// 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->is_console = true;

        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 = 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 (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);