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/*

 *      AMD Elan SC520 processor Watchdog Timer driver for Linux 2.4.x

 *

 *      Based on acquirewdt.c by Alan Cox,

 *           and sbc60xxwdt.c by Jakob Oestergaard <jakob@ostenfeld.dk>

 *

 *      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

 *

 *  Theory of operation:

 *  A Watchdog Timer (WDT) is a hardware circuit that can

 *  reset the computer system in case of a software fault.

 *  You probably knew that already.

 *

 *  Usually a userspace daemon will notify the kernel WDT driver

 *  via the /proc/watchdog special device file that userspace is

 *  still alive, at regular intervals.  When such a notification

 *  occurs, the driver will usually tell the hardware watchdog

 *  that everything is in order, and that the watchdog should wait

 *  for yet another little while to reset the system.

 *  If userspace fails (RAM error, kernel bug, whatever), the

 *  notifications cease to occur, and the hardware watchdog will

 *  reset the system (causing a reboot) after the timeout occurs.

 *

 *  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.

 */

#include <linux/module.h>

#include <linux/version.h>

#include <linux/types.h>

#include <linux/errno.h>

#include <linux/kernel.h>

#include <linux/timer.h>

#include <linux/sched.h>

#include <linux/miscdevice.h>

#include <linux/watchdog.h>

#include <linux/slab.h>

#include <linux/ioport.h>

#include <linux/fcntl.h>

#include <linux/smp_lock.h>

#include <asm/io.h>

#include <asm/uaccess.h>

#include <asm/system.h>

#include <linux/notifier.h>

#include <linux/reboot.h>

#include <linux/init.h>

/*

 * The SC520 can timeout anywhere from 492us to 32.21s.

 * 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 WDT_HEARTBEAT (HZ * 30)

/*

 * 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

 */

#define TIMEOUT_EXPONENT ( 1 << 3 )  /* 0x08 = 2.01s */

/* #define MMCR_BASE_DEFAULT 0xfffef000 */

#define MMCR_BASE_DEFAULT ((__u16 *)0xffffe)

#define OFFS_WDTMRCTL ((unsigned int)0xcb0)

#define WDT_ENB 0x8000          /* [15] Watchdog Timer Enable */

#define WDT_WRST_ENB 0x4000     /* [14] Watchdog Timer Reset Enable */

#define OUR_NAME "sc520_wdt"

#define WRT_DOG(data) *wdtmrctl=data

static __u16 *wdtmrctl;

static void wdt_timer_ping(unsigned long);

static struct timer_list timer;

static unsigned long next_heartbeat;

static unsigned long wdt_is_open;

static int wdt_expect_close;

#ifdef CONFIG_WATCHDOG_NOWAYOUT

static int nowayout = 1;

#else

static int nowayout = 0;

#endif

MODULE_PARM(nowayout,"i");

MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default=CONFIG_WATCHDOG_NOWAYOUT)");

static spinlock_t 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 */

                timer.expires = jiffies + WDT_INTERVAL;

                add_timer(&timer);

        } else {

                printk(OUR_NAME ": Heartbeat lost! Will not ping the watchdog\n");

        }

}

/*

 * Utility routines

 */

static void wdt_config(int writeval)

{

        __u16 dummy;

        unsigned long flags;

        /* buy some time (ping) */

        spin_lock_irqsave(&wdt_spinlock, flags);

        dummy=readw(wdtmrctl);  /* ensure write synchronization */

        writew(0xAAAA, wdtmrctl);

        writew(0x5555, wdtmrctl);

        /* 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 void wdt_startup(void)

{

        next_heartbeat = jiffies + WDT_HEARTBEAT;

        /* Start the timer */

        timer.expires = jiffies + WDT_INTERVAL;

        add_timer(&timer);

        wdt_config(WDT_ENB | WDT_WRST_ENB | TIMEOUT_EXPONENT);

        printk(OUR_NAME ": Watchdog timer is now enabled.\n");

}

static void wdt_turnoff(void)

{

        if (!nowayout) {

                /* Stop the timer */

                del_timer(&timer);

                wdt_config(0);

                printk(OUR_NAME ": Watchdog timer is now disabled...\n");

        }

}

/*

 * /dev/watchdog handling

 */

static ssize_t fop_write(struct file * file, const char * buf, size_t count, loff_t * ppos)

{

        /* We can't seek */

        if(ppos != &file->f_pos)

                return -ESPIPE;

        /* See if we got the magic character */

        if(count)

        {

                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 = 1;

                }

                /* Well, anyhow someone wrote to us, we should return that favour */

                next_heartbeat = jiffies + WDT_HEARTBEAT;

                return 1;

        }

        return 0;

}

static int fop_open(struct inode * inode, struct file * file)

{

        switch(MINOR(inode->i_rdev))

        {

                case WATCHDOG_MINOR:

                        /* Just in case we're already talking to someone... */

                        if(test_and_set_bit(0, &wdt_is_open))

                                return -EBUSY;

                        /* Good, fire up the show */

                        wdt_startup();

                        if (nowayout) {

                                MOD_INC_USE_COUNT;

                        }

                        return 0;

                default:

                        return -ENODEV;

        }

}

static int fop_close(struct inode * inode, struct file * file)

{

        if(MINOR(inode->i_rdev) == WATCHDOG_MINOR)

        {

                if(wdt_expect_close)

                        wdt_turnoff();

                else {

                        del_timer(&timer);

                        printk(OUR_NAME ": device file closed unexpectedly. Will not stop the WDT!\n");

                }

        }

        clear_bit(0, &wdt_is_open);

        return 0;

}

static long long fop_llseek(struct file *file, long long offset, int origin)

{

        return -ESPIPE;

}

static int fop_ioctl(struct inode *inode, struct file *file, unsigned int cmd,

        unsigned long arg)

{

        static struct watchdog_info ident=

        {

                WDIOF_MAGICCLOSE,

                1,

                "SC520"

        };

        switch(cmd)

        {

                default:

                        return -ENOIOCTLCMD;

                case WDIOC_GETSUPPORT:

                        return copy_to_user((struct watchdog_info *)arg, &ident, sizeof(ident))?-EFAULT:0;

                case WDIOC_KEEPALIVE:

                        next_heartbeat = jiffies + WDT_HEARTBEAT;

                        return 0;

        }

}

static struct file_operations wdt_fops = {

        owner:          THIS_MODULE,

        llseek:         fop_llseek,

        write:          fop_write,

        open:           fop_open,

        release:        fop_close,

        ioctl:          fop_ioctl

};

static struct miscdevice wdt_miscdev = {

        WATCHDOG_MINOR,

        "watchdog",

        &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=

{

        wdt_notify_sys,

        0,

};

static void __exit sc520_wdt_unload(void)

{

        wdt_turnoff();

        /* Deregister */

        misc_deregister(&wdt_miscdev);

        iounmap(wdtmrctl);

        unregister_reboot_notifier(&wdt_notifier);

}

static int __init sc520_wdt_init(void)

{

        int rc = -EBUSY;

        unsigned long cbar;

        spin_lock_init(&wdt_spinlock);

        init_timer(&timer);

        timer.function = wdt_timer_ping;

        timer.data = 0;

        rc = misc_register(&wdt_miscdev);

        if (rc)

                goto err_out_region2;

        rc = register_reboot_notifier(&wdt_notifier);

        if (rc)

                goto err_out_miscdev;

        /* get the Base Address Register */

        cbar = inl_p(0xfffc);

        printk(OUR_NAME ": CBAR: 0x%08lx\n", cbar);

        /* check if MMCR aliasing bit is set */

        if (cbar & 0x80000000) {

                printk(OUR_NAME ": MMCR Aliasing enabled.\n");

                wdtmrctl = (__u16 *)(cbar & 0x3fffffff);

        } else {

                printk(OUR_NAME "!!! WARNING !!!\n"

                  "\t MMCR Aliasing found NOT enabled!\n"

                  "\t Using default value of: %p\n"

                  "\t This has not been tested!\n"

                  "\t Please email Scott Jennings <smj@oro.net>\n"

                  "\t  and Bill Jennings <bj@oro.net> if it works!\n"

                  , MMCR_BASE_DEFAULT

                  );

          wdtmrctl = MMCR_BASE_DEFAULT;

        }

        wdtmrctl = (__u16 *)((char *)wdtmrctl + OFFS_WDTMRCTL);

        wdtmrctl = ioremap((unsigned long)wdtmrctl, 2);

        printk(KERN_INFO OUR_NAME ": WDT driver for SC520 initialised.\n");

        return 0;

err_out_miscdev:

        misc_deregister(&wdt_miscdev);

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");

EXPORT_NO_SYMBOLS;