/*
   * Copyright 2010-2011 Picochip Ltd., Jamie Iles
   * http://www.picochip.com
   *
   * 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.
   *
   * This file implements a driver for the Synopsys DesignWare watchdog device
   * in the many subsystems. The watchdog has 16 different timeout periods
   * and these are a function of the input clock frequency.
   *
   * The DesignWare watchdog cannot be stopped once it has been started so we
   * use a software timer to implement a ping that will keep the watchdog alive.
   * If we receive an expected close for the watchdog then we keep the timer
   * running, otherwise the timer is stopped and the watchdog will expire.
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/bitops.h>
  #include <linux/clk.h>
  #include <linux/device.h>
  #include <linux/err.h>
  #include <linux/fs.h>
  #include <linux/io.h>
  #include <linux/kernel.h>
  #include <linux/miscdevice.h>
  #include <linux/module.h>
  #include <linux/moduleparam.h>
  #include <linux/of.h>
  #include <linux/pm.h>
  #include <linux/platform_device.h>
  #include <linux/spinlock.h>
  #include <linux/timer.h>
  #include <linux/uaccess.h>
  #include <linux/watchdog.h>
  
  #define WDOG_CONTROL_REG_OFFSET		    0x00
  #define WDOG_CONTROL_REG_WDT_EN_MASK	    0x01
  #define WDOG_TIMEOUT_RANGE_REG_OFFSET	    0x04
  #define WDOG_CURRENT_COUNT_REG_OFFSET	    0x08
  #define WDOG_COUNTER_RESTART_REG_OFFSET     0x0c
  #define WDOG_COUNTER_RESTART_KICK_VALUE	    0x76
  
  /* The maximum TOP (timeout period) value that can be set in the watchdog. */
  #define DW_WDT_MAX_TOP		15
  
  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) ")");
  
  #define WDT_TIMEOUT		(HZ / 2)
  
  static struct {
  	spinlock_t		lock;
  	void __iomem		*regs;
  	struct clk		*clk;
  	unsigned long		in_use;
  	unsigned long		next_heartbeat;
  	struct timer_list	timer;
  	int			expect_close;
  } dw_wdt;
  
  static inline int dw_wdt_is_enabled(void)
  {
  	return readl(dw_wdt.regs + WDOG_CONTROL_REG_OFFSET) &
  		WDOG_CONTROL_REG_WDT_EN_MASK;
  }
  
  static inline int dw_wdt_top_in_seconds(unsigned top)
  {
  	/*
  	 * There are 16 possible timeout values in 0..15 where the number of
  	 * cycles is 2 ^ (16 + i) and the watchdog counts down.
  	 */
  	return (1 << (16 + top)) / clk_get_rate(dw_wdt.clk);
  }
  
  static int dw_wdt_get_top(void)
  {
  	int top = readl(dw_wdt.regs + WDOG_TIMEOUT_RANGE_REG_OFFSET) & 0xF;
  
  	return dw_wdt_top_in_seconds(top);
  }
  
  static inline void dw_wdt_set_next_heartbeat(void)
  {
  	dw_wdt.next_heartbeat = jiffies + dw_wdt_get_top() * HZ;
  }
  
  static int dw_wdt_set_top(unsigned top_s)
  {
  	int i, top_val = DW_WDT_MAX_TOP;
  
  	/*
  	 * Iterate over the timeout values until we find the closest match. We
  	 * always look for >=.
  	 */
  	for (i = 0; i <= DW_WDT_MAX_TOP; ++i)
  		if (dw_wdt_top_in_seconds(i) >= top_s) {
  			top_val = i;
  			break;
  		}
  
  	/* Set the new value in the watchdog. */
  	writel(top_val, dw_wdt.regs + WDOG_TIMEOUT_RANGE_REG_OFFSET);
  
  	dw_wdt_set_next_heartbeat();
  
  	return dw_wdt_top_in_seconds(top_val);
  }
  
  static void dw_wdt_keepalive(void)
  {
  	writel(WDOG_COUNTER_RESTART_KICK_VALUE, dw_wdt.regs +
  	       WDOG_COUNTER_RESTART_REG_OFFSET);
  }
  
  static void dw_wdt_ping(unsigned long data)
  {
  	if (time_before(jiffies, dw_wdt.next_heartbeat) ||
  	    (!nowayout && !dw_wdt.in_use)) {
  		dw_wdt_keepalive();
  		mod_timer(&dw_wdt.timer, jiffies + WDT_TIMEOUT);
  	} else
  		pr_crit("keepalive missed, machine will reset
  ");
  }
  
  static int dw_wdt_open(struct inode *inode, struct file *filp)
  {
  	if (test_and_set_bit(0, &dw_wdt.in_use))
  		return -EBUSY;
  
  	/* Make sure we don't get unloaded. */
  	__module_get(THIS_MODULE);
  
  	spin_lock(&dw_wdt.lock);
  	if (!dw_wdt_is_enabled()) {
  		/*
  		 * The watchdog is not currently enabled. Set the timeout to
  		 * the maximum and then start it.
  		 */
  		dw_wdt_set_top(DW_WDT_MAX_TOP);
  		writel(WDOG_CONTROL_REG_WDT_EN_MASK,
  		       dw_wdt.regs + WDOG_CONTROL_REG_OFFSET);
  	}
  
  	dw_wdt_set_next_heartbeat();
  
  	spin_unlock(&dw_wdt.lock);
  
  	return nonseekable_open(inode, filp);
  }
  
  static ssize_t dw_wdt_write(struct file *filp, const char __user *buf,
  			    size_t len, loff_t *offset)
  {
  	if (!len)
  		return 0;
  
  	if (!nowayout) {
  		size_t i;
  
  		dw_wdt.expect_close = 0;
  
  		for (i = 0; i < len; ++i) {
  			char c;
  
  			if (get_user(c, buf + i))
  				return -EFAULT;
  
  			if (c == 'V') {
  				dw_wdt.expect_close = 1;
  				break;
  			}
  		}
  	}
  
  	dw_wdt_set_next_heartbeat();
  	mod_timer(&dw_wdt.timer, jiffies + WDT_TIMEOUT);
  
  	return len;
  }
  
  static u32 dw_wdt_time_left(void)
  {
  	return readl(dw_wdt.regs + WDOG_CURRENT_COUNT_REG_OFFSET) /
  		clk_get_rate(dw_wdt.clk);
  }
  
  static const struct watchdog_info dw_wdt_ident = {
  	.options	= WDIOF_KEEPALIVEPING | WDIOF_SETTIMEOUT |
  			  WDIOF_MAGICCLOSE,
  	.identity	= "Synopsys DesignWare Watchdog",
  };
  
  static long dw_wdt_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
  {
  	unsigned long val;
  	int timeout;
  
  	switch (cmd) {
  	case WDIOC_GETSUPPORT:
  		return copy_to_user((void __user *)arg, &dw_wdt_ident,
  				    sizeof(dw_wdt_ident)) ? -EFAULT : 0;
  
  	case WDIOC_GETSTATUS:
  	case WDIOC_GETBOOTSTATUS:
  		return put_user(0, (int __user *)arg);
  
  	case WDIOC_KEEPALIVE:
  		dw_wdt_set_next_heartbeat();
  		return 0;
  
  	case WDIOC_SETTIMEOUT:
  		if (get_user(val, (int __user *)arg))
  			return -EFAULT;
  		timeout = dw_wdt_set_top(val);
  		return put_user(timeout , (int __user *)arg);
  
  	case WDIOC_GETTIMEOUT:
  		return put_user(dw_wdt_get_top(), (int __user *)arg);
  
  	case WDIOC_GETTIMELEFT:
  		/* Get the time left until expiry. */
  		if (get_user(val, (int __user *)arg))
  			return -EFAULT;
  		return put_user(dw_wdt_time_left(), (int __user *)arg);
  
  	default:
  		return -ENOTTY;
  	}
  }
  
  static int dw_wdt_release(struct inode *inode, struct file *filp)
  {
  	clear_bit(0, &dw_wdt.in_use);
  
  	if (!dw_wdt.expect_close) {
  		del_timer(&dw_wdt.timer);
  
  		if (!nowayout)
  			pr_crit("unexpected close, system will reboot soon
  ");
  		else
  			pr_crit("watchdog cannot be disabled, system will reboot soon
  ");
  	}
  
  	dw_wdt.expect_close = 0;
  
  	return 0;
  }
  
  #ifdef CONFIG_PM_SLEEP
  static int dw_wdt_suspend(struct device *dev)
  {
  	clk_disable_unprepare(dw_wdt.clk);
  
  	return 0;
  }
  
  static int dw_wdt_resume(struct device *dev)
  {
  	int err = clk_prepare_enable(dw_wdt.clk);
  
  	if (err)
  		return err;
  
  	dw_wdt_keepalive();
  
  	return 0;
  }
  #endif /* CONFIG_PM_SLEEP */
  
  static SIMPLE_DEV_PM_OPS(dw_wdt_pm_ops, dw_wdt_suspend, dw_wdt_resume);
  
  static const struct file_operations wdt_fops = {
  	.owner		= THIS_MODULE,
  	.llseek		= no_llseek,
  	.open		= dw_wdt_open,
  	.write		= dw_wdt_write,
  	.unlocked_ioctl	= dw_wdt_ioctl,
  	.release	= dw_wdt_release
  };
  
  static struct miscdevice dw_wdt_miscdev = {
  	.fops		= &wdt_fops,
  	.name		= "watchdog",
  	.minor		= WATCHDOG_MINOR,
  };
  
  static int dw_wdt_drv_probe(struct platform_device *pdev)
  {
  	int ret;
  	struct resource *mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  
  	if (!mem)
  		return -EINVAL;
  
  	dw_wdt.regs = devm_ioremap_resource(&pdev->dev, mem);
  	if (IS_ERR(dw_wdt.regs))
  		return PTR_ERR(dw_wdt.regs);
  
  	dw_wdt.clk = devm_clk_get(&pdev->dev, NULL);
  	if (IS_ERR(dw_wdt.clk))
  		return PTR_ERR(dw_wdt.clk);
  
  	ret = clk_prepare_enable(dw_wdt.clk);
  	if (ret)
  		return ret;
  
  	spin_lock_init(&dw_wdt.lock);
  
  	ret = misc_register(&dw_wdt_miscdev);
  	if (ret)
  		goto out_disable_clk;
  
  	dw_wdt_set_next_heartbeat();
  	setup_timer(&dw_wdt.timer, dw_wdt_ping, 0);
  	mod_timer(&dw_wdt.timer, jiffies + WDT_TIMEOUT);
  
  	return 0;
  
  out_disable_clk:
  	clk_disable_unprepare(dw_wdt.clk);
  
  	return ret;
  }
  
  static int dw_wdt_drv_remove(struct platform_device *pdev)
  {
  	misc_deregister(&dw_wdt_miscdev);
  
  	clk_disable_unprepare(dw_wdt.clk);
  
  	return 0;
  }
  
  #ifdef CONFIG_OF
  static const struct of_device_id dw_wdt_of_match[] = {
  	{ .compatible = "snps,dw-wdt", },
  	{ /* sentinel */ }
  };
  MODULE_DEVICE_TABLE(of, dw_wdt_of_match);
  #endif
  
  static struct platform_driver dw_wdt_driver = {
  	.probe		= dw_wdt_drv_probe,
  	.remove		= dw_wdt_drv_remove,
  	.driver		= {
  		.name	= "dw_wdt",
  		.owner	= THIS_MODULE,
  		.of_match_table = of_match_ptr(dw_wdt_of_match),
  		.pm	= &dw_wdt_pm_ops,
  	},
  };
  
  module_platform_driver(dw_wdt_driver);
  
  MODULE_AUTHOR("Jamie Iles");
  MODULE_DESCRIPTION("Synopsys DesignWare Watchdog Driver");
  MODULE_LICENSE("GPL");