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.
9 #define pr_fmt(fmt) "[elmcan] " fmt
11 #include <linux/init.h>
12 #include <linux/module.h>
13 #include <linux/moduleparam.h>
15 #include <linux/atomic.h>
16 #include <linux/bitops.h>
17 #include <linux/ctype.h>
18 #include <linux/delay.h>
19 #include <linux/errno.h>
20 #include <linux/if_ether.h>
21 #include <linux/kernel.h>
22 #include <linux/list.h>
23 #include <linux/netdevice.h>
24 #include <linux/skbuff.h>
25 #include <linux/spinlock.h>
26 #include <linux/string.h>
27 #include <linux/tty.h>
28 #include <linux/tty_ldisc.h>
29 #include <linux/version.h>
30 #include <linux/workqueue.h>
32 #include <uapi/linux/tty.h>
34 #include <linux/can.h>
35 #include <linux/can/dev.h>
36 #include <linux/can/error.h>
37 #include <linux/can/led.h>
38 #include <linux/can/rx-offload.h>
40 MODULE_ALIAS_LDISC(N_DEVELOPMENT);
41 MODULE_DESCRIPTION("ELM327 based CAN interface");
42 MODULE_LICENSE("GPL");
43 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");
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 skb = alloc_can_err_skb(elm->dev, &frame);
326 frame->data[5] = 'R';
327 frame->data[6] = 'I';
328 frame->data[7] = 'P';
330 elm327_feed_frame_to_netdev(elm, skb);
332 netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
334 elm->hw_failure = true;
335 can_bus_off(elm->dev);
338 /* Compare a buffer to a fixed string */
339 static inline int _memstrcmp(const u8 *mem, const char *str)
341 return memcmp(mem, str, strlen(str));
344 /* Compare buffer to string length, then compare buffer to fixed string.
345 * This ensures two things:
346 * - It flags cases where the fixed string is only the start of the
347 * buffer, rather than exactly all of it.
348 * - It avoids byte comparisons in case the length doesn't match.
350 static inline int _len_memstrcmp(const u8 *mem, size_t mem_len, const char *str)
352 size_t str_len = strlen(str);
354 return (mem_len != str_len) || memcmp(mem, str, str_len);
357 /* Assumes elm->lock taken. */
358 static void elm327_parse_error(struct elmcan *elm, size_t len)
360 struct can_frame *frame;
363 skb = alloc_can_err_skb(elm->dev, &frame);
365 /* It's okay to return here:
366 * The outer parsing loop will drop this UART buffer.
370 /* Filter possible error messages based on length of RX'd line */
371 if (!_len_memstrcmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
373 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
374 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUFFER FULL")) {
375 /* This will only happen if the last data line was complete.
376 * Otherwise, elm327_parse_frame() will heuristically
377 * emit this kind of error frame instead.
379 frame->can_id |= CAN_ERR_CRTL;
380 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
381 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS ERROR")) {
382 frame->can_id |= CAN_ERR_BUSERROR;
383 } else if (!_len_memstrcmp(elm->rxbuf, len, "CAN ERROR")) {
384 frame->can_id |= CAN_ERR_PROT;
385 } else if (!_len_memstrcmp(elm->rxbuf, len, "<RX ERROR")) {
386 frame->can_id |= CAN_ERR_PROT;
387 } else if (!_len_memstrcmp(elm->rxbuf, len, "BUS BUSY")) {
388 frame->can_id |= CAN_ERR_PROT;
389 frame->data[2] = CAN_ERR_PROT_OVERLOAD;
390 } else if (!_len_memstrcmp(elm->rxbuf, len, "FB ERROR")) {
391 frame->can_id |= CAN_ERR_PROT;
392 frame->data[2] = CAN_ERR_PROT_TX;
393 } else if (len == 5 && !_memstrcmp(elm->rxbuf, "ERR")) {
394 /* ERR is followed by two digits, hence line length 5 */
395 netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
396 elm->rxbuf[3], elm->rxbuf[4]);
397 frame->can_id |= CAN_ERR_CRTL;
399 /* Something else has happened.
400 * Maybe garbage on the UART line.
401 * Emit a generic error frame.
405 elm327_feed_frame_to_netdev(elm, skb);
408 /* Parse CAN frames coming as ASCII from ELM327.
409 * They can be of various formats:
411 * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
412 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
414 * where D = DLC, PL = payload byte
416 * Instead of a payload, RTR indicates a remote request.
418 * We will use the spaces and line length to guess the format.
420 * Assumes elm->lock taken.
422 static int elm327_parse_frame(struct elmcan *elm, size_t len)
424 struct can_frame *frame;
430 skb = alloc_can_skb(elm->dev, &frame);
434 /* Find first non-hex and non-space character:
435 * - In the simplest case, there is none.
436 * - For RTR frames, 'R' is the first non-hex character.
437 * - An error message may replace the end of the data line.
439 for (hexlen = 0; hexlen <= len; hexlen++) {
440 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
441 elm->rxbuf[hexlen] != ' ') {
446 /* Sanity check whether the line is really a clean hexdump,
447 * or terminated by an error message, or contains garbage.
450 !isdigit(elm->rxbuf[hexlen]) &&
451 !isupper(elm->rxbuf[hexlen]) &&
452 '<' != elm->rxbuf[hexlen] &&
453 ' ' != elm->rxbuf[hexlen]) {
454 /* The line is likely garbled anyway, so bail.
455 * The main code will restart listening.
460 /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
461 * No out-of-bounds access:
462 * We use the fact that we can always read from elm->rxbuf.
464 if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
465 elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
466 elm->rxbuf[13] == ' ') {
467 frame->can_id = CAN_EFF_FLAG;
469 } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
473 /* This is not a well-formatted data line.
474 * Assume it's an error message.
479 if (hexlen < datastart) {
480 /* The line is too short to be a valid frame hex dump.
481 * Something interrupted the hex dump or it is invalid.
486 /* From here on all chars up to buf[hexlen] are hex or spaces,
487 * at well-defined offsets.
490 /* Read CAN data length */
491 frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
494 if (frame->can_id & CAN_EFF_FLAG) {
495 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
496 | (hex_to_bin(elm->rxbuf[1]) << 24)
497 | (hex_to_bin(elm->rxbuf[3]) << 20)
498 | (hex_to_bin(elm->rxbuf[4]) << 16)
499 | (hex_to_bin(elm->rxbuf[6]) << 12)
500 | (hex_to_bin(elm->rxbuf[7]) << 8)
501 | (hex_to_bin(elm->rxbuf[9]) << 4)
502 | (hex_to_bin(elm->rxbuf[10]) << 0);
504 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
505 | (hex_to_bin(elm->rxbuf[1]) << 4)
506 | (hex_to_bin(elm->rxbuf[2]) << 0);
509 /* Check for RTR frame */
510 if (elm->rxfill >= hexlen + 3 &&
511 !_memstrcmp(&elm->rxbuf[hexlen], "RTR")) {
512 frame->can_id |= CAN_RTR_FLAG;
515 /* Is the line long enough to hold the advertised payload?
516 * Note: RTR frames have a DLC, but no actual payload.
518 if (!(frame->can_id & CAN_RTR_FLAG) &&
519 (hexlen < frame->len * 3 + datastart)) {
521 * Probably the ELM327's RS232 TX buffer was full.
522 * Emit an error frame and exit.
524 frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
525 frame->len = CAN_ERR_DLC;
526 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
527 elm327_feed_frame_to_netdev(elm, skb);
529 /* Signal failure to parse.
530 * The line will be re-parsed as an error line, which will fail.
531 * However, this will correctly drop the state machine back into
537 /* Parse the data nibbles. */
538 for (i = 0; i < frame->len; i++) {
539 frame->data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
540 | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
543 /* Feed the frame to the network layer. */
544 elm327_feed_frame_to_netdev(elm, skb);
549 /* Assumes elm->lock taken. */
550 static void elm327_parse_line(struct elmcan *elm, size_t len)
552 /* Skip empty lines */
556 /* Skip echo lines */
557 if (elm->drop_next_line) {
558 elm->drop_next_line = 0;
560 } else if (!_memstrcmp(elm->rxbuf, "AT")) {
564 /* Regular parsing */
565 switch (elm->state) {
567 if (elm327_parse_frame(elm, len)) {
568 /* Parse an error line. */
569 elm327_parse_error(elm, len);
572 elm327_kick_into_cmd_mode(elm);
580 /* Assumes elm->lock taken. */
581 static void elm327_handle_prompt(struct elmcan *elm)
583 struct can_frame *frame = &elm->can_frame_to_send;
584 char local_txbuf[20];
586 if (!elm->cmds_todo) {
587 /* Enter CAN monitor mode */
588 elm327_send(elm, "ATMA\r", 5);
589 elm->state = ELM_RECEIVING;
594 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
595 if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
596 strcpy(local_txbuf, *elm->next_init_cmd);
598 elm->next_init_cmd++;
599 if (!(*elm->next_init_cmd)) {
600 clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
604 } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
605 sprintf(local_txbuf, "ATCSM%i\r",
606 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
608 } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo)) {
609 sprintf(local_txbuf, "ATR%i\r",
610 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
612 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
613 sprintf(local_txbuf, "ATPC\r");
614 set_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);
616 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
617 sprintf(local_txbuf, "ATPB%04X\r",
620 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
621 sprintf(local_txbuf, "ATCP%02X\r",
622 (frame->can_id & CAN_EFF_MASK) >> 24);
624 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
625 sprintf(local_txbuf, "ATSH%06X\r",
626 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
628 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
629 sprintf(local_txbuf, "ATSH%03X\r",
630 frame->can_id & CAN_SFF_MASK);
632 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
633 if (frame->can_id & CAN_RTR_FLAG) {
634 /* Send an RTR frame. Their DLC is fixed.
635 * Some chips don't send them at all.
637 sprintf(local_txbuf, "ATRTR\r");
639 /* Send a regular CAN data frame */
642 for (i = 0; i < frame->len; i++) {
643 sprintf(&local_txbuf[2 * i], "%02X",
647 sprintf(&local_txbuf[2 * i], "\r");
650 elm->drop_next_line = 1;
651 elm->state = ELM_RECEIVING;
654 elm327_send(elm, local_txbuf, strlen(local_txbuf));
657 static bool elm327_is_ready_char(char c)
659 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
660 * Probably bad hardware.
662 return (c & 0x3f) == ELM327_READY_CHAR;
665 /* Assumes elm->lock taken. */
666 static void elm327_drop_bytes(struct elmcan *elm, size_t i)
668 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
672 /* Assumes elm->lock taken. */
673 static void elm327_parse_rxbuf(struct elmcan *elm)
677 switch (elm->state) {
682 case ELM_GETDUMMYCHAR:
684 /* Wait for 'y' or '>' */
687 for (i = 0; i < elm->rxfill; i++) {
688 if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
689 elm327_send(elm, "\r", 1);
690 elm->state = ELM_GETPROMPT;
693 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
694 elm327_send(elm, ELM327_DUMMY_STRING, 1);
700 elm327_drop_bytes(elm, i);
707 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
708 elm327_handle_prompt(elm);
714 /* Find <CR> delimiting feedback lines. */
716 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
721 if (len == ELM327_SIZE_RXBUF) {
722 /* Line exceeds buffer. It's probably all garbage.
723 * Did we even connect at the right baud rate?
726 "RX buffer overflow. Faulty ELM327 or UART?\n");
727 elm327_hw_failure(elm);
729 } else if (len == elm->rxfill) {
730 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
731 /* The ELM327's AT ST response timeout ran out,
732 * so we got a prompt.
733 * Clear RX buffer and restart listening.
737 elm327_handle_prompt(elm);
741 /* No <CR> found - we haven't received a full line yet.
742 * Wait for more data.
747 /* We have a full line to parse. */
748 elm327_parse_line(elm, len);
750 /* Remove parsed data from RX buffer. */
751 elm327_drop_bytes(elm, len + 1);
753 /* More data to parse? */
755 elm327_parse_rxbuf(elm);
759 /* Dummy needed to use can_rx_offload */
760 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
761 unsigned int n, u32 *timestamp,
764 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
766 return ERR_PTR(-ENOBUFS);
769 static int elmcan_netdev_open(struct net_device *dev)
771 struct elmcan *elm = netdev_priv(dev);
774 spin_lock_bh(&elm->lock);
775 if (elm->hw_failure) {
776 netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
777 spin_unlock_bh(&elm->lock);
782 spin_unlock_bh(&elm->lock);
786 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
787 err = open_candev(dev);
789 spin_unlock_bh(&elm->lock);
794 spin_unlock_bh(&elm->lock);
796 elm->offload.mailbox_read = elmcan_mailbox_read;
797 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
803 can_rx_offload_enable(&elm->offload);
805 can_led_event(dev, CAN_LED_EVENT_OPEN);
806 elm->can.state = CAN_STATE_ERROR_ACTIVE;
807 netif_start_queue(dev);
812 static int elmcan_netdev_close(struct net_device *dev)
814 struct elmcan *elm = netdev_priv(dev);
816 netif_stop_queue(dev);
818 spin_lock_bh(&elm->lock);
820 /* Interrupt whatever we're doing right now */
821 elm327_send(elm, ELM327_DUMMY_STRING, 1);
823 /* Clear the wakeup bit, as the netdev will be down and thus
824 * the wakeup handler won't clear it
826 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
828 spin_unlock_bh(&elm->lock);
830 flush_work(&elm->tx_work);
832 spin_unlock_bh(&elm->lock);
835 can_rx_offload_disable(&elm->offload);
836 elm->can.state = CAN_STATE_STOPPED;
837 can_rx_offload_del(&elm->offload);
839 can_led_event(dev, CAN_LED_EVENT_STOP);
844 /* Send a can_frame to a TTY. */
845 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
846 struct net_device *dev)
848 struct elmcan *elm = netdev_priv(dev);
849 struct can_frame *frame = (struct can_frame *)skb->data;
851 if (!netif_running(dev)) {
852 netdev_warn(elm->dev, "xmit: iface is down.\n");
856 /* BHs are already disabled, so no spin_lock_bh().
857 * See Documentation/networking/netdevices.txt
859 spin_lock(&elm->lock);
861 /* We shouldn't get here after a hardware fault:
862 * can_bus_off() calls netif_carrier_off()
864 WARN_ON_ONCE(elm->hw_failure);
868 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
869 spin_unlock(&elm->lock);
873 netif_stop_queue(dev);
875 elm327_send_frame(elm, frame);
876 spin_unlock(&elm->lock);
878 dev->stats.tx_packets++;
879 dev->stats.tx_bytes += frame->len;
881 can_led_event(dev, CAN_LED_EVENT_TX);
888 static const struct net_device_ops elmcan_netdev_ops = {
889 .ndo_open = elmcan_netdev_open,
890 .ndo_stop = elmcan_netdev_close,
891 .ndo_start_xmit = elmcan_netdev_start_xmit,
892 .ndo_change_mtu = can_change_mtu,
895 /* Get a reference to our struct, taking into account locks/refcounts.
896 * This is to ensure ordering in case we are shutting down, and to ensure
897 * there is a refcount at all (otherwise tty->disc_data may be freed and
898 * before we increment the refcount).
899 * Use this for anything that can race against elmcan_ldisc_close().
901 static struct elmcan *get_elm(struct tty_struct *tty)
906 spin_lock_bh(&elmcan_discdata_lock);
907 elm = (struct elmcan *)tty->disc_data;
910 spin_unlock_bh(&elmcan_discdata_lock);
914 got_ref = atomic_inc_not_zero(&elm->refcount);
915 spin_unlock_bh(&elmcan_discdata_lock);
923 static void put_elm(struct elmcan *elm)
925 atomic_dec(&elm->refcount);
928 static bool elmcan_is_valid_rx_char(char c)
930 return (isdigit(c) ||
932 c == ELM327_DUMMY_CHAR ||
933 c == ELM327_READY_CHAR ||
944 /* Handle incoming ELM327 ASCII data.
945 * This will not be re-entered while running, but other ldisc
946 * functions may be called in parallel.
948 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
949 static void elmcan_ldisc_rx(struct tty_struct *tty,
950 const unsigned char *cp, char *fp, int count)
952 static void elmcan_ldisc_rx(struct tty_struct *tty,
953 const unsigned char *cp, const char *fp, int count)
956 struct elmcan *elm = get_elm(tty);
961 spin_lock_bh(&elm->lock);
966 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
968 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
970 elm327_hw_failure(elm);
975 /* Ignore NUL characters, which the PIC microcontroller may
976 * inadvertently insert due to a known hardware bug.
977 * See ELM327 documentation, which refers to a Microchip PIC
981 /* Check for stray characters on the UART line.
982 * Likely caused by bad hardware.
984 if (!elmcan_is_valid_rx_char(*cp)) {
986 "Received illegal character %02x.\n",
988 elm327_hw_failure(elm);
993 elm->rxbuf[elm->rxfill++] = *cp;
1000 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
1002 elm327_hw_failure(elm);
1007 elm327_parse_rxbuf(elm);
1010 spin_unlock_bh(&elm->lock);
1014 /* Write out remaining transmit buffer.
1015 * Scheduled when TTY is writable.
1017 static void elmcan_ldisc_tx_worker(struct work_struct *work)
1019 /* No need to use get_elm() here, as we'll always flush workers
1020 * before destroying the elmcan object.
1022 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
1025 spin_lock_bh(&elm->lock);
1026 if (elm->hw_failure) {
1027 spin_unlock_bh(&elm->lock);
1031 if (!elm->tty || !netif_running(elm->dev)) {
1032 spin_unlock_bh(&elm->lock);
1036 if (elm->txleft <= 0) {
1037 /* Our TTY write buffer is empty:
1038 * Allow netdev to hand us another packet
1040 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1041 spin_unlock_bh(&elm->lock);
1042 netif_wake_queue(elm->dev);
1046 actual = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
1048 netdev_err(elm->dev,
1049 "Failed to write to tty %s.\n",
1051 elm327_hw_failure(elm);
1052 spin_unlock_bh(&elm->lock);
1056 elm->txleft -= actual;
1057 elm->txhead += actual;
1058 spin_unlock_bh(&elm->lock);
1061 /* Called by the driver when there's room for more data. */
1062 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1064 struct elmcan *elm = get_elm(tty);
1069 schedule_work(&elm->tx_work);
1074 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1075 * or 7/8 of that. Divisors are 1 to 64.
1076 * Currently we don't implement support for 7/8 rates.
1078 static const u32 elmcan_bitrate_const[64] = {
1079 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1080 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1081 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1082 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1083 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1084 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1085 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1086 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1089 /* Dummy needed to use bitrate_const */
1090 static int elmcan_do_set_bittiming(struct net_device *netdev)
1095 static int elmcan_ldisc_open(struct tty_struct *tty)
1097 struct net_device *dev;
1101 if (!capable(CAP_NET_ADMIN))
1104 if (!tty->ops->write)
1107 dev = alloc_candev(sizeof(struct elmcan), 0);
1110 elm = netdev_priv(dev);
1112 elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
1118 /* Configure TTY interface */
1119 tty->receive_room = 65536; /* We don't flow control */
1120 elm->txleft = 0; /* Clear TTY TX buffer */
1121 spin_lock_init(&elm->lock);
1122 atomic_set(&elm->refcount, 1);
1123 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1125 /* Configure CAN metadata */
1126 elm->can.state = CAN_STATE_STOPPED;
1127 elm->can.bitrate_const = elmcan_bitrate_const;
1128 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1129 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1130 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1132 /* Configure netdev interface */
1134 dev->netdev_ops = &elmcan_netdev_ops;
1136 /* Mark ldisc channel as alive */
1138 tty->disc_data = elm;
1140 devm_can_led_init(elm->dev);
1143 err = register_candev(elm->dev);
1147 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1153 free_candev(elm->dev);
1157 /* Close down an elmcan channel.
1158 * This means flushing out any pending queues, and then returning.
1159 * This call is serialized against other ldisc functions:
1160 * Once this is called, no other ldisc function of ours is entered.
1162 * We also use this function for a hangup event.
1164 static void elmcan_ldisc_close(struct tty_struct *tty)
1166 struct elmcan *elm = get_elm(tty);
1171 /* unregister_netdev() calls .ndo_stop() so we don't have to. */
1172 unregister_candev(elm->dev);
1174 /* Decrease the refcount twice, once for our own get_elm(),
1175 * and once to remove the count of 1 that we set in _open().
1176 * Once it reaches 0, we can safely destroy it.
1181 while (atomic_read(&elm->refcount) > 0)
1182 msleep_interruptible(10);
1184 /* At this point, all ldisc calls to us have become no-ops. */
1186 flush_work(&elm->tx_work);
1188 /* Mark channel as dead */
1189 spin_lock_bh(&elm->lock);
1190 tty->disc_data = NULL;
1192 spin_unlock_bh(&elm->lock);
1194 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1197 free_candev(elm->dev);
1200 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1201 static int elmcan_ldisc_hangup(struct tty_struct *tty)
1203 static void elmcan_ldisc_hangup(struct tty_struct *tty)
1206 elmcan_ldisc_close(tty);
1207 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1212 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1213 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1216 unsigned int cmd, unsigned long arg)
1218 struct elmcan *elm = get_elm(tty);
1226 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1227 if (copy_to_user((void __user *)arg, elm->dev->name, tmp)) {
1241 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1242 return tty_mode_ioctl(tty, file, cmd, arg);
1244 return tty_mode_ioctl(tty, cmd, arg);
1249 static struct tty_ldisc_ops elmcan_ldisc = {
1250 .owner = THIS_MODULE,
1252 .num = N_DEVELOPMENT,
1253 .receive_buf = elmcan_ldisc_rx,
1254 .write_wakeup = elmcan_ldisc_tx_wakeup,
1255 .open = elmcan_ldisc_open,
1256 .close = elmcan_ldisc_close,
1257 .hangup = elmcan_ldisc_hangup,
1258 .ioctl = elmcan_ldisc_ioctl,
1261 static int __init elmcan_init(void)
1265 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1266 status = tty_register_ldisc(N_DEVELOPMENT, &elmcan_ldisc);
1268 status = tty_register_ldisc(&elmcan_ldisc);
1271 pr_err("Can't register line discipline\n");
1276 static void __exit elmcan_exit(void)
1278 /* This will only be called when all channels have been closed by
1279 * userspace - tty_ldisc.c takes care of the module's refcount.
1281 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1284 status = tty_unregister_ldisc(N_DEVELOPMENT);
1286 pr_err("Can't unregister line discipline (error: %d)\n",
1289 tty_unregister_ldisc(&elmcan_ldisc);
1293 module_init(elmcan_init);
1294 module_exit(elmcan_exit);