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 /* Assumes elm->lock taken. */
347 static void elm327_parse_error(struct elmcan *elm, int len)
349 struct can_frame frame;
351 memset(&frame, 0, sizeof(frame));
352 frame.can_id = CAN_ERR_FLAG;
353 frame.can_dlc = CAN_ERR_DLC;
357 if (!memcmp(elm->rxbuf, "UNABLE TO CONNECT", 17)) {
359 "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
363 if (!memcmp(elm->rxbuf, "BUFFER FULL", 11)) {
364 /* This case will only happen if the last data
366 * Otherwise, elm327_parse_frame() will heuristically
367 * emit this error frame instead.
369 frame.can_id |= CAN_ERR_CRTL;
370 frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
374 if (!memcmp(elm->rxbuf, "BUS ERROR", 9))
375 frame.can_id |= CAN_ERR_BUSERROR;
376 if (!memcmp(elm->rxbuf, "CAN ERROR", 9))
377 frame.can_id |= CAN_ERR_PROT;
378 if (!memcmp(elm->rxbuf, "<RX ERROR", 9))
379 frame.can_id |= CAN_ERR_PROT;
382 if (!memcmp(elm->rxbuf, "BUS BUSY", 8)) {
383 frame.can_id |= CAN_ERR_PROT;
384 frame.data[2] = CAN_ERR_PROT_OVERLOAD;
386 if (!memcmp(elm->rxbuf, "FB ERROR", 8)) {
387 frame.can_id |= CAN_ERR_PROT;
388 frame.data[2] = CAN_ERR_PROT_TX;
392 if (!memcmp(elm->rxbuf, "ERR", 3)) {
393 netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
394 elm->rxbuf[3], elm->rxbuf[4]);
395 frame.can_id |= CAN_ERR_CRTL;
399 /* Something else has happened.
400 * Maybe garbage on the UART line.
401 * Emit a generic error frame.
406 elm327_feed_frame_to_netdev(elm, &frame);
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, int len)
425 struct can_frame frame;
430 memset(&frame, 0, sizeof(frame));
432 /* Find first non-hex and non-space character:
433 * - In the simplest case, there is none.
434 * - For RTR frames, 'R' is the first non-hex character.
435 * - An error message may replace the end of the data line.
437 for (hexlen = 0; hexlen <= len; hexlen++) {
438 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
439 elm->rxbuf[hexlen] != ' ') {
444 /* If we accept stray characters coming in:
445 * Check for stray characters on a payload line.
446 * No idea what causes this.
448 if (accept_flaky_uart &&
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.can_dlc = (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 !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) {
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.can_dlc * 3 + datastart)) {
520 /* Incomplete frame. */
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.can_dlc = CAN_ERR_DLC;
527 frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
528 elm327_feed_frame_to_netdev(elm, &frame);
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.can_dlc; 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, &frame);
550 /* Assumes elm->lock taken. */
551 static void elm327_parse_line(struct elmcan *elm, int len)
553 /* Skip empty lines */
557 /* Skip echo lines */
558 if (elm->drop_next_line) {
559 elm->drop_next_line = 0;
561 } else if (elm->rxbuf[0] == 'A' && elm->rxbuf[1] == 'T') {
565 /* Regular parsing */
566 switch (elm->state) {
568 if (elm327_parse_frame(elm, len)) {
569 /* Parse an error line. */
570 elm327_parse_error(elm, len);
573 elm327_kick_into_cmd_mode(elm);
581 /* Assumes elm->lock taken. */
582 static void elm327_handle_prompt(struct elmcan *elm)
584 struct can_frame *frame = &elm->can_frame;
585 char local_txbuf[20];
587 if (!elm->cmds_todo) {
588 /* Enter CAN monitor mode */
589 elm327_send(elm, "ATMA\r", 5);
590 elm->state = ELM_RECEIVING;
595 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
596 if (test_bit(TODO_INIT, &elm->cmds_todo)) {
597 strcpy(local_txbuf, *elm->next_init_cmd);
599 elm->next_init_cmd++;
600 if (!(*elm->next_init_cmd)) {
601 clear_bit(TODO_INIT, &elm->cmds_todo);
602 netdev_info(elm->dev, "Initialization finished.\n");
605 } else if (test_and_clear_bit(TODO_SILENT_MONITOR, &elm->cmds_todo)) {
606 sprintf(local_txbuf, "ATCSM%i\r",
607 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
609 } else if (test_and_clear_bit(TODO_RESPONSES, &elm->cmds_todo)) {
610 sprintf(local_txbuf, "ATR%i\r",
611 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
613 } else if (test_and_clear_bit(TODO_CAN_CONFIG, &elm->cmds_todo)) {
614 sprintf(local_txbuf, "ATPC\r");
615 set_bit(TODO_CAN_CONFIG_PART2, &elm->cmds_todo);
617 } else if (test_and_clear_bit(TODO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
618 sprintf(local_txbuf, "ATPB%04X\r",
621 } else if (test_and_clear_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
622 sprintf(local_txbuf, "ATCP%02X\r",
623 (frame->can_id & CAN_EFF_MASK) >> 24);
625 } else if (test_and_clear_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo)) {
626 sprintf(local_txbuf, "ATSH%06X\r",
627 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
629 } else if (test_and_clear_bit(TODO_CANID_11BIT, &elm->cmds_todo)) {
630 sprintf(local_txbuf, "ATSH%03X\r",
631 frame->can_id & CAN_SFF_MASK);
633 } else if (test_and_clear_bit(TODO_CAN_DATA, &elm->cmds_todo)) {
634 if (frame->can_id & CAN_RTR_FLAG) {
635 /* Send an RTR frame. Their DLC is fixed.
636 * Some chips don't send them at all.
638 sprintf(local_txbuf, "ATRTR\r");
640 /* Send a regular CAN data frame */
643 for (i = 0; i < frame->can_dlc; i++) {
644 sprintf(&local_txbuf[2 * i], "%02X",
648 sprintf(&local_txbuf[2 * i], "\r");
651 elm->drop_next_line = 1;
652 elm->state = ELM_RECEIVING;
655 elm327_send(elm, local_txbuf, strlen(local_txbuf));
658 static bool elm327_is_ready_char(char c)
660 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
661 * Probably bad hardware.
663 return (c & 0x3f) == ELM327_READY_CHAR;
666 /* Assumes elm->lock taken. */
667 static void elm327_drop_bytes(struct elmcan *elm, int i)
669 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
673 /* Assumes elm->lock taken. */
674 static void elm327_parse_rxbuf(struct elmcan *elm)
678 switch (elm->state) {
683 case ELM_GETMAGICCHAR:
685 /* Wait for 'y' or '>' */
688 for (i = 0; i < elm->rxfill; i++) {
689 if (elm->rxbuf[i] == ELM327_MAGIC_CHAR) {
690 elm327_send(elm, "\r", 1);
691 elm->state = ELM_GETPROMPT;
694 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
695 elm327_send(elm, ELM327_MAGIC_STRING, 1);
701 elm327_drop_bytes(elm, i);
708 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
709 elm327_handle_prompt(elm);
715 /* Find <CR> delimiting feedback lines. */
717 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
722 if (len == ELM327_SIZE_RXBUF) {
723 /* Line exceeds buffer. It's probably all garbage.
724 * Did we even connect at the right baud rate?
727 "RX buffer overflow. Faulty ELM327 or UART?\n");
728 elm327_hw_failure(elm);
730 } else if (len == elm->rxfill) {
731 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
732 /* The ELM327's AT ST response timeout ran out,
733 * so we got a prompt.
734 * Clear RX buffer and restart listening.
738 elm327_handle_prompt(elm);
742 /* No <CR> found - we haven't received a full line yet.
743 * Wait for more data.
748 /* We have a full line to parse. */
749 elm327_parse_line(elm, len);
751 /* Remove parsed data from RX buffer. */
752 elm327_drop_bytes(elm, len + 1);
754 /* More data to parse? */
756 elm327_parse_rxbuf(elm);
760 /* Dummy needed to use can_rx_offload */
761 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
762 unsigned int n, u32 *timestamp,
765 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
767 return ERR_PTR(-ENOBUFS);
770 static int elmcan_netdev_open(struct net_device *dev)
772 struct elmcan *elm = netdev_priv(dev);
775 spin_lock_bh(&elm->lock);
776 if (elm->hw_failure) {
777 netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
778 spin_unlock_bh(&elm->lock);
783 spin_unlock_bh(&elm->lock);
787 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
788 err = open_candev(dev);
790 spin_unlock_bh(&elm->lock);
795 spin_unlock_bh(&elm->lock);
797 elm->offload.mailbox_read = elmcan_mailbox_read;
798 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
804 can_rx_offload_enable(&elm->offload);
806 can_led_event(dev, CAN_LED_EVENT_OPEN);
807 elm->can.state = CAN_STATE_ERROR_ACTIVE;
808 netif_start_queue(dev);
813 static int elmcan_netdev_close(struct net_device *dev)
815 struct elmcan *elm = netdev_priv(dev);
817 netif_stop_queue(dev);
819 spin_lock_bh(&elm->lock);
821 /* Interrupt whatever we're doing right now */
822 elm327_send(elm, ELM327_MAGIC_STRING, 1);
824 /* Clear the wakeup bit, as the netdev will be down and thus
825 * the wakeup handler won't clear it
827 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
829 spin_unlock_bh(&elm->lock);
831 flush_work(&elm->tx_work);
833 spin_unlock_bh(&elm->lock);
836 can_rx_offload_disable(&elm->offload);
837 elm->can.state = CAN_STATE_STOPPED;
838 can_rx_offload_del(&elm->offload);
840 can_led_event(dev, CAN_LED_EVENT_STOP);
845 /* Send a can_frame to a TTY. */
846 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
847 struct net_device *dev)
849 struct elmcan *elm = netdev_priv(dev);
850 struct can_frame *frame = (struct can_frame *)skb->data;
852 if (skb->len != sizeof(struct can_frame))
855 if (!netif_running(dev)) {
856 netdev_warn(elm->dev, "xmit: iface is down.\n");
860 /* BHs are already disabled, so no spin_lock_bh().
861 * See Documentation/networking/netdevices.txt
863 spin_lock(&elm->lock);
865 /* We shouldn't get here after a hardware fault:
866 * can_bus_off() calls netif_carrier_off()
868 WARN_ON_ONCE(elm->hw_failure);
872 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
873 spin_unlock(&elm->lock);
877 netif_stop_queue(dev);
879 elm327_send_frame(elm, frame);
880 spin_unlock(&elm->lock);
882 dev->stats.tx_packets++;
883 dev->stats.tx_bytes += frame->can_dlc;
885 can_led_event(dev, CAN_LED_EVENT_TX);
892 static const struct net_device_ops elmcan_netdev_ops = {
893 .ndo_open = elmcan_netdev_open,
894 .ndo_stop = elmcan_netdev_close,
895 .ndo_start_xmit = elmcan_netdev_start_xmit,
896 .ndo_change_mtu = can_change_mtu,
899 /* Get a reference to our struct, taking into account locks/refcounts.
900 * This is to ensure ordering in case we are shutting down, and to ensure
901 * there is a refcount at all (otherwise tty->disc_data may be freed and
902 * before we increment the refcount).
903 * Use this for anything that can race against elmcan_ldisc_close().
905 static struct elmcan *get_elm(struct tty_struct *tty)
910 spin_lock_bh(&elmcan_discdata_lock);
911 elm = (struct elmcan *)tty->disc_data;
914 spin_unlock_bh(&elmcan_discdata_lock);
918 got_ref = atomic_inc_not_zero(&elm->refcount);
919 spin_unlock_bh(&elmcan_discdata_lock);
927 static void put_elm(struct elmcan *elm)
929 atomic_dec(&elm->refcount);
932 static bool elmcan_is_valid_rx_char(char c)
934 return (accept_flaky_uart ||
937 c == ELM327_MAGIC_CHAR ||
938 c == ELM327_READY_CHAR ||
949 /* Handle incoming ELM327 ASCII data.
950 * This will not be re-entered while running, but other ldisc
951 * functions may be called in parallel.
953 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
954 static void elmcan_ldisc_rx(struct tty_struct *tty,
955 const unsigned char *cp, char *fp, int count)
957 static void elmcan_ldisc_rx(struct tty_struct *tty,
958 const unsigned char *cp, const char *fp, int count)
961 struct elmcan *elm = get_elm(tty);
966 spin_lock_bh(&elm->lock);
971 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
973 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
975 elm327_hw_failure(elm);
980 /* Ignore NUL characters, which the PIC microcontroller may
981 * inadvertently insert due to a known hardware bug.
982 * See ELM327 documentation, which refers to a Microchip PIC
986 /* Check for stray characters on the UART line.
987 * Likely caused by bad hardware.
989 if (!elmcan_is_valid_rx_char(*cp)) {
991 "Received illegal character %02x.\n",
993 elm327_hw_failure(elm);
998 elm->rxbuf[elm->rxfill++] = *cp;
1005 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
1007 elm327_hw_failure(elm);
1012 elm327_parse_rxbuf(elm);
1015 spin_unlock_bh(&elm->lock);
1019 /* Write out remaining transmit buffer.
1020 * Scheduled when TTY is writable.
1022 static void elmcan_ldisc_tx_worker(struct work_struct *work)
1024 /* No need to use get_elm() here, as we'll always flush workers
1025 * before destroying the elmcan object.
1027 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
1030 spin_lock_bh(&elm->lock);
1031 if (elm->hw_failure) {
1032 spin_unlock_bh(&elm->lock);
1036 if (!elm->tty || !netif_running(elm->dev)) {
1037 spin_unlock_bh(&elm->lock);
1041 if (elm->txleft <= 0) {
1042 /* Our TTY write buffer is empty:
1043 * Allow netdev to hand us another packet
1045 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1046 spin_unlock_bh(&elm->lock);
1047 netif_wake_queue(elm->dev);
1051 actual = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
1053 netdev_err(elm->dev,
1054 "Failed to write to tty %s.\n",
1056 elm327_hw_failure(elm);
1057 spin_unlock_bh(&elm->lock);
1061 elm->txleft -= actual;
1062 elm->txhead += actual;
1063 spin_unlock_bh(&elm->lock);
1066 /* Called by the driver when there's room for more data. */
1067 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1069 struct elmcan *elm = get_elm(tty);
1074 schedule_work(&elm->tx_work);
1079 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1080 * or 7/8 of that. Divisors are 1 to 64.
1081 * Currently we don't implement support for 7/8 rates.
1083 static const u32 elmcan_bitrate_const[64] = {
1084 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1085 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1086 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1087 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1088 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1089 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1090 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1091 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1094 /* Dummy needed to use bitrate_const */
1095 static int elmcan_do_set_bittiming(struct net_device *netdev)
1100 static int elmcan_ldisc_open(struct tty_struct *tty)
1102 struct net_device *dev;
1106 if (!capable(CAP_NET_ADMIN))
1109 if (!tty->ops->write)
1112 dev = alloc_candev(sizeof(struct elmcan), 0);
1115 elm = netdev_priv(dev);
1117 elm->txbuf = kmalloc(ELM327_SIZE_TXBUF, GFP_KERNEL);
1123 /* Configure TTY interface */
1124 tty->receive_room = 65536; /* We don't flow control */
1125 elm->txleft = 0; /* Clear TTY TX buffer */
1126 spin_lock_init(&elm->lock);
1127 atomic_set(&elm->refcount, 1);
1128 INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
1130 /* Configure CAN metadata */
1131 elm->can.state = CAN_STATE_STOPPED;
1132 elm->can.bitrate_const = elmcan_bitrate_const;
1133 elm->can.bitrate_const_cnt = ARRAY_SIZE(elmcan_bitrate_const);
1134 elm->can.do_set_bittiming = elmcan_do_set_bittiming;
1135 elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
1137 /* Configure netdev interface */
1139 dev->netdev_ops = &elmcan_netdev_ops;
1141 /* Mark ldisc channel as alive */
1143 tty->disc_data = elm;
1145 devm_can_led_init(elm->dev);
1148 err = register_candev(elm->dev);
1152 netdev_info(elm->dev, "elmcan on %s.\n", tty->name);
1158 free_candev(elm->dev);
1162 /* Close down an elmcan channel.
1163 * This means flushing out any pending queues, and then returning.
1164 * This call is serialized against other ldisc functions:
1165 * Once this is called, no other ldisc function of ours is entered.
1167 * We also use this function for a hangup event.
1169 static void elmcan_ldisc_close(struct tty_struct *tty)
1171 struct elmcan *elm = get_elm(tty);
1176 /* unregister_netdev() calls .ndo_stop() so we don't have to. */
1177 unregister_candev(elm->dev);
1179 /* Decrease the refcount twice, once for our own get_elm(),
1180 * and once to remove the count of 1 that we set in _open().
1181 * Once it reaches 0, we can safely destroy it.
1186 while (atomic_read(&elm->refcount) > 0)
1187 msleep_interruptible(10);
1189 /* At this point, all ldisc calls to us have become no-ops. */
1191 flush_work(&elm->tx_work);
1193 /* Mark channel as dead */
1194 spin_lock_bh(&elm->lock);
1195 tty->disc_data = NULL;
1197 spin_unlock_bh(&elm->lock);
1199 netdev_info(elm->dev, "elmcan off %s.\n", tty->name);
1202 free_candev(elm->dev);
1205 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1206 static int elmcan_ldisc_hangup(struct tty_struct *tty)
1208 static void elmcan_ldisc_hangup(struct tty_struct *tty)
1211 elmcan_ldisc_close(tty);
1212 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1217 static int elmcan_ldisc_ioctl(struct tty_struct *tty,
1218 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,17,0)
1221 unsigned int cmd, unsigned long arg)
1223 struct elmcan *elm = get_elm(tty);
1231 tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
1232 if (copy_to_user((void __user *)arg, elm->dev->name, tmp)) {
1246 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,16,0)
1247 return tty_mode_ioctl(tty, file, cmd, arg);
1249 return tty_mode_ioctl(tty, cmd, arg);
1254 static struct tty_ldisc_ops elmcan_ldisc = {
1255 .owner = THIS_MODULE,
1258 .receive_buf = elmcan_ldisc_rx,
1259 .write_wakeup = elmcan_ldisc_tx_wakeup,
1260 .open = elmcan_ldisc_open,
1261 .close = elmcan_ldisc_close,
1262 .hangup = elmcan_ldisc_hangup,
1263 .ioctl = elmcan_ldisc_ioctl,
1266 static int __init elmcan_init(void)
1270 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1271 status = tty_register_ldisc(N_ELMCAN, &elmcan_ldisc);
1273 status = tty_register_ldisc(&elmcan_ldisc);
1276 pr_err("Can't register line discipline\n");
1281 static void __exit elmcan_exit(void)
1283 /* This will only be called when all channels have been closed by
1284 * userspace - tty_ldisc.c takes care of the module's refcount.
1286 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1289 status = tty_unregister_ldisc(N_ELMCAN);
1291 pr_err("Can't unregister line discipline (error: %d)\n",
1294 tty_unregister_ldisc(&elmcan_ldisc);
1298 module_init(elmcan_init);
1299 module_exit(elmcan_exit);