path: root/drivers/net/can/can327.c

// 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>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#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(CAN