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/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 * N_DEVELOPMENT will likely be defined from Linux 5.18 onwards:
47 * https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git/commit/?h=tty-next&id=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 256
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_TX_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;
91 /* TTY and netdev devices that we're bridging */
92 struct tty_struct *tty;
93 struct net_device *dev;
95 /* Per-channel lock */
98 /* Keep track of how many things are using this struct.
99 * Once it reaches 0, we are in the process of cleaning up,
100 * and new operations will be cancelled immediately.
101 * Use atomic_t rather than refcount_t because we deliberately
102 * decrement to 0, and refcount_dec() spills a WARN_ONCE in
107 /* Stop the channel on hardware failure.
108 * Once this is true, nothing will be sent to the TTY.
113 struct work_struct tx_work; /* Flushes TTY TX buffer */
114 unsigned char *txbuf;
115 unsigned char *txhead; /* Pointer to next TX byte */
116 int txleft; /* Bytes left to TX */
119 unsigned char rxbuf[ELM327_SIZE_RXBUF];
132 /* The CAN frame and config the ELM327 is sending/using,
133 * or will send/use after finishing all cmds_todo
135 struct can_frame can_frame_to_send;
136 unsigned short can_config;
137 unsigned long can_bitrate;
138 unsigned char can_bitrate_divisor;
139 int silent_monitoring;
141 /* Things we have yet to send */
142 char **next_init_cmd;
143 unsigned long cmds_todo;
146 /* A lock for all tty->disc_data handled by this ldisc.
147 * This is to prevent a case where tty->disc_data is set to NULL,
148 * yet someone is still trying to dereference it.
149 * Without this, we cannot do a clean shutdown.
151 static DEFINE_SPINLOCK(elmcan_discdata_lock);
153 static inline void elm327_hw_failure(struct elmcan *elm);
155 /* Assumes elm->lock taken. */
156 static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
163 memcpy(elm->txbuf, buf, len);
165 /* Order of next two lines is *very* important.
166 * When we are sending a little amount of data,
167 * the transfer may be completed inside the ops->write()
168 * routine, because it's running with interrupts enabled.
169 * In this case we *never* got WRITE_WAKEUP event,
170 * if we did not request it before write operation.
171 * 14 Oct 1994 Dmitry Gorodchanin.
173 set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
174 actual = elm->tty->ops->write(elm->tty, elm->txbuf, len);
177 "Failed to write to tty %s.\n",
179 elm327_hw_failure(elm);
183 elm->txleft = len - actual;
184 elm->txhead = elm->txbuf + actual;
187 /* Take the ELM327 out of almost any state and back into command mode.
188 * We send ELM327_DUMMY_CHAR which will either abort any running
189 * operation, or be echoed back to us in case we're already in command
192 * Assumes elm->lock taken.
194 static void elm327_kick_into_cmd_mode(struct elmcan *elm)
196 if (elm->state != ELM_GETDUMMYCHAR && elm->state != ELM_GETPROMPT) {
197 elm327_send(elm, ELM327_DUMMY_STRING, 1);
199 elm->state = ELM_GETDUMMYCHAR;
203 /* Schedule a CAN frame and necessary config changes to be sent to the TTY.
205 * Assumes elm->lock taken.
207 static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
209 /* Schedule any necessary changes in ELM327's CAN configuration */
210 if (elm->can_frame_to_send.can_id != frame->can_id) {
211 /* Set the new CAN ID for transmission. */
212 if ((frame->can_id & CAN_EFF_FLAG)
213 ^ (elm->can_frame_to_send.can_id & CAN_EFF_FLAG)) {
214 elm->can_config = (frame->can_id & CAN_EFF_FLAG
216 : ELM327_CAN_CONFIG_SEND_SFF)
217 | ELM327_CAN_CONFIG_VARIABLE_DLC
218 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
219 | elm->can_bitrate_divisor;
221 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
224 if (frame->can_id & CAN_EFF_FLAG) {
225 clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
226 set_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
227 set_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
229 set_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
230 clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
231 clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
235 /* Schedule the CAN frame itself. */
236 elm->can_frame_to_send = *frame;
237 set_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo);
239 elm327_kick_into_cmd_mode(elm);
242 /* ELM327 initialization sequence.
244 * Assumes elm->lock taken.
246 static char *elm327_init_script[] = {
247 "AT WS\r", /* v1.0: Warm Start */
248 "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
249 "AT M0\r", /* v1.0: Memory Off */
250 "AT AL\r", /* v1.0: Allow Long messages */
251 "AT BI\r", /* v1.0: Bypass Initialization */
252 "AT CAF0\r", /* v1.0: CAN Auto Formatting Off */
253 "AT CFC0\r", /* v1.0: CAN Flow Control Off */
254 "AT CF 000\r", /* v1.0: Reset CAN ID Filter */
255 "AT CM 000\r", /* v1.0: Reset CAN ID Mask */
256 "AT E1\r", /* v1.0: Echo On */
257 "AT H1\r", /* v1.0: Headers On */
258 "AT L0\r", /* v1.0: Linefeeds Off */
259 "AT SH 7DF\r", /* v1.0: Set CAN sending ID to 0x7df */
260 "AT ST FF\r", /* v1.0: Set maximum Timeout for response after TX */
261 "AT AT0\r", /* v1.2: Adaptive Timing Off */
262 "AT D1\r", /* v1.3: Print DLC On */
263 "AT S1\r", /* v1.3: Spaces On */
264 "AT TP B\r", /* v1.0: Try Protocol B */
268 static void elm327_init(struct elmcan *elm)
270 elm->state = ELM_NOTINIT;
271 elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
273 elm->drop_next_line = 0;
275 /* We can only set the bitrate as a fraction of 500000.
276 * The bit timing constants in elmcan_bittiming_const will
277 * limit the user to the right values.
279 elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
280 elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
281 | ELM327_CAN_CONFIG_VARIABLE_DLC
282 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
283 | elm->can_bitrate_divisor;
285 /* Configure ELM327 and then start monitoring */
286 elm->next_init_cmd = &elm327_init_script[0];
287 set_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
288 set_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
289 set_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo);
290 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
292 elm327_kick_into_cmd_mode(elm);
295 /* Assumes elm->lock taken. */
296 static void elm327_feed_frame_to_netdev(struct elmcan *elm,
299 if (!netif_running(elm->dev))
302 /* Queue for NAPI pickup.
303 * rx-offload will update stats and LEDs for us.
305 if (can_rx_offload_queue_tail(&elm->offload, skb))
306 elm->dev->stats.rx_fifo_errors++;
308 #if LINUX_VERSION_CODE >= KERNEL_VERSION(5,15,0)
310 can_rx_offload_irq_finish(&elm->offload);
314 /* Called when we're out of ideas and just want it all to end.
315 * Assumes elm->lock taken.
317 static inline void elm327_hw_failure(struct elmcan *elm)
319 struct can_frame *frame;
322 elm->hw_failure = true;
324 elm->can.can_stats.bus_off++;
325 netif_stop_queue(elm->dev);
326 elm->can.state = CAN_STATE_BUS_OFF;
327 can_bus_off(elm->dev);
329 netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
331 skb = alloc_can_err_skb(elm->dev, &frame);
335 frame->can_id |= CAN_ERR_BUSOFF;
336 elm327_feed_frame_to_netdev(elm, skb);
339 /* Compare a buffer to a fixed string */
340 static inline int _memstrcmp(const u8 *mem, const char *str)
342 return memcmp(mem, str, strlen(str));
345 /* Compare buffer to string length, then compare buffer to fixed string.
346 * This ensures two things:
347 * - It flags cases where the fixed string is only the start of the
348 * buffer, rather than exactly all of it.
349 * - It avoids byte comparisons in case the length doesn't match.
351 static inline int _len_memstrcmp(const u8 *mem, size_t mem_len, const char *str)
353 size_t str_len = strlen(str);
355 return (mem_len != str_len) || memcmp(mem, str, str_len);
358 /* Assumes elm->lock taken. */
359 static void elm327_parse_error(struct elmcan *elm, size_t len)
361 struct can_frame *frame;
364 skb = alloc_can_err_skb(elm->dev, &frame);
366 /* It's okay to return here:
367 * The outer parsing loop will drop this UART buffer.
371 /* Filter possible error messages based on length of RX'd line */
372 if (!_len_memstrcmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
374 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
375 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUFFER FULL")) {
376 /* This will only happen if the last data line was complete.
377 * Otherwise, elm327_parse_frame() will heuristically
378 * emit this kind of error frame instead.
380 frame->can_id |= CAN_ERR_CRTL;
381 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
382 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS ERROR")) {
383 frame->can_id |= CAN_ERR_BUSERROR;
384 } else if (!_len_memstrcmp(elm->rxbuf, len, "CAN ERROR")) {
385 frame->can_id |= CAN_ERR_PROT;
386 } else if (!_len_memstrcmp(elm->rxbuf, len, "<RX ERROR")) {
387 frame->can_id |= CAN_ERR_PROT;
388 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS BUSY")) {
389 frame->can_id |= CAN_ERR_PROT;
390 frame->data[2] = CAN_ERR_PROT_OVERLOAD;
391 } else if (!_len_memstrcmp(elm->rxbuf, len, "FB ERROR")) {
392 frame->can_id |= CAN_ERR_PROT;
393 frame->data[2] = CAN_ERR_PROT_TX;
394 } else if (len == 5 && !_memstrcmp(elm->rxbuf, "ERR")) {
395 /* ERR is followed by two digits, hence line length 5 */
396 netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
397 elm->rxbuf[3], elm->rxbuf[4]);
398 frame->can_id |= CAN_ERR_CRTL;
400 /* Something else has happened.
401 * Maybe garbage on the UART line.
402 * Emit a generic error frame.
406 elm327_feed_frame_to_netdev(elm, skb);
409 /* Parse CAN frames coming as ASCII from ELM327.
410 * They can be of various formats:
412 * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
413 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
415 * where D = DLC, PL = payload byte
417 * Instead of a payload, RTR indicates a remote request.
419 * We will use the spaces and line length to guess the format.
421 * Assumes elm->lock taken.
423 static int elm327_parse_frame(struct elmcan *elm, size_t len)
425 struct can_frame *frame;
431 skb = alloc_can_skb(elm->dev, &frame);
435 /* Find first non-hex and non-space character:
436 * - In the simplest case, there is none.
437 * - For RTR frames, 'R' is the first non-hex character.
438 * - An error message may replace the end of the data line.
440 for (hexlen = 0; hexlen <= len; hexlen++) {
441 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
442 elm->rxbuf[hexlen] != ' ') {
447 /* Sanity check whether the line is really a clean hexdump,
448 * or terminated by an error message, or contains garbage.
451 !isdigit(elm->rxbuf[hexlen]) &&
452 !isupper(elm->rxbuf[hexlen]) &&
453 '<' != elm->rxbuf[hexlen] &&
454 ' ' != elm->rxbuf[hexlen]) {
455 /* The line is likely garbled anyway, so bail.
456 * The main code will restart listening.
461 /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
462 * No out-of-bounds access:
463 * We use the fact that we can always read from elm->rxbuf.
465 if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
466 elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
467 elm->rxbuf[13] == ' ') {
468 frame->can_id = CAN_EFF_FLAG;
470 } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
474 /* This is not a well-formatted data line.
475 * Assume it's an error message.
480 if (hexlen < datastart) {
481 /* The line is too short to be a valid frame hex dump.
482 * Something interrupted the hex dump or it is invalid.
487 /* From here on all chars up to buf[hexlen] are hex or spaces,
488 * at well-defined offsets.
491 /* Read CAN data length */
492 frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
495 if (frame->can_id & CAN_EFF_FLAG) {
496 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
497 | (hex_to_bin(elm->rxbuf[1]) << 24)
498 | (hex_to_bin(elm->rxbuf[3]) << 20)
499 | (hex_to_bin(elm->rxbuf[4]) << 16)
500 | (hex_to_bin(elm->rxbuf[6]) << 12)
501 | (hex_to_bin(elm->rxbuf[7]) << 8)
502 | (hex_to_bin(elm->rxbuf[9]) << 4)
503 | (hex_to_bin(elm->rxbuf[10]) << 0);
505 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
506 | (hex_to_bin(elm->rxbuf[1]) << 4)
507 | (hex_to_bin(elm->rxbuf[2]) << 0);
510 /* Check for RTR frame */
511 if (elm->rxfill >= hexlen + 3 &&
512 !_memstrcmp(&elm->rxbuf[hexlen], "RTR")) {
513 frame->can_id |= CAN_RTR_FLAG;
516 /* Is the line long enough to hold the advertised payload?
517 * Note: RTR frames have a DLC, but no actual payload.
519 if (!(frame->can_id & CAN_RTR_FLAG) &&
520 (hexlen < frame->len * 3 + datastart)) {
522 * Probably the ELM327's RS232 TX buffer was full.
523 * Emit an error frame and exit.
525 frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
526 frame->len = CAN_ERR_DLC;
527 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
528 elm327_feed_frame_to_netdev(elm, skb);
530 /* Signal failure to parse.
531 * The line will be re-parsed as an error line, which will fail.
532 * However, this will correctly drop the state machine back into
538 /* Parse the data nibbles. */
539 for (i = 0; i < frame->len; i++) {
540 frame->data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
541 | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
544 /* Feed the frame to the network layer. */
545 elm327_feed_frame_to_netdev(elm, skb);
550 /* Assumes elm->lock taken. */
551 static void elm327_parse_line(struct elmcan *elm, size_t len)
553 /* Skip empty lines */
557 /* Skip echo lines */
558 if (elm->drop_next_line) {
559 elm->drop_next_line = 0;
561 } else if (!_memstrcmp(elm->rxbuf, "AT")) {
565 /* Regular parsing */
566 if (elm->state == ELM_RECEIVING
567 && elm327_parse_frame(elm, len)) {
568 /* Parse an error line. */
569 elm327_parse_error(elm, len);
572 elm327_kick_into_cmd_mode(elm);
576 /* Assumes elm->lock taken. */
577 static void elm327_handle_prompt(struct elmcan *elm)
579 struct can_frame *frame = &elm->can_frame_to_send;
580 char local_txbuf[20];
582 if (!elm->cmds_todo) {
583 /* Enter CAN monitor mode */
584 elm327_send(elm, "ATMA\r", 5);
585 elm->state = ELM_RECEIVING;
590 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
591 if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
592 strcpy(local_txbuf, *elm->next_init_cmd);
594 elm->next_init_cmd++;
595 if (!(*elm->next_init_cmd)) {
596 clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
600 } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
601 sprintf(local_txbuf, "ATCSM%i\r",
602 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
604 } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo)) {
605 sprintf(local_txbuf, "ATR%i\r",
606 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
608 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
609 sprintf(local_txbuf, "ATPC\r");
610 set_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);
612 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
613 sprintf(local_txbuf, "ATPB%04X\r",
616 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
617 sprintf(local_txbuf, "ATCP%02X\r",
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 sprintf(local_txbuf, "ATSH%06X\r",
622 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
624 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
625 sprintf(local_txbuf, "ATSH%03X\r",
626 frame->can_id & CAN_SFF_MASK);
628 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
629 if (frame->can_id & CAN_RTR_FLAG) {
630 /* Send an RTR frame. Their DLC is fixed.
631 * Some chips don't send them at all.
633 sprintf(local_txbuf, "ATRTR\r");
635 /* Send a regular CAN data frame */
638 for (i = 0; i < frame->len; i++) {
639 sprintf(&local_txbuf[2 * i], "%02X",
643 sprintf(&local_txbuf[2 * i], "\r");
646 elm->drop_next_line = 1;
647 elm->state = ELM_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 /* Assumes elm->lock taken. */
662 static void elm327_drop_bytes(struct elmcan *elm, size_t i)
664 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
668 /* Assumes elm->lock taken. */
669 static void elm327_parse_rxbuf(struct elmcan *elm)
674 switch (elm->state) {
679 case ELM_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 = ELM_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);
702 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
703 elm327_handle_prompt(elm);
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 /* Dummy needed to use can_rx_offload */
755 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
756 unsigned int n, u32 *timestamp,
759 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
761 return ERR_PTR(-ENOBUFS);
764 static int elmcan_netdev_open(struct net_device *dev)
766 struct elmcan *elm = netdev_priv(dev);
769 spin_lock_bh(&elm->lock);
770 if (elm->hw_failure) {
771 netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
772 spin_unlock_bh(&elm->lock);
777 spin_unlock_bh(&elm->lock);
781 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
782 err = open_candev(dev);
784 spin_unlock_bh(&elm->lock);
789 spin_unlock_bh(&elm->lock);
791 elm->offload.mailbox_read = elmcan_mailbox_read;
792 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
798 can_rx_offload_enable(&elm->offload);
800 can_led_event(dev, CAN_LED_EVENT_OPEN);
801 elm->can.state = CAN_STATE_ERROR_ACTIVE;
802 netif_start_queue(dev);
807 static int elmcan_netdev_close(struct net_device *dev)
809 struct elmcan *elm = netdev_priv(dev);
811 netif_stop_queue(dev);
813 spin_lock_bh(&elm->lock);
815 /* Interrupt whatever we're doing right now */
816 elm327_send(elm, ELM327_DUMMY_STRING, 1);
818 /* Clear the wakeup bit, as the netdev will be down and thus
819 * the wakeup handler won't clear it
821 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
823 spin_unlock_bh(&elm->lock);
825 flush_work(&elm->tx_work);
827 spin_unlock_bh(&elm->lock);
830 can_rx_offload_disable(&elm->offload);
831 elm->can.state = CAN_STATE_STOPPED;
832 can_rx_offload_del(&elm->offload);
834 can_led_event(dev, CAN_LED_EVENT_STOP);
839 /* Send a can_frame to a TTY. */
840 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
841 struct net_device *dev)
843 struct elmcan *elm = netdev_priv(dev);
844 struct can_frame *frame = (struct can_frame *)skb->data;
846 /* BHs are already disabled, so no spin_lock_bh().
847 * See Documentation/networking/netdevices.txt
849 spin_lock(&elm->lock);
851 /* We shouldn't get here after a hardware fault:
852 * can_bus_off() calls netif_carrier_off()
854 WARN_ON_ONCE(elm->hw_failure);
858 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
859 spin_unlock(&elm->lock);
863 netif_stop_queue(dev);
865 elm327_send_frame(elm, frame);
866 spin_unlock(&elm->lock);
868 dev->stats.tx_packets++;
869 dev->stats.tx_bytes += frame->len;
871 can_led_event(dev, CAN_LED_EVENT_TX);
878 static const struct net_device_ops elmcan_netdev_ops = {
879 .ndo_open = elmcan_netdev_open,
880 .ndo_stop = elmcan_netdev_close,
881 .ndo_start_xmit = elmcan_netdev_start_xmit,
882 .ndo_change_mtu = can_change_mtu,
885 /* Get a reference to our struct, taking into account locks/refcounts.
886 * This is to ensure ordering in case we are shutting down, and to ensure
887 * there is a refcount at all (otherwise tty->disc_data may be freed and
888 * before we increment the refcount).
889 * Use this for anything that can race against elmcan_ldisc_close().
891 static struct elmcan *get_elm(struct tty_struct *tty)
896 spin_lock_bh(&elmcan_discdata_lock);
897 elm = (struct elmcan *)tty->disc_data;
900 spin_unlock_bh(&elmcan_discdata_lock);
904 got_ref = atomic_inc_not_zero(&elm->refcount);
905 spin_unlock_bh(&elmcan_discdata_lock);
913 static void put_elm(struct elmcan *elm)
915 atomic_dec(&elm->refcount);
918 static bool elmcan_is_valid_rx_char(char c)
920 return (isdigit(c) ||
922 c == ELM327_DUMMY_CHAR ||
923 c == ELM327_READY_CHAR ||
934 /* Handle incoming ELM327 ASCII data.
935 * This will not be re-entered while running, but other ldisc
936 * functions may be called in parallel.
938 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
939 static void elmcan_ldisc_rx(struct tty_struct *tty,
940 const unsigned char *cp, char *fp, int count)
942 static void elmcan_ldisc_rx(struct tty_struct *tty,
943 const unsigned char *cp, const char *fp, int count)
946 struct elmcan *elm = get_elm(tty);
951 spin_lock_bh(&elm->lock);
956 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
958 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
960 elm327_hw_failure(elm);
965 /* Ignore NUL characters, which the PIC microcontroller may
966 * inadvertently insert due to a known hardware bug.
967 * See ELM327 documentation, which refers to a Microchip PIC
971 /* Check for stray characters on the UART line.
972 * Likely caused by bad hardware.
974 if (!elmcan_is_valid_rx_char(*cp)) {
976 "Received illegal character %02x.\n",
978 elm327_hw_failure(elm);
983 elm->rxbuf[elm->rxfill++] = *cp;
990 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
992 elm327_hw_failure(elm);
997 elm327_parse_rxbuf(elm);
1000 spin_unlock_bh(&elm->lock);
1004 /* Write out remaining transmit buffer.
1005 * Scheduled when TTY is writable.
1007 static void elmcan_ldisc_tx_worker(struct work_struct *work)
1009 /* No need to use get_elm() here, as we'll always flush workers
1010 * before destroying the elmcan object.
1012 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
1015 spin_lock_bh(&elm->lock);
1016 if (elm->hw_failure) {
1017 spin_unlock_bh(&elm->lock);
1021 if (!elm->tty || !netif_running(elm->dev)) {
1022 spin_unlock_bh(&elm->lock);
1026 if (elm->txleft <= 0) {
1027 /* Our TTY write buffer is empty:
1028 * Allow netdev to hand us another packet
1030 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1031 spin_unlock_bh(&elm->lock);
1032 netif_wake_queue(elm->dev);
1036 actual = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
1038 netdev_err(elm->dev,
1039 "Failed to write to tty %s.\n",
1041 elm327_hw_failure(elm);
1042 spin_unlock_bh(&elm->lock);
1046 elm->txleft -= actual;
1047 elm->txhead += actual;
1048 spin_unlock_bh(&elm->lock);
1051 /* Called by the driver when there's room for more data. */
1052 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1054 struct elmcan *elm = get_elm(tty);
1059 schedule_work(&elm->tx_work);
1064 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1065 * or 7/8 of that. Divisors are 1 to 64.
1066 * Currently we don't implement support for 7/8 rates.
1068 static const u32 elmcan_bitrate_const[64] = {
1069 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1070 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1071 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1072 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1073 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1074 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1075 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1076 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1079 /* Dummy needed to use bitrate_const */
1080 static int elmcan_do_set_bittiming(struct net_device *netdev)
1085 static int elmcan_ldisc_open(struct tty_struct *tty)
1087 struct net_device *dev;
1091 if (!capable(CAP_NET_ADMIN))
1094 if (!tty->ops->write)
1097 dev = alloc_candev(sizeof(struct elmcan), 0);
1100 elm = netdev_priv(dev);
1102 elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
1108 /* Configure TTY interface */
1109 tty->receive_room = 65536; /* We don't flow control */
1110 elm->txleft = 0; /* Clear TTY TX buffer */
1111 spin_lock_init(&elm->lock);
1112 atomic_set(&elm->refcount, 1);
1113 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1115 /* Configure CAN metadata */
1116 elm->can.state = CAN_STATE_STOPPED;
1117 elm->can.bitrate_const = elmcan_bitrate_const;
1118 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1119 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1120 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1122 /* Configure netdev interface */
1124 dev->netdev_ops = &elmcan_netdev_ops;
1126 /* Mark ldisc channel as alive */
1128 tty->disc_data = elm;
1130 devm_can_led_init(elm->dev);
1133 err = register_candev(elm->dev);
1137 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1143 free_candev(elm->dev);
1147 /* Close down an elmcan channel.
1148 * This means flushing out any pending queues, and then returning.
1149 * This call is serialized against other ldisc functions:
1150 * Once this is called, no other ldisc function of ours is entered.
1152 * We also use this function for a hangup event.
1154 static void elmcan_ldisc_close(struct tty_struct *tty)
1156 struct elmcan *elm = get_elm(tty);
1161 /* unregister_netdev() calls .ndo_stop() so we don't have to. */
1162 unregister_candev(elm->dev);
1164 /* Decrease the refcount twice, once for our own get_elm(),
1165 * and once to remove the count of 1 that we set in _open().
1166 * Once it reaches 0, we can safely destroy it.
1171 while (atomic_read(&elm->refcount) > 0)
1172 msleep_interruptible(10);
1174 /* At this point, all ldisc calls to us have become no-ops. */
1176 flush_work(&elm->tx_work);
1178 /* Mark channel as dead */
1179 spin_lock_bh(&elm->lock);
1180 tty->disc_data = NULL;
1182 spin_unlock_bh(&elm->lock);
1184 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1187 free_candev(elm->dev);
1190 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1191 static int elmcan_ldisc_hangup(struct tty_struct *tty)
1193 static void elmcan_ldisc_hangup(struct tty_struct *tty)
1196 elmcan_ldisc_close(tty);
1197 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1202 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1203 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1206 unsigned int cmd, unsigned long arg)
1208 struct elmcan *elm = get_elm(tty);
1216 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1217 if (copy_to_user((void __user *)arg, elm->dev->name, tmp)) {
1231 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1232 return tty_mode_ioctl(tty, file, cmd, arg);
1234 return tty_mode_ioctl(tty, cmd, arg);
1239 static struct tty_ldisc_ops elmcan_ldisc = {
1240 .owner = THIS_MODULE,
1242 .num = N_DEVELOPMENT,
1243 .receive_buf = elmcan_ldisc_rx,
1244 .write_wakeup = elmcan_ldisc_tx_wakeup,
1245 .open = elmcan_ldisc_open,
1246 .close = elmcan_ldisc_close,
1247 .hangup = elmcan_ldisc_hangup,
1248 .ioctl = elmcan_ldisc_ioctl,
1251 static int __init elmcan_init(void)
1255 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1256 status = tty_register_ldisc(N_DEVELOPMENT, &elmcan_ldisc);
1258 status = tty_register_ldisc(&elmcan_ldisc);
1261 pr_err("Can't register line discipline\n");
1266 static void __exit elmcan_exit(void)
1268 /* This will only be called when all channels have been closed by
1269 * userspace - tty_ldisc.c takes care of the module's refcount.
1271 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1274 status = tty_unregister_ldisc(N_DEVELOPMENT);
1276 pr_err("Can't unregister line discipline (error: %d)\n",
1279 tty_unregister_ldisc(&elmcan_ldisc);
1283 module_init(elmcan_init);
1284 module_exit(elmcan_exit);
1286 MODULE_ALIAS_LDISC(N_DEVELOPMENT);
1287 MODULE_DESCRIPTION("ELM327 based CAN interface");
1288 MODULE_LICENSE("GPL");
1289 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");