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_ELMCAN);
41 MODULE_DESCRIPTION("ELM327 based CAN interface");
42 MODULE_LICENSE("GPL");
43 MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");
45 /* If this is enabled, we'll try to make the best of the situation
46 * even if we receive unexpected characters on the line.
48 * Handle with care, it's likely your hardware is unreliable!
50 static bool accept_flaky_uart;
51 module_param_named(accept_flaky_uart, accept_flaky_uart, bool, 0444);
52 MODULE_PARM_DESC(accept_flaky_uart, "Don't bail at the first invalid character. Behavior undefined.");
54 /* Line discipline ID number */
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_MAGIC_CHAR 'y'
70 #define ELM327_MAGIC_STRING "y"
71 #define ELM327_READY_CHAR '>'
73 /* Bits in elm->cmds_todo */
78 TODO_CANID_29BIT_HIGH,
79 TODO_CAN_CONFIG_PART2,
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 /* Keep track of how many things are using this struct.
100 * Once it reaches 0, we are in the process of cleaning up,
101 * and new operations will be cancelled immediately.
102 * Use atomic_t rather than refcount_t because we deliberately
103 * decrement to 0, and refcount_dec() spills a WARN_ONCE in
108 /* Stop the channel on hardware failure.
109 * Once this is true, nothing will be sent to the TTY.
114 struct work_struct tx_work; /* Flushes TTY TX buffer */
115 unsigned char *txbuf;
116 unsigned char *txhead; /* Pointer to next TX byte */
117 int txleft; /* Bytes left to TX */
120 unsigned char rxbuf[ELM327_SIZE_RXBUF];
133 /* The CAN frame and config the ELM327 is sending/using,
134 * or will send/use after finishing all cmds_todo
136 struct can_frame can_frame;
137 unsigned short can_config;
138 unsigned long can_bitrate;
139 unsigned char can_bitrate_divisor;
140 int silent_monitoring;
142 /* Things we have yet to send */
143 char **next_init_cmd;
144 unsigned long cmds_todo;
147 /* A lock for all tty->disc_data handled by this ldisc.
148 * This is to prevent a case where tty->disc_data is set to NULL,
149 * yet someone is still trying to dereference it.
150 * Without this, we cannot do a clean shutdown.
152 static DEFINE_SPINLOCK(elmcan_discdata_lock);
154 static inline void elm327_hw_failure(struct elmcan *elm);
156 /* Assumes elm->lock taken. */
157 static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
164 memcpy(elm->txbuf, buf, len);
166 /* Order of next two lines is *very* important.
167 * When we are sending a little amount of data,
168 * the transfer may be completed inside the ops->write()
169 * routine, because it's running with interrupts enabled.
170 * In this case we *never* got WRITE_WAKEUP event,
171 * if we did not request it before write operation.
172 * 14 Oct 1994 Dmitry Gorodchanin.
174 set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
175 actual = elm->tty->ops->write(elm->tty, elm->txbuf, len);
178 "Failed to write to tty %s.\n",
180 elm327_hw_failure(elm);
184 elm->txleft = len - actual;
185 elm->txhead = elm->txbuf + actual;
188 /* Take the ELM327 out of almost any state and back into command mode.
189 * We send ELM327_MAGIC_CHAR which will either abort any running
190 * operation, or be echoed back to us in case we're already in command
193 * Assumes elm->lock taken.
195 static void elm327_kick_into_cmd_mode(struct elmcan *elm)
197 if (elm->state != ELM_GETMAGICCHAR && elm->state != ELM_GETPROMPT) {
198 elm327_send(elm, ELM327_MAGIC_STRING, 1);
200 elm->state = ELM_GETMAGICCHAR;
204 /* Schedule a CAN frame and necessary config changes to be sent to the TTY.
206 * Assumes elm->lock taken.
208 static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
210 /* Schedule any necessary changes in ELM327's CAN configuration */
211 if (elm->can_frame.can_id != frame->can_id) {
212 /* Set the new CAN ID for transmission. */
213 if ((frame->can_id & CAN_EFF_FLAG)
214 ^ (elm->can_frame.can_id & CAN_EFF_FLAG)) {
215 elm->can_config = (frame->can_id & CAN_EFF_FLAG
217 : ELM327_CAN_CONFIG_SEND_SFF)
218 | ELM327_CAN_CONFIG_VARIABLE_DLC
219 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
220 | elm->can_bitrate_divisor;
222 set_bit(TODO_CAN_CONFIG, &elm->cmds_todo);
225 if (frame->can_id & CAN_EFF_FLAG) {
226 clear_bit(TODO_CANID_11BIT, &elm->cmds_todo);
227 set_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo);
228 set_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo);
230 set_bit(TODO_CANID_11BIT, &elm->cmds_todo);
231 clear_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo);
232 clear_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo);
236 /* Schedule the CAN frame itself. */
237 elm->can_frame = *frame;
238 set_bit(TODO_CAN_DATA, &elm->cmds_todo);
240 elm327_kick_into_cmd_mode(elm);
243 /* ELM327 initialization sequence.
245 * Assumes elm->lock taken.
247 static char *elm327_init_script[] = {
248 "AT WS\r", /* v1.0: Warm Start */
249 "AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
250 "AT M0\r", /* v1.0: Memory Off */
251 "AT AL\r", /* v1.0: Allow Long messages */
252 "AT BI\r", /* v1.0: Bypass Initialization */
253 "AT CAF0\r", /* v1.0: CAN Auto Formatting Off */
254 "AT CFC0\r", /* v1.0: CAN Flow Control Off */
255 "AT CF 000\r", /* v1.0: Reset CAN ID Filter */
256 "AT CM 000\r", /* v1.0: Reset CAN ID Mask */
257 "AT E1\r", /* v1.0: Echo On */
258 "AT H1\r", /* v1.0: Headers On */
259 "AT L0\r", /* v1.0: Linefeeds Off */
260 "AT SH 7DF\r", /* v1.0: Set CAN sending ID to 0x7df */
261 "AT ST FF\r", /* v1.0: Set maximum Timeout for response after TX */
262 "AT AT0\r", /* v1.2: Adaptive Timing Off */
263 "AT D1\r", /* v1.3: Print DLC On */
264 "AT S1\r", /* v1.3: Spaces On */
265 "AT TP B\r", /* v1.0: Try Protocol B */
269 static void elm327_init(struct elmcan *elm)
271 elm->state = ELM_NOTINIT;
272 elm->can_frame.can_id = 0x7df;
274 elm->drop_next_line = 0;
276 /* We can only set the bitrate as a fraction of 500000.
277 * The bit timing constants in elmcan_bittiming_const will
278 * limit the user to the right values.
280 elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
281 elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
282 | ELM327_CAN_CONFIG_VARIABLE_DLC
283 | ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
284 | elm->can_bitrate_divisor;
286 /* Configure ELM327 and then start monitoring */
287 elm->next_init_cmd = &elm327_init_script[0];
288 set_bit(TODO_INIT, &elm->cmds_todo);
289 set_bit(TODO_SILENT_MONITOR, &elm->cmds_todo);
290 set_bit(TODO_RESPONSES, &elm->cmds_todo);
291 set_bit(TODO_CAN_CONFIG, &elm->cmds_todo);
293 elm327_kick_into_cmd_mode(elm);
296 /* Assumes elm->lock taken. */
297 static void elm327_feed_frame_to_netdev(struct elmcan *elm,
298 const struct can_frame *frame)
300 struct can_frame *cf;
303 if (!netif_running(elm->dev))
306 skb = alloc_can_skb(elm->dev, &cf);
311 memcpy(cf, frame, sizeof(struct can_frame));
313 /* Queue for NAPI pickup.
314 * rx-offload will update stats and LEDs for us.
316 if (can_rx_offload_queue_tail(&elm->offload, skb))
317 elm->dev->stats.rx_fifo_errors++;
319 #if LINUX_VERSION_CODE >= KERNEL_VERSION(5,15,0)
321 can_rx_offload_irq_finish(&elm->offload);
325 /* Called when we're out of ideas and just want it all to end.
326 * Assumes elm->lock taken.
328 static inline void elm327_hw_failure(struct elmcan *elm)
330 struct can_frame frame;
332 memset(&frame, 0, sizeof(frame));
333 frame.can_id = CAN_ERR_FLAG;
334 frame.can_dlc = CAN_ERR_DLC;
338 elm327_feed_frame_to_netdev(elm, &frame);
340 netdev_err(elm->dev, "ELM327 misbehaved. Blocking further communication.\n");
342 elm->hw_failure = true;
343 can_bus_off(elm->dev);
346 /* Compare a buffer to a fixed string */
347 static int _memstrcmp(const u8 *mem, const char *str)
349 return memcmp(mem, str, strlen(str));
352 /* Assumes elm->lock taken. */
353 static void elm327_parse_error(struct elmcan *elm, int len)
355 struct can_frame frame;
357 memset(&frame, 0, sizeof(frame));
358 frame.can_id = CAN_ERR_FLAG;
359 frame.can_dlc = CAN_ERR_DLC;
361 /* Filter possible error messages based on length of RX'd line */
364 if (!_memstrcmp(elm->rxbuf, "UNABLE TO CONNECT")) {
366 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
370 if (!_memstrcmp(elm->rxbuf, "BUFFER FULL")) {
371 /* This case will only happen if the last data
373 * Otherwise, elm327_parse_frame() will heuristically
374 * emit this error frame instead.
376 frame.can_id |= CAN_ERR_CRTL;
377 frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
381 if (!_memstrcmp(elm->rxbuf, "BUS ERROR"))
382 frame.can_id |= CAN_ERR_BUSERROR;
383 if (!_memstrcmp(elm->rxbuf, "CAN ERROR"))
384 frame.can_id |= CAN_ERR_PROT;
385 if (!_memstrcmp(elm->rxbuf, "<RX ERROR"))
386 frame.can_id |= CAN_ERR_PROT;
389 if (!_memstrcmp(elm->rxbuf, "BUS BUSY")) {
390 frame.can_id |= CAN_ERR_PROT;
391 frame.data[2] = CAN_ERR_PROT_OVERLOAD;
393 if (!_memstrcmp(elm->rxbuf, "FB ERROR")) {
394 frame.can_id |= CAN_ERR_PROT;
395 frame.data[2] = CAN_ERR_PROT_TX;
398 case 5: /* ERR is followed by two digits, hence line length 5 */
399 if (!_memstrcmp(elm->rxbuf, "ERR")) {
400 netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
401 elm->rxbuf[3], elm->rxbuf[4]);
402 frame.can_id |= CAN_ERR_CRTL;
406 /* Something else has happened.
407 * Maybe garbage on the UART line.
408 * Emit a generic error frame.
413 elm327_feed_frame_to_netdev(elm, &frame);
416 /* Parse CAN frames coming as ASCII from ELM327.
417 * They can be of various formats:
419 * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
420 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
422 * where D = DLC, PL = payload byte
424 * Instead of a payload, RTR indicates a remote request.
426 * We will use the spaces and line length to guess the format.
428 * Assumes elm->lock taken.
430 static int elm327_parse_frame(struct elmcan *elm, int len)
432 struct can_frame frame;
437 memset(&frame, 0, sizeof(frame));
439 /* Find first non-hex and non-space character:
440 * - In the simplest case, there is none.
441 * - For RTR frames, 'R' is the first non-hex character.
442 * - An error message may replace the end of the data line.
444 for (hexlen = 0; hexlen <= len; hexlen++) {
445 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
446 elm->rxbuf[hexlen] != ' ') {
451 /* If we accept stray characters coming in:
452 * Check for stray characters on a payload line.
453 * No idea what causes this.
455 if (accept_flaky_uart &&
457 !isdigit(elm->rxbuf[hexlen]) &&
458 !isupper(elm->rxbuf[hexlen]) &&
459 '<' != elm->rxbuf[hexlen] &&
460 ' ' != elm->rxbuf[hexlen]) {
461 /* The line is likely garbled anyway, so bail.
462 * The main code will restart listening.
467 /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
468 * No out-of-bounds access:
469 * We use the fact that we can always read from elm->rxbuf.
471 if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
472 elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
473 elm->rxbuf[13] == ' ') {
474 frame.can_id = CAN_EFF_FLAG;
476 } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
480 /* This is not a well-formatted data line.
481 * Assume it's an error message.
486 if (hexlen < datastart) {
487 /* The line is too short to be a valid frame hex dump.
488 * Something interrupted the hex dump or it is invalid.
493 /* From here on all chars up to buf[hexlen] are hex or spaces,
494 * at well-defined offsets.
497 /* Read CAN data length */
498 frame.can_dlc = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
501 if (frame.can_id & CAN_EFF_FLAG) {
502 frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
503 | (hex_to_bin(elm->rxbuf[1]) << 24)
504 | (hex_to_bin(elm->rxbuf[3]) << 20)
505 | (hex_to_bin(elm->rxbuf[4]) << 16)
506 | (hex_to_bin(elm->rxbuf[6]) << 12)
507 | (hex_to_bin(elm->rxbuf[7]) << 8)
508 | (hex_to_bin(elm->rxbuf[9]) << 4)
509 | (hex_to_bin(elm->rxbuf[10]) << 0);
511 frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
512 | (hex_to_bin(elm->rxbuf[1]) << 4)
513 | (hex_to_bin(elm->rxbuf[2]) << 0);
516 /* Check for RTR frame */
517 if (elm->rxfill >= hexlen + 3 &&
518 !_memstrcmp(&elm->rxbuf[hexlen], "RTR")) {
519 frame.can_id |= CAN_RTR_FLAG;
522 /* Is the line long enough to hold the advertised payload?
523 * Note: RTR frames have a DLC, but no actual payload.
525 if (!(frame.can_id & CAN_RTR_FLAG) &&
526 (hexlen < frame.can_dlc * 3 + datastart)) {
527 /* Incomplete frame. */
529 /* Probably the ELM327's RS232 TX buffer was full.
530 * Emit an error frame and exit.
532 frame.can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
533 frame.can_dlc = CAN_ERR_DLC;
534 frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
535 elm327_feed_frame_to_netdev(elm, &frame);
537 /* Signal failure to parse.
538 * The line will be re-parsed as an error line, which will fail.
539 * However, this will correctly drop the state machine back into
545 /* Parse the data nibbles. */
546 for (i = 0; i < frame.can_dlc; i++) {
547 frame.data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
548 | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
551 /* Feed the frame to the network layer. */
552 elm327_feed_frame_to_netdev(elm, &frame);
557 /* Assumes elm->lock taken. */
558 static void elm327_parse_line(struct elmcan *elm, int len)
560 /* Skip empty lines */
564 /* Skip echo lines */
565 if (elm->drop_next_line) {
566 elm->drop_next_line = 0;
568 } else if (!_memstrcmp(elm->rxbuf, "AT")) {
572 /* Regular parsing */
573 switch (elm->state) {
575 if (elm327_parse_frame(elm, len)) {
576 /* Parse an error line. */
577 elm327_parse_error(elm, len);
580 elm327_kick_into_cmd_mode(elm);
588 /* Assumes elm->lock taken. */
589 static void elm327_handle_prompt(struct elmcan *elm)
591 struct can_frame *frame = &elm->can_frame;
592 char local_txbuf[20];
594 if (!elm->cmds_todo) {
595 /* Enter CAN monitor mode */
596 elm327_send(elm, "ATMA\r", 5);
597 elm->state = ELM_RECEIVING;
602 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
603 if (test_bit(TODO_INIT, &elm->cmds_todo)) {
604 strcpy(local_txbuf, *elm->next_init_cmd);
606 elm->next_init_cmd++;
607 if (!(*elm->next_init_cmd)) {
608 clear_bit(TODO_INIT, &elm->cmds_todo);
609 netdev_info(elm->dev, "Initialization finished.\n");
612 } else if (test_and_clear_bit(TODO_SILENT_MONITOR, &elm->cmds_todo)) {
613 sprintf(local_txbuf, "ATCSM%i\r",
614 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
616 } else if (test_and_clear_bit(TODO_RESPONSES, &elm->cmds_todo)) {
617 sprintf(local_txbuf, "ATR%i\r",
618 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
620 } else if (test_and_clear_bit(TODO_CAN_CONFIG, &elm->cmds_todo)) {
621 sprintf(local_txbuf, "ATPC\r");
622 set_bit(TODO_CAN_CONFIG_PART2, &elm->cmds_todo);
624 } else if (test_and_clear_bit(TODO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
625 sprintf(local_txbuf, "ATPB%04X\r",
628 } else if (test_and_clear_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
629 sprintf(local_txbuf, "ATCP%02X\r",
630 (frame->can_id & CAN_EFF_MASK) >> 24);
632 } else if (test_and_clear_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo)) {
633 sprintf(local_txbuf, "ATSH%06X\r",
634 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
636 } else if (test_and_clear_bit(TODO_CANID_11BIT, &elm->cmds_todo)) {
637 sprintf(local_txbuf, "ATSH%03X\r",
638 frame->can_id & CAN_SFF_MASK);
640 } else if (test_and_clear_bit(TODO_CAN_DATA, &elm->cmds_todo)) {
641 if (frame->can_id & CAN_RTR_FLAG) {
642 /* Send an RTR frame. Their DLC is fixed.
643 * Some chips don't send them at all.
645 sprintf(local_txbuf, "ATRTR\r");
647 /* Send a regular CAN data frame */
650 for (i = 0; i < frame->can_dlc; i++) {
651 sprintf(&local_txbuf[2 * i], "%02X",
655 sprintf(&local_txbuf[2 * i], "\r");
658 elm->drop_next_line = 1;
659 elm->state = ELM_RECEIVING;
662 elm327_send(elm, local_txbuf, strlen(local_txbuf));
665 static bool elm327_is_ready_char(char c)
667 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
668 * Probably bad hardware.
670 return (c & 0x3f) == ELM327_READY_CHAR;
673 /* Assumes elm->lock taken. */
674 static void elm327_drop_bytes(struct elmcan *elm, int i)
676 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
680 /* Assumes elm->lock taken. */
681 static void elm327_parse_rxbuf(struct elmcan *elm)
685 switch (elm->state) {
690 case ELM_GETMAGICCHAR:
692 /* Wait for 'y' or '>' */
695 for (i = 0; i < elm->rxfill; i++) {
696 if (elm->rxbuf[i] == ELM327_MAGIC_CHAR) {
697 elm327_send(elm, "\r", 1);
698 elm->state = ELM_GETPROMPT;
701 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
702 elm327_send(elm, ELM327_MAGIC_STRING, 1);
708 elm327_drop_bytes(elm, i);
715 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
716 elm327_handle_prompt(elm);
722 /* Find <CR> delimiting feedback lines. */
724 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
729 if (len == ELM327_SIZE_RXBUF) {
730 /* Line exceeds buffer. It's probably all garbage.
731 * Did we even connect at the right baud rate?
734 "RX buffer overflow. Faulty ELM327 or UART?\n");
735 elm327_hw_failure(elm);
737 } else if (len == elm->rxfill) {
738 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
739 /* The ELM327's AT ST response timeout ran out,
740 * so we got a prompt.
741 * Clear RX buffer and restart listening.
745 elm327_handle_prompt(elm);
749 /* No <CR> found - we haven't received a full line yet.
750 * Wait for more data.
755 /* We have a full line to parse. */
756 elm327_parse_line(elm, len);
758 /* Remove parsed data from RX buffer. */
759 elm327_drop_bytes(elm, len + 1);
761 /* More data to parse? */
763 elm327_parse_rxbuf(elm);
767 /* Dummy needed to use can_rx_offload */
768 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
769 unsigned int n, u32 *timestamp,
772 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
774 return ERR_PTR(-ENOBUFS);
777 static int elmcan_netdev_open(struct net_device *dev)
779 struct elmcan *elm = netdev_priv(dev);
782 spin_lock_bh(&elm->lock);
783 if (elm->hw_failure) {
784 netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
785 spin_unlock_bh(&elm->lock);
790 spin_unlock_bh(&elm->lock);
794 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
795 err = open_candev(dev);
797 spin_unlock_bh(&elm->lock);
802 spin_unlock_bh(&elm->lock);
804 elm->offload.mailbox_read = elmcan_mailbox_read;
805 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
811 can_rx_offload_enable(&elm->offload);
813 can_led_event(dev, CAN_LED_EVENT_OPEN);
814 elm->can.state = CAN_STATE_ERROR_ACTIVE;
815 netif_start_queue(dev);
820 static int elmcan_netdev_close(struct net_device *dev)
822 struct elmcan *elm = netdev_priv(dev);
824 netif_stop_queue(dev);
826 spin_lock_bh(&elm->lock);
828 /* Interrupt whatever we're doing right now */
829 elm327_send(elm, ELM327_MAGIC_STRING, 1);
831 /* Clear the wakeup bit, as the netdev will be down and thus
832 * the wakeup handler won't clear it
834 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
836 spin_unlock_bh(&elm->lock);
838 flush_work(&elm->tx_work);
840 spin_unlock_bh(&elm->lock);
843 can_rx_offload_disable(&elm->offload);
844 elm->can.state = CAN_STATE_STOPPED;
845 can_rx_offload_del(&elm->offload);
847 can_led_event(dev, CAN_LED_EVENT_STOP);
852 /* Send a can_frame to a TTY. */
853 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
854 struct net_device *dev)
856 struct elmcan *elm = netdev_priv(dev);
857 struct can_frame *frame = (struct can_frame *)skb->data;
859 if (skb->len != sizeof(struct can_frame))
862 if (!netif_running(dev)) {
863 netdev_warn(elm->dev, "xmit: iface is down.\n");
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->hw_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->can_dlc;
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 /* Get a reference to our struct, taking into account locks/refcounts.
907 * This is to ensure ordering in case we are shutting down, and to ensure
908 * there is a refcount at all (otherwise tty->disc_data may be freed and
909 * before we increment the refcount).
910 * Use this for anything that can race against elmcan_ldisc_close().
912 static struct elmcan *get_elm(struct tty_struct *tty)
917 spin_lock_bh(&elmcan_discdata_lock);
918 elm = (struct elmcan *)tty->disc_data;
921 spin_unlock_bh(&elmcan_discdata_lock);
925 got_ref = atomic_inc_not_zero(&elm->refcount);
926 spin_unlock_bh(&elmcan_discdata_lock);
934 static void put_elm(struct elmcan *elm)
936 atomic_dec(&elm->refcount);
939 static bool elmcan_is_valid_rx_char(char c)
941 return (accept_flaky_uart ||
944 c == ELM327_MAGIC_CHAR ||
945 c == ELM327_READY_CHAR ||
956 /* Handle incoming ELM327 ASCII data.
957 * This will not be re-entered while running, but other ldisc
958 * functions may be called in parallel.
960 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
961 static void elmcan_ldisc_rx(struct tty_struct *tty,
962 const unsigned char *cp, char *fp, int count)
964 static void elmcan_ldisc_rx(struct tty_struct *tty,
965 const unsigned char *cp, const char *fp, int count)
968 struct elmcan *elm = get_elm(tty);
973 spin_lock_bh(&elm->lock);
978 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
980 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
982 elm327_hw_failure(elm);
987 /* Ignore NUL characters, which the PIC microcontroller may
988 * inadvertently insert due to a known hardware bug.
989 * See ELM327 documentation, which refers to a Microchip PIC
993 /* Check for stray characters on the UART line.
994 * Likely caused by bad hardware.
996 if (!elmcan_is_valid_rx_char(*cp)) {
998 "Received illegal character %02x.\n",
1000 elm327_hw_failure(elm);
1005 elm->rxbuf[elm->rxfill++] = *cp;
1012 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
1014 elm327_hw_failure(elm);
1019 elm327_parse_rxbuf(elm);
1022 spin_unlock_bh(&elm->lock);
1026 /* Write out remaining transmit buffer.
1027 * Scheduled when TTY is writable.
1029 static void elmcan_ldisc_tx_worker(struct work_struct *work)
1031 /* No need to use get_elm() here, as we'll always flush workers
1032 * before destroying the elmcan object.
1034 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
1037 spin_lock_bh(&elm->lock);
1038 if (elm->hw_failure) {
1039 spin_unlock_bh(&elm->lock);
1043 if (!elm->tty || !netif_running(elm->dev)) {
1044 spin_unlock_bh(&elm->lock);
1048 if (elm->txleft <= 0) {
1049 /* Our TTY write buffer is empty:
1050 * Allow netdev to hand us another packet
1052 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1053 spin_unlock_bh(&elm->lock);
1054 netif_wake_queue(elm->dev);
1058 actual = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
1060 netdev_err(elm->dev,
1061 "Failed to write to tty %s.\n",
1063 elm327_hw_failure(elm);
1064 spin_unlock_bh(&elm->lock);
1068 elm->txleft -= actual;
1069 elm->txhead += actual;
1070 spin_unlock_bh(&elm->lock);
1073 /* Called by the driver when there's room for more data. */
1074 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1076 struct elmcan *elm = get_elm(tty);
1081 schedule_work(&elm->tx_work);
1086 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1087 * or 7/8 of that. Divisors are 1 to 64.
1088 * Currently we don't implement support for 7/8 rates.
1090 static const u32 elmcan_bitrate_const[64] = {
1091 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1092 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1093 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1094 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1095 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1096 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1097 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1098 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1101 /* Dummy needed to use bitrate_const */
1102 static int elmcan_do_set_bittiming(struct net_device *netdev)
1107 static int elmcan_ldisc_open(struct tty_struct *tty)
1109 struct net_device *dev;
1113 if (!capable(CAP_NET_ADMIN))
1116 if (!tty->ops->write)
1119 dev = alloc_candev(sizeof(struct elmcan), 0);
1122 elm = netdev_priv(dev);
1124 elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
1130 /* Configure TTY interface */
1131 tty->receive_room = 65536; /* We don't flow control */
1132 elm->txleft = 0; /* Clear TTY TX buffer */
1133 spin_lock_init(&elm->lock);
1134 atomic_set(&elm->refcount, 1);
1135 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1137 /* Configure CAN metadata */
1138 elm->can.state = CAN_STATE_STOPPED;
1139 elm->can.bitrate_const = elmcan_bitrate_const;
1140 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1141 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1142 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1144 /* Configure netdev interface */
1146 dev->netdev_ops = &elmcan_netdev_ops;
1148 /* Mark ldisc channel as alive */
1150 tty->disc_data = elm;
1152 devm_can_led_init(elm->dev);
1155 err = register_candev(elm->dev);
1159 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1165 free_candev(elm->dev);
1169 /* Close down an elmcan channel.
1170 * This means flushing out any pending queues, and then returning.
1171 * This call is serialized against other ldisc functions:
1172 * Once this is called, no other ldisc function of ours is entered.
1174 * We also use this function for a hangup event.
1176 static void elmcan_ldisc_close(struct tty_struct *tty)
1178 struct elmcan *elm = get_elm(tty);
1183 /* unregister_netdev() calls .ndo_stop() so we don't have to. */
1184 unregister_candev(elm->dev);
1186 /* Decrease the refcount twice, once for our own get_elm(),
1187 * and once to remove the count of 1 that we set in _open().
1188 * Once it reaches 0, we can safely destroy it.
1193 while (atomic_read(&elm->refcount) > 0)
1194 msleep_interruptible(10);
1196 /* At this point, all ldisc calls to us have become no-ops. */
1198 flush_work(&elm->tx_work);
1200 /* Mark channel as dead */
1201 spin_lock_bh(&elm->lock);
1202 tty->disc_data = NULL;
1204 spin_unlock_bh(&elm->lock);
1206 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1209 free_candev(elm->dev);
1212 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1213 static int elmcan_ldisc_hangup(struct tty_struct *tty)
1215 static void elmcan_ldisc_hangup(struct tty_struct *tty)
1218 elmcan_ldisc_close(tty);
1219 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1224 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1225 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1228 unsigned int cmd, unsigned long arg)
1230 struct elmcan *elm = get_elm(tty);
1238 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1239 if (copy_to_user((void __user *)arg, elm->dev->name, tmp)) {
1253 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1254 return tty_mode_ioctl(tty, file, cmd, arg);
1256 return tty_mode_ioctl(tty, cmd, arg);
1261 static struct tty_ldisc_ops elmcan_ldisc = {
1262 .owner = THIS_MODULE,
1265 .receive_buf = elmcan_ldisc_rx,
1266 .write_wakeup = elmcan_ldisc_tx_wakeup,
1267 .open = elmcan_ldisc_open,
1268 .close = elmcan_ldisc_close,
1269 .hangup = elmcan_ldisc_hangup,
1270 .ioctl = elmcan_ldisc_ioctl,
1273 static int __init elmcan_init(void)
1277 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1278 status = tty_register_ldisc(N_ELMCAN, &elmcan_ldisc);
1280 status = tty_register_ldisc(&elmcan_ldisc);
1283 pr_err("Can't register line discipline\n");
1288 static void __exit elmcan_exit(void)
1290 /* This will only be called when all channels have been closed by
1291 * userspace - tty_ldisc.c takes care of the module's refcount.
1293 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1296 status = tty_unregister_ldisc(N_ELMCAN);
1298 pr_err("Can't unregister line discipline (error: %d)\n",
1301 tty_unregister_ldisc(&elmcan_ldisc);
1305 module_init(elmcan_init);
1306 module_exit(elmcan_exit);