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Subject[RFC 5/5] serial: Remove KGDB NMI serial driver
Date
This driver provided a special ttyNMI0 port to enable NMI debugging
capabilities for kgdb but it remained in silos with the serial
core/drivers which made it a bit odd to enable using serial device
interrupt and hence remained unused.

But now with the serial core/drivers becoming NMI aware which in turn
provides NMI debugging capabilities via magic sysrq, there is no specific
reason to keep this special driver. So remove it instead.

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
---
drivers/tty/serial/Kconfig | 19 ---
drivers/tty/serial/Makefile | 1 -
drivers/tty/serial/kgdb_nmi.c | 383 ------------------------------------------
drivers/tty/serial/kgdboc.c | 8 -
include/linux/kgdb.h | 10 --
5 files changed, 421 deletions(-)
delete mode 100644 drivers/tty/serial/kgdb_nmi.c

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 780908d..625d283 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -176,25 +176,6 @@ config SERIAL_ATMEL_TTYAT

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 ($3#33).
- This is because this console driver processes the input in NMI
- context, and thus is able to intercept the magic sequence.
-
- Note that since the console interprets input and uses polling
- communication methods, for things like PPP you still must fully
- detach debugger port from the KGDB NMI (i.e. disable_nmi), and
- use raw console.
-
- If unsure, say N.
-
config SERIAL_MESON
tristate "Meson serial port support"
depends on ARCH_MESON
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index d056ee6..9ea6263 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -93,5 +93,4 @@ obj-$(CONFIG_SERIAL_SIFIVE) += sifive.o
# 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
diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c
deleted file mode 100644
index 6004c0c..0000000
--- a/drivers/tty/serial/kgdb_nmi.c
+++ /dev/null
@@ -1,383 +0,0 @@
-// 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 = -1;
- 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 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 = alloc_tty_driver(1);
- if (!kgdb_nmi_tty_driver) {
- pr_err("%s: cannot allocate tty\n", __func__);
- return -ENOMEM;
- }
- 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->flags = TTY_DRIVER_REAL_RAW;
- 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:
- put_tty_driver(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;
-
- ret = tty_unregister_driver(kgdb_nmi_tty_driver);
- if (ret)
- return ret;
- put_tty_driver(kgdb_nmi_tty_driver);
-
- return 0;
-}
-EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console);
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 84ffede..e959e72 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -158,8 +158,6 @@ static void cleanup_kgdboc(void)
if (configured != 1)
return;

- if (kgdb_unregister_nmi_console())
- return;
kgdboc_unregister_kbd();
kgdb_unregister_io_module(&kgdboc_io_ops);
}
@@ -210,16 +208,10 @@ static int configure_kgdboc(void)
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;
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index 529116b..2e8c5de 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -294,16 +294,6 @@ extern const struct kgdb_arch arch_kgdb_ops;

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);
-extern bool kgdb_nmi_poll_knock(void);
-#else
-static inline int kgdb_register_nmi_console(void) { return 0; }
-static inline int kgdb_unregister_nmi_console(void) { return 0; }
-static inline bool kgdb_nmi_poll_knock(void) { return true; }
-#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;
--
2.7.4
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