1 // SPDX-License-Identifier: GPL-2.0
2 /* ELM327 based CAN interface driver (tty line discipline)
4 * This driver started as a derivative of linux/drivers/net/can/slcan.c
5 * and my thanks go to the original authors for their inspiration.
7 * elmcan.c Author : Max Staudt <max-linux@enpas.org>
8 * slcan.c Author : Oliver Hartkopp <socketcan@hartkopp.net>
9 * slip.c Authors : Laurence Culhane <loz@holmes.demon.co.uk>
10 * Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
13 #define pr_fmt(fmt) "elmcan: " fmt
15 #include <linux/init.h>
16 #include <linux/module.h>
17 #include <linux/moduleparam.h>
19 #include <linux/atomic.h>
20 #include <linux/bitops.h>
21 #include <linux/ctype.h>
22 #include <linux/delay.h>
23 #include <linux/errno.h>
24 #include <linux/if_ether.h>
25 #include <linux/kernel.h>
26 #include <linux/list.h>
27 #include <linux/lockdep.h>
28 #include <linux/netdevice.h>
29 #include <linux/skbuff.h>
30 #include <linux/spinlock.h>
31 #include <linux/string.h>
32 #include <linux/tty.h>
33 #include <linux/tty_ldisc.h>
34 #include <linux/version.h>
35 #include <linux/workqueue.h>
37 #include <uapi/linux/tty.h>
39 #include <linux/can.h>
40 #include <linux/can/dev.h>
41 #include <linux/can/error.h>
42 #include <linux/can/led.h>
43 #include <linux/can/rx-offload.h>
45 /* Line discipline ID number.
46 * Starting with Linux v5.18-rc1, N_DEVELOPMENT is defined as 29:
47 * https://github.com/torvalds/linux/commit/c2faf737abfb10f88f2d2612d573e9edc3c42c37
50 #define N_DEVELOPMENT 29
53 /* Compatibility for Linux < 5.11 */
54 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,11,0)
58 #define ELM327_NAPI_WEIGHT 4
60 #define ELM327_SIZE_RXBUF 224
61 #define ELM327_SIZE_TXBUF 32
63 #define ELM327_CAN_CONFIG_SEND_SFF 0x8000
64 #define ELM327_CAN_CONFIG_VARIABLE_DLC 0x4000
65 #define ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF 0x2000
66 #define ELM327_CAN_CONFIG_BAUDRATE_MULT_8_7 0x1000
68 #define ELM327_DUMMY_CHAR 'y'
69 #define ELM327_DUMMY_STRING "y"
70 #define ELM327_READY_CHAR '>'
72 /* Bits in elm->cmds_todo */
73 enum elm327_to_to_do_bits {
74 ELM327_TX_DO_CAN_DATA = 0,
75 ELM327_TX_DO_CANID_11BIT,
76 ELM327_TX_DO_CANID_29BIT_LOW,
77 ELM327_TX_DO_CANID_29BIT_HIGH,
78 ELM327_TX_DO_CAN_CONFIG_PART2,
79 ELM327_TX_DO_CAN_CONFIG,
80 ELM327_TX_DO_RESPONSES,
81 ELM327_TX_DO_SILENT_MONITOR,
86 /* This must be the first member when using alloc_candev() */
89 struct can_rx_offload offload;
92 u8 rxbuf[ELM327_SIZE_RXBUF];
93 u8 txbuf[ELM327_SIZE_TXBUF] ____cacheline_aligned;
95 /* Per-channel lock */
98 /* TTY and netdev devices that we're bridging */
99 struct tty_struct *tty;
100 struct net_device *dev;
102 /* TTY buffer accounting */
103 struct work_struct tx_work; /* Flushes TTY TX buffer */
104 u8 *txhead; /* Next TX byte */
105 size_t txleft; /* Bytes left to TX */
106 int rxfill; /* Bytes already RX'd in buffer */
110 ELM327_STATE_NOTINIT = 0,
111 ELM327_STATE_GETDUMMYCHAR,
112 ELM327_STATE_GETPROMPT,
113 ELM327_STATE_RECEIVING,
116 /* Things we have yet to send */
117 char **next_init_cmd;
118 unsigned long cmds_todo;
120 /* The CAN frame and config the ELM327 is sending/using,
121 * or will send/use after finishing all cmds_todo
123 struct can_frame can_frame_to_send;
125 u8 can_bitrate_divisor;
130 /* Stop the channel on UART side hardware failure, e.g. stray
131 * characters or neverending lines. This may be caused by bad
132 * UART wiring, a bad ELM327, a bad UART bridge...
133 * Once this is true, nothing will be sent to the TTY.
135 bool uart_side_failure;
138 static inline void elm327_uart_side_failure(struct elmcan *elm);
140 static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
144 lockdep_assert_held(&elm->lock);
146 if (elm->uart_side_failure)
149 memcpy(elm->txbuf, buf, len);
151 /* Order of next two lines is *very* important.
152 * When we are sending a little amount of data,
153 * the transfer may be completed inside the ops->write()
154 * routine, because it's running with interrupts enabled.
155 * In this case we *never* got WRITE_WAKEUP event,
156 * if we did not request it before write operation.
157 * 14 Oct 1994 Dmitry Gorodchanin.
159 set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
160 written = elm->tty->ops->write(elm->tty, elm->txbuf, len);
163 "Failed to write to tty %s.\n",
165 elm327_uart_side_failure(elm);
169 elm->txleft = len - written;
170 elm->txhead = elm->txbuf + written;
173 /* Take the ELM327 out of almost any state and back into command mode.
174 * We send ELM327_DUMMY_CHAR which will either abort any running
175 * operation, or be echoed back to us in case we're already in command
178 static void elm327_kick_into_cmd_mode(struct elmcan *elm)
180 lockdep_assert_held(&elm->lock);
182 if (elm->state != ELM327_STATE_GETDUMMYCHAR &&
183 elm->state != ELM327_STATE_GETPROMPT) {
184 elm327_send(elm, ELM327_DUMMY_STRING, 1);
186 elm->state = ELM327_STATE_GETDUMMYCHAR;
190 /* Schedule a CAN frame and necessary config changes to be sent to the TTY. */
191 static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
193 lockdep_assert_held(&elm->lock);
195 /* Schedule any necessary changes in ELM327's CAN configuration */
196 if (elm->can_frame_to_send.can_id != frame->can_id) {
197 /* Set the new CAN ID for transmission. */
198 if ((frame->can_id & CAN_EFF_FLAG) ^
199 (elm->can_frame_to_send.can_id & CAN_EFF_FLAG)) {
200 elm->can_config = (frame->can_id & CAN_EFF_FLAG
202 : ELM327_CAN_CONFIG_SEND_SFF)
203 | ELM327_CAN_CONFIG_VARIABLE_DLC
204 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
205 | elm->can_bitrate_divisor;
207 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
210 if (frame->can_id & CAN_EFF_FLAG) {
211 clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
212 set_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
213 set_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
215 set_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo);
216 clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
217 clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
221 /* Schedule the CAN frame itself. */
222 elm->can_frame_to_send = *frame;
223 set_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo);
225 elm327_kick_into_cmd_mode(elm);
228 /* ELM327 initialisation sequence.
229 * The line length is limited by the buffer in elm327_handle_prompt().
231 static char *elm327_init_script[] = {
232 "AT WS\r", /* v1.0: Warm Start */
233 "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
234 "AT M0\r", /* v1.0: Memory Off */
235 "AT AL\r", /* v1.0: Allow Long messages */
236 "AT BI\r", /* v1.0: Bypass Initialisation */
237 "AT CAF0\r", /* v1.0: CAN Auto Formatting Off */
238 "AT CFC0\r", /* v1.0: CAN Flow Control Off */
239 "AT CF 000\r", /* v1.0: Reset CAN ID Filter */
240 "AT CM 000\r", /* v1.0: Reset CAN ID Mask */
241 "AT E1\r", /* v1.0: Echo On */
242 "AT H1\r", /* v1.0: Headers On */
243 "AT L0\r", /* v1.0: Linefeeds Off */
244 "AT SH 7DF\r", /* v1.0: Set CAN sending ID to 0x7df */
245 "AT ST FF\r", /* v1.0: Set maximum Timeout for response after TX */
246 "AT AT0\r", /* v1.2: Adaptive Timing Off */
247 "AT D1\r", /* v1.3: Print DLC On */
248 "AT S1\r", /* v1.3: Spaces On */
249 "AT TP B\r", /* v1.0: Try Protocol B */
253 static void elm327_init(struct elmcan *elm)
255 lockdep_assert_held(&elm->lock);
257 elm->state = ELM327_STATE_NOTINIT;
258 elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
260 elm->drop_next_line = 0;
262 /* We can only set the bitrate as a fraction of 500000.
263 * The bit timing constants in elmcan_bittiming_const will
264 * limit the user to the right values.
266 elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
267 elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
268 | ELM327_CAN_CONFIG_VARIABLE_DLC
269 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
270 | elm->can_bitrate_divisor;
272 /* Configure ELM327 and then start monitoring */
273 elm->next_init_cmd = &elm327_init_script[0];
274 set_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
275 set_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
276 set_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo);
277 set_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
279 elm327_kick_into_cmd_mode(elm);
282 static void elm327_feed_frame_to_netdev(struct elmcan *elm,
285 lockdep_assert_held(&elm->lock);
287 if (!netif_running(elm->dev))
290 /* Queue for NAPI pickup.
291 * rx-offload will update stats and LEDs for us.
293 if (can_rx_offload_queue_tail(&elm->offload, skb))
294 elm->dev->stats.rx_fifo_errors++;
296 #if LINUX_VERSION_CODE >= KERNEL_VERSION(5,15,0)
298 can_rx_offload_irq_finish(&elm->offload);
302 /* Called when we're out of ideas and just want it all to end. */
303 static inline void elm327_uart_side_failure(struct elmcan *elm)
305 struct can_frame *frame;
308 lockdep_assert_held(&elm->lock);
310 elm->uart_side_failure = true;
312 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
314 elm->can.can_stats.bus_off++;
315 netif_stop_queue(elm->dev);
316 elm->can.state = CAN_STATE_BUS_OFF;
317 can_bus_off(elm->dev);
319 netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
321 skb = alloc_can_err_skb(elm->dev, &frame);
325 frame->can_id |= CAN_ERR_BUSOFF;
326 elm327_feed_frame_to_netdev(elm, skb);
329 /* Compare buffer to string length, then compare buffer to fixed string.
330 * This ensures two things:
331 * - It flags cases where the fixed string is only the start of the
332 * buffer, rather than exactly all of it.
333 * - It avoids byte comparisons in case the length doesn't match.
335 * strncmp() cannot be used here because it accepts the following wrong case:
336 * strncmp("CAN ER", "CAN ERROR", 6);
337 * This must fail, hence this helper function.
339 static inline int check_len_then_cmp(const u8 *mem, size_t mem_len, const char *str)
341 size_t str_len = strlen(str);
343 return (mem_len == str_len) && !memcmp(mem, str, str_len);
346 static void elm327_parse_error(struct elmcan *elm, size_t len)
348 struct can_frame *frame;
351 lockdep_assert_held(&elm->lock);
353 skb = alloc_can_err_skb(elm->dev, &frame);
355 /* It's okay to return here:
356 * The outer parsing loop will drop this UART buffer.
360 /* Filter possible error messages based on length of RX'd line */
361 if (check_len_then_cmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
363 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
364 } else if (check_len_then_cmp(elm->rxbuf, len, "BUFFER FULL")) {
365 /* This will only happen if the last data line was complete.
366 * Otherwise, elm327_parse_frame() will heuristically
367 * emit this kind of error frame instead.
369 frame->can_id |= CAN_ERR_CRTL;
370 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
371 } else if (check_len_then_cmp(elm->rxbuf, len, "BUS ERROR")) {
372 frame->can_id |= CAN_ERR_BUSERROR;
373 } else if (check_len_then_cmp(elm->rxbuf, len, "CAN ERROR")) {
374 frame->can_id |= CAN_ERR_PROT;
375 } else if (check_len_then_cmp(elm->rxbuf, len, "<RX ERROR")) {
376 frame->can_id |= CAN_ERR_PROT;
377 } else if (check_len_then_cmp(elm->rxbuf, len, "BUS BUSY")) {
378 frame->can_id |= CAN_ERR_PROT;
379 frame->data[2] = CAN_ERR_PROT_OVERLOAD;
380 } else if (check_len_then_cmp(elm->rxbuf, len, "FB ERROR")) {
381 frame->can_id |= CAN_ERR_PROT;
382 frame->data[2] = CAN_ERR_PROT_TX;
383 } else if (len == 5 && !memcmp(elm->rxbuf, "ERR", 3)) {
384 /* ERR is followed by two digits, hence line length 5 */
385 netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
386 elm->rxbuf[3], elm->rxbuf[4]);
387 frame->can_id |= CAN_ERR_CRTL;
389 /* Something else has happened.
390 * Maybe garbage on the UART line.
391 * Emit a generic error frame.
395 elm327_feed_frame_to_netdev(elm, skb);
398 /* Parse CAN frames coming as ASCII from ELM327.
399 * They can be of various formats:
401 * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
402 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
404 * where D = DLC, PL = payload byte
406 * Instead of a payload, RTR indicates a remote request.
408 * We will use the spaces and line length to guess the format.
410 static int elm327_parse_frame(struct elmcan *elm, size_t len)
412 struct can_frame *frame;
418 lockdep_assert_held(&elm->lock);
420 skb = alloc_can_skb(elm->dev, &frame);
424 /* Find first non-hex and non-space character:
425 * - In the simplest case, there is none.
426 * - For RTR frames, 'R' is the first non-hex character.
427 * - An error message may replace the end of the data line.
429 for (hexlen = 0; hexlen <= len; hexlen++) {
430 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
431 elm->rxbuf[hexlen] != ' ') {
436 /* Sanity check whether the line is really a clean hexdump,
437 * or terminated by an error message, or contains garbage.
440 !isdigit(elm->rxbuf[hexlen]) &&
441 !isupper(elm->rxbuf[hexlen]) &&
442 '<' != elm->rxbuf[hexlen] &&
443 ' ' != elm->rxbuf[hexlen]) {
444 /* The line is likely garbled anyway, so bail.
445 * The main code will restart listening.
450 /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
451 * No out-of-bounds access:
452 * We use the fact that we can always read from elm->rxbuf.
454 if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
455 elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
456 elm->rxbuf[13] == ' ') {
457 frame->can_id = CAN_EFF_FLAG;
459 } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
462 /* This is not a well-formatted data line.
463 * Assume it's an error message.
468 if (hexlen < datastart) {
469 /* The line is too short to be a valid frame hex dump.
470 * Something interrupted the hex dump or it is invalid.
475 /* From here on all chars up to buf[hexlen] are hex or spaces,
476 * at well-defined offsets.
479 /* Read CAN data length */
480 frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
483 if (frame->can_id & CAN_EFF_FLAG) {
484 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
485 | (hex_to_bin(elm->rxbuf[1]) << 24)
486 | (hex_to_bin(elm->rxbuf[3]) << 20)
487 | (hex_to_bin(elm->rxbuf[4]) << 16)
488 | (hex_to_bin(elm->rxbuf[6]) << 12)
489 | (hex_to_bin(elm->rxbuf[7]) << 8)
490 | (hex_to_bin(elm->rxbuf[9]) << 4)
491 | (hex_to_bin(elm->rxbuf[10]) << 0);
493 frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
494 | (hex_to_bin(elm->rxbuf[1]) << 4)
495 | (hex_to_bin(elm->rxbuf[2]) << 0);
498 /* Check for RTR frame */
499 if (elm->rxfill >= hexlen + 3 &&
500 !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) {
501 frame->can_id |= CAN_RTR_FLAG;
504 /* Is the line long enough to hold the advertised payload?
505 * Note: RTR frames have a DLC, but no actual payload.
507 if (!(frame->can_id & CAN_RTR_FLAG) &&
508 (hexlen < frame->len * 3 + datastart)) {
510 * Probably the ELM327's RS232 TX buffer was full.
511 * Emit an error frame and exit.
513 frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
514 frame->len = CAN_ERR_DLC;
515 frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
516 elm327_feed_frame_to_netdev(elm, skb);
518 /* Signal failure to parse.
519 * The line will be re-parsed as an error line, which will fail.
520 * However, this will correctly drop the state machine back into
526 /* Parse the data nibbles. */
527 for (i = 0; i < frame->len; i++) {
528 frame->data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
529 | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
532 /* Feed the frame to the network layer. */
533 elm327_feed_frame_to_netdev(elm, skb);
538 static void elm327_parse_line(struct elmcan *elm, size_t len)
540 lockdep_assert_held(&elm->lock);
542 /* Skip empty lines */
546 /* Skip echo lines */
547 if (elm->drop_next_line) {
548 elm->drop_next_line = 0;
550 } else if (!memcmp(elm->rxbuf, "AT", 2)) {
554 /* Regular parsing */
555 if (elm->state == ELM327_STATE_RECEIVING &&
556 elm327_parse_frame(elm, len)) {
557 /* Parse an error line. */
558 elm327_parse_error(elm, len);
561 elm327_kick_into_cmd_mode(elm);
565 static void elm327_handle_prompt(struct elmcan *elm)
567 struct can_frame *frame = &elm->can_frame_to_send;
568 /* Size this buffer for the largest ELM327 line we may generate,
569 * which is currently an 8 byte CAN frame's payload hexdump.
570 * Items in elm327_init_script must fit here, too!
572 char local_txbuf[sizeof("0102030405060708\r")];
574 lockdep_assert_held(&elm->lock);
576 if (!elm->cmds_todo) {
577 /* Enter CAN monitor mode */
578 elm327_send(elm, "ATMA\r", 5);
579 elm->state = ELM327_STATE_RECEIVING;
581 /* We will be in the default state once this command is
582 * sent, so enable the TX packet queue.
584 netif_wake_queue(elm->dev);
589 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
590 if (test_bit(ELM327_TX_DO_INIT, &elm->cmds_todo)) {
591 snprintf(local_txbuf, sizeof(local_txbuf),
593 *elm->next_init_cmd);
595 elm->next_init_cmd++;
596 if (!(*elm->next_init_cmd)) {
597 clear_bit(ELM327_TX_DO_INIT, &elm->cmds_todo);
601 } else if (test_and_clear_bit(ELM327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
602 snprintf(local_txbuf, sizeof(local_txbuf),
604 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
606 } else if (test_and_clear_bit(ELM327_TX_DO_RESPONSES, &elm->cmds_todo)) {
607 snprintf(local_txbuf, sizeof(local_txbuf),
609 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
611 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
612 snprintf(local_txbuf, sizeof(local_txbuf),
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 snprintf(local_txbuf, sizeof(local_txbuf),
621 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
622 snprintf(local_txbuf, sizeof(local_txbuf),
624 (frame->can_id & CAN_EFF_MASK) >> 24);
626 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
627 snprintf(local_txbuf, sizeof(local_txbuf),
629 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
631 } else if (test_and_clear_bit(ELM327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
632 snprintf(local_txbuf, sizeof(local_txbuf),
634 frame->can_id & CAN_SFF_MASK);
636 } else if (test_and_clear_bit(ELM327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
637 if (frame->can_id & CAN_RTR_FLAG) {
638 /* Send an RTR frame. Their DLC is fixed.
639 * Some chips don't send them at all.
641 snprintf(local_txbuf, sizeof(local_txbuf),
644 /* Send a regular CAN data frame */
647 for (i = 0; i < frame->len; i++) {
648 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
653 snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
657 elm->drop_next_line = 1;
658 elm->state = ELM327_STATE_RECEIVING;
660 /* We will be in the default state once this command is
661 * sent, so enable the TX packet queue.
663 netif_wake_queue(elm->dev);
666 elm327_send(elm, local_txbuf, strlen(local_txbuf));
669 static bool elm327_is_ready_char(char c)
671 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
672 * Probably bad hardware.
674 return (c & 0x3f) == ELM327_READY_CHAR;
677 static void elm327_drop_bytes(struct elmcan *elm, size_t i)
679 lockdep_assert_held(&elm->lock);
681 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
685 static void elm327_parse_rxbuf(struct elmcan *elm)
690 lockdep_assert_held(&elm->lock);
692 switch (elm->state) {
693 case ELM327_STATE_NOTINIT:
697 case ELM327_STATE_GETDUMMYCHAR:
699 /* Wait for 'y' or '>' */
700 for (i = 0; i < elm->rxfill; i++) {
701 if (elm->rxbuf[i] == ELM327_DUMMY_CHAR) {
702 elm327_send(elm, "\r", 1);
703 elm->state = ELM327_STATE_GETPROMPT;
706 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
707 elm327_send(elm, ELM327_DUMMY_STRING, 1);
713 elm327_drop_bytes(elm, i);
718 case ELM327_STATE_GETPROMPT:
720 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
721 elm327_handle_prompt(elm);
726 case ELM327_STATE_RECEIVING:
727 /* Find <CR> delimiting feedback lines. */
729 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
734 if (len == ELM327_SIZE_RXBUF) {
735 /* Line exceeds buffer. It's probably all garbage.
736 * Did we even connect at the right baud rate?
739 "RX buffer overflow. Faulty ELM327 or UART?\n");
740 elm327_uart_side_failure(elm);
742 } else if (len == elm->rxfill) {
743 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
744 /* The ELM327's AT ST response timeout ran out,
745 * so we got a prompt.
746 * Clear RX buffer and restart listening.
750 elm327_handle_prompt(elm);
754 /* No <CR> found - we haven't received a full line yet.
755 * Wait for more data.
760 /* We have a full line to parse. */
761 elm327_parse_line(elm, len);
763 /* Remove parsed data from RX buffer. */
764 elm327_drop_bytes(elm, len + 1);
766 /* More data to parse? */
768 elm327_parse_rxbuf(elm);
772 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
773 /* Dummy needed to use can_rx_offload */
774 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
775 unsigned int n, u32 *timestamp,
778 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
780 return ERR_PTR(-ENOBUFS);
784 static int elmcan_netdev_open(struct net_device *dev)
786 struct elmcan *elm = netdev_priv(dev);
789 spin_lock_bh(&elm->lock);
792 spin_unlock_bh(&elm->lock);
796 if (elm->uart_side_failure)
797 netdev_warn(elm->dev, "Reopening netdev after a UART side fault has been detected.\n");
799 /* Clear TTY buffers */
803 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
804 err = open_candev(dev);
806 spin_unlock_bh(&elm->lock);
811 spin_unlock_bh(&elm->lock);
813 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,10,0)
814 elm->offload.mailbox_read = elmcan_mailbox_read;
815 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
817 err = can_rx_offload_add_manual(dev, &elm->offload, ELM327_NAPI_WEIGHT);
824 can_rx_offload_enable(&elm->offload);
826 can_led_event(dev, CAN_LED_EVENT_OPEN);
827 elm->can.state = CAN_STATE_ERROR_ACTIVE;
828 netif_start_queue(dev);
833 static int elmcan_netdev_close(struct net_device *dev)
835 struct elmcan *elm = netdev_priv(dev);
837 /* Interrupt whatever the ELM327 is doing right now */
838 spin_lock_bh(&elm->lock);
839 elm327_send(elm, ELM327_DUMMY_STRING, 1);
840 spin_unlock_bh(&elm->lock);
842 netif_stop_queue(dev);
844 /* Give UART one final chance to flush. */
845 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
846 flush_work(&elm->tx_work);
848 can_rx_offload_disable(&elm->offload);
849 elm->can.state = CAN_STATE_STOPPED;
850 can_rx_offload_del(&elm->offload);
852 can_led_event(dev, CAN_LED_EVENT_STOP);
857 /* Send a can_frame to a TTY. */
858 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
859 struct net_device *dev)
861 struct elmcan *elm = netdev_priv(dev);
862 struct can_frame *frame = (struct can_frame *)skb->data;
864 if (can_dropped_invalid_skb(dev, skb))
867 /* BHs are already disabled, so no spin_lock_bh().
868 * See Documentation/networking/netdevices.txt
870 spin_lock(&elm->lock);
872 /* We shouldn't get here after a hardware fault:
873 * can_bus_off() calls netif_carrier_off()
875 WARN_ON_ONCE(elm->uart_side_failure);
878 elm->uart_side_failure ||
879 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
880 spin_unlock(&elm->lock);
884 netif_stop_queue(dev);
886 elm327_send_frame(elm, frame);
887 spin_unlock(&elm->lock);
889 dev->stats.tx_packets++;
890 dev->stats.tx_bytes += frame->len;
892 can_led_event(dev, CAN_LED_EVENT_TX);
899 static const struct net_device_ops elmcan_netdev_ops = {
900 .ndo_open = elmcan_netdev_open,
901 .ndo_stop = elmcan_netdev_close,
902 .ndo_start_xmit = elmcan_netdev_start_xmit,
903 .ndo_change_mtu = can_change_mtu,
906 static bool elmcan_is_valid_rx_char(char c)
908 return (isdigit(c) ||
910 c == ELM327_DUMMY_CHAR ||
911 c == ELM327_READY_CHAR ||
922 /* Handle incoming ELM327 ASCII data.
923 * This will not be re-entered while running, but other ldisc
924 * functions may be called in parallel.
926 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
927 static void elmcan_ldisc_rx(struct tty_struct *tty,
928 const unsigned char *cp, char *fp, int count)
930 static void elmcan_ldisc_rx(struct tty_struct *tty,
931 const unsigned char *cp, const char *fp, int count)
934 struct elmcan *elm = (struct elmcan *)tty->disc_data;
936 spin_lock_bh(&elm->lock);
938 if (elm->uart_side_failure)
941 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
943 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
945 elm327_uart_side_failure(elm);
950 /* Ignore NUL characters, which the PIC microcontroller may
951 * inadvertently insert due to a known hardware bug.
952 * See ELM327 documentation, which refers to a Microchip PIC
956 /* Check for stray characters on the UART line.
957 * Likely caused by bad hardware.
959 if (!elmcan_is_valid_rx_char(*cp)) {
961 "Received illegal character %02x.\n",
963 elm327_uart_side_failure(elm);
968 elm->rxbuf[elm->rxfill++] = *cp;
975 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
977 elm327_uart_side_failure(elm);
982 elm327_parse_rxbuf(elm);
985 spin_unlock_bh(&elm->lock);
988 /* Write out remaining transmit buffer.
989 * Scheduled when TTY is writable.
991 static void elmcan_ldisc_tx_worker(struct work_struct *work)
993 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
996 if (elm->uart_side_failure)
999 spin_lock_bh(&elm->lock);
1002 written = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
1004 netdev_err(elm->dev,
1005 "Failed to write to tty %s.\n",
1007 elm327_uart_side_failure(elm);
1008 spin_unlock_bh(&elm->lock);
1012 elm->txleft -= written;
1013 elm->txhead += written;
1017 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1018 spin_unlock_bh(&elm->lock);
1020 spin_unlock_bh(&elm->lock);
1024 /* Called by the driver when there's room for more data. */
1025 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1027 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1029 schedule_work(&elm->tx_work);
1032 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1033 * or 7/8 of that. Divisors are 1 to 64.
1034 * Currently we don't implement support for 7/8 rates.
1036 static const u32 elmcan_bitrate_const[64] = {
1037 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1038 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1039 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1040 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1041 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1042 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1043 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1044 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1047 /* Dummy needed to use bitrate_const */
1048 static int elmcan_do_set_bittiming(struct net_device *netdev)
1053 static int elmcan_ldisc_open(struct tty_struct *tty)
1055 struct net_device *dev;
1059 if (!capable(CAP_NET_ADMIN))
1062 if (!tty->ops->write)
1065 dev = alloc_candev(sizeof(struct elmcan), 0);
1068 elm = netdev_priv(dev);
1070 /* Configure TTY interface */
1071 tty->receive_room = 65536; /* We don't flow control */
1072 spin_lock_init(&elm->lock);
1073 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1075 /* Configure CAN metadata */
1076 elm->can.bitrate_const = elmcan_bitrate_const;
1077 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1078 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1079 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1081 /* Configure netdev interface */
1083 dev->netdev_ops = &elmcan_netdev_ops;
1085 /* Mark ldisc channel as alive */
1087 tty->disc_data = elm;
1089 devm_can_led_init(elm->dev);
1092 err = register_candev(elm->dev);
1096 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1101 free_candev(elm->dev);
1105 /* Close down an elmcan channel.
1106 * This means flushing out any pending queues, and then returning.
1107 * This call is serialized against other ldisc functions:
1108 * Once this is called, no other ldisc function of ours is entered.
1110 * We also use this function for a hangup event.
1112 static void elmcan_ldisc_close(struct tty_struct *tty)
1114 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1116 /* unregister_netdev() calls .ndo_stop() so we don't have to.
1117 * Our .ndo_stop() also flushes the TTY write wakeup handler,
1118 * so we can safely set elm->tty = NULL after this.
1120 unregister_candev(elm->dev);
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);
1130 free_candev(elm->dev);
1133 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1134 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1137 unsigned int cmd, unsigned long arg)
1139 struct elmcan *elm = (struct elmcan *)tty->disc_data;
1144 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1145 if (copy_to_user((void __user *)arg, elm->dev->name, tmp))
1153 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1154 return tty_mode_ioctl(tty, file, cmd, arg);
1156 return tty_mode_ioctl(tty, cmd, arg);
1161 static struct tty_ldisc_ops elmcan_ldisc = {
1162 .owner = THIS_MODULE,
1164 .num = N_DEVELOPMENT,
1165 .receive_buf = elmcan_ldisc_rx,
1166 .write_wakeup = elmcan_ldisc_tx_wakeup,
1167 .open = elmcan_ldisc_open,
1168 .close = elmcan_ldisc_close,
1169 .ioctl = elmcan_ldisc_ioctl,
1172 static int __init elmcan_init(void)
1176 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1177 status = tty_register_ldisc(N_DEVELOPMENT, &elmcan_ldisc);
1179 status = tty_register_ldisc(&elmcan_ldisc);
1182 pr_err("Can't register line discipline\n");
1187 static void __exit elmcan_exit(void)
1189 /* This will only be called when all channels have been closed by
1190 * userspace - tty_ldisc.c takes care of the module's refcount.
1192 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1195 status = tty_unregister_ldisc(N_DEVELOPMENT);
1197 pr_err("Can't unregister line discipline (error: %d)\n",
1200 tty_unregister_ldisc(&elmcan_ldisc);
1204 module_init(elmcan_init);
1205 module_exit(elmcan_exit);
1207 MODULE_ALIAS_LDISC(N_DEVELOPMENT);
1208 MODULE_DESCRIPTION("ELM327 based CAN interface");
1209 MODULE_LICENSE("GPL");
1210 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");