/*
   *	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
  ");
  }
  
  /*
   *	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);
  	/* 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
  ");
  	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...
  ");
  	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!
  ");
  		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
  ",
  			WATCHDOG_TIMEOUT);
  	}
  
  	wdtmrctl = ioremap(MMCR_BASE + OFFS_WDTMRCTL, 2);
  	if (!wdtmrctl) {
  		pr_err("Unable to remap memory
  ");
  		rc = -ENOMEM;
  		goto err_out_region2;
  	}
  
  	rc = register_reboot_notifier(&wdt_notifier);
  	if (rc) {
  		pr_err("cannot register reboot notifier (err=%d)
  ", rc);
  		goto err_out_ioremap;
  	}
  
  	rc = misc_register(&wdt_miscdev);
  	if (rc) {
  		pr_err("cannot register miscdev on minor=%d (err=%d)
  ",
  		       WATCHDOG_MINOR, rc);
  		goto err_out_notifier;
  	}
  
  	pr_info("WDT driver for SC520 initialised. timeout=%d sec (nowayout=%d)
  ",
  		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");