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 * 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_hw_failure(struct elmcan *elm)
299 struct can_frame *frame;
302 lockdep_assert_held(elm->lock);
304 elm->hw_failure = true;
306 elm->can.can_stats.bus_off++;
307 netif_stop_queue(elm->dev);
308 elm->can.state = CAN_STATE_BUS_OFF;
309 can_bus_off(elm->dev);
311 netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
313 skb = alloc_can_err_skb(elm->dev, &frame);
317 frame->can_id |= CAN_ERR_BUSOFF;
318 elm327_feed_frame_to_netdev(elm, skb);
321 /* Compare buffer to string length, then compare buffer to fixed string.
322 * This ensures two things:
323 * - It flags cases where the fixed string is only the start of the
324 * buffer, rather than exactly all of it.
325 * - It avoids byte comparisons in case the length doesn't match.
327 * strncmp() cannot be used here because it accepts the following wrong case:
328 * strncmp("CAN ER", "CAN ERROR", 6);
329 * This must fail, hence this helper function.
331 static inline int check_len_then_cmp(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 (check_len_then_cmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
355 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
356 } else if (check_len_then_cmp(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 (check_len_then_cmp(elm->rxbuf, len, "BUS ERROR")) {
364 frame->can_id |= CAN_ERR_BUSERROR;
365 } else if (check_len_then_cmp(elm->rxbuf, len, "CAN ERROR")) {
366 frame->can_id |= CAN_ERR_PROT;
367 } else if (check_len_then_cmp(elm->rxbuf, len, "<RX ERROR")) {
368 frame->can_id |= CAN_ERR_PROT;
369 } else if (check_len_then_cmp(elm->rxbuf, len, "BUS BUSY")) {
370 frame->can_id |= CAN_ERR_PROT;
371 frame->data[2] = CAN_ERR_PROT_OVERLOAD;
372 } else if (check_len_then_cmp(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 && !memcmp(elm->rxbuf, "ERR", 3)) {
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 !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) {
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 (!memcmp(elm->rxbuf, "AT", 2)) {
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 /* Size this buffer for the largest ELM327 line we may generate,
561 * which is currently an 8 byte CAN frame's payload hexdump.
562 * Items in elm327_init_script must fit here, too!
564 char local_txbuf[sizeof("0102030405060708\r")];
566 lockdep_assert_held(elm->lock);
568 if (!elm->cmds_todo) {
569 /* Enter CAN monitor mode */
570 elm327_send(elm, "ATMA\r", 5);
571 elm->state = ELM327_STATE_RECEIVING;
576 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
577 if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
578 snprintf(local_txbuf, sizeof(local_txbuf),
580 *elm->next_init_cmd);
582 elm->next_init_cmd++;
583 if (!(*elm->next_init_cmd)) {
584 clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
588 } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
589 snprintf(local_txbuf, sizeof(local_txbuf),
591 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
593 } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo)) {
594 snprintf(local_txbuf, sizeof(local_txbuf),
596 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
598 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
599 snprintf(local_txbuf, sizeof(local_txbuf),
601 set_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);
603 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
604 snprintf(local_txbuf, sizeof(local_txbuf),
608 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
609 snprintf(local_txbuf, sizeof(local_txbuf),
611 (frame->can_id & CAN_EFF_MASK) >> 24);
613 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
614 snprintf(local_txbuf, sizeof(local_txbuf),
616 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
618 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
619 snprintf(local_txbuf, sizeof(local_txbuf),
621 frame->can_id & CAN_SFF_MASK);
623 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
624 if (frame->can_id & CAN_RTR_FLAG) {
625 /* Send an RTR frame. Their DLC is fixed.
626 * Some chips don't send them at all.
628 snprintf(local_txbuf, sizeof(local_txbuf),
631 /* Send a regular CAN data frame */
634 for (i = 0; i < frame->len; i++) {
635 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
640 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
644 elm->drop_next_line = 1;
645 elm->state = ELM327_STATE_RECEIVING;
648 elm327_send(elm, local_txbuf, strlen(local_txbuf));
651 static bool elm327_is_ready_char(char c)
653 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
654 * Probably bad hardware.
656 return (c & 0x3f) == ELM327_READY_CHAR;
659 static void elm327_drop_bytes(struct elmcan *elm, size_t i)
661 lockdep_assert_held(elm->lock);
663 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
667 static void elm327_parse_rxbuf(struct elmcan *elm)
672 lockdep_assert_held(elm->lock);
674 switch (elm->state) {
675 case ELM327_STATE_NOTINIT:
679 case ELM327_STATE_GETDUMMYCHAR:
681 /* Wait for 'y' or '>' */
682 for (i = 0; i < elm->rxfill; i++) {
683 if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
684 elm327_send(elm, "\r", 1);
685 elm->state = ELM327_STATE_GETPROMPT;
688 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
689 elm327_send(elm, ELM327_DUMMY_STRING, 1);
695 elm327_drop_bytes(elm, i);
700 case ELM327_STATE_GETPROMPT:
702 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
703 elm327_handle_prompt(elm);
708 case ELM327_STATE_RECEIVING:
709 /* Find <CR> delimiting feedback lines. */
711 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
716 if (len == ELM327_SIZE_RXBUF) {
717 /* Line exceeds buffer. It's probably all garbage.
718 * Did we even connect at the right baud rate?
721 "RX buffer overflow. Faulty ELM327 or UART?\n");
722 elm327_hw_failure(elm);
724 } else if (len == elm->rxfill) {
725 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
726 /* The ELM327's AT ST response timeout ran out,
727 * so we got a prompt.
728 * Clear RX buffer and restart listening.
732 elm327_handle_prompt(elm);
736 /* No <CR> found - we haven't received a full line yet.
737 * Wait for more data.
742 /* We have a full line to parse. */
743 elm327_parse_line(elm, len);
745 /* Remove parsed data from RX buffer. */
746 elm327_drop_bytes(elm, len + 1);
748 /* More data to parse? */
750 elm327_parse_rxbuf(elm);
754 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
755 /* Dummy needed to use can_rx_offload */
756 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
757 unsigned int n, u32 *timestamp,
760 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
762 return ERR_PTR(-ENOBUFS);
766 static int elmcan_netdev_open(struct net_device *dev)
768 struct elmcan *elm = netdev_priv(dev);
771 spin_lock_bh(&elm->lock);
772 if (elm->hw_failure) {
773 netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
774 spin_unlock_bh(&elm->lock);
779 spin_unlock_bh(&elm->lock);
783 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
784 err = open_candev(dev);
786 spin_unlock_bh(&elm->lock);
791 spin_unlock_bh(&elm->lock);
793 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
794 elm->offload.mailbox_read = elmcan_mailbox_read;
795 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
797 err = can_rx_offload_add_manual(dev, &elm->offload, ELM327_NAPI_WEIGHT);
804 can_rx_offload_enable(&elm->offload);
806 can_led_event(dev, CAN_LED_EVENT_OPEN);
807 elm->can.state = CAN_STATE_ERROR_ACTIVE;
808 netif_start_queue(dev);
813 static int elmcan_netdev_close(struct net_device *dev)
815 struct elmcan *elm = netdev_priv(dev);
817 netif_stop_queue(dev);
819 spin_lock_bh(&elm->lock);
821 /* Interrupt whatever we're doing right now */
822 elm327_send(elm, ELM327_DUMMY_STRING, 1);
824 /* Clear the wakeup bit, as the netdev will be down and thus
825 * the wakeup handler won't clear it
827 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
829 spin_unlock_bh(&elm->lock);
831 flush_work(&elm->tx_work);
833 spin_unlock_bh(&elm->lock);
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->hw_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);
929 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
931 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
933 elm327_hw_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_hw_failure(elm);
956 elm->rxbuf[elm->rxfill++] = *cp;
963 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
965 elm327_hw_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);
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_hw_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 elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
1065 /* Configure TTY interface */
1066 tty->receive_room = 65536; /* We don't flow control */
1067 elm->txleft = 0; /* Clear TTY TX buffer */
1068 spin_lock_init(&elm->lock);
1069 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1071 /* Configure CAN metadata */
1072 elm->can.bitrate_const = elmcan_bitrate_const;
1073 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1074 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1075 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1077 /* Configure netdev interface */
1079 dev->netdev_ops = &elmcan_netdev_ops;
1081 /* Mark ldisc channel as alive */
1083 tty->disc_data = elm;
1085 devm_can_led_init(elm->dev);
1088 err = register_candev(elm->dev);
1092 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1098 free_candev(elm->dev);
1102 /* Close down an elmcan channel.
1103 * This means flushing out any pending queues, and then returning.
1104 * This call is serialized against other ldisc functions:
1105 * Once this is called, no other ldisc function of ours is entered.
1107 * We also use this function for a hangup event.
1109 static void elmcan_ldisc_close(struct tty_struct *tty)
1111 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1113 /* unregister_netdev() calls .ndo_stop() so we don't have to. */
1114 unregister_candev(elm->dev);
1116 /* Ensure that our worker won't be rescheduled */
1117 clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
1118 flush_work(&elm->tx_work);
1120 /* Mark channel as dead */
1121 spin_lock_bh(&elm->lock);
1122 tty->disc_data = NULL;
1124 spin_unlock_bh(&elm->lock);
1126 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1129 free_candev(elm->dev);
1132 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1133 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1136 unsigned int cmd, unsigned long arg)
1138 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1143 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1144 if (copy_to_user((void __user *)arg, elm->dev->name, tmp))
1152 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1153 return tty_mode_ioctl(tty, file, cmd, arg);
1155 return tty_mode_ioctl(tty, cmd, arg);
1160 static struct tty_ldisc_ops elmcan_ldisc = {
1161 .owner = THIS_MODULE,
1163 .num = N_DEVELOPMENT,
1164 .receive_buf = elmcan_ldisc_rx,
1165 .write_wakeup = elmcan_ldisc_tx_wakeup,
1166 .open = elmcan_ldisc_open,
1167 .close = elmcan_ldisc_close,
1168 .ioctl = elmcan_ldisc_ioctl,
1171 static int __init elmcan_init(void)
1175 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1176 status = tty_register_ldisc(N_DEVELOPMENT, &elmcan_ldisc);
1178 status = tty_register_ldisc(&elmcan_ldisc);
1181 pr_err("Can't register line discipline\n");
1186 static void __exit elmcan_exit(void)
1188 /* This will only be called when all channels have been closed by
1189 * userspace - tty_ldisc.c takes care of the module's refcount.
1191 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1194 status = tty_unregister_ldisc(N_DEVELOPMENT);
1196 pr_err("Can't unregister line discipline (error: %d)\n",
1199 tty_unregister_ldisc(&elmcan_ldisc);
1203 module_init(elmcan_init);
1204 module_exit(elmcan_exit);
1206 MODULE_ALIAS_LDISC(N_DEVELOPMENT);
1207 MODULE_DESCRIPTION("ELM327 based CAN interface");
1208 MODULE_LICENSE("GPL");
1209 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");