xref: /openbmc/linux/drivers/usb/serial/ch341.c (revision 2612e3bbc0386368a850140a6c9b990cd496a5ec)

// 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 <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 */

/* 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_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_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(sizeof(struct ch341_private), GFP_KERNEL);
	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;
}

/* 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);
}

/*
 * 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 uint16_t ch341_break_reg =
			((uint16_t) 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);
	int r;
	uint16_t reg_contents;
	uint8_t break_reg[2];

	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 = {
		.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 v2");