// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  MachZ ZF-Logic Watchdog Timer driver for Linux
 *
 *  The author does NOT admit liability nor provide warranty for
 *  any of this software. This material is provided "AS-IS" in
 *  the hope that it may be useful for others.
 *
 *  Author: Fernando Fuganti <fuganti@conectiva.com.br>
 *
 *  Based on sbc60xxwdt.c by Jakob Oestergaard
 *
 *  We have two timers (wd#1, wd#2) driven by a 32 KHz clock with the
 *  following periods:
 *      wd#1 - 2 seconds;
 *      wd#2 - 7.2 ms;
 *  After the expiration of wd#1, it can generate a NMI, SCI, SMI, or
 *  a system RESET and it starts wd#2 that unconditionally will RESET
 *  the system when the counter reaches zero.
 *
 *  14-Dec-2001 Matt Domsch <Matt_Domsch@dell.com>
 *      Added nowayout module option to override CONFIG_WATCHDOG_NOWAYOUT
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/types.h>
#include <linux/timer.h>
#include <linux/jiffies.h>
#include <linux/miscdevice.h>
#include <linux/watchdog.h>
#include <linux/fs.h>
#include <linux/ioport.h>
#include <linux/notifier.h>
#include <linux/reboot.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/uaccess.h>


/* ports */
#define ZF_IOBASE       0x218
#define INDEX           0x218
#define DATA_B          0x219
#define DATA_W          0x21A
#define DATA_D          0x21A

/* indexes */                   /* size */
#define ZFL_VERSION     0x02    /* 16   */
#define CONTROL         0x10    /* 16   */
#define STATUS          0x12    /* 8    */
#define COUNTER_1       0x0C    /* 16   */
#define COUNTER_2       0x0E    /* 8    */
#define PULSE_LEN       0x0F    /* 8    */

/* controls */
#define ENABLE_WD1      0x0001
#define ENABLE_WD2      0x0002
#define RESET_WD1       0x0010
#define RESET_WD2       0x0020
#define GEN_SCI         0x0100
#define GEN_NMI         0x0200
#define GEN_SMI         0x0400
#define GEN_RESET       0x0800


/* utilities */

#define WD1     0
#define WD2     1

#define zf_writew(port, data)  { outb(port, INDEX); outw(data, DATA_W); }
#define zf_writeb(port, data)  { outb(port, INDEX); outb(data, DATA_B); }
#define zf_get_ZFL_version()   zf_readw(ZFL_VERSION)


static unsigned short zf_readw(unsigned char port)
{
        outb(port, INDEX);
        return inw(DATA_W);
}


MODULE_AUTHOR("Fernando Fuganti <fuganti@conectiva.com.br>");
MODULE_DESCRIPTION("MachZ ZF-Logic Watchdog driver");
MODULE_LICENSE("GPL");

static bool nowayout = WATCHDOG_NOWAYOUT;
module_param(nowayout, bool, 0);
MODULE_PARM_DESC(nowayout,
                "Watchdog cannot be stopped once started (default="
                                __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");

#define PFX "machzwd"

static const struct watchdog_info zf_info = {
        .options                = WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
        .firmware_version       = 1,
        .identity               = "ZF-Logic watchdog",
};


/*
 * action refers to action taken when watchdog resets
 * 0 = GEN_RESET
 * 1 = GEN_SMI
 * 2 = GEN_NMI
 * 3 = GEN_SCI
 * defaults to GEN_RESET (0)
 */
static int action;
module_param(action, int, 0);
MODULE_PARM_DESC(action, "after watchdog resets, generate: "
                                "0 = RESET(*)  1 = SMI  2 = NMI  3 = SCI");

static void zf_ping(struct timer_list *unused);

static int zf_action = GEN_RESET;
static unsigned long zf_is_open;
static char zf_expect_close;
static DEFINE_SPINLOCK(zf_port_lock);
static DEFINE_TIMER(zf_timer, zf_ping);
static unsigned long next_heartbeat;


/* timeout for user land heart beat (10 seconds) */
#define ZF_USER_TIMEO (HZ*10)

/* timeout for hardware watchdog (~500ms) */
#define ZF_HW_TIMEO (HZ/2)

/* number of ticks on WD#1 (driven by a 32KHz clock, 2s) */
#define ZF_CTIMEOUT 0xffff

#ifndef ZF_DEBUG
#define dprintk(format, args...)
#else
#define dprintk(format, args...)                                        \
        pr_debug(":%s:%d: " format, __func__, __LINE__ , ## args)
#endif


static inline void zf_set_status(unsigned char new)
{
        zf_writeb(STATUS, new);
}


/* CONTROL register functions */

static inline unsigned short zf_get_control(void)
{
        return zf_readw(CONTROL);
}

static inline void zf_set_control(unsigned short new)
{
        zf_writew(CONTROL, new);
}


/* WD#? counter functions */
/*
 *      Just set counter value
 */

static inline void zf_set_timer(unsigned short new, unsigned char n)
{
        switch (n) {
        case WD1:
                zf_writew(COUNTER_1, new);
                fallthrough;
        case WD2:
                zf_writeb(COUNTER_2, new > 0xff ? 0xff : new);
                fallthrough;
        default:
                return;
        }
}

/*
 * stop hardware timer
 */
static void zf_timer_off(void)
{
        unsigned int ctrl_reg = 0;
        unsigned long flags;

        /* stop internal ping */
        del_timer_sync(&zf_timer);

        spin_lock_irqsave(&zf_port_lock, flags);
        /* stop watchdog timer */
        ctrl_reg = zf_get_control();
        ctrl_reg |= (ENABLE_WD1|ENABLE_WD2);    /* disable wd1 and wd2 */
        ctrl_reg &= ~(ENABLE_WD1|ENABLE_WD2);
        zf_set_control(ctrl_reg);
        spin_unlock_irqrestore(&zf_port_lock, flags);

        pr_info("Watchdog timer is now disabled\n");
}


/*
 * start hardware timer
 */
static void zf_timer_on(void)
{
        unsigned int ctrl_reg = 0;
        unsigned long flags;

        spin_lock_irqsave(&zf_port_lock, flags);

        zf_writeb(PULSE_LEN, 0xff);

        zf_set_timer(ZF_CTIMEOUT, WD1);

        /* user land ping */
        next_heartbeat = jiffies + ZF_USER_TIMEO;

        /* start the timer for internal ping */
        mod_timer(&zf_timer, jiffies + ZF_HW_TIMEO);

        /* start watchdog timer */
        ctrl_reg = zf_get_control();
        ctrl_reg |= (ENABLE_WD1|zf_action);
        zf_set_control(ctrl_reg);
        spin_unlock_irqrestore(&zf_port_lock, flags);

        pr_info("Watchdog timer is now enabled\n");
}


static void zf_ping(struct timer_list *unused)
{
        unsigned int ctrl_reg = 0;
        unsigned long flags;

        zf_writeb(COUNTER_2, 0xff);

        if (time_before(jiffies, next_heartbeat)) {
                dprintk("time_before: %ld\n", next_heartbeat - jiffies);
                /*
                 * reset event is activated by transition from 0 to 1 on
                 * RESET_WD1 bit and we assume that it is already zero...
                 */

                spin_lock_irqsave(&zf_port_lock, flags);
                ctrl_reg = zf_get_control();
                ctrl_reg |= RESET_WD1;
                zf_set_control(ctrl_reg);

                /* ...and nothing changes until here */
                ctrl_reg &= ~(RESET_WD1);
                zf_set_control(ctrl_reg);
                spin_unlock_irqrestore(&zf_port_lock, flags);

                mod_timer(&zf_timer, jiffies + ZF_HW_TIMEO);
        } else
                pr_crit("I will reset your machine\n");
}

static ssize_t zf_write(struct file *file, const char __user *buf, size_t count,
                                                                loff_t *ppos)
{
        /* See if we got the magic character */
        if (count) {
                /*
                 * no need to check for close confirmation
                 * no way to disable watchdog ;)
                 */
                if (!nowayout) {
                        size_t ofs;
                        /*
                         * note: just in case someone wrote the magic character
                         * five months ago...
                         */
                        zf_expect_close = 0;

                        /* now scan */
                        for (ofs = 0; ofs != count; ofs++) {
                                char c;
                                if (get_user(c, buf + ofs))
                                        return -EFAULT;
                                if (c == 'V') {
                                        zf_expect_close = 42;
                                        dprintk("zf_expect_close = 42\n");
                                }
                        }
                }

                /*
                 * Well, anyhow someone wrote to us,
                 * we should return that favour
                 */
                next_heartbeat = jiffies + ZF_USER_TIMEO;
                dprintk("user ping at %ld\n", jiffies);
        }
        return count;
}

static long zf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        void __user *argp = (void __user *)arg;
        int __user *p = argp;
        switch (cmd) {
        case WDIOC_GETSUPPORT:
                if (copy_to_user(argp, &zf_info, sizeof(zf_info)))
                        return -EFAULT;
                break;
        case WDIOC_GETSTATUS:
        case WDIOC_GETBOOTSTATUS:
                return put_user(0, p);
        case WDIOC_KEEPALIVE:
                zf_ping(NULL);
                break;
        default:
                return -ENOTTY;
        }
        return 0;
}

static int zf_open(struct inode *inode, struct file *file)
{
        if (test_and_set_bit(0, &zf_is_open))
                return -EBUSY;
        if (nowayout)
                __module_get(THIS_MODULE);
        zf_timer_on();
        return stream_open(inode, file);
}

static int zf_close(struct inode *inode, struct file *file)
{
        if (zf_expect_close == 42)
                zf_timer_off();
        else {
                del_timer(&zf_timer);
                pr_err("device file closed unexpectedly. Will not stop the WDT!\n");
        }
        clear_bit(0, &zf_is_open);
        zf_expect_close = 0;
        return 0;
}

/*
 * Notifier for system down
 */

static int zf_notify_sys(struct notifier_block *this, unsigned long code,
                                                                void *unused)
{
        if (code == SYS_DOWN || code == SYS_HALT)
                zf_timer_off();
        return NOTIFY_DONE;
}

static const struct file_operations zf_fops = {
        .owner          = THIS_MODULE,
        .llseek         = no_llseek,
        .write          = zf_write,
        .unlocked_ioctl = zf_ioctl,
        .compat_ioctl   = compat_ptr_ioctl,
        .open           = zf_open,
        .release        = zf_close,
};

static struct miscdevice zf_miscdev = {
        .minor = WATCHDOG_MINOR,
        .name = "watchdog",
        .fops = &zf_fops,
};


/*
 * The device needs to learn about soft shutdowns in order to
 * turn the timebomb registers off.
 */
static struct notifier_block zf_notifier = {
        .notifier_call = zf_notify_sys,
};

static void __init zf_show_action(int act)
{
        static const char * const str[] = { "RESET", "SMI", "NMI", "SCI" };

        pr_info("Watchdog using action = %s\n", str[act]);
}

static int __init zf_init(void)
{
        int ret;

        pr_info("MachZ ZF-Logic Watchdog driver initializing\n");

        ret = zf_get_ZFL_version();
        if (!ret || ret == 0xffff) {
                pr_warn("no ZF-Logic found\n");
                return -ENODEV;
        }

        if (action <= 3 && action >= 0)
                zf_action = zf_action >> action;
        else
                action = 0;

        zf_show_action(action);

        if (!request_region(ZF_IOBASE, 3, "MachZ ZFL WDT")) {
                pr_err("cannot reserve I/O ports at %d\n", ZF_IOBASE);
                ret = -EBUSY;
                goto no_region;
        }

        ret = register_reboot_notifier(&zf_notifier);
        if (ret) {
                pr_err("can't register reboot notifier (err=%d)\n", ret);
                goto no_reboot;
        }

        ret = misc_register(&zf_miscdev);
        if (ret) {
                pr_err("can't misc_register on minor=%d\n", WATCHDOG_MINOR);
                goto no_misc;
        }

        zf_set_status(0);
        zf_set_control(0);

        return 0;

no_misc:
        unregister_reboot_notifier(&zf_notifier);
no_reboot:
        release_region(ZF_IOBASE, 3);
no_region:
        return ret;
}


static void __exit zf_exit(void)
{
        zf_timer_off();

        misc_deregister(&zf_miscdev);
        unregister_reboot_notifier(&zf_notifier);
        release_region(ZF_IOBASE, 3);
}

module_init(zf_init);
module_exit(zf_exit);