/*
 *	60xx Single Board Computer Watchdog Timer driver for Linux 2.2.x
 *
 *      Based on acquirewdt.c by Alan Cox.
 *
 *	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 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.
 *
 *	(c) Copyright 2000    Jakob Oestergaard <jakob@ostenfeld.dk>
 *
 *           12/4 - 2000      [Initial revision]
 *           25/4 - 2000      Added /dev/watchdog 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 the other Linux WDT 
 *  drivers in several ways:
 *  *)  The driver will ping the watchdog by itself, because this
 *      particular WDT has a very short timeout (one second) and it
 *      would be insane to count on any userspace daemon always
 *      getting scheduled within that time frame.
 *  *)  This driver expects the userspace daemon to send a specific
 *      character code ('V') to /dev/watchdog before closing the
 *      /dev/watchdog file.  If the userspace daemon closes the file
 *      without sending this special character, the driver will assume
 *      that the daemon (and userspace in general) died, and will
 *      stop pinging the WDT without disabling it first.  This will
 *      cause a reboot.
 *
 *  Why `V' ?  Well, `V' is the character in ASCII for the value 86,
 *  and we all know that 86 is _the_ most random number in the universe.
 *  Therefore it is the letter that has the slightest chance of occurring
 *  by chance, when the system becomes corrupted.
 *
 */

#include <linux/config.h>
#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/malloc.h>
#include <linux/ioport.h>
#include <linux/fcntl.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>

#define OUR_NAME "sbc60xxwdt"

/*
 * You must set these - The driver cannot probe for the settings
 */
 
#define WDT_STOP 0x45
#define WDT_START 0x443

/*
 * The 60xx board can use watchdog timeout values from one second
 * to several minutes.  The default is one second, so 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 10 seconds.
 * If the daemon pulses us every 5 seconds, we can still afford
 * a 5 second scheduling delay on the (high priority) daemon. That
 * should be sufficient for a box under any load.
 */
#define WDT_HEARTBEAT (HZ * 10)

static void wdt_timer_ping(unsigned long);
static struct timer_list timer = { 0, 0, WDT_INTERVAL, 0, wdt_timer_ping };
static unsigned long next_heartbeat = 0;
static int wdt_is_open = 0;
static int wdt_expect_close = 0;

/*
 *	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 by reading from WDT_START */
    inb_p(WDT_START);
    /* 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_startup(void)
{
  next_heartbeat = jiffies + WDT_HEARTBEAT;

  /* Start the timer */
  timer.expires = jiffies + WDT_INTERVAL;
  add_timer(&timer);
  printk(OUR_NAME ": Watchdog timer is now enabled.\n");  
}

static void wdt_turnoff(void)
{
  /* Stop the timer */
  del_timer(&timer);
  inb_p(WDT_STOP);
  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 0;
}

static ssize_t fop_read(struct file * file, char * buf, size_t count, loff_t * ppos)
{
  /* No can do */
  return -EINVAL;
}

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(wdt_is_open)
      return -EBUSY;

    /* Good, fire up the show */

    MOD_INC_USE_COUNT;

    wdt_is_open = 1;
    wdt_startup();
    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");
    }
  }

  wdt_is_open = 0;

  MOD_DEC_USE_COUNT;
  return 0;
}


static struct file_operations wdt_fops = {
  0,
  fop_read,
  fop_write,
  0,  /* readdir */
  0,  /* select */
  0,  /* ioctl */
  0,  /* mmap */
  fop_open,
  0,  /* flush */
  fop_close
};

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,
	0
};

#ifdef MODULE

#define sbc60xxwdt_init init_module

void cleanup_module(void)
{
  wdt_turnoff();

  /* Deregister */

  misc_deregister(&wdt_miscdev);

  unregister_reboot_notifier(&wdt_notifier);

  release_region(WDT_STOP,1);
  release_region(WDT_START,1);
}

#endif

__initfunc(int sbc60xxwdt_init(void))
{
  printk(OUR_NAME ": WDT driver for 60XX single board computer initialising.\n");

  misc_register(&wdt_miscdev);

  request_region(WDT_STOP, 1, "SBC 60XX WDT");
  request_region(WDT_START, 1, "SBC 60XX WDT");
  register_reboot_notifier(&wdt_notifier);

  return 0;
}

