Import first public commit

6 files changed, 1701 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3adf3be
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,11 @@
+*~
+*.o
+
+elmcan-usermode
+
+*.cmd
+*.ko
+*.mod.c
+modules.order
+Module.symvers
+.tmp_versions
diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000..d159169
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,339 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
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+    This is free software, and you are welcome to redistribute it
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+The hypothetical commands `show w' and `show c' should show the appropriate
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+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  <signature of Ty Coon>, 1 April 1989
+  Ty Coon, President of Vice
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+This General Public License does not permit incorporating your program into
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diff --git a/module/Makefile b/module/Makefile
new file mode 100644
index 0000000..120df6b
--- /dev/null
+++ b/module/Makefile
@@ -0,0 +1,7 @@
+obj-m += elmcan.o
+
+all:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
+
+clean:
+	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
diff --git a/module/attach-me.sh b/module/attach-me.sh
new file mode 100755
index 0000000..d0c130c
--- /dev/null
+++ b/module/attach-me.sh
@@ -0,0 +1,3 @@
+#!/bin/bash
+
+sudo ldattach --debug --speed 38400 --eightbits --noparity --onestopbit --iflag -ICRNL,INLCR,-IXOFF 26 $@
diff --git a/module/elmcan.c b/module/elmcan.c
new file mode 100644
index 0000000..1e72461
--- /dev/null
+++ b/module/elmcan.c
@@ -0,0 +1,1062 @@
+/*
+ * elmcan.c - ELM327 based CAN interface driver
+ *            (tty line discipline)
+ *
+ * This file is derived from linux/drivers/net/can/slcan.c
+ *
+ * elmcan.c Author : Max Staudt <elmcan@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>
+ *
+ * SPDX-License-Identifier: GPL-2.0
+ *
+ */
+
+#define pr_fmt(fmt) "[elmcan] " fmt
+
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+
+#include <linux/bitops.h>
+#include <linux/errno.h>
+#include <linux/if_ether.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/tty.h>
+#include <linux/workqueue.h>
+
+#include <linux/can.h>
+#include <linux/can/dev.h>
+#include <linux/can/error.h>
+#include <linux/can/led.h>
+
+
+MODULE_ALIAS_LDISC(N_ELMCAN);
+MODULE_DESCRIPTION("ELM327 based CAN interface");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Max Staudt <max-linux@enpas.org>");
+
+/* Line discipline ID number */
+#ifndef N_ELMCAN
+#define N_ELMCAN 26
+#endif
+
+#define ELM327_CAN_CONFIG_SEND_SFF           0x8000
+#define ELM327_CAN_CONFIG_VARIABLE_DLC       0x4000
+#define ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF  0x2000
+#define ELM327_CAN_CONFIG_BAUDRATE_MULT_8_7  0x1000
+
+#define ELM327_MAGIC_CHAR 'y'
+#define ELM327_MAGIC_STRING "y"
+
+
+/* Bits in elm->cmds_todo */
+enum ELM_TODO {
+	ELM_TODO_CAN_DATA = 0,
+	ELM_TODO_CANID_11BIT,
+	ELM_TODO_CANID_29BIT_LOW,
+	ELM_TODO_CANID_29BIT_HIGH,
+	ELM_TODO_CAN_CONFIG,
+	ELM_TODO_RESPONSES,
+	ELM_TODO_SILENT_MONITOR,
+	ELM_TODO_INIT
+};
+
+
+struct elmcan {
+	/* This must be the first member when using alloc_candev() */
+	struct can_priv can;
+
+	/* TTY and netdev devices that we're bridging */
+	struct tty_struct	*tty;
+	struct net_device	*dev;
+
+	int			magic;
+
+	/* Per-channel lock */
+	spinlock_t		lock;
+
+	/* TTY TX helpers */
+	struct work_struct	tx_work;	/* Flushes TTY TX buffer   */
+	unsigned char		txbuf[32];
+	unsigned char		*txhead;	/* Pointer to next TX byte */
+	int			txleft;		/* Bytes left to TX */
+
+	/* TTY RX helpers */
+	unsigned char rxbuf[256];
+	int rxfill;
+
+	/* State machine */
+	enum {
+		ELM_NOTINIT = 0,
+		ELM_GETMAGICCHAR,
+		ELM_GETPROMPT,
+		ELM_RECEIVING,
+	} state;
+
+	int drop_next_line;
+
+	/* The CAN frame and config the ELM327 is sending/using,
+	 * or will send/use after finishing all cmds_todo */
+	struct can_frame can_frame;
+	unsigned short can_config;
+	unsigned long can_bitrate;
+	unsigned char can_bitrate_divisor;
+	int silent_monitoring;
+
+	/* Things we have yet to send */
+	char **next_init_cmd;
+	unsigned long cmds_todo;
+};
+
+
+static DEFINE_SPINLOCK(elmcan_open_lock);
+
+
+
+
+ /************************************************************************
+  *			ELM327: Transmission				 *
+  ************************************************************************/
+
+static void elm327_send(struct elmcan *elm, const void *buf, size_t len)
+{
+	int actual;
+
+	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);
+	actual = elm->tty->ops->write(elm->tty, elm->txbuf, len);
+	elm->txleft = len - actual;
+	elm->txhead = elm->txbuf + actual;
+}
+
+
+static void elm327_kick_into_cmd_mode(struct elmcan *elm)
+{
+	if (elm->state != ELM_GETMAGICCHAR && elm->state != ELM_GETPROMPT) {
+		elm327_send(elm, ELM327_MAGIC_STRING, 1);
+
+		elm->state = ELM_GETMAGICCHAR;
+		elm->rxfill = 0;
+	}
+}
+
+
+static void elm327_send_frame(struct elmcan *elm, struct can_frame *frame)
+{
+	if (elm->can_frame.can_id != frame->can_id) {
+		/* Set the new CAN ID for transmission. */
+		if ((frame->can_id & CAN_EFF_FLAG) ^ (elm->can_frame.can_id & CAN_EFF_FLAG)) {
+			elm->can_config = (frame->can_id & CAN_EFF_FLAG ? 0 : ELM327_CAN_CONFIG_SEND_SFF)
+					| ELM327_CAN_CONFIG_VARIABLE_DLC
+					| ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
+					| elm->can_bitrate_divisor;
+
+			set_bit(ELM_TODO_CAN_CONFIG, &elm->cmds_todo);
+		}
+
+		if (frame->can_id & CAN_EFF_FLAG) {
+			clear_bit(ELM_TODO_CANID_11BIT, &elm->cmds_todo);
+			set_bit(ELM_TODO_CANID_29BIT_LOW, &elm->cmds_todo);
+			set_bit(ELM_TODO_CANID_29BIT_HIGH, &elm->cmds_todo);
+		} else {
+			set_bit(ELM_TODO_CANID_11BIT, &elm->cmds_todo);
+			clear_bit(ELM_TODO_CANID_29BIT_LOW, &elm->cmds_todo);
+			clear_bit(ELM_TODO_CANID_29BIT_HIGH, &elm->cmds_todo);
+		}
+	}
+
+	elm->can_frame = *frame;
+	set_bit(ELM_TODO_CAN_DATA, &elm->cmds_todo);
+
+	elm327_kick_into_cmd_mode(elm);
+}
+
+
+
+ /************************************************************************
+  *			ELM327: Initialization sequence			 *
+  ************************************************************************/
+
+static char *elm327_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 Initialization */
+	"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 elm327_init(struct elmcan *elm)
+{
+	elm->state = ELM_NOTINIT;
+	elm->can_frame.can_id = 0x7df;
+	elm->rxfill = 0;
+	elm->drop_next_line = 0;
+
+	/* We can only set the bitrate as a fraction of 500000.
+	 * The bit timing constants in elmcan_bittiming_const will
+	 * limit the user to the right values.
+	 */
+	elm->can_bitrate_divisor = 500000 / elm->can.bittiming.bitrate;
+	elm->can_config = ELM327_CAN_CONFIG_SEND_SFF
+			| ELM327_CAN_CONFIG_VARIABLE_DLC
+			| ELM327_CAN_CONFIG_RECV_BOTH_SFF_EFF
+			| elm->can_bitrate_divisor;
+
+	/* Configure ELM327 and then start monitoring */
+	elm->next_init_cmd = &elm327_init_script[0];
+	set_bit(ELM_TODO_INIT, &elm->cmds_todo);
+	set_bit(ELM_TODO_SILENT_MONITOR, &elm->cmds_todo);
+	set_bit(ELM_TODO_RESPONSES, &elm->cmds_todo);
+	set_bit(ELM_TODO_CAN_CONFIG, &elm->cmds_todo);
+
+	elm327_kick_into_cmd_mode(elm);
+}
+
+
+
+ /************************************************************************
+  *			ELM327: Reception -> netdev glue		 *
+  ************************************************************************/
+
+static void elm327_feed_frame_to_netdev(struct elmcan *elm, const struct can_frame *frame)
+{
+	struct can_frame *cf;
+	struct sk_buff *skb;
+
+	if (!netif_running(elm->dev)) {
+		return;
+	}
+
+	skb = alloc_can_skb(elm->dev, &cf);
+
+	if (!skb)
+		return;
+
+	memcpy(cf, frame, sizeof(struct can_frame));
+
+	elm->dev->stats.rx_packets++;
+	elm->dev->stats.rx_bytes += frame->can_dlc;
+	netif_rx_ni(skb);
+
+	can_led_event(elm->dev, CAN_LED_EVENT_RX);
+}
+
+
+
+ /************************************************************************
+  *			ELM327: Panic handler				 *
+  ************************************************************************/
+
+static inline void elm327_panic(struct elmcan *elm)
+{
+	struct can_frame frame = {0};
+
+	frame.can_id = CAN_ERR_FLAG | CAN_ERR_RESTARTED;
+	frame.can_dlc = CAN_ERR_DLC;
+	elm327_feed_frame_to_netdev(elm, &frame);
+
+	pr_err("ELM327 misbehaved. Re-initializing.\n");
+
+	elm->can.can_stats.restarts++;
+	elm327_init(elm);
+}
+
+
+
+ /************************************************************************
+  *			ELM327: Reception parser			 *
+  ************************************************************************/
+
+static void elm327_parse_error(struct elmcan *elm, int len)
+{
+	struct can_frame frame = {0};
+
+	frame.can_id = CAN_ERR_FLAG;
+	frame.can_dlc = CAN_ERR_DLC;
+
+	switch(len) {
+		case 17:
+			if (!memcmp(elm->rxbuf, "UNABLE TO CONNECT", 17)) {
+				pr_err("The ELM327 reported UNABLE TO CONNECT. Please check your setup.\n");
+			}
+			break;
+		case 11:
+			if (!memcmp(elm->rxbuf, "BUFFER FULL", 11)) {
+				/* This case will only happen if the last data
+				 * line was complete.
+				 * Otherwise, elm327_parse_frame() will emit the
+				 * error frame instead.
+				 */
+				frame.can_id |= CAN_ERR_CRTL;
+				frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
+			}
+			break;
+		case 9:
+			if (!memcmp(elm->rxbuf, "BUS ERROR", 9)) {
+				frame.can_id |= CAN_ERR_BUSERROR;
+			}
+			if (!memcmp(elm->rxbuf, "CAN ERROR", 9)
+				|| !memcmp(elm->rxbuf, "<RX ERROR", 9)) {
+				frame.can_id |= CAN_ERR_PROT;
+			}
+			break;
+		case 8:
+			if (!memcmp(elm->rxbuf, "BUS BUSY", 8)) {
+				frame.can_id |= CAN_ERR_PROT;
+				frame.data[2] = CAN_ERR_PROT_OVERLOAD;
+			}
+			if (!memcmp(elm->rxbuf, "FB ERROR", 8)) {
+				frame.can_id |= CAN_ERR_PROT;
+				frame.data[2] = CAN_ERR_PROT_TX;
+			}
+			break;
+		case 5:
+			if (!memcmp(elm->rxbuf, "ERR", 3)) {
+				pr_err("The 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;
+			}
+			break;
+		default:
+			/* Don't emit an error frame if we're unsure */
+			return;
+	}
+
+	elm327_feed_frame_to_netdev(elm, &frame);
+}
+
+
+static int elm327_parse_frame(struct elmcan *elm, int len)
+{
+	struct can_frame frame = {0};
+	int hexlen;
+	int datastart;
+	int i;
+
+	/* 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;
+		}
+	}
+
+	/* 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] == ' ') {
+		frame.can_id = 0;
+		datastart = 6;
+	} else {
+		/* This is not a well-formatted data line.
+		 * Assume it's an error message. */
+		return 1;
+	}
+
+	if (hexlen < datastart) {
+		/* The line is too short to be a valid frame hex dump.
+		 * Something interrupted the hex dump or it is invalid. */
+		return 1;
+	}
+
+	/* From here on all chars up to buf[hexlen] are hex or spaces,
+	 * at well-defined offsets. */
+
+	/* Read CAN data length */
+	frame.can_dlc = (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
+	    && elm->rxbuf[hexlen + 0] == 'R'
+	    && elm->rxbuf[hexlen + 1] == 'T'
+	    && elm->rxbuf[hexlen + 2] == 'R') {
+		frame.can_id |= CAN_RTR_FLAG;
+	}
+
+	/* Is the line long enough to hold the advertised payload? */
+	if (!(frame.can_id & CAN_RTR_FLAG) && (hexlen < frame.can_dlc * 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.can_dlc = CAN_ERR_DLC;
+		frame.data[1] = CAN_ERR_CRTL_RX_OVERFLOW;
+		elm327_feed_frame_to_netdev(elm, &frame);
+
+		/* 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 2;
+	}
+
+	/* Parse the data nibbles. */
+	for (i = 0; i < frame.can_dlc; i++) {
+		frame.data[i] = (hex_to_bin(elm->rxbuf[datastart+3*i]) << 4)
+                                | (hex_to_bin(elm->rxbuf[datastart+3*i+1]) << 0);
+	}
+
+	/* Feed the frame to the network layer. */
+	elm327_feed_frame_to_netdev(elm, &frame);
+
+	return 0;
+}
+
+
+static void elm327_parse_line(struct elmcan *elm, int len)
+{
+	/* Skip empty lines */
+	if (!len) {
+		return;
+	}
+
+	/* Skip echo lines */
+	if (elm->drop_next_line) {
+		elm->drop_next_line = 0;
+		return;
+	} else if (elm->rxbuf[0] == 'A' && elm->rxbuf[1] == 'T') {
+		return;
+	}
+
+	/* Regular parsing */
+	switch(elm->state) {
+		case ELM_RECEIVING:
+			if (elm327_parse_frame(elm, len)) {
+				/* Parse an error line. */
+				elm327_parse_error(elm, len);
+
+				/* After the error line, we expect a prompt. */
+				elm->state = ELM_GETPROMPT;
+			}
+			break;
+		default:
+			break;
+	}
+}
+
+
+static void elm327_handle_prompt(struct elmcan *elm)
+{
+	if (elm->cmds_todo) {
+		struct can_frame *frame = &elm->can_frame;
+		char txbuf[20];
+
+		if (test_bit(ELM_TODO_INIT, &elm->cmds_todo)) {
+			elm327_send(elm, *elm->next_init_cmd, strlen(*elm->next_init_cmd));
+			elm->next_init_cmd++;
+			if (!(*elm->next_init_cmd)) {
+				clear_bit(ELM_TODO_INIT, &elm->cmds_todo);
+				pr_info("%s: Initialization finished.\n", elm->dev->name);
+			}
+
+			/* Some chips are unreliable and need extra time after
+			 * init commands, as seen with a clone.
+			 * So let's do a dummy get-cmd-prompt dance. */
+			elm->state = ELM_NOTINIT;
+			elm327_kick_into_cmd_mode(elm);
+		} else if (test_and_clear_bit(ELM_TODO_SILENT_MONITOR, &elm->cmds_todo)) {
+			snprintf(txbuf, sizeof(txbuf), "ATCSM%i\r", !(!(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)));
+		} else if (test_and_clear_bit(ELM_TODO_RESPONSES, &elm->cmds_todo)) {
+			snprintf(txbuf, sizeof(txbuf), "ATR%i\r", !(elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY));
+		} else if (test_and_clear_bit(ELM_TODO_CAN_CONFIG, &elm->cmds_todo)) {
+			snprintf(txbuf, sizeof(txbuf), "ATPB%04X\r", elm->can_config);
+		} else if (test_and_clear_bit(ELM_TODO_CANID_29BIT_HIGH, &elm->cmds_todo)) {
+			snprintf(txbuf, sizeof(txbuf), "ATCP%02X\r", (frame->can_id & CAN_EFF_MASK) >> 24);
+		} else if (test_and_clear_bit(ELM_TODO_CANID_29BIT_LOW, &elm->cmds_todo)) {
+			snprintf(txbuf, sizeof(txbuf), "ATSH%06X\r", frame->can_id & CAN_EFF_MASK & ((1 << 24) - 1));
+		} else if (test_and_clear_bit(ELM_TODO_CANID_11BIT, &elm->cmds_todo)) {
+			snprintf(txbuf, sizeof(txbuf), "ATSH%03X\r", frame->can_id & CAN_SFF_MASK);
+		} else if (test_and_clear_bit(ELM_TODO_CAN_DATA, &elm->cmds_todo)) {
+			if (frame->can_id & CAN_RTR_FLAG) {
+				snprintf(txbuf, sizeof(txbuf), "ATRTR\r");
+			} else {
+				int i;
+
+				for (i = 0; i < frame->can_dlc; i++) {
+					sprintf(&txbuf[2*i], "%02X", frame->data[i]);
+				}
+
+				sprintf(&txbuf[2*i], "\r");
+			}
+
+			elm->drop_next_line = 1;
+			elm->state = ELM_RECEIVING;
+		}
+
+		elm327_send(elm, txbuf, strlen(txbuf));
+	} else {
+		/* Enter CAN monitor mode */
+		elm327_send(elm, "ATMA\r", 5);
+		elm->state = ELM_RECEIVING;
+	}
+}
+
+
+static void elm327_drop_bytes(struct elmcan *elm, int i)
+{
+	memmove(&elm->rxbuf[0], &elm->rxbuf[i], sizeof(elm->rxbuf) - i);
+	elm->rxfill -= i;
+}
+
+
+static void elm327_parse_rxbuf(struct elmcan *elm)
+{
+	int len;
+
+	switch (elm->state) {
+	case ELM_NOTINIT:
+		elm->rxfill = 0;
+		return;
+
+	case ELM_GETMAGICCHAR:
+	{
+		/* Wait for 'y' or '>' */
+		int i;
+
+		for (i = 0; i < elm->rxfill; i++) {
+			if (elm->rxbuf[i] == ELM327_MAGIC_CHAR) {
+				elm327_send(elm, "\r", 1);
+				elm->state = ELM_GETPROMPT;
+				i++;
+				break;
+			} else if (elm->rxbuf[i] == '>') {
+				elm327_send(elm, ELM327_MAGIC_STRING, 1);
+				i++;
+				break;
+			}
+		}
+
+		elm327_drop_bytes(elm, i);
+
+		return;
+	}
+
+	case ELM_GETPROMPT:
+		/* Wait for '>' */
+		if (elm->rxbuf[elm->rxfill - 1] == '>') {
+			elm327_handle_prompt(elm);
+		}
+
+		elm->rxfill = 0;
+		return;
+
+	case ELM_RECEIVING:
+		/* Find <CR> delimiting feedback lines. */
+		for (len = 0;
+		     (len < elm->rxfill) && (elm->rxbuf[len] != '\r');
+		     len++) {
+			/* empty loop */
+		}
+
+		if (len == sizeof(elm->rxbuf)) {
+			/* Line exceeds buffer. It's probably all garbage.
+			 * Did we even connect at the right baud rate? */
+			pr_err("RX buffer overflow. Faulty ELM327 connected?\n");
+			elm327_panic(elm);
+		} else if (len == elm->rxfill) {
+			if (elm->state == ELM_RECEIVING
+				&& 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;
+
+				elm327_handle_prompt(elm);
+				return;
+			} else {
+				/* We haven't received a full line yet. Wait for more data. */
+				return;
+			}
+		}
+
+		/* We have a full line to parse. */
+		elm327_parse_line(elm, len);
+
+		/* Remove parsed data from RX buffer. */
+		elm327_drop_bytes(elm, len+1);
+
+		/* More data to parse? */
+		if (elm->rxfill) {
+			elm327_parse_rxbuf(elm);
+		}
+	}
+}
+
+
+
+
+
+ /************************************************************************
+  *				netdev					 *
+  ************************************************************************/
+
+/* Netdevice DOWN -> UP routine */
+static int elmcan_netdev_open(struct net_device *dev)
+{
+	struct elmcan *elm = netdev_priv(dev);
+	int err;
+
+	spin_lock_bh(&elm->lock);
+	if (elm->tty == NULL) {
+		spin_unlock_bh(&elm->lock);
+		return -ENODEV;
+	}
+
+	/* open_candev() checks for elm->can.bittiming.bitrate != 0 */
+	err = open_candev(dev);
+	if (err) {
+		spin_unlock_bh(&elm->lock);
+		return err;
+	}
+
+	/* Initialize the ELM327 */
+	elm327_init(elm);
+	spin_unlock_bh(&elm->lock);
+
+	can_led_event(dev, CAN_LED_EVENT_OPEN);
+	elm->can.state = CAN_STATE_ERROR_ACTIVE;
+	netif_start_queue(dev);
+
+	return 0;
+}
+
+/* Netdevice UP -> DOWN routine */
+static int elmcan_netdev_close(struct net_device *dev)
+{
+	struct elmcan *elm = netdev_priv(dev);
+
+	spin_lock_bh(&elm->lock);
+	if (elm->tty) {
+		/* TTY discipline is running. */
+
+		/* Interrupt whatever we're doing right now */
+		elm327_send(elm, ELM327_MAGIC_STRING, 1);
+
+		/* Clear the wakeup bit, as the netdev will be down and thus
+		 * the wakeup handler won't clear it
+		 */
+		clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
+
+		spin_unlock_bh(&elm->lock);
+
+		flush_work(&elm->tx_work);
+	} else {
+		spin_unlock_bh(&elm->lock);
+	}
+
+	elm->can.state = CAN_STATE_STOPPED;
+	netif_stop_queue(dev);
+	close_candev(dev);
+	can_led_event(dev, CAN_LED_EVENT_STOP);
+
+	return 0;
+}
+
+/* Send a can_frame to a TTY queue. */
+static netdev_tx_t elmcan_netdev_start_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	struct elmcan *elm = netdev_priv(dev);
+	struct can_frame *frame = (struct can_frame *) skb->data;
+
+	if (skb->len != sizeof(struct can_frame))
+		goto out;
+
+	if (!netif_running(dev))  {
+		pr_warn("%s: xmit: iface is down\n", dev->name);
+		goto out;
+	}
+
+	/* BHs are already disabled, so no spin_lock_bh().
+	 * See Documentation/networking/netdevices.txt
+	 */
+	spin_lock(&elm->lock);
+	if (elm->tty == NULL
+		|| elm->can.ctrlmode & CAN_CTRLMODE_LISTENONLY) {
+		spin_unlock(&elm->lock);
+		goto out;
+	}
+
+	netif_stop_queue(dev);
+
+	elm327_send_frame(elm, frame);
+	spin_unlock(&elm->lock);
+
+	dev->stats.tx_packets++;
+	dev->stats.tx_bytes += frame->can_dlc;
+
+	can_led_event(dev, CAN_LED_EVENT_TX);
+
+out:
+	kfree_skb(skb);
+	return NETDEV_TX_OK;
+}
+
+static int elmcan_netdev_change_mtu(struct net_device *dev, int new_mtu)
+{
+	return -EINVAL;
+}
+
+static const struct net_device_ops elmcan_netdev_ops = {
+	.ndo_open	= elmcan_netdev_open,
+	.ndo_stop	= elmcan_netdev_close,
+	.ndo_start_xmit	= elmcan_netdev_start_xmit,
+	.ndo_change_mtu	= elmcan_netdev_change_mtu,
+};
+
+
+
+
+
+ /************************************************************************
+  *			Line discipline					 *
+  ************************************************************************/
+
+/*
+ * Handle the 'receiver data ready' interrupt.
+ * This function is called by the 'tty_io' module in the kernel when
+ * a block of ELM327 CAN data has been received, which can now be parsed
+ * and sent on to some IP layer for further processing. This will not
+ * be re-entered while running but other ldisc functions may be called
+ * in parallel
+ */
+static void elmcan_ldisc_rx(struct tty_struct *tty,
+			const unsigned char *cp, char *fp, int count)
+{
+	struct elmcan *elm = (struct elmcan *) tty->disc_data;
+
+	if (!elm)
+		return;
+
+	/* Read the characters out of the buffer */
+	while (count-- && elm->rxfill < sizeof(elm->rxbuf)) {
+		if (fp && *fp++) {
+			pr_err("Error in received character stream. Check your wiring.");
+
+			spin_lock_bh(&elm->lock);
+			elm327_panic(elm);
+			spin_unlock_bh(&elm->lock);
+			return;
+		}
+		if (*cp != 0) {
+			elm->rxbuf[elm->rxfill++] = *cp;
+		}
+		cp++;
+	}
+
+	if (count >= 0) {
+		pr_err("Receive buffer overflowed. Bad chip or wiring?");
+
+		spin_lock_bh(&elm->lock);
+		elm327_panic(elm);
+		spin_unlock_bh(&elm->lock);
+		return;
+	}
+
+	spin_lock_bh(&elm->lock);
+	elm327_parse_rxbuf(elm);
+	spin_unlock_bh(&elm->lock);
+}
+
+/* Write out remaining transmit buffer.
+ * Scheduled when TTY is writable.
+ */
+static void elmcan_ldisc_tx_worker(struct work_struct *work)
+{
+	struct elmcan *elm = container_of(work, struct elmcan, tx_work);
+	ssize_t actual;
+
+	spin_lock_bh(&elm->lock);
+	/* First make sure we're connected. */
+	if (!elm->tty || !netif_running(elm->dev)) {
+		spin_unlock_bh(&elm->lock);
+		return;
+	}
+
+	if (elm->txleft <= 0)  {
+		/* Our TTY write buffer is empty:
+		 * We can start transmission of another packet
+		 */
+		clear_bit(TTY_DO_WRITE_WAKEUP, &elm->tty->flags);
+		spin_unlock_bh(&elm->lock);
+		netif_wake_queue(elm->dev);
+		return;
+	}
+
+	actual = elm->tty->ops->write(elm->tty, elm->txhead, elm->txleft);
+	if (actual < 0) {
+		pr_err("Failed to write to tty for %s.\n", elm->dev->name);
+		elm327_panic(elm);
+	}
+
+	elm->txleft -= actual;
+	elm->txhead += actual;
+	spin_unlock_bh(&elm->lock);
+}
+
+
+/*
+ * Called by the driver when there's room for more data.
+ * Schedule the transmit.
+ */
+static void elmcan_ldisc_tx_wakeup(struct tty_struct *tty)
+{
+	struct elmcan *elm = tty->disc_data;
+
+	schedule_work(&elm->tx_work);
+}
+
+
+
+/* Some fake bit timings to allow bitrate setting */
+static const struct can_bittiming_const elmcan_bittiming_const = {
+	.name = "elmcan",
+	.tseg1_min = 1,
+	.tseg1_max = 1,
+	.tseg2_min = 0,
+	.tseg2_max = 0,
+	.sjw_max = 1,
+	.brp_min = 1,
+	.brp_max = 500,
+	.brp_inc = 1,
+};
+
+/*
+ * Open the high-level part of the elmcan channel.
+ * This function is called by the TTY module when the
+ * elmcan line discipline is called for.
+ *
+ * Called in process context serialized from other ldisc calls.
+ */
+static int elmcan_ldisc_open(struct tty_struct *tty)
+{
+	struct net_device *dev;
+	struct elmcan *elm;
+	int err;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (!tty->ops->write)
+		return -EOPNOTSUPP;
+
+	elm = tty->disc_data;
+
+	/* First make sure we're not already connected.
+	 * Also, protect against simlutaneous open calls. */
+	spin_lock_bh(&elmcan_open_lock);
+	if (elm) {
+		spin_unlock_bh(&elmcan_open_lock);
+		return -EEXIST;
+	}
+	spin_unlock_bh(&elmcan_open_lock);
+
+	/* OK.  Find a free elmcan channel to use. */
+	dev = alloc_candev(sizeof(struct elmcan), 0);
+	if (!dev)
+		return -ENFILE;
+	elm = netdev_priv(dev);
+
+	/* Configure TTY interface */
+	tty->receive_room = 65536; /* We don't flow control */
+	elm->txleft = 0; /* Clear TTY TX buffer */
+	spin_lock_init(&elm->lock);
+	INIT_WORK(&elm->tx_work, elmcan_ldisc_tx_worker);
+
+	/* Configure CAN metadata */
+	elm->can.state = CAN_STATE_STOPPED;
+	elm->can.clock.freq = 1000000;
+	elm->can.bittiming_const = &elmcan_bittiming_const;
+	elm->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY;
+
+	/* Configure netlink interface */
+	elm->dev = dev;
+	dev->netdev_ops = &elmcan_netdev_ops;
+
+	/* Mark ldisc channel as alive */
+	elm->tty = tty;
+	tty->disc_data = elm;
+
+	devm_can_led_init(elm->dev);
+
+	/* Let 'er rip */
+	err = register_candev(elm->dev);
+	if (err) {
+		free_candev(elm->dev);
+		return err;
+	}
+
+	return 0;
+}
+
+/*
+ * Close down an elmcan channel.
+ * This means flushing out any pending queues, and then returning. This
+ * call is serialized against other ldisc functions.
+ *
+ * We also use this method for a hangup event.
+ */
+static void elmcan_ldisc_close(struct tty_struct *tty)
+{
+	struct elmcan *elm = (struct elmcan *) tty->disc_data;
+
+	/* First make sure we're connected. */
+	if (!elm)
+		return;
+
+	/* Flush network side */
+	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);
+
+	/* Flush TTY side */
+	flush_work(&elm->tx_work);
+
+	/* Free our memory */
+	free_candev(elm->dev);
+}
+
+static int elmcan_ldisc_hangup(struct tty_struct *tty)
+{
+	elmcan_ldisc_close(tty);
+	return 0;
+}
+
+/* Perform I/O control on an active elmcan channel. */
+static int elmcan_ldisc_ioctl(struct tty_struct *tty, struct file *file,
+			unsigned int cmd, unsigned long arg)
+{
+	struct elmcan *elm = (struct elmcan *) tty->disc_data;
+	unsigned int tmp;
+
+	/* First make sure we're connected. */
+	if (!elm)
+		return -EINVAL;
+
+	switch (cmd) {
+	case SIOCGIFNAME:
+		tmp = strlen(elm->dev->name) + 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, file, cmd, arg);
+	}
+}
+
+static struct tty_ldisc_ops elmcan_ldisc = {
+	.owner		= THIS_MODULE,
+	.magic		= TTY_LDISC_MAGIC,
+	.name		= "elmcan",
+	.receive_buf	= elmcan_ldisc_rx,
+	.write_wakeup	= elmcan_ldisc_tx_wakeup,
+	.open		= elmcan_ldisc_open,
+	.close		= elmcan_ldisc_close,
+	.hangup		= elmcan_ldisc_hangup,
+	.ioctl		= elmcan_ldisc_ioctl,
+};
+
+
+
+
+
+ /************************************************************************
+  *			Module init/exit				 *
+  ************************************************************************/
+
+static int __init elmcan_init(void)
+{
+	int status;
+
+	pr_info("ELM327 based best-effort CAN interface driver\n");
+	pr_info("This device is severely limited as a CAN interface, see documentation.\n");
+
+	/* Fill in our line protocol discipline, and register it */
+	status = tty_register_ldisc(N_ELMCAN, &elmcan_ldisc);
+	if (status) {
+		pr_err("can't register line discipline\n");
+	}
+	return status;
+}
+
+static void __exit elmcan_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.
+	 */
+	int status;
+
+	status = tty_unregister_ldisc(N_ELMCAN);
+	if (status) {
+		pr_err("Can't unregister line discipline (error: %d)\n", status);
+	}
+}
+
+module_init(elmcan_init);
+module_exit(elmcan_exit);
diff --git a/readme.rst b/readme.rst
new file mode 100644
index 0000000..4911664
--- /dev/null
+++ b/readme.rst
@@ -0,0 +1,279 @@
+Linux SocketCAN driver for ELM327
+==================================
+
+Authors
+--------
+
+Max Staudt <elmcan@enpas.org>
+
+
+
+Motivation
+-----------
+
+CAN adapters are expensive, few, and far between.
+ELM327 interfaces are cheap and plentiful.
+
+This driver aims to lower the initial cost for hackers interested in
+working with CAN buses.
+
+
+
+Introduction
+-------------
+
+This driver is an effort to turn abundant ELM327 based OBD interfaces
+into full-fledged (as far as possible) CAN interfaces.
+
+Since the ELM327 was never meant to be a stand-alone CAN controller,
+the driver has to switch between its modes asa quickly as possible in
+order to approximate full-duplex operation.
+
+As such, elmcan is a best-effort driver. However, this is more than
+enough to implement simple request-response protocols (such as OBD II),
+and to monitor broadcast messages on a bus (such as in a vehicle).
+
+Most ELM327s come as nondescript serial devices, attached via USB or
+Bluetooth. The driver cannot recognize them by itself, and as such it
+is up to the user to attach it in form of a TTY line discipline
+(similar to PPP, SLIP, slcan, ...).
+
+This driver is meant for ELM327 versions 1.4b and up, see below for
+known limitations in older controllers and clones.
+
+
+
+Data sheet
+-----------
+
+The official data sheets can be found at ELM electronics' home page:
+
+  https://www.elmelectronics.com/
+
+
+
+How to check the controller version
+------------------------------------
+
+Use a terminal program to attach to the controller.
+
+After issuing the "``AT WS``" command, the controller will respond with
+its version::
+
+    >AT WS
+
+
+    ELM327 v1.4b
+
+    >
+
+
+
+How to attach the line discipline
+----------------------------------
+
+Every ELM327 chip is factory programmed to operate at a serial setting
+of 38400 baud/s, 8 data bits, no parity, 1 stopbit.
+
+The line discipline can be attached on a command prompt as follows::
+
+    sudo ldattach \
+           --debug \
+           --speed 38400 \
+           --eightbits \
+           --noparity \
+           --onestopbit \
+           --iflag -ICRNL,INLCR,-IXOFF \
+           26 \
+           /dev/ttyUSB0
+
+To change the ELM327's serial settings, please refer to its data
+sheet. This needs to be done before attaching the line discipline.
+
+
+
+Known limitations of the controller
+------------------------------------
+
+- All versions
+
+  No automatic full duplex operation is supported. The driver will
+  switch between input/output mode as quickly as possible.
+
+  The length of outgoing RTR frames cannot be set. In fact, some
+  clones (tested with one identifying as "``v1.5``") are unable to
+  send RTR frames at all.
+
+  We don't have a way to get real-time notifications on CAN errors.
+  While there is a command (``AT CS``) to retrieve some basic stats,
+  we don't poll it as it would force us to interrupt reception mode.
+
+
+- Versions prior to 1.4b
+
+  These versions do not send CAN ACKs when in monitoring mode (AT MA).
+  However, they do send ACKs while waiting for a reply immediately
+  after sending a frame. The driver maximizes this time to make the
+  controller as useful as possible.
+
+  Starting with version 1.4b, the ELM327 supports the "``AT CSM``"
+  command, and the "listen-only" CAN option will take effect.
+
+
+- Versions prior to 1.4
+
+  These chips do not support the "``AT PB``" command, and thus cannot
+  change bitrate or SFF/EFF mode on-the-fly. This will have to be
+  programmed by the user before attaching the line discipline. See the
+  data sheet for details.
+
+
+- Versions prior to 1.3
+
+  These chips cannot be used at all with elmcan. They do not support
+  the "``AT D1``", which is necessary to avoid parsing conflicts on
+  incoming data, as well as distinction of RTR frame lengths.
+
+  Specifically, this allows for easy distinction of SFF and EFF
+  frames, and to check whether frames are complete. While it is possible
+  to deduce the type and length from the length of the line the ELM327
+  sends us, this method fails when the ELM327's UART output buffer
+  overruns. It may abort sending in the middle of the line, which will
+  then be mistaken for something else.
+
+
+
+Known limitations of the driver
+--------------------------------
+
+- No 8/7 timing.
+
+  ELM327 can only set CAN bitrates that are of the form 500000/n, where
+  n is an integer divisor.
+  However there is an exception: With a separate flag, it may set the
+  speed to be 8/7 of the speed indicated by the divisor.
+  This mode is not currently implemented.
+
+- No evaluation of command responses.
+
+  The ELM327 will reply with OK when a command is understood, and with ?
+  when it is not. The driver does not currently check this, and simply
+  assumes that the chip understands every command.
+  The driver is built such that functionality degrades gracefully
+  nevertheless. See the section on known limitations of the controller.
+
+- No use of hardware CAN ID filtering
+
+  An ELM327's UART sending buffer will easily overflow on heavy CAN bus
+  load, resulting in the "``BUFFER FULL``" message. Using the hardware
+  filters available through "``AT CF xxx``" and "``AT CM xxx``" would be
+  helpful here, however SocketCAN does not currently provide a facility
+  to make use of such hardware features.
+
+- No BUS-OFF state and automatic restart
+
+  We currently reset the ELM327 and generate error frames manually.
+  In the future, we may be able to use ``can_bus_off()`` and its siblings.
+
+
+
+Communication example
+----------------------
+
+This is a short and incomplete introduction on how to talk to an ELM327.
+
+
+The ELM327 has two modes:
+
+- Command mode
+- Reception mode
+
+In command mode, it expects one command per line, terminated by CR.
+By default, the prompt is a "``>``", after which a command can be
+entered::
+
+    >ATE1
+    OK
+    >
+
+The init script in the driver switches off several configuration options
+that are only meaningful in the original OBD scenario the chip is meant
+for, and are actually a hindrance for elmcan.
+
+
+When a command is not recognized, such as by an older version of the
+ELM327, a question mark is printed as a response instead of OK::
+
+    >ATUNKNOWN
+    ?
+    >
+
+At present, elmcan does not evaluate this response and silently assumes
+that all commands are recognized. It is structured such that it will
+degrade gracefully when a command is unknown. See the sections above on
+known limitations for details.
+
+
+When a CAN frame is to be sent, the target address is configured, after
+which the frame is sent as a command that consists of the data's hex
+dump::
+
+    >ATSH123
+    OK
+    >DEADBEEF12345678
+    OK
+    >
+
+The above interaction sends the frame "``DE AD BE EF 12 34 56 78``" with
+the 11 bit CAN ID ``0x123``.
+For this to function, the controller must be configured for 11 bit CAN
+ID sending mode (using "``AT PB``", see code or datasheet).
+
+
+Once a frame has been sent and wait-for-reply mode is on (ATR1,
+configured on listen-only=off), or when the reply timeout expires and
+the driver sets the controller into monitoring mode (``ATMA``), the ELM327
+will send one line for each received CAN frame, consisting of CAN ID,
+DLC, and data::
+
+    123 8 DEADBEEF12345678
+
+For 29 bit CAN frames, the address format is slightly different, which
+elmcan uses to tell the two apart::
+
+    12 34 56 78 8 DEADBEEF12345678
+
+The ELM327 will receive both 11 and 29 bit frames - the current CAN
+config (``ATPB``) does not matter.
+
+
+If the ELM327's internal UART sending buffer runs full, it will abort
+the monitoring mode, print "BUFFER FULL" and drop back into command
+mode. Note that in this case, unlike with other error messages, the
+error message may appear on the same line as the last (usually
+incomplete) data frame::
+
+    12 34 56 78 8 DEADBEEF123 BUFFER FULL
+
+
+
+To Do list for future development
+----------------------------------
+
+- Handle ``write()`` error
+
+- Rename ``elm327_panic()``
+
+- No auto-restart in ``elm327_panic()``?
+
+- Stop current function when in ``elm327_panic()``
+
+- ``if (!elm)``: Race with ``ldisc_close()``
+
+- ``elm->dev``: Race in ``ldisc_ioctl()``
+
+- DMA capable rx/tx buffers
+
+- fixup constants, constant for '``>``'
+
+- flushing of ``tx_work`` is too late in ``ldisc_close()``