/*
 * Copyright 2007, Frank A Kingswood <frank@kingswood-consulting.co.uk>
 * Copyright 2007, Werner Cornelius <werner@cornelius-consult.de>
 * Copyright 2009, Boris Hajduk <boris@hajduk.org>
 *
 * ch341.c implements a serial port driver for the Winchiphead CH341.
 *
 * The CH341 device can be used to implement an RS232 asynchronous
 * serial port, an IEEE-1284 parallel printer port or a memory-like
 * interface. In all cases the CH341 supports an I2C interface as well.
 * This driver only supports the asynchronous serial interface.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License version
 * 2 as published by the Free Software Foundation.
 */

#include <linux/kernel.h>
#include <linux/tty.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/usb.h>
#include <linux/usb/serial.h>
#include <linux/serial.h>
#include <asm/unaligned.h>

#define DEFAULT_BAUD_RATE 9600
#define DEFAULT_TIMEOUT   1000

/* flags for IO-Bits */
#define CH341_BIT_RTS (1 << 6)
#define CH341_BIT_DTR (1 << 5)

/******************************/
/* interrupt pipe definitions */
/******************************/
/* always 4 interrupt bytes */
/* first irq byte normally 0x08 */
/* second irq byte base 0x7d + below */
/* third irq byte base 0x94 + below */
/* fourth irq byte normally 0xee */

/* second interrupt byte */
#define CH341_MULT_STAT 0x04 /* multiple status since last interrupt event */

/* status returned in third interrupt answer byte, inverted in data
   from irq */
#define CH341_BIT_CTS 0x01
#define CH341_BIT_DSR 0x02
#define CH341_BIT_RI  0x04
#define CH341_BIT_DCD 0x08
#define CH341_BITS_MODEM_STAT 0x0f /* all bits */

/*******************************/
/* baudrate calculation factor */
/*******************************/
#define CH341_BAUDBASE_FACTOR 1532620800
#define CH341_BAUDBASE_DIVMAX 3

/* Break support - the information used to implement this was gleaned from
 * the Net/FreeBSD uchcom.c driver by Takanori Watanabe.  Domo arigato.
 */

#define CH341_REQ_WRITE_REG    0x9A
#define CH341_REQ_READ_REG     0x95
#define CH341_REG_BREAK1       0x05
#define CH341_REG_BREAK2       0x18
#define CH341_NBREAK_BITS_REG1 0x01
#define CH341_NBREAK_BITS_REG2 0x40


static const struct usb_device_id id_table[] = {
        { USB_DEVICE(0x4348, 0x5523) },
        { USB_DEVICE(0x1a86, 0x7523) },
        { USB_DEVICE(0x1a86, 0x5523) },
        { },
};
MODULE_DEVICE_TABLE(usb, id_table);

struct ch341_private {
        spinlock_t lock; /* access lock */
        unsigned baud_rate; /* set baud rate */
        u8 line_control; /* set line control value RTS/DTR */
        u8 line_status; /* active status of modem control inputs */
};

static void ch341_set_termios(struct tty_struct *tty,
                              struct usb_serial_port *port,
                              struct ktermios *old_termios);

static int ch341_control_out(struct usb_device *dev, u8 request,
                             u16 value, u16 index)
{
        int r;

        dev_dbg(&dev->dev, "ch341_control_out(%02x,%02x,%04x,%04x)\n",
                USB_DIR_OUT|0x40, (int)request, (int)value, (int)index);

        r = usb_control_msg(dev, usb_sndctrlpipe(dev, 0), request,
                            USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_OUT,
                            value, index, NULL, 0, DEFAULT_TIMEOUT);

        return r;
}

static int ch341_control_in(struct usb_device *dev,
                            u8 request, u16 value, u16 index,
                            char *buf, unsigned bufsize)
{
        int r;

        dev_dbg(&dev->dev, "ch341_control_in(%02x,%02x,%04x,%04x,%p,%u)\n",
                USB_DIR_IN|0x40, (int)request, (int)value, (int)index, buf,
                (int)bufsize);

        r = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0), request,
                            USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
                            value, index, buf, bufsize, DEFAULT_TIMEOUT);
        return r;
}

static int ch341_set_baudrate(struct usb_device *dev,
                              struct ch341_private *priv)
{
        short a, b;
        int r;
        unsigned long factor;
        short divisor;

        if (!priv->baud_rate)
                return -EINVAL;
        factor = (CH341_BAUDBASE_FACTOR / priv->baud_rate);
        divisor = CH341_BAUDBASE_DIVMAX;

        while ((factor > 0xfff0) && divisor) {
                factor >>= 3;
                divisor--;
        }

        if (factor > 0xfff0)
                return -EINVAL;

        factor = 0x10000 - factor;
        a = (factor & 0xff00) | divisor;
        b = factor & 0xff;

        r = ch341_control_out(dev, 0x9a, 0x1312, a);
        if (!r)
                r = ch341_control_out(dev, 0x9a, 0x0f2c, b);

        return r;
}

static int ch341_set_handshake(struct usb_device *dev, u8 control)
{
        return ch341_control_out(dev, 0xa4, ~control, 0);
}

static int ch341_get_status(struct usb_device *dev, struct ch341_private *priv)
{
        char *buffer;
        int r;
        const unsigned size = 8;
        unsigned long flags;

        buffer = kmalloc(size, GFP_KERNEL);
        if (!buffer)
                return -ENOMEM;

        r = ch341_control_in(dev, 0x95, 0x0706, 0, buffer, size);
        if (r < 0)
                goto out;

        /* setup the private status if available */
        if (r == 2) {
                r = 0;
                spin_lock_irqsave(&priv->lock, flags);
                priv->line_status = (~(*buffer)) & CH341_BITS_MODEM_STAT;
                spin_unlock_irqrestore(&priv->lock, flags);
        } else
                r = -EPROTO;

out:    kfree(buffer);
        return r;
}

/* -------------------------------------------------------------------------- */

static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
{
        char *buffer;
        int r;
        const unsigned size = 8;

        buffer = kmalloc(size, GFP_KERNEL);
        if (!buffer)
                return -ENOMEM;

        /* expect two bytes 0x27 0x00 */
        r = ch341_control_in(dev, 0x5f, 0, 0, buffer, size);
        if (r < 0)
                goto out;

        r = ch341_control_out(dev, 0xa1, 0, 0);
        if (r < 0)
                goto out;

        r = ch341_set_baudrate(dev, priv);
        if (r < 0)
                goto out;

        /* expect two bytes 0x56 0x00 */
        r = ch341_control_in(dev, 0x95, 0x2518, 0, buffer, size);
        if (r < 0)
                goto out;

        r = ch341_control_out(dev, 0x9a, 0x2518, 0x0050);
        if (r < 0)
                goto out;

        /* expect 0xff 0xee */
        r = ch341_get_status(dev, priv);
        if (r < 0)
                goto out;

        r = ch341_control_out(dev, 0xa1, 0x501f, 0xd90a);
        if (r < 0)
                goto out;

        r = ch341_set_baudrate(dev, priv);
        if (r < 0)
                goto out;

        r = ch341_set_handshake(dev, priv->line_control);
        if (r < 0)
                goto out;

        /* expect 0x9f 0xee */
        r = ch341_get_status(dev, priv);

out:    kfree(buffer);
        return r;
}

static int ch341_port_probe(struct usb_serial_port *port)
{
        struct ch341_private *priv;
        int r;

        priv = kzalloc(sizeof(struct ch341_private), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        spin_lock_init(&priv->lock);
        priv->baud_rate = DEFAULT_BAUD_RATE;
        priv->line_control = CH341_BIT_RTS | CH341_BIT_DTR;

        r = ch341_configure(port->serial->dev, priv);
        if (r < 0)
                goto error;

        usb_set_serial_port_data(port, priv);
        return 0;

error:  kfree(priv);
        return r;
}

static int ch341_port_remove(struct usb_serial_port *port)
{
        struct ch341_private *priv;

        priv = usb_get_serial_port_data(port);
        kfree(priv);

        return 0;
}

static int ch341_carrier_raised(struct usb_serial_port *port)
{
        struct ch341_private *priv = usb_get_serial_port_data(port);
        if (priv->line_status & CH341_BIT_DCD)
                return 1;
        return 0;
}

static void ch341_dtr_rts(struct usb_serial_port *port, int on)
{
        struct ch341_private *priv = usb_get_serial_port_data(port);
        unsigned long flags;

        /* drop DTR and RTS */
        spin_lock_irqsave(&priv->lock, flags);
        if (on)
                priv->line_control |= CH341_BIT_RTS | CH341_BIT_DTR;
        else
                priv->line_control &= ~(CH341_BIT_RTS | CH341_BIT_DTR);
        spin_unlock_irqrestore(&priv->lock, flags);
        ch341_set_handshake(port->serial->dev, priv->line_control);
}

static void ch341_close(struct usb_serial_port *port)
{
        usb_serial_generic_close(port);
        usb_kill_urb(port->interrupt_in_urb);
}


/* open this device, set default parameters */
static int ch341_open(struct tty_struct *tty, struct usb_serial_port *port)
{
        struct usb_serial *serial = port->serial;
        struct ch341_private *priv = usb_get_serial_port_data(port);
        int r;

        r = ch341_configure(serial->dev, priv);
        if (r)
                goto out;

        if (tty)
                ch341_set_termios(tty, port, NULL);

        dev_dbg(&port->dev, "%s - submitting interrupt urb\n", __func__);
        r = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);
        if (r) {
                dev_err(&port->dev, "%s - failed to submit interrupt urb: %d\n",
                        __func__, r);
                goto out;
        }

        r = usb_serial_generic_open(tty, port);

out:    return r;
}

/* Old_termios contains the original termios settings and
 * tty->termios contains the new setting to be used.
 */
static void ch341_set_termios(struct tty_struct *tty,
                struct usb_serial_port *port, struct ktermios *old_termios)
{
        struct ch341_private *priv = usb_get_serial_port_data(port);
        unsigned baud_rate;
        unsigned long flags;

        baud_rate = tty_get_baud_rate(tty);

        priv->baud_rate = baud_rate;

        if (baud_rate) {
                spin_lock_irqsave(&priv->lock, flags);
                priv->line_control |= (CH341_BIT_DTR | CH341_BIT_RTS);
                spin_unlock_irqrestore(&priv->lock, flags);
                ch341_set_baudrate(port->serial->dev, priv);
        } else {
                spin_lock_irqsave(&priv->lock, flags);
                priv->line_control &= ~(CH341_BIT_DTR | CH341_BIT_RTS);
                spin_unlock_irqrestore(&priv->lock, flags);
        }

        ch341_set_handshake(port->serial->dev, priv->line_control);

        /* Unimplemented:
         * (cflag & CSIZE) : data bits [5, 8]
         * (cflag & PARENB) : parity {NONE, EVEN, ODD}
         * (cflag & CSTOPB) : stop bits [1, 2]
         */
}

static void ch341_break_ctl(struct tty_struct *tty, int break_state)
{
        const uint16_t ch341_break_reg =
                        ((uint16_t) CH341_REG_BREAK2 << 8) | CH341_REG_BREAK1;
        struct usb_serial_port *port = tty->driver_data;
        int r;
        uint16_t reg_contents;
        uint8_t *break_reg;

        break_reg = kmalloc(2, GFP_KERNEL);
        if (!break_reg)
                return;

        r = ch341_control_in(port->serial->dev, CH341_REQ_READ_REG,
                        ch341_break_reg, 0, break_reg, 2);
        if (r < 0) {
                dev_err(&port->dev, "%s - USB control read error (%d)\n",
                                __func__, r);
                goto out;
        }
        dev_dbg(&port->dev, "%s - initial ch341 break register contents - reg1: %x, reg2: %x\n",
                __func__, break_reg[0], break_reg[1]);
        if (break_state != 0) {
                dev_dbg(&port->dev, "%s - Enter break state requested\n", __func__);
                break_reg[0] &= ~CH341_NBREAK_BITS_REG1;
                break_reg[1] &= ~CH341_NBREAK_BITS_REG2;
        } else {
                dev_dbg(&port->dev, "%s - Leave break state requested\n", __func__);
                break_reg[0] |= CH341_NBREAK_BITS_REG1;
                break_reg[1] |= CH341_NBREAK_BITS_REG2;
        }
        dev_dbg(&port->dev, "%s - New ch341 break register contents - reg1: %x, reg2: %x\n",
                __func__, break_reg[0], break_reg[1]);
        reg_contents = get_unaligned_le16(break_reg);
        r = ch341_control_out(port->serial->dev, CH341_REQ_WRITE_REG,
                        ch341_break_reg, reg_contents);
        if (r < 0)
                dev_err(&port->dev, "%s - USB control write error (%d)\n",
                                __func__, r);
out:
        kfree(break_reg);
}

static int ch341_tiocmset(struct tty_struct *tty,
                          unsigned int set, unsigned int clear)
{
        struct usb_serial_port *port = tty->driver_data;
        struct ch341_private *priv = usb_get_serial_port_data(port);
        unsigned long flags;
        u8 control;

        spin_lock_irqsave(&priv->lock, flags);
        if (set & TIOCM_RTS)
                priv->line_control |= CH341_BIT_RTS;
        if (set & TIOCM_DTR)
                priv->line_control |= CH341_BIT_DTR;
        if (clear & TIOCM_RTS)
                priv->line_control &= ~CH341_BIT_RTS;
        if (clear & TIOCM_DTR)
                priv->line_control &= ~CH341_BIT_DTR;
        control = priv->line_control;
        spin_unlock_irqrestore(&priv->lock, flags);

        return ch341_set_handshake(port->serial->dev, control);
}

static void ch341_update_line_status(struct usb_serial_port *port,
                                        unsigned char *data, size_t len)
{
        struct ch341_private *priv = usb_get_serial_port_data(port);
        struct tty_struct *tty;
        unsigned long flags;
        u8 status;
        u8 delta;

        if (len < 4)
                return;

        status = ~data[2] & CH341_BITS_MODEM_STAT;

        spin_lock_irqsave(&priv->lock, flags);
        delta = status ^ priv->line_status;
        priv->line_status = status;
        spin_unlock_irqrestore(&priv->lock, flags);

        if (data[1] & CH341_MULT_STAT)
                dev_dbg(&port->dev, "%s - multiple status change\n", __func__);

        if (!delta)
                return;

        if (delta & CH341_BIT_CTS)
                port->icount.cts++;
        if (delta & CH341_BIT_DSR)
                port->icount.dsr++;
        if (delta & CH341_BIT_RI)
                port->icount.rng++;
        if (delta & CH341_BIT_DCD) {
                port->icount.dcd++;
                tty = tty_port_tty_get(&port->port);
                if (tty) {
                        usb_serial_handle_dcd_change(port, tty,
                                                status & CH341_BIT_DCD);
                        tty_kref_put(tty);
                }
        }

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

static void ch341_read_int_callback(struct urb *urb)
{
        struct usb_serial_port *port = urb->context;
        unsigned char *data = urb->transfer_buffer;
        unsigned int len = urb->actual_length;
        int status;

        switch (urb->status) {
        case 0:
                /* success */
                break;
        case -ECONNRESET:
        case -ENOENT:
        case -ESHUTDOWN:
                /* this urb is terminated, clean up */
                dev_dbg(&urb->dev->dev, "%s - urb shutting down: %d\n",
                        __func__, urb->status);
                return;
        default:
                dev_dbg(&urb->dev->dev, "%s - nonzero urb status: %d\n",
                        __func__, urb->status);
                goto exit;
        }

        usb_serial_debug_data(&port->dev, __func__, len, data);
        ch341_update_line_status(port, data, len);
exit:
        status = usb_submit_urb(urb, GFP_ATOMIC);
        if (status) {
                dev_err(&urb->dev->dev, "%s - usb_submit_urb failed: %d\n",
                        __func__, status);
        }
}

static int ch341_tiocmget(struct tty_struct *tty)
{
        struct usb_serial_port *port = tty->driver_data;
        struct ch341_private *priv = usb_get_serial_port_data(port);
        unsigned long flags;
        u8 mcr;
        u8 status;
        unsigned int result;

        spin_lock_irqsave(&priv->lock, flags);
        mcr = priv->line_control;
        status = priv->line_status;
        spin_unlock_irqrestore(&priv->lock, flags);

        result = ((mcr & CH341_BIT_DTR)         ? TIOCM_DTR : 0)
                  | ((mcr & CH341_BIT_RTS)      ? TIOCM_RTS : 0)
                  | ((status & CH341_BIT_CTS)   ? TIOCM_CTS : 0)
                  | ((status & CH341_BIT_DSR)   ? TIOCM_DSR : 0)
                  | ((status & CH341_BIT_RI)    ? TIOCM_RI  : 0)
                  | ((status & CH341_BIT_DCD)   ? TIOCM_CD  : 0);

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

        return result;
}

static int ch341_reset_resume(struct usb_serial *serial)
{
        struct ch341_private *priv;

        priv = usb_get_serial_port_data(serial->port[0]);

        /* reconfigure ch341 serial port after bus-reset */
        ch341_configure(serial->dev, priv);

        return 0;
}

static struct usb_serial_driver ch341_device = {
        .driver = {
                .owner  = THIS_MODULE,
                .name   = "ch341-uart",
        },
        .id_table          = id_table,
        .num_ports         = 1,
        .open              = ch341_open,
        .dtr_rts           = ch341_dtr_rts,
        .carrier_raised    = ch341_carrier_raised,
        .close             = ch341_close,
        .set_termios       = ch341_set_termios,
        .break_ctl         = ch341_break_ctl,
        .tiocmget          = ch341_tiocmget,
        .tiocmset          = ch341_tiocmset,
        .tiocmiwait        = usb_serial_generic_tiocmiwait,
        .read_int_callback = ch341_read_int_callback,
        .port_probe        = ch341_port_probe,
        .port_remove       = ch341_port_remove,
        .reset_resume      = ch341_reset_resume,
};

static struct usb_serial_driver * const serial_drivers[] = {
        &ch341_device, NULL
};

module_usb_serial_driver(serial_drivers, id_table);

MODULE_LICENSE("GPL");