcan channel.
1105 * This means flushing out any pending queues, and then returning.
1106 * This call is serialized against other ldisc functions:
1107 * Once this is called, no other ldisc function of ours is entered.
1109 * We also use this function for a hangup event.
1111 static void elmcan_ldisc_close(struct tty_struct *tty)
1113 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1115 /* unregister_netdev() calls .ndo_stop() so we don't have to. */
1116 unregister_candev(elm->dev);
1118 /* Ensure that our worker won't be rescheduled */
1119 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
1120 flush_work(&elm->tx_work);
1122 /* Mark channel as dead */
1123 spin_lock_bh(&elm->lock);
1124 tty->disc_data = NULL;
1126 spin_unlock_bh(&elm->lock);
1128 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1131 free_candev(elm->dev);
1134 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1135 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1138 unsigned int cmd, unsigned long arg)
1140 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1145 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1146 if (copy_to_user((void __user *)arg, elm->dev->name, tmp))
1154 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1155 return tty_mode_ioctl(tty, file, cmd, arg);
1157 return tty_mode_ioctl(tty, cmd, arg);
1162 static struct tty_ldisc_ops elmcan_ldisc = {
1163 .owner = THIS_MODULE,
1165 .num = N_DEVELOPMENT,
1166 .receive_buf = elmcan_ldisc_rx,
1167 .write_wakeup = elmcan_ldisc_tx_wakeup,
1168 .open = elmcan_ldisc_open,
1169 .close = elmcan_ldisc_close,
1170 .ioctl = elmcan_ldisc_ioctl,
1173 static int __init elmcan_init(void)
1177 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1178 status = tty_register_ldisc(N_DEVELOPMENT, &elmcan_ldisc);
1180 status = tty_register_ldisc(&elmcan_ldisc);
1183 pr_err("Can't register line discipline\n");
1188 static void __exit elmcan_exit(void)
1190 /* This will only be called when all channels have been closed by
1191 * userspace - tty_ldisc.c takes care of the module's refcount.
1193 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1196 status = tty_unregister_ldisc(N_DEVELOPMENT);
1198 pr_err("Can't unregister line discipline (error: %d)\n",
1201 tty_unregister_ldisc(&elmcan_ldisc);
1205 module_init(elmcan_init);
1206 module_exit(elmcan_exit);
1208 MODULE_ALIAS_LDISC(N_DEVELOPMENT);
1209 MODULE_DESCRIPTION("ELM327 based CAN interface");
1210 MODULE_LICENSE("GPL");
1211 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");