Merge tag 'usb-serial-4.18-rc1' of https://git.kernel.org/pub/scm/linux/kernel/git/johan/usb-serial into usb-next

Johan writes:

USB-serial updates for v4.18-rc1

Here are the USB-serial updates for 4.18-rc1, including:

 - support for hardware-assisted XON/XOFF output flow control for pl2303
 - fix for a long-standing IXON/IXOFF mixup in ftdi_sio
 - blacklist of two apparently unused dwm-158 modem interfaces that
   confused some user space daemon (option)
 - add missing const to a tty helper currently used by USB serial only

Included are also various clean ups.

All have been in linux-next with no reported issues.

Signed-off-by: Johan Hovold <johan@kernel.org>

7 files changed, 99 insertions, 123 deletions

diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index d9b561d89432..d99fec44036c 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -290,7 +290,7 @@ EXPORT_SYMBOL(tty_termios_copy_hw);
  *	between the two termios structures, or a speed change is needed.
  */
 
-int tty_termios_hw_change(struct ktermios *a, struct ktermios *b)
+int tty_termios_hw_change(const struct ktermios *a, const struct ktermios *b)
 {
 	if (a->c_ispeed != b->c_ispeed || a->c_ospeed != b->c_ospeed)
 		return 1;
diff --git a/drivers/usb/serial/bus.c b/drivers/usb/serial/bus.c
index 9e265eb92611..eb0195cf37dd 100644
--- a/drivers/usb/serial/bus.c
+++ b/drivers/usb/serial/bus.c
@@ -60,7 +60,8 @@ static int usb_serial_device_probe(struct device *dev)
 	}
 
 	minor = port->minor;
-	tty_dev = tty_register_device(usb_serial_tty_driver, minor, dev);
+	tty_dev = tty_port_register_device(&port->port, usb_serial_tty_driver,
+					   minor, dev);
 	if (IS_ERR(tty_dev)) {
 		retval = PTR_ERR(tty_dev);
 		goto err_port_remove;
diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 7ea221d42dba..b5cef322826f 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -54,15 +54,14 @@ struct ftdi_private {
 	int custom_divisor;	/* custom_divisor kludge, this is for
 				   baud_base (different from what goes to the
 				   chip!) */
-	__u16 last_set_data_urb_value ;
-				/* the last data state set - needed for doing
-				 * a break
-				 */
+	u16 last_set_data_value; /* the last data state set - needed for doing
+				  * a break
+				  */
 	int flags;		/* some ASYNC_xxxx flags are supported */
 	unsigned long last_dtr_rts;	/* saved modem control outputs */
 	char prev_status;        /* Used for TIOCMIWAIT */
 	char transmit_empty;	/* If transmitter is empty or not */
-	__u16 interface;	/* FT2232C, FT2232H or FT4232H port interface
+	u16 interface;		/* FT2232C, FT2232H or FT4232H port interface
 				   (0 for FT232/245) */
 
 	speed_t force_baud;	/* if non-zero, force the baud rate to
@@ -1063,10 +1062,10 @@ static int ftdi_get_modem_status(struct usb_serial_port *port,
 
 static unsigned short int ftdi_232am_baud_base_to_divisor(int baud, int base);
 static unsigned short int ftdi_232am_baud_to_divisor(int baud);
-static __u32 ftdi_232bm_baud_base_to_divisor(int baud, int base);
-static __u32 ftdi_232bm_baud_to_divisor(int baud);
-static __u32 ftdi_2232h_baud_base_to_divisor(int baud, int base);
-static __u32 ftdi_2232h_baud_to_divisor(int baud);
+static u32 ftdi_232bm_baud_base_to_divisor(int baud, int base);
+static u32 ftdi_232bm_baud_to_divisor(int baud);
+static u32 ftdi_2232h_baud_base_to_divisor(int baud, int base);
+static u32 ftdi_2232h_baud_to_divisor(int baud);
 
 static struct usb_serial_driver ftdi_sio_device = {
 	.driver = {
@@ -1136,14 +1135,14 @@ static unsigned short int ftdi_232am_baud_to_divisor(int baud)
 	 return ftdi_232am_baud_base_to_divisor(baud, 48000000);
 }
 
-static __u32 ftdi_232bm_baud_base_to_divisor(int baud, int base)
+static u32 ftdi_232bm_baud_base_to_divisor(int baud, int base)
 {
 	static const unsigned char divfrac[8] = { 0, 3, 2, 4, 1, 5, 6, 7 };
-	__u32 divisor;
+	u32 divisor;
 	/* divisor shifted 3 bits to the left */
 	int divisor3 = base / 2 / baud;
 	divisor = divisor3 >> 3;
-	divisor |= (__u32)divfrac[divisor3 & 0x7] << 14;
+	divisor |= (u32)divfrac[divisor3 & 0x7] << 14;
 	/* Deal with special cases for highest baud rates. */
 	if (divisor == 1)
 		divisor = 0;
@@ -1152,22 +1151,22 @@ static __u32 ftdi_232bm_baud_base_to_divisor(int baud, int base)
 	return divisor;
 }
 
-static __u32 ftdi_232bm_baud_to_divisor(int baud)
+static u32 ftdi_232bm_baud_to_divisor(int baud)
 {
 	 return ftdi_232bm_baud_base_to_divisor(baud, 48000000);
 }
 
-static __u32 ftdi_2232h_baud_base_to_divisor(int baud, int base)
+static u32 ftdi_2232h_baud_base_to_divisor(int baud, int base)
 {
 	static const unsigned char divfrac[8] = { 0, 3, 2, 4, 1, 5, 6, 7 };
-	__u32 divisor;
+	u32 divisor;
 	int divisor3;
 
 	/* hi-speed baud rate is 10-bit sampling instead of 16-bit */
 	divisor3 = base * 8 / (baud * 10);
 
 	divisor = divisor3 >> 3;
-	divisor |= (__u32)divfrac[divisor3 & 0x7] << 14;
+	divisor |= (u32)divfrac[divisor3 & 0x7] << 14;
 	/* Deal with special cases for highest baud rates. */
 	if (divisor == 1)
 		divisor = 0;
@@ -1182,7 +1181,7 @@ static __u32 ftdi_2232h_baud_base_to_divisor(int baud, int base)
 	return divisor;
 }
 
-static __u32 ftdi_2232h_baud_to_divisor(int baud)
+static u32 ftdi_2232h_baud_to_divisor(int baud)
 {
 	 return ftdi_2232h_baud_base_to_divisor(baud, 120000000);
 }
@@ -1195,7 +1194,7 @@ static int update_mctrl(struct usb_serial_port *port, unsigned int set,
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 	struct device *dev = &port->dev;
-	unsigned urb_value;
+	unsigned value;
 	int rv;
 
 	if (((set | clear) & (TIOCM_DTR | TIOCM_RTS)) == 0) {
@@ -1204,20 +1203,20 @@ static int update_mctrl(struct usb_serial_port *port, unsigned int set,
 	}
 
 	clear &= ~set;	/* 'set' takes precedence over 'clear' */
-	urb_value = 0;
+	value = 0;
 	if (clear & TIOCM_DTR)
-		urb_value |= FTDI_SIO_SET_DTR_LOW;
+		value |= FTDI_SIO_SET_DTR_LOW;
 	if (clear & TIOCM_RTS)
-		urb_value |= FTDI_SIO_SET_RTS_LOW;
+		value |= FTDI_SIO_SET_RTS_LOW;
 	if (set & TIOCM_DTR)
-		urb_value |= FTDI_SIO_SET_DTR_HIGH;
+		value |= FTDI_SIO_SET_DTR_HIGH;
 	if (set & TIOCM_RTS)
-		urb_value |= FTDI_SIO_SET_RTS_HIGH;
+		value |= FTDI_SIO_SET_RTS_HIGH;
 	rv = usb_control_msg(port->serial->dev,
 			       usb_sndctrlpipe(port->serial->dev, 0),
 			       FTDI_SIO_SET_MODEM_CTRL_REQUEST,
 			       FTDI_SIO_SET_MODEM_CTRL_REQUEST_TYPE,
-			       urb_value, priv->interface,
+			       value, priv->interface,
 			       NULL, 0, WDR_TIMEOUT);
 	if (rv < 0) {
 		dev_dbg(dev, "%s Error from MODEM_CTRL urb: DTR %s, RTS %s\n",
@@ -1236,12 +1235,12 @@ static int update_mctrl(struct usb_serial_port *port, unsigned int set,
 }
 
 
-static __u32 get_ftdi_divisor(struct tty_struct *tty,
+static u32 get_ftdi_divisor(struct tty_struct *tty,
 						struct usb_serial_port *port)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 	struct device *dev = &port->dev;
-	__u32 div_value = 0;
+	u32 div_value = 0;
 	int div_okay = 1;
 	int baud;
 
@@ -1299,7 +1298,7 @@ static __u32 get_ftdi_divisor(struct tty_struct *tty,
 	case FT232RL: /* FT232RL chip */
 	case FTX:     /* FT-X series */
 		if (baud <= 3000000) {
-			__u16 product_id = le16_to_cpu(
+			u16 product_id = le16_to_cpu(
 				port->serial->dev->descriptor.idProduct);
 			if (((product_id == FTDI_NDI_HUC_PID)		||
 			     (product_id == FTDI_NDI_SPECTRA_SCU_PID)	||
@@ -1346,26 +1345,26 @@ static __u32 get_ftdi_divisor(struct tty_struct *tty,
 static int change_speed(struct tty_struct *tty, struct usb_serial_port *port)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
-	__u16 urb_value;
-	__u16 urb_index;
-	__u32 urb_index_value;
+	u16 value;
+	u16 index;
+	u32 index_value;
 	int rv;
 
-	urb_index_value = get_ftdi_divisor(tty, port);
-	urb_value = (__u16)urb_index_value;
-	urb_index = (__u16)(urb_index_value >> 16);
+	index_value = get_ftdi_divisor(tty, port);
+	value = (u16)index_value;
+	index = (u16)(index_value >> 16);
 	if ((priv->chip_type == FT2232C) || (priv->chip_type == FT2232H) ||
 		(priv->chip_type == FT4232H) || (priv->chip_type == FT232H)) {
 		/* Probably the BM type needs the MSB of the encoded fractional
 		 * divider also moved like for the chips above. Any infos? */
-		urb_index = (__u16)((urb_index << 8) | priv->interface);
+		index = (u16)((index << 8) | priv->interface);
 	}
 
 	rv = usb_control_msg(port->serial->dev,
 			    usb_sndctrlpipe(port->serial->dev, 0),
 			    FTDI_SIO_SET_BAUDRATE_REQUEST,
 			    FTDI_SIO_SET_BAUDRATE_REQUEST_TYPE,
-			    urb_value, urb_index,
+			    value, index,
 			    NULL, 0, WDR_SHORT_TIMEOUT);
 	return rv;
 }
@@ -2140,29 +2139,29 @@ static void ftdi_break_ctl(struct tty_struct *tty, int break_state)
 {
 	struct usb_serial_port *port = tty->driver_data;
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
-	__u16 urb_value;
+	u16 value;
 
 	/* break_state = -1 to turn on break, and 0 to turn off break */
 	/* see drivers/char/tty_io.c to see it used */
-	/* last_set_data_urb_value NEVER has the break bit set in it */
+	/* last_set_data_value NEVER has the break bit set in it */
 
 	if (break_state)
-		urb_value = priv->last_set_data_urb_value | FTDI_SIO_SET_BREAK;
+		value = priv->last_set_data_value | FTDI_SIO_SET_BREAK;
 	else
-		urb_value = priv->last_set_data_urb_value;
+		value = priv->last_set_data_value;
 
 	if (usb_control_msg(port->serial->dev,
 			usb_sndctrlpipe(port->serial->dev, 0),
 			FTDI_SIO_SET_DATA_REQUEST,
 			FTDI_SIO_SET_DATA_REQUEST_TYPE,
-			urb_value , priv->interface,
+			value , priv->interface,
 			NULL, 0, WDR_TIMEOUT) < 0) {
 		dev_err(&port->dev, "%s FAILED to enable/disable break state (state was %d)\n",
 			__func__, break_state);
 	}
 
 	dev_dbg(&port->dev, "%s break state is %d - urb is %d\n", __func__,
-		break_state, urb_value);
+		break_state, value);
 
 }
 
@@ -2192,12 +2191,8 @@ static void ftdi_set_termios(struct tty_struct *tty,
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 	struct ktermios *termios = &tty->termios;
 	unsigned int cflag = termios->c_cflag;
-	__u16 urb_value; /* will hold the new flags */
-
-	/* Added for xon/xoff support */
-	unsigned int iflag = termios->c_iflag;
-	unsigned char vstop;
-	unsigned char vstart;
+	u16 value, index;
+	int ret;
 
 	/* Force baud rate if this device requires it, unless it is set to
 	   B0. */
@@ -2258,44 +2253,44 @@ static void ftdi_set_termios(struct tty_struct *tty,
 no_skip:
 	/* Set number of data bits, parity, stop bits */
 
-	urb_value = 0;
-	urb_value |= (cflag & CSTOPB ? FTDI_SIO_SET_DATA_STOP_BITS_2 :
-		      FTDI_SIO_SET_DATA_STOP_BITS_1);
+	value = 0;
+	value |= (cflag & CSTOPB ? FTDI_SIO_SET_DATA_STOP_BITS_2 :
+			FTDI_SIO_SET_DATA_STOP_BITS_1);
 	if (cflag & PARENB) {
 		if (cflag & CMSPAR)
-			urb_value |= cflag & PARODD ?
-				     FTDI_SIO_SET_DATA_PARITY_MARK :
-				     FTDI_SIO_SET_DATA_PARITY_SPACE;
+			value |= cflag & PARODD ?
+					FTDI_SIO_SET_DATA_PARITY_MARK :
+					FTDI_SIO_SET_DATA_PARITY_SPACE;
 		else
-			urb_value |= cflag & PARODD ?
-				     FTDI_SIO_SET_DATA_PARITY_ODD :
-				     FTDI_SIO_SET_DATA_PARITY_EVEN;
+			value |= cflag & PARODD ?
+					FTDI_SIO_SET_DATA_PARITY_ODD :
+					FTDI_SIO_SET_DATA_PARITY_EVEN;
 	} else {
-		urb_value |= FTDI_SIO_SET_DATA_PARITY_NONE;
+		value |= FTDI_SIO_SET_DATA_PARITY_NONE;
 	}
 	switch (cflag & CSIZE) {
 	case CS5:
 		dev_dbg(ddev, "Setting CS5 quirk\n");
 		break;
 	case CS7:
-		urb_value |= 7;
+		value |= 7;
 		dev_dbg(ddev, "Setting CS7\n");
 		break;
 	default:
 	case CS8:
-		urb_value |= 8;
+		value |= 8;
 		dev_dbg(ddev, "Setting CS8\n");
 		break;
 	}
 
 	/* This is needed by the break command since it uses the same command
 	   - but is or'ed with this value  */
-	priv->last_set_data_urb_value = urb_value;
+	priv->last_set_data_value = value;
 
 	if (usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
 			    FTDI_SIO_SET_DATA_REQUEST,
 			    FTDI_SIO_SET_DATA_REQUEST_TYPE,
-			    urb_value , priv->interface,
+			    value , priv->interface,
 			    NULL, 0, WDR_SHORT_TIMEOUT) < 0) {
 		dev_err(ddev, "%s FAILED to set databits/stopbits/parity\n",
 			__func__);
@@ -2326,65 +2321,30 @@ no_data_parity_stop_changes:
 			set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
 	}
 
-	/* Set flow control */
-	/* Note device also supports DTR/CD (ugh) and Xon/Xoff in hardware */
 no_c_cflag_changes:
-	if (cflag & CRTSCTS) {
-		dev_dbg(ddev, "%s Setting to CRTSCTS flow control\n", __func__);
-		if (usb_control_msg(dev,
-				    usb_sndctrlpipe(dev, 0),
-				    FTDI_SIO_SET_FLOW_CTRL_REQUEST,
-				    FTDI_SIO_SET_FLOW_CTRL_REQUEST_TYPE,
-				    0 , (FTDI_SIO_RTS_CTS_HS | priv->interface),
-				    NULL, 0, WDR_TIMEOUT) < 0) {
-			dev_err(ddev, "urb failed to set to rts/cts flow control\n");
-		}
+	/* Set hardware-assisted flow control */
+	value = 0;
+
+	if (C_CRTSCTS(tty)) {
+		dev_dbg(&port->dev, "enabling rts/cts flow control\n");
+		index = FTDI_SIO_RTS_CTS_HS;
+	} else if (I_IXON(tty)) {
+		dev_dbg(&port->dev, "enabling xon/xoff flow control\n");
+		index = FTDI_SIO_XON_XOFF_HS;
+		value = STOP_CHAR(tty) << 8 | START_CHAR(tty);
 	} else {
-		/*
-		 * Xon/Xoff code
-		 *
-		 * Check the IXOFF status in the iflag component of the
-		 * termios structure. If IXOFF is not set, the pre-xon/xoff
-		 * code is executed.
-		 */
-		if (iflag & IXOFF) {
-			dev_dbg(ddev, "%s  request to enable xonxoff iflag=%04x\n",
-				__func__, iflag);
-			/* Try to enable the XON/XOFF on the ftdi_sio
-			 * Set the vstart and vstop -- could have been done up
-			 * above where a lot of other dereferencing is done but
-			 * that would be very inefficient as vstart and vstop
-			 * are not always needed.
-			 */
-			vstart = termios->c_cc[VSTART];
-			vstop = termios->c_cc[VSTOP];
-			urb_value = (vstop << 8) | (vstart);
-
-			if (usb_control_msg(dev,
-					    usb_sndctrlpipe(dev, 0),
-					    FTDI_SIO_SET_FLOW_CTRL_REQUEST,
-					    FTDI_SIO_SET_FLOW_CTRL_REQUEST_TYPE,
-					    urb_value , (FTDI_SIO_XON_XOFF_HS
-							 | priv->interface),
-					    NULL, 0, WDR_TIMEOUT) < 0) {
-				dev_err(&port->dev, "urb failed to set to "
-					"xon/xoff flow control\n");
-			}
-		} else {
-			/* else clause to only run if cflag ! CRTSCTS and iflag
-			 * ! XOFF. CHECKME Assuming XON/XOFF handled by tty
-			 * stack - not by device */
-			dev_dbg(ddev, "%s Turning off hardware flow control\n", __func__);
-			if (usb_control_msg(dev,
-					    usb_sndctrlpipe(dev, 0),
-					    FTDI_SIO_SET_FLOW_CTRL_REQUEST,
-					    FTDI_SIO_SET_FLOW_CTRL_REQUEST_TYPE,
-					    0, priv->interface,
-					    NULL, 0, WDR_TIMEOUT) < 0) {
-				dev_err(ddev, "urb failed to clear flow control\n");
-			}
-		}
+		dev_dbg(&port->dev, "disabling flow control\n");
+		index = FTDI_SIO_DISABLE_FLOW_CTRL;
 	}
+
+	index |= priv->interface;
+
+	ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
+			FTDI_SIO_SET_FLOW_CTRL_REQUEST,
+			FTDI_SIO_SET_FLOW_CTRL_REQUEST_TYPE,
+			value, index, NULL, 0, WDR_TIMEOUT);
+	if (ret < 0)
+		dev_err(&port->dev, "failed to set flow control: %d\n", ret);
 }
 
 /*
diff --git a/drivers/usb/serial/option.c b/drivers/usb/serial/option.c
index 2058852a87fa..664e61f16b6a 100644
--- a/drivers/usb/serial/option.c
+++ b/drivers/usb/serial/option.c
@@ -1916,7 +1916,8 @@ static const struct usb_device_id option_ids[] = {
 	{ USB_DEVICE_INTERFACE_CLASS(0x2001, 0x7d01, 0xff) },			/* D-Link DWM-156 (variant) */
 	{ USB_DEVICE_INTERFACE_CLASS(0x2001, 0x7d02, 0xff) },
 	{ USB_DEVICE_INTERFACE_CLASS(0x2001, 0x7d03, 0xff) },
-	{ USB_DEVICE_INTERFACE_CLASS(0x2001, 0x7d04, 0xff) },			/* D-Link DWM-158 */
+	{ USB_DEVICE_INTERFACE_CLASS(0x2001, 0x7d04, 0xff),			/* D-Link DWM-158 */
+	 .driver_info = RSVD(4) | RSVD(5) },
 	{ USB_DEVICE_INTERFACE_CLASS(0x2001, 0x7d0e, 0xff) },			/* D-Link DWM-157 C1 */
 	{ USB_DEVICE_INTERFACE_CLASS(0x2001, 0x7e19, 0xff),			/* D-Link DWM-221 B1 */
 	  .driver_info = RSVD(4) },
diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index 46dd09da2434..5d1a1931967e 100644
--- a/drivers/usb/serial/pl2303.c
+++ b/drivers/usb/serial/pl2303.c
@@ -533,6 +533,17 @@ static int pl2303_set_line_request(struct usb_serial_port *port,
 	return 0;
 }
 
+static bool pl2303_termios_change(const struct ktermios *a, const struct ktermios *b)
+{
+	bool ixon_change;
+
+	ixon_change = ((a->c_iflag ^ b->c_iflag) & (IXON | IXANY)) ||
+			a->c_cc[VSTART] != b->c_cc[VSTART] ||
+			a->c_cc[VSTOP] != b->c_cc[VSTOP];
+
+	return tty_termios_hw_change(a, b) || ixon_change;
+}
+
 static void pl2303_set_termios(struct tty_struct *tty,
 		struct usb_serial_port *port, struct ktermios *old_termios)
 {
@@ -544,7 +555,7 @@ static void pl2303_set_termios(struct tty_struct *tty,
 	int ret;
 	u8 control;
 
-	if (old_termios && !tty_termios_hw_change(&tty->termios, old_termios))
+	if (old_termios && !pl2303_termios_change(&tty->termios, old_termios))
 		return;
 
 	buf = kzalloc(7, GFP_KERNEL);
@@ -662,6 +673,9 @@ static void pl2303_set_termios(struct tty_struct *tty,
 			pl2303_vendor_write(serial, 0x0, 0x41);
 		else
 			pl2303_vendor_write(serial, 0x0, 0x61);
+	} else if (I_IXON(tty) && !I_IXANY(tty) && START_CHAR(tty) == 0x11 &&
+			STOP_CHAR(tty) == 0x13) {
+		pl2303_vendor_write(serial, 0x0, 0xc0);
 	} else {
 		pl2303_vendor_write(serial, 0x0, 0x0);
 	}
diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 790e0cbe3da9..44ecf0e2be9d 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -192,7 +192,7 @@ static int serial_install(struct tty_driver *driver, struct tty_struct *tty)
 	if (retval)
 		goto error_get_interface;
 
-	retval = tty_port_install(&port->port, driver, tty);
+	retval = tty_standard_install(driver, tty);
 	if (retval)
 		goto error_init_termios;
 
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 1dd587ba6d88..955cd0c93d84 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -527,7 +527,7 @@ static inline speed_t tty_get_baud_rate(struct tty_struct *tty)
 }
 
 extern void tty_termios_copy_hw(struct ktermios *new, struct ktermios *old);
-extern int tty_termios_hw_change(struct ktermios *a, struct ktermios *b);
+extern int tty_termios_hw_change(const struct ktermios *a, const struct ktermios *b);
 extern int tty_set_termios(struct tty_struct *tty, struct ktermios *kt);
 
 extern struct tty_ldisc *tty_ldisc_ref(struct tty_struct *);