Revert "tty/serial: Add kgdb_nmi driver"

This reverts commit 0c57dfcc6c1d037243c2f8fbf62eab3633326ec0.

The functionality was supoosed to be used by a later patch in the
series that never landed [1]. Drop it.

NOTE: part of functionality was already reverted by commit
39d0be87438a ("serial: kgdb_nmi: Remove unused knock code"). Also note
that this revert is not a clean revert given code changes that have
happened in the meantime.

It's obvious that nobody is using this code since the two exposed
functions (kgdb_register_nmi_console() and
kgdb_unregister_nmi_console()) are both no-ops if
"arch_kgdb_ops.enable_nmi" is not defined. No architectures define it.

[1] https://lore.kernel.org/lkml/[e-mail]/

Signed-off-by: Douglas Anderson <[e-mail]>
Acked-by: Andy Shevchenko <[e-mail]>
Link: URL [1]
Link: https://lore.kernel.org/r/20250129082535.1.Ia095eac1ae357f87d23e7af2206741f5d40788f1@changeid
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/Kconfig

···
 
 	  Say Y if you have an external 8250/16C550 UART.  If unsure, say N.
 
-config SERIAL_KGDB_NMI
-	bool "Serial console over KGDB NMI debugger port"
-	depends on KGDB_SERIAL_CONSOLE
-	help
-	  This special driver allows you to temporary use NMI debugger port
-	  as a normal console (assuming that the port is attached to KGDB).
-
-	  Unlike KDB's disable_nmi command, with this driver you are always
-	  able to go back to the debugger using KGDB escape sequence ($3#33).
-	  This is because this console driver processes the input in NMI
-	  context, and thus is able to intercept the magic sequence.
-
-	  Note that since the console interprets input and uses polling
-	  communication methods, for things like PPP you still must fully
-	  detach debugger port from the KGDB NMI (i.e. disable_nmi), and
-	  use raw console.
-
-	  If unsure, say N.
-
 config SERIAL_MESON
 	tristate "Meson serial port support"
 	depends on ARCH_MESON || COMPILE_TEST

drivers/tty/serial/Makefile

···
 # GPIOLIB helpers for modem control lines
 obj-$(CONFIG_SERIAL_MCTRL_GPIO)	+= serial_mctrl_gpio.o
 
-obj-$(CONFIG_SERIAL_KGDB_NMI) += kgdb_nmi.o
 obj-$(CONFIG_KGDB_SERIAL_CONSOLE) += kgdboc.o
 obj-$(CONFIG_SERIAL_NUVOTON_MA35D1) += ma35d1_serial.o

drivers/tty/serial/kgdb_nmi.c

···
-// SPDX-License-Identifier: GPL-2.0
-/*
- * KGDB NMI serial console
- *
- * Copyright 2010 Google, Inc.
- *		  Arve Hjønnevåg <[e-mail]>
- *		  Colin Cross <[e-mail]>
- * Copyright 2012 Linaro Ltd.
- *		  Anton Vorontsov <[e-mail]>
- */
-
-#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 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;
-
-/*
- * 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 ssize_t kgdb_nmi_tty_write(struct tty_struct *tty, const u8 *buf,
-				  size_t 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);

drivers/tty/serial/kgdboc.c

···
 	if (configured != 1)
 		return;
 
-	if (kgdb_unregister_nmi_console())
-		return;
 	kgdboc_unregister_kbd();
 	kgdb_unregister_io_module(&kgdboc_io_ops);
 }
···
 	if (err)
 		goto noconfig;
 
-	err = kgdb_register_nmi_console();
-	if (err)
-		goto nmi_con_failed;
-
 	configured = 1;
 
 	return 0;
 
-nmi_con_failed:
-	kgdb_unregister_io_module(&kgdboc_io_ops);
 noconfig:
 	kgdboc_unregister_kbd();
 	configured = 0;

include/linux/kgdb.h

···
 
 extern unsigned long kgdb_arch_pc(int exception, struct pt_regs *regs);
 
-#ifdef CONFIG_SERIAL_KGDB_NMI
-extern int kgdb_register_nmi_console(void);
-extern int kgdb_unregister_nmi_console(void);
-#else
-static inline int kgdb_register_nmi_console(void) { return 0; }
-static inline int kgdb_unregister_nmi_console(void) { return 0; }
-#endif
-
 extern int kgdb_register_io_module(struct kgdb_io *local_kgdb_io_ops);
 extern void kgdb_unregister_io_module(struct kgdb_io *local_kgdb_io_ops);
 extern struct kgdb_io *dbg_io_ops;