/*
 * Garmin GPS driver
 *
 * Copyright (C) 2004 Hermann Kneissel herkne@users.sourceforge.net
 *
 * The latest version of the driver can be found at
 * http://sourceforge.net/projects/garmin-gps/
 *
 * This driver has been derived from v2.1 of the visor driver.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111 USA
 */

#include <linux/config.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/timer.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
#include <linux/module.h>
#include <linux/spinlock.h>
#include <asm/uaccess.h>
#include <linux/usb.h>

/* the mode to be set when the port ist opened */
static int initial_mode = 1;

/* debug flag */
static int debug = 0;

#include "usb-serial.h"

#define GARMIN_VENDOR_ID             0x091E

/*
 * Version Information
 */

#define VERSION_MAJOR	0
#define VERSION_MINOR	23

#define _STR(s) #s
#define _DRIVER_VERSION(a,b) "v" _STR(a) "." _STR(b)
#define DRIVER_VERSION _DRIVER_VERSION(VERSION_MAJOR, VERSION_MINOR)
#define DRIVER_AUTHOR "hermann kneissel"
#define DRIVER_DESC "garmin gps driver"

/* error codes returned by the driver */
#define EINVPKT	1000	/* invalid packet structure */


// size of the header of a packet using the usb protocol
#define GARMIN_PKTHDR_LENGTH	12

// max. possible size of a packet using the serial protocol 
#define MAX_SERIAL_PKT_SIZ (3+255+3)

// max. possible size of a packet with worst case stuffing
#define MAX_SERIAL_PKT_SIZ_STUFFED MAX_SERIAL_PKT_SIZ+256

// size of a buffer able to hold a complete (no stuffing) packet
// (the document protocol does not contain packets with a larger
//  size, but in theory a packet may be 64k+12 bytes - if in
//  later protocol versions larger packet sizes occur, this value
//  should be increased accordingly, so the input buffer is always 
//  large enough the store a complete packet inclusive header)
#define GPS_IN_BUFSIZ  (GARMIN_PKTHDR_LENGTH+MAX_SERIAL_PKT_SIZ) 

// size of a buffer able to hold a complete (incl. stuffing) packet
#define GPS_OUT_BUFSIZ (GARMIN_PKTHDR_LENGTH+MAX_SERIAL_PKT_SIZ_STUFFED) 

// where to place the packet id of a serial packet, so we can
// prepend the usb-packet header without the need to move the
// packets data
#define GSP_INITIAL_OFFSET (GARMIN_PKTHDR_LENGTH-2)

// max. size of incoming private packets (header+1 param)
#define PRIVPKTSIZ (GARMIN_PKTHDR_LENGTH+4)

#define GARMIN_LAYERID_TRANSPORT  0
#define GARMIN_LAYERID_APPL      20
// our own layer-id to use for some control mechanisms
#define GARMIN_LAYERID_PRIVATE	0x01106E4B

#define GARMIN_PKTID_PVT_DATA	51
#define GARMIN_PKTID_L001_COMMAND_DATA 10

#define CMND_ABORT_TRANSFER 0

// packet ids used in private layer
#define PRIV_PKTID_SET_DEBUG	1
#define PRIV_PKTID_SET_MODE	2
#define PRIV_PKTID_INFO_REQ	3
#define PRIV_PKTID_INFO_RESP	4
#define PRIV_PKTID_RESET_REQ	5
#define PRIV_PKTID_SET_DEF_MODE	6


#define ETX	0x03
#define DLE	0x10
#define ACK	0x06
#define NAK	0x15

/* structure used to queue incoming packets */
struct garmin_packet {
	struct list_head  list;
	int               seq;
	int               size; // the real size of the data array, always > 0
	__u8              data[1];
};

/* structure used to keep the current state of the driver */
struct garmin_data {
	__u8   state;
	__u16  flags;
	__u8   mode;
	__u8   ignorePkts;
	__u8   count;
	__u8   pkt_id;
	__u32  serial_num;
	struct timer_list timer;
	struct usb_serial_port *port;
	int    seq_counter;
	int    insize;
	int    outsize;
	__u8   inbuffer [GPS_IN_BUFSIZ];  /* tty -> usb */
	__u8   outbuffer[GPS_OUT_BUFSIZ]; /* usb -> tty */
	__u8   privpkt[4*6];
	spinlock_t lock;
	struct list_head pktlist;
};


#define STATE_NEW            0
#define STATE_INITIAL_DELAY  1
#define STATE_TIMEOUT        2
#define STATE_SESSION_REQ1   3
#define STATE_SESSION_REQ2   4
#define STATE_ACTIVE         5

#define STATE_RESET	     8
#define STATE_DISCONNECTED   9
#define STATE_WAIT_TTY_ACK  10
#define STATE_GSP_WAIT_DATA 11

#define MODE_NATIVE          0
#define MODE_GARMIN_SERIAL   1

// Flags used in garmin_data.flags:
#define FLAGS_SESSION_REPLY_MASK  0x00C0
#define FLAGS_SESSION_REPLY1_SEEN 0x0080
#define FLAGS_SESSION_REPLY2_SEEN 0x0040
#define FLAGS_BULK_IN_ACTIVE      0x0020
#define FLAGS_THROTTLED           0x0010
#define CLEAR_HALT_REQUIRED       0x0001

#define FLAGS_QUEUING             0x0100
#define FLAGS_APP_RESP_SEEN       0x0200
#define FLAGS_APP_REQ_SEEN        0x0400
#define FLAGS_DROP_DATA           0x0800

#define FLAGS_GSP_SKIP            0x1000
#define FLAGS_GSP_DLESEEN         0x2000


/* function prototypes */
static void gsp_next_packet(struct garmin_data * garmin_data_p);
static int  garmin_write_bulk(struct usb_serial_port *port,
			     const unsigned char *buf, int count);

/* some special packets to be send or received */
static unsigned char const GARMIN_START_SESSION_REQ[]
	= { 0, 0, 0, 0,  5, 0, 0, 0, 0, 0, 0, 0 };
static unsigned char const GARMIN_START_SESSION_REQ2[]
	= { 0, 0, 0, 0, 16, 0, 0, 0, 0, 0, 0, 0 };
static unsigned char const GARMIN_START_SESSION_REPLY[]
	= { 0, 0, 0, 0,  6, 0, 0, 0, 4, 0, 0, 0 };
static unsigned char const GARMIN_SESSION_ACTIVE_REPLY[]
	= { 0, 0, 0, 0, 17, 0, 0, 0, 4, 0, 0, 0, 0, 16, 0, 0 };
static unsigned char const GARMIN_BULK_IN_AVAIL_REPLY[]
	= { 0, 0, 0, 0,  2, 0, 0, 0, 0, 0, 0, 0 };
static unsigned char const GARMIN_APP_LAYER_REPLY[]
	= { 0x14, 0, 0, 0 };
static unsigned char const GARMIN_START_PVT_REQ[]
	= { 20, 0, 0, 0,  10, 0, 0, 0, 2, 0, 0, 0, 49, 0 };
static unsigned char const GARMIN_STOP_PVT_REQ[]
	= { 20, 0, 0, 0,  10, 0, 0, 0, 2, 0, 0, 0, 50, 0 };
static unsigned char const GARMIN_STOP_TRANSFER_REQ[]
	= { 20, 0, 0, 0,  10, 0, 0, 0, 2, 0, 0, 0, 0, 0 };
static unsigned char const GARMIN_STOP_TRANSFER_REQ_V2[]
	= { 20, 0, 0, 0,  10, 0, 0, 0, 1, 0, 0, 0, 0 };
static unsigned char const PRIVATE_REQ[]
	=    { 0x4B, 0x6E, 0x10, 0x01,  0xFF, 0, 0, 0, 0xFF, 0, 0, 0 };


static struct usb_device_id id_table [] = {
	/* the same device id seems to be used by all usb enabled gps devices */
	{ USB_DEVICE(GARMIN_VENDOR_ID, 3 ) },
	{ }					/* Terminating entry */
};

MODULE_DEVICE_TABLE (usb, id_table);

static struct usb_driver garmin_driver = {
	.owner =	THIS_MODULE,
	.name =		"garmin_gps",
	.probe =	usb_serial_probe,
	.disconnect =	usb_serial_disconnect,
	.id_table =	id_table,
};


static inline int noResponseFromAppLayer(struct garmin_data * garmin_data_p)
{
	return ((garmin_data_p->flags
				& (FLAGS_APP_REQ_SEEN|FLAGS_APP_RESP_SEEN))
	        == FLAGS_APP_REQ_SEEN);
}


static inline int getLayerId(const __u8 *usbPacket)
{
	return __le32_to_cpup((__le32 *)(usbPacket));
}

static inline int getPacketId(const __u8 *usbPacket)
{
	return __le32_to_cpup((__le32 *)(usbPacket+4));
}

static inline int getDataLength(const __u8 *usbPacket)
{
	return __le32_to_cpup((__le32 *)(usbPacket+8));
}


/*
 * check if the usb-packet in buf contains an abort-transfer command.
 * (if yes, all queued data will be dropped)
 */
static inline int isAbortTrfCmnd(const unsigned char *buf)
{
	if (0 == memcmp(buf, GARMIN_STOP_TRANSFER_REQ, 
	                sizeof(GARMIN_STOP_TRANSFER_REQ)) ||
	    0 == memcmp(buf, GARMIN_STOP_TRANSFER_REQ_V2, 
	                sizeof(GARMIN_STOP_TRANSFER_REQ_V2)))
		return 1;
	else
		return 0;
}


static void send_to_tty(struct usb_serial_port *port,
                        char *data, unsigned int actual_length)
{
	struct tty_struct *tty = port->tty;
	int i;

	if (tty && actual_length) {

		usb_serial_debug_data(debug, &port->dev, 
					__FUNCTION__, actual_length, data);

		for (i = 0; i < actual_length ; ++i) {
			/* if we insert more than TTY_FLIPBUF_SIZE characters,
			   we drop them. */
			if(tty->flip.count >= TTY_FLIPBUF_SIZE) {
				tty_flip_buffer_push(tty);
			}
			/* this doesn't actually push the data through unless
			   tty->low_latency is set */
			tty_insert_flip_char(tty, data[i], 0);
		}
		tty_flip_buffer_push(tty);
	}
}


/******************************************************************************
 * packet queue handling
 ******************************************************************************/

/*
 * queue a received (usb-)packet for later processing
 */
static int pkt_add(struct garmin_data * garmin_data_p,
                   unsigned char *data, unsigned int data_length)
{
	int result = 0;
	unsigned long flags;
	struct garmin_packet *pkt;

	/* process only packets containg data ... */
	if (data_length) {
		garmin_data_p->flags |= FLAGS_QUEUING;
		pkt = kmalloc(sizeof(struct garmin_packet)+data_length,
		              GFP_ATOMIC);
		if (pkt == NULL) {
			dev_err(&garmin_data_p->port->dev, "out of memory\n");
			return 0;
		}
		pkt->size = data_length;
		memcpy(pkt->data, data, data_length);

		spin_lock_irqsave(&garmin_data_p->lock, flags);
		result = list_empty(&garmin_data_p->pktlist);
		pkt->seq = garmin_data_p->seq_counter++;
		list_add_tail(&pkt->list, &garmin_data_p->pktlist);
		spin_unlock_irqrestore(&garmin_data_p->lock, flags);

		/* in serial mode, if someone is waiting for data from
		   the device, iconvert and send the next packet to tty. */
		if (result && (garmin_data_p->state == STATE_GSP_WAIT_DATA)) {
			gsp_next_packet(garmin_data_p);
		}
	}
	return result;
}


/* get the next pending packet */
static struct garmin_packet *pkt_pop(struct garmin_data * garmin_data_p)
{
	unsigned long flags;
	struct garmin_packet *result = NULL;

	spin_lock_irqsave(&garmin_data_p->lock, flags);
	if (!list_empty(&garmin_data_p->pktlist)) {
		result = (struct garmin_packet *)garmin_data_p->pktlist.next;
		list_del(&result->list);
	}
	spin_unlock_irqrestore(&garmin_data_p->lock, flags);
	return result;
}


/* free up all queued data */
static void pkt_clear(struct garmin_data * garmin_data_p)
{
	unsigned long flags;
	struct garmin_packet *result = NULL;

	dbg("%s", __FUNCTION__);

	spin_lock_irqsave(&garmin_data_p->lock, flags);
	while (!list_empty(&garmin_data_p->pktlist)) {
		result = (struct garmin_packet *)garmin_data_p->pktlist.next;
		list_del(&result->list);
		kfree(result);
	}
	spin_unlock_irqrestore(&garmin_data_p->lock, flags);
}


/******************************************************************************
 * garmin serial protocol handling handling
 ******************************************************************************/

/* send an ack packet back to the tty */
static int gsp_send_ack(struct garmin_data * garmin_data_p, __u8 pkt_id)
{
	__u8 pkt[10];
        __u8 cksum = 0;
        __u8 *ptr = pkt;
        unsigned  l = 0;

	dbg("%s - pkt-id: 0x%X.", __FUNCTION__, 0xFF & pkt_id);

	*ptr++ = DLE;
	*ptr++ = ACK;
	cksum += ACK;

	*ptr++ = 2;
	cksum += 2;

	*ptr++ = pkt_id;
	cksum += pkt_id;

	if (pkt_id == DLE) {
		*ptr++ = DLE;
	}

	*ptr++ = 0;
	*ptr++ = 0xFF & (-cksum);
	*ptr++ = DLE;
	*ptr++ = ETX;

	l = ptr-pkt;

	send_to_tty(garmin_data_p->port, pkt, l);
	return 0;
}


/*
 * called for a complete packet received from tty layer
 *
 * the complete packet (pkzid ... cksum) is in garmin_data_p->inbuf starting
 * at GSP_INITIAL_OFFSET.
 *
 * count - number of bytes in the input buffer including space reserved for
 *         the usb header: GSP_INITIAL_OFFSET + number of bytes in packet 
 *         (including pkt-id, data-length a. cksum)
 */
static int gsp_rec_packet(struct garmin_data * garmin_data_p, int count)
{
	const __u8* recpkt = garmin_data_p->inbuffer+GSP_INITIAL_OFFSET;
        __le32 *usbdata = (__le32 *) garmin_data_p->inbuffer;

	int cksum = 0;
	int n = 0;
	int pktid = recpkt[0];
	int size = recpkt[1];

	usb_serial_debug_data(debug, &garmin_data_p->port->dev,
			       __FUNCTION__, count-GSP_INITIAL_OFFSET, recpkt);

	if (size != (count-GSP_INITIAL_OFFSET-3)) {
		dbg("%s - invalid size, expected %d bytes, got %d",
			__FUNCTION__, size, (count-GSP_INITIAL_OFFSET-3));
		return -EINVPKT;
	}

	cksum += *recpkt++;
	cksum += *recpkt++;

	// sanity check, remove after test ...
	if ((__u8*)&(usbdata[3]) != recpkt) {
		dbg("%s - ptr mismatch %p - %p",
			__FUNCTION__, &(usbdata[4]), recpkt);
		return -EINVPKT;
	}

	while (n < size) {
		cksum += *recpkt++;
		n++;
	}

       if ((0xff & (cksum + *recpkt)) != 0) {
                dbg("%s - invalid checksum, expected %02x, got %02x",
                        __FUNCTION__, 0xff & -cksum, 0xff & *recpkt);
                return -EINVPKT;
        }

	usbdata[0] = __cpu_to_le32(GARMIN_LAYERID_APPL);
	usbdata[1] = __cpu_to_le32(pktid);
	usbdata[2] = __cpu_to_le32(size);

	garmin_write_bulk (garmin_data_p->port, garmin_data_p->inbuffer,
			   GARMIN_PKTHDR_LENGTH+size);

	/* if this was an abort-transfer command, flush all
	   queued data. */
	if (isAbortTrfCmnd(garmin_data_p->inbuffer)) {
		garmin_data_p->flags |= FLAGS_DROP_DATA;
		pkt_clear(garmin_data_p);
	}

	return count;
}


/*
 * Called for data received from tty
 *
 * buf contains the data read, it may span more than one packet or even
 * incomplete packets
 *
 * input record should be a serial-record, but it may not be complete.
 * Copy it into our local buffer, until an etx is seen (or an error
 * occurs).
 * Once the record is complete, convert into a usb packet and send it
 * to the bulk pipe, send an ack back to the tty.
 *
 * If the input is an ack, just send the last queued packet to the
 * tty layer.
 *
 * if the input is an abort command, drop all queued data.
 */

static int gsp_receive(struct garmin_data * garmin_data_p,
                       const unsigned char *buf, int count)
{
	int offs = 0;
	int ack_or_nak_seen = 0;
	int i = 0;
	__u8 *dest = garmin_data_p->inbuffer;
	int size = garmin_data_p->insize;
	// dleSeen: set if last byte read was a DLE
	int dleSeen = garmin_data_p->flags & FLAGS_GSP_DLESEEN;
	// skip: if set, skip incoming data until possible start of
	//       new packet
	int skip = garmin_data_p->flags & FLAGS_GSP_SKIP;
	__u8 data;

	dbg("%s - dle=%d skip=%d size=%d count=%d",
		__FUNCTION__, dleSeen, skip, size, count);

	if (size == 0) {
		size = GSP_INITIAL_OFFSET;
	}

	while (offs < count) {

		data = *(buf+offs);
		offs ++;

		if (data == DLE) {
			if (skip) { /* start of a new pkt */
				skip = 0;
				size = GSP_INITIAL_OFFSET;
				dleSeen = 1;
			} else if (dleSeen) {
				dest[size++] = data;
				dleSeen = 0;
			} else {
				dleSeen = 1;
			}
		} else if (data == ETX) {
			if (dleSeen) {
				/* packet complete */

				data = dest[GSP_INITIAL_OFFSET];

				if (data == ACK) {
					ack_or_nak_seen = ACK;
					dbg("ACK packet complete.");
				} else if (data == NAK) {
					ack_or_nak_seen = NAK;
					dbg("NAK packet complete.");
				} else {
					dbg("packet complete "
						        "- id=0x%X.",
						        0xFF & data);
					gsp_rec_packet(garmin_data_p, size);
				}

				skip = 1;
				size = GSP_INITIAL_OFFSET;
				dleSeen = 0;
			} else {
				dest[size++] = data;
			}
		} else if (!skip) {

			if (dleSeen) {
				dbg("non-masked DLE at %d - restarting", i);
				size = GSP_INITIAL_OFFSET;
				dleSeen = 0;
			}

			dest[size++] = data;
		}

		if (size >= GPS_IN_BUFSIZ) {
			dbg("%s - packet too large.", __FUNCTION__);
			skip = 1;
			size = GSP_INITIAL_OFFSET;
			dleSeen = 0;
		}
	}

	garmin_data_p->insize = size;

	// copy flags back to structure
	if (skip)
		garmin_data_p->flags |= FLAGS_GSP_SKIP;
	else
		garmin_data_p->flags &= ~FLAGS_GSP_SKIP;

	if (dleSeen)
		garmin_data_p->flags |= FLAGS_GSP_DLESEEN;
	else
		garmin_data_p->flags &= ~FLAGS_GSP_DLESEEN;

	if (ack_or_nak_seen) {
		garmin_data_p->state = STATE_GSP_WAIT_DATA;
		gsp_next_packet(garmin_data_p);
	}

	return count;
}


/*
 * Sends a usb packet to the tty
 *
 * Assumes, that all packages and at an usb-packet boundary.
 *
 * return <0 on error, 0 if packet is incomplete or > 0 if packet was sent
 */
static int gsp_send(struct garmin_data * garmin_data_p,
		    const unsigned char *buf, int count)
{
	const unsigned char *src;
	unsigned char *dst;
	int pktid = 0;
	int datalen = 0;
	int cksum = 0;
	int i=0;
	int k;

	dbg("%s - state %d - %d bytes.", __FUNCTION__,
	         garmin_data_p->state, count);

	k = garmin_data_p->outsize;
	if ((k+count) > GPS_OUT_BUFSIZ) {
		dbg("packet too large");
		garmin_data_p->outsize = 0;
		return -4;
	}

	memcpy(garmin_data_p->outbuffer+k, buf, count);
	k += count;
	garmin_data_p->outsize = k;

	if (k >= GARMIN_PKTHDR_LENGTH) {
		pktid  = getPacketId(garmin_data_p->outbuffer);
		datalen= getDataLength(garmin_data_p->outbuffer);
		i = GARMIN_PKTHDR_LENGTH + datalen;
		if (k < i)
			return 0;
	} else {
		return 0;
	}

	dbg("%s - %d bytes in buffer, %d bytes in pkt.", __FUNCTION__,
	         k, i);

	/* garmin_data_p->outbuffer now contains a complete packet */

	usb_serial_debug_data(debug, &garmin_data_p->port->dev,
		                   __FUNCTION__, k, garmin_data_p->outbuffer);

	garmin_data_p->outsize = 0;

	if (GARMIN_LAYERID_APPL != getLayerId(garmin_data_p->outbuffer)) {
		dbg("not an application packet (%d)", 
		        getLayerId(garmin_data_p->outbuffer));
		return -1;
	}

	if (pktid > 255) {
		dbg("packet-id %d too large", pktid);
		return -2;
	}

	if (datalen > 255) {
		dbg("packet-size %d too large", datalen);
		return -3;
	}

	/* the serial protocol should be able to handle this packet */

	k = 0;
	src = garmin_data_p->outbuffer+GARMIN_PKTHDR_LENGTH;
	for (i=0; i<datalen; i++) {
		if (*src++ == DLE)
			k++;
	}

	src = garmin_data_p->outbuffer+GARMIN_PKTHDR_LENGTH;
	if (k > (GARMIN_PKTHDR_LENGTH-2)) {
		/* can't add stuffing DLEs in place, move data to end 
                   of buffer ... */
		dst = garmin_data_p->outbuffer+GPS_OUT_BUFSIZ-datalen;
		memcpy(dst, src, datalen);
		src = dst;
	}

	dst = garmin_data_p->outbuffer;

	*dst++ = DLE;
	*dst++ = pktid;
	cksum += pktid;
	*dst++ = datalen;
	cksum += datalen;
	if (datalen == DLE)
		*dst++ = DLE;

	for (i=0; i<datalen; i++) {
		__u8 c = *src++;
		*dst++ = c;
		cksum += c;
		if (c == DLE)
			*dst++ = DLE;
	}
		
	cksum = 0xFF & -cksum;
	*dst++ = cksum;
	if (cksum == DLE)
		*dst++ = DLE;
	*dst++ = DLE;
	*dst++ = ETX;

	i = dst-garmin_data_p->outbuffer;

	send_to_tty(garmin_data_p->port, garmin_data_p->outbuffer, i);

	garmin_data_p->pkt_id = pktid;
	garmin_data_p->state  = STATE_WAIT_TTY_ACK;

	return i;
}


/*
 * Process the next pending data packet - if there is one
 */
static void gsp_next_packet(struct garmin_data * garmin_data_p)
{
	struct garmin_packet *pkt = NULL;

	while ((pkt = pkt_pop(garmin_data_p)) != NULL) {
		dbg("%s - next pkt: %d", __FUNCTION__, pkt->seq);
		if (gsp_send(garmin_data_p, pkt->data, pkt->size) > 0) {
			kfree(pkt);
			return;
		}
		kfree(pkt);
	}
}


/******************************************************************************
 * garmin native mode
 ******************************************************************************/


/*
 * Called for data received from tty
 *
 * The input data is expected to be in garmin usb-packet format.
 *
 * buf contains the data read, it may span more than one packet
 * or even incomplete packets
 */
static int nat_receive(struct garmin_data * garmin_data_p,
                       const unsigned char *buf, int count)
{
	__u8 * dest;
	int offs = 0;
	int result = count;
	int len;

	while (offs < count) {
		// if buffer contains header, copy rest of data
		if (garmin_data_p->insize >= GARMIN_PKTHDR_LENGTH)
			len = GARMIN_PKTHDR_LENGTH
			      +getDataLength(garmin_data_p->inbuffer);
		else
			len = GARMIN_PKTHDR_LENGTH;

		if (len >= GPS_IN_BUFSIZ) {
			/* seem to be an invalid packet, ignore rest of input */
			dbg("%s - packet size too large: %d",
			        __FUNCTION__, len);
			garmin_data_p->insize = 0;
			count = 0;
			result = -EINVPKT;
		} else {
			len -= garmin_data_p->insize;
			if (len > (count-offs))
				len = (count-offs);
			if (len > 0) {
				dest = garmin_data_p->inbuffer
				       	+garmin_data_p->insize;
				memcpy(dest, buf+offs, len);
				garmin_data_p->insize += len;
				offs += len;
			}
		}

		/* do we have a complete packet ? */
		if (garmin_data_p->insize >= GARMIN_PKTHDR_LENGTH) {
			len = GARMIN_PKTHDR_LENGTH+
			   getDataLength(garmin_data_p->inbuffer);
			if (garmin_data_p->insize >= len) {
				garmin_write_bulk (garmin_data_p->port,
				                   garmin_data_p->inbuffer,
				                   len);
				garmin_data_p->insize = 0;

				/* if this was an abort-transfer command,
				   flush all queued data. */
				if (isAbortTrfCmnd(garmin_data_p->inbuffer)) {
					garmin_data_p->flags |= FLAGS_DROP_DATA;
					pkt_clear(garmin_data_p);
				}
			}
		}
	}
	return result;
}


/******************************************************************************
 * private packets
 ******************************************************************************/

static void priv_status_resp(struct usb_serial_port *port)
{
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);
	__le32 *pkt = (__le32 *)garmin_data_p->privpkt;

	pkt[0] = __cpu_to_le32(GARMIN_LAYERID_PRIVATE);
	pkt[1] = __cpu_to_le32(PRIV_PKTID_INFO_RESP);
	pkt[2] = __cpu_to_le32(12);
	pkt[3] = __cpu_to_le32(VERSION_MAJOR << 16 | VERSION_MINOR);
	pkt[4] = __cpu_to_le32(garmin_data_p->mode);
	pkt[5] = __cpu_to_le32(garmin_data_p->serial_num);

	send_to_tty(port, (__u8*)pkt, 6*4);
}


/******************************************************************************
 * Garmin specific driver functions
 ******************************************************************************/

static int process_resetdev_request(struct usb_serial_port *port)
{
	int status;
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);

	garmin_data_p->flags &= ~(CLEAR_HALT_REQUIRED);
	garmin_data_p->state = STATE_RESET;
	garmin_data_p->serial_num = 0;

	usb_kill_urb (port->interrupt_in_urb);
	dbg("%s - usb_reset_device", __FUNCTION__ );
	status = usb_reset_device(port->serial->dev);
	if (status)
		dbg("%s - usb_reset_device failed: %d",
			__FUNCTION__, status);
	return status;
}


/*
 * clear all cached data
 */
static int garmin_clear(struct garmin_data * garmin_data_p)
{
	int status = 0;

	struct usb_serial_port *port = garmin_data_p->port;

	if (port != NULL && garmin_data_p->flags & FLAGS_APP_RESP_SEEN) {
		/* send a terminate command */
		status = garmin_write_bulk(port, GARMIN_STOP_TRANSFER_REQ,
		                           sizeof(GARMIN_STOP_TRANSFER_REQ));
	}

	/* flush all queued data */
	pkt_clear(garmin_data_p);

	garmin_data_p->insize = 0;
	garmin_data_p->outsize = 0;

	return status;
}


static int garmin_init_session(struct usb_serial_port *port)
{
	struct usb_serial *serial = port->serial;
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);
	int status = 0;

	if (status == 0) {
		usb_kill_urb (port->interrupt_in_urb);

		dbg("%s - adding interrupt input", __FUNCTION__);
		port->interrupt_in_urb->dev = serial->dev;
		status = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);
		if (status)
			dev_err(&serial->dev->dev,
			        "%s - failed submitting interrupt urb,"
				" error %d\n",
			        __FUNCTION__, status);
	}

	if (status == 0) {
		dbg("%s - starting session ...", __FUNCTION__);
		garmin_data_p->state = STATE_ACTIVE;
		status = garmin_write_bulk(port, GARMIN_START_SESSION_REQ,
		                           sizeof(GARMIN_START_SESSION_REQ));

		if (status >= 0) {

			garmin_data_p->ignorePkts++;

			/* not needed, but the win32 driver does it too ... */
			status = garmin_write_bulk(port,
						   GARMIN_START_SESSION_REQ2,
			                           sizeof(GARMIN_START_SESSION_REQ2));
			if (status >= 0) {
				status = 0;
				garmin_data_p->ignorePkts++;
			}
		}
	}

	return status;
}


static int garmin_open (struct usb_serial_port *port, struct file *filp)
{
	int status = 0;
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);

	dbg("%s - port %d", __FUNCTION__, port->number);

	/*
	 * Force low_latency on so that our tty_push actually forces the data
	 * through, otherwise it is scheduled, and with high data rates (like
	 * with OHCI) data can get lost.
	 */
	if (port->tty)
		port->tty->low_latency = 1;

	garmin_data_p->mode  = initial_mode;
	garmin_data_p->count = 0;
	garmin_data_p->flags = 0;

	/* shutdown any bulk reads that might be going on */
	usb_kill_urb (port->write_urb);
	usb_kill_urb (port->read_urb);

	if (garmin_data_p->state == STATE_RESET) {
		status = garmin_init_session(port);
	}

	garmin_data_p->state = STATE_ACTIVE;

	return status;
}


static void garmin_close (struct usb_serial_port *port, struct file * filp)
{
	struct usb_serial *serial = port->serial;
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);

	dbg("%s - port %d - mode=%d state=%d flags=0x%X", __FUNCTION__,
		port->number, garmin_data_p->mode,
		garmin_data_p->state, garmin_data_p->flags);

	if (!serial)
		return;

	garmin_clear(garmin_data_p);

	/* shutdown our urbs */
	usb_kill_urb (port->read_urb);
	usb_kill_urb (port->write_urb);

	if (noResponseFromAppLayer(garmin_data_p) ||
	    ((garmin_data_p->flags & CLEAR_HALT_REQUIRED) != 0)) {
		process_resetdev_request(port);
		garmin_data_p->state = STATE_RESET;
	} else {
		garmin_data_p->state = STATE_DISCONNECTED;
	}
}


static void garmin_write_bulk_callback (struct urb *urb, struct pt_regs *regs)
{
	struct usb_serial_port *port = (struct usb_serial_port *)urb->context;
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);

	/* free up the transfer buffer, as usb_free_urb() does not do this */
	kfree (urb->transfer_buffer);

	dbg("%s - port %d", __FUNCTION__, port->number);

	if (urb->status) {
		dbg("%s - nonzero write bulk status received: %d",
			__FUNCTION__, urb->status);
		garmin_data_p->flags |= CLEAR_HALT_REQUIRED;
	}

	schedule_work(&port->work);
}


static int garmin_write_bulk (struct usb_serial_port *port,
                              const unsigned char *buf, int count)
{
	struct usb_serial *serial = port->serial;
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);
	struct urb *urb;
	unsigned char *buffer;
	int status;

	dbg("%s - port %d, state %d", __FUNCTION__, port->number,
		garmin_data_p->state);

	garmin_data_p->flags &= ~FLAGS_DROP_DATA;

	buffer = kmalloc (count, GFP_ATOMIC);
	if (!buffer) {
		dev_err(&port->dev, "out of memory\n");
		return -ENOMEM;
	}

	urb = usb_alloc_urb(0, GFP_ATOMIC);
	if (!urb) {
		dev_err(&port->dev, "no more free urbs\n");
		kfree (buffer);
		return -ENOMEM;
	}

	memcpy (buffer, buf, count);

	usb_serial_debug_data(debug, &port->dev, __FUNCTION__, count, buffer);

	usb_fill_bulk_urb (urb, serial->dev,
			 	usb_sndbulkpipe (serial->dev,
				port->bulk_out_endpointAddress),
				buffer, count,
				garmin_write_bulk_callback, port);
	urb->transfer_flags |= URB_ZERO_PACKET;

	if (GARMIN_LAYERID_APPL == getLayerId(buffer)) {
		garmin_data_p->flags |= FLAGS_APP_REQ_SEEN;
		if (garmin_data_p->mode == MODE_GARMIN_SERIAL)  {
			pkt_clear(garmin_data_p);
			garmin_data_p->state = STATE_GSP_WAIT_DATA;
		}
	}

	/* send it down the pipe */
	status = usb_submit_urb(urb, GFP_ATOMIC);
	if (status) {
		dev_err(&port->dev,
		        "%s - usb_submit_urb(write bulk) "
		        "failed with status = %d\n",
				__FUNCTION__, status);
		count = status;
	} else {

		if (GARMIN_LAYERID_APPL == getLayerId(buffer)
		    && (garmin_data_p->mode == MODE_GARMIN_SERIAL))  {

			gsp_send_ack(garmin_data_p, buffer[4]);
		}
	}

	/* we are done with this urb, so let the host driver
	 * really free it when it is finished with it */
	usb_free_urb (urb);

	return count;
}


static int garmin_write (struct usb_serial_port *port,
                         const unsigned char *buf, int count)
{
	int pktid, pktsiz, len;
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);
	__le32 *privpkt = (__le32 *)garmin_data_p->privpkt;

	usb_serial_debug_data(debug, &port->dev, __FUNCTION__, count, buf);

	/* check for our private packets */
	if (count >= GARMIN_PKTHDR_LENGTH) {

		len = PRIVPKTSIZ;
		if (count < len)
			len = count;

		memcpy(garmin_data_p->privpkt, buf, len);

		pktsiz = getDataLength(garmin_data_p->privpkt);
		pktid  = getPacketId(garmin_data_p->privpkt);

		if (count == (GARMIN_PKTHDR_LENGTH+pktsiz)
		    && GARMIN_LAYERID_PRIVATE == getLayerId(garmin_data_p->privpkt)) {

			dbg("%s - processing private request %d",
				__FUNCTION__, pktid);

			// drop all unfinished transfers
			garmin_clear(garmin_data_p);

			switch(pktid) {

			case PRIV_PKTID_SET_DEBUG:
				if (pktsiz != 4)
					return -EINVPKT;
				debug = __le32_to_cpu(privpkt[3]);
				dbg("%s - debug level set to 0x%X",
					__FUNCTION__, debug);
				break;

			case PRIV_PKTID_SET_MODE:
				if (pktsiz != 4)
					return -EINVPKT;
				garmin_data_p->mode = __le32_to_cpu(privpkt[3]);
				dbg("%s - mode set to %d",
					__FUNCTION__, garmin_data_p->mode);
				break;

			case PRIV_PKTID_INFO_REQ:
				priv_status_resp(port);
				break;

			case PRIV_PKTID_RESET_REQ:
				garmin_data_p->flags |= FLAGS_APP_REQ_SEEN;
				break;

			case PRIV_PKTID_SET_DEF_MODE:
				if (pktsiz != 4)
					return -EINVPKT;
				initial_mode = __le32_to_cpu(privpkt[3]);
				dbg("%s - initial_mode set to %d",
					__FUNCTION__,
					garmin_data_p->mode);
				break;
			}
			return count;
		}
	}

	if (garmin_data_p->mode == MODE_GARMIN_SERIAL) {
		return gsp_receive(garmin_data_p, buf, count);
	} else {	/* MODE_NATIVE */
		return nat_receive(garmin_data_p, buf, count);
	}
}


static int garmin_write_room (struct usb_serial_port *port)
{
	/*
	 * Report back the bytes currently available in the output buffer.
	 */
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);
	return GPS_OUT_BUFSIZ-garmin_data_p->outsize;
}


static int garmin_chars_in_buffer (struct usb_serial_port *port)
{
	/*
	 * Report back the number of bytes currently in our input buffer.
         * Will this lock up the driver - the buffer contains an incomplete
         * package which will not be written to the device until it
         * has been completed ?
         */
	//struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);
	//return garmin_data_p->insize;
	return 0;
}


static void garmin_read_process(struct garmin_data * garmin_data_p,
				 unsigned char *data, unsigned data_length)
{
	if (garmin_data_p->flags & FLAGS_DROP_DATA) {
		/* abort-transfer cmd is actice */
		dbg("%s - pkt dropped", __FUNCTION__);
	} else if (garmin_data_p->state != STATE_DISCONNECTED &&
	           garmin_data_p->state != STATE_RESET ) {

		/* remember any appl.layer packets, so we know
		   if a reset is required or not when closing
		   the device */
		if (0 == memcmp(data, GARMIN_APP_LAYER_REPLY,
		                sizeof(GARMIN_APP_LAYER_REPLY)))
			garmin_data_p->flags |= FLAGS_APP_RESP_SEEN;

		/* if throttling is active or postprecessing is required
		   put the received data in th input queue, otherwise
		   send it directly to the tty port */
		if (garmin_data_p->flags & FLAGS_QUEUING) {
			pkt_add(garmin_data_p, data, data_length);
		} else if (garmin_data_p->mode == MODE_GARMIN_SERIAL) {
			if (getLayerId(data) == GARMIN_LAYERID_APPL) {
				pkt_add(garmin_data_p, data, data_length);
			}
		} else {
			send_to_tty(garmin_data_p->port, data, data_length);
		}
	}
}


static void garmin_read_bulk_callback (struct urb *urb, struct pt_regs *regs)
{
	struct usb_serial_port *port = (struct usb_serial_port *)urb->context;
	struct usb_serial *serial =  port->serial;
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);
	unsigned char *data = urb->transfer_buffer;
	int status;

	dbg("%s - port %d", __FUNCTION__, port->number);

	if (!serial) {
		dbg("%s - bad serial pointer, exiting", __FUNCTION__);
		return;
	}

	if (urb->status) {
		dbg("%s - nonzero read bulk status received: %d",
			__FUNCTION__, urb->status);
		return;
	}

	usb_serial_debug_data(debug, &port->dev, 
				__FUNCTION__, urb->actual_length, data);

	garmin_read_process(garmin_data_p, data, urb->actual_length);

	/* Continue trying to read until nothing more is received  */
	if (urb->actual_length > 0) {
		usb_fill_bulk_urb (port->read_urb, serial->dev,
			   usb_rcvbulkpipe (serial->dev,
					    port->bulk_in_endpointAddress),
			   port->read_urb->transfer_buffer,
			   port->read_urb->transfer_buffer_length,
			   garmin_read_bulk_callback, port);
		status = usb_submit_urb(port->read_urb, GFP_ATOMIC);
		if (status)
			dev_err(&port->dev,
				"%s - failed resubmitting read urb, error %d\n",
			        __FUNCTION__, status);
	}
	return;
}


static void garmin_read_int_callback (struct urb *urb, struct pt_regs *regs)
{
	int status;
	struct usb_serial_port *port = (struct usb_serial_port *)urb->context;
	struct usb_serial *serial = port->serial;
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);
	unsigned char *data = urb->transfer_buffer;

	switch (urb->status) {
	case 0:
		/* success */
		break;
	case -ECONNRESET:
	case -ENOENT:
	case -ESHUTDOWN:
		/* this urb is terminated, clean up */
		dbg("%s - urb shutting down with status: %d",
			__FUNCTION__, urb->status);
		return;
	default:
		dbg("%s - nonzero urb status received: %d",
			__FUNCTION__, urb->status);
		return;
	}

	usb_serial_debug_data(debug, &port->dev, __FUNCTION__, 
				urb->actual_length, urb->transfer_buffer);

	if (urb->actual_length == sizeof(GARMIN_BULK_IN_AVAIL_REPLY) &&
	    0 == memcmp(data, GARMIN_BULK_IN_AVAIL_REPLY,
		        sizeof(GARMIN_BULK_IN_AVAIL_REPLY))) {

		dbg("%s - bulk data available.", __FUNCTION__);

		/* bulk data available */
		usb_fill_bulk_urb (port->read_urb, serial->dev,
				usb_rcvbulkpipe (serial->dev,
				port->bulk_in_endpointAddress),
				port->read_urb->transfer_buffer,
				port->read_urb->transfer_buffer_length,
				garmin_read_bulk_callback, port);
		status = usb_submit_urb(port->read_urb, GFP_KERNEL);
		if (status) {
			dev_err(&port->dev,
				"%s - failed submitting read urb, error %d\n",
			__FUNCTION__, status);
		}

	} else if (urb->actual_length == (4+sizeof(GARMIN_START_SESSION_REPLY))
			 && 0 == memcmp(data, GARMIN_START_SESSION_REPLY,
			                sizeof(GARMIN_START_SESSION_REPLY))) {

		garmin_data_p->flags |= FLAGS_SESSION_REPLY1_SEEN;

		/* save the serial number */
		garmin_data_p->serial_num 
			= __le32_to_cpup((__le32*)(data+GARMIN_PKTHDR_LENGTH));

		dbg("%s - start-of-session reply seen - serial %u.",
			__FUNCTION__, garmin_data_p->serial_num);
	}

	if (garmin_data_p->ignorePkts) {
		/* this reply belongs to a request generated by the driver,
		   ignore it. */
		dbg("%s - pkt ignored (%d)",
			__FUNCTION__, garmin_data_p->ignorePkts);
		garmin_data_p->ignorePkts--;
	} else {
		garmin_read_process(garmin_data_p, data, urb->actual_length);
	}

	port->interrupt_in_urb->dev = port->serial->dev;
	status = usb_submit_urb (urb, GFP_ATOMIC);
	if (status)
		dev_err(&urb->dev->dev,
			"%s - Error %d submitting interrupt urb\n",
			__FUNCTION__, status);
}


/*
 * Sends the next queued packt to the tty port (garmin native mode only)
 * and then sets a timer to call itself again until all queued data
 * is sent.
 */
static int garmin_flush_queue(struct garmin_data * garmin_data_p)
{
	struct garmin_packet *pkt;

	if ((garmin_data_p->flags & FLAGS_THROTTLED) == 0) {
		pkt = pkt_pop(garmin_data_p);
		if (pkt != NULL) {

			send_to_tty(garmin_data_p->port, pkt->data, pkt->size);
			kfree(pkt);
			mod_timer(&garmin_data_p->timer, (1)+jiffies);

		} else {
			garmin_data_p->flags &= ~FLAGS_QUEUING;
		}
	}
	return 0;
}


static void garmin_throttle (struct usb_serial_port *port)
{
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);

	dbg("%s - port %d", __FUNCTION__, port->number);
	/* set flag, data received will be put into a queue
	   for later processing */
	garmin_data_p->flags |= FLAGS_QUEUING|FLAGS_THROTTLED;
}


static void garmin_unthrottle (struct usb_serial_port *port)
{
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);

	dbg("%s - port %d", __FUNCTION__, port->number);
	garmin_data_p->flags &= ~FLAGS_THROTTLED;

	/* in native mode send queued data to tty, in
	   serial mode nothing needs to be done here */
	if (garmin_data_p->mode == MODE_NATIVE)
		garmin_flush_queue(garmin_data_p);
}


/*
 * The timer is currently only used to send queued packets to
 * the tty in cases where the protocol provides no own handshaking
 * to initiate the transfer.
 */
static void timeout_handler(unsigned long data)
{
	struct garmin_data *garmin_data_p = (struct garmin_data *) data;

	/* send the next queued packet to the tty port */
	if (garmin_data_p->mode == MODE_NATIVE)
		if (garmin_data_p->flags & FLAGS_QUEUING)
			garmin_flush_queue(garmin_data_p);
}


static int garmin_attach (struct usb_serial *serial)
{
	int status = 0;
	struct usb_serial_port *port = serial->port[0];
	struct garmin_data * garmin_data_p = NULL;

	dbg("%s", __FUNCTION__);

	garmin_data_p = kmalloc (sizeof(struct garmin_data), GFP_KERNEL);
	if (garmin_data_p == NULL) {
		dev_err(&port->dev, "%s - Out of memory\n", __FUNCTION__);
		return -ENOMEM;
	}
	memset (garmin_data_p, 0, sizeof(struct garmin_data));
	init_timer(&garmin_data_p->timer);
	spin_lock_init(&garmin_data_p->lock);
	INIT_LIST_HEAD(&garmin_data_p->pktlist);
	//garmin_data_p->timer.expires = jiffies + session_timeout;
	garmin_data_p->timer.data = (unsigned long)garmin_data_p;
	garmin_data_p->timer.function = timeout_handler;
	garmin_data_p->port = port;
	garmin_data_p->state = 0;
	garmin_data_p->count = 0;
	usb_set_serial_port_data(port, garmin_data_p);

	status = garmin_init_session(port);

	return status;
}


static void garmin_shutdown (struct usb_serial *serial)
{
	struct usb_serial_port *port = serial->port[0];
	struct garmin_data * garmin_data_p = usb_get_serial_port_data(port);

	dbg("%s", __FUNCTION__);

	usb_kill_urb (port->interrupt_in_urb);
	del_timer_sync(&garmin_data_p->timer);
	kfree (garmin_data_p);
	usb_set_serial_port_data(port, NULL);
}


/* All of the device info needed */
static struct usb_serial_device_type garmin_device = {
	.owner               = THIS_MODULE,
	.name                = "Garmin GPS usb/tty",
	.short_name          = "garmin_gps",
	.id_table            = id_table,
	.num_interrupt_in    = 1,
	.num_bulk_in         = 1,
	.num_bulk_out        = 1,
	.num_ports           = 1,
	.open                = garmin_open,
	.close               = garmin_close,
	.throttle            = garmin_throttle,
	.unthrottle          = garmin_unthrottle,
	.attach              = garmin_attach,
	.shutdown            = garmin_shutdown,
	.write               = garmin_write,
	.write_room          = garmin_write_room,
	.chars_in_buffer     = garmin_chars_in_buffer,
	.write_bulk_callback = garmin_write_bulk_callback,
	.read_bulk_callback  = garmin_read_bulk_callback,
	.read_int_callback   = garmin_read_int_callback,
};


static int __init garmin_init (void)
{
	int retval;

	retval = usb_serial_register(&garmin_device);
	if (retval)
		goto failed_garmin_register;
	retval = usb_register(&garmin_driver);
	if (retval)
		goto failed_usb_register;
	info(DRIVER_DESC " " DRIVER_VERSION);

	return 0;
failed_usb_register:
	usb_serial_deregister(&garmin_device);
failed_garmin_register:
	return retval;
}


static void __exit garmin_exit (void)
{
	usb_deregister (&garmin_driver);
	usb_serial_deregister (&garmin_device);
}


module_init(garmin_init);
module_exit(garmin_exit);

MODULE_AUTHOR( DRIVER_AUTHOR );
MODULE_DESCRIPTION( DRIVER_DESC );
MODULE_LICENSE("GPL");

module_param(debug, bool, S_IWUSR | S_IRUGO);
MODULE_PARM_DESC(debug, "Debug enabled or not");
module_param(initial_mode, int, S_IRUGO);
MODULE_PARM_DESC(initial_mode, "Initial mode");