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    SubjectRe: [PATCH 07/11] tty/serial: Add kgdb_nmi driver
    On 09/13/2012 10:03 AM, Anton Vorontsov wrote:
    > This special driver makes it possible to temporary use NMI debugger port
    > as a normal console by issuing 'nmi_console' command (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 it is still better to fully
    > detach debugger port from the KGDB NMI (i.e. disable_nmi), and use raw
    > console.
    >
    > Usually, to enter the debugger one have to type the magic sequence, so
    > initially the kernel will print the following prompt on the NMI debugger
    > console:
    >
    > Type $3#33 to enter the debugger>
    >
    > For convenience, there is a kgdb_fiq.knock kernel command line option,
    > when set to 0, this turns the special command to just a return key
    > press, so the kernel will be printing this:
    >
    > Hit <return> to enter the debugger>
    >
    > This is more convenient for long debugging sessions, although it makes
    > nmi_console feature somewhat useless.
    >
    > And for the cases when NMI connected to a dedicated button, the knocking
    > can be disabled altogether by setting kgdb_fiq.knock to -1.
    >
    > Suggested-by: Colin Cross <ccross@android.com>
    > Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
    > ---
    > drivers/tty/serial/Kconfig | 19 ++
    > drivers/tty/serial/Makefile | 1 +
    > drivers/tty/serial/kgdb_nmi.c | 396 ++++++++++++++++++++++++++++++++++++++++++
    > drivers/tty/serial/kgdboc.c | 6 +
    > include/linux/kgdb.h | 10 ++
    > 5 files changed, 432 insertions(+)
    > create mode 100644 drivers/tty/serial/kgdb_nmi.c
    >
    > diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
    > index 26907cf..b22e45b 100644
    > --- a/drivers/tty/serial/Kconfig
    > +++ b/drivers/tty/serial/Kconfig
    > @@ -141,6 +141,25 @@ 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 ($3#33).
    > + This is because this console driver processes the input in NMI
    > + context, and thus is able to intercept the magic sequence.
    > +
    > + Note that since the console interprets input and uses polling
    > + communication methods, for things like PPP you still must fully
    > + detach debugger port from the KGDB NMI (i.e. disable_nmi), and
    > + use raw console.
    > +
    > + If unsure, say N.
    > +
    > config SERIAL_KS8695
    > bool "Micrel KS8695 (Centaur) serial port support"
    > depends on ARCH_KS8695
    > diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
    > index ce88667..4f694da 100644
    > --- a/drivers/tty/serial/Makefile
    > +++ b/drivers/tty/serial/Makefile
    > @@ -61,6 +61,7 @@ obj-$(CONFIG_SERIAL_MSM_HS) += msm_serial_hs.o
    > obj-$(CONFIG_SERIAL_NETX) += netx-serial.o
    > obj-$(CONFIG_SERIAL_OF_PLATFORM) += of_serial.o
    > obj-$(CONFIG_SERIAL_OF_PLATFORM_NWPSERIAL) += nwpserial.o
    > +obj-$(CONFIG_SERIAL_KGDB_NMI) += kgdb_nmi.o
    > obj-$(CONFIG_SERIAL_KS8695) += serial_ks8695.o
    > obj-$(CONFIG_SERIAL_OMAP) += omap-serial.o
    > obj-$(CONFIG_SERIAL_ALTERA_UART) += altera_uart.o
    > diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c
    > new file mode 100644
    > index 0000000..57bf744
    > --- /dev/null
    > +++ b/drivers/tty/serial/kgdb_nmi.c
    > @@ -0,0 +1,396 @@
    > +/*
    > + * 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>
    > + *
    > + * 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/kernel.h>
    > +#include <linux/module.h>
    > +#include <linux/compiler.h>
    > +#include <linux/init.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/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 bool kgdb_nmi_tty_enabled;
    > +
    > +static void kgdb_nmi_console_write(struct console *co, const char *s, uint c)
    > +{
    > + int i;
    > +
    > + if (!kgdb_nmi_tty_enabled || atomic_read(&kgdb_active) >= 0)
    > + return;
    > +
    > + 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",
    > + .write = kgdb_nmi_console_write,
    > + .device = kgdb_nmi_console_device,
    > + .flags = CON_PRINTBUFFER | CON_ANYTIME | CON_ENABLED,
    > + .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 tasklet_struct tlet;
    > + STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo;
    > +};
    > +
    > +static struct kgdb_nmi_tty_priv *kgdb_nmi_port_to_priv(struct tty_port *port)
    > +{
    > + return container_of(port, struct kgdb_nmi_tty_priv, port);
    > +}
    > +
    > +/*
    > + * Our debugging console is polled in a tasklet, so we'll check for input
    > + * every tick. In HZ-less mode, we should program the next tick. We have
    > + * to use the lowlevel stuff as no locks should be grabbed.
    > + */
    > +#ifdef CONFIG_HIGH_RES_TIMERS
    > +static void kgdb_tty_poke(void)
    > +{
    > + tick_program_event(ktime_get(), 0);
    > +}
    > +#else
    > +static inline void kgdb_tty_poke(void) {}
    > +#endif
    > +
    > +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. Tasklet
    > + * 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 = kgdb_nmi_port_to_priv(kgdb_nmi_port);
    > + kfifo_in(&priv->fifo, &c, 1);
    > + kgdb_tty_poke();
    > +}
    > +
    > +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 = 0;
    > +
    > + 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 = 1;
    > + } else {
    > + n = 0;
    > + }
    > +
    > + if (kgdb_nmi_tty_enabled) {
    > + 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>", 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 1;
    > +
    > + while (1) {
    > + int ret;
    > +
    > + ret = kgdb_nmi_poll_one_knock();
    > + if (ret == NO_POLL_CHAR)
    > + return 0;
    > + else if (ret == 1)
    > + break;
    > + }
    > + return 1;
    > +}
    > +
    > +/*
    > + * 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(unsigned long data)
    > +{
    > + struct kgdb_nmi_tty_priv *priv = (void *)data;
    > + struct tty_struct *tty;
    > + char ch;
    > +
    > + tasklet_schedule(&priv->tlet);
    > +
    > + if (likely(!kgdb_nmi_tty_enabled || !kfifo_len(&priv->fifo)))
    > + return;
    > +
    > + /* Port is there, but tty might be hung up, check. */
    > + tty = tty_port_tty_get(kgdb_nmi_port);
    > + if (!tty)
    > + return;
    > +
    > + while (kfifo_out(&priv->fifo, &ch, 1))
    > + tty_insert_flip_char(priv->port.tty, ch, TTY_NORMAL);
    > + tty_flip_buffer_push(priv->port.tty);
    > +
    > + tty_kref_put(tty);
    > +}
    > +
    > +static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty)
    > +{
    > + struct kgdb_nmi_tty_priv *priv = tty->driver_data;
    > +
    > + kgdb_nmi_port = port;
    > + tasklet_schedule(&priv->tlet);
    > + return 0;
    > +}
    > +
    > +static void kgdb_nmi_tty_shutdown(struct tty_port *port)
    > +{
    > + struct kgdb_nmi_tty_priv *priv = port->tty->driver_data;
    > +
    > + tasklet_kill(&priv->tlet);
    > + 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);
    > + tasklet_init(&priv->tlet, kgdb_nmi_tty_receiver, (unsigned long)priv);
    > + 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 nstall tty port: %d\n", __func__, ret);
    > + goto err;
    > + }
    > + return 0;
    > +err:
    > + 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;
    > + kfree(priv);
    > +}
    > +
    > +static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file)
    > +{
    > + struct kgdb_nmi_tty_priv *priv = tty->driver_data;
    > +
    > + return tty_port_open(&priv->port, tty, file);
    > +}
    > +
    > +static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file)
    > +{
    > + struct kgdb_nmi_tty_priv *priv = tty->driver_data;
    > +
    > + 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,
    > +};
    > +
    > +static int kgdb_nmi_enable_console(int argc, const char *argv[])
    > +{
    > + kgdb_nmi_tty_enabled = !(argc == 1 && !strcmp(argv[1], "off"));
    > + return 0;
    > +}
    > +
    > +int kgdb_register_nmi_console(void)
    > +{
    > + int ret;
    > +
    > + 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;
    > + }
    > +
    > + ret = kdb_register("nmi_console", kgdb_nmi_enable_console, "[off]",
    > + "switch to Linux NMI console", 0);
    > + if (ret) {
    > + pr_err("%s: can't register kdb command: %d\n", __func__, ret);
    > + goto err_kdb_reg;
    > + }
    > +
    > + register_console(&kgdb_nmi_console);
    > + kgdb_enable_nmi(1);
    > +
    > + return 0;
    > +err_kdb_reg:
    > + tty_unregister_driver(kgdb_nmi_tty_driver);
    > +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;
    > +
    > + kgdb_enable_nmi(0);
    > + kdb_unregister("nmi_console");
    > +
    > + 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 2b42a01..ed97cfd 100644
    > --- a/drivers/tty/serial/kgdboc.c
    > +++ b/drivers/tty/serial/kgdboc.c
    > @@ -145,6 +145,8 @@ __setup("kgdboc=", kgdboc_option_setup);
    >
    > static void cleanup_kgdboc(void)
    > {
    > + if (kgdb_unregister_nmi_console())
    > + return;
    > kgdboc_unregister_kbd();
    > if (configured == 1)
    > kgdb_unregister_io_module(&kgdboc_io_ops);
    > @@ -198,6 +200,10 @@ do_register:
    > if (err)
    > goto noconfig;
    >
    > + err = kgdb_register_nmi_console();
    > + if (err)
    > + goto noconfig;
    > +


    Just one question on this one, what do you expect to happen, or how does this work when you use a different serial port for example on a board that has a real serial port and an FIQ port? It was not obvious that there was a path to check if the port you are registering is an FIQ enabled port and then call the kgdb_register_nmi_console at that point.

    Jason.
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