// SPDX-License-Identifier: GPL-2.0
/*
 * 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.
 */

#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 <linux/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 */

/* 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_READ_VERSION 0x5F
#define CH341_REQ_WRITE_REG    0x9A
#define CH341_REQ_READ_REG     0x95
#define CH341_REQ_SERIAL_INIT  0xA1
#define CH341_REQ_MODEM_CTRL   0xA4

#define CH341_REG_BREAK        0x05
#define CH341_REG_PRESCALER    0x12
#define CH341_REG_DIVISOR      0x13
#define CH341_REG_LCR          0x18
#define CH341_REG_LCR2         0x25
#define CH341_REG_FLOW_CTL     0x27

#define CH341_NBREAK_BITS      0x01

#define CH341_LCR_ENABLE_RX    0x80
#define CH341_LCR_ENABLE_TX    0x40
#define CH341_LCR_MARK_SPACE   0x20
#define CH341_LCR_PAR_EVEN     0x10
#define CH341_LCR_ENABLE_PAR   0x08
#define CH341_LCR_STOP_BITS_2  0x04
#define CH341_LCR_CS8          0x03
#define CH341_LCR_CS7          0x02
#define CH341_LCR_CS6          0x01
#define CH341_LCR_CS5          0x00

#define CH341_FLOW_CTL_NONE    0x00
#define CH341_FLOW_CTL_RTSCTS  0x01

#define CH341_QUIRK_LIMITED_PRESCALER   BIT(0)
#define CH341_QUIRK_SIMULATE_BREAK      BIT(1)

static const struct usb_device_id id_table[] = {
        { USB_DEVICE(0x1a86, 0x5523) },
        { USB_DEVICE(0x1a86, 0x7522) },
        { USB_DEVICE(0x1a86, 0x7523) },
        { USB_DEVICE(0x2184, 0x0057) },
        { USB_DEVICE(0x4348, 0x5523) },
        { USB_DEVICE(0x9986, 0x7523) },
        { },
};
MODULE_DEVICE_TABLE(usb, id_table);

struct ch341_private {
        spinlock_t lock; /* access lock */
        unsigned baud_rate; /* set baud rate */
        u8 mcr;
        u8 msr;
        u8 lcr;

        unsigned long quirks;
        u8 version;

        unsigned long break_end;
};

static void ch341_set_termios(struct tty_struct *tty,
                              struct usb_serial_port *port,
                              const 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, "%s - (%02x,%04x,%04x)\n", __func__,
                request, value, 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);
        if (r < 0)
                dev_err(&dev->dev, "failed to send control message: %d\n", r);

        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, "%s - (%02x,%04x,%04x,%u)\n", __func__,
                request, value, index, bufsize);

        r = usb_control_msg_recv(dev, 0, request,
                                 USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
                                 value, index, buf, bufsize, DEFAULT_TIMEOUT,
                                 GFP_KERNEL);
        if (r) {
                dev_err(&dev->dev, "failed to receive control message: %d\n",
                        r);
                return r;
        }

        return 0;
}

#define CH341_CLKRATE           48000000
#define CH341_CLK_DIV(ps, fact) (1 << (12 - 3 * (ps) - (fact)))
#define CH341_MIN_RATE(ps)      (CH341_CLKRATE / (CH341_CLK_DIV((ps), 1) * 512))

static const speed_t ch341_min_rates[] = {
        CH341_MIN_RATE(0),
        CH341_MIN_RATE(1),
        CH341_MIN_RATE(2),
        CH341_MIN_RATE(3),
};

/* Supported range is 46 to 3000000 bps. */
#define CH341_MIN_BPS   DIV_ROUND_UP(CH341_CLKRATE, CH341_CLK_DIV(0, 0) * 256)
#define CH341_MAX_BPS   (CH341_CLKRATE / (CH341_CLK_DIV(3, 0) * 2))

/*
 * The device line speed is given by the following equation:
 *
 *      baudrate = 48000000 / (2^(12 - 3 * ps - fact) * div), where
 *
 *              0 <= ps <= 3,
 *              0 <= fact <= 1,
 *              2 <= div <= 256 if fact = 0, or
 *              9 <= div <= 256 if fact = 1
 */
static int ch341_get_divisor(struct ch341_private *priv, speed_t speed)
{
        unsigned int fact, div, clk_div;
        bool force_fact0 = false;
        int ps;

        /*
         * Clamp to supported range, this makes the (ps < 0) and (div < 2)
         * sanity checks below redundant.
         */
        speed = clamp_val(speed, CH341_MIN_BPS, CH341_MAX_BPS);

        /*
         * Start with highest possible base clock (fact = 1) that will give a
         * divisor strictly less than 512.
         */
        fact = 1;
        for (ps = 3; ps >= 0; ps--) {
                if (speed > ch341_min_rates[ps])
                        break;
        }

        if (ps < 0)
                return -EINVAL;

        /* Determine corresponding divisor, rounding down. */
        clk_div = CH341_CLK_DIV(ps, fact);
        div = CH341_CLKRATE / (clk_div * speed);

        /* Some devices require a lower base clock if ps < 3. */
        if (ps < 3 && (priv->quirks & CH341_QUIRK_LIMITED_PRESCALER))
                force_fact0 = true;

        /* Halve base clock (fact = 0) if required. */
        if (div < 9 || div > 255 || force_fact0) {
                div /= 2;
                clk_div *= 2;
                fact = 0;
        }

        if (div < 2)
                return -EINVAL;

        /*
         * Pick next divisor if resulting rate is closer to the requested one,
         * scale up to avoid rounding errors on low rates.
         */
        if (16 * CH341_CLKRATE / (clk_div * div) - 16 * speed >=
                        16 * speed - 16 * CH341_CLKRATE / (clk_div * (div + 1)))
                div++;

        /*
         * Prefer lower base clock (fact = 0) if even divisor.
         *
         * Note that this makes the receiver more tolerant to errors.
         */
        if (fact == 1 && div % 2 == 0) {
                div /= 2;
                fact = 0;
        }

        return (0x100 - div) << 8 | fact << 2 | ps;
}

static int ch341_set_baudrate_lcr(struct usb_device *dev,
                                  struct ch341_private *priv,
                                  speed_t baud_rate, u8 lcr)
{
        int val;
        int r;

        if (!baud_rate)
                return -EINVAL;

        val = ch341_get_divisor(priv, baud_rate);
        if (val < 0)
                return -EINVAL;

        /*
         * CH341A buffers data until a full endpoint-size packet (32 bytes)
         * has been received unless bit 7 is set.
         *
         * At least one device with version 0x27 appears to have this bit
         * inverted.
         */
        if (priv->version > 0x27)
                val |= BIT(7);

        r = ch341_control_out(dev, CH341_REQ_WRITE_REG,
                              CH341_REG_DIVISOR << 8 | CH341_REG_PRESCALER,
                              val);
        if (r)
                return r;

        /*
         * Chip versions before version 0x30 as read using
         * CH341_REQ_READ_VERSION used separate registers for line control
         * (stop bits, parity and word length). Version 0x30 and above use
         * CH341_REG_LCR only and CH341_REG_LCR2 is always set to zero.
         */
        if (priv->version < 0x30)
                return 0;

        r = ch341_control_out(dev, CH341_REQ_WRITE_REG,
                              CH341_REG_LCR2 << 8 | CH341_REG_LCR, lcr);
        if (r)
                return r;

        return r;
}

static int ch341_set_handshake(struct usb_device *dev, u8 control)
{
        return ch341_control_out(dev, CH341_REQ_MODEM_CTRL, ~control, 0);
}

static int ch341_get_status(struct usb_device *dev, struct ch341_private *priv)
{
        const unsigned int size = 2;
        u8 buffer[2];
        int r;
        unsigned long flags;

        r = ch341_control_in(dev, CH341_REQ_READ_REG, 0x0706, 0, buffer, size);
        if (r)
                return r;

        spin_lock_irqsave(&priv->lock, flags);
        priv->msr = (~(*buffer)) & CH341_BITS_MODEM_STAT;
        spin_unlock_irqrestore(&priv->lock, flags);

        return 0;
}

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

static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
{
        const unsigned int size = 2;
        u8 buffer[2];
        int r;

        /* expect two bytes 0x27 0x00 */
        r = ch341_control_in(dev, CH341_REQ_READ_VERSION, 0, 0, buffer, size);
        if (r)
                return r;

        priv->version = buffer[0];
        dev_dbg(&dev->dev, "Chip version: 0x%02x\n", priv->version);

        r = ch341_control_out(dev, CH341_REQ_SERIAL_INIT, 0, 0);
        if (r < 0)
                return r;

        r = ch341_set_baudrate_lcr(dev, priv, priv->baud_rate, priv->lcr);
        if (r < 0)
                return r;

        r = ch341_set_handshake(dev, priv->mcr);
        if (r < 0)
                return r;

        return 0;
}

static int ch341_detect_quirks(struct usb_serial_port *port)
{
        struct ch341_private *priv = usb_get_serial_port_data(port);
        struct usb_device *udev = port->serial->dev;
        const unsigned int size = 2;
        unsigned long quirks = 0;
        u8 buffer[2];
        int r;

        /*
         * A subset of CH34x devices does not support all features. The
         * prescaler is limited and there is no support for sending a RS232
         * break condition. A read failure when trying to set up the latter is
         * used to detect these devices.
         */
        r = usb_control_msg_recv(udev, 0, CH341_REQ_READ_REG,
                                 USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
                                 CH341_REG_BREAK, 0, &buffer, size,
                                 DEFAULT_TIMEOUT, GFP_KERNEL);
        if (r == -EPIPE) {
                dev_info(&port->dev, "break control not supported, using simulated break\n");
                quirks = CH341_QUIRK_LIMITED_PRESCALER | CH341_QUIRK_SIMULATE_BREAK;
                r = 0;
        } else if (r) {
                dev_err(&port->dev, "failed to read break control: %d\n", r);
        }

        if (quirks) {
                dev_dbg(&port->dev, "enabling quirk flags: 0x%02lx\n", quirks);
                priv->quirks |= quirks;
        }

        return r;
}

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

        priv = kzalloc_obj(struct ch341_private);
        if (!priv)
                return -ENOMEM;

        spin_lock_init(&priv->lock);
        priv->baud_rate = DEFAULT_BAUD_RATE;
        /*
         * Some CH340 devices appear unable to change the initial LCR
         * settings, so set a sane 8N1 default.
         */
        priv->lcr = CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX | CH341_LCR_CS8;

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

        usb_set_serial_port_data(port, priv);

        r = ch341_detect_quirks(port);
        if (r < 0)
                goto error;

        return 0;

error:  kfree(priv);
        return r;
}

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

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

static int ch341_carrier_raised(struct usb_serial_port *port)
{
        struct ch341_private *priv = usb_get_serial_port_data(port);
        if (priv->msr & 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->mcr |= CH341_BIT_RTS | CH341_BIT_DTR;
        else
                priv->mcr &= ~(CH341_BIT_RTS | CH341_BIT_DTR);
        spin_unlock_irqrestore(&priv->lock, flags);
        ch341_set_handshake(port->serial->dev, priv->mcr);
}

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 ch341_private *priv = usb_get_serial_port_data(port);
        int r;

        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);
                return r;
        }

        r = ch341_get_status(port->serial->dev, priv);
        if (r < 0) {
                dev_err(&port->dev, "failed to read modem status: %d\n", r);
                goto err_kill_interrupt_urb;
        }

        r = usb_serial_generic_open(tty, port);
        if (r)
                goto err_kill_interrupt_urb;

        return 0;

err_kill_interrupt_urb:
        usb_kill_urb(port->interrupt_in_urb);

        return r;
}

static void ch341_set_flow_control(struct tty_struct *tty,
                                   struct usb_serial_port *port,
                                   const struct ktermios *old_termios)
{
        u16 flow_ctl;
        int r;

        if (C_CRTSCTS(tty))
                flow_ctl = CH341_FLOW_CTL_RTSCTS;
        else
                flow_ctl = CH341_FLOW_CTL_NONE;

        r = ch341_control_out(port->serial->dev,
                              CH341_REQ_WRITE_REG,
                              (CH341_REG_FLOW_CTL << 8) | CH341_REG_FLOW_CTL,
                              (flow_ctl << 8) | flow_ctl);
        if (r < 0 && old_termios) {
                tty->termios.c_cflag &= ~CRTSCTS;
                tty->termios.c_cflag |= (old_termios->c_cflag & CRTSCTS);
        }
}

/* 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,
                              const struct ktermios *old_termios)
{
        struct ch341_private *priv = usb_get_serial_port_data(port);
        unsigned baud_rate;
        unsigned long flags;
        u8 lcr;
        int r;

        /* redundant changes may cause the chip to lose bytes */
        if (old_termios && !tty_termios_hw_change(&tty->termios, old_termios))
                return;

        baud_rate = tty_get_baud_rate(tty);

        lcr = CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX;

        switch (C_CSIZE(tty)) {
        case CS5:
                lcr |= CH341_LCR_CS5;
                break;
        case CS6:
                lcr |= CH341_LCR_CS6;
                break;
        case CS7:
                lcr |= CH341_LCR_CS7;
                break;
        case CS8:
                lcr |= CH341_LCR_CS8;
                break;
        }

        if (C_PARENB(tty)) {
                lcr |= CH341_LCR_ENABLE_PAR;
                if (C_PARODD(tty) == 0)
                        lcr |= CH341_LCR_PAR_EVEN;
                if (C_CMSPAR(tty))
                        lcr |= CH341_LCR_MARK_SPACE;
        }

        if (C_CSTOPB(tty))
                lcr |= CH341_LCR_STOP_BITS_2;

        if (baud_rate) {
                priv->baud_rate = baud_rate;

                r = ch341_set_baudrate_lcr(port->serial->dev, priv,
                                           priv->baud_rate, lcr);
                if (r < 0 && old_termios) {
                        priv->baud_rate = tty_termios_baud_rate(old_termios);
                        tty_termios_copy_hw(&tty->termios, old_termios);
                } else if (r == 0) {
                        priv->lcr = lcr;
                }
        }

        spin_lock_irqsave(&priv->lock, flags);
        if (C_BAUD(tty) == B0)
                priv->mcr &= ~(CH341_BIT_DTR | CH341_BIT_RTS);
        else if (old_termios && (old_termios->c_cflag & CBAUD) == B0)
                priv->mcr |= (CH341_BIT_DTR | CH341_BIT_RTS);
        spin_unlock_irqrestore(&priv->lock, flags);

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

        ch341_set_flow_control(tty, port, old_termios);
}

/*
 * A subset of all CH34x devices don't support a real break condition and
 * reading CH341_REG_BREAK fails (see also ch341_detect_quirks). This function
 * simulates a break condition by lowering the baud rate to the minimum
 * supported by the hardware upon enabling the break condition and sending
 * a NUL byte.
 *
 * Incoming data is corrupted while the break condition is being simulated.
 *
 * Normally the duration of the break condition can be controlled individually
 * by userspace using TIOCSBRK and TIOCCBRK or by passing an argument to
 * TCSBRKP. Due to how the simulation is implemented the duration can't be
 * controlled. The duration is always about (1s / 46bd * 9bit) = 196ms.
 */
static int ch341_simulate_break(struct tty_struct *tty, int break_state)
{
        struct usb_serial_port *port = tty->driver_data;
        struct ch341_private *priv = usb_get_serial_port_data(port);
        unsigned long now, delay;
        int r, r2;

        if (break_state != 0) {
                dev_dbg(&port->dev, "enter break state requested\n");

                r = ch341_set_baudrate_lcr(port->serial->dev, priv,
                                CH341_MIN_BPS,
                                CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX | CH341_LCR_CS8);
                if (r < 0) {
                        dev_err(&port->dev,
                                "failed to change baud rate to %u: %d\n",
                                CH341_MIN_BPS, r);
                        goto restore;
                }

                r = tty_put_char(tty, '\0');
                if (r < 0) {
                        dev_err(&port->dev,
                                "failed to write NUL byte for simulated break condition: %d\n",
                                r);
                        goto restore;
                }

                /*
                 * Compute expected transmission duration including safety
                 * margin. The original baud rate is only restored after the
                 * computed point in time.
                 *
                 * 11 bits = 1 start, 8 data, 1 stop, 1 margin
                 */
                priv->break_end = jiffies + (11 * HZ / CH341_MIN_BPS);

                return 0;
        }

        dev_dbg(&port->dev, "leave break state requested\n");

        now = jiffies;

        if (time_before(now, priv->break_end)) {
                /* Wait until NUL byte is written */
                delay = priv->break_end - now;
                dev_dbg(&port->dev,
                        "wait %d ms while transmitting NUL byte at %u baud\n",
                        jiffies_to_msecs(delay), CH341_MIN_BPS);
                schedule_timeout_interruptible(delay);
        }

        r = 0;
restore:
        /* Restore original baud rate */
        r2 = ch341_set_baudrate_lcr(port->serial->dev, priv, priv->baud_rate,
                        priv->lcr);
        if (r2 < 0) {
                dev_err(&port->dev,
                        "restoring original baud rate of %u failed: %d\n",
                        priv->baud_rate, r2);
                return r2;
        }

        return r;
}

static int ch341_break_ctl(struct tty_struct *tty, int break_state)
{
        const u16 ch341_break_reg = (CH341_REG_LCR << 8) | CH341_REG_BREAK;
        struct usb_serial_port *port = tty->driver_data;
        struct ch341_private *priv = usb_get_serial_port_data(port);
        u16 reg_contents;
        u8 break_reg[2];
        int r;

        if (priv->quirks & CH341_QUIRK_SIMULATE_BREAK)
                return ch341_simulate_break(tty, break_state);

        r = ch341_control_in(port->serial->dev, CH341_REQ_READ_REG,
                        ch341_break_reg, 0, break_reg, 2);
        if (r) {
                dev_err(&port->dev, "%s - USB control read error (%d)\n",
                                __func__, r);
                if (r > 0)
                        r = -EIO;
                return r;
        }
        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;
                break_reg[1] &= ~CH341_LCR_ENABLE_TX;
        } else {
                dev_dbg(&port->dev, "%s - Leave break state requested\n", __func__);
                break_reg[0] |= CH341_NBREAK_BITS;
                break_reg[1] |= CH341_LCR_ENABLE_TX;
        }
        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);
                return r;
        }

        return 0;
}

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

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

static void ch341_update_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->msr;
        priv->msr = 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_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->mcr;
        status = priv->msr;
        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 usb_serial_port *port = serial->port[0];
        struct ch341_private *priv;
        int ret;

        priv = usb_get_serial_port_data(port);
        if (!priv)
                return 0;

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

        if (tty_port_initialized(&port->port)) {
                ret = usb_submit_urb(port->interrupt_in_urb, GFP_NOIO);
                if (ret) {
                        dev_err(&port->dev, "failed to submit interrupt urb: %d\n",
                                ret);
                        return ret;
                }

                ret = ch341_get_status(port->serial->dev, priv);
                if (ret < 0) {
                        dev_err(&port->dev, "failed to read modem status: %d\n",
                                ret);
                }
        }

        return usb_serial_generic_resume(serial);
}

static struct usb_serial_driver ch341_device = {
        .driver = {
                .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_DESCRIPTION("Winchiphead CH341 USB Serial driver");
MODULE_LICENSE("GPL v2");