5 files changed, 441 insertions, 0 deletions

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 2a9659dfb74c..233fbaaf2559 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 ($3#33).
+          This is because this console driver processes the input in NMI
+          context, and thus is able to intercept the magic sequence.
+
+          Note that since the console interprets input and uses polling
+          communication methods, for things like PPP you still must fully
+          detach debugger port from the KGDB NMI (i.e. disable_nmi), and
+          use raw console.
+
+          If unsure, say N.
+
 config SERIAL_KS8695
         bool "Micrel KS8695 (Centaur) serial port support"
         depends on ARCH_KS8695
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index ce88667cfd17..4f694dafa719 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -61,6 +61,7 @@ obj-$(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 000000000000..d185247ba1aa
--- /dev/null
+++ b/drivers/tty/serial/kgdb_nmi.c
@@ -0,0 +1,402 @@
+/*
+ * 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>", (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 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 install 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;
+
+        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;
+        }
+
+        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);
+        arch_kgdb_ops.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;
+
+        if (!arch_kgdb_ops.enable_nmi)
+                return 0;
+        arch_kgdb_ops.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 2b42a01a81c6..3f63d834cbc9 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);
@@ -198,11 +200,18 @@ do_register:
         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();
         config[0] = 0;
         configured = 0;
         cleanup_kgdboc();
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index 7800cce284db..4dff0c6ed58f 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -286,6 +286,16 @@ extern struct kgdb_arch		arch_kgdb_ops;
 
 extern unsigned long __weak 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 1; }
+#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;