/*
 *      AMD Elan SC520 processor Watchdog Timer driver
 *
 *      Based on acquirewdt.c by Alan Cox,
 *           and sbc60xxwdt.c by Jakob Oestergaard <jakob@unthought.net>
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 *
 *      The authors do 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.
 *
 *      (c) Copyright 2001    Scott Jennings <linuxdrivers@oro.net>
 *           9/27 - 2001      [Initial release]
 *
 *      Additional fixes Alan Cox
 *      -       Fixed formatting
 *      -       Removed debug printks
 *      -       Fixed SMP built kernel deadlock
 *      -       Switched to private locks not lock_kernel
 *      -       Used ioremap/writew/readw
 *      -       Added NOWAYOUT support
 *      4/12 - 2002 Changes by Rob Radez <rob@osinvestor.com>
 *      -       Change comments
 *      -       Eliminate fop_llseek
 *      -       Change CONFIG_WATCHDOG_NOWAYOUT semantics
 *      -       Add KERN_* tags to printks
 *      -       fix possible wdt_is_open race
 *      -       Report proper capabilities in watchdog_info
 *      -       Add WDIOC_{GETSTATUS, GETBOOTSTATUS, SETTIMEOUT,
 *              GETTIMEOUT, SETOPTIONS} ioctls
 *      09/8 - 2003 Changes by Wim Van Sebroeck <wim@iguana.be>
 *      -       cleanup of trailing spaces
 *      -       added extra printk's for startup problems
 *      -       use module_param
 *      -       made timeout (the emulated heartbeat) a module_param
 *      -       made the keepalive ping an internal subroutine
 *      3/27 - 2004 Changes by Sean Young <sean@mess.org>
 *      -       set MMCR_BASE to 0xfffef000
 *      -       CBAR does not need to be read
 *      -       removed debugging printks
 *
 *  This WDT driver is different from most other Linux WDT
 *  drivers in that the driver will ping the watchdog by itself,
 *  because this particular WDT has a very short timeout (1.6
 *  seconds) and it would be insane to count on any userspace
 *  daemon always getting scheduled within that time frame.
 *
 *  This driver uses memory mapped IO, and spinlock.
 */

#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/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/jiffies.h>
#include <linux/io.h>
#include <linux/uaccess.h>


/*
 * The AMD Elan SC520 timeout value is 492us times a power of 2 (0-7)
 *
 *   0: 492us    2: 1.01s    4: 4.03s   6: 16.22s
 *   1: 503ms    3: 2.01s    5: 8.05s   7: 32.21s
 *
 * We will program the SC520 watchdog for a timeout of 2.01s.
 * If we reset the watchdog every ~250ms we should be safe.
 */

#define WDT_INTERVAL (HZ/4+1)

/*
 * We must not require too good response from the userspace daemon.
 * Here we require the userspace daemon to send us a heartbeat
 * char to /dev/watchdog every 30 seconds.
 */

#define WATCHDOG_TIMEOUT 30             /* 30 sec default timeout */
/* in seconds, will be multiplied by HZ to get seconds to wait for a ping */
static int timeout = WATCHDOG_TIMEOUT;
module_param(timeout, int, 0);
MODULE_PARM_DESC(timeout,
        "Watchdog timeout in seconds. (1 <= timeout <= 3600, default="
                                __MODULE_STRING(WATCHDOG_TIMEOUT) ")");

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) ")");

/*
 * AMD Elan SC520 - Watchdog Timer Registers
 */
#define MMCR_BASE       0xfffef000      /* The default base address */
#define OFFS_WDTMRCTL   0xCB0   /* Watchdog Timer Control Register */

/* WDT Control Register bit definitions */
#define WDT_EXP_SEL_01  0x0001  /* [01] Time-out = 496 us (with 33 Mhz clk). */
#define WDT_EXP_SEL_02  0x0002  /* [02] Time-out = 508 ms (with 33 Mhz clk). */
#define WDT_EXP_SEL_03  0x0004  /* [03] Time-out = 1.02 s (with 33 Mhz clk). */
#define WDT_EXP_SEL_04  0x0008  /* [04] Time-out = 2.03 s (with 33 Mhz clk). */
#define WDT_EXP_SEL_05  0x0010  /* [05] Time-out = 4.07 s (with 33 Mhz clk). */
#define WDT_EXP_SEL_06  0x0020  /* [06] Time-out = 8.13 s (with 33 Mhz clk). */
#define WDT_EXP_SEL_07  0x0040  /* [07] Time-out = 16.27s (with 33 Mhz clk). */
#define WDT_EXP_SEL_08  0x0080  /* [08] Time-out = 32.54s (with 33 Mhz clk). */
#define WDT_IRQ_FLG     0x1000  /* [12] Interrupt Request Flag */
#define WDT_WRST_ENB    0x4000  /* [14] Watchdog Timer Reset Enable */
#define WDT_ENB         0x8000  /* [15] Watchdog Timer Enable */

static __u16 __iomem *wdtmrctl;

static void wdt_timer_ping(unsigned long);
static DEFINE_TIMER(timer, wdt_timer_ping, 0, 0);
static unsigned long next_heartbeat;
static unsigned long wdt_is_open;
static char wdt_expect_close;
static DEFINE_SPINLOCK(wdt_spinlock);

/*
 *      Whack the dog
 */

static void wdt_timer_ping(unsigned long data)
{
        /* If we got a heartbeat pulse within the WDT_US_INTERVAL
         * we agree to ping the WDT
         */
        if (time_before(jiffies, next_heartbeat)) {
                /* Ping the WDT */
                spin_lock(&wdt_spinlock);
                writew(0xAAAA, wdtmrctl);
                writew(0x5555, wdtmrctl);
                spin_unlock(&wdt_spinlock);

                /* Re-set the timer interval */
                mod_timer(&timer, jiffies + WDT_INTERVAL);
        } else
                pr_warn("Heartbeat lost! Will not ping the watchdog\n");
}

/*
 *      Utility routines
 */

static void wdt_config(int writeval)
{
        unsigned long flags;

        /* buy some time (ping) */
        spin_lock_irqsave(&wdt_spinlock, flags);
        readw(wdtmrctl);        /* ensure write synchronization */
        writew(0xAAAA, wdtmrctl);
        writew(0x5555, wdtmrctl);
        /* unlock WDT = make WDT configuration register writable one time */
        writew(0x3333, wdtmrctl);
        writew(0xCCCC, wdtmrctl);
        /* write WDT configuration register */
        writew(writeval, wdtmrctl);
        spin_unlock_irqrestore(&wdt_spinlock, flags);
}

static int wdt_startup(void)
{
        next_heartbeat = jiffies + (timeout * HZ);

        /* Start the timer */
        mod_timer(&timer, jiffies + WDT_INTERVAL);

        /* Start the watchdog */
        wdt_config(WDT_ENB | WDT_WRST_ENB | WDT_EXP_SEL_04);

        pr_info("Watchdog timer is now enabled\n");
        return 0;
}

static int wdt_turnoff(void)
{
        /* Stop the timer */
        del_timer(&timer);

        /* Stop the watchdog */
        wdt_config(0);

        pr_info("Watchdog timer is now disabled...\n");
        return 0;
}

static int wdt_keepalive(void)
{
        /* user land ping */
        next_heartbeat = jiffies + (timeout * HZ);
        return 0;
}

static int wdt_set_heartbeat(int t)
{
        if ((t < 1) || (t > 3600))      /* arbitrary upper limit */
                return -EINVAL;

        timeout = t;
        return 0;
}

/*
 *      /dev/watchdog handling
 */

static ssize_t fop_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 ofs;

                        /* note: just in case someone wrote the magic character
                         * five months ago... */
                        wdt_expect_close = 0;

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

                /* Well, anyhow someone wrote to us, we should
                   return that favour */
                wdt_keepalive();
        }
        return count;
}

static int fop_open(struct inode *inode, struct file *file)
{
        /* Just in case we're already talking to someone... */
        if (test_and_set_bit(0, &wdt_is_open))
                return -EBUSY;
        if (nowayout)
                __module_get(THIS_MODULE);

        /* Good, fire up the show */
        wdt_startup();
        return nonseekable_open(inode, file);
}

static int fop_close(struct inode *inode, struct file *file)
{
        if (wdt_expect_close == 42)
                wdt_turnoff();
        else {
                pr_crit("Unexpected close, not stopping watchdog!\n");
                wdt_keepalive();
        }
        clear_bit(0, &wdt_is_open);
        wdt_expect_close = 0;
        return 0;
}

static long fop_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 = {
                .options = WDIOF_KEEPALIVEPING | WDIOF_SETTIMEOUT
                                                        | WDIOF_MAGICCLOSE,
                .firmware_version = 1,
                .identity = "SC520",
        };

        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:
        {
                int new_options, retval = -EINVAL;

                if (get_user(new_options, p))
                        return -EFAULT;

                if (new_options & WDIOS_DISABLECARD) {
                        wdt_turnoff();
                        retval = 0;
                }

                if (new_options & WDIOS_ENABLECARD) {
                        wdt_startup();
                        retval = 0;
                }

                return retval;
        }
        case WDIOC_KEEPALIVE:
                wdt_keepalive();
                return 0;
        case WDIOC_SETTIMEOUT:
        {
                int new_timeout;

                if (get_user(new_timeout, p))
                        return -EFAULT;

                if (wdt_set_heartbeat(new_timeout))
                        return -EINVAL;

                wdt_keepalive();
                /* Fall through */
        }
        case WDIOC_GETTIMEOUT:
                return put_user(timeout, p);
        default:
                return -ENOTTY;
        }
}

static const struct file_operations wdt_fops = {
        .owner          = THIS_MODULE,
        .llseek         = no_llseek,
        .write          = fop_write,
        .open           = fop_open,
        .release        = fop_close,
        .unlocked_ioctl = fop_ioctl,
};

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

/*
 *      Notifier for system down
 */

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

/*
 *      The WDT needs to learn about soft shutdowns in order to
 *      turn the timebomb registers off.
 */

static struct notifier_block wdt_notifier = {
        .notifier_call = wdt_notify_sys,
};

static void __exit sc520_wdt_unload(void)
{
        if (!nowayout)
                wdt_turnoff();

        /* Deregister */
        misc_deregister(&wdt_miscdev);
        unregister_reboot_notifier(&wdt_notifier);
        iounmap(wdtmrctl);
}

static int __init sc520_wdt_init(void)
{
        int rc = -EBUSY;

        /* Check that the timeout value is within it's range ;
           if not reset to the default */
        if (wdt_set_heartbeat(timeout)) {
                wdt_set_heartbeat(WATCHDOG_TIMEOUT);
                pr_info("timeout value must be 1 <= timeout <= 3600, using %d\n",
                        WATCHDOG_TIMEOUT);
        }

        wdtmrctl = ioremap(MMCR_BASE + OFFS_WDTMRCTL, 2);
        if (!wdtmrctl) {
                pr_err("Unable to remap memory\n");
                rc = -ENOMEM;
                goto err_out_region2;
        }

        rc = register_reboot_notifier(&wdt_notifier);
        if (rc) {
                pr_err("cannot register reboot notifier (err=%d)\n", rc);
                goto err_out_ioremap;
        }

        rc = misc_register(&wdt_miscdev);
        if (rc) {
                pr_err("cannot register miscdev on minor=%d (err=%d)\n",
                       WATCHDOG_MINOR, rc);
                goto err_out_notifier;
        }

        pr_info("WDT driver for SC520 initialised. timeout=%d sec (nowayout=%d)\n",
                timeout, nowayout);

        return 0;

err_out_notifier:
        unregister_reboot_notifier(&wdt_notifier);
err_out_ioremap:
        iounmap(wdtmrctl);
err_out_region2:
        return rc;
}

module_init(sc520_wdt_init);
module_exit(sc520_wdt_unload);

MODULE_AUTHOR("Scott and Bill Jennings");
MODULE_DESCRIPTION(
        "Driver for watchdog timer in AMD \"Elan\" SC520 uProcessor");
MODULE_LICENSE("GPL");