// SPDX-License-Identifier: GPL-2.0+
/*
 *      Acquire Single Board Computer Watchdog Timer driver
 *
 *      Based on wdt.c. Original copyright messages:
 *
 *      (c) Copyright 1996 Alan Cox <alan@lxorguk.ukuu.org.uk>,
 *                                              All Rights Reserved.
 *
 *      Neither Alan Cox nor CymruNet Ltd. admit liability nor provide
 *      warranty for any of this software. This material is provided
 *      "AS-IS" and at no charge.
 *
 *      (c) Copyright 1995    Alan Cox <alan@lxorguk.ukuu.org.uk>
 *
 *      14-Dec-2001 Matt Domsch <Matt_Domsch@dell.com>
 *          Added nowayout module option to override CONFIG_WATCHDOG_NOWAYOUT
 *          Can't add timeout - driver doesn't allow changing value
 */

/*
 *      Theory of Operation:
 *              The Watch-Dog Timer is provided to ensure that standalone
 *              Systems can always recover from catastrophic conditions that
 *              caused the CPU to crash. This condition may have occurred by
 *              external EMI or a software bug. When the CPU stops working
 *              correctly, hardware on the board will either perform a hardware
 *              reset (cold boot) or a non-maskable interrupt (NMI) to bring the
 *              system back to a known state.
 *
 *              The Watch-Dog Timer is controlled by two I/O Ports.
 *                443 hex       - Read  - Enable or refresh the Watch-Dog Timer
 *                043 hex       - Read  - Disable the Watch-Dog Timer
 *
 *              To enable the Watch-Dog Timer, a read from I/O port 443h must
 *              be performed. This will enable and activate the countdown timer
 *              which will eventually time out and either reset the CPU or cause
 *              an NMI depending on the setting of a jumper. To ensure that this
 *              reset condition does not occur, the Watch-Dog Timer must be
 *              periodically refreshed by reading the same I/O port 443h.
 *              The Watch-Dog Timer is disabled by reading I/O port 043h.
 *
 *              The Watch-Dog Timer Time-Out Period is set via jumpers.
 *              It can be 1, 2, 10, 20, 110 or 220 seconds.
 */

/*
 *      Includes, defines, variables, module parameters, ...
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

/* Includes */
#include <linux/module.h>               /* For module specific items */
#include <linux/moduleparam.h>          /* For new moduleparam's */
#include <linux/types.h>                /* For standard types (like size_t) */
#include <linux/errno.h>                /* For the -ENODEV/... values */
#include <linux/kernel.h>               /* For printk/panic/... */
#include <linux/miscdevice.h>           /* For struct miscdevice */
#include <linux/watchdog.h>             /* For the watchdog specific items */
#include <linux/fs.h>                   /* For file operations */
#include <linux/ioport.h>               /* For io-port access */
#include <linux/platform_device.h>      /* For platform_driver framework */
#include <linux/init.h>                 /* For __init/__exit/... */
#include <linux/uaccess.h>              /* For copy_to_user/put_user/... */
#include <linux/io.h>                   /* For inb/outb/... */

/* Module information */
#define DRV_NAME "acquirewdt"
#define WATCHDOG_NAME "Acquire WDT"
/* There is no way to see what the correct time-out period is */
#define WATCHDOG_HEARTBEAT 0

/* internal variables */
/* the watchdog platform device */
static struct platform_device *acq_platform_device;
static unsigned long acq_is_open;
static char expect_close;

/* module parameters */
/* You must set this - there is no sane way to probe for this board. */
static int wdt_stop = 0x43;
module_param(wdt_stop, int, 0);
MODULE_PARM_DESC(wdt_stop, "Acquire WDT 'stop' io port (default 0x43)");

/* You must set this - there is no sane way to probe for this board. */
static int wdt_start = 0x443;
module_param(wdt_start, int, 0);
MODULE_PARM_DESC(wdt_start, "Acquire WDT 'start' io port (default 0x443)");

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) ")");

/*
 *      Watchdog Operations
 */

static void acq_keepalive(void)
{
        /* Write a watchdog value */
        inb_p(wdt_start);
}

static void acq_stop(void)
{
        /* Turn the card off */
        inb_p(wdt_stop);
}

/*
 *      /dev/watchdog handling
 */

static ssize_t acq_write(struct file *file, const char __user *buf,
                                                size_t count, loff_t *ppos)
{
        /* See if we got the magic character 'V' and reload the timer */
        if (count) {
                if (!nowayout) {
                        size_t i;
                        /* note: just in case someone wrote the magic character
                           five months ago... */
                        expect_close = 0;
                        /* scan to see whether or not we got the
                           magic character */
                        for (i = 0; i != count; i++) {
                                char c;
                                if (get_user(c, buf + i))
                                        return -EFAULT;
                                if (c == 'V')
                                        expect_close = 42;
                        }
                }
                /* Well, anyhow someone wrote to us, we should
                                return that favour */
                acq_keepalive();
        }
        return count;
}

static long acq_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
        int options, retval = -EINVAL;
        void __user *argp = (void __user *)arg;
        int __user *p = argp;
        static const struct watchdog_info ident = {
                .options = WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
                .firmware_version = 1,
                .identity = WATCHDOG_NAME,
        };

        switch (cmd) {
        case WDIOC_GETSUPPORT:
                return copy_to_user(argp, &ident, sizeof(ident)) ? -EFAULT : 0;

        case WDIOC_GETSTATUS:
        case WDIOC_GETBOOTSTATUS:
                return put_user(0, p);

        case WDIOC_SETOPTIONS:
        {
                if (get_user(options, p))
                        return -EFAULT;
                if (options & WDIOS_DISABLECARD) {
                        acq_stop();
                        retval = 0;
                }
                if (options & WDIOS_ENABLECARD) {
                        acq_keepalive();
                        retval = 0;
                }
                return retval;
        }
        case WDIOC_KEEPALIVE:
                acq_keepalive();
                return 0;

        case WDIOC_GETTIMEOUT:
                return put_user(WATCHDOG_HEARTBEAT, p);

        default:
                return -ENOTTY;
        }
}

static int acq_open(struct inode *inode, struct file *file)
{
        if (test_and_set_bit(0, &acq_is_open))
                return -EBUSY;

        if (nowayout)
                __module_get(THIS_MODULE);

        /* Activate */
        acq_keepalive();
        return stream_open(inode, file);
}

static int acq_close(struct inode *inode, struct file *file)
{
        if (expect_close == 42) {
                acq_stop();
        } else {
                pr_crit("Unexpected close, not stopping watchdog!\n");
                acq_keepalive();
        }
        clear_bit(0, &acq_is_open);
        expect_close = 0;
        return 0;
}

/*
 *      Kernel Interfaces
 */

static const struct file_operations acq_fops = {
        .owner          = THIS_MODULE,
        .write          = acq_write,
        .unlocked_ioctl = acq_ioctl,
        .compat_ioctl   = compat_ptr_ioctl,
        .open           = acq_open,
        .release        = acq_close,
};

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

/*
 *      Init & exit routines
 */

static int __init acq_probe(struct platform_device *dev)
{
        int ret;

        if (wdt_stop != wdt_start) {
                if (!request_region(wdt_stop, 1, WATCHDOG_NAME)) {
                        pr_err("I/O address 0x%04x already in use\n", wdt_stop);
                        ret = -EIO;
                        goto out;
                }
        }

        if (!request_region(wdt_start, 1, WATCHDOG_NAME)) {
                pr_err("I/O address 0x%04x already in use\n", wdt_start);
                ret = -EIO;
                goto unreg_stop;
        }
        ret = misc_register(&acq_miscdev);
        if (ret != 0) {
                pr_err("cannot register miscdev on minor=%d (err=%d)\n",
                       WATCHDOG_MINOR, ret);
                goto unreg_regions;
        }
        pr_info("initialized. (nowayout=%d)\n", nowayout);

        return 0;
unreg_regions:
        release_region(wdt_start, 1);
unreg_stop:
        if (wdt_stop != wdt_start)
                release_region(wdt_stop, 1);
out:
        return ret;
}

static void acq_remove(struct platform_device *dev)
{
        misc_deregister(&acq_miscdev);
        release_region(wdt_start, 1);
        if (wdt_stop != wdt_start)
                release_region(wdt_stop, 1);
}

static void acq_shutdown(struct platform_device *dev)
{
        /* Turn the WDT off if we have a soft shutdown */
        acq_stop();
}

static struct platform_driver acquirewdt_driver = {
        .remove         = acq_remove,
        .shutdown       = acq_shutdown,
        .driver         = {
                .name   = DRV_NAME,
        },
};

static int __init acq_init(void)
{
        int err;

        pr_info("WDT driver for Acquire single board computer initialising\n");

        acq_platform_device = platform_device_register_simple(DRV_NAME,
                                                                -1, NULL, 0);
        if (IS_ERR(acq_platform_device))
                return PTR_ERR(acq_platform_device);

        err = platform_driver_probe(&acquirewdt_driver, acq_probe);
        if (err)
                goto unreg_platform_device;
        return 0;

unreg_platform_device:
        platform_device_unregister(acq_platform_device);
        return err;
}

static void __exit acq_exit(void)
{
        platform_device_unregister(acq_platform_device);
        platform_driver_unregister(&acquirewdt_driver);
        pr_info("Watchdog Module Unloaded\n");
}

module_init(acq_init);
module_exit(acq_exit);

MODULE_AUTHOR("David Woodhouse");
MODULE_DESCRIPTION("Acquire Inc. Single Board Computer Watchdog Timer driver");
MODULE_LICENSE("GPL");