// SPDX-License-Identifier: GPL-2.0
/*
 * Based on the same principle as kgdboe using the NETPOLL api, this
 * driver uses a console polling api to implement a gdb serial inteface
 * which is multiplexed on a console port.
 *
 * Maintainer: Jason Wessel <jason.wessel@windriver.com>
 *
 * 2007-2008 (c) Jason Wessel - Wind River Systems, Inc.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/ctype.h>
#include <linux/kgdb.h>
#include <linux/kdb.h>
#include <linux/tty.h>
#include <linux/console.h>
#include <linux/vt_kern.h>
#include <linux/input.h>
#include <linux/irq_work.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/serial_core.h>

#define MAX_CONFIG_LEN          40

static struct kgdb_io           kgdboc_io_ops;

/* -1 = init not run yet, 0 = unconfigured, 1 = configured. */
static int configured           = -1;
static DEFINE_MUTEX(config_mutex);

static char config[MAX_CONFIG_LEN];
static struct kparam_string kps = {
        .string                 = config,
        .maxlen                 = MAX_CONFIG_LEN,
};

static int kgdboc_use_kms;  /* 1 if we use kernel mode switching */
static struct tty_driver        *kgdb_tty_driver;
static int                      kgdb_tty_line;

static struct platform_device *kgdboc_pdev;

#if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE)
static struct kgdb_io           kgdboc_earlycon_io_ops;
static int                      (*earlycon_orig_exit)(struct console *con);
#endif /* IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */

/*
 * When we leave the debug trap handler we need to reset the keyboard status
 * (since the original keyboard state gets partially clobbered by kdb use of
 * the keyboard).
 *
 * The path to deliver the reset is somewhat circuitous.
 *
 * To deliver the reset we register an input handler, reset the keyboard and
 * then deregister the input handler. However, to get this done right, we do
 * have to carefully manage the calling context because we can only register
 * input handlers from task context.
 *
 * In particular we need to trigger the action from the debug trap handler with
 * all its NMI and/or NMI-like oddities. To solve this the kgdboc trap exit code
 * (the "post_exception" callback) uses irq_work_queue(), which is NMI-safe, to
 * schedule a callback from a hardirq context. From there we have to defer the
 * work again, this time using schedule_work(), to get a callback using the
 * system workqueue, which runs in task context.
 */
#ifdef CONFIG_KDB_KEYBOARD
static int kgdboc_reset_connect(struct input_handler *handler,
                                struct input_dev *dev,
                                const struct input_device_id *id)
{
        input_reset_device(dev);

        /* Return an error - we do not want to bind, just to reset */
        return -ENODEV;
}

static void kgdboc_reset_disconnect(struct input_handle *handle)
{
        /* We do not expect anyone to actually bind to us */
        BUG();
}

static const struct input_device_id kgdboc_reset_ids[] = {
        {
                .flags = INPUT_DEVICE_ID_MATCH_EVBIT,
                .evbit = { BIT_MASK(EV_KEY) },
        },
        { }
};

static struct input_handler kgdboc_reset_handler = {
        .connect        = kgdboc_reset_connect,
        .disconnect     = kgdboc_reset_disconnect,
        .name           = "kgdboc_reset",
        .id_table       = kgdboc_reset_ids,
};

static DEFINE_MUTEX(kgdboc_reset_mutex);

static void kgdboc_restore_input_helper(struct work_struct *dummy)
{
        /*
         * We need to take a mutex to prevent several instances of
         * this work running on different CPUs so they don't try
         * to register again already registered handler.
         */
        mutex_lock(&kgdboc_reset_mutex);

        if (input_register_handler(&kgdboc_reset_handler) == 0)
                input_unregister_handler(&kgdboc_reset_handler);

        mutex_unlock(&kgdboc_reset_mutex);
}

static DECLARE_WORK(kgdboc_restore_input_work, kgdboc_restore_input_helper);

static void kgdboc_queue_restore_input_helper(struct irq_work *unused)
{
        schedule_work(&kgdboc_restore_input_work);
}

static DEFINE_IRQ_WORK(kgdboc_restore_input_irq_work, kgdboc_queue_restore_input_helper);

static void kgdboc_restore_input(void)
{
        if (likely(system_state == SYSTEM_RUNNING))
                irq_work_queue(&kgdboc_restore_input_irq_work);
}

static int kgdboc_register_kbd(char **cptr)
{
        if (strncmp(*cptr, "kbd", 3) == 0 ||
                strncmp(*cptr, "kdb", 3) == 0) {
                if (kdb_poll_idx < KDB_POLL_FUNC_MAX) {
                        kdb_poll_funcs[kdb_poll_idx] = kdb_get_kbd_char;
                        kdb_poll_idx++;
                        if (cptr[0][3] == ',')
                                *cptr += 4;
                        else
                                return 1;
                }
        }
        return 0;
}

static void kgdboc_unregister_kbd(void)
{
        int i;

        for (i = 0; i < kdb_poll_idx; i++) {
                if (kdb_poll_funcs[i] == kdb_get_kbd_char) {
                        kdb_poll_idx--;
                        kdb_poll_funcs[i] = kdb_poll_funcs[kdb_poll_idx];
                        kdb_poll_funcs[kdb_poll_idx] = NULL;
                        i--;
                }
        }
        irq_work_sync(&kgdboc_restore_input_irq_work);
        flush_work(&kgdboc_restore_input_work);
}
#else /* ! CONFIG_KDB_KEYBOARD */
#define kgdboc_register_kbd(x) 0
#define kgdboc_unregister_kbd()
#define kgdboc_restore_input()
#endif /* ! CONFIG_KDB_KEYBOARD */

#if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE)
static void cleanup_earlycon(void)
{
        if (kgdboc_earlycon_io_ops.cons)
                kgdb_unregister_io_module(&kgdboc_earlycon_io_ops);
}
#else /* !IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */
static inline void cleanup_earlycon(void) { }
#endif /* !IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */

static void cleanup_kgdboc(void)
{
        cleanup_earlycon();

        if (configured != 1)
                return;

        kgdboc_unregister_kbd();
        kgdb_unregister_io_module(&kgdboc_io_ops);
}

static int configure_kgdboc(void)
{
        struct tty_driver *p;
        int tty_line = 0;
        int err = -ENODEV;
        char *cptr = config;
        struct console *cons;
        int cookie;

        if (!strlen(config) || isspace(config[0])) {
                err = 0;
                goto noconfig;
        }

        kgdboc_io_ops.cons = NULL;
        kgdb_tty_driver = NULL;

        kgdboc_use_kms = 0;
        if (strncmp(cptr, "kms,", 4) == 0) {
                cptr += 4;
                kgdboc_use_kms = 1;
        }

        if (kgdboc_register_kbd(&cptr))
                goto do_register;

        p = tty_find_polling_driver(cptr, &tty_line);
        if (!p)
                goto noconfig;

        /*
         * Take console_lock to serialize device() callback with
         * other console operations. For example, fg_console is
         * modified under console_lock when switching vt.
         */
        console_lock();

        cookie = console_srcu_read_lock();
        for_each_console_srcu(cons) {
                int idx;
                if (cons->device && cons->device(cons, &idx) == p &&
                    idx == tty_line) {
                        kgdboc_io_ops.cons = cons;
                        break;
                }
        }
        console_srcu_read_unlock(cookie);

        console_unlock();

        kgdb_tty_driver = p;
        kgdb_tty_line = tty_line;

do_register:
        err = kgdb_register_io_module(&kgdboc_io_ops);
        if (err)
                goto noconfig;

        configured = 1;

        return 0;

noconfig:
        kgdboc_unregister_kbd();
        configured = 0;

        return err;
}

static int kgdboc_probe(struct platform_device *pdev)
{
        int ret = 0;

        mutex_lock(&config_mutex);
        if (configured != 1) {
                ret = configure_kgdboc();

                /* Convert "no device" to "defer" so we'll keep trying */
                if (ret == -ENODEV)
                        ret = -EPROBE_DEFER;
        }
        mutex_unlock(&config_mutex);

        return ret;
}

static struct platform_driver kgdboc_platform_driver = {
        .probe = kgdboc_probe,
        .driver = {
                .name = "kgdboc",
                .suppress_bind_attrs = true,
        },
};

static int __init init_kgdboc(void)
{
        int ret;

        /*
         * kgdboc is a little bit of an odd "platform_driver".  It can be
         * up and running long before the platform_driver object is
         * created and thus doesn't actually store anything in it.  There's
         * only one instance of kgdb so anything is stored as global state.
         * The platform_driver is only created so that we can leverage the
         * kernel's mechanisms (like -EPROBE_DEFER) to call us when our
         * underlying tty is ready.  Here we init our platform driver and
         * then create the single kgdboc instance.
         */
        ret = platform_driver_register(&kgdboc_platform_driver);
        if (ret)
                return ret;

        kgdboc_pdev = platform_device_alloc("kgdboc", PLATFORM_DEVID_NONE);
        if (!kgdboc_pdev) {
                ret = -ENOMEM;
                goto err_did_register;
        }

        ret = platform_device_add(kgdboc_pdev);
        if (!ret)
                return 0;

        platform_device_put(kgdboc_pdev);

err_did_register:
        platform_driver_unregister(&kgdboc_platform_driver);
        return ret;
}

static void exit_kgdboc(void)
{
        mutex_lock(&config_mutex);
        cleanup_kgdboc();
        mutex_unlock(&config_mutex);

        platform_device_unregister(kgdboc_pdev);
        platform_driver_unregister(&kgdboc_platform_driver);
}

static int kgdboc_get_char(void)
{
        if (!kgdb_tty_driver)
                return -1;
        return kgdb_tty_driver->ops->poll_get_char(kgdb_tty_driver,
                                                kgdb_tty_line);
}

static void kgdboc_put_char(u8 chr)
{
        if (!kgdb_tty_driver)
                return;
        kgdb_tty_driver->ops->poll_put_char(kgdb_tty_driver,
                                        kgdb_tty_line, chr);
}

static int param_set_kgdboc_var(const char *kmessage,
                                const struct kernel_param *kp)
{
        size_t len = strlen(kmessage);
        int ret = 0;

        if (len >= MAX_CONFIG_LEN) {
                pr_err("config string too long\n");
                return -ENOSPC;
        }

        if (kgdb_connected) {
                pr_err("Cannot reconfigure while KGDB is connected.\n");
                return -EBUSY;
        }

        mutex_lock(&config_mutex);

        strcpy(config, kmessage);
        /* Chop out \n char as a result of echo */
        if (len && config[len - 1] == '\n')
                config[len - 1] = '\0';

        if (configured == 1)
                cleanup_kgdboc();

        /*
         * Configure with the new params as long as init already ran.
         * Note that we can get called before init if someone loads us
         * with "modprobe kgdboc kgdboc=..." or if they happen to use
         * the odd syntax of "kgdboc.kgdboc=..." on the kernel command.
         */
        if (configured >= 0)
                ret = configure_kgdboc();

        /*
         * If we couldn't configure then clear out the config.  Note that
         * specifying an invalid config on the kernel command line vs.
         * through sysfs have slightly different behaviors.  If we fail
         * to configure what was specified on the kernel command line
         * we'll leave it in the 'config' and return -EPROBE_DEFER from
         * our probe.  When specified through sysfs userspace is
         * responsible for loading the tty driver before setting up.
         */
        if (ret)
                config[0] = '\0';

        mutex_unlock(&config_mutex);

        return ret;
}

static int dbg_restore_graphics;

static void kgdboc_pre_exp_handler(void)
{
        if (!dbg_restore_graphics && kgdboc_use_kms) {
                dbg_restore_graphics = 1;
                con_debug_enter(vc_cons[fg_console].d);
        }
        /* Increment the module count when the debugger is active */
        if (!kgdb_connected)
                try_module_get(THIS_MODULE);
}

static void kgdboc_post_exp_handler(void)
{
        /* decrement the module count when the debugger detaches */
        if (!kgdb_connected)
                module_put(THIS_MODULE);
        if (kgdboc_use_kms && dbg_restore_graphics) {
                dbg_restore_graphics = 0;
                con_debug_leave();
        }
        kgdboc_restore_input();
}

static struct kgdb_io kgdboc_io_ops = {
        .name                   = "kgdboc",
        .read_char              = kgdboc_get_char,
        .write_char             = kgdboc_put_char,
        .pre_exception          = kgdboc_pre_exp_handler,
        .post_exception         = kgdboc_post_exp_handler,
};

#if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE)
static int kgdboc_option_setup(char *opt)
{
        if (!opt) {
                pr_err("config string not provided\n");
                return 1;
        }

        if (strlen(opt) >= MAX_CONFIG_LEN) {
                pr_err("config string too long\n");
                return 1;
        }
        strcpy(config, opt);

        return 1;
}

__setup("kgdboc=", kgdboc_option_setup);


/* This is only available if kgdboc is a built in for early debugging */
static int __init kgdboc_early_init(char *opt)
{
        kgdboc_option_setup(opt);
        configure_kgdboc();
        return 0;
}

early_param("ekgdboc", kgdboc_early_init);

static int kgdboc_earlycon_get_char(void)
{
        char c;

        if (!kgdboc_earlycon_io_ops.cons->read(kgdboc_earlycon_io_ops.cons,
                                               &c, 1))
                return NO_POLL_CHAR;

        return c;
}

static void kgdboc_earlycon_put_char(u8 chr)
{
        kgdboc_earlycon_io_ops.cons->write(kgdboc_earlycon_io_ops.cons, &chr,
                                           1);
}

static void kgdboc_earlycon_pre_exp_handler(void)
{
        struct console *con;
        static bool already_warned;
        int cookie;

        if (already_warned)
                return;

        /*
         * When the first normal console comes up the kernel will take all
         * the boot consoles out of the list.  Really, we should stop using
         * the boot console when it does that but until a TTY is registered
         * we have no other choice so we keep using it.  Since not all
         * serial drivers might be OK with this, print a warning once per
         * boot if we detect this case.
         */
        cookie = console_srcu_read_lock();
        for_each_console_srcu(con) {
                if (con == kgdboc_earlycon_io_ops.cons)
                        break;
        }
        console_srcu_read_unlock(cookie);
        if (con)
                return;

        already_warned = true;
        pr_warn("kgdboc_earlycon is still using bootconsole\n");
}

static int kgdboc_earlycon_deferred_exit(struct console *con)
{
        /*
         * If we get here it means the boot console is going away but we
         * don't yet have a suitable replacement.  Don't pass through to
         * the original exit routine.  We'll call it later in our deinit()
         * function.  For now, restore the original exit() function pointer
         * as a sentinal that we've hit this point.
         */
        con->exit = earlycon_orig_exit;

        return 0;
}

static void kgdboc_earlycon_deinit(void)
{
        if (!kgdboc_earlycon_io_ops.cons)
                return;

        if (kgdboc_earlycon_io_ops.cons->exit == kgdboc_earlycon_deferred_exit)
                /*
                 * kgdboc_earlycon is exiting but original boot console exit
                 * was never called (AKA kgdboc_earlycon_deferred_exit()
                 * didn't ever run).  Undo our trap.
                 */
                kgdboc_earlycon_io_ops.cons->exit = earlycon_orig_exit;
        else if (kgdboc_earlycon_io_ops.cons->exit)
                /*
                 * We skipped calling the exit() routine so we could try to
                 * keep using the boot console even after it went away.  We're
                 * finally done so call the function now.
                 */
                kgdboc_earlycon_io_ops.cons->exit(kgdboc_earlycon_io_ops.cons);

        kgdboc_earlycon_io_ops.cons = NULL;
}

static struct kgdb_io kgdboc_earlycon_io_ops = {
        .name                   = "kgdboc_earlycon",
        .read_char              = kgdboc_earlycon_get_char,
        .write_char             = kgdboc_earlycon_put_char,
        .pre_exception          = kgdboc_earlycon_pre_exp_handler,
        .deinit                 = kgdboc_earlycon_deinit,
};

#define MAX_CONSOLE_NAME_LEN (sizeof((struct console *) 0)->name)
static char kgdboc_earlycon_param[MAX_CONSOLE_NAME_LEN] __initdata;
static bool kgdboc_earlycon_late_enable __initdata;

static int __init kgdboc_earlycon_init(char *opt)
{
        struct console *con;

        kdb_init(KDB_INIT_EARLY);

        /*
         * Look for a matching console, or if the name was left blank just
         * pick the first one we find.
         */

        /*
         * Hold the console_list_lock to guarantee that no consoles are
         * unregistered until the kgdboc_earlycon setup is complete.
         * Trapping the exit() callback relies on exit() not being
         * called until the trap is setup. This also allows safe
         * traversal of the console list and race-free reading of @flags.
         */
        console_list_lock();
        for_each_console(con) {
                if (con->write && con->read &&
                    (!opt || !opt[0] || strcmp(con->name, opt) == 0))
                        break;
        }

        if (!con) {
                /*
                 * Both earlycon and kgdboc_earlycon are initialized during
                 * early parameter parsing. We cannot guarantee earlycon gets
                 * in first and, in any case, on ACPI systems earlycon may
                 * defer its own initialization (usually to somewhere within
                 * setup_arch() ). To cope with either of these situations
                 * we can defer our own initialization to a little later in
                 * the boot.
                 */
                if (!kgdboc_earlycon_late_enable) {
                        pr_info("No suitable earlycon yet, will try later\n");
                        if (opt)
                                strscpy(kgdboc_earlycon_param, opt,
                                        sizeof(kgdboc_earlycon_param));
                        kgdboc_earlycon_late_enable = true;
                } else {
                        pr_info("Couldn't find kgdb earlycon\n");
                }
                goto unlock;
        }

        kgdboc_earlycon_io_ops.cons = con;
        pr_info("Going to register kgdb with earlycon '%s'\n", con->name);
        if (kgdb_register_io_module(&kgdboc_earlycon_io_ops) != 0) {
                kgdboc_earlycon_io_ops.cons = NULL;
                pr_info("Failed to register kgdb with earlycon\n");
        } else {
                /* Trap exit so we can keep earlycon longer if needed. */
                earlycon_orig_exit = con->exit;
                con->exit = kgdboc_earlycon_deferred_exit;
        }

unlock:
        console_list_unlock();

        /* Non-zero means malformed option so we always return zero */
        return 0;
}

early_param("kgdboc_earlycon", kgdboc_earlycon_init);

/*
 * This is only intended for the late adoption of an early console.
 *
 * It is not a reliable way to adopt regular consoles because we can not
 * control what order console initcalls are made and, in any case, many
 * regular consoles are registered much later in the boot process than
 * the console initcalls!
 */
static int __init kgdboc_earlycon_late_init(void)
{
        if (kgdboc_earlycon_late_enable)
                kgdboc_earlycon_init(kgdboc_earlycon_param);
        return 0;
}
console_initcall(kgdboc_earlycon_late_init);

#endif /* IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE) */

module_init(init_kgdboc);
module_exit(exit_kgdboc);
module_param_call(kgdboc, param_set_kgdboc_var, param_get_string, &kps, 0644);
MODULE_PARM_DESC(kgdboc, "<serial_device>[,baud]");
MODULE_DESCRIPTION("KGDB Console TTY Driver");
MODULE_LICENSE("GPL");