drivers/tty/n_r3964.c

// SPDX-License-Identifier: GPL-1.0+
/* r3964 linediscipline for linux
 *
 * -----------------------------------------------------------
 * Copyright by 
 * Philips Automation Projects
 * Kassel (Germany)
 * -----------------------------------------------------------
 * Author:
 * L. Haag
 *
 * $Log: n_r3964.c,v $
 * Revision 1.10  2001/03/18 13:02:24  dwmw2
 * Fix timer usage, use spinlocks properly.
 *
 * Revision 1.9  2001/03/18 12:52:14  dwmw2
 * Merge changes in 2.4.2
 *
 * Revision 1.8  2000/03/23 14:14:54  dwmw2
 * Fix race in sleeping in r3964_read()
 *
 * Revision 1.7  1999/28/08 11:41:50  dwmw2
 * Port to 2.3 kernel
 *
 * Revision 1.6  1998/09/30 00:40:40  dwmw2
 * Fixed compilation on 2.0.x kernels
 * Updated to newly registered tty-ldisc number 9
 *
 * Revision 1.5  1998/09/04 21:57:36  dwmw2
 * Signal handling bug fixes, port to 2.1.x.
 *
 * Revision 1.4  1998/04/02 20:26:59  lhaag
 * select, blocking, ...
 *
 * Revision 1.3  1998/02/12 18:58:43  root
 * fixed some memory leaks
 * calculation of checksum characters
 *
 * Revision 1.2  1998/02/07 13:03:34  root
 * ioctl read_telegram
 *
 * Revision 1.1  1998/02/06 19:21:03  root
 * Initial revision
 *
 *
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/interrupt.h>
#include <linux/ptrace.h>
#include <linux/ioport.h>
#include <linux/in.h>
#include <linux/slab.h>
#include <linux/tty.h>
#include <linux/errno.h>
#include <linux/string.h>	/* used in new tty drivers */
#include <linux/signal.h>	/* used in new tty drivers */
#include <linux/ioctl.h>
#include <linux/n_r3964.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/uaccess.h>

/*#define DEBUG_QUEUE*/

/* Log successful handshake and protocol operations  */
/*#define DEBUG_PROTO_S*/

/* Log handshake and protocol errors: */
/*#define DEBUG_PROTO_E*/

/* Log Linediscipline operations (open, close, read, write...): */
/*#define DEBUG_LDISC*/

/* Log module and memory operations (init, cleanup; kmalloc, kfree): */
/*#define DEBUG_MODUL*/

/* Macro helpers for debug output: */
#define TRACE(format, args...) printk("r3964: " format "\n" , ## args)

#ifdef DEBUG_MODUL
#define TRACE_M(format, args...) printk("r3964: " format "\n" , ## args)
#else
#define TRACE_M(fmt, arg...) do {} while (0)
#endif
#ifdef DEBUG_PROTO_S
#define TRACE_PS(format, args...) printk("r3964: " format "\n" , ## args)
#else
#define TRACE_PS(fmt, arg...) do {} while (0)
#endif
#ifdef DEBUG_PROTO_E
#define TRACE_PE(format, args...) printk("r3964: " format "\n" , ## args)
#else
#define TRACE_PE(fmt, arg...) do {} while (0)
#endif
#ifdef DEBUG_LDISC
#define TRACE_L(format, args...) printk("r3964: " format "\n" , ## args)
#else
#define TRACE_L(fmt, arg...) do {} while (0)
#endif
#ifdef DEBUG_QUEUE
#define TRACE_Q(format, args...) printk("r3964: " format "\n" , ## args)
#else
#define TRACE_Q(fmt, arg...) do {} while (0)
#endif
static void add_tx_queue(struct r3964_info *, struct r3964_block_header *);
static void remove_from_tx_queue(struct r3964_info *pInfo, int error_code);
static void put_char(struct r3964_info *pInfo, unsigned char ch);
static void trigger_transmit(struct r3964_info *pInfo);
static void retry_transmit(struct r3964_info *pInfo);
static void transmit_block(struct r3964_info *pInfo);
static void receive_char(struct r3964_info *pInfo, const unsigned char c);
static void receive_error(struct r3964_info *pInfo, const char flag);
static void on_timeout(struct timer_list *t);
static int enable_signals(struct r3964_info *pInfo, struct pid *pid, int arg);
static int read_telegram(struct r3964_info *pInfo, struct pid *pid,
		unsigned char __user * buf);
static void add_msg(struct r3964_client_info *pClient, int msg_id, int arg,
		int error_code, struct r3964_block_header *pBlock);
static struct r3964_message *remove_msg(struct r3964_info *pInfo,
		struct r3964_client_info *pClient);
static void remove_client_block(struct r3964_info *pInfo,
		struct r3964_client_info *pClient);

static int r3964_open(struct tty_struct *tty);
static void r3964_close(struct tty_struct *tty);
static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
		unsigned char __user * buf, size_t nr);
static ssize_t r3964_write(struct tty_struct *tty, struct file *file,
		const unsigned char *buf, size_t nr);
static int r3964_ioctl(struct tty_struct *tty, struct file *file,
		unsigned int cmd, unsigned long arg);
static void r3964_set_termios(struct tty_struct *tty, struct ktermios *old);
static unsigned int r3964_poll(struct tty_struct *tty, struct file *file,
		struct poll_table_struct *wait);
static void r3964_receive_buf(struct tty_struct *tty, const unsigned char *cp,
		char *fp, int count);

static struct tty_ldisc_ops tty_ldisc_N_R3964 = {
	.owner = THIS_MODULE,
	.magic = TTY_LDISC_MAGIC,
	.name = "R3964",
	.open = r3964_open,
	.close = r3964_close,
	.read = r3964_read,
	.write = r3964_write,
	.ioctl = r3964_ioctl,
	.set_termios = r3964_set_termios,
	.poll = r3964_poll,
	.receive_buf = r3964_receive_buf,
};

static void dump_block(const unsigned char *block, unsigned int length)
{
	unsigned int i, j;
	char linebuf[16 * 3 + 1];

	for (i = 0; i < length; i += 16) {
		for (j = 0; (j < 16) && (j + i < length); j++) {
			sprintf(linebuf + 3 * j, "%02x ", block[i + j]);
		}
		linebuf[3 * j] = '\0';
		TRACE_PS("%s", linebuf);
	}
}

/*************************************************************
 * Driver initialisation
 *************************************************************/

/*************************************************************
 * Module support routines
 *************************************************************/

static void __exit r3964_exit(void)
{
	int status;

	TRACE_M("cleanup_module()");

	status = tty_unregister_ldisc(N_R3964);

	if (status != 0) {
		printk(KERN_ERR "r3964: error unregistering linediscipline: "
				"%d\n", status);
	} else {
		TRACE_L("linediscipline successfully unregistered");
	}
}

static int __init r3964_init(void)
{
	int status;

	printk("r3964: Philips r3964 Driver $Revision: 1.10 $\n");

	/*
	 * Register the tty line discipline
	 */

	status = tty_register_ldisc(N_R3964, &tty_ldisc_N_R3964);
	if (status == 0) {
		TRACE_L("line discipline %d registered", N_R3964);
		TRACE_L("flags=%x num=%x", tty_ldisc_N_R3964.flags,
			tty_ldisc_N_R3964.num);
		TRACE_L("open=%p", tty_ldisc_N_R3964.open);
		TRACE_L("tty_ldisc_N_R3964 = %p", &tty_ldisc_N_R3964);
	} else {
		printk(KERN_ERR "r3964: error registering line discipline: "
				"%d\n", status);
	}
	return status;
}

module_init(r3964_init);
module_exit(r3964_exit);

/*************************************************************
 * Protocol implementation routines
 *************************************************************/

static void add_tx_queue(struct r3964_info *pInfo,
			 struct r3964_block_header *pHeader)
{
	unsigned long flags;

	spin_lock_irqsave(&pInfo->lock, flags);

	pHeader->next = NULL;

	if (pInfo->tx_last == NULL) {
		pInfo->tx_first = pInfo->tx_last = pHeader;
	} else {
		pInfo->tx_last->next = pHeader;
		pInfo->tx_last = pHeader;
	}

	spin_unlock_irqrestore(&pInfo->lock, flags);

	TRACE_Q("add_tx_queue %p, length %d, tx_first = %p",
		pHeader, pHeader->length, pInfo->tx_first);
}

static void remove_from_tx_queue(struct r3964_info *pInfo, int error_code)
{
	struct r3964_block_header *pHeader;
	unsigned long flags;
#ifdef DEBUG_QUEUE
	struct r3964_block_header *pDump;
#endif

	pHeader = pInfo->tx_first;

	if (pHeader == NULL)
		return;

#ifdef DEBUG_QUEUE
	printk("r3964: remove_from_tx_queue: %p, length %u - ",
		pHeader, pHeader->length);
	for (pDump = pHeader; pDump; pDump = pDump->next)
		printk("%p ", pDump);
	printk("\n");
#endif

	if (pHeader->owner) {
		if (error_code) {
			add_msg(pHeader->owner, R3964_MSG_ACK, 0,
				error_code, NULL);
		} else {
			add_msg(pHeader->owner, R3964_MSG_ACK, pHeader->length,
				error_code, NULL);
		}
		wake_up_interruptible(&pInfo->tty->read_wait);
	}

	spin_lock_irqsave(&pInfo->lock, flags);

	pInfo->tx_first = pHeader->next;
	if (pInfo->tx_first == NULL) {
		pInfo->tx_last = NULL;
	}

	spin_unlock_irqrestore(&pInfo->lock, flags);

	kfree(pHeader);
	TRACE_M("remove_from_tx_queue - kfree %p", pHeader);

	TRACE_Q("remove_from_tx_queue: tx_first = %p, tx_last = %p",
		pInfo->tx_first, pInfo->tx_last);
}

static void add_rx_queue(struct r3964_info *pInfo,
			 struct r3964_block_header *pHeader)
{
	unsigned long flags;

	spin_lock_irqsave(&pInfo->lock, flags);

	pHeader->next = NULL;

	if (pInfo->rx_last == NULL) {
		pInfo->rx_first = pInfo->rx_last = pHeader;
	} else {
		pInfo->rx_last->next = pHeader;
		pInfo->rx_last = pHeader;
	}
	pInfo->blocks_in_rx_queue++;

	spin_unlock_irqrestore(&pInfo->lock, flags);

	TRACE_Q("add_rx_queue: %p, length = %d, rx_first = %p, count = %d",
		pHeader, pHeader->length,
		pInfo->rx_first, pInfo->blocks_in_rx_queue);
}

static void remove_from_rx_queue(struct r3964_info *pInfo,
				 struct r3964_block_header *pHeader)
{
	unsigned long flags;
	struct r3964_block_header *pFind;

	if (pHeader == NULL)
		return;

	TRACE_Q("remove_from_rx_queue: rx_first = %p, rx_last = %p, count = %d",
		pInfo->rx_first, pInfo->rx_last, pInfo->blocks_in_rx_queue);
	TRACE_Q("remove_from_rx_queue: %p, length %u",
		pHeader, pHeader->length);

	spin_lock_irqsave(&pInfo->lock, flags);

	if (pInfo->rx_first == pHeader) {
		/* Remove the first block in the linked list: */
		pInfo->rx_first = pHeader->next;

		if (pInfo->rx_first == NULL) {
			pInfo->rx_last = NULL;
		}
		pInfo->blocks_in_rx_queue--;
	} else {
		/* Find block to remove: */
		for (pFind = pInfo->rx_first; pFind; pFind = pFind->next) {
			if (pFind->next == pHeader) {
				/* Got it. */
				pFind->next = pHeader->next;
				pInfo->blocks_in_rx_queue--;
				if (pFind->next == NULL) {
					/* Oh, removed the last one! */
					pInfo->rx_last = pFind;
				}
				break;
			}
		}
	}

	spin_unlock_irqrestore(&pInfo->lock, flags);

	kfree(pHeader);
	TRACE_M("remove_from_rx_queue - kfree %p", pHeader);

	TRACE_Q("remove_from_rx_queue: rx_first = %p, rx_last = %p, count = %d",
		pInfo->rx_first, pInfo->rx_last, pInfo->blocks_in_rx_queue);
}

static void put_char(struct r3964_info *pInfo, unsigned char ch)
{
	struct tty_struct *tty = pInfo->tty;
	/* FIXME: put_char should not be called from an IRQ */
	tty_put_char(tty, ch);
	pInfo->bcc ^= ch;
}

static void flush(struct r3964_info *pInfo)
{
	struct tty_struct *tty = pInfo->tty;

	if (tty == NULL || tty->ops->flush_chars == NULL)
		return;
	tty->ops->flush_chars(tty);
}

static void trigger_transmit(struct r3964_info *pInfo)
{
	unsigned long flags;

	spin_lock_irqsave(&pInfo->lock, flags);

	if ((pInfo->state == R3964_IDLE) && (pInfo->tx_first != NULL)) {
		pInfo->state = R3964_TX_REQUEST;
		pInfo->nRetry = 0;
		pInfo->flags &= ~R3964_ERROR;
		mod_timer(&pInfo->tmr, jiffies + R3964_TO_QVZ);

		spin_unlock_irqrestore(&pInfo->lock, flags);

		TRACE_PS("trigger_transmit - sent STX");

		put_char(pInfo, STX);
		flush(pInfo);

		pInfo->bcc = 0;
	} else {
		spin_unlock_irqrestore(&pInfo->lock, flags);
	}
}

static void retry_transmit(struct r3964_info *pInfo)
{
	if (pInfo->nRetry < R3964_MAX_RETRIES) {
		TRACE_PE("transmission failed. Retry #%d", pInfo->nRetry);
		pInfo->bcc = 0;
		put_char(pInfo, STX);
		flush(pInfo);
		pInfo->state = R3964_TX_REQUEST;
		pInfo->nRetry++;
		mod_timer(&pInfo->tmr, jiffies + R3964_TO_QVZ);
	} else {
		TRACE_PE("transmission failed after %d retries",
			 R3964_MAX_RETRIES);

		remove_from_tx_queue(pInfo, R3964_TX_FAIL);

		put_char(pInfo, NAK);
		flush(pInfo);
		pInfo->state = R3964_IDLE;

		trigger_transmit(pInfo);
	}
}

static void transmit_block(struct r3964_info *pInfo)
{
	struct tty_struct *tty = pInfo->tty;
	struct r3964_block_header *pBlock = pInfo->tx_first;
	int room = 0;

	if (tty == NULL || pBlock == NULL) {
		return;
	}

	room = tty_write_room(tty);

	TRACE_PS("transmit_block %p, room %d, length %d",
		 pBlock, room, pBlock->length);

	while (pInfo->tx_position < pBlock->length) {
		if (room < 2)
			break;

		if (pBlock->data[pInfo->tx_position] == DLE) {
			/* send additional DLE char: */
			put_char(pInfo, DLE);
		}
		put_char(pInfo, pBlock->data[pInfo->tx_position++]);

		room--;
	}

	if ((pInfo->tx_position == pBlock->length) && (room >= 3)) {
		put_char(pInfo, DLE);
		put_char(pInfo, ETX);
		if (pInfo->flags & R3964_BCC) {
			put_char(pInfo, pInfo->bcc);
		}
		pInfo->state = R3964_WAIT_FOR_TX_ACK;
		mod_timer(&pInfo->tmr, jiffies + R3964_TO_QVZ);
	}
	flush(pInfo);
}

static void on_receive_block(struct r3964_info *pInfo)
{
	unsigned int length;
	struct r3964_client_info *pClient;
	struct r3964_block_header *pBlock;

	length = pInfo->rx_position;

	/* compare byte checksum characters: */
	if (pInfo->flags & R3964_BCC) {
		if (pInfo->bcc != pInfo->last_rx) {
			TRACE_PE("checksum error - got %x but expected %x",
				 pInfo->last_rx, pInfo->bcc);
			pInfo->flags |= R3964_CHECKSUM;
		}
	}

	/* check for errors (parity, overrun,...): */
	if (pInfo->flags & R3964_ERROR) {
		TRACE_PE("on_receive_block - transmission failed error %x",
			 pInfo->flags & R3964_ERROR);

		put_char(pInfo, NAK);
		flush(pInfo);
		if (pInfo->nRetry < R3964_MAX_RETRIES) {
			pInfo->state = R3964_WAIT_FOR_RX_REPEAT;
			pInfo->nRetry++;
			mod_timer(&pInfo->tmr, jiffies + R3964_TO_RX_PANIC);
		} else {
			TRACE_PE("on_receive_block - failed after max retries");
			pInfo->state = R3964_IDLE;
		}
		return;
	}

	/* received block; submit DLE: */
	put_char(pInfo, DLE);
	flush(pInfo);
	del_timer_sync(&pInfo->tmr);
	TRACE_PS(" rx success: got %d chars", length);

	/* prepare struct r3964_block_header: */
	pBlock = kmalloc(length + sizeof(struct r3964_block_header),
			GFP_KERNEL);
	TRACE_M("on_receive_block - kmalloc %p", pBlock);

	if (pBlock == NULL)
		return;

	pBlock->length = length;
	pBlock->data = ((unsigned char *)pBlock) +
			sizeof(struct r3964_block_header);
	pBlock->locks = 0;
	pBlock->next = NULL;
	pBlock->owner = NULL;

	memcpy(pBlock->data, pInfo->rx_buf, length);

	/* queue block into rx_queue: */
	add_rx_queue(pInfo, pBlock);

	/* notify attached client processes: */
	for (pClient = pInfo->firstClient; pClient; pClient = pClient->next) {
		if (pClient->sig_flags & R3964_SIG_DATA) {
			add_msg(pClient, R3964_MSG_DATA, length, R3964_OK,
				pBlock);
		}
	}
	wake_up_interruptible(&pInfo->tty->read_wait);

	pInfo->state = R3964_IDLE;

	trigger_transmit(pInfo);
}

static void receive_char(struct r3964_info *pInfo, const unsigned char c)
{
	switch (pInfo->state) {
	case R3964_TX_REQUEST:
		if (c == DLE) {
			TRACE_PS("TX_REQUEST - got DLE");

			pInfo->state = R3964_TRANSMITTING;
			pInfo->tx_position = 0;

			transmit_block(pInfo);
		} else if (c == STX) {
			if (pInfo->nRetry == 0) {
				TRACE_PE("TX_REQUEST - init conflict");
				if (pInfo->priority == R3964_SLAVE) {
					goto start_receiving;
				}
			} else {
				TRACE_PE("TX_REQUEST - secondary init "
					"conflict!? Switching to SLAVE mode "
					"for next rx.");
				goto start_receiving;
			}
		} else {
			TRACE_PE("TX_REQUEST - char != DLE: %x", c);
			retry_transmit(pInfo);
		}
		break;
	case R3964_TRANSMITTING:
		if (c == NAK) {
			TRACE_PE("TRANSMITTING - got NAK");
			retry_transmit(pInfo);
		} else {
			TRACE_PE("TRANSMITTING - got invalid char");

			pInfo->state = R3964_WAIT_ZVZ_BEFORE_TX_RETRY;
			mod_timer(&pInfo->tmr, jiffies + R3964_TO_ZVZ);
		}
		break;
	case R3964_WAIT_FOR_TX_ACK:
		if (c == DLE) {
			TRACE_PS("WAIT_FOR_TX_ACK - got DLE");
			remove_from_tx_queue(pInfo, R3964_OK);

			pInfo->state = R3964_IDLE;
			trigger_transmit(pInfo);
		} else {
			retry_transmit(pInfo);
		}
		break;
	case R3964_WAIT_FOR_RX_REPEAT:
		/* FALLTHROUGH */
	case R3964_IDLE:
		if (c == STX) {
			/* Prevent rx_queue from overflow: */
			if (pInfo->blocks_in_rx_queue >=
			    R3964_MAX_BLOCKS_IN_RX_QUEUE) {
				TRACE_PE("IDLE - got STX but no space in "
						"rx_queue!");
				pInfo->state = R3964_WAIT_FOR_RX_BUF;
				mod_timer(&pInfo->tmr,
					  jiffies + R3964_TO_NO_BUF);
				break;
			}
start_receiving:
			/* Ok, start receiving: */
			TRACE_PS("IDLE - got STX");
			pInfo->rx_position = 0;
			pInfo->last_rx = 0;
			pInfo->flags &= ~R3964_ERROR;
			pInfo->state = R3964_RECEIVING;
			mod_timer(&pInfo->tmr, jiffies + R3964_TO_ZVZ);
			pInfo->nRetry = 0;
			put_char(pInfo, DLE);
			flush(pInfo);
			pInfo->bcc = 0;
		}
		break;
	case R3964_RECEIVING:
		if (pInfo->rx_position < RX_BUF_SIZE) {
			pInfo->bcc ^= c;

			if (c == DLE) {
				if (pInfo->last_rx == DLE) {
					pInfo->last_rx = 0;
					goto char_to_buf;
				}
				pInfo->last_rx = DLE;
				break;
			} else if ((c == ETX) && (pInfo->last_rx == DLE)) {
				if (pInfo->flags & R3964_BCC) {
					pInfo->state = R3964_WAIT_FOR_BCC;
					mod_timer(&pInfo->tmr,
						  jiffies + R3964_TO_ZVZ);
				} else {
					on_receive_block(pInfo);
				}
			} else {
				pInfo->last_rx = c;
char_to_buf:
				pInfo->rx_buf[pInfo->rx_position++] = c;
				mod_timer(&pInfo->tmr, jiffies + R3964_TO_ZVZ);
			}
		}
		/* else: overflow-msg? BUF_SIZE>MTU; should not happen? */
		break;
	case R3964_WAIT_FOR_BCC:
		pInfo->last_rx = c;
		on_receive_block(pInfo);
		break;
	}
}

static void receive_error(struct r3964_info *pInfo, const char flag)
{
	switch (flag) {
	case TTY_NORMAL:
		break;
	case TTY_BREAK:
		TRACE_PE("received break");
		pInfo->flags |= R3964_BREAK;
		break;
	case TTY_PARITY:
		TRACE_PE("parity error");
		pInfo->flags |= R3964_PARITY;
		break;
	case TTY_FRAME:
		TRACE_PE("frame error");
		pInfo->flags |= R3964_FRAME;
		break;
	case TTY_OVERRUN:
		TRACE_PE("frame overrun");
		pInfo->flags |= R3964_OVERRUN;
		break;
	default:
		TRACE_PE("receive_error - unknown flag %d", flag);
		pInfo->flags |= R3964_UNKNOWN;
		break;
	}
}

static void on_timeout(struct timer_list *t)
{
	struct r3964_info *pInfo = from_timer(pInfo, t, tmr);

	switch (pInfo->state) {
	case R3964_TX_REQUEST:
		TRACE_PE("TX_REQUEST - timeout");
		retry_transmit(pInfo);
		break;
	case R3964_WAIT_ZVZ_BEFORE_TX_RETRY:
		put_char(pInfo, NAK);
		flush(pInfo);
		retry_transmit(pInfo);
		break;
	case R3964_WAIT_FOR_TX_ACK:
		TRACE_PE("WAIT_FOR_TX_ACK - timeout");
		retry_transmit(pInfo);
		break;
	case R3964_WAIT_FOR_RX_BUF:
		TRACE_PE("WAIT_FOR_RX_BUF - timeout");
		put_char(pInfo, NAK);
		flush(pInfo);
		pInfo->state = R3964_IDLE;
		break;
	case R3964_RECEIVING:
		TRACE_PE("RECEIVING - timeout after %d chars",
			 pInfo->rx_position);
		put_char(pInfo, NAK);
		flush(pInfo);
		pInfo->state = R3964_IDLE;
		break;
	case R3964_WAIT_FOR_RX_REPEAT:
		TRACE_PE("WAIT_FOR_RX_REPEAT - timeout");
		pInfo->state = R3964_IDLE;
		break;
	case R3964_WAIT_FOR_BCC:
		TRACE_PE("WAIT_FOR_BCC - timeout");
		put_char(pInfo, NAK);
		flush(pInfo);
		pInfo->state = R3964_IDLE;
		break;
	}
}

static struct r3964_client_info *findClient(struct r3964_info *pInfo,
		struct pid *pid)
{
	struct r3964_client_info *pClient;

	for (pClient = pInfo->firstClient; pClient; pClient = pClient->next) {
		if (pClient->pid == pid) {
			return pClient;
		}
	}
	return NULL;
}

static int enable_signals(struct r3964_info *pInfo, struct pid *pid, int arg)
{
	struct r3964_client_info *pClient;
	struct r3964_client_info **ppClient;
	struct r3964_message *pMsg;

	if ((arg & R3964_SIG_ALL) == 0) {
		/* Remove client from client list */
		for (ppClient = &pInfo->firstClient; *ppClient;
		     ppClient = &(*ppClient)->next) {
			pClient = *ppClient;

			if (pClient->pid == pid) {
				TRACE_PS("removing client %d from client list",
					 pid_nr(pid));
				*ppClient = pClient->next;
				while (pClient->msg_count) {
					pMsg = remove_msg(pInfo, pClient);
					if (pMsg) {
						kfree(pMsg);
						TRACE_M("enable_signals - msg "
							"kfree %p", pMsg);
					}
				}
				put_pid(pClient->pid);
				kfree(pClient);
				TRACE_M("enable_signals - kfree %p", pClient);
				return 0;
			}
		}
		return -EINVAL;
	} else {
		pClient = findClient(pInfo, pid);
		if (pClient) {
			/* update signal options */
			pClient->sig_flags = arg;
		} else {
			/* add client to client list */
			pClient = kmalloc(sizeof(struct r3964_client_info),
					GFP_KERNEL);
			TRACE_M("enable_signals - kmalloc %p", pClient);
			if (pClient == NULL)
				return -ENOMEM;

			TRACE_PS("add client %d to client list", pid_nr(pid));
			spin_lock_init(&pClient->lock);
			pClient->sig_flags = arg;
			pClient->pid = get_pid(pid);
			pClient->next = pInfo->firstClient;
			pClient->first_msg = NULL;
			pClient->last_msg = NULL;
			pClient->next_block_to_read = NULL;
			pClient->msg_count = 0;
			pInfo->firstClient = pClient;
		}
	}

	return 0;
}

static int read_telegram(struct r3964_info *pInfo, struct pid *pid,
			 unsigned char __user * buf)
{
	struct r3964_client_info *pClient;
	struct r3964_block_header *block;

	if (!buf) {
		return -EINVAL;
	}

	pClient = findClient(pInfo, pid);
	if (pClient == NULL) {
		return -EINVAL;
	}

	block = pClient->next_block_to_read;
	if (!block) {
		return 0;
	} else {
		if (copy_to_user(buf, block->data, block->length))
			return -EFAULT;

		remove_client_block(pInfo, pClient);
		return block->length;
	}

	return -EINVAL;
}

static void add_msg(struct r3964_client_info *pClient, int msg_id, int arg,
		int error_code, struct r3964_block_header *pBlock)
{
	struct r3964_message *pMsg;
	unsigned long flags;

	if (pClient->msg_count < R3964_MAX_MSG_COUNT - 1) {
queue_the_message:

		pMsg = kmalloc(sizeof(struct r3964_message),
				error_code ? GFP_ATOMIC : GFP_KERNEL);
		TRACE_M("add_msg - kmalloc %p", pMsg);
		if (pMsg == NULL) {
			return;
		}

		spin_lock_irqsave(&pClient->lock, flags);

		pMsg->msg_id = msg_id;
		pMsg->arg = arg;
		pMsg->error_code = error_code;
		pMsg->block = pBlock;
		pMsg->next = NULL;

		if (pClient->last_msg == NULL) {
			pClient->first_msg = pClient->last_msg = pMsg;
		} else {
			pClient->last_msg->next = pMsg;
			pClient->last_msg = pMsg;
		}

		pClient->msg_count++;

		if (pBlock != NULL) {
			pBlock->locks++;
		}
		spin_unlock_irqrestore(&pClient->lock, flags);
	} else {
		if ((pClient->last_msg->msg_id == R3964_MSG_ACK)
		    && (pClient->last_msg->error_code == R3964_OVERFLOW)) {
			pClient->last_msg->arg++;
			TRACE_PE("add_msg - inc prev OVERFLOW-msg");
		} else {
			msg_id = R3964_MSG_ACK;
			arg = 0;
			error_code = R3964_OVERFLOW;
			pBlock = NULL;
			TRACE_PE("add_msg - queue OVERFLOW-msg");
			goto queue_the_message;
		}
	}
	/* Send SIGIO signal to client process: */
	if (pClient->sig_flags & R3964_USE_SIGIO) {
		kill_pid(pClient->pid, SIGIO, 1);
	}
}

static struct r3964_message *remove_msg(struct r3964_info *pInfo,
					struct r3964_client_info *pClient)
{
	struct r3964_message *pMsg = NULL;
	unsigned long flags;

	if (pClient->first_msg) {
		spin_lock_irqsave(&pClient->lock, flags);

		pMsg = pClient->first_msg;
		pClient->first_msg = pMsg->next;
		if (pClient->first_msg == NULL) {
			pClient->last_msg = NULL;
		}

		pClient->msg_count--;
		if (pMsg->block) {
			remove_client_block(pInfo, pClient);
			pClient->next_block_to_read = pMsg->block;
		}
		spin_unlock_irqrestore(&pClient->lock, flags);
	}
	return pMsg;
}

static void remove_client_block(struct r3964_info *pInfo,
				struct r3964_client_info *pClient)
{
	struct r3964_block_header *block;

	TRACE_PS("remove_client_block PID %d", pid_nr(pClient->pid));

	block = pClient->next_block_to_read;
	if (block) {
		block->locks--;
		if (block->locks == 0) {
			remove_from_rx_queue(pInfo, block);
		}
	}
	pClient->next_block_to_read = NULL;
}

/*************************************************************
 * Line discipline routines
 *************************************************************/

static int r3964_open(struct tty_struct *tty)
{
	struct r3964_info *pInfo;

	TRACE_L("open");
	TRACE_L("tty=%p, PID=%d, disc_data=%p",
		tty, current->pid, tty->disc_data);

	pInfo = kmalloc(sizeof(struct r3964_info), GFP_KERNEL);
	TRACE_M("r3964_open - info kmalloc %p", pInfo);

	if (!pInfo) {
		printk(KERN_ERR "r3964: failed to alloc info structure\n");
		return -ENOMEM;
	}

	pInfo->rx_buf = kmalloc(RX_BUF_SIZE, GFP_KERNEL);
	TRACE_M("r3964_open - rx_buf kmalloc %p", pInfo->rx_buf);

	if (!pInfo->rx_buf) {
		printk(KERN_ERR "r3964: failed to alloc receive buffer\n");
		kfree(pInfo);
		TRACE_M("r3964_open - info kfree %p", pInfo);
		return -ENOMEM;
	}

	pInfo->tx_buf = kmalloc(TX_BUF_SIZE, GFP_KERNEL);
	TRACE_M("r3964_open - tx_buf kmalloc %p", pInfo->tx_buf);

	if (!pInfo->tx_buf) {
		printk(KERN_ERR "r3964: failed to alloc transmit buffer\n");
		kfree(pInfo->rx_buf);
		TRACE_M("r3964_open - rx_buf kfree %p", pInfo->rx_buf);
		kfree(pInfo);
		TRACE_M("r3964_open - info kfree %p", pInfo);
		return -ENOMEM;
	}

	spin_lock_init(&pInfo->lock);
	mutex_init(&pInfo->read_lock);
	pInfo->tty = tty;
	pInfo->priority = R3964_MASTER;
	pInfo->rx_first = pInfo->rx_last = NULL;
	pInfo->tx_first = pInfo->tx_last = NULL;
	pInfo->rx_position = 0;
	pInfo->tx_position = 0;
	pInfo->last_rx = 0;
	pInfo->blocks_in_rx_queue = 0;
	pInfo->firstClient = NULL;
	pInfo->state = R3964_IDLE;
	pInfo->flags = R3964_DEBUG;
	pInfo->nRetry = 0;

	tty->disc_data = pInfo;
	tty->receive_room = 65536;

	timer_setup(&pInfo->tmr, on_timeout, 0);

	return 0;
}

static void r3964_close(struct tty_struct *tty)
{
	struct r3964_info *pInfo = tty->disc_data;
	struct r3964_client_info *pClient, *pNext;
	struct r3964_message *pMsg;
	struct r3964_block_header *pHeader, *pNextHeader;
	unsigned long flags;

	TRACE_L("close");

	/*
	 * Make sure that our task queue isn't activated.  If it
	 * is, take it out of the linked list.
	 */
	del_timer_sync(&pInfo->tmr);

	/* Remove client-structs and message queues: */
	pClient = pInfo->firstClient;
	while (pClient) {
		pNext = pClient->next;
		while (pClient->msg_count) {
			pMsg = remove_msg(pInfo, pClient);
			if (pMsg) {
				kfree(pMsg);
				TRACE_M("r3964_close - msg kfree %p", pMsg);
			}
		}
		put_pid(pClient->pid);
		kfree(pClient);
		TRACE_M("r3964_close - client kfree %p", pClient);
		pClient = pNext;
	}
	/* Remove jobs from tx_queue: */
	spin_lock_irqsave(&pInfo->lock, flags);
	pHeader = pInfo->tx_first;
	pInfo->tx_first = pInfo->tx_last = NULL;
	spin_unlock_irqrestore(&pInfo->lock, flags);

	while (pHeader) {
		pNextHeader = pHeader->next;
		kfree(pHeader);
		pHeader = pNextHeader;
	}

	/* Free buffers: */
	kfree(pInfo->rx_buf);
	TRACE_M("r3964_close - rx_buf kfree %p", pInfo->rx_buf);
	kfree(pInfo->tx_buf);
	TRACE_M("r3964_close - tx_buf kfree %p", pInfo->tx_buf);
	kfree(pInfo);
	TRACE_M("r3964_close - info kfree %p", pInfo);
}

static ssize_t r3964_read(struct tty_struct *tty, struct file *file,
			  unsigned char __user * buf, size_t nr)
{
	struct r3964_info *pInfo = tty->disc_data;
	struct r3964_client_info *pClient;
	struct r3964_message *pMsg;
	struct r3964_client_message theMsg;
	int ret;

	TRACE_L("read()");

	/*
	 *	Internal serialization of reads.
	 */
	if (file->f_flags & O_NONBLOCK) {
		if (!mutex_trylock(&pInfo->read_lock))
			return -EAGAIN;
	} else {
		if (mutex_lock_interruptible(&pInfo->read_lock))
			return -ERESTARTSYS;
	}

	pClient = findClient(pInfo, task_pid(current));
	if (pClient) {
		pMsg = remove_msg(pInfo, pClient);
		if (pMsg == NULL) {
			/* no messages available. */
			if (file->f_flags & O_NONBLOCK) {
				ret = -EAGAIN;
				goto unlock;
			}
			/* block until there is a message: */
			wait_event_interruptible(tty->read_wait,
					(pMsg = remove_msg(pInfo, pClient)));
		}

		/* If we still haven't got a message, we must have been signalled */

		if (!pMsg) {
			ret = -EINTR;
			goto unlock;
		}

		/* deliver msg to client process: */
		theMsg.msg_id = pMsg->msg_id;
		theMsg.arg = pMsg->arg;
		theMsg.error_code = pMsg->error_code;
		ret = sizeof(struct r3964_client_message);

		kfree(pMsg);
		TRACE_M("r3964_read - msg kfree %p", pMsg);

		if (copy_to_user(buf, &theMsg, ret)) {
			ret = -EFAULT;
			goto unlock;
		}

		TRACE_PS("read - return %d", ret);
		goto unlock;
	}
	ret = -EPERM;
unlock:
	mutex_unlock(&pInfo->read_lock);
	return ret;
}

static ssize_t r3964_write(struct tty_struct *tty, struct file *file,
			   const unsigned char *data, size_t count)
{
	struct r3964_info *pInfo = tty->disc_data;
	struct r3964_block_header *pHeader;
	struct r3964_client_info *pClient;
	unsigned char *new_data;

	TRACE_L("write request, %d characters", count);
/* 
 * Verify the pointers 
 */

	if (!pInfo)
		return -EIO;

/*
 * Ensure that the caller does not wish to send too much.
 */
	if (count > R3964_MTU) {
		if (pInfo->flags & R3964_DEBUG) {
			TRACE_L(KERN_WARNING "r3964_write: truncating user "
				"packet from %u to mtu %d", count, R3964_MTU);
		}
		count = R3964_MTU;
	}
/*
 * Allocate a buffer for the data and copy it from the buffer with header prepended
 */
	new_data = kmalloc(count + sizeof(struct r3964_block_header),
			GFP_KERNEL);
	TRACE_M("r3964_write - kmalloc %p", new_data);
	if (new_data == NULL) {
		if (pInfo->flags & R3964_DEBUG) {
			printk(KERN_ERR "r3964_write: no memory\n");
		}
		return -ENOSPC;
	}

	pHeader = (struct r3964_block_header *)new_data;
	pHeader->data = new_data + sizeof(struct r3964_block_header);
	pHeader->length = count;
	pHeader->locks = 0;
	pHeader->owner = NULL;

	pClient = findClient(pInfo, task_pid(current));
	if (pClient) {
		pHeader->owner = pClient;
	}

	memcpy(pHeader->data, data, count);	/* We already verified this */

	if (pInfo->flags & R3964_DEBUG) {
		dump_block(pHeader->data, count);
	}

/*
 * Add buffer to transmit-queue:
 */
	add_tx_queue(pInfo, pHeader);
	trigger_transmit(pInfo);

	return 0;
}

static int r3964_ioctl(struct tty_struct *tty, struct file *file,
		unsigned int cmd, unsigned long arg)
{
	struct r3964_info *pInfo = tty->disc_data;
	if (pInfo == NULL)
		return -EINVAL;
	switch (cmd) {
	case R3964_ENABLE_SIGNALS:
		return enable_signals(pInfo, task_pid(current), arg);
	case R3964_SETPRIORITY:
		if (arg < R3964_MASTER || arg > R3964_SLAVE)
			return -EINVAL;
		pInfo->priority = arg & 0xff;
		return 0;
	case R3964_USE_BCC:
		if (arg)
			pInfo->flags |= R3964_BCC;
		else
			pInfo->flags &= ~R3964_BCC;
		return 0;
	case R3964_READ_TELEGRAM:
		return read_telegram(pInfo, task_pid(current),
				(unsigned char __user *)arg);
	default:
		return -ENOIOCTLCMD;
	}
}

static void r3964_set_termios(struct tty_struct *tty, struct ktermios *old)
{
	TRACE_L("set_termios");
}

/* Called without the kernel lock held - fine */
static unsigned int r3964_poll(struct tty_struct *tty, struct file *file,
			struct poll_table_struct *wait)
{
	struct r3964_info *pInfo = tty->disc_data;
	struct r3964_client_info *pClient;
	struct r3964_message *pMsg = NULL;
	unsigned long flags;
	int result = POLLOUT;

	TRACE_L("POLL");

	pClient = findClient(pInfo, task_pid(current));
	if (pClient) {
		poll_wait(file, &tty->read_wait, wait);
		spin_lock_irqsave(&pInfo->lock, flags);
		pMsg = pClient->first_msg;
		spin_unlock_irqrestore(&pInfo->lock, flags);
		if (pMsg)
			result |= POLLIN | POLLRDNORM;
	} else {
		result = -EINVAL;
	}
	return result;
}

static void r3964_receive_buf(struct tty_struct *tty, const unsigned char *cp,
			char *fp, int count)
{
	struct r3964_info *pInfo = tty->disc_data;
	const unsigned char *p;
	char *f, flags = TTY_NORMAL;
	int i;

	for (i = count, p = cp, f = fp; i; i--, p++) {
		if (f)
			flags = *f++;
		if (flags == TTY_NORMAL) {
			receive_char(pInfo, *p);
		} else {
			receive_error(pInfo, flags);
		}

	}
}

MODULE_LICENSE("GPL");
MODULE_ALIAS_LDISC(N_R3964);