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 /* Don't emit an error frame if we're unsure */
403 elm327_feed_frame_to_netdev(elm, &frame);
406 /* Parse CAN frames coming as ASCII from ELM327.
407 * They can be of various formats:
409 * 29-bit ID (EFF): 12 34 56 78 D PL PL PL PL PL PL PL PL
410 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
412 * where D = DLC, PL = payload byte
414 * Instead of a payload, RTR indicates a remote request.
416 * We will use the spaces and line length to guess the format.
418 * Assumes elm->lock taken.
420 static int elm327_parse_frame(struct elmcan *elm, int len)
422 struct can_frame frame;
427 memset(&frame, 0, sizeof(frame));
429 /* Find first non-hex and non-space character:
430 * - In the simplest case, there is none.
431 * - For RTR frames, 'R' is the first non-hex character.
432 * - An error message may replace the end of the data line.
434 for (hexlen = 0; hexlen <= len; hexlen++) {
435 if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
436 elm->rxbuf[hexlen] != ' ') {
441 /* If we accept stray characters coming in:
442 * Check for stray characters on a payload line.
443 * No idea what causes this.
445 if (accept_flaky_uart &&
447 !isdigit(elm->rxbuf[hexlen]) &&
448 !isupper(elm->rxbuf[hexlen]) &&
449 '<' != elm->rxbuf[hexlen] &&
450 ' ' != elm->rxbuf[hexlen]) {
451 /* The line is likely garbled anyway, so bail.
452 * The main code will restart listening.
454 elm327_kick_into_cmd_mode(elm);
458 /* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
459 * No out-of-bounds access:
460 * We use the fact that we can always read from elm->rxbuf.
462 if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
463 elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
464 elm->rxbuf[13] == ' ') {
465 frame.can_id = CAN_EFF_FLAG;
467 } else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
471 /* This is not a well-formatted data line.
472 * Assume it's an error message.
477 if (hexlen < datastart) {
478 /* The line is too short to be a valid frame hex dump.
479 * Something interrupted the hex dump or it is invalid.
484 /* From here on all chars up to buf[hexlen] are hex or spaces,
485 * at well-defined offsets.
488 /* Read CAN data length */
489 frame.can_dlc = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);
492 if (frame.can_id & CAN_EFF_FLAG) {
493 frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 28)
494 | (hex_to_bin(elm->rxbuf[1]) << 24)
495 | (hex_to_bin(elm->rxbuf[3]) << 20)
496 | (hex_to_bin(elm->rxbuf[4]) << 16)
497 | (hex_to_bin(elm->rxbuf[6]) << 12)
498 | (hex_to_bin(elm->rxbuf[7]) << 8)
499 | (hex_to_bin(elm->rxbuf[9]) << 4)
500 | (hex_to_bin(elm->rxbuf[10]) << 0);
502 frame.can_id |= (hex_to_bin(elm->rxbuf[0]) << 8)
503 | (hex_to_bin(elm->rxbuf[1]) << 4)
504 | (hex_to_bin(elm->rxbuf[2]) << 0);
507 /* Check for RTR frame */
508 if (elm->rxfill >= hexlen + 3 &&
509 !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) {
510 frame.can_id |= CAN_RTR_FLAG;
513 /* Is the line long enough to hold the advertised payload?
514 * Note: RTR frames have a DLC, but no actual payload.
516 if (!(frame.can_id & CAN_RTR_FLAG) &&
517 (hexlen < frame.can_dlc * 3 + datastart)) {
518 /* Incomplete frame. */
520 /* Probably the ELM327's RS232 TX buffer was full.
521 * Emit an error frame and exit.
523 frame.can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
524 frame.can_dlc = CAN_ERR_DLC;
525 frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
526 elm327_feed_frame_to_netdev(elm, &frame);
528 /* Signal failure to parse.
529 * The line will be re-parsed as an error line, which will fail.
530 * However, this will correctly drop the state machine back into
536 /* Parse the data nibbles. */
537 for (i = 0; i < frame.can_dlc; i++) {
538 frame.data[i] = (hex_to_bin(elm->rxbuf[datastart + 3*i]) << 4)
539 | (hex_to_bin(elm->rxbuf[datastart + 3*i + 1]));
542 /* Feed the frame to the network layer. */
543 elm327_feed_frame_to_netdev(elm, &frame);
548 /* Assumes elm->lock taken. */
549 static void elm327_parse_line(struct elmcan *elm, int len)
551 /* Skip empty lines */
555 /* Skip echo lines */
556 if (elm->drop_next_line) {
557 elm->drop_next_line = 0;
559 } else if (elm->rxbuf[0] == 'A' && elm->rxbuf[1] == 'T') {
563 /* Regular parsing */
564 switch (elm->state) {
566 if (elm327_parse_frame(elm, len)) {
567 /* Parse an error line. */
568 elm327_parse_error(elm, len);
571 elm327_kick_into_cmd_mode(elm);
579 /* Assumes elm->lock taken. */
580 static void elm327_handle_prompt(struct elmcan *elm)
582 struct can_frame *frame = &elm->can_frame;
583 char local_txbuf[20];
585 if (!elm->cmds_todo) {
586 /* Enter CAN monitor mode */
587 elm327_send(elm, "ATMA\r", 5);
588 elm->state = ELM_RECEIVING;
593 /* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
594 if (test_bit(TODO_INIT, &elm->cmds_todo)) {
595 strcpy(local_txbuf, *elm->next_init_cmd);
597 elm->next_init_cmd++;
598 if (!(*elm->next_init_cmd)) {
599 clear_bit(TODO_INIT, &elm->cmds_todo);
600 netdev_info(elm->dev, "Initialization finished.\n");
603 } else if (test_and_clear_bit(TODO_SILENT_MONITOR, &elm->cmds_todo)) {
604 sprintf(local_txbuf, "ATCSM%i\r",
605 !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
607 } else if (test_and_clear_bit(TODO_RESPONSES, &elm->cmds_todo)) {
608 sprintf(local_txbuf, "ATR%i\r",
609 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
611 } else if (test_and_clear_bit(TODO_CAN_CONFIG, &elm->cmds_todo)) {
612 sprintf(local_txbuf, "ATPC\r");
613 set_bit(TODO_CAN_CONFIG_PART2, &elm->cmds_todo);
615 } else if (test_and_clear_bit(TODO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
616 sprintf(local_txbuf, "ATPB%04X\r",
619 } else if (test_and_clear_bit(TODO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
620 sprintf(local_txbuf, "ATCP%02X\r",
621 (frame->can_id & CAN_EFF_MASK) >> 24);
623 } else if (test_and_clear_bit(TODO_CANID_29BIT_LOW, &elm->cmds_todo)) {
624 sprintf(local_txbuf, "ATSH%06X\r",
625 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
627 } else if (test_and_clear_bit(TODO_CANID_11BIT, &elm->cmds_todo)) {
628 sprintf(local_txbuf, "ATSH%03X\r",
629 frame->can_id & CAN_SFF_MASK);
631 } else if (test_and_clear_bit(TODO_CAN_DATA, &elm->cmds_todo)) {
632 if (frame->can_id & CAN_RTR_FLAG) {
633 /* Send an RTR frame. Their DLC is fixed.
634 * Some chips don't send them at all.
636 sprintf(local_txbuf, "ATRTR\r");
638 /* Send a regular CAN data frame */
641 for (i = 0; i < frame->can_dlc; i++) {
642 sprintf(&local_txbuf[2 * i], "%02X",
646 sprintf(&local_txbuf[2 * i], "\r");
649 elm->drop_next_line = 1;
650 elm->state = ELM_RECEIVING;
653 elm327_send(elm, local_txbuf, strlen(local_txbuf));
656 static bool elm327_is_ready_char(char c)
658 /* Bits 0xc0 are sometimes set (randomly), hence the mask.
659 * Probably bad hardware.
661 return (c & 0x3f) == ELM327_READY_CHAR;
664 /* Assumes elm->lock taken. */
665 static void elm327_drop_bytes(struct elmcan *elm, int i)
667 memmove(&elm->rxbuf[0], &elm->rxbuf[i], ELM327_SIZE_RXBUF - i);
671 /* Assumes elm->lock taken. */
672 static void elm327_parse_rxbuf(struct elmcan *elm)
676 switch (elm->state) {
681 case ELM_GETMAGICCHAR:
683 /* Wait for 'y' or '>' */
686 for (i = 0; i < elm->rxfill; i++) {
687 if (elm->rxbuf[i] == ELM327_MAGIC_CHAR) {
688 elm327_send(elm, "\r", 1);
689 elm->state = ELM_GETPROMPT;
692 } else if (elm327_is_ready_char(elm->rxbuf[i])) {
693 elm327_send(elm, ELM327_MAGIC_STRING, 1);
699 elm327_drop_bytes(elm, i);
706 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
707 elm327_handle_prompt(elm);
713 /* Find <CR> delimiting feedback lines. */
715 (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
720 if (len == ELM327_SIZE_RXBUF) {
721 /* Line exceeds buffer. It's probably all garbage.
722 * Did we even connect at the right baud rate?
725 "RX buffer overflow. Faulty ELM327 or UART?\n");
726 elm327_hw_failure(elm);
728 } else if (len == elm->rxfill) {
729 if (elm327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
730 /* The ELM327's AT ST response timeout ran out,
731 * so we got a prompt.
732 * Clear RX buffer and restart listening.
736 elm327_handle_prompt(elm);
740 /* No <CR> found - we haven't received a full line yet.
741 * Wait for more data.
746 /* We have a full line to parse. */
747 elm327_parse_line(elm, len);
749 /* Remove parsed data from RX buffer. */
750 elm327_drop_bytes(elm, len + 1);
752 /* More data to parse? */
754 elm327_parse_rxbuf(elm);
758 /* Dummy needed to use can_rx_offload */
759 static struct sk_buff *elmcan_mailbox_read(struct can_rx_offload *offload,
760 unsigned int n, u32 *timestamp,
763 WARN_ON_ONCE(1); /* This function is a dummy, so don't call it! */
765 return ERR_PTR(-ENOBUFS);
768 static int elmcan_netdev_open(struct net_device *dev)
770 struct elmcan *elm = netdev_priv(dev);
773 spin_lock_bh(&elm->lock);
774 if (elm->hw_failure) {
775 netdev_err(elm->dev, "Refusing to open interface after a hardware fault has been detected.\n");
776 spin_unlock_bh(&elm->lock);
781 spin_unlock_bh(&elm->lock);
785 /* open_candev() checks for elm->can.bittiming.bitrate != 0 */
786 err = open_candev(dev);
788 spin_unlock_bh(&elm->lock);
793 spin_unlock_bh(&elm->lock);
795 elm->offload.mailbox_read = elmcan_mailbox_read;
796 err = can_rx_offload_add_fifo(dev, &elm->offload, ELM327_NAPI_WEIGHT);
802 can_rx_offload_enable(&elm->offload);
804 can_led_event(dev, CAN_LED_EVENT_OPEN);
805 elm->can.state = CAN_STATE_ERROR_ACTIVE;
806 netif_start_queue(dev);
811 static int elmcan_netdev_close(struct net_device *dev)
813 struct elmcan *elm = netdev_priv(dev);
815 netif_stop_queue(dev);
817 spin_lock_bh(&elm->lock);
819 /* Interrupt whatever we're doing right now */
820 elm327_send(elm, ELM327_MAGIC_STRING, 1);
822 /* Clear the wakeup bit, as the netdev will be down and thus
823 * the wakeup handler won't clear it
825 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
827 spin_unlock_bh(&elm->lock);
829 flush_work(&elm->tx_work);
831 spin_unlock_bh(&elm->lock);
834 can_rx_offload_disable(&elm->offload);
835 elm->can.state = CAN_STATE_STOPPED;
836 can_rx_offload_del(&elm->offload);
838 can_led_event(dev, CAN_LED_EVENT_STOP);
843 /* Send a can_frame to a TTY. */
844 static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb,
845 struct net_device *dev)
847 struct elmcan *elm = netdev_priv(dev);
848 struct can_frame *frame = (struct can_frame *)skb->data;
850 if (skb->len != sizeof(struct can_frame))
853 if (!netif_running(dev)) {
854 netdev_warn(elm->dev, "xmit: iface is down.\n");
858 /* BHs are already disabled, so no spin_lock_bh().
859 * See Documentation/networking/netdevices.txt
861 spin_lock(&elm->lock);
863 /* We shouldn't get here after a hardware fault:
864 * can_bus_off() calls netif_carrier_off()
866 WARN_ON_ONCE(elm->hw_failure);
870 elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
871 spin_unlock(&elm->lock);
875 netif_stop_queue(dev);
877 elm327_send_frame(elm, frame);
878 spin_unlock(&elm->lock);
880 dev->stats.tx_packets++;
881 dev->stats.tx_bytes += frame->can_dlc;
883 can_led_event(dev, CAN_LED_EVENT_TX);
890 static const struct net_device_ops elmcan_netdev_ops = {
891 .ndo_open = elmcan_netdev_open,
892 .ndo_stop = elmcan_netdev_close,
893 .ndo_start_xmit = elmcan_netdev_start_xmit,
894 .ndo_change_mtu = can_change_mtu,
897 /* Get a reference to our struct, taking into account locks/refcounts.
898 * This is to ensure ordering in case we are shutting down, and to ensure
899 * there is a refcount at all (otherwise tty->disc_data may be freed and
900 * before we increment the refcount).
901 * Use this for anything that can race against elmcan_ldisc_close().
903 static struct elmcan *get_elm(struct tty_struct *tty)
908 spin_lock_bh(&elmcan_discdata_lock);
909 elm = (struct elmcan *)tty->disc_data;
912 spin_unlock_bh(&elmcan_discdata_lock);
916 got_ref = atomic_inc_not_zero(&elm->refcount);
917 spin_unlock_bh(&elmcan_discdata_lock);
925 static void put_elm(struct elmcan *elm)
927 atomic_dec(&elm->refcount);
930 static bool elmcan_is_valid_rx_char(char c)
932 return (accept_flaky_uart ||
935 c == ELM327_MAGIC_CHAR ||
936 c == ELM327_READY_CHAR ||
947 /* Handle incoming ELM327 ASCII data.
948 * This will not be re-entered while running, but other ldisc
949 * functions may be called in parallel.
951 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
952 static void elmcan_ldisc_rx(struct tty_struct *tty,
953 const unsigned char *cp, char *fp, int count)
955 static void elmcan_ldisc_rx(struct tty_struct *tty,
956 const unsigned char *cp, const char *fp, int count)
959 struct elmcan *elm = get_elm(tty);
964 spin_lock_bh(&elm->lock);
969 while (count-- && elm->rxfill < ELM327_SIZE_RXBUF) {
971 netdev_err(elm->dev, "Error in received character stream. Check your wiring.");
973 elm327_hw_failure(elm);
978 /* Ignore NUL characters, which the PIC microcontroller may
979 * inadvertently insert due to a known hardware bug.
980 * See ELM327 documentation, which refers to a Microchip PIC
984 /* Check for stray characters on the UART line.
985 * Likely caused by bad hardware.
987 if (!elmcan_is_valid_rx_char(*cp)) {
989 "Received illegal character %02x.\n",
991 elm327_hw_failure(elm);
996 elm->rxbuf[elm->rxfill++] = *cp;
1003 netdev_err(elm->dev, "Receive buffer overflowed. Bad chip or wiring?");
1005 elm327_hw_failure(elm);
1010 elm327_parse_rxbuf(elm);
1013 spin_unlock_bh(&elm->lock);
1017 /* Write out remaining transmit buffer.
1018 * Scheduled when TTY is writable.
1020 static void elmcan_ldisc_tx_worker(struct work_struct *work)
1022 /* No need to use get_elm() here, as we'll always flush workers
1023 * before destroying the elmcan object.
1025 struct elmcan *elm = container_of(work, struct elmcan, tx_work);
1028 spin_lock_bh(&elm->lock);
1029 if (elm->hw_failure) {
1030 spin_unlock_bh(&elm->lock);
1034 if (!elm->tty || !netif_running(elm->dev)) {
1035 spin_unlock_bh(&elm->lock);
1039 if (elm->txleft <= 0) {
1040 /* Our TTY write buffer is empty:
1041 * Allow netdev to hand us another packet
1043 clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
1044 spin_unlock_bh(&elm->lock);
1045 netif_wake_queue(elm->dev);
1049 actual = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
1051 netdev_err(elm->dev,
1052 "Failed to write to tty %s.\n",
1054 elm327_hw_failure(elm);
1055 spin_unlock_bh(&elm->lock);
1059 elm->txleft -= actual;
1060 elm->txhead += actual;
1061 spin_unlock_bh(&elm->lock);
1064 /* Called by the driver when there's room for more data. */
1065 static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
1067 struct elmcan *elm = get_elm(tty);
1072 schedule_work(&elm->tx_work);
1077 /* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
1078 * or 7/8 of that. Divisors are 1 to 64.
1079 * Currently we don't implement support for 7/8 rates.
1081 static const u32 elmcan_bitrate_const[64] = {
1082 7812, 7936, 8064, 8196, 8333, 8474, 8620, 8771,
1083 8928, 9090, 9259, 9433, 9615, 9803, 10000, 10204,
1084 10416, 10638, 10869, 11111, 11363, 11627, 11904, 12195,
1085 12500, 12820, 13157, 13513, 13888, 14285, 14705, 15151,
1086 15625, 16129, 16666, 17241, 17857, 18518, 19230, 20000,
1087 20833, 21739, 22727, 23809, 25000, 26315, 27777, 29411,
1088 31250, 33333, 35714, 38461, 41666, 45454, 50000, 55555,
1089 62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
1092 /* Dummy needed to use bitrate_const */
1093 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 pr_info("ELM327 based best effort CAN interface driver\n");
1271 pr_info("This device is severely limited as a CAN interface, see documentation.\n");
1273 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1274 status = tty_register_ldisc(N_ELMCAN, &elmcan_ldisc);
1276 status = tty_register_ldisc(&elmcan_ldisc);
1279 pr_err("Can't register line discipline\n");
1284 static void __exit elmcan_exit(void)
1286 /* This will only be called when all channels have been closed by
1287 * userspace - tty_ldisc.c takes care of the module's refcount.
1289 #if LINUX_VERSION_CODE < KERNEL_VERSION(5,14,0)
1292 status = tty_unregister_ldisc(N_ELMCAN);
1294 pr_err("Can't unregister line discipline (error: %d)\n",
1297 tty_unregister_ldisc(&elmcan_ldisc);
1301 module_init(elmcan_init);
1302 module_exit(elmcan_exit);