can327.c 30.2 KB
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// SPDX-License-Identifier: GPL-2.0
/* ELM327 based CAN interface driver (tty line discipline)
 *
 * This driver started as a derivative of linux/drivers/net/can/slcan.c
 * and my thanks go to the original authors for their inspiration.
 *
 * can327.c Author : Max Staudt <max-linux@enpas.org>
 * slcan.c Author  : Oliver Hartkopp <socketcan@hartkopp.net>
 * slip.c Authors  : Laurence Culhane <loz@holmes.demon.co.uk>
 *                   Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>
 */

13
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/init.h>
#include <linux/module.h>

#include <linux/bitops.h>
#include <linux/ctype.h>
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/lockdep.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/tty.h>
#include <linux/tty_ldisc.h>
#include <linux/workqueue.h>

#include <uapi/linux/tty.h>

#include <linux/can.h>
#include <linux/can/dev.h>
#include <linux/can/error.h>
#include <linux/can/rx-offload.h>

#define CAN327_NAPI_WEIGHT 4

#define CAN327_SIZE_TXBUF 32
#define CAN327_SIZE_RXBUF 1024

#define CAN327_CAN_CONFIG_SEND_SFF 0x8000
#define CAN327_CAN_CONFIG_VARIABLE_DLC 0x4000
#define CAN327_CAN_CONFIG_RECV_BOTH_SFF_EFF 0x2000
#define CAN327_CAN_CONFIG_BAUDRATE_MULT_8_7 0x1000

#define CAN327_DUMMY_CHAR 'y'
#define CAN327_DUMMY_STRING "y"
#define CAN327_READY_CHAR '>'

/* Bits in elm->cmds_todo */
enum can327_tx_do {
	CAN327_TX_DO_CAN_DATA = 0,
	CAN327_TX_DO_CANID_11BIT,
	CAN327_TX_DO_CANID_29BIT_LOW,
	CAN327_TX_DO_CANID_29BIT_HIGH,
	CAN327_TX_DO_CAN_CONFIG_PART2,
	CAN327_TX_DO_CAN_CONFIG,
	CAN327_TX_DO_RESPONSES,
	CAN327_TX_DO_SILENT_MONITOR,
	CAN327_TX_DO_INIT,
};

struct can327 {
	/* This must be the first member when using alloc_candev() */
	struct can_priv can;

	struct can_rx_offload offload;

	/* TTY buffers */
	u8 txbuf[CAN327_SIZE_TXBUF];
	u8 rxbuf[CAN327_SIZE_RXBUF];

	/* Per-channel lock */
	spinlock_t lock;

	/* TTY and netdev devices that we're bridging */
	struct tty_struct *tty;
	struct net_device *dev;

	/* TTY buffer accounting */
	struct work_struct tx_work;	/* Flushes TTY TX buffer */
	u8 *txhead;			/* Next TX byte */
	size_t txleft;			/* Bytes left to TX */
	int rxfill;			/* Bytes already RX'd in buffer */

	/* State machine */
	enum {
		CAN327_STATE_NOTINIT = 0,
		CAN327_STATE_GETDUMMYCHAR,
		CAN327_STATE_GETPROMPT,
		CAN327_STATE_RECEIVING,
	} state;

	/* Things we have yet to send */
	char **next_init_cmd;
	unsigned long cmds_todo;

	/* The CAN frame and config the ELM327 is sending/using,
	 * or will send/use after finishing all cmds_todo
	 */
	struct can_frame can_frame_to_send;
	u16 can_config;
	u8 can_bitrate_divisor;

	/* Parser state */
	bool drop_next_line;

	/* Stop the channel on UART side hardware failure, e.g. stray
	 * characters or neverending lines. This may be caused by bad
	 * UART wiring, a bad ELM327, a bad UART bridge...
	 * Once this is true, nothing will be sent to the TTY.
	 */
	bool uart_side_failure;
};

static inline void can327_uart_side_failure(struct can327 *elm);

static void can327_send(struct can327 *elm, const void *buf, size_t len)
{
	int written;

	lockdep_assert_held(&elm->lock);

	if (elm->uart_side_failure)
		return;

	memcpy(elm->txbuf, buf, len);

	/* Order of next two lines is *very* important.
	 * When we are sending a little amount of data,
	 * the transfer may be completed inside the ops->write()
	 * routine, because it's running with interrupts enabled.
	 * In this case we *never* got WRITE_WAKEUP event,
	 * if we did not request it before write operation.
	 *       14 Oct 1994  Dmitry Gorodchanin.
	 */
	set_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
	written = elm->tty->ops->write(elm->tty, elm->txbuf, len);
	if (written < 0) {
		netdev_err(elm->dev, "Failed to write to tty %s.\n",
			   elm->tty->name);
		can327_uart_side_failure(elm);
		return;
	}

	elm->txleft = len - written;
	elm->txhead = elm->txbuf + written;
}

/* Take the ELM327 out of almost any state and back into command mode.
 * We send CAN327_DUMMY_CHAR which will either abort any running
 * operation, or be echoed back to us in case we're already in command
 * mode.
 */
static void can327_kick_into_cmd_mode(struct can327 *elm)
{
	lockdep_assert_held(&elm->lock);

	if (elm->state != CAN327_STATE_GETDUMMYCHAR &&
	    elm->state != CAN327_STATE_GETPROMPT) {
		can327_send(elm, CAN327_DUMMY_STRING, 1);

		elm->state = CAN327_STATE_GETDUMMYCHAR;
	}
}

/* Schedule a CAN frame and necessary config changes to be sent to the TTY. */
static void can327_send_frame(struct can327 *elm, struct can_frame *frame)
{
	lockdep_assert_held(&elm->lock);

	/* Schedule any necessary changes in ELM327's CAN configuration */
	if (elm->can_frame_to_send.can_id != frame->can_id) {
		/* Set the new CAN ID for transmission. */
		if ((frame->can_id ^ elm->can_frame_to_send.can_id)
		    & CAN_EFF_FLAG) {
			elm->can_config =
				(frame->can_id & CAN_EFF_FLAG ? 0 : CAN327_CAN_CONFIG_SEND_SFF) |
				CAN327_CAN_CONFIG_VARIABLE_DLC |
				CAN327_CAN_CONFIG_RECV_BOTH_SFF_EFF |
				elm->can_bitrate_divisor;

			set_bit(CAN327_TX_DO_CAN_CONFIG, &elm->cmds_todo);
		}

		if (frame->can_id & CAN_EFF_FLAG) {
			clear_bit(CAN327_TX_DO_CANID_11BIT, &elm->cmds_todo);
			set_bit(CAN327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo);
			set_bit(CAN327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo);
		} else {
			set_bit(CAN327_TX_DO_CANID_11BIT, &elm->cmds_todo);
			clear_bit(CAN327_TX_DO_CANID_29BIT_LOW,
				  &elm->cmds_todo);
			clear_bit(CAN327_TX_DO_CANID_29BIT_HIGH,
				  &elm->cmds_todo);
		}
	}

	/* Schedule the CAN frame itself. */
	elm->can_frame_to_send = *frame;
	set_bit(CAN327_TX_DO_CAN_DATA, &elm->cmds_todo);

	can327_kick_into_cmd_mode(elm);
}

/* ELM327 initialisation sequence.
 * The line length is limited by the buffer in can327_handle_prompt().
 */
static char *can327_init_script[] = {
	"AT WS\r",        /* v1.0: Warm Start */
	"AT PP FF OFF\r", /* v1.0: All Programmable Parameters Off */
	"AT M0\r",        /* v1.0: Memory Off */
	"AT AL\r",        /* v1.0: Allow Long messages */
	"AT BI\r",        /* v1.0: Bypass Initialisation */
	"AT CAF0\r",      /* v1.0: CAN Auto Formatting Off */
	"AT CFC0\r",      /* v1.0: CAN Flow Control Off */
	"AT CF 000\r",    /* v1.0: Reset CAN ID Filter */
	"AT CM 000\r",    /* v1.0: Reset CAN ID Mask */
	"AT E1\r",        /* v1.0: Echo On */
	"AT H1\r",        /* v1.0: Headers On */
	"AT L0\r",        /* v1.0: Linefeeds Off */
	"AT SH 7DF\r",    /* v1.0: Set CAN sending ID to 0x7df */
	"AT ST FF\r",     /* v1.0: Set maximum Timeout for response after TX */
	"AT AT0\r",       /* v1.2: Adaptive Timing Off */
	"AT D1\r",        /* v1.3: Print DLC On */
	"AT S1\r",        /* v1.3: Spaces On */
	"AT TP B\r",      /* v1.0: Try Protocol B */
	NULL
};

static void can327_init_device(struct can327 *elm)
{
	lockdep_assert_held(&elm->lock);

	elm->state = CAN327_STATE_NOTINIT;
	elm->can_frame_to_send.can_id = 0x7df; /* ELM327 HW default */
	elm->rxfill = 0;
	elm->drop_next_line = 0;

	/* We can only set the bitrate as a fraction of 500000.
	 * The bitrates listed in can327_bitrate_const will
	 * limit the user to the right values.
	 */
	elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
	elm->can_config =
		CAN327_CAN_CONFIG_SEND_SFF | CAN327_CAN_CONFIG_VARIABLE_DLC |
		CAN327_CAN_CONFIG_RECV_BOTH_SFF_EFF | elm->can_bitrate_divisor;

	/* Configure ELM327 and then start monitoring */
	elm->next_init_cmd = &can327_init_script[0];
	set_bit(CAN327_TX_DO_INIT, &elm->cmds_todo);
	set_bit(CAN327_TX_DO_SILENT_MONITOR, &elm->cmds_todo);
	set_bit(CAN327_TX_DO_RESPONSES, &elm->cmds_todo);
	set_bit(CAN327_TX_DO_CAN_CONFIG, &elm->cmds_todo);

	can327_kick_into_cmd_mode(elm);
}

static void can327_feed_frame_to_netdev(struct can327 *elm, struct sk_buff *skb)
{
	lockdep_assert_held(&elm->lock);

	if (!netif_running(elm->dev))
		return;

	/* Queue for NAPI pickup.
	 * rx-offload will update stats and LEDs for us.
	 */
	if (can_rx_offload_queue_tail(&elm->offload, skb))
		elm->dev->stats.rx_fifo_errors++;

	/* Wake NAPI */
	can_rx_offload_irq_finish(&elm->offload);
}

/* Called when we're out of ideas and just want it all to end. */
static inline void can327_uart_side_failure(struct can327 *elm)
{
	struct can_frame *frame;
	struct sk_buff *skb;

	lockdep_assert_held(&elm->lock);

	elm->uart_side_failure = true;

	clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);

	elm->can.can_stats.bus_off++;
	netif_stop_queue(elm->dev);
	elm->can.state = CAN_STATE_BUS_OFF;
	can_bus_off(elm->dev);

	netdev_err(elm->dev,
		   "ELM327 misbehaved. Blocking further communication.\n");

	skb = alloc_can_err_skb(elm->dev, &frame);
	if (!skb)
		return;

	frame->can_id |= CAN_ERR_BUSOFF;
	can327_feed_frame_to_netdev(elm, skb);
}

/* Compares a byte buffer (non-NUL terminated) to the payload part of
 * a string, and returns true iff the buffer (content *and* length) is
 * exactly that string, without the terminating NUL byte.
 *
 * Example: If reference is "BUS ERROR", then this returns true iff nbytes == 9
 *          and !memcmp(buf, "BUS ERROR", 9).
 *
 * The reason to use strings is so we can easily include them in the C
 * code, and to avoid hardcoding lengths.
 */
static inline bool can327_rxbuf_cmp(const u8 *buf, size_t nbytes,
				    const char *reference)
{
	size_t ref_len = strlen(reference);

	return (nbytes == ref_len) && !memcmp(buf, reference, ref_len);
}

static void can327_parse_error(struct can327 *elm, size_t len)
{
	struct can_frame *frame;
	struct sk_buff *skb;

	lockdep_assert_held(&elm->lock);

	skb = alloc_can_err_skb(elm->dev, &frame);
	if (!skb)
		/* It's okay to return here:
		 * The outer parsing loop will drop this UART buffer.
		 */
		return;

	/* Filter possible error messages based on length of RX'd line */
	if (can327_rxbuf_cmp(elm->rxbuf, len, "UNABLE TO CONNECT")) {
		netdev_err(elm->dev,
			   "ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "BUFFER FULL")) {
		/* This will only happen if the last data line was complete.
		 * Otherwise, can327_parse_frame() will heuristically
		 * emit this kind of error frame instead.
		 */
		frame->can_id |= CAN_ERR_CRTL;
		frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "BUS ERROR")) {
		frame->can_id |= CAN_ERR_BUSERROR;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "CAN ERROR")) {
		frame->can_id |= CAN_ERR_PROT;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "<RX ERROR")) {
		frame->can_id |= CAN_ERR_PROT;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "BUS BUSY")) {
		frame->can_id |= CAN_ERR_PROT;
		frame->data[2] = CAN_ERR_PROT_OVERLOAD;
	} else if (can327_rxbuf_cmp(elm->rxbuf, len, "FB ERROR")) {
		frame->can_id |= CAN_ERR_PROT;
		frame->data[2] = CAN_ERR_PROT_TX;
	} else if (len == 5 && !memcmp(elm->rxbuf, "ERR", 3)) {
		/* ERR is followed by two digits, hence line length 5 */
		netdev_err(elm->dev, "ELM327 reported an ERR%c%c. Please power it off and on again.\n",
			   elm->rxbuf[3], elm->rxbuf[4]);
		frame->can_id |= CAN_ERR_CRTL;
	} else {
		/* Something else has happened.
		 * Maybe garbage on the UART line.
		 * Emit a generic error frame.
		 */
	}

	can327_feed_frame_to_netdev(elm, skb);
}

/* Parse CAN frames coming as ASCII from ELM327.
 * They can be of various formats:
 *
 * 29-bit ID (EFF):  12 34 56 78 D PL PL PL PL PL PL PL PL
 * 11-bit ID (!EFF): 123 D PL PL PL PL PL PL PL PL
 *
 * where D = DLC, PL = payload byte
 *
 * Instead of a payload, RTR indicates a remote request.
 *
 * We will use the spaces and line length to guess the format.
 */
static int can327_parse_frame(struct can327 *elm, size_t len)
{
	struct can_frame *frame;
	struct sk_buff *skb;
	int hexlen;
	int datastart;
	int i;

	lockdep_assert_held(&elm->lock);

	skb = alloc_can_skb(elm->dev, &frame);
	if (!skb)
		return -ENOMEM;

	/* Find first non-hex and non-space character:
	 *  - In the simplest case, there is none.
	 *  - For RTR frames, 'R' is the first non-hex character.
	 *  - An error message may replace the end of the data line.
	 */
	for (hexlen = 0; hexlen <= len; hexlen++) {
		if (hex_to_bin(elm->rxbuf[hexlen]) < 0 &&
		    elm->rxbuf[hexlen] != ' ') {
			break;
		}
	}

	/* Sanity check whether the line is really a clean hexdump,
	 * or terminated by an error message, or contains garbage.
	 */
	if (hexlen < len && !isdigit(elm->rxbuf[hexlen]) &&
	    !isupper(elm->rxbuf[hexlen]) && '<' != elm->rxbuf[hexlen] &&
	    ' ' != elm->rxbuf[hexlen]) {
		/* The line is likely garbled anyway, so bail.
		 * The main code will restart listening.
		 */
		kfree_skb(skb);
		return -ENODATA;
	}

	/* Use spaces in CAN ID to distinguish 29 or 11 bit address length.
	 * No out-of-bounds access:
	 * We use the fact that we can always read from elm->rxbuf.
	 */
	if (elm->rxbuf[2] == ' ' && elm->rxbuf[5] == ' ' &&
	    elm->rxbuf[8] == ' ' && elm->rxbuf[11] == ' ' &&
	    elm->rxbuf[13] == ' ') {
		frame->can_id = CAN_EFF_FLAG;
		datastart = 14;
	} else if (elm->rxbuf[3] == ' ' && elm->rxbuf[5] == ' ') {
		datastart = 6;
	} else {
		/* This is not a well-formatted data line.
		 * Assume it's an error message.
		 */
		kfree_skb(skb);
		return -ENODATA;
	}

	if (hexlen < datastart) {
		/* The line is too short to be a valid frame hex dump.
		 * Something interrupted the hex dump or it is invalid.
		 */
		kfree_skb(skb);
		return -ENODATA;
	}

	/* From here on all chars up to buf[hexlen] are hex or spaces,
	 * at well-defined offsets.
	 */

	/* Read CAN data length */
	frame->len = (hex_to_bin(elm->rxbuf[datastart - 2]) << 0);

	/* Read CAN ID */
	if (frame->can_id & CAN_EFF_FLAG) {
		frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 28) |
				 (hex_to_bin(elm->rxbuf[1]) << 24) |
				 (hex_to_bin(elm->rxbuf[3]) << 20) |
				 (hex_to_bin(elm->rxbuf[4]) << 16) |
				 (hex_to_bin(elm->rxbuf[6]) << 12) |
				 (hex_to_bin(elm->rxbuf[7]) << 8) |
				 (hex_to_bin(elm->rxbuf[9]) << 4) |
				 (hex_to_bin(elm->rxbuf[10]) << 0);
	} else {
		frame->can_id |= (hex_to_bin(elm->rxbuf[0]) << 8) |
				 (hex_to_bin(elm->rxbuf[1]) << 4) |
				 (hex_to_bin(elm->rxbuf[2]) << 0);
	}

	/* Check for RTR frame */
	if (elm->rxfill >= hexlen + 3 &&
	    !memcmp(&elm->rxbuf[hexlen], "RTR", 3)) {
		frame->can_id |= CAN_RTR_FLAG;
	}

	/* Is the line long enough to hold the advertised payload?
	 * Note: RTR frames have a DLC, but no actual payload.
	 */
	if (!(frame->can_id & CAN_RTR_FLAG) &&
	    (hexlen < frame->len * 3 + datastart)) {
		/* Incomplete frame.
		 * Probably the ELM327's RS232 TX buffer was full.
		 * Emit an error frame and exit.
		 */
		frame->can_id = CAN_ERR_FLAG | CAN_ERR_CRTL;
		frame->len = CAN_ERR_DLC;
		frame->data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
		can327_feed_frame_to_netdev(elm, skb);

		/* Signal failure to parse.
		 * The line will be re-parsed as an error line, which will fail.
		 * However, this will correctly drop the state machine back into
		 * command mode.
		 */
		return -ENODATA;
	}

	/* Parse the data nibbles. */
	for (i = 0; i < frame->len; i++) {
		frame->data[i] =
			(hex_to_bin(elm->rxbuf[datastart + 3 * i]) << 4) |
			(hex_to_bin(elm->rxbuf[datastart + 3 * i + 1]));
	}

	/* Feed the frame to the network layer. */
	can327_feed_frame_to_netdev(elm, skb);

	return 0;
}

static void can327_parse_line(struct can327 *elm, size_t len)
{
	lockdep_assert_held(&elm->lock);

	/* Skip empty lines */
	if (!len)
		return;

	/* Skip echo lines */
	if (elm->drop_next_line) {
		elm->drop_next_line = 0;
		return;
	} else if (!memcmp(elm->rxbuf, "AT", 2)) {
		return;
	}

	/* Regular parsing */
	if (elm->state == CAN327_STATE_RECEIVING &&
	    can327_parse_frame(elm, len)) {
		/* Parse an error line. */
		can327_parse_error(elm, len);

		/* Start afresh. */
		can327_kick_into_cmd_mode(elm);
	}
}

static void can327_handle_prompt(struct can327 *elm)
{
	struct can_frame *frame = &elm->can_frame_to_send;
	/* Size this buffer for the largest ELM327 line we may generate,
	 * which is currently an 8 byte CAN frame's payload hexdump.
	 * Items in can327_init_script must fit here, too!
	 */
	char local_txbuf[sizeof("0102030405060708\r")];

	lockdep_assert_held(&elm->lock);

	if (!elm->cmds_todo) {
		/* Enter CAN monitor mode */
		can327_send(elm, "ATMA\r", 5);
		elm->state = CAN327_STATE_RECEIVING;

		/* We will be in the default state once this command is
		 * sent, so enable the TX packet queue.
		 */
		netif_wake_queue(elm->dev);

		return;
	}

	/* Reconfigure ELM327 step by step as indicated by elm->cmds_todo */
	if (test_bit(CAN327_TX_DO_INIT, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf), "%s",
			 *elm->next_init_cmd);

		elm->next_init_cmd++;
		if (!(*elm->next_init_cmd)) {
			clear_bit(CAN327_TX_DO_INIT, &elm->cmds_todo);
			/* Init finished. */
		}

	} else if (test_and_clear_bit(CAN327_TX_DO_SILENT_MONITOR, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATCSM%i\r",
			 !!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));

	} else if (test_and_clear_bit(CAN327_TX_DO_RESPONSES, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATR%i\r",
			 !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));

	} else if (test_and_clear_bit(CAN327_TX_DO_CAN_CONFIG, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATPC\r");
		set_bit(CAN327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo);

	} else if (test_and_clear_bit(CAN327_TX_DO_CAN_CONFIG_PART2, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATPB%04X\r",
			 elm->can_config);

	} else if (test_and_clear_bit(CAN327_TX_DO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATCP%02X\r",
			 (frame->can_id & CAN_EFF_MASK) >> 24);

	} else if (test_and_clear_bit(CAN327_TX_DO_CANID_29BIT_LOW, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATSH%06X\r",
			 frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));

	} else if (test_and_clear_bit(CAN327_TX_DO_CANID_11BIT, &elm->cmds_todo)) {
		snprintf(local_txbuf, sizeof(local_txbuf),
			 "ATSH%03X\r",
			 frame->can_id & CAN_SFF_MASK);

	} else if (test_and_clear_bit(CAN327_TX_DO_CAN_DATA, &elm->cmds_todo)) {
		if (frame->can_id & CAN_RTR_FLAG) {
			/* Send an RTR frame. Their DLC is fixed.
			 * Some chips don't send them at all.
			 */
			snprintf(local_txbuf, sizeof(local_txbuf), "ATRTR\r");
		} else {
			/* Send a regular CAN data frame */
			int i;

			for (i = 0; i < frame->len; i++) {
				snprintf(&local_txbuf[2 * i],
					 sizeof(local_txbuf), "%02X",
					 frame->data[i]);
			}

			snprintf(&local_txbuf[2 * i], sizeof(local_txbuf),
				 "\r");
		}

		elm->drop_next_line = 1;
		elm->state = CAN327_STATE_RECEIVING;

		/* We will be in the default state once this command is
		 * sent, so enable the TX packet queue.
		 */
		netif_wake_queue(elm->dev);
	}

	can327_send(elm, local_txbuf, strlen(local_txbuf));
}

static bool can327_is_ready_char(char c)
{
	/* Bits 0xc0 are sometimes set (randomly), hence the mask.
	 * Probably bad hardware.
	 */
	return (c & 0x3f) == CAN327_READY_CHAR;
}

static void can327_drop_bytes(struct can327 *elm, size_t i)
{
	lockdep_assert_held(&elm->lock);

	memmove(&elm->rxbuf[0], &elm->rxbuf[i], CAN327_SIZE_RXBUF - i);
	elm->rxfill -= i;
}

static void can327_parse_rxbuf(struct can327 *elm, size_t first_new_char_idx)
{
	size_t len, pos;

	lockdep_assert_held(&elm->lock);

	switch (elm->state) {
	case CAN327_STATE_NOTINIT:
		elm->rxfill = 0;
		break;

	case CAN327_STATE_GETDUMMYCHAR:
		/* Wait for 'y' or '>' */
		for (pos = 0; pos < elm->rxfill; pos++) {
			if (elm->rxbuf[pos] == CAN327_DUMMY_CHAR) {
				can327_send(elm, "\r", 1);
				elm->state = CAN327_STATE_GETPROMPT;
				pos++;
				break;
			} else if (can327_is_ready_char(elm->rxbuf[pos])) {
				can327_send(elm, CAN327_DUMMY_STRING, 1);
				pos++;
				break;
			}
		}

		can327_drop_bytes(elm, pos);
		break;

	case CAN327_STATE_GETPROMPT:
		/* Wait for '>' */
		if (can327_is_ready_char(elm->rxbuf[elm->rxfill - 1]))
			can327_handle_prompt(elm);

		elm->rxfill = 0;
		break;

	case CAN327_STATE_RECEIVING:
		/* Find <CR> delimiting feedback lines. */
		len = first_new_char_idx;
		while (len < elm->rxfill && elm->rxbuf[len] != '\r')
			len++;

		if (len == CAN327_SIZE_RXBUF) {
			/* Assume the buffer ran full with garbage.
			 * Did we even connect at the right baud rate?
			 */
			netdev_err(elm->dev,
				   "RX buffer overflow. Faulty ELM327 or UART?\n");
			can327_uart_side_failure(elm);
		} else if (len == elm->rxfill) {
			if (can327_is_ready_char(elm->rxbuf[elm->rxfill - 1])) {
				/* The ELM327's AT ST response timeout ran out,
				 * so we got a prompt.
				 * Clear RX buffer and restart listening.
				 */
				elm->rxfill = 0;

				can327_handle_prompt(elm);
			}

			/* No <CR> found - we haven't received a full line yet.
			 * Wait for more data.
			 */
		} else {
			/* We have a full line to parse. */
			can327_parse_line(elm, len);

			/* Remove parsed data from RX buffer. */
			can327_drop_bytes(elm, len + 1);

			/* More data to parse? */
			if (elm->rxfill)
				can327_parse_rxbuf(elm, 0);
		}
	}
}

static int can327_netdev_open(struct net_device *dev)
{
	struct can327 *elm = netdev_priv(dev);
	int err;

	spin_lock_bh(&elm->lock);

	if (!elm->tty) {
		spin_unlock_bh(&elm->lock);
		return -ENODEV;
	}

	if (elm->uart_side_failure)
		netdev_warn(elm->dev,
			    "Reopening netdev after a UART side fault has been detected.\n");

	/* Clear TTY buffers */
	elm->rxfill = 0;
	elm->txleft = 0;

	/* open_candev() checks for elm->can.bittiming.bitrate != 0 */
	err = open_candev(dev);
	if (err) {
		spin_unlock_bh(&elm->lock);
		return err;
	}

	can327_init_device(elm);
	spin_unlock_bh(&elm->lock);

	err = can_rx_offload_add_manual(dev, &elm->offload, CAN327_NAPI_WEIGHT);
	if (err) {
		close_candev(dev);
		return err;
	}

	can_rx_offload_enable(&elm->offload);

	elm->can.state = CAN_STATE_ERROR_ACTIVE;
	netif_start_queue(dev);

	return 0;
}

static int can327_netdev_close(struct net_device *dev)
{
	struct can327 *elm = netdev_priv(dev);

	/* Interrupt whatever the ELM327 is doing right now */
	spin_lock_bh(&elm->lock);
	can327_send(elm, CAN327_DUMMY_STRING, 1);
	spin_unlock_bh(&elm->lock);

	netif_stop_queue(dev);

	/* Give UART one final chance to flush. */
	clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
	flush_work(&elm->tx_work);

	can_rx_offload_disable(&elm->offload);
	elm->can.state = CAN_STATE_STOPPED;
	can_rx_offload_del(&elm->offload);
	close_candev(dev);

	return 0;
}

/* Send a can_frame to a TTY. */
static netdev_tx_t can327_netdev_start_xmit(struct sk_buff *skb,
					    struct net_device *dev)
{
	struct can327 *elm = netdev_priv(dev);
	struct can_frame *frame = (struct can_frame *)skb->data;

	if (can_dropped_invalid_skb(dev, skb))
		return NETDEV_TX_OK;

	/* We shouldn't get here after a hardware fault:
	 * can_bus_off() calls netif_carrier_off()
	 */
	if (elm->uart_side_failure) {
		WARN_ON_ONCE(elm->uart_side_failure);
		goto out;
	}

	netif_stop_queue(dev);

	/* BHs are already disabled, so no spin_lock_bh().
830
	 * See Documentation/networking/netdevices.rst
831 832 833 834 835 836 837 838
	 */
	spin_lock(&elm->lock);
	can327_send_frame(elm, frame);
	spin_unlock(&elm->lock);

	dev->stats.tx_packets++;
	dev->stats.tx_bytes += frame->can_id & CAN_RTR_FLAG ? 0 : frame->len;

839 840
	skb_tx_timestamp(skb);

841 842 843 844 845 846 847 848 849 850 851 852
out:
	kfree_skb(skb);
	return NETDEV_TX_OK;
}

static const struct net_device_ops can327_netdev_ops = {
	.ndo_open = can327_netdev_open,
	.ndo_stop = can327_netdev_close,
	.ndo_start_xmit = can327_netdev_start_xmit,
	.ndo_change_mtu = can_change_mtu,
};

853 854 855 856
static const struct ethtool_ops can327_ethtool_ops = {
	.get_ts_info = ethtool_op_get_ts_info,
};

857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040
static bool can327_is_valid_rx_char(u8 c)
{
	static const bool lut_char_is_valid['z'] = {
		['\r'] = true,
		[' '] = true,
		['.'] = true,
		['0'] = true, true, true, true, true,
		['5'] = true, true, true, true, true,
		['<'] = true,
		[CAN327_READY_CHAR] = true,
		['?'] = true,
		['A'] = true, true, true, true, true, true, true,
		['H'] = true, true, true, true, true, true, true,
		['O'] = true, true, true, true, true, true, true,
		['V'] = true, true, true, true, true,
		['a'] = true,
		['b'] = true,
		['v'] = true,
		[CAN327_DUMMY_CHAR] = true,
	};
	BUILD_BUG_ON(CAN327_DUMMY_CHAR >= 'z');

	return (c < ARRAY_SIZE(lut_char_is_valid) && lut_char_is_valid[c]);
}

/* Handle incoming ELM327 ASCII data.
 * This will not be re-entered while running, but other ldisc
 * functions may be called in parallel.
 */
static void can327_ldisc_rx(struct tty_struct *tty, const unsigned char *cp,
			    const char *fp, int count)
{
	struct can327 *elm = (struct can327 *)tty->disc_data;
	size_t first_new_char_idx;

	if (elm->uart_side_failure)
		return;

	spin_lock_bh(&elm->lock);

	/* Store old rxfill, so can327_parse_rxbuf() will have
	 * the option of skipping already checked characters.
	 */
	first_new_char_idx = elm->rxfill;

	while (count-- && elm->rxfill < CAN327_SIZE_RXBUF) {
		if (fp && *fp++) {
			netdev_err(elm->dev,
				   "Error in received character stream. Check your wiring.");

			can327_uart_side_failure(elm);

			spin_unlock_bh(&elm->lock);
			return;
		}

		/* Ignore NUL characters, which the PIC microcontroller may
		 * inadvertently insert due to a known hardware bug.
		 * See ELM327 documentation, which refers to a Microchip PIC
		 * bug description.
		 */
		if (*cp) {
			/* Check for stray characters on the UART line.
			 * Likely caused by bad hardware.
			 */
			if (!can327_is_valid_rx_char(*cp)) {
				netdev_err(elm->dev,
					   "Received illegal character %02x.\n",
					   *cp);
				can327_uart_side_failure(elm);

				spin_unlock_bh(&elm->lock);
				return;
			}

			elm->rxbuf[elm->rxfill++] = *cp;
		}

		cp++;
	}

	if (count >= 0) {
		netdev_err(elm->dev,
			   "Receive buffer overflowed. Bad chip or wiring? count = %i",
			   count);

		can327_uart_side_failure(elm);

		spin_unlock_bh(&elm->lock);
		return;
	}

	can327_parse_rxbuf(elm, first_new_char_idx);
	spin_unlock_bh(&elm->lock);
}

/* Write out remaining transmit buffer.
 * Scheduled when TTY is writable.
 */
static void can327_ldisc_tx_worker(struct work_struct *work)
{
	struct can327 *elm = container_of(work, struct can327, tx_work);
	ssize_t written;

	if (elm->uart_side_failure)
		return;

	spin_lock_bh(&elm->lock);

	if (elm->txleft) {
		written = elm->tty->ops->write(elm->tty, elm->txhead,
					       elm->txleft);
		if (written < 0) {
			netdev_err(elm->dev, "Failed to write to tty %s.\n",
				   elm->tty->name);
			can327_uart_side_failure(elm);

			spin_unlock_bh(&elm->lock);
			return;
		}

		elm->txleft -= written;
		elm->txhead += written;
	}

	if (!elm->txleft)
		clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);

	spin_unlock_bh(&elm->lock);
}

/* Called by the driver when there's room for more data. */
static void can327_ldisc_tx_wakeup(struct tty_struct *tty)
{
	struct can327 *elm = (struct can327 *)tty->disc_data;

	schedule_work(&elm->tx_work);
}

/* ELM327 can only handle bitrates that are integer divisors of 500 kHz,
 * or 7/8 of that. Divisors are 1 to 64.
 * Currently we don't implement support for 7/8 rates.
 */
static const u32 can327_bitrate_const[] = {
	7812,  7936,  8064,  8196,   8333,   8474,   8620,   8771,
	8928,  9090,  9259,  9433,   9615,   9803,   10000,  10204,
	10416, 10638, 10869, 11111,  11363,  11627,  11904,  12195,
	12500, 12820, 13157, 13513,  13888,  14285,  14705,  15151,
	15625, 16129, 16666, 17241,  17857,  18518,  19230,  20000,
	20833, 21739, 22727, 23809,  25000,  26315,  27777,  29411,
	31250, 33333, 35714, 38461,  41666,  45454,  50000,  55555,
	62500, 71428, 83333, 100000, 125000, 166666, 250000, 500000
};

static int can327_ldisc_open(struct tty_struct *tty)
{
	struct net_device *dev;
	struct can327 *elm;
	int err;

	if (!capable(CAP_NET_ADMIN))
		return -EPERM;

	if (!tty->ops->write)
		return -EOPNOTSUPP;

	dev = alloc_candev(sizeof(struct can327), 0);
	if (!dev)
		return -ENFILE;
	elm = netdev_priv(dev);

	/* Configure TTY interface */
	tty->receive_room = 65536; /* We don't flow control */
	spin_lock_init(&elm->lock);
	INIT_WORK(&elm->tx_work, can327_ldisc_tx_worker);

	/* Configure CAN metadata */
	elm->can.bitrate_const = can327_bitrate_const;
	elm->can.bitrate_const_cnt = ARRAY_SIZE(can327_bitrate_const);
	elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;

	/* Configure netdev interface */
	elm->dev = dev;
	dev->netdev_ops = &can327_netdev_ops;
1041
	dev->ethtool_ops = &can327_ethtool_ops;
1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109

	/* Mark ldisc channel as alive */
	elm->tty = tty;
	tty->disc_data = elm;

	/* Let 'er rip */
	err = register_candev(elm->dev);
	if (err) {
		free_candev(elm->dev);
		return err;
	}

	netdev_info(elm->dev, "can327 on %s.\n", tty->name);

	return 0;
}

/* Close down a can327 channel.
 * This means flushing out any pending queues, and then returning.
 * This call is serialized against other ldisc functions:
 * Once this is called, no other ldisc function of ours is entered.
 *
 * We also use this function for a hangup event.
 */
static void can327_ldisc_close(struct tty_struct *tty)
{
	struct can327 *elm = (struct can327 *)tty->disc_data;

	/* unregister_netdev() calls .ndo_stop() so we don't have to.
	 * Our .ndo_stop() also flushes the TTY write wakeup handler,
	 * so we can safely set elm->tty = NULL after this.
	 */
	unregister_candev(elm->dev);

	/* Mark channel as dead */
	spin_lock_bh(&elm->lock);
	tty->disc_data = NULL;
	elm->tty = NULL;
	spin_unlock_bh(&elm->lock);

	netdev_info(elm->dev, "can327 off %s.\n", tty->name);

	free_candev(elm->dev);
}

static int can327_ldisc_ioctl(struct tty_struct *tty, unsigned int cmd,
			      unsigned long arg)
{
	struct can327 *elm = (struct can327 *)tty->disc_data;
	unsigned int tmp;

	switch (cmd) {
	case SIOCGIFNAME:
		tmp = strnlen(elm->dev->name, IFNAMSIZ - 1) + 1;
		if (copy_to_user((void __user *)arg, elm->dev->name, tmp))
			return -EFAULT;
		return 0;

	case SIOCSIFHWADDR:
		return -EINVAL;

	default:
		return tty_mode_ioctl(tty, cmd, arg);
	}
}

static struct tty_ldisc_ops can327_ldisc = {
	.owner = THIS_MODULE,
1110
	.name = KBUILD_MODNAME,
1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144
	.num = N_CAN327,
	.receive_buf = can327_ldisc_rx,
	.write_wakeup = can327_ldisc_tx_wakeup,
	.open = can327_ldisc_open,
	.close = can327_ldisc_close,
	.ioctl = can327_ldisc_ioctl,
};

static int __init can327_init(void)
{
	int status;

	status = tty_register_ldisc(&can327_ldisc);
	if (status)
		pr_err("Can't register line discipline\n");

	return status;
}

static void __exit can327_exit(void)
{
	/* This will only be called when all channels have been closed by
	 * userspace - tty_ldisc.c takes care of the module's refcount.
	 */
	tty_unregister_ldisc(&can327_ldisc);
}

module_init(can327_init);
module_exit(can327_exit);

MODULE_ALIAS_LDISC(N_CAN327);
MODULE_DESCRIPTION("ELM327 based CAN interface");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Max Staudt <max@enpas.org>");