[PATCH 3/3] minitty: minimal TTY support replacement for serial ports

[Nicolas Pitre]

This is a minimal TTY layer replacement for embedded systems with limited
capabilities. This supports only serial ports, supports only a subset of
the default line discipline, and dispense with anything that is of no use
for a small embedded system.

Signed-off-by: Nicolas Pitre <nico@xxxxxxxxxx>
---
 drivers/tty/Kconfig                                |   10 +-
 drivers/tty/Makefile                               |    1 +
 drivers/tty/serial/Kconfig                         |   12 +-
 drivers/tty/serial/Makefile                        |    3 +
 .../tty/serial/{serial_core.c => fulltty_serial.c} |    0
 drivers/tty/serial/minitty_serial.c                | 2091 ++++++++++++++++++++
 include/linux/tty_flip.h                           |    4 +
 7 files changed, 2116 insertions(+), 5 deletions(-)
 rename drivers/tty/serial/{serial_core.c => fulltty_serial.c} (100%)
 create mode 100644 drivers/tty/serial/minitty_serial.c

diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
index 95103054c0..8517c353d8 100644
--- a/drivers/tty/Kconfig
+++ b/drivers/tty/Kconfig
@@ -2,10 +2,12 @@ config TTY
 	bool "Enable TTY" if EXPERT
 	default y
 	---help---
-	  Allows you to remove TTY support which can save space, and
-	  blocks features that require TTY from inclusion in the kernel.
-	  TTY is required for any text terminals or serial port
-	  communication. Most users should leave this enabled.
+	  Allows you to remove the full-featured TTY support which can save
+	  space, and blocks features that require it from inclusion in the
+	  kernel. TTY support is required for any text terminals or serial
+	  port communication. If turned off, a much smaller TTY implementation
+	  that only supports serial ports in a limited capacity may be
+	  selected instead. Most users should leave this enabled.
 
 if TTY
 
diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
index 1461be6b90..9b7b3418cd 100644
--- a/drivers/tty/Makefile
+++ b/drivers/tty/Makefile
@@ -1,5 +1,6 @@
 obj-$(CONFIG_TTY)		+= tty_io.o n_tty.o tty_ioctl.o tty_ldisc.o \
 				   tty_buffer.o tty_port.o tty_mutex.o tty_ldsem.o tty_baudrate.o
+obj-$(CONFIG_MINITTY_SERIAL)	+= tty_baudrate.o
 obj-$(CONFIG_LEGACY_PTYS)	+= pty.o
 obj-$(CONFIG_UNIX98_PTYS)	+= pty.o
 obj-$(CONFIG_AUDIT)		+= tty_audit.o
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 6117ac8da4..a552387a39 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -2,7 +2,17 @@
 # Serial device configuration
 #
 
-if TTY
+config MINITTY_SERIAL
+	bool "Enable mini TTY for serial ports"
+	depends on !TTY
+	default y
+	help
+	  This enables a much smaller TTY implementation that only supports
+	  serial ports in a limited capacity. This is however sufficient for
+	  many embedded use cases that use serial ports mainly as a debug
+	  console where the saving in kernel code size is welcome.
+
+if TTY || MINITTY_SERIAL
 
 menu "Serial drivers"
 	depends on HAS_IOMEM
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index 2d6288bc45..970af02c86 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -2,7 +2,10 @@
 # Makefile for the kernel serial device drivers.
 #
 
+serial_core-$(CONFIG_TTY) := fulltty_serial.o
+serial_core-$(CONFIG_MINITTY_SERIAL) := minitty_serial.o
 obj-$(CONFIG_SERIAL_CORE) += serial_core.o
+
 obj-$(CONFIG_SERIAL_21285) += 21285.o
 
 obj-$(CONFIG_SERIAL_EARLYCON) += earlycon.o
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/fulltty_serial.c
similarity index 100%
rename from drivers/tty/serial/serial_core.c
rename to drivers/tty/serial/fulltty_serial.c
diff --git a/drivers/tty/serial/minitty_serial.c b/drivers/tty/serial/minitty_serial.c
new file mode 100644
index 0000000000..c8e91b2c54
--- /dev/null
+++ b/drivers/tty/serial/minitty_serial.c
@@ -0,0 +1,2091 @@
+/*
+ * Smallest shortcut replacement for tty and serial core layers.
+ *
+ * Based mainly on tty_io.c, n_tty.c and serial_core.c from many smart people.
+ *
+ * Created by:  Nicolas Pitre, January 2017
+ * Copyright:   (C) 2017  Linaro Limited
+ *
+ * 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/init.h>
+#include <linux/module.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/ctype.h>
+#include <linux/console.h>
+#include <linux/of.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/mutex.h>
+#include <linux/poll.h>
+#include <linux/sched.h>
+#include <linux/sched/signal.h>
+#include <linux/serial_core.h>
+#include <linux/signal.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+
+struct minitty_data {
+	struct uart_state state;
+	struct ktermios termios;
+	struct mutex mutex;
+	unsigned char *rx_buf;
+	int rx_head, rx_vetted, rx_tail;
+	int rx_lines, column, canon_start_pos;
+	bool rx_raw;
+	bool rx_overflow;
+	wait_queue_head_t write_wait;
+	wait_queue_head_t read_wait;
+	struct work_struct rx_work;
+	struct cdev cdev;
+	struct device *dev;
+	int usecount;
+};
+
+#define RX_BUF_SIZE PAGE_SIZE
+#define RX_BUF_WRAP(x) ((x) & (RX_BUF_SIZE - 1))
+
+/*
+ * Functions called back by low level UART drivers when
+ * the TX buffer is getting near empty.
+ */
+void uart_write_wakeup(struct uart_port *port)
+{
+	struct uart_state *state = port->state;
+	struct minitty_data *mtty = container_of(state, typeof(*mtty), state);
+
+	wake_up_interruptible_poll(&mtty->write_wait, POLLOUT);
+}
+EXPORT_SYMBOL(uart_write_wakeup);
+
+static void
+uart_update_mctrl(struct uart_port *port, unsigned int set, unsigned int clear)
+{
+	unsigned long flags;
+	unsigned int old;
+
+	spin_lock_irqsave(&port->lock, flags);
+	old = port->mctrl;
+	port->mctrl = (old & ~clear) | set;
+	if (old != port->mctrl)
+		port->ops->set_mctrl(port, port->mctrl);
+	spin_unlock_irqrestore(&port->lock, flags);
+}
+
+#define uart_set_mctrl(port, set)	uart_update_mctrl(port, set, 0)
+#define uart_clear_mctrl(port, clear)	uart_update_mctrl(port, 0, clear)
+
+static void uart_change_pm(struct uart_state *state,
+			   enum uart_pm_state pm_state)
+{
+	struct uart_port *port =state->uart_port; 
+
+	if (state->pm_state != pm_state) {
+		if (port && port->ops->pm)
+			port->ops->pm(port, pm_state, state->pm_state);
+		state->pm_state = pm_state;
+	}
+}
+
+int uart_suspend_port(struct uart_driver *drv, struct uart_port *port)
+{
+	return -EPROTONOSUPPORT;
+}
+EXPORT_SYMBOL(uart_suspend_port);
+
+int uart_resume_port(struct uart_driver *drv, struct uart_port *port)
+{
+	return -EPROTONOSUPPORT;
+}
+EXPORT_SYMBOL(uart_resume_port);
+
+/*
+ *	Are the two ports equivalent?
+ */
+int uart_match_port(struct uart_port *port1, struct uart_port *port2)
+{
+	if (port1->iotype != port2->iotype)
+		return 0;
+
+	switch (port1->iotype) {
+	case UPIO_PORT:
+		return (port1->iobase == port2->iobase);
+	case UPIO_HUB6:
+		return (port1->iobase == port2->iobase) &&
+		       (port1->hub6   == port2->hub6);
+	case UPIO_MEM:
+	case UPIO_MEM16:
+	case UPIO_MEM32:
+	case UPIO_MEM32BE:
+	case UPIO_AU:
+	case UPIO_TSI:
+		return (port1->mapbase == port2->mapbase);
+	}
+	return 0;
+}
+EXPORT_SYMBOL(uart_match_port);
+
+/**
+ *	uart_handle_dcd_change - handle a change of carrier detect state
+ *	@port: uart_port structure for the open port
+ *	@status: new carrier detect status, nonzero if active
+ *
+ *	Caller must hold port->lock
+ */
+void uart_handle_dcd_change(struct uart_port *port, unsigned int status)
+{
+	port->icount.dcd++;
+}
+EXPORT_SYMBOL_GPL(uart_handle_dcd_change);
+
+/**
+ *	uart_handle_cts_change - handle a change of clear-to-send state
+ *	@port: uart_port structure for the open port
+ *	@status: new clear to send status, nonzero if active
+ *
+ *	Caller must hold port->lock
+ */
+void uart_handle_cts_change(struct uart_port *port, unsigned int status)
+{
+	port->icount.cts++;
+
+	if (uart_softcts_mode(port)) {
+		if (port->hw_stopped) {
+			if (status) {
+				port->hw_stopped = 0;
+				port->ops->start_tx(port);
+				uart_write_wakeup(port);
+			}
+		} else {
+			if (!status) {
+				port->hw_stopped = 1;
+				port->ops->stop_tx(port);
+			}
+		}
+	}
+}
+EXPORT_SYMBOL_GPL(uart_handle_cts_change);
+
+/**
+ *	uart_update_timeout - update per-port FIFO timeout.
+ *	@port:  uart_port structure describing the port
+ *	@cflag: termios cflag value
+ *	@baud:  speed of the port
+ *
+ *	Set the port FIFO timeout value.  The @cflag value should
+ *	reflect the actual hardware settings.
+ */
+void
+uart_update_timeout(struct uart_port *port, unsigned int cflag,
+		    unsigned int baud)
+{
+	unsigned int bits;
+
+	/* byte size and parity */
+	switch (cflag & CSIZE) {
+	case CS5:
+		bits = 7;
+		break;
+	case CS6:
+		bits = 8;
+		break;
+	case CS7:
+		bits = 9;
+		break;
+	default:
+		bits = 10;
+		break; /* CS8 */
+	}
+
+	if (cflag & CSTOPB)
+		bits++;
+	if (cflag & PARENB)
+		bits++;
+
+	/*
+	 * The total number of bits to be transmitted in the fifo.
+	 */
+	bits = bits * port->fifosize;
+
+	/*
+	 * Figure the timeout to send the above number of bits.
+	 * Add .02 seconds of slop
+	 */
+	port->timeout = (HZ * bits) / baud + HZ/50;
+}
+EXPORT_SYMBOL(uart_update_timeout);
+
+/**
+ *	uart_get_baud_rate - return baud rate for a particular port
+ *	@port: uart_port structure describing the port in question.
+ *	@termios: desired termios settings.
+ *	@old: old termios (or NULL)
+ *	@min: minimum acceptable baud rate
+ *	@max: maximum acceptable baud rate
+ *
+ *	Decode the termios structure into a numeric baud rate,
+ *	mapping the %B0 rate to 9600 baud.
+ *
+ *	If the new baud rate is invalid, try the old termios setting.
+ *	If it's still invalid, go with the closest acceptable.
+ *
+ *	Update the @termios structure to reflect the baud rate
+ *	we're actually going to be using. Don't do this for the case
+ *	where B0 is requested ("hang up").
+ */
+unsigned int
+uart_get_baud_rate(struct uart_port *port, struct ktermios *termios,
+		   struct ktermios *old, unsigned int min, unsigned int max)
+{
+	unsigned int baud;
+	bool hung_up = false;
+
+	baud = termios->c_ospeed;
+
+	/* Special case: B0 rate. */
+	if (baud == 0) {
+		hung_up = true;
+		baud = 9600;
+	}
+
+	if (old && (baud < min || baud > max))
+		baud = old->c_ospeed;
+	if (baud < min)
+		baud = min;
+	else if (baud > max)
+		baud = max;
+
+	if (!hung_up)
+		termios->c_ispeed = termios->c_ospeed = baud;
+	
+	return baud;
+}
+EXPORT_SYMBOL(uart_get_baud_rate);
+
+/**
+ *	uart_get_divisor - return uart clock divisor
+ *	@port: uart_port structure describing the port.
+ *	@baud: desired baud rate
+ *
+ *	Calculate the uart clock divisor for the port.
+ */
+unsigned int
+uart_get_divisor(struct uart_port *port, unsigned int baud)
+{
+	return DIV_ROUND_CLOSEST(port->uartclk, 16 * baud);
+}
+EXPORT_SYMBOL(uart_get_divisor);
+
+static void uart_start_tx(struct minitty_data *mtty)
+{
+	struct uart_port *port = mtty->state.uart_port;
+	spin_lock_irq(&port->lock);
+	if (!port->hw_stopped)
+		port->ops->start_tx(port);
+	spin_unlock_irq(&port->lock);
+}
+
+static int uart_chars_in_buffer(struct minitty_data *mtty)
+{
+	struct uart_state *state = &mtty->state;
+	struct uart_port *port = mtty->state.uart_port;
+	int ret;
+
+	spin_lock_irq(&port->lock);
+	ret = uart_circ_chars_pending(&state->xmit);
+	spin_unlock_irq(&port->lock);
+	return ret;
+}
+
+static void uart_flush_tx_buffer(struct minitty_data *mtty)
+{
+	struct uart_state *state = &mtty->state;
+	struct uart_port *port = mtty->state.uart_port;
+
+	spin_lock_irq(&port->lock);
+	uart_circ_clear(&state->xmit);
+	if (port->ops->flush_buffer)
+		port->ops->flush_buffer(port);
+	spin_unlock_irq(&port->lock);
+	uart_write_wakeup(port);
+}
+
+static int uart_get_lsr_info(struct minitty_data *mtty, unsigned int __user *p)
+{
+	struct uart_state *state = &mtty->state;
+	struct uart_port *port = mtty->state.uart_port;
+	unsigned int result;
+
+	mutex_lock(&mtty->mutex);
+	result = port->ops->tx_empty(port);
+
+	/*
+	 * If we're about to load something into the transmit
+	 * register, we'll pretend the transmitter isn't empty to
+	 * avoid a race condition (depending on when the transmit
+	 * interrupt happens).
+	 */
+	if (port->x_char ||
+	    ((uart_circ_chars_pending(&state->xmit) > 0) &&
+	     !uart_tx_stopped(port)))
+		result &= ~TIOCSER_TEMT;
+	mutex_unlock(&mtty->mutex);
+	return put_user(result, p);
+}
+
+static int uart_tiocmget(struct minitty_data *mtty, int __user *p)
+{
+	struct uart_port *port = mtty->state.uart_port;
+	int ret = -EIO;
+
+	mutex_lock(&mtty->mutex);
+	ret = port->mctrl;
+	spin_lock_irq(&port->lock);
+	ret |= port->ops->get_mctrl(port);
+	spin_unlock_irq(&port->lock);
+	mutex_unlock(&mtty->mutex);
+	if (ret >= 0)
+		ret = put_user(ret, p);
+	return ret;
+}
+
+static int
+uart_tiocmset(struct minitty_data *mtty, unsigned int cmd, unsigned __user *p)
+{
+	struct uart_port *port = mtty->state.uart_port;
+	unsigned int set, clear, val;
+	int ret;
+
+	ret = get_user(val, p);
+	if (ret)
+		return ret;
+	set = clear = 0;
+	switch (cmd) {
+	case TIOCMBIS:
+		set = val;
+		break;
+	case TIOCMBIC:
+		clear = val;
+		break;
+	case TIOCMSET:
+		set = val;
+		clear = ~val;
+		break;
+	}
+	set &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP;
+	clear &= TIOCM_DTR|TIOCM_RTS|TIOCM_OUT1|TIOCM_OUT2|TIOCM_LOOP;
+
+	mutex_lock(&mtty->mutex);
+	uart_update_mctrl(port, set, clear);
+	mutex_unlock(&mtty->mutex);
+	return 0;
+}
+
+static int uart_break_ctl(struct minitty_data *mtty, int break_state)
+{
+	struct uart_port *port = mtty->state.uart_port;
+	int ret = -EIO;
+
+	mutex_lock(&mtty->mutex);
+	port->ops->break_ctl(port, break_state);
+	mutex_unlock(&mtty->mutex);
+	return ret;
+}
+
+/*
+ * Wait for any of the 4 modem inputs (DCD,RI,DSR,CTS) to change
+ * - mask passed in arg for lines of interest
+ *   (use |'ed TIOCM_RNG/DSR/CD/CTS for masking)
+ * Caller should use TIOCGICOUNT to see which one it was
+ */
+static int uart_wait_modem_status(struct minitty_data *mtty, unsigned long arg)
+{
+	struct uart_port *uport = mtty->state.uart_port;
+	struct tty_port *port = &mtty->state.port;
+	DECLARE_WAITQUEUE(wait, current);
+	struct uart_icount cprev, cnow;
+	int ret;
+
+	/*
+	 * note the counters on entry
+	 */
+	spin_lock_irq(&uport->lock);
+	memcpy(&cprev, &uport->icount, sizeof(struct uart_icount));
+	if (uport->ops->enable_ms)
+		uport->ops->enable_ms(uport);
+	spin_unlock_irq(&uport->lock);
+
+	add_wait_queue(&port->delta_msr_wait, &wait);
+	for (;;) {
+		spin_lock_irq(&uport->lock);
+		memcpy(&cnow, &uport->icount, sizeof(struct uart_icount));
+		spin_unlock_irq(&uport->lock);
+
+		set_current_state(TASK_INTERRUPTIBLE);
+
+		if (((arg & TIOCM_RNG) && (cnow.rng != cprev.rng)) ||
+		    ((arg & TIOCM_DSR) && (cnow.dsr != cprev.dsr)) ||
+		    ((arg & TIOCM_CD)  && (cnow.dcd != cprev.dcd)) ||
+		    ((arg & TIOCM_CTS) && (cnow.cts != cprev.cts))) {
+			ret = 0;
+			break;
+		}
+
+		schedule();
+
+		/* see if a signal did it */
+		if (signal_pending(current)) {
+			ret = -ERESTARTSYS;
+			break;
+		}
+
+		cprev = cnow;
+	}
+	__set_current_state(TASK_RUNNING);
+	remove_wait_queue(&port->delta_msr_wait, &wait);
+
+	return ret;
+}
+
+/*
+ * Get counter of input serial line interrupts (DCD,RI,DSR,CTS)
+ * NB: both 1->0 and 0->1 transitions are counted except for
+ *     RI where only 0->1 is counted.
+ */
+static int uart_tiocgicount(struct minitty_data *mtty, void __user *p)
+{
+	struct uart_port *port = mtty->state.uart_port;
+	struct serial_icounter_struct icount;
+	struct uart_icount cnow;
+
+	spin_lock_irq(&port->lock);
+	memcpy(&cnow, &port->icount, sizeof(struct uart_icount));
+	spin_unlock_irq(&port->lock);
+
+	memset(&icount, 0, sizeof(icount));
+	icount.cts         = cnow.cts;
+	icount.dsr         = cnow.dsr;
+	icount.rng         = cnow.rng;
+	icount.dcd         = cnow.dcd;
+	icount.rx          = cnow.rx;
+	icount.tx          = cnow.tx;
+	icount.frame       = cnow.frame;
+	icount.overrun     = cnow.overrun;
+	icount.parity      = cnow.parity;
+	icount.brk         = cnow.brk;
+	icount.buf_overrun = cnow.buf_overrun;
+	if (copy_to_user(p, &icount, sizeof(icount)))
+		return -EFAULT;
+	return 0;
+}
+
+static void uart_change_speed(struct minitty_data *mtty,
+			      struct ktermios *old_termios)
+{
+	struct uart_port *port = mtty->state.uart_port;
+	struct ktermios *termios = &mtty->termios;
+	int hw_stopped;
+
+	port->ops->set_termios(port, termios, old_termios);
+
+	/*
+	 * Set modem status enables based on termios cflag
+	 */
+	spin_lock_irq(&port->lock);
+	if (termios->c_cflag & CRTSCTS)
+		port->status |= UPSTAT_CTS_ENABLE;
+	else
+		port->status &= ~UPSTAT_CTS_ENABLE;
+
+	if (termios->c_cflag & CLOCAL)
+		port->status &= ~UPSTAT_DCD_ENABLE;
+	else
+		port->status |= UPSTAT_DCD_ENABLE;
+
+	/* reset sw-assisted CTS flow control based on (possibly) new mode */
+	hw_stopped = port->hw_stopped;
+	port->hw_stopped = uart_softcts_mode(port) &&
+				!(port->ops->get_mctrl(port) & TIOCM_CTS);
+	if (port->hw_stopped) {
+		if (!hw_stopped)
+			port->ops->stop_tx(port);
+	} else {
+		if (hw_stopped)
+			port->ops->start_tx(port);
+	}
+	spin_unlock_irq(&port->lock);
+}
+
+static void uart_set_termios(struct minitty_data *mtty,
+			     struct ktermios *old_termios)
+{
+	struct uart_port *port = mtty->state.uart_port;
+	unsigned int cflag = mtty->termios.c_cflag;
+	unsigned int iflag_mask = IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK;
+	bool sw_changed = false;
+
+	/*
+	 * Drivers doing software flow control also need to know
+	 * about changes to these input settings.
+	 */
+	if (port->flags & UPF_SOFT_FLOW) {
+		iflag_mask |= IXANY|IXON|IXOFF;
+		sw_changed =
+		   mtty->termios.c_cc[VSTART] != old_termios->c_cc[VSTART] ||
+		   mtty->termios.c_cc[VSTOP] != old_termios->c_cc[VSTOP];
+	}
+
+	/*
+	 * These are the bits that are used to setup various
+	 * flags in the low level driver. We can ignore the Bfoo
+	 * bits in c_cflag; c_[io]speed will always be set
+	 * appropriately by set_termios(). 
+	 */
+	if ((cflag ^ old_termios->c_cflag) == 0 &&
+	    mtty->termios.c_ospeed == old_termios->c_ospeed &&
+	    mtty->termios.c_ispeed == old_termios->c_ispeed &&
+	    ((mtty->termios.c_iflag ^ old_termios->c_iflag) & iflag_mask) == 0 &&
+	    !sw_changed)
+		return;
+
+	uart_change_speed(mtty, old_termios);
+	/* reload cflag from termios; port driver may have overriden flags */
+	cflag = mtty->termios.c_cflag;
+
+	/* Handle transition to B0 status */
+	if ((old_termios->c_cflag & CBAUD) && !(cflag & CBAUD))
+		uart_clear_mctrl(port, TIOCM_RTS | TIOCM_DTR);
+	/* Handle transition away from B0 status */
+	else if (!(old_termios->c_cflag & CBAUD) && (cflag & CBAUD)) {
+		unsigned int mask = TIOCM_DTR;
+		if (!(cflag & CRTSCTS))
+			mask |= TIOCM_RTS;
+		uart_set_mctrl(port, mask);
+	}
+}
+
+static void uart_wait_until_sent(struct minitty_data *mtty)
+{
+	struct uart_port *port = mtty->state.uart_port;
+	unsigned long char_time, expire, timeout;
+
+	/*
+	 * Set the check interval to be 1/5 of the estimated time to
+	 * send a single character, and make it at least 1.
+	 *
+	 * Note: we have to use pretty tight timings here to satisfy
+	 * the NIST-PCTS.
+	 */
+	char_time = (port->timeout - HZ/50) / port->fifosize;
+	char_time = char_time / 5;
+	if (char_time == 0)
+		char_time = 1;
+
+	/*
+	 * If the transmitter hasn't cleared in twice the approximate
+	 * amount of time to send the entire FIFO, it probably won't
+	 * ever clear.  This assumes the UART isn't doing flow
+	 * control, which is currently the case.  Hence, if it ever
+	 * takes longer than port->timeout, this is probably due to a
+	 * UART bug of some kind.  So, we clamp the timeout parameter at
+	 * 2*port->timeout.
+	 */
+	timeout = 2 * port->timeout;
+
+	expire = jiffies + timeout;
+	while (!port->ops->tx_empty(port)) {
+		        msleep_interruptible(jiffies_to_msecs(char_time));
+			        if (signal_pending(current))
+					                break;
+				        if (time_after(jiffies, expire))
+						                break;
+	}
+}
+
+static void mtty_wait_until_sent(struct minitty_data *mtty)
+{
+	long timeout = MAX_SCHEDULE_TIMEOUT;
+
+	timeout = wait_event_interruptible_timeout(mtty->write_wait,
+			                !uart_chars_in_buffer(mtty), timeout);
+	if (timeout > 0)
+		uart_wait_until_sent(mtty);
+}
+
+static void mtty_set_termios(struct minitty_data *mtty,
+			     struct ktermios *old_termios)
+{
+	bool was_raw = mtty->rx_raw;
+
+	mtty->rx_raw = !I_IGNCR(mtty) && !I_ICRNL(mtty) && !I_INLCR(mtty) &&
+		       !L_ICANON(mtty) && !L_ISIG(mtty) && !L_ECHO(mtty);
+	if (!mtty->rx_raw && was_raw)
+		mtty->rx_lines = mtty->column = mtty->canon_start_pos = 0;
+
+	/* mark things we don't support. */
+	mtty->termios.c_iflag |= IGNBRK | IGNPAR;
+	mtty->termios.c_iflag &= ~(ISTRIP | IUCLC | IXON | IXOFF);
+	mtty->termios.c_lflag &= ~IEXTEN;
+
+	/* The termios change make the tty ready for I/O */
+	wake_up_interruptible(&mtty->write_wait);
+	wake_up_interruptible(&mtty->read_wait);
+}
+
+static int set_termios(struct minitty_data *mtty, unsigned int cmd,
+		       void __user *arg)
+{
+	struct ktermios new_termios, old_termios;
+	int ret;
+
+	mutex_lock(&mtty->mutex);
+	new_termios = mtty->termios;
+	mutex_unlock(&mtty->mutex);
+
+	switch (cmd) {
+	case TCSETAF:
+	case TCSETAW:
+	case TCSETA:
+		ret = user_termio_to_kernel_termios(&new_termios,
+						    (struct termio __user *)arg);
+		break;
+#ifdef TCGETS2
+	case TCSETSF2:
+	case TCSETSW2:
+	case TCSETS2:
+		ret = user_termios_to_kernel_termios(&new_termios,
+						     (struct termios2 __user *)arg);
+		break;
+	default:
+		ret = user_termios_to_kernel_termios_1(&new_termios,
+						       (struct termios __user *)arg);
+		break;
+#else
+	default:
+		ret = user_termios_to_kernel_termios(&new_termios,
+						     (struct termios __user *)arg);
+		break;
+#endif
+	}
+	if (ret)
+		return -EFAULT;
+
+	switch (cmd) {
+	case TCSETSF:
+#ifdef TCGETS2
+	case TCSETSF2:
+#endif
+	case TCSETAF:
+		uart_flush_tx_buffer(mtty);
+	}
+
+	switch (cmd) {
+	case TCSETSF:
+	case TCSETSW:
+#ifdef TCGETS2
+	case TCSETSF2:
+	case TCSETSW2:
+#endif
+	case TCSETAF:
+	case TCSETAW:
+		mtty_wait_until_sent(mtty);
+		if (signal_pending(current))
+			return -ERESTARTSYS;
+	}
+
+	/*
+	 * If old style Bfoo values are used then load c_ispeed/c_ospeed
+	 * with the real speed so its unconditionally usable.
+	 */
+	new_termios.c_ispeed = tty_termios_input_baud_rate(&new_termios);
+	new_termios.c_ospeed = tty_termios_baud_rate(&new_termios);
+
+	mutex_lock(&mtty->mutex);
+	old_termios = mtty->termios;
+	mtty->termios = new_termios;
+	mtty_set_termios(mtty, &old_termios);
+	uart_set_termios(mtty, &old_termios);
+	mutex_unlock(&mtty->mutex);
+	return 0;
+}
+
+static int tiocsetd(int __user *p)
+{
+	int ldisc;
+
+	if (get_user(ldisc, p))
+		return -EFAULT;
+	if (ldisc != N_TTY)
+		return -EINVAL;
+	return 0;
+}
+
+static int tiocgetd(int __user *p)
+{
+	return put_user(N_TTY, p);
+}
+
+static void copy_termios(struct minitty_data *mtty, struct ktermios *kterm)
+{
+	mutex_lock(&mtty->mutex);
+	*kterm = mtty->termios;
+	mutex_unlock(&mtty->mutex);
+}
+
+static long minitty_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct minitty_data *mtty = file->private_data;
+	struct uart_port *port = mtty->state.uart_port;
+	void __user *p = (void __user *)arg;
+	struct ktermios kterm;
+	int ret = -ENOIOCTLCMD;
+
+	switch (cmd) {
+	case TIOCSETD:
+		return tiocsetd(p);
+	case TIOCGETD:
+		return tiocgetd(p);
+	case TIOCSBRK:
+		return uart_break_ctl(mtty, -1);
+	case TIOCCBRK:
+		return uart_break_ctl(mtty, 0);
+	case TIOCMGET:
+		return uart_tiocmget(mtty, p);
+	case TIOCMSET:
+	case TIOCMBIC:
+	case TIOCMBIS:
+		return uart_tiocmset(mtty, cmd, p);
+	case TIOCGICOUNT:
+		return uart_tiocgicount(mtty, p);
+	case TIOCMIWAIT:
+		return uart_wait_modem_status(mtty, arg);
+	case TIOCSERGETLSR:
+		return uart_get_lsr_info(mtty, p);
+
+#ifndef TCGETS2
+	case TCGETS:
+		copy_termios(mtty, &kterm);
+		if (kernel_termios_to_user_termios((struct termios __user *)arg, &kterm))
+			return -EFAULT;
+		return 0;
+#else
+	case TCGETS:
+		copy_termios(mtty, &kterm);
+		if (kernel_termios_to_user_termios_1((struct termios __user *)arg, &kterm))
+			return -EFAULT;
+		return 0;
+	case TCGETS2:
+		copy_termios(mtty, &kterm);
+		if (kernel_termios_to_user_termios((struct termios2 __user *)arg, &kterm))
+			return -EFAULT;
+		return 0;
+	case TCSETSF2:
+	case TCSETSW2:
+	case TCSETS2:
+#endif
+	case TCSETSF:
+	case TCSETSW:
+	case TCSETS:
+	case TCSETAF:
+	case TCSETAW:
+	case TCSETA:
+		return set_termios(mtty, cmd, p);
+	case TCGETA:
+		copy_termios(mtty, &kterm);
+		if (kernel_termios_to_user_termio((struct termio __user *)arg, &kterm))
+			return -EFAULT;
+		return 0;
+
+	default:
+		mutex_lock(&mtty->mutex);
+		if (port->ops->ioctl)
+			ret = port->ops->ioctl(port, cmd, arg);
+		mutex_unlock(&mtty->mutex);
+		break;
+	}
+
+	if (ret == -ENOIOCTLCMD)
+		ret = -EINVAL;
+	return ret;
+}
+
+/*
+ * Functions called back by low level UART drivers to provide
+ * an RX character. We simply ignore characters with errors here.
+ */
+
+int tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
+{
+	struct uart_state *state = container_of(port, struct uart_state, port);
+	struct minitty_data *mtty = container_of(state, typeof(*mtty), state);
+
+	if (flag == TTY_NORMAL) {
+		int tail = smp_load_acquire(&mtty->rx_tail);
+		int head = mtty->rx_head;
+		int next = RX_BUF_WRAP(head + 1);
+		/*
+		 * Advance head only if buffer is not full.
+		 * Keep on overwriting last char otherwise.
+		 */
+		mtty->rx_buf[head] = ch;
+		if (next != tail) {
+			smp_store_release(&mtty->rx_head, next);
+			return 1;
+		} else {
+			smp_store_release(&mtty->rx_overflow, true);
+		}
+	}		
+	return 0;
+}
+EXPORT_SYMBOL(tty_insert_flip_char);
+
+void uart_insert_char(struct uart_port *port, unsigned int status,
+		      unsigned int overrun, unsigned int ch, unsigned int flag)
+{
+	struct uart_state *state = port->state;
+	struct minitty_data *mtty = container_of(state, typeof(*mtty), state);
+
+	if (flag == TTY_NORMAL) {
+		int tail = smp_load_acquire(&mtty->rx_tail);
+		int head = mtty->rx_head;
+		int next = RX_BUF_WRAP(head + 1);
+		/*
+		 * Advance head only if buffer is not full.
+		 * Keep on overwriting last char otherwise.
+		 */
+		mtty->rx_buf[head] = ch;
+		if (next != tail) {
+			smp_store_release(&mtty->rx_head, next);
+		} else {
+			smp_store_release(&mtty->rx_overflow, true);
+			port->icount.buf_overrun++;
+		}
+	}
+}
+EXPORT_SYMBOL_GPL(uart_insert_char);
+
+void tty_schedule_flip(struct tty_port *port)
+{
+	struct uart_state *state = container_of(port, struct uart_state, port);
+	struct minitty_data *mtty = container_of(state, typeof(*mtty), state);
+
+	queue_work(system_unbound_wq, &mtty->rx_work);
+}
+EXPORT_SYMBOL(tty_schedule_flip);
+
+void tty_flip_buffer_push(struct tty_port *port)
+{
+	tty_schedule_flip(port);
+}
+EXPORT_SYMBOL(tty_flip_buffer_push);
+
+/*
+ * Line Discipline Stuff
+ */
+
+static bool is_utf8_continuation(struct minitty_data *mtty, unsigned char c)
+{
+	return (I_IUTF8(mtty) && (c & 0xc0) == 0x80);
+}
+
+static bool is_line_termination(struct minitty_data *mtty, unsigned char c)
+{
+	return (c == '\n' || c == EOF_CHAR(mtty) || c == EOL_CHAR(mtty));
+}
+
+/*
+ * Queue the provided character string in its entirety or nothing.
+ * Return true if queued, false otherwise.
+ */
+static bool queue_tx_chars(struct minitty_data *mtty, unsigned char *s, int len)
+{
+	struct circ_buf *circ = &mtty->state.xmit;
+	int head, tail, space;
+
+	tail = smp_load_acquire(&circ->tail);
+	head = circ->head;
+	space = CIRC_SPACE(head, tail, UART_XMIT_SIZE);
+	if (space < len)
+		return false;
+	while (len--) {
+		circ->buf[head] = *s++;
+		head = (head + 1) & (UART_XMIT_SIZE - 1);
+	}
+	smp_store_release(&circ->head, head);
+	return true;
+}
+
+/*
+ * Queue characters in their cooked sequence.
+ * Return true if queued, or false otherwise.
+ */
+static bool tx_cooked_char(struct minitty_data *mtty, unsigned char c)
+{
+	int spaces, next_col = mtty->column;
+
+	switch (c) {
+	case '\n':
+		if (O_ONLRET(mtty))
+			next_col = 0;
+		if (O_ONLCR(mtty)) {
+			if (!queue_tx_chars(mtty, "\r\n", 2))
+				return false;
+			mtty->column = mtty->canon_start_pos = 0;
+			return true;
+		}
+		break;
+	case '\r':
+		if (O_ONOCR(mtty) && mtty->column == 0)
+			return true;
+		if (O_OCRNL(mtty)) {
+			c = '\n';
+			if (O_ONLRET(mtty))
+				next_col = 0;
+		} else
+			next_col = 0;
+		break;
+	case '\t':
+		spaces = 8 - (mtty->column & 7);
+		if (O_TABDLY(mtty) == XTABS) {
+			if (!queue_tx_chars(mtty, "        ", spaces))
+				return false;
+			mtty->column += spaces;
+			return true;
+		}
+		next_col += spaces;
+		break;
+	case '\b':
+		if (next_col > 0)
+			next_col--;
+		break;
+	default:
+		if (iscntrl(c))
+			break;
+		if (is_utf8_continuation(mtty, c))
+			break;
+		next_col++;
+		break;
+	}
+	if (!queue_tx_chars(mtty, &c, 1))
+		return false;
+	mtty->column = next_col;
+	if (next_col == 0)
+		mtty->canon_start_pos = 0;
+	return true;
+}
+
+/*
+ * Queue echoed characters, converting CTRL sequences into "^X" if need be.
+ * Return true if queued, or false otherwise.
+ */
+static bool echo_rx_char(struct minitty_data *mtty, unsigned char c)
+{
+	if (L_ECHOCTL(mtty) && iscntrl(c) && c != '\t' && c != '\n') {
+		unsigned char buf[2];
+		buf[0] = '^';
+		buf[1] = c ^ 0100;
+		return queue_tx_chars(mtty, buf, 2);
+	}
+	if (O_OPOST(mtty))
+		return tx_cooked_char(mtty, c);
+	else
+		return queue_tx_chars(mtty, &c, 1);
+}
+
+/*
+ * Remove character from RX buffer at given position by shifting
+ * all preceding characters ahead.
+ */
+static void eat_rx_char(struct minitty_data *mtty, int pos)
+{
+	unsigned char *buf = mtty->rx_buf;
+	int tail = mtty->rx_tail;
+	int bottom = (tail <= pos) ? tail : 0;
+
+	memmove(&buf[bottom+1], &buf[bottom], pos - bottom);
+	if (tail > pos) {
+		buf[0] = buf[RX_BUF_SIZE-1];
+		memmove(&buf[tail+1], &buf[tail], RX_BUF_SIZE - 1 - tail);
+	}
+	smp_store_release(&mtty->rx_tail, RX_BUF_WRAP(tail + 1));
+}
+
+/*
+ * Create needed erase sequence according to the erase character c at
+ * position pos in the RX buffer. The erase sequence is sent for each
+ * erased characters and only if that succeeds then the character is
+ * actually removed from the buffer. The erase character itself is removed
+ * last so if the whole erase sequence cannot be completed then this can
+ * be resumed later.
+ */
+static bool erase_rx_char(struct minitty_data *mtty, unsigned char c, int pos)
+{
+	int prev_pos = RX_BUF_WRAP(pos - 1);
+	bool seen_alnum = false;
+
+	while (pos != mtty->rx_tail) {
+		unsigned char prev_c = mtty->rx_buf[prev_pos];
+
+		if (is_line_termination(mtty, prev_c)) {
+			/* End of previous line: we don't erase further. */
+			break;
+		}
+
+		if (is_utf8_continuation(mtty, prev_c)) {
+			/* UTF8 continuation char: we just drop it */
+			eat_rx_char(mtty, prev_pos);
+			continue;
+		}
+
+		if (c == WERASE_CHAR(mtty) && seen_alnum && !isalnum(prev_c)) {
+			/* Beginning of previous word: we don't erase further */
+			break;
+		}
+
+		if (prev_c == '\t') {
+			/* depends on characters before the tab */
+			int spaces = 0;
+			int i = prev_pos;
+			while (i != mtty->rx_tail) {
+				unsigned char before;
+				i = RX_BUF_WRAP(i - 1);
+				before = mtty->rx_buf[i];
+				if (before == '\t')
+					break;
+				if (is_line_termination(mtty, before))
+					break;
+				if (L_ECHOCTL(mtty) && iscntrl(before))
+					spaces += 2;
+				else if (is_utf8_continuation(mtty, before))
+					continue;
+				else if (!iscntrl(before))
+					spaces++;
+			}
+			if (i == mtty->rx_tail)
+				spaces += mtty->canon_start_pos;
+			spaces = 8 - (spaces & 7);
+			if (!queue_tx_chars(mtty, "\b\b\b\b\b\b\b\b", spaces))
+				return false;
+			mtty->column -= spaces;
+		} else if (L_ECHOCTL(mtty) && iscntrl(prev_c)) {
+			/* control chars were printed as "^X" */
+			if (!queue_tx_chars(mtty, "\b\b  \b\b", 6))
+				return false;
+			mtty->column -= 2;
+		} else if (!iscntrl(prev_c)) {
+			if (!queue_tx_chars(mtty, "\b \b", 3))
+				return false;
+			mtty->column -= 1;
+		}
+
+		/* erase sequence sent, now remove the char from the buffer */
+		eat_rx_char(mtty, prev_pos);
+
+		if (c == ERASE_CHAR(mtty))
+			break;
+	}
+
+	/* Finally remove the erase character itself. */
+	eat_rx_char(mtty, pos);
+	return true;
+}
+
+/*
+ * Process RX bytes: canonical mode, echo, signals, etc.
+ * This might not process all RX characters if e.g. there is not enough
+ * room in the TX buffer to contain corresponding echo sequences.
+ */
+static void minitty_process_rx(struct minitty_data *mtty)
+{
+	bool xmit = false;
+	int i, head;
+       
+	head = smp_load_acquire(&mtty->rx_head);
+
+	if (mtty->rx_raw) {
+		smp_store_release(&mtty->rx_vetted, head);
+		return;
+	}
+
+	/*
+	 * RX overflow mitigation: evaluate the last received character
+	 * stored at the very head of the buffer in case it might be a
+	 * signal or newline character that could kick the reader into
+	 * action. We potentially overwrite the last vetted character but
+	 * we're past any concern for lost characters at this point.
+	 */
+	if (unlikely(mtty->rx_overflow)) {
+		WRITE_ONCE(mtty->rx_overflow, false);
+		if (RX_BUF_WRAP(head + 1) == mtty->rx_tail) {
+			i = RX_BUF_WRAP(head - 1);
+			mtty->rx_buf[i] = mtty->rx_buf[head];
+			if (mtty->rx_vetted == head)
+				mtty->rx_vetted = i;
+		}
+	}
+
+	for (i = mtty->rx_vetted; i != head; i = RX_BUF_WRAP(i + 1)) {
+		unsigned char c = mtty->rx_buf[i];
+
+		if (c == '\r') {
+			if (I_IGNCR(mtty)) {
+				eat_rx_char(mtty, i);
+				continue;
+			}
+			if (I_ICRNL(mtty))
+				mtty->rx_buf[i] = c = '\n';
+		} else if (c == '\n' && I_INLCR(mtty))
+			mtty->rx_buf[i] = c = '\r';
+
+		if (L_ICANON(mtty)) {
+			if ((L_ECHOE(mtty) && c == ERASE_CHAR(mtty)) ||
+			    (L_ECHOE(mtty) && c == WERASE_CHAR(mtty)) ||
+			    (L_ECHOK(mtty) && c == KILL_CHAR(mtty))) {
+				xmit = true;
+				if (!erase_rx_char(mtty, c, i))
+						break;
+				continue;
+			}
+			if (is_line_termination(mtty, c)) {
+				mtty->rx_lines++;
+				if (c != '\n')
+					continue;
+			}
+		}
+
+		if (L_ECHO(mtty) || (c == '\n' && L_ECHONL(mtty))) {
+			xmit = true;
+			if (!echo_rx_char(mtty, c))
+				break;
+		}
+	}
+
+	smp_store_release(&mtty->rx_vetted, i);
+
+	if (xmit)
+		uart_start_tx(mtty);
+}
+
+static bool rx_data_available(struct minitty_data *mtty, bool poll)
+{
+	bool data_avail = (mtty->rx_tail != mtty->rx_vetted);
+	if (data_avail && !L_ICANON(mtty)) {
+		int amt = poll && !TIME_CHAR(mtty) && MIN_CHAR(mtty) ?
+				MIN_CHAR(mtty) : 1;
+		data_avail = RX_BUF_WRAP(mtty->rx_vetted - mtty->rx_tail) >= amt;
+	} else if (data_avail && !mtty->rx_lines) {
+		/* wait for a full line */
+		data_avail = false;
+	} else if (!data_avail && mtty->rx_lines) {
+		/*
+		 * This may happen if the RX buffer was flushed by a signal
+		 * or during RX overflow. Let's just reset it to zero.
+		 */
+		mtty->rx_lines = 0;
+	}
+	return data_avail;
+}
+
+static void uart_rx_work(struct work_struct *work)
+{
+	struct minitty_data *mtty = container_of(work, typeof(*mtty), rx_work);
+
+	mutex_lock(&mtty->mutex);
+	minitty_process_rx(mtty);
+	if (rx_data_available(mtty, true))
+		wake_up_interruptible_poll(&mtty->read_wait, POLLIN);
+	mutex_unlock(&mtty->mutex);
+}
+
+static ssize_t minitty_raw_read(struct minitty_data *mtty, char __user *buf,
+				size_t count)
+{
+	int head, tail, len, ret = 0;
+
+	head = smp_load_acquire(&mtty->rx_vetted); 
+	tail = mtty->rx_tail;
+	do {
+		len = CIRC_CNT(head, tail, RX_BUF_SIZE);
+		if (len > count)
+			len = count;
+		if (copy_to_user(buf, mtty->rx_buf+tail, len) != 0)
+			return -EFAULT;
+		tail = RX_BUF_WRAP(tail + len);
+		buf += len;
+		count -= len;
+		ret += len;
+	} while (count && len && tail == 0);
+	smp_store_release(&mtty->rx_tail, tail);
+	return ret;
+}
+
+static ssize_t minitty_cooked_read(struct minitty_data *mtty, char __user *buf,
+				   size_t count)
+{
+	int head, tail, i, ret;
+	bool eol = false;
+
+	head = smp_load_acquire(&mtty->rx_vetted);
+	tail = mtty->rx_tail;
+
+	/* First, locate the end-of-line marker if any. */
+	for (i = tail; i != head && count; i = RX_BUF_WRAP(i + 1), count--) {
+		unsigned char c = mtty->rx_buf[i];
+		if (is_line_termination(mtty, c)) {
+			eol = true;
+			break;
+		}
+	}
+
+	count = CIRC_CNT(i, tail, RX_BUF_SIZE);
+
+	if (eol) {
+		/* Include the line delimiter except for EOF */
+		if (mtty->rx_buf[i] != EOF_CHAR(mtty))
+			count++;
+		i = RX_BUF_WRAP(i + 1);
+	}
+
+	ret = minitty_raw_read(mtty, buf, count);
+	if (ret >= 0 && eol) {
+		/* we consumed a whole line */
+		mtty->rx_lines--;
+		/* adjust tail in case EOF was skipped */
+		smp_store_release(&mtty->rx_tail, i);
+	}
+	return ret;
+}
+
+static ssize_t minitty_read(struct file *file, char __user *buf,
+			    size_t count, loff_t *ppos)
+{
+	struct minitty_data *mtty = file->private_data;
+	char __user *buf0 = buf;
+	DEFINE_WAIT_FUNC(wait, woken_wake_function);
+	int minimum, time;
+	long timeout;
+	int ret = 0;
+
+	mutex_lock(&mtty->mutex);
+
+	minimum = time = 0;
+	timeout = MAX_SCHEDULE_TIMEOUT;
+	if (!L_ICANON(mtty)) {
+		minimum = MIN_CHAR(mtty);
+		if (minimum) {
+			time = (HZ / 10) * TIME_CHAR(mtty);
+		} else {
+			timeout = (HZ / 10) * TIME_CHAR(mtty);
+			minimum = 1;
+		}
+	}
+
+	add_wait_queue(&mtty->read_wait, &wait);
+
+	while (count) {
+		minitty_process_rx(mtty);
+
+		if (!rx_data_available(mtty, false)) {
+			if (!timeout)
+				break;
+			if (file->f_flags & O_NONBLOCK) {
+				ret = -EAGAIN;
+				break;
+			}
+			if (signal_pending(current)) {
+				ret = -ERESTARTSYS;
+				break;
+			}
+			mutex_unlock(&mtty->mutex);
+			timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
+					     timeout);
+			mutex_lock(&mtty->mutex);
+			continue;
+		}
+
+		if (L_ICANON(mtty)) {
+			ret = minitty_cooked_read(mtty, buf, count);
+			if (ret > 0)
+				buf += ret;
+			break;
+		}
+
+		ret = minitty_raw_read(mtty, buf, count);
+		if (ret < 0)
+			break;
+		buf += ret;
+		count -= ret;
+		if (buf - buf0 >= minimum)
+			break;
+		if (time)
+			timeout = time;
+	}
+
+	remove_wait_queue(&mtty->read_wait, &wait);
+	mutex_unlock(&mtty->mutex);
+	if (buf - buf0)
+		ret = buf - buf0;
+	return ret;
+}
+
+static ssize_t minitty_raw_write(struct minitty_data *mtty, const char __user *buf,
+				 size_t count)
+{
+	struct circ_buf *circ = &mtty->state.xmit;
+	int head, tail, len, ret = 0;
+
+	tail = smp_load_acquire(&circ->tail);
+	head = circ->head;
+	do {
+		len = CIRC_SPACE_TO_END(head, tail, UART_XMIT_SIZE);
+		if (len > count)
+			len = count;
+		if (copy_from_user(circ->buf + head, buf, len) != 0)
+			return -EFAULT;
+		head = (head + len) & (UART_XMIT_SIZE - 1);
+		buf += len;
+		count -= len;
+		ret += len;
+	} while (count && len && head == 0);
+	smp_store_release(&circ->head, head);
+
+	uart_start_tx(mtty);
+	return ret;
+}
+
+static ssize_t minitty_cooked_write(struct minitty_data *mtty, const char __user *buf,
+				    size_t count)
+{
+	const char __user *buf0 = buf;
+
+	while (count--) {
+		unsigned char c;
+		if (get_user(c, buf) != 0)
+			return -EFAULT;
+		if (!tx_cooked_char(mtty, c))
+			break;
+		buf++;
+	}
+	mtty->canon_start_pos = mtty->column;
+
+	uart_start_tx(mtty);
+	return buf - buf0;
+}
+
+static ssize_t minitty_write(struct file *file, const char __user *buf,
+			     size_t count, loff_t *ppos)
+{
+	struct minitty_data *mtty = file->private_data;
+	const char __user *buf0 = buf;
+	DEFINE_WAIT_FUNC(wait, woken_wake_function);
+	int ret;
+
+	mutex_lock(&mtty->mutex);
+	add_wait_queue(&mtty->write_wait, &wait);
+
+	while (1) {
+		/* give priority to RX echo and signals */
+		minitty_process_rx(mtty);
+
+		if (signal_pending(current)) {
+			ret = -ERESTARTSYS;
+			break;
+		}
+
+		if (O_OPOST(mtty))
+			ret = minitty_cooked_write(mtty, buf, count);
+		else
+			ret = minitty_raw_write(mtty, buf, count);
+		if (ret < 0)
+			break;
+		buf += ret;
+		count -= ret;
+		if (!count)
+			break;
+		if (file->f_flags & O_NONBLOCK) {
+			ret = -EAGAIN;
+			break;
+		}
+		mutex_unlock(&mtty->mutex);
+		wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
+		mutex_lock(&mtty->mutex);
+	}
+
+	remove_wait_queue(&mtty->write_wait, &wait);
+	mutex_unlock(&mtty->mutex);
+	return (buf - buf0) ? buf - buf0 : ret;
+}
+
+static unsigned int minitty_poll(struct file *file, poll_table *wait)
+{
+	struct minitty_data *mtty = file->private_data;
+	struct uart_port *port = mtty->state.uart_port;
+	unsigned int mask = 0;
+
+	mutex_lock(&mtty->mutex);
+
+	poll_wait(file, &mtty->read_wait, wait);
+	poll_wait(file, &mtty->write_wait, wait);
+
+	if (rx_data_available(mtty, true)) {
+		mask |= POLLIN | POLLRDNORM;
+	} else {
+		minitty_process_rx(mtty);
+		if (rx_data_available(mtty, true))
+			mask |= POLLIN | POLLRDNORM;
+	}
+
+	if (!port->hw_stopped) {
+		struct circ_buf *circ = &mtty->state.xmit;
+		int tail = smp_load_acquire(&circ->tail);
+		int head = circ->head;
+		int count = CIRC_CNT(head, tail, UART_XMIT_SIZE);
+		if (count < WAKEUP_CHARS)
+			mask |= POLLOUT | POLLWRNORM;
+	}
+
+	mutex_unlock(&mtty->mutex);
+
+	return mask;
+}
+
+static int uart_port_startup(struct minitty_data *mtty)
+{
+	struct uart_state *state = &mtty->state;
+	struct uart_port *port = state->uart_port;
+	unsigned long page;
+	int ret;
+
+	/* Make sure the device is in D0 state. */
+	uart_change_pm(state, UART_PM_STATE_ON);
+
+	/* Initialise and allocate the transmit buffer. */
+	page = get_zeroed_page(GFP_KERNEL);
+	if (!page)
+		return -ENOMEM;
+	state->xmit.buf = (unsigned char *) page;
+	uart_circ_clear(&state->xmit);
+
+	/* Initialise and allocate the receive buffer. */
+	page = get_zeroed_page(GFP_KERNEL);
+	if (!page) {
+		ret = -ENOMEM;
+		goto err_free_tx;
+	}
+	mtty->rx_buf = (unsigned char *) page;
+	mtty->rx_head = mtty->rx_tail = mtty->rx_vetted = mtty->rx_lines = 0;
+	mtty->rx_overflow = false;
+
+	ret = port->ops->startup(port);
+	if (ret)
+		goto err_free_rx;
+
+	if (uart_console(port) && port->cons->cflag) {
+		mtty->termios.c_cflag = port->cons->cflag;
+		port->cons->cflag = 0;
+	}
+
+	/* Initialise the hardware port settings. */
+	uart_change_speed(mtty, NULL);
+
+	/*
+	 * Setup the RTS and DTR signals once the
+	 * port is open and ready to respond.
+	 */
+	uart_set_mctrl(port, TIOCM_RTS | TIOCM_DTR);
+
+	return 0;
+
+err_free_rx:
+	free_page((unsigned long)mtty->rx_buf);
+	mtty->rx_buf = NULL;
+err_free_tx:
+	free_page((unsigned long)state->xmit.buf);
+	state->xmit.buf = NULL;
+	return ret;
+}
+
+/*
+ * This routine will shutdown a serial port; interrupts are disabled, and
+ * DTR is dropped if the hangup on close termio flag is on.
+ */
+static void uart_port_shutdown(struct minitty_data *mtty)
+{
+	struct uart_state *state = &mtty->state;
+	struct uart_port *port = state->uart_port;
+
+	spin_lock_irq(&port->lock);
+	port->ops->stop_rx(port);
+	spin_unlock_irq(&port->lock);
+
+	if (uart_console(port))
+		port->cons->cflag = mtty->termios.c_cflag;
+
+	/* Turn off DTR and RTS early. */
+	if (C_HUPCL(mtty))
+		uart_clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
+
+	/* Free the IRQ and disable the port. */
+	port->ops->shutdown(port);
+	synchronize_irq(port->irq);
+
+	/* Free the transmit buffer page. */
+	free_page((unsigned long)state->xmit.buf);
+	state->xmit.buf = NULL;
+
+	/* Free the receive buffer page. */
+	free_page((unsigned long)mtty->rx_buf);
+	mtty->rx_buf = NULL;
+}
+
+static int minitty_open(struct inode *inode, struct file *file)
+{
+	struct minitty_data *mtty = NULL;
+	dev_t devt = inode->i_rdev;
+	int ret = 0;
+
+	if (devt == MKDEV(TTYAUX_MAJOR, 1)) {
+		struct console *co;
+		struct uart_driver *drv;
+		console_lock();
+		for_each_console(co) {
+			if (co->device  != uart_console_device)
+				continue;
+			drv = co->data;
+			mtty = container_of(drv->state, typeof(*mtty), state);
+			mtty +=	co->index;
+			break;
+		}
+		console_unlock();
+		if (!mtty)
+			return -ENODEV;
+	} else {
+		mtty = container_of(inode->i_cdev, typeof(*mtty), cdev);
+	}
+
+	nonseekable_open(inode, file);
+
+	file->private_data = mtty;
+
+	mutex_lock(&mtty->mutex);
+	if (!mtty->usecount++) {
+		ret = uart_port_startup(mtty);
+		if (ret)
+			mtty->usecount--;
+	}
+	mutex_unlock(&mtty->mutex);
+	return ret;
+}
+
+static int minitty_release(struct inode *inode, struct file *file)
+{
+	struct minitty_data *mtty = file->private_data;
+	struct uart_state *state = &mtty->state;
+	struct uart_port *port = state->uart_port;
+
+	mutex_lock(&mtty->mutex);
+	mtty->usecount--;
+	if (!mtty->usecount) {
+		uart_flush_tx_buffer(mtty);
+		uart_port_shutdown(mtty);
+		if (!uart_console(port))
+			uart_change_pm(state, UART_PM_STATE_OFF);
+	}
+	mutex_unlock(&mtty->mutex);
+	return 0;
+}
+
+static const struct file_operations minitty_fops = {
+	.llseek		= no_llseek,
+	.read		= minitty_read,
+	.write		= minitty_write,
+	.poll		= minitty_poll,
+	.unlocked_ioctl	= minitty_ioctl,
+	.open		= minitty_open,
+	.release	= minitty_release,
+};
+
+struct class *minitty_class;
+
+#if defined(CONFIG_SERIAL_CORE_CONSOLE) || defined(CONFIG_CONSOLE_POLL)
+/**
+ *	uart_console_write - write a console message to a serial port
+ *	@port: the port to write the message
+ *	@s: array of characters
+ *	@count: number of characters in string to write
+ *	@putchar: function to write character to port
+ */
+void uart_console_write(struct uart_port *port, const char *s,
+			unsigned int count,
+			void (*putchar)(struct uart_port *, int))
+{
+	unsigned int i;
+
+	for (i = 0; i < count; i++, s++) {
+		if (*s == '\n')
+			putchar(port, '\r');
+		putchar(port, *s);
+	}
+}
+EXPORT_SYMBOL_GPL(uart_console_write);
+
+/*
+ *	Check whether an invalid uart number has been specified, and
+ *	if so, search for the first available port that does have
+ *	console support.
+ */
+struct uart_port * __init
+uart_get_console(struct uart_port *ports, int nr, struct console *co)
+{
+	int idx = co->index;
+
+	if (idx < 0 || idx >= nr || (ports[idx].iobase == 0 &&
+				     ports[idx].membase == NULL))
+		for (idx = 0; idx < nr; idx++)
+			if (ports[idx].iobase != 0 ||
+			    ports[idx].membase != NULL)
+				break;
+
+	co->index = idx;
+
+	return ports + idx;
+}
+
+/**
+ *	uart_parse_earlycon - Parse earlycon options
+ *	@p:	  ptr to 2nd field (ie., just beyond '<name>,')
+ *	@iotype:  ptr for decoded iotype (out)
+ *	@addr:    ptr for decoded mapbase/iobase (out)
+ *	@options: ptr for <options> field; NULL if not present (out)
+ *
+ *	Decodes earlycon kernel command line parameters of the form
+ *	   earlycon=<name>,io|mmio|mmio16|mmio32|mmio32be|mmio32native,<addr>,<options>
+ *	   console=<name>,io|mmio|mmio16|mmio32|mmio32be|mmio32native,<addr>,<options>
+ *
+ *	The optional form
+ *	   earlycon=<name>,0x<addr>,<options>
+ *	   console=<name>,0x<addr>,<options>
+ *	is also accepted; the returned @iotype will be UPIO_MEM.
+ *
+ *	Returns 0 on success or -EINVAL on failure
+ */
+int uart_parse_earlycon(char *p, unsigned char *iotype, resource_size_t *addr,
+			char **options)
+{
+	if (strncmp(p, "mmio,", 5) == 0) {
+		*iotype = UPIO_MEM;
+		p += 5;
+	} else if (strncmp(p, "mmio16,", 7) == 0) {
+		*iotype = UPIO_MEM16;
+		p += 7;
+	} else if (strncmp(p, "mmio32,", 7) == 0) {
+		*iotype = UPIO_MEM32;
+		p += 7;
+	} else if (strncmp(p, "mmio32be,", 9) == 0) {
+		*iotype = UPIO_MEM32BE;
+		p += 9;
+	} else if (strncmp(p, "mmio32native,", 13) == 0) {
+		*iotype = IS_ENABLED(CONFIG_CPU_BIG_ENDIAN) ?
+			UPIO_MEM32BE : UPIO_MEM32;
+		p += 13;
+	} else if (strncmp(p, "io,", 3) == 0) {
+		*iotype = UPIO_PORT;
+		p += 3;
+	} else if (strncmp(p, "0x", 2) == 0) {
+		*iotype = UPIO_MEM;
+	} else {
+		return -EINVAL;
+	}
+
+	/*
+	 * Before you replace it with kstrtoull(), think about options separator
+	 * (',') it will not tolerate
+	 */
+	*addr = simple_strtoull(p, NULL, 0);
+	p = strchr(p, ',');
+	if (p)
+		p++;
+
+	*options = p;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(uart_parse_earlycon);
+
+/**
+ *	uart_parse_options - Parse serial port baud/parity/bits/flow control.
+ *	@options: pointer to option string
+ *	@baud: pointer to an 'int' variable for the baud rate.
+ *	@parity: pointer to an 'int' variable for the parity.
+ *	@bits: pointer to an 'int' variable for the number of data bits.
+ *	@flow: pointer to an 'int' variable for the flow control character.
+ *
+ *	uart_parse_options decodes a string containing the serial console
+ *	options.  The format of the string is <baud><parity><bits><flow>,
+ *	eg: 115200n8r
+ */
+void
+uart_parse_options(char *options, int *baud, int *parity, int *bits, int *flow)
+{
+	char *s = options;
+
+	*baud = simple_strtoul(s, NULL, 10);
+	while (*s >= '0' && *s <= '9')
+		s++;
+	if (*s)
+		*parity = *s++;
+	if (*s)
+		*bits = *s++ - '0';
+	if (*s)
+		*flow = *s;
+}
+EXPORT_SYMBOL_GPL(uart_parse_options);
+
+/**
+ *	uart_set_options - setup the serial console parameters
+ *	@port: pointer to the serial ports uart_port structure
+ *	@co: console pointer
+ *	@baud: baud rate
+ *	@parity: parity character - 'n' (none), 'o' (odd), 'e' (even)
+ *	@bits: number of data bits
+ *	@flow: flow control character - 'r' (rts)
+ */
+int
+uart_set_options(struct uart_port *port, struct console *co,
+		 int baud, int parity, int bits, int flow)
+{
+	struct ktermios termios;
+	static struct ktermios dummy;
+
+	/*
+	 * Ensure that the serial console lock is initialised
+	 * early.
+	 * If this port is a console, then the spinlock is already
+	 * initialised.
+	 */
+	if (!(uart_console(port) && (port->cons->flags & CON_ENABLED)))
+		spin_lock_init(&port->lock);
+
+	memset(&termios, 0, sizeof(struct ktermios));
+
+	termios.c_cflag |= CREAD | HUPCL | CLOCAL;
+	tty_termios_encode_baud_rate(&termios, baud, baud);
+
+	if (bits == 7)
+		termios.c_cflag |= CS7;
+	else
+		termios.c_cflag |= CS8;
+
+	switch (parity) {
+	case 'o': case 'O':
+		termios.c_cflag |= PARODD;
+		/*fall through*/
+	case 'e': case 'E':
+		termios.c_cflag |= PARENB;
+		break;
+	}
+
+	if (flow == 'r')
+		termios.c_cflag |= CRTSCTS;
+
+	/*
+	 * some uarts on other side don't support no flow control.
+	 * So we set * DTR in host uart to make them happy
+	 */
+	port->mctrl |= TIOCM_DTR;
+
+	port->ops->set_termios(port, &termios, &dummy);
+	/*
+	 * Allow the setting of the UART parameters with a NULL console
+	 * too:
+	 */
+	if (co)
+		co->cflag = termios.c_cflag;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(uart_set_options);
+#endif /* CONFIG_SERIAL_CORE_CONSOLE */
+
+static int
+uart_configure_port(struct uart_driver *drv, struct uart_state *state,
+		    struct uart_port *port)
+{
+	unsigned int flags;
+
+	/*
+	 * If there isn't a port here, don't do anything further.
+	 */
+	if (!port->iobase && !port->mapbase && !port->membase)
+		return -ENXIO;
+
+	/*
+	 * Now do the auto configuration stuff.  Note that config_port
+	 * is expected to claim the resources and map the port for us.
+	 */
+	flags = 0;
+	if (port->flags & UPF_BOOT_AUTOCONF) {
+		if (!(port->flags & UPF_FIXED_TYPE)) {
+			port->type = PORT_UNKNOWN;
+			flags |= UART_CONFIG_TYPE;
+		}
+		port->ops->config_port(port, flags);
+	}
+
+	if (port->type != PORT_UNKNOWN) {
+		unsigned long flags;
+
+		pr_info("%s%d %s\n", drv->dev_name, port->line,
+			port->ops->type ? port->ops->type(port) : "");
+
+		/* Power up port for set_mctrl() */
+		uart_change_pm(state, UART_PM_STATE_ON);
+
+		/*
+		 * Ensure that the modem control lines are de-activated.
+		 * keep the DTR setting that is set in uart_set_options()
+		 * We probably don't need a spinlock around this, but
+		 */
+		spin_lock_irqsave(&port->lock, flags);
+		port->ops->set_mctrl(port, port->mctrl & TIOCM_DTR);
+		spin_unlock_irqrestore(&port->lock, flags);
+
+		/*
+		 * If this driver supports console, and it hasn't been
+		 * successfully registered yet, try to re-register it.
+		 * It may be that the port was not available.
+		 */
+		if (port->cons && !(port->cons->flags & CON_ENABLED))
+			register_console(port->cons);
+
+		/*
+		 * Power down all ports by default, except the
+		 * console if we have one.
+		 */
+		if (!uart_console(port))
+			uart_change_pm(state, UART_PM_STATE_OFF);
+
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
+/**
+ *	uart_add_one_port - attach a driver-defined port structure
+ *	@drv: pointer to the uart low level driver structure for this port
+ *	@port: uart port structure to use for this port.
+ */
+int uart_add_one_port(struct uart_driver *drv, struct uart_port *port)
+{
+	unsigned int index = port->line;
+	dev_t devt = MKDEV(drv->major, drv->minor) + index;
+	struct minitty_data *mtty;
+	struct uart_state *state;
+	int ret;
+
+	mtty = container_of(drv->state, typeof(*mtty), state) + index;
+	state = &mtty->state;
+
+	state->uart_port = port;
+	state->pm_state = UART_PM_STATE_UNDEFINED;
+	port->state = state;
+	port->cons = drv->cons;
+	port->minor = drv->minor + index;
+
+	/* our default termios */
+	mtty->termios.c_iflag = ICRNL;
+	mtty->termios.c_oflag = OPOST | ONLCR;
+	mtty->termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
+	mtty->termios.c_lflag = ICANON | ECHO | ECHOE | ECHOK | ECHOKE | ECHOCTL;
+	mtty->termios.c_ispeed = 9600;
+	mtty->termios.c_ospeed = 9600;
+	memcpy(mtty->termios.c_cc, INIT_C_CC, sizeof(cc_t)*NCCS);
+
+	mutex_init(&mtty->mutex);
+	init_waitqueue_head(&mtty->write_wait);
+	init_waitqueue_head(&mtty->read_wait);
+	INIT_WORK(&mtty->rx_work, uart_rx_work);
+
+	/*
+	 * If this port is a console, then the spinlock is already
+	 * initialised.
+	 */
+	if (!(uart_console(port) && (port->cons->flags & CON_ENABLED)))
+		spin_lock_init(&port->lock);
+	if (port->cons && port->dev)
+		of_console_check(port->dev->of_node, port->cons->name, index);
+
+	ret = uart_configure_port(drv, state, port);
+	/*
+	 * We don't support setserial so no point registering a nonexistent
+	 * device . Silently ignore this port if not present.
+	 */
+	if (ret) {
+		ret = 0;
+		goto out;
+	}
+
+	state->port.console = uart_console(port);
+
+	cdev_init(&mtty->cdev, &minitty_fops);
+	mtty->cdev.owner = drv->owner;
+	ret = cdev_add(&mtty->cdev, devt, 1);
+	if (ret)
+		goto out;
+	mtty->dev = device_create(minitty_class, port->dev, devt, mtty,
+				  "%s%d", drv->dev_name, index);
+	if (IS_ERR(mtty->dev)) {
+		ret = PTR_ERR(mtty->dev);
+		goto err_cdev_del;
+	}
+
+	return 0;
+
+err_cdev_del:
+	cdev_del(&mtty->cdev);
+out:
+	return ret;
+}
+EXPORT_SYMBOL(uart_add_one_port);
+
+/**
+ *	uart_remove_one_port - detach a driver defined port structure
+ *	@drv: pointer to the uart low level driver structure for this port
+ *	@port: uart port structure for this port
+ *
+ *	This unhooks the specified port structure from the core driver.
+ *	No further calls will be made to the low-level code for this port.
+ */
+int uart_remove_one_port(struct uart_driver *drv, struct uart_port *port)
+{
+	unsigned int index = port->line;
+	dev_t devt = MKDEV(drv->major, drv->minor) + index;
+	struct minitty_data *mtty;
+	struct uart_state *state;
+
+	mtty = container_of(drv->state, typeof(*mtty), state) + index;
+	state = &mtty->state;
+	BUG_ON(state != port->state);
+
+	device_destroy(minitty_class, devt);
+	cdev_del(&mtty->cdev);
+
+	if (uart_console(port))
+		unregister_console(port->cons);
+
+	if (port->type != PORT_UNKNOWN && port->ops->release_port)
+		port->ops->release_port(port);
+	port->type = PORT_UNKNOWN;
+	state->uart_port = NULL;
+
+	return 0;
+}
+EXPORT_SYMBOL(uart_remove_one_port);
+
+/**
+ *	uart_register_driver - register a driver with the uart core layer
+ *	@drv: low level driver structure
+ *
+ *	Register a uart driver. The per-port structures should be
+ *	registered using uart_add_one_port after this call has succeeded.
+ */
+int uart_register_driver(struct uart_driver *drv)
+{
+	struct minitty_data *mtty;
+	int ret;
+
+	BUG_ON(drv->state);
+
+	mtty = kzalloc(sizeof(*mtty) * drv->nr, GFP_KERNEL);
+	if (!mtty)
+		return -ENOMEM;
+
+	if (!drv->major) {
+		dev_t devt;
+		ret = alloc_chrdev_region(&devt, drv->minor, drv->nr, drv->driver_name);
+		drv->major = MAJOR(devt);
+		drv->minor = MINOR(devt);
+	} else {
+		dev_t devt = MKDEV(drv->major, drv->minor);
+		ret = register_chrdev_region(devt, drv->nr, drv->driver_name);
+	}
+	if (ret < 0)
+		goto err;
+
+	drv->state = &mtty->state;
+	return 0;
+
+err:
+	kfree(mtty);
+	return ret;
+}
+EXPORT_SYMBOL(uart_register_driver);
+
+/**
+ *	uart_unregister_driver - remove a driver from the uart core layer
+ *	@drv: low level driver structure
+ *
+ *	Remove all references to a driver from the core driver.  The low
+ *	level driver must have removed all its ports via the
+ *	uart_remove_one_port() if it registered them with uart_add_one_port().
+ */
+void uart_unregister_driver(struct uart_driver *drv)
+{
+	dev_t devt = MKDEV(drv->major, drv->minor);
+	struct minitty_data *mtty;
+
+	unregister_chrdev_region(devt, drv->nr);
+	mtty = container_of(drv->state, typeof(*mtty), state);
+	drv->state = NULL;
+	kfree(mtty);
+}
+EXPORT_SYMBOL(uart_unregister_driver);
+
+void do_SAK(struct tty_struct *tty)
+{
+}
+EXPORT_SYMBOL(do_SAK);
+
+struct tty_driver *uart_console_device(struct console *co, int *index)
+{
+	return NULL;
+}
+
+static struct cdev console_cdev;
+
+static char *minitty_devnode(struct device *dev, umode_t *mode)
+{
+	if (!mode)
+		return NULL;
+	if (dev->devt == MKDEV(TTYAUX_MAJOR, 0) ||
+			dev->devt == MKDEV(TTYAUX_MAJOR, 2))
+		*mode = 0666;
+	return NULL;
+}
+
+static int __init minitty_class_init(void)
+{
+	minitty_class = class_create(THIS_MODULE, "tty");
+	if (IS_ERR(minitty_class))
+		return PTR_ERR(minitty_class);
+	minitty_class->devnode = minitty_devnode;
+	return 0;
+}
+postcore_initcall(minitty_class_init);
+
+int __init minitty_init(void)
+{
+	dev_t devt = MKDEV(TTYAUX_MAJOR, 1);
+	cdev_init(&console_cdev, &minitty_fops);
+	if (cdev_add(&console_cdev, devt, 1) ||
+	    register_chrdev_region(devt, 1, "/dev/console") < 0)
+		panic("Couldn't register /dev/console driver\n");
+	device_create(minitty_class, NULL, devt, NULL, "console");
+	return 0;
+}
+device_initcall(minitty_init);
diff --git a/include/linux/tty_flip.h b/include/linux/tty_flip.h
index c28dd523f9..5393513298 100644
--- a/include/linux/tty_flip.h
+++ b/include/linux/tty_flip.h
@@ -13,6 +13,7 @@ extern int tty_prepare_flip_string(struct tty_port *port,
 extern void tty_flip_buffer_push(struct tty_port *port);
 void tty_schedule_flip(struct tty_port *port);
 
+#ifndef CONFIG_MINITTY_SERIAL
 static inline int tty_insert_flip_char(struct tty_port *port,
 					unsigned char ch, char flag)
 {
@@ -28,6 +29,9 @@ static inline int tty_insert_flip_char(struct tty_port *port,
 	}
 	return tty_insert_flip_string_flags(port, &ch, &flag, 1);
 }
+#else
+int tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag);
+#endif
 
 static inline int tty_insert_flip_string(struct tty_port *port,
 		const unsigned char *chars, size_t size)
-- 
2.9.3