// SPDX-License-Identifier: GPL-2.0-or-later
/* drivers/char/watchdog/scx200_wdt.c

   National Semiconductor SCx200 Watchdog support

   Copyright (c) 2001,2002 Christer Weinigel <wingel@nano-system.com>

   Some code taken from:
   National Semiconductor PC87307/PC97307 (ala SC1200) WDT driver
   (c) Copyright 2002 Zwane Mwaikambo <zwane@commfireservices.com>


   The author(s) of this software shall not be held liable for damages
   of any nature resulting due to the use of this software. This
   software is provided AS-IS with no warranties. */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/init.h>
#include <linux/miscdevice.h>
#include <linux/watchdog.h>
#include <linux/notifier.h>
#include <linux/reboot.h>
#include <linux/fs.h>
#include <linux/ioport.h>
#include <linux/scx200.h>
#include <linux/uaccess.h>
#include <linux/io.h>

#define DEBUG

MODULE_AUTHOR("Christer Weinigel <wingel@nano-system.com>");
MODULE_DESCRIPTION("NatSemi SCx200 Watchdog Driver");
MODULE_LICENSE("GPL");

static int margin = 60;         /* in seconds */
module_param(margin, int, 0);
MODULE_PARM_DESC(margin, "Watchdog margin in seconds");

static bool nowayout = WATCHDOG_NOWAYOUT;
module_param(nowayout, bool, 0);
MODULE_PARM_DESC(nowayout, "Disable watchdog shutdown on close");

static u16 wdto_restart;
static char expect_close;
static unsigned long open_lock;
static DEFINE_SPINLOCK(scx_lock);

/* Bits of the WDCNFG register */
#define W_ENABLE 0x00fa         /* Enable watchdog */
#define W_DISABLE 0x0000        /* Disable watchdog */

/* The scaling factor for the timer, this depends on the value of W_ENABLE */
#define W_SCALE (32768/1024)

static void scx200_wdt_ping(void)
{
        spin_lock(&scx_lock);
        outw(wdto_restart, scx200_cb_base + SCx200_WDT_WDTO);
        spin_unlock(&scx_lock);
}

static void scx200_wdt_update_margin(void)
{
        pr_info("timer margin %d seconds\n", margin);
        wdto_restart = margin * W_SCALE;
}

static void scx200_wdt_enable(void)
{
        pr_debug("enabling watchdog timer, wdto_restart = %d\n", wdto_restart);

        spin_lock(&scx_lock);
        outw(0, scx200_cb_base + SCx200_WDT_WDTO);
        outb(SCx200_WDT_WDSTS_WDOVF, scx200_cb_base + SCx200_WDT_WDSTS);
        outw(W_ENABLE, scx200_cb_base + SCx200_WDT_WDCNFG);
        spin_unlock(&scx_lock);

        scx200_wdt_ping();
}

static void scx200_wdt_disable(void)
{
        pr_debug("disabling watchdog timer\n");

        spin_lock(&scx_lock);
        outw(0, scx200_cb_base + SCx200_WDT_WDTO);
        outb(SCx200_WDT_WDSTS_WDOVF, scx200_cb_base + SCx200_WDT_WDSTS);
        outw(W_DISABLE, scx200_cb_base + SCx200_WDT_WDCNFG);
        spin_unlock(&scx_lock);
}

static int scx200_wdt_open(struct inode *inode, struct file *file)
{
        /* only allow one at a time */
        if (test_and_set_bit(0, &open_lock))
                return -EBUSY;
        scx200_wdt_enable();

        return stream_open(inode, file);
}

static int scx200_wdt_release(struct inode *inode, struct file *file)
{
        if (expect_close != 42)
                pr_warn("watchdog device closed unexpectedly, will not disable the watchdog timer\n");
        else if (!nowayout)
                scx200_wdt_disable();
        expect_close = 0;
        clear_bit(0, &open_lock);

        return 0;
}

static int scx200_wdt_notify_sys(struct notifier_block *this,
                                      unsigned long code, void *unused)
{
        if (code == SYS_HALT || code == SYS_POWER_OFF)
                if (!nowayout)
                        scx200_wdt_disable();

        return NOTIFY_DONE;
}

static struct notifier_block scx200_wdt_notifier = {
        .notifier_call = scx200_wdt_notify_sys,
};

static ssize_t scx200_wdt_write(struct file *file, const char __user *data,
                                     size_t len, loff_t *ppos)
{
        /* check for a magic close character */
        if (len) {
                size_t i;

                scx200_wdt_ping();

                expect_close = 0;
                for (i = 0; i < len; ++i) {
                        char c;
                        if (get_user(c, data + i))
                                return -EFAULT;
                        if (c == 'V')
                                expect_close = 42;
                }

                return len;
        }

        return 0;
}

static long scx200_wdt_ioctl(struct file *file, unsigned int cmd,
                                                        unsigned long arg)
{
        void __user *argp = (void __user *)arg;
        int __user *p = argp;
        static const struct watchdog_info ident = {
                .identity = "NatSemi SCx200 Watchdog",
                .firmware_version = 1,
                .options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING |
                                                WDIOF_MAGICCLOSE,
        };
        int new_margin;

        switch (cmd) {
        case WDIOC_GETSUPPORT:
                if (copy_to_user(argp, &ident, sizeof(ident)))
                        return -EFAULT;
                return 0;
        case WDIOC_GETSTATUS:
        case WDIOC_GETBOOTSTATUS:
                if (put_user(0, p))
                        return -EFAULT;
                return 0;
        case WDIOC_KEEPALIVE:
                scx200_wdt_ping();
                return 0;
        case WDIOC_SETTIMEOUT:
                if (get_user(new_margin, p))
                        return -EFAULT;
                if (new_margin < 1)
                        return -EINVAL;
                margin = new_margin;
                scx200_wdt_update_margin();
                scx200_wdt_ping();
                fallthrough;
        case WDIOC_GETTIMEOUT:
                if (put_user(margin, p))
                        return -EFAULT;
                return 0;
        default:
                return -ENOTTY;
        }
}

static const struct file_operations scx200_wdt_fops = {
        .owner = THIS_MODULE,
        .write = scx200_wdt_write,
        .unlocked_ioctl = scx200_wdt_ioctl,
        .compat_ioctl   = compat_ptr_ioctl,
        .open = scx200_wdt_open,
        .release = scx200_wdt_release,
};

static struct miscdevice scx200_wdt_miscdev = {
        .minor = WATCHDOG_MINOR,
        .name = "watchdog",
        .fops = &scx200_wdt_fops,
};

static int __init scx200_wdt_init(void)
{
        int r;

        pr_debug("NatSemi SCx200 Watchdog Driver\n");

        /* check that we have found the configuration block */
        if (!scx200_cb_present())
                return -ENODEV;

        if (!request_region(scx200_cb_base + SCx200_WDT_OFFSET,
                            SCx200_WDT_SIZE,
                            "NatSemi SCx200 Watchdog")) {
                pr_warn("watchdog I/O region busy\n");
                return -EBUSY;
        }

        scx200_wdt_update_margin();
        scx200_wdt_disable();

        r = register_reboot_notifier(&scx200_wdt_notifier);
        if (r) {
                pr_err("unable to register reboot notifier\n");
                release_region(scx200_cb_base + SCx200_WDT_OFFSET,
                                SCx200_WDT_SIZE);
                return r;
        }

        r = misc_register(&scx200_wdt_miscdev);
        if (r) {
                unregister_reboot_notifier(&scx200_wdt_notifier);
                release_region(scx200_cb_base + SCx200_WDT_OFFSET,
                                SCx200_WDT_SIZE);
                return r;
        }

        return 0;
}

static void __exit scx200_wdt_cleanup(void)
{
        misc_deregister(&scx200_wdt_miscdev);
        unregister_reboot_notifier(&scx200_wdt_notifier);
        release_region(scx200_cb_base + SCx200_WDT_OFFSET,
                       SCx200_WDT_SIZE);
}

module_init(scx200_wdt_init);
module_exit(scx200_wdt_cleanup);