// SPDX-License-Identifier: GPL-2.0+
/*
 * USB Cypress M8 driver
 *
 *      Copyright (C) 2004
 *          Lonnie Mendez (dignome@gmail.com)
 *      Copyright (C) 2003,2004
 *          Neil Whelchel (koyama@firstlight.net)
 *
 * See Documentation/usb/usb-serial.rst for more information on using this
 * driver
 *
 * See http://geocities.com/i0xox0i for information on this driver and the
 * earthmate usb device.
 */

/* Thanks to Neil Whelchel for writing the first cypress m8 implementation
   for linux. */
/* Thanks to cypress for providing references for the hid reports. */
/* Thanks to Jiang Zhang for providing links and for general help. */
/* Code originates and was built up from ftdi_sio, belkin, pl2303 and others.*/


#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/tty.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/spinlock.h>
#include <linux/usb.h>
#include <linux/usb/serial.h>
#include <linux/serial.h>
#include <linux/kfifo.h>
#include <linux/delay.h>
#include <linux/uaccess.h>
#include <asm/unaligned.h>

#include "cypress_m8.h"


static bool stats;
static int interval;
static bool unstable_bauds;

#define DRIVER_AUTHOR "Lonnie Mendez <dignome@gmail.com>, Neil Whelchel <koyama@firstlight.net>"
#define DRIVER_DESC "Cypress USB to Serial Driver"

/* write buffer size defines */
#define CYPRESS_BUF_SIZE        1024

static const struct usb_device_id id_table_earthmate[] = {
        { USB_DEVICE(VENDOR_ID_DELORME, PRODUCT_ID_EARTHMATEUSB) },
        { USB_DEVICE(VENDOR_ID_DELORME, PRODUCT_ID_EARTHMATEUSB_LT20) },
        { }                                             /* Terminating entry */
};

static const struct usb_device_id id_table_cyphidcomrs232[] = {
        { USB_DEVICE(VENDOR_ID_CYPRESS, PRODUCT_ID_CYPHIDCOM) },
        { USB_DEVICE(VENDOR_ID_SAI, PRODUCT_ID_CYPHIDCOM) },
        { USB_DEVICE(VENDOR_ID_POWERCOM, PRODUCT_ID_UPS) },
        { USB_DEVICE(VENDOR_ID_FRWD, PRODUCT_ID_CYPHIDCOM_FRWD) },
        { }                                             /* Terminating entry */
};

static const struct usb_device_id id_table_nokiaca42v2[] = {
        { USB_DEVICE(VENDOR_ID_DAZZLE, PRODUCT_ID_CA42) },
        { }                                             /* Terminating entry */
};

static const struct usb_device_id id_table_combined[] = {
        { USB_DEVICE(VENDOR_ID_DELORME, PRODUCT_ID_EARTHMATEUSB) },
        { USB_DEVICE(VENDOR_ID_DELORME, PRODUCT_ID_EARTHMATEUSB_LT20) },
        { USB_DEVICE(VENDOR_ID_CYPRESS, PRODUCT_ID_CYPHIDCOM) },
        { USB_DEVICE(VENDOR_ID_SAI, PRODUCT_ID_CYPHIDCOM) },
        { USB_DEVICE(VENDOR_ID_POWERCOM, PRODUCT_ID_UPS) },
        { USB_DEVICE(VENDOR_ID_FRWD, PRODUCT_ID_CYPHIDCOM_FRWD) },
        { USB_DEVICE(VENDOR_ID_DAZZLE, PRODUCT_ID_CA42) },
        { }                                             /* Terminating entry */
};

MODULE_DEVICE_TABLE(usb, id_table_combined);

enum packet_format {
        packet_format_1,  /* b0:status, b1:payload count */
        packet_format_2   /* b0[7:3]:status, b0[2:0]:payload count */
};

struct cypress_private {
        spinlock_t lock;                   /* private lock */
        int chiptype;                      /* identifier of device, for quirks/etc */
        int bytes_in;                      /* used for statistics */
        int bytes_out;                     /* used for statistics */
        int cmd_count;                     /* used for statistics */
        int cmd_ctrl;                      /* always set this to 1 before issuing a command */
        struct kfifo write_fifo;           /* write fifo */
        int write_urb_in_use;              /* write urb in use indicator */
        int write_urb_interval;            /* interval to use for write urb */
        int read_urb_interval;             /* interval to use for read urb */
        int comm_is_ok;                    /* true if communication is (still) ok */
        __u8 line_control;                 /* holds dtr / rts value */
        __u8 current_status;               /* received from last read - info on dsr,cts,cd,ri,etc */
        __u8 current_config;               /* stores the current configuration byte */
        __u8 rx_flags;                     /* throttling - used from whiteheat/ftdi_sio */
        enum packet_format pkt_fmt;        /* format to use for packet send / receive */
        int get_cfg_unsafe;                /* If true, the CYPRESS_GET_CONFIG is unsafe */
        int baud_rate;                     /* stores current baud rate in
                                              integer form */
        char prev_status;                  /* used for TIOCMIWAIT */
};

/* function prototypes for the Cypress USB to serial device */
static int  cypress_earthmate_port_probe(struct usb_serial_port *port);
static int  cypress_hidcom_port_probe(struct usb_serial_port *port);
static int  cypress_ca42v2_port_probe(struct usb_serial_port *port);
static void cypress_port_remove(struct usb_serial_port *port);
static int  cypress_open(struct tty_struct *tty, struct usb_serial_port *port);
static void cypress_close(struct usb_serial_port *port);
static void cypress_dtr_rts(struct usb_serial_port *port, int on);
static int  cypress_write(struct tty_struct *tty, struct usb_serial_port *port,
                        const unsigned char *buf, int count);
static void cypress_send(struct usb_serial_port *port);
static unsigned int cypress_write_room(struct tty_struct *tty);
static void cypress_earthmate_init_termios(struct tty_struct *tty);
static void cypress_set_termios(struct tty_struct *tty,
                        struct usb_serial_port *port, struct ktermios *old);
static int  cypress_tiocmget(struct tty_struct *tty);
static int  cypress_tiocmset(struct tty_struct *tty,
                        unsigned int set, unsigned int clear);
static unsigned int cypress_chars_in_buffer(struct tty_struct *tty);
static void cypress_throttle(struct tty_struct *tty);
static void cypress_unthrottle(struct tty_struct *tty);
static void cypress_set_dead(struct usb_serial_port *port);
static void cypress_read_int_callback(struct urb *urb);
static void cypress_write_int_callback(struct urb *urb);

static struct usb_serial_driver cypress_earthmate_device = {
        .driver = {
                .owner =                THIS_MODULE,
                .name =                 "earthmate",
        },
        .description =                  "DeLorme Earthmate USB",
        .id_table =                     id_table_earthmate,
        .num_ports =                    1,
        .port_probe =                   cypress_earthmate_port_probe,
        .port_remove =                  cypress_port_remove,
        .open =                         cypress_open,
        .close =                        cypress_close,
        .dtr_rts =                      cypress_dtr_rts,
        .write =                        cypress_write,
        .write_room =                   cypress_write_room,
        .init_termios =                 cypress_earthmate_init_termios,
        .set_termios =                  cypress_set_termios,
        .tiocmget =                     cypress_tiocmget,
        .tiocmset =                     cypress_tiocmset,
        .tiocmiwait =                   usb_serial_generic_tiocmiwait,
        .chars_in_buffer =              cypress_chars_in_buffer,
        .throttle =                     cypress_throttle,
        .unthrottle =                   cypress_unthrottle,
        .read_int_callback =            cypress_read_int_callback,
        .write_int_callback =           cypress_write_int_callback,
};

static struct usb_serial_driver cypress_hidcom_device = {
        .driver = {
                .owner =                THIS_MODULE,
                .name =                 "cyphidcom",
        },
        .description =                  "HID->COM RS232 Adapter",
        .id_table =                     id_table_cyphidcomrs232,
        .num_ports =                    1,
        .port_probe =                   cypress_hidcom_port_probe,
        .port_remove =                  cypress_port_remove,
        .open =                         cypress_open,
        .close =                        cypress_close,
        .dtr_rts =                      cypress_dtr_rts,
        .write =                        cypress_write,
        .write_room =                   cypress_write_room,
        .set_termios =                  cypress_set_termios,
        .tiocmget =                     cypress_tiocmget,
        .tiocmset =                     cypress_tiocmset,
        .tiocmiwait =                   usb_serial_generic_tiocmiwait,
        .chars_in_buffer =              cypress_chars_in_buffer,
        .throttle =                     cypress_throttle,
        .unthrottle =                   cypress_unthrottle,
        .read_int_callback =            cypress_read_int_callback,
        .write_int_callback =           cypress_write_int_callback,
};

static struct usb_serial_driver cypress_ca42v2_device = {
        .driver = {
                .owner =                THIS_MODULE,
                .name =                 "nokiaca42v2",
        },
        .description =                  "Nokia CA-42 V2 Adapter",
        .id_table =                     id_table_nokiaca42v2,
        .num_ports =                    1,
        .port_probe =                   cypress_ca42v2_port_probe,
        .port_remove =                  cypress_port_remove,
        .open =                         cypress_open,
        .close =                        cypress_close,
        .dtr_rts =                      cypress_dtr_rts,
        .write =                        cypress_write,
        .write_room =                   cypress_write_room,
        .set_termios =                  cypress_set_termios,
        .tiocmget =                     cypress_tiocmget,
        .tiocmset =                     cypress_tiocmset,
        .tiocmiwait =                   usb_serial_generic_tiocmiwait,
        .chars_in_buffer =              cypress_chars_in_buffer,
        .throttle =                     cypress_throttle,
        .unthrottle =                   cypress_unthrottle,
        .read_int_callback =            cypress_read_int_callback,
        .write_int_callback =           cypress_write_int_callback,
};

static struct usb_serial_driver * const serial_drivers[] = {
        &cypress_earthmate_device, &cypress_hidcom_device,
        &cypress_ca42v2_device, NULL
};

/*****************************************************************************
 * Cypress serial helper functions
 *****************************************************************************/

/* FRWD Dongle hidcom needs to skip reset and speed checks */
static inline bool is_frwd(struct usb_device *dev)
{
        return ((le16_to_cpu(dev->descriptor.idVendor) == VENDOR_ID_FRWD) &&
                (le16_to_cpu(dev->descriptor.idProduct) == PRODUCT_ID_CYPHIDCOM_FRWD));
}

static int analyze_baud_rate(struct usb_serial_port *port, speed_t new_rate)
{
        struct cypress_private *priv;
        priv = usb_get_serial_port_data(port);

        if (unstable_bauds)
                return new_rate;

        /* FRWD Dongle uses 115200 bps */
        if (is_frwd(port->serial->dev))
                return new_rate;

        /*
         * The general purpose firmware for the Cypress M8 allows for
         * a maximum speed of 57600bps (I have no idea whether DeLorme
         * chose to use the general purpose firmware or not), if you
         * need to modify this speed setting for your own project
         * please add your own chiptype and modify the code likewise.
         * The Cypress HID->COM device will work successfully up to
         * 115200bps (but the actual throughput is around 3kBps).
         */
        if (port->serial->dev->speed == USB_SPEED_LOW) {
                /*
                 * Mike Isely <isely@pobox.com> 2-Feb-2008: The
                 * Cypress app note that describes this mechanism
                 * states the the low-speed part can't handle more
                 * than 800 bytes/sec, in which case 4800 baud is the
                 * safest speed for a part like that.
                 */
                if (new_rate > 4800) {
                        dev_dbg(&port->dev,
                                "%s - failed setting baud rate, device incapable speed %d\n",
                                __func__, new_rate);
                        return -1;
                }
        }
        switch (priv->chiptype) {
        case CT_EARTHMATE:
                if (new_rate <= 600) {
                        /* 300 and 600 baud rates are supported under
                         * the generic firmware, but are not used with
                         * NMEA and SiRF protocols */
                        dev_dbg(&port->dev,
                                "%s - failed setting baud rate, unsupported speed of %d on Earthmate GPS\n",
                                __func__, new_rate);
                        return -1;
                }
                break;
        default:
                break;
        }
        return new_rate;
}


/* This function can either set or retrieve the current serial line settings */
static int cypress_serial_control(struct tty_struct *tty,
        struct usb_serial_port *port, speed_t baud_rate, int data_bits,
        int stop_bits, int parity_enable, int parity_type, int reset,
        int cypress_request_type)
{
        int new_baudrate = 0, retval = 0, tries = 0;
        struct cypress_private *priv;
        struct device *dev = &port->dev;
        u8 *feature_buffer;
        const unsigned int feature_len = 5;
        unsigned long flags;

        priv = usb_get_serial_port_data(port);

        if (!priv->comm_is_ok)
                return -ENODEV;

        feature_buffer = kcalloc(feature_len, sizeof(u8), GFP_KERNEL);
        if (!feature_buffer)
                return -ENOMEM;

        switch (cypress_request_type) {
        case CYPRESS_SET_CONFIG:
                /* 0 means 'Hang up' so doesn't change the true bit rate */
                new_baudrate = priv->baud_rate;
                if (baud_rate && baud_rate != priv->baud_rate) {
                        dev_dbg(dev, "%s - baud rate is changing\n", __func__);
                        retval = analyze_baud_rate(port, baud_rate);
                        if (retval >= 0) {
                                new_baudrate = retval;
                                dev_dbg(dev, "%s - New baud rate set to %d\n",
                                        __func__, new_baudrate);
                        }
                }
                dev_dbg(dev, "%s - baud rate is being sent as %d\n", __func__,
                        new_baudrate);

                /* fill the feature_buffer with new configuration */
                put_unaligned_le32(new_baudrate, feature_buffer);
                feature_buffer[4] |= data_bits - 5;   /* assign data bits in 2 bit space ( max 3 ) */
                /* 1 bit gap */
                feature_buffer[4] |= (stop_bits << 3);   /* assign stop bits in 1 bit space */
                feature_buffer[4] |= (parity_enable << 4);   /* assign parity flag in 1 bit space */
                feature_buffer[4] |= (parity_type << 5);   /* assign parity type in 1 bit space */
                /* 1 bit gap */
                feature_buffer[4] |= (reset << 7);   /* assign reset at end of byte, 1 bit space */

                dev_dbg(dev, "%s - device is being sent this feature report:\n", __func__);
                dev_dbg(dev, "%s - %02X - %02X - %02X - %02X - %02X\n", __func__,
                        feature_buffer[0], feature_buffer[1],
                        feature_buffer[2], feature_buffer[3],
                        feature_buffer[4]);

                do {
                        retval = usb_control_msg(port->serial->dev,
                                        usb_sndctrlpipe(port->serial->dev, 0),
                                        HID_REQ_SET_REPORT,
                                        USB_DIR_OUT | USB_RECIP_INTERFACE | USB_TYPE_CLASS,
                                        0x0300, 0, feature_buffer,
                                        feature_len, 500);

                        if (tries++ >= 3)
                                break;

                } while (retval != feature_len &&
                         retval != -ENODEV);

                if (retval != feature_len) {
                        dev_err(dev, "%s - failed sending serial line settings - %d\n",
                                __func__, retval);
                        cypress_set_dead(port);
                } else {
                        spin_lock_irqsave(&priv->lock, flags);
                        priv->baud_rate = new_baudrate;
                        priv->current_config = feature_buffer[4];
                        spin_unlock_irqrestore(&priv->lock, flags);
                        /* If we asked for a speed change encode it */
                        if (baud_rate)
                                tty_encode_baud_rate(tty,
                                        new_baudrate, new_baudrate);
                }
        break;
        case CYPRESS_GET_CONFIG:
                if (priv->get_cfg_unsafe) {
                        /* Not implemented for this device,
                           and if we try to do it we're likely
                           to crash the hardware. */
                        retval = -ENOTTY;
                        goto out;
                }
                dev_dbg(dev, "%s - retrieving serial line settings\n", __func__);
                do {
                        retval = usb_control_msg(port->serial->dev,
                                        usb_rcvctrlpipe(port->serial->dev, 0),
                                        HID_REQ_GET_REPORT,
                                        USB_DIR_IN | USB_RECIP_INTERFACE | USB_TYPE_CLASS,
                                        0x0300, 0, feature_buffer,
                                        feature_len, 500);

                        if (tries++ >= 3)
                                break;
                } while (retval != feature_len
                                                && retval != -ENODEV);

                if (retval != feature_len) {
                        dev_err(dev, "%s - failed to retrieve serial line settings - %d\n",
                                __func__, retval);
                        cypress_set_dead(port);
                        goto out;
                } else {
                        spin_lock_irqsave(&priv->lock, flags);
                        /* store the config in one byte, and later
                           use bit masks to check values */
                        priv->current_config = feature_buffer[4];
                        priv->baud_rate = get_unaligned_le32(feature_buffer);
                        spin_unlock_irqrestore(&priv->lock, flags);
                }
        }
        spin_lock_irqsave(&priv->lock, flags);
        ++priv->cmd_count;
        spin_unlock_irqrestore(&priv->lock, flags);
out:
        kfree(feature_buffer);
        return retval;
} /* cypress_serial_control */


static void cypress_set_dead(struct usb_serial_port *port)
{
        struct cypress_private *priv = usb_get_serial_port_data(port);
        unsigned long flags;

        spin_lock_irqsave(&priv->lock, flags);
        if (!priv->comm_is_ok) {
                spin_unlock_irqrestore(&priv->lock, flags);
                return;
        }
        priv->comm_is_ok = 0;
        spin_unlock_irqrestore(&priv->lock, flags);

        dev_err(&port->dev, "cypress_m8 suspending failing port %d - "
                "interval might be too short\n", port->port_number);
}


/*****************************************************************************
 * Cypress serial driver functions
 *****************************************************************************/


static int cypress_generic_port_probe(struct usb_serial_port *port)
{
        struct usb_serial *serial = port->serial;
        struct cypress_private *priv;

        if (!port->interrupt_out_urb || !port->interrupt_in_urb) {
                dev_err(&port->dev, "required endpoint is missing\n");
                return -ENODEV;
        }

        priv = kzalloc(sizeof(struct cypress_private), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        priv->comm_is_ok = !0;
        spin_lock_init(&priv->lock);
        if (kfifo_alloc(&priv->write_fifo, CYPRESS_BUF_SIZE, GFP_KERNEL)) {
                kfree(priv);
                return -ENOMEM;
        }

        /* Skip reset for FRWD device. It is a workaound:
           device hangs if it receives SET_CONFIGURE in Configured
           state. */
        if (!is_frwd(serial->dev))
                usb_reset_configuration(serial->dev);

        priv->cmd_ctrl = 0;
        priv->line_control = 0;
        priv->rx_flags = 0;
        /* Default packet format setting is determined by packet size.
           Anything with a size larger then 9 must have a separate
           count field since the 3 bit count field is otherwise too
           small.  Otherwise we can use the slightly more compact
           format.  This is in accordance with the cypress_m8 serial
           converter app note. */
        if (port->interrupt_out_size > 9)
                priv->pkt_fmt = packet_format_1;
        else
                priv->pkt_fmt = packet_format_2;

        if (interval > 0) {
                priv->write_urb_interval = interval;
                priv->read_urb_interval = interval;
                dev_dbg(&port->dev, "%s - read & write intervals forced to %d\n",
                        __func__, interval);
        } else {
                priv->write_urb_interval = port->interrupt_out_urb->interval;
                priv->read_urb_interval = port->interrupt_in_urb->interval;
                dev_dbg(&port->dev, "%s - intervals: read=%d write=%d\n",
                        __func__, priv->read_urb_interval,
                        priv->write_urb_interval);
        }
        usb_set_serial_port_data(port, priv);

        port->port.drain_delay = 256;

        return 0;
}


static int cypress_earthmate_port_probe(struct usb_serial_port *port)
{
        struct usb_serial *serial = port->serial;
        struct cypress_private *priv;
        int ret;

        ret = cypress_generic_port_probe(port);
        if (ret) {
                dev_dbg(&port->dev, "%s - Failed setting up port\n", __func__);
                return ret;
        }

        priv = usb_get_serial_port_data(port);
        priv->chiptype = CT_EARTHMATE;
        /* All Earthmate devices use the separated-count packet
           format!  Idiotic. */
        priv->pkt_fmt = packet_format_1;
        if (serial->dev->descriptor.idProduct !=
                                cpu_to_le16(PRODUCT_ID_EARTHMATEUSB)) {
                /* The old original USB Earthmate seemed able to
                   handle GET_CONFIG requests; everything they've
                   produced since that time crashes if this command is
                   attempted :-( */
                dev_dbg(&port->dev,
                        "%s - Marking this device as unsafe for GET_CONFIG commands\n",
                        __func__);
                priv->get_cfg_unsafe = !0;
        }

        return 0;
}

static int cypress_hidcom_port_probe(struct usb_serial_port *port)
{
        struct cypress_private *priv;
        int ret;

        ret = cypress_generic_port_probe(port);
        if (ret) {
                dev_dbg(&port->dev, "%s - Failed setting up port\n", __func__);
                return ret;
        }

        priv = usb_get_serial_port_data(port);
        priv->chiptype = CT_CYPHIDCOM;

        return 0;
}

static int cypress_ca42v2_port_probe(struct usb_serial_port *port)
{
        struct cypress_private *priv;
        int ret;

        ret = cypress_generic_port_probe(port);
        if (ret) {
                dev_dbg(&port->dev, "%s - Failed setting up port\n", __func__);
                return ret;
        }

        priv = usb_get_serial_port_data(port);
        priv->chiptype = CT_CA42V2;

        return 0;
}

static void cypress_port_remove(struct usb_serial_port *port)
{
        struct cypress_private *priv;

        priv = usb_get_serial_port_data(port);

        kfifo_free(&priv->write_fifo);
        kfree(priv);
}

static int cypress_open(struct tty_struct *tty, struct usb_serial_port *port)
{
        struct cypress_private *priv = usb_get_serial_port_data(port);
        struct usb_serial *serial = port->serial;
        unsigned long flags;
        int result = 0;

        if (!priv->comm_is_ok)
                return -EIO;

        /* clear halts before open */
        usb_clear_halt(serial->dev, 0x81);
        usb_clear_halt(serial->dev, 0x02);

        spin_lock_irqsave(&priv->lock, flags);
        /* reset read/write statistics */
        priv->bytes_in = 0;
        priv->bytes_out = 0;
        priv->cmd_count = 0;
        priv->rx_flags = 0;
        spin_unlock_irqrestore(&priv->lock, flags);

        /* Set termios */
        cypress_send(port);

        if (tty)
                cypress_set_termios(tty, port, NULL);

        /* setup the port and start reading from the device */
        usb_fill_int_urb(port->interrupt_in_urb, serial->dev,
                usb_rcvintpipe(serial->dev, port->interrupt_in_endpointAddress),
                port->interrupt_in_urb->transfer_buffer,
                port->interrupt_in_urb->transfer_buffer_length,
                cypress_read_int_callback, port, priv->read_urb_interval);
        result = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);

        if (result) {
                dev_err(&port->dev,
                        "%s - failed submitting read urb, error %d\n",
                                                        __func__, result);
                cypress_set_dead(port);
        }

        return result;
} /* cypress_open */

static void cypress_dtr_rts(struct usb_serial_port *port, int on)
{
        struct cypress_private *priv = usb_get_serial_port_data(port);
        /* drop dtr and rts */
        spin_lock_irq(&priv->lock);
        if (on == 0)
                priv->line_control = 0;
        else 
                priv->line_control = CONTROL_DTR | CONTROL_RTS;
        priv->cmd_ctrl = 1;
        spin_unlock_irq(&priv->lock);
        cypress_write(NULL, port, NULL, 0);
}

static void cypress_close(struct usb_serial_port *port)
{
        struct cypress_private *priv = usb_get_serial_port_data(port);
        unsigned long flags;

        spin_lock_irqsave(&priv->lock, flags);
        kfifo_reset_out(&priv->write_fifo);
        spin_unlock_irqrestore(&priv->lock, flags);

        dev_dbg(&port->dev, "%s - stopping urbs\n", __func__);
        usb_kill_urb(port->interrupt_in_urb);
        usb_kill_urb(port->interrupt_out_urb);

        if (stats)
                dev_info(&port->dev, "Statistics: %d Bytes In | %d Bytes Out | %d Commands Issued\n",
                        priv->bytes_in, priv->bytes_out, priv->cmd_count);
} /* cypress_close */


static int cypress_write(struct tty_struct *tty, struct usb_serial_port *port,
                                        const unsigned char *buf, int count)
{
        struct cypress_private *priv = usb_get_serial_port_data(port);

        dev_dbg(&port->dev, "%s - %d bytes\n", __func__, count);

        /* line control commands, which need to be executed immediately,
           are not put into the buffer for obvious reasons.
         */
        if (priv->cmd_ctrl) {
                count = 0;
                goto finish;
        }

        if (!count)
                return count;

        count = kfifo_in_locked(&priv->write_fifo, buf, count, &priv->lock);

finish:
        cypress_send(port);

        return count;
} /* cypress_write */


static void cypress_send(struct usb_serial_port *port)
{
        int count = 0, result, offset, actual_size;
        struct cypress_private *priv = usb_get_serial_port_data(port);
        struct device *dev = &port->dev;
        unsigned long flags;

        if (!priv->comm_is_ok)
                return;

        dev_dbg(dev, "%s - interrupt out size is %d\n", __func__,
                port->interrupt_out_size);

        spin_lock_irqsave(&priv->lock, flags);
        if (priv->write_urb_in_use) {
                dev_dbg(dev, "%s - can't write, urb in use\n", __func__);
                spin_unlock_irqrestore(&priv->lock, flags);
                return;
        }
        spin_unlock_irqrestore(&priv->lock, flags);

        /* clear buffer */
        memset(port->interrupt_out_urb->transfer_buffer, 0,
                                                port->interrupt_out_size);

        spin_lock_irqsave(&priv->lock, flags);
        switch (priv->pkt_fmt) {
        default:
        case packet_format_1:
                /* this is for the CY7C64013... */
                offset = 2;
                port->interrupt_out_buffer[0] = priv->line_control;
                break;
        case packet_format_2:
                /* this is for the CY7C63743... */
                offset = 1;
                port->interrupt_out_buffer[0] = priv->line_control;
                break;
        }

        if (priv->line_control & CONTROL_RESET)
                priv->line_control &= ~CONTROL_RESET;

        if (priv->cmd_ctrl) {
                priv->cmd_count++;
                dev_dbg(dev, "%s - line control command being issued\n", __func__);
                spin_unlock_irqrestore(&priv->lock, flags);
                goto send;
        } else
                spin_unlock_irqrestore(&priv->lock, flags);

        count = kfifo_out_locked(&priv->write_fifo,
                                        &port->interrupt_out_buffer[offset],
                                        port->interrupt_out_size - offset,
                                        &priv->lock);
        if (count == 0)
                return;

        switch (priv->pkt_fmt) {
        default:
        case packet_format_1:
                port->interrupt_out_buffer[1] = count;
                break;
        case packet_format_2:
                port->interrupt_out_buffer[0] |= count;
        }

        dev_dbg(dev, "%s - count is %d\n", __func__, count);

send:
        spin_lock_irqsave(&priv->lock, flags);
        priv->write_urb_in_use = 1;
        spin_unlock_irqrestore(&priv->lock, flags);

        if (priv->cmd_ctrl)
                actual_size = 1;
        else
                actual_size = count +
                              (priv->pkt_fmt == packet_format_1 ? 2 : 1);

        usb_serial_debug_data(dev, __func__, port->interrupt_out_size,
                              port->interrupt_out_urb->transfer_buffer);

        usb_fill_int_urb(port->interrupt_out_urb, port->serial->dev,
                usb_sndintpipe(port->serial->dev, port->interrupt_out_endpointAddress),
                port->interrupt_out_buffer, actual_size,
                cypress_write_int_callback, port, priv->write_urb_interval);
        result = usb_submit_urb(port->interrupt_out_urb, GFP_ATOMIC);
        if (result) {
                dev_err_console(port,
                                "%s - failed submitting write urb, error %d\n",
                                                        __func__, result);
                priv->write_urb_in_use = 0;
                cypress_set_dead(port);
        }

        spin_lock_irqsave(&priv->lock, flags);
        if (priv->cmd_ctrl)
                priv->cmd_ctrl = 0;

        /* do not count the line control and size bytes */
        priv->bytes_out += count;
        spin_unlock_irqrestore(&priv->lock, flags);

        usb_serial_port_softint(port);
} /* cypress_send */


/* returns how much space is available in the soft buffer */
static unsigned int cypress_write_room(struct tty_struct *tty)
{
        struct usb_serial_port *port = tty->driver_data;
        struct cypress_private *priv = usb_get_serial_port_data(port);
        unsigned int room;
        unsigned long flags;

        spin_lock_irqsave(&priv->lock, flags);
        room = kfifo_avail(&priv->write_fifo);
        spin_unlock_irqrestore(&priv->lock, flags);

        dev_dbg(&port->dev, "%s - returns %u\n", __func__, room);
        return room;
}


static int cypress_tiocmget(struct tty_struct *tty)
{
        struct usb_serial_port *port = tty->driver_data;
        struct cypress_private *priv = usb_get_serial_port_data(port);
        __u8 status, control;
        unsigned int result = 0;
        unsigned long flags;

        spin_lock_irqsave(&priv->lock, flags);
        control = priv->line_control;
        status = priv->current_status;
        spin_unlock_irqrestore(&priv->lock, flags);

        result = ((control & CONTROL_DTR)        ? TIOCM_DTR : 0)
                | ((control & CONTROL_RTS)       ? TIOCM_RTS : 0)
                | ((status & UART_CTS)        ? TIOCM_CTS : 0)
                | ((status & UART_DSR)        ? TIOCM_DSR : 0)
                | ((status & UART_RI)         ? TIOCM_RI  : 0)
                | ((status & UART_CD)         ? TIOCM_CD  : 0);

        dev_dbg(&port->dev, "%s - result = %x\n", __func__, result);

        return result;
}


static int cypress_tiocmset(struct tty_struct *tty,
                               unsigned int set, unsigned int clear)
{
        struct usb_serial_port *port = tty->driver_data;
        struct cypress_private *priv = usb_get_serial_port_data(port);
        unsigned long flags;

        spin_lock_irqsave(&priv->lock, flags);
        if (set & TIOCM_RTS)
                priv->line_control |= CONTROL_RTS;
        if (set & TIOCM_DTR)
                priv->line_control |= CONTROL_DTR;
        if (clear & TIOCM_RTS)
                priv->line_control &= ~CONTROL_RTS;
        if (clear & TIOCM_DTR)
                priv->line_control &= ~CONTROL_DTR;
        priv->cmd_ctrl = 1;
        spin_unlock_irqrestore(&priv->lock, flags);

        return cypress_write(tty, port, NULL, 0);
}

static void cypress_earthmate_init_termios(struct tty_struct *tty)
{
        tty_encode_baud_rate(tty, 4800, 4800);
}

static void cypress_set_termios(struct tty_struct *tty,
        struct usb_serial_port *port, struct ktermios *old_termios)
{
        struct cypress_private *priv = usb_get_serial_port_data(port);
        struct device *dev = &port->dev;
        int data_bits, stop_bits, parity_type, parity_enable;
        unsigned int cflag;
        unsigned long flags;
        __u8 oldlines;
        int linechange = 0;

        /* Unsupported features need clearing */
        tty->termios.c_cflag &= ~(CMSPAR|CRTSCTS);

        cflag = tty->termios.c_cflag;

        /* set number of data bits, parity, stop bits */
        /* when parity is disabled the parity type bit is ignored */

        /* 1 means 2 stop bits, 0 means 1 stop bit */
        stop_bits = cflag & CSTOPB ? 1 : 0;

        if (cflag & PARENB) {
                parity_enable = 1;
                /* 1 means odd parity, 0 means even parity */
                parity_type = cflag & PARODD ? 1 : 0;
        } else
                parity_enable = parity_type = 0;

        data_bits = tty_get_char_size(cflag);

        spin_lock_irqsave(&priv->lock, flags);
        oldlines = priv->line_control;
        if ((cflag & CBAUD) == B0) {
                /* drop dtr and rts */
                dev_dbg(dev, "%s - dropping the lines, baud rate 0bps\n", __func__);
                priv->line_control &= ~(CONTROL_DTR | CONTROL_RTS);
        } else
                priv->line_control = (CONTROL_DTR | CONTROL_RTS);
        spin_unlock_irqrestore(&priv->lock, flags);

        dev_dbg(dev, "%s - sending %d stop_bits, %d parity_enable, %d parity_type, %d data_bits (+5)\n",
                __func__, stop_bits, parity_enable, parity_type, data_bits);

        cypress_serial_control(tty, port, tty_get_baud_rate(tty),
                        data_bits, stop_bits,
                        parity_enable, parity_type,
                        0, CYPRESS_SET_CONFIG);

        /* we perform a CYPRESS_GET_CONFIG so that the current settings are
         * filled into the private structure this should confirm that all is
         * working if it returns what we just set */
        cypress_serial_control(tty, port, 0, 0, 0, 0, 0, 0, CYPRESS_GET_CONFIG);

        /* Here we can define custom tty settings for devices; the main tty
         * termios flag base comes from empeg.c */

        spin_lock_irqsave(&priv->lock, flags);
        if (priv->chiptype == CT_EARTHMATE && priv->baud_rate == 4800) {
                dev_dbg(dev, "Using custom termios settings for a baud rate of 4800bps.\n");
                /* define custom termios settings for NMEA protocol */

                tty->termios.c_iflag /* input modes - */
                        &= ~(IGNBRK  /* disable ignore break */
                        | BRKINT     /* disable break causes interrupt */
                        | PARMRK     /* disable mark parity errors */
                        | ISTRIP     /* disable clear high bit of input char */
                        | INLCR      /* disable translate NL to CR */
                        | IGNCR      /* disable ignore CR */
                        | ICRNL      /* disable translate CR to NL */
                        | IXON);     /* disable enable XON/XOFF flow control */

                tty->termios.c_oflag /* output modes */
                        &= ~OPOST;    /* disable postprocess output char */

                tty->termios.c_lflag /* line discipline modes */
                        &= ~(ECHO     /* disable echo input characters */
                        | ECHONL      /* disable echo new line */
                        | ICANON      /* disable erase, kill, werase, and rprnt
                                         special characters */
                        | ISIG        /* disable interrupt, quit, and suspend
                                         special characters */
                        | IEXTEN);    /* disable non-POSIX special characters */
        } /* CT_CYPHIDCOM: Application should handle this for device */

        linechange = (priv->line_control != oldlines);
        spin_unlock_irqrestore(&priv->lock, flags);

        /* if necessary, set lines */
        if (linechange) {
                priv->cmd_ctrl = 1;
                cypress_write(tty, port, NULL, 0);
        }
} /* cypress_set_termios */


/* returns amount of data still left in soft buffer */
static unsigned int cypress_chars_in_buffer(struct tty_struct *tty)
{
        struct usb_serial_port *port = tty->driver_data;
        struct cypress_private *priv = usb_get_serial_port_data(port);
        unsigned int chars;
        unsigned long flags;

        spin_lock_irqsave(&priv->lock, flags);
        chars = kfifo_len(&priv->write_fifo);
        spin_unlock_irqrestore(&priv->lock, flags);

        dev_dbg(&port->dev, "%s - returns %u\n", __func__, chars);
        return chars;
}


static void cypress_throttle(struct tty_struct *tty)
{
        struct usb_serial_port *port = tty->driver_data;
        struct cypress_private *priv = usb_get_serial_port_data(port);

        spin_lock_irq(&priv->lock);
        priv->rx_flags = THROTTLED;
        spin_unlock_irq(&priv->lock);
}


static void cypress_unthrottle(struct tty_struct *tty)
{
        struct usb_serial_port *port = tty->driver_data;
        struct cypress_private *priv = usb_get_serial_port_data(port);
        int actually_throttled, result;

        spin_lock_irq(&priv->lock);
        actually_throttled = priv->rx_flags & ACTUALLY_THROTTLED;
        priv->rx_flags = 0;
        spin_unlock_irq(&priv->lock);

        if (!priv->comm_is_ok)
                return;

        if (actually_throttled) {
                result = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);

                if (result) {
                        dev_err(&port->dev, "%s - failed submitting read urb, "
                                        "error %d\n", __func__, result);
                        cypress_set_dead(port);
                }
        }
}


static void cypress_read_int_callback(struct urb *urb)
{
        struct usb_serial_port *port = urb->context;
        struct cypress_private *priv = usb_get_serial_port_data(port);
        struct device *dev = &urb->dev->dev;
        struct tty_struct *tty;
        unsigned char *data = urb->transfer_buffer;
        unsigned long flags;
        char tty_flag = TTY_NORMAL;
        int bytes = 0;
        int result;
        int i = 0;
        int status = urb->status;

        switch (status) {
        case 0: /* success */
                break;
        case -ECONNRESET:
        case -ENOENT:
        case -ESHUTDOWN:
                /* precursor to disconnect so just go away */
                return;
        case -EPIPE:
                /* Can't call usb_clear_halt while in_interrupt */
                fallthrough;
        default:
                /* something ugly is going on... */
                dev_err(dev, "%s - unexpected nonzero read status received: %d\n",
                        __func__, status);
                cypress_set_dead(port);
                return;
        }

        spin_lock_irqsave(&priv->lock, flags);
        if (priv->rx_flags & THROTTLED) {
                dev_dbg(dev, "%s - now throttling\n", __func__);
                priv->rx_flags |= ACTUALLY_THROTTLED;
                spin_unlock_irqrestore(&priv->lock, flags);
                return;
        }
        spin_unlock_irqrestore(&priv->lock, flags);

        tty = tty_port_tty_get(&port->port);
        if (!tty) {
                dev_dbg(dev, "%s - bad tty pointer - exiting\n", __func__);
                return;
        }

        spin_lock_irqsave(&priv->lock, flags);
        result = urb->actual_length;
        switch (priv->pkt_fmt) {
        default:
        case packet_format_1:
                /* This is for the CY7C64013... */
                priv->current_status = data[0] & 0xF8;
                bytes = data[1] + 2;
                i = 2;
                break;
        case packet_format_2:
                /* This is for the CY7C63743... */
                priv->current_status = data[0] & 0xF8;
                bytes = (data[0] & 0x07) + 1;
                i = 1;
                break;
        }
        spin_unlock_irqrestore(&priv->lock, flags);
        if (result < bytes) {
                dev_dbg(dev,
                        "%s - wrong packet size - received %d bytes but packet said %d bytes\n",
                        __func__, result, bytes);
                goto continue_read;
        }

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

        spin_lock_irqsave(&priv->lock, flags);
        /* check to see if status has changed */
        if (priv->current_status != priv->prev_status) {
                u8 delta = priv->current_status ^ priv->prev_status;

                if (delta & UART_MSR_MASK) {
                        if (delta & UART_CTS)
                                port->icount.cts++;
                        if (delta & UART_DSR)
                                port->icount.dsr++;
                        if (delta & UART_RI)
                                port->icount.rng++;
                        if (delta & UART_CD)
                                port->icount.dcd++;

                        wake_up_interruptible(&port->port.delta_msr_wait);
                }

                priv->prev_status = priv->current_status;
        }
        spin_unlock_irqrestore(&priv->lock, flags);

        /* hangup, as defined in acm.c... this might be a bad place for it
         * though */
        if (tty && !C_CLOCAL(tty) && !(priv->current_status & UART_CD)) {
                dev_dbg(dev, "%s - calling hangup\n", __func__);
                tty_hangup(tty);
                goto continue_read;
        }

        /* There is one error bit... I'm assuming it is a parity error
         * indicator as the generic firmware will set this bit to 1 if a
         * parity error occurs.
         * I can not find reference to any other error events. */
        spin_lock_irqsave(&priv->lock, flags);
        if (priv->current_status & CYP_ERROR) {
                spin_unlock_irqrestore(&priv->lock, flags);
                tty_flag = TTY_PARITY;
                dev_dbg(dev, "%s - Parity Error detected\n", __func__);
        } else
                spin_unlock_irqrestore(&priv->lock, flags);

        /* process read if there is data other than line status */
        if (bytes > i) {
                tty_insert_flip_string_fixed_flag(&port->port, data + i,
                                tty_flag, bytes - i);
                tty_flip_buffer_push(&port->port);
        }

        spin_lock_irqsave(&priv->lock, flags);
        /* control and status byte(s) are also counted */
        priv->bytes_in += bytes;
        spin_unlock_irqrestore(&priv->lock, flags);

continue_read:
        tty_kref_put(tty);

        /* Continue trying to always read */

        if (priv->comm_is_ok) {
                usb_fill_int_urb(port->interrupt_in_urb, port->serial->dev,
                                usb_rcvintpipe(port->serial->dev,
                                        port->interrupt_in_endpointAddress),
                                port->interrupt_in_urb->transfer_buffer,
                                port->interrupt_in_urb->transfer_buffer_length,
                                cypress_read_int_callback, port,
                                priv->read_urb_interval);
                result = usb_submit_urb(port->interrupt_in_urb, GFP_ATOMIC);
                if (result && result != -EPERM) {
                        dev_err(dev, "%s - failed resubmitting read urb, error %d\n",
                                __func__, result);
                        cypress_set_dead(port);
                }
        }
} /* cypress_read_int_callback */


static void cypress_write_int_callback(struct urb *urb)
{
        struct usb_serial_port *port = urb->context;
        struct cypress_private *priv = usb_get_serial_port_data(port);
        struct device *dev = &urb->dev->dev;
        int status = urb->status;

        switch (status) {
        case 0:
                /* success */
                break;
        case -ECONNRESET:
        case -ENOENT:
        case -ESHUTDOWN:
                /* this urb is terminated, clean up */
                dev_dbg(dev, "%s - urb shutting down with status: %d\n",
                        __func__, status);
                priv->write_urb_in_use = 0;
                return;
        case -EPIPE:
                /* Cannot call usb_clear_halt while in_interrupt */
                fallthrough;
        default:
                dev_err(dev, "%s - unexpected nonzero write status received: %d\n",
                        __func__, status);
                cypress_set_dead(port);
                break;
        }
        priv->write_urb_in_use = 0;

        /* send any buffered data */
        cypress_send(port);
}

module_usb_serial_driver(serial_drivers, id_table_combined);

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

module_param(stats, bool, 0644);
MODULE_PARM_DESC(stats, "Enable statistics or not");
module_param(interval, int, 0644);
MODULE_PARM_DESC(interval, "Overrides interrupt interval");
module_param(unstable_bauds, bool, 0644);
MODULE_PARM_DESC(unstable_bauds, "Allow unstable baud rates");