drivers/tty/serial/kgdb_nmi.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * KGDB NMI serial console
  *
  * Copyright 2010 Google, Inc.
  *		  Arve Hjønnevåg <arve@android.com>
  *		  Colin Cross <ccross@android.com>
  * Copyright 2012 Linaro Ltd.
  *		  Anton Vorontsov <anton.vorontsov@linaro.org>
  */

 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/compiler.h>
 #include <linux/slab.h>
 #include <linux/errno.h>
 #include <linux/atomic.h>
 #include <linux/console.h>
 #include <linux/tty.h>
 #include <linux/tty_driver.h>
 #include <linux/tty_flip.h>
 #include <linux/serial_core.h>
 #include <linux/interrupt.h>
 #include <linux/hrtimer.h>
 #include <linux/tick.h>
 #include <linux/kfifo.h>
 #include <linux/kgdb.h>
 #include <linux/kdb.h>

 static int kgdb_nmi_knock = 1;
 module_param_named(knock, kgdb_nmi_knock, int, 0600);
 MODULE_PARM_DESC(knock, "if set to 1 (default), the special '$3#33' command " \
 			"must be used to enter the debugger; when set to 0, " \
 			"hitting return key is enough to enter the debugger; " \
 			"when set to -1, the debugger is entered immediately " \
 			"upon NMI");

 static char *kgdb_nmi_magic = "$3#33";
 module_param_named(magic, kgdb_nmi_magic, charp, 0600);
 MODULE_PARM_DESC(magic, "magic sequence to enter NMI debugger (default $3#33)");

 static atomic_t kgdb_nmi_num_readers = ATOMIC_INIT(0);

 static int kgdb_nmi_console_setup(struct console *co, char *options)
 {
 	arch_kgdb_ops.enable_nmi(1);

 	/* The NMI console uses the dbg_io_ops to issue console messages. To
 	 * avoid duplicate messages during kdb sessions we must inform kdb's
 	 * I/O utilities that messages sent to the console will automatically
 	 * be displayed on the dbg_io.
 	 */
 	dbg_io_ops->cons = co;

 	return 0;
 }

 static void kgdb_nmi_console_write(struct console *co, const char *s, uint c)
 {
 	int i;

 	for (i = 0; i < c; i++)
 		dbg_io_ops->write_char(s[i]);
 }

 static struct tty_driver *kgdb_nmi_tty_driver;

 static struct tty_driver *kgdb_nmi_console_device(struct console *co, int *idx)
 {
 	*idx = co->index;
 	return kgdb_nmi_tty_driver;
 }

 static struct console kgdb_nmi_console = {
 	.name	= "ttyNMI",
 	.setup  = kgdb_nmi_console_setup,
 	.write	= kgdb_nmi_console_write,
 	.device	= kgdb_nmi_console_device,
 	.flags	= CON_PRINTBUFFER | CON_ANYTIME,
 	.index	= -1,
 };

 /*
  * This is usually the maximum rate on debug ports. We make fifo large enough
  * to make copy-pasting to the terminal usable.
  */
 #define KGDB_NMI_BAUD		115200
 #define KGDB_NMI_FIFO_SIZE	roundup_pow_of_two(KGDB_NMI_BAUD / 8 / HZ)

 struct kgdb_nmi_tty_priv {
 	struct tty_port port;
 	struct timer_list timer;
 	STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo;
 };

 static struct tty_port *kgdb_nmi_port;

 static void kgdb_tty_recv(int ch)
 {
 	struct kgdb_nmi_tty_priv *priv;
 	char c = ch;

 	if (!kgdb_nmi_port || ch < 0)
 		return;
 	/*
 	 * Can't use port->tty->driver_data as tty might be not there. Timer
 	 * will check for tty and will get the ref, but here we don't have to
 	 * do that, and actually, we can't: we're in NMI context, no locks are
 	 * possible.
 	 */
 	priv = container_of(kgdb_nmi_port, struct kgdb_nmi_tty_priv, port);
 	kfifo_in(&priv->fifo, &c, 1);
 }

 static int kgdb_nmi_poll_one_knock(void)
 {
 	static int n;
 	int c;
 	const char *magic = kgdb_nmi_magic;
 	size_t m = strlen(magic);
 	bool printch = false;

 	c = dbg_io_ops->read_char();
 	if (c == NO_POLL_CHAR)
 		return c;

 	if (!kgdb_nmi_knock && (c == '\r' || c == '\n')) {
 		return 1;
 	} else if (c == magic[n]) {
 		n = (n + 1) % m;
 		if (!n)
 			return 1;
 		printch = true;
 	} else {
 		n = 0;
 	}

 	if (atomic_read(&kgdb_nmi_num_readers)) {
 		kgdb_tty_recv(c);
 		return 0;
 	}

 	if (printch) {
 		kdb_printf("%c", c);
 		return 0;
 	}

 	kdb_printf("\r%s %s to enter the debugger> %*s",
 		   kgdb_nmi_knock ? "Type" : "Hit",
 		   kgdb_nmi_knock ? magic  : "<return>", (int)m, "");
 	while (m--)
 		kdb_printf("\b");
 	return 0;
 }

 /**
  * kgdb_nmi_poll_knock - Check if it is time to enter the debugger
  *
  * "Serial ports are often noisy, especially when muxed over another port (we
  * often use serial over the headset connector). Noise on the async command
  * line just causes characters that are ignored, on a command line that blocked
  * execution noise would be catastrophic." -- Colin Cross
  *
  * So, this function implements KGDB/KDB knocking on the serial line: we won't
  * enter the debugger until we receive a known magic phrase (which is actually
  * "$3#33", known as "escape to KDB" command. There is also a relaxed variant
  * of knocking, i.e. just pressing the return key is enough to enter the
  * debugger. And if knocking is disabled, the function always returns 1.
  */
 bool kgdb_nmi_poll_knock(void)
 {
 	if (kgdb_nmi_knock < 0)
 		return true;

 	while (1) {
 		int ret;

 		ret = kgdb_nmi_poll_one_knock();
 		if (ret == NO_POLL_CHAR)
 			return false;
 		else if (ret == 1)
 			break;
 	}
 	return true;
 }

 /*
  * The tasklet is cheap, it does not cause wakeups when reschedules itself,
  * instead it waits for the next tick.
  */
 static void kgdb_nmi_tty_receiver(struct timer_list *t)
 {
 	struct kgdb_nmi_tty_priv *priv = from_timer(priv, t, timer);
 	char ch;

 	priv->timer.expires = jiffies + (HZ/100);
 	add_timer(&priv->timer);

 	if (likely(!atomic_read(&kgdb_nmi_num_readers) ||
 		   !kfifo_len(&priv->fifo)))
 		return;

 	while (kfifo_out(&priv->fifo, &ch, 1))
 		tty_insert_flip_char(&priv->port, ch, TTY_NORMAL);
 	tty_flip_buffer_push(&priv->port);
 }

 static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty)
 {
 	struct kgdb_nmi_tty_priv *priv =
 	    container_of(port, struct kgdb_nmi_tty_priv, port);

 	kgdb_nmi_port = port;
 	priv->timer.expires = jiffies + (HZ/100);
 	add_timer(&priv->timer);

 	return 0;
 }

 static void kgdb_nmi_tty_shutdown(struct tty_port *port)
 {
 	struct kgdb_nmi_tty_priv *priv =
 	    container_of(port, struct kgdb_nmi_tty_priv, port);

 	del_timer(&priv->timer);
 	kgdb_nmi_port = NULL;
 }

 static const struct tty_port_operations kgdb_nmi_tty_port_ops = {
 	.activate	= kgdb_nmi_tty_activate,
 	.shutdown	= kgdb_nmi_tty_shutdown,
 };

 static int kgdb_nmi_tty_install(struct tty_driver *drv, struct tty_struct *tty)
 {
 	struct kgdb_nmi_tty_priv *priv;
 	int ret;

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

 	INIT_KFIFO(priv->fifo);
 	timer_setup(&priv->timer, kgdb_nmi_tty_receiver, 0);
 	tty_port_init(&priv->port);
 	priv->port.ops = &kgdb_nmi_tty_port_ops;
 	tty->driver_data = priv;

 	ret = tty_port_install(&priv->port, drv, tty);
 	if (ret) {
 		pr_err("%s: can't install tty port: %d\n", __func__, ret);
 		goto err;
 	}
 	return 0;
 err:
 	tty_port_destroy(&priv->port);
 	kfree(priv);
 	return ret;
 }

 static void kgdb_nmi_tty_cleanup(struct tty_struct *tty)
 {
 	struct kgdb_nmi_tty_priv *priv = tty->driver_data;

 	tty->driver_data = NULL;
 	tty_port_destroy(&priv->port);
 	kfree(priv);
 }

 static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file)
 {
 	struct kgdb_nmi_tty_priv *priv = tty->driver_data;
 	unsigned int mode = file->f_flags & O_ACCMODE;
 	int ret;

 	ret = tty_port_open(&priv->port, tty, file);
 	if (!ret && (mode == O_RDONLY || mode == O_RDWR))
 		atomic_inc(&kgdb_nmi_num_readers);

 	return ret;
 }

 static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file)
 {
 	struct kgdb_nmi_tty_priv *priv = tty->driver_data;
 	unsigned int mode = file->f_flags & O_ACCMODE;

 	if (mode == O_RDONLY || mode == O_RDWR)
 		atomic_dec(&kgdb_nmi_num_readers);

 	tty_port_close(&priv->port, tty, file);
 }

 static void kgdb_nmi_tty_hangup(struct tty_struct *tty)
 {
 	struct kgdb_nmi_tty_priv *priv = tty->driver_data;

 	tty_port_hangup(&priv->port);
 }

 static unsigned int kgdb_nmi_tty_write_room(struct tty_struct *tty)
 {
 	/* Actually, we can handle any amount as we use polled writes. */
 	return 2048;
 }

 static int kgdb_nmi_tty_write(struct tty_struct *tty, const unchar *buf, int c)
 {
 	int i;

 	for (i = 0; i < c; i++)
 		dbg_io_ops->write_char(buf[i]);
 	return c;
 }

 static const struct tty_operations kgdb_nmi_tty_ops = {
 	.open		= kgdb_nmi_tty_open,
 	.close		= kgdb_nmi_tty_close,
 	.install	= kgdb_nmi_tty_install,
 	.cleanup	= kgdb_nmi_tty_cleanup,
 	.hangup		= kgdb_nmi_tty_hangup,
 	.write_room	= kgdb_nmi_tty_write_room,
 	.write		= kgdb_nmi_tty_write,
 };

 int kgdb_register_nmi_console(void)
 {
 	int ret;

 	if (!arch_kgdb_ops.enable_nmi)
 		return 0;

 	kgdb_nmi_tty_driver = tty_alloc_driver(1, TTY_DRIVER_REAL_RAW);
 	if (IS_ERR(kgdb_nmi_tty_driver)) {
 		pr_err("%s: cannot allocate tty\n", __func__);
 		return PTR_ERR(kgdb_nmi_tty_driver);
 	}
 	kgdb_nmi_tty_driver->driver_name	= "ttyNMI";
 	kgdb_nmi_tty_driver->name		= "ttyNMI";
 	kgdb_nmi_tty_driver->num		= 1;
 	kgdb_nmi_tty_driver->type		= TTY_DRIVER_TYPE_SERIAL;
 	kgdb_nmi_tty_driver->subtype		= SERIAL_TYPE_NORMAL;
 	kgdb_nmi_tty_driver->init_termios	= tty_std_termios;
 	tty_termios_encode_baud_rate(&kgdb_nmi_tty_driver->init_termios,
 				     KGDB_NMI_BAUD, KGDB_NMI_BAUD);
 	tty_set_operations(kgdb_nmi_tty_driver, &kgdb_nmi_tty_ops);

 	ret = tty_register_driver(kgdb_nmi_tty_driver);
 	if (ret) {
 		pr_err("%s: can't register tty driver: %d\n", __func__, ret);
 		goto err_drv_reg;
 	}

 	register_console(&kgdb_nmi_console);

 	return 0;
 err_drv_reg:
 	tty_driver_kref_put(kgdb_nmi_tty_driver);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(kgdb_register_nmi_console);

 int kgdb_unregister_nmi_console(void)
 {
 	int ret;

 	if (!arch_kgdb_ops.enable_nmi)
 		return 0;
 	arch_kgdb_ops.enable_nmi(0);

 	ret = unregister_console(&kgdb_nmi_console);
 	if (ret)
 		return ret;

 	tty_unregister_driver(kgdb_nmi_tty_driver);
 	tty_driver_kref_put(kgdb_nmi_tty_driver);

 	return 0;
 }
 EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console);
	// SPDX-License-Identifier: GPL-2.0
	/*
	* KGDB NMI serial console
	*
	* Copyright 2010 Google, Inc.
	* Arve Hjønnevåg <arve@android.com>
	* Colin Cross <ccross@android.com>
	* Copyright 2012 Linaro Ltd.
	* Anton Vorontsov <anton.vorontsov@linaro.org>
	*/

	#include <linux/kernel.h>
	#include <linux/module.h>
	#include <linux/compiler.h>
	#include <linux/slab.h>
	#include <linux/errno.h>
	#include <linux/atomic.h>
	#include <linux/console.h>
	#include <linux/tty.h>
	#include <linux/tty_driver.h>
	#include <linux/tty_flip.h>
	#include <linux/serial_core.h>
	#include <linux/interrupt.h>
	#include <linux/hrtimer.h>
	#include <linux/tick.h>
	#include <linux/kfifo.h>
	#include <linux/kgdb.h>
	#include <linux/kdb.h>

	static int kgdb_nmi_knock = 1;
	module_param_named(knock, kgdb_nmi_knock, int, 0600);
	MODULE_PARM_DESC(knock, "if set to 1 (default), the special '$3#33' command " \
	"must be used to enter the debugger; when set to 0, " \
	"hitting return key is enough to enter the debugger; " \
	"when set to -1, the debugger is entered immediately " \
	"upon NMI");

	static char *kgdb_nmi_magic = "$3#33";
	module_param_named(magic, kgdb_nmi_magic, charp, 0600);
	MODULE_PARM_DESC(magic, "magic sequence to enter NMI debugger (default $3#33)");

	static atomic_t kgdb_nmi_num_readers = ATOMIC_INIT(0);

	static int kgdb_nmi_console_setup(struct console co, char options)
	{
	arch_kgdb_ops.enable_nmi(1);

	/* The NMI console uses the dbg_io_ops to issue console messages. To
	* avoid duplicate messages during kdb sessions we must inform kdb's
	* I/O utilities that messages sent to the console will automatically
	* be displayed on the dbg_io.
	*/
	dbg_io_ops->cons = co;

	return 0;
	}

	static void kgdb_nmi_console_write(struct console co, const char s, uint c)
	{
	int i;

	for (i = 0; i < c; i++)
	dbg_io_ops->write_char(s[i]);
	}

	static struct tty_driver *kgdb_nmi_tty_driver;

	static struct tty_driver kgdb_nmi_console_device(struct console co, int *idx)
	{
	*idx = co->index;
	return kgdb_nmi_tty_driver;
	}

	static struct console kgdb_nmi_console = {
	.name = "ttyNMI",
	.setup = kgdb_nmi_console_setup,
	.write = kgdb_nmi_console_write,
	.device = kgdb_nmi_console_device,
	.flags = CON_PRINTBUFFER \| CON_ANYTIME,
	.index = -1,
	};

	/*
	* This is usually the maximum rate on debug ports. We make fifo large enough
	* to make copy-pasting to the terminal usable.
	*/
	#define KGDB_NMI_BAUD 115200
	#define KGDB_NMI_FIFO_SIZE roundup_pow_of_two(KGDB_NMI_BAUD / 8 / HZ)

	struct kgdb_nmi_tty_priv {
	struct tty_port port;
	struct timer_list timer;
	STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo;
	};

	static struct tty_port *kgdb_nmi_port;

	static void kgdb_tty_recv(int ch)
	{
	struct kgdb_nmi_tty_priv *priv;
	char c = ch;

	if (!kgdb_nmi_port \|\| ch < 0)
	return;
	/*
	* Can't use port->tty->driver_data as tty might be not there. Timer
	* will check for tty and will get the ref, but here we don't have to
	* do that, and actually, we can't: we're in NMI context, no locks are
	* possible.
	*/
	priv = container_of(kgdb_nmi_port, struct kgdb_nmi_tty_priv, port);
	kfifo_in(&priv->fifo, &c, 1);
	}

	static int kgdb_nmi_poll_one_knock(void)
	{
	static int n;
	int c;
	const char *magic = kgdb_nmi_magic;
	size_t m = strlen(magic);
	bool printch = false;

	c = dbg_io_ops->read_char();
	if (c == NO_POLL_CHAR)
	return c;

	if (!kgdb_nmi_knock && (c == '\r' \|\| c == '\n')) {
	return 1;
	} else if (c == magic[n]) {
	n = (n + 1) % m;
	if (!n)
	return 1;
	printch = true;
	} else {
	n = 0;
	}

	if (atomic_read(&kgdb_nmi_num_readers)) {
	kgdb_tty_recv(c);
	return 0;
	}

	if (printch) {
	kdb_printf("%c", c);
	return 0;
	}

	kdb_printf("\r%s %s to enter the debugger> %*s",
	kgdb_nmi_knock ? "Type" : "Hit",
	kgdb_nmi_knock ? magic : "<return>", (int)m, "");
	while (m--)
	kdb_printf("\b");
	return 0;
	}

	/**
	* kgdb_nmi_poll_knock - Check if it is time to enter the debugger
	*
	* "Serial ports are often noisy, especially when muxed over another port (we
	* often use serial over the headset connector). Noise on the async command
	* line just causes characters that are ignored, on a command line that blocked
	* execution noise would be catastrophic." -- Colin Cross
	*
	* So, this function implements KGDB/KDB knocking on the serial line: we won't
	* enter the debugger until we receive a known magic phrase (which is actually
	* "$3#33", known as "escape to KDB" command. There is also a relaxed variant
	* of knocking, i.e. just pressing the return key is enough to enter the
	* debugger. And if knocking is disabled, the function always returns 1.
	*/
	bool kgdb_nmi_poll_knock(void)
	{
	if (kgdb_nmi_knock < 0)
	return true;

	while (1) {
	int ret;

	ret = kgdb_nmi_poll_one_knock();
	if (ret == NO_POLL_CHAR)
	return false;
	else if (ret == 1)
	break;
	}
	return true;
	}

	/*
	* The tasklet is cheap, it does not cause wakeups when reschedules itself,
	* instead it waits for the next tick.
	*/
	static void kgdb_nmi_tty_receiver(struct timer_list *t)
	{
	struct kgdb_nmi_tty_priv *priv = from_timer(priv, t, timer);
	char ch;

	priv->timer.expires = jiffies + (HZ/100);
	add_timer(&priv->timer);

	if (likely(!atomic_read(&kgdb_nmi_num_readers) \|\|
	!kfifo_len(&priv->fifo)))
	return;

	while (kfifo_out(&priv->fifo, &ch, 1))
	tty_insert_flip_char(&priv->port, ch, TTY_NORMAL);
	tty_flip_buffer_push(&priv->port);
	}

	static int kgdb_nmi_tty_activate(struct tty_port port, struct tty_struct tty)
	{
	struct kgdb_nmi_tty_priv *priv =
	container_of(port, struct kgdb_nmi_tty_priv, port);

	kgdb_nmi_port = port;
	priv->timer.expires = jiffies + (HZ/100);
	add_timer(&priv->timer);

	return 0;
	}

	static void kgdb_nmi_tty_shutdown(struct tty_port *port)
	{
	struct kgdb_nmi_tty_priv *priv =
	container_of(port, struct kgdb_nmi_tty_priv, port);

	del_timer(&priv->timer);
	kgdb_nmi_port = NULL;
	}

	static const struct tty_port_operations kgdb_nmi_tty_port_ops = {
	.activate = kgdb_nmi_tty_activate,
	.shutdown = kgdb_nmi_tty_shutdown,
	};

	static int kgdb_nmi_tty_install(struct tty_driver drv, struct tty_struct tty)
	{
	struct kgdb_nmi_tty_priv *priv;
	int ret;

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

	INIT_KFIFO(priv->fifo);
	timer_setup(&priv->timer, kgdb_nmi_tty_receiver, 0);
	tty_port_init(&priv->port);
	priv->port.ops = &kgdb_nmi_tty_port_ops;
	tty->driver_data = priv;

	ret = tty_port_install(&priv->port, drv, tty);
	if (ret) {
	pr_err("%s: can't install tty port: %d\n", __func__, ret);
	goto err;
	}
	return 0;
	err:
	tty_port_destroy(&priv->port);
	kfree(priv);
	return ret;
	}

	static void kgdb_nmi_tty_cleanup(struct tty_struct *tty)
	{
	struct kgdb_nmi_tty_priv *priv = tty->driver_data;

	tty->driver_data = NULL;
	tty_port_destroy(&priv->port);
	kfree(priv);
	}

	static int kgdb_nmi_tty_open(struct tty_struct tty, struct file file)
	{
	struct kgdb_nmi_tty_priv *priv = tty->driver_data;
	unsigned int mode = file->f_flags & O_ACCMODE;
	int ret;

	ret = tty_port_open(&priv->port, tty, file);
	if (!ret && (mode == O_RDONLY \|\| mode == O_RDWR))
	atomic_inc(&kgdb_nmi_num_readers);

	return ret;
	}

	static void kgdb_nmi_tty_close(struct tty_struct tty, struct file file)
	{
	struct kgdb_nmi_tty_priv *priv = tty->driver_data;
	unsigned int mode = file->f_flags & O_ACCMODE;

	if (mode == O_RDONLY \|\| mode == O_RDWR)
	atomic_dec(&kgdb_nmi_num_readers);

	tty_port_close(&priv->port, tty, file);
	}

	static void kgdb_nmi_tty_hangup(struct tty_struct *tty)
	{
	struct kgdb_nmi_tty_priv *priv = tty->driver_data;

	tty_port_hangup(&priv->port);
	}

	static unsigned int kgdb_nmi_tty_write_room(struct tty_struct *tty)
	{
	/* Actually, we can handle any amount as we use polled writes. */
	return 2048;
	}

	static int kgdb_nmi_tty_write(struct tty_struct tty, const unchar buf, int c)
	{
	int i;

	for (i = 0; i < c; i++)
	dbg_io_ops->write_char(buf[i]);
	return c;
	}

	static const struct tty_operations kgdb_nmi_tty_ops = {
	.open = kgdb_nmi_tty_open,
	.close = kgdb_nmi_tty_close,
	.install = kgdb_nmi_tty_install,
	.cleanup = kgdb_nmi_tty_cleanup,
	.hangup = kgdb_nmi_tty_hangup,
	.write_room = kgdb_nmi_tty_write_room,
	.write = kgdb_nmi_tty_write,
	};

	int kgdb_register_nmi_console(void)
	{
	int ret;

	if (!arch_kgdb_ops.enable_nmi)
	return 0;

	kgdb_nmi_tty_driver = tty_alloc_driver(1, TTY_DRIVER_REAL_RAW);
	if (IS_ERR(kgdb_nmi_tty_driver)) {
	pr_err("%s: cannot allocate tty\n", __func__);
	return PTR_ERR(kgdb_nmi_tty_driver);
	}
	kgdb_nmi_tty_driver->driver_name = "ttyNMI";
	kgdb_nmi_tty_driver->name = "ttyNMI";
	kgdb_nmi_tty_driver->num = 1;
	kgdb_nmi_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
	kgdb_nmi_tty_driver->subtype = SERIAL_TYPE_NORMAL;
	kgdb_nmi_tty_driver->init_termios = tty_std_termios;
	tty_termios_encode_baud_rate(&kgdb_nmi_tty_driver->init_termios,
	KGDB_NMI_BAUD, KGDB_NMI_BAUD);
	tty_set_operations(kgdb_nmi_tty_driver, &kgdb_nmi_tty_ops);

	ret = tty_register_driver(kgdb_nmi_tty_driver);
	if (ret) {
	pr_err("%s: can't register tty driver: %d\n", __func__, ret);
	goto err_drv_reg;
	}

	register_console(&kgdb_nmi_console);

	return 0;
	err_drv_reg:
	tty_driver_kref_put(kgdb_nmi_tty_driver);
	return ret;
	}
	EXPORT_SYMBOL_GPL(kgdb_register_nmi_console);

	int kgdb_unregister_nmi_console(void)
	{
	int ret;

	if (!arch_kgdb_ops.enable_nmi)
	return 0;
	arch_kgdb_ops.enable_nmi(0);

	ret = unregister_console(&kgdb_nmi_console);
	if (ret)
	return ret;

	tty_unregister_driver(kgdb_nmi_tty_driver);
	tty_driver_kref_put(kgdb_nmi_tty_driver);

	return 0;
	}
	EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console);