/*
   * Driver for watchdog device controlled through GPIO-line
   *
   * Author: 2013, Alexander Shiyan <shc_work@mail.ru>
   *
   * 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.
   */
  
  #include <linux/err.h>
  #include <linux/delay.h>
  #include <linux/module.h>
  #include <linux/notifier.h>
  #include <linux/of_gpio.h>
  #include <linux/platform_device.h>
  #include <linux/reboot.h>
  #include <linux/watchdog.h>
  
  #define SOFT_TIMEOUT_MIN	1
  #define SOFT_TIMEOUT_DEF	60
  #define SOFT_TIMEOUT_MAX	0xffff
  
  enum {
  	HW_ALGO_TOGGLE,
  	HW_ALGO_LEVEL,
  };
  
  struct gpio_wdt_priv {
  	int			gpio;
  	bool			active_low;
  	bool			state;
  	unsigned int		hw_algo;
  	unsigned int		hw_margin;
  	unsigned long		last_jiffies;
  	struct notifier_block	notifier;
  	struct timer_list	timer;
  	struct watchdog_device	wdd;
  };
  
  static void gpio_wdt_disable(struct gpio_wdt_priv *priv)
  {
  	gpio_set_value_cansleep(priv->gpio, !priv->active_low);
  
  	/* Put GPIO back to tristate */
  	if (priv->hw_algo == HW_ALGO_TOGGLE)
  		gpio_direction_input(priv->gpio);
  }
  
  static int gpio_wdt_start(struct watchdog_device *wdd)
  {
  	struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);
  
  	priv->state = priv->active_low;
  	gpio_direction_output(priv->gpio, priv->state);
  	priv->last_jiffies = jiffies;
  	mod_timer(&priv->timer, priv->last_jiffies + priv->hw_margin);
  
  	return 0;
  }
  
  static int gpio_wdt_stop(struct watchdog_device *wdd)
  {
  	struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);
  
  	mod_timer(&priv->timer, 0);
  	gpio_wdt_disable(priv);
  
  	return 0;
  }
  
  static int gpio_wdt_ping(struct watchdog_device *wdd)
  {
  	struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);
  
  	priv->last_jiffies = jiffies;
  
  	return 0;
  }
  
  static int gpio_wdt_set_timeout(struct watchdog_device *wdd, unsigned int t)
  {
  	wdd->timeout = t;
  
  	return gpio_wdt_ping(wdd);
  }
  
  static void gpio_wdt_hwping(unsigned long data)
  {
  	struct watchdog_device *wdd = (struct watchdog_device *)data;
  	struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);
  
  	if (time_after(jiffies, priv->last_jiffies +
  		       msecs_to_jiffies(wdd->timeout * 1000))) {
  		dev_crit(wdd->dev, "Timer expired. System will reboot soon!
  ");
  		return;
  	}
  
  	/* Restart timer */
  	mod_timer(&priv->timer, jiffies + priv->hw_margin);
  
  	switch (priv->hw_algo) {
  	case HW_ALGO_TOGGLE:
  		/* Toggle output pin */
  		priv->state = !priv->state;
  		gpio_set_value_cansleep(priv->gpio, priv->state);
  		break;
  	case HW_ALGO_LEVEL:
  		/* Pulse */
  		gpio_set_value_cansleep(priv->gpio, !priv->active_low);
  		udelay(1);
  		gpio_set_value_cansleep(priv->gpio, priv->active_low);
  		break;
  	}
  }
  
  static int gpio_wdt_notify_sys(struct notifier_block *nb, unsigned long code,
  			       void *unused)
  {
  	struct gpio_wdt_priv *priv = container_of(nb, struct gpio_wdt_priv,
  						  notifier);
  
  	mod_timer(&priv->timer, 0);
  
  	switch (code) {
  	case SYS_HALT:
  	case SYS_POWER_OFF:
  		gpio_wdt_disable(priv);
  		break;
  	default:
  		break;
  	}
  
  	return NOTIFY_DONE;
  }
  
  static const struct watchdog_info gpio_wdt_ident = {
  	.options	= WDIOF_MAGICCLOSE | WDIOF_KEEPALIVEPING |
  			  WDIOF_SETTIMEOUT,
  	.identity	= "GPIO Watchdog",
  };
  
  static const struct watchdog_ops gpio_wdt_ops = {
  	.owner		= THIS_MODULE,
  	.start		= gpio_wdt_start,
  	.stop		= gpio_wdt_stop,
  	.ping		= gpio_wdt_ping,
  	.set_timeout	= gpio_wdt_set_timeout,
  };
  
  static int gpio_wdt_probe(struct platform_device *pdev)
  {
  	struct gpio_wdt_priv *priv;
  	enum of_gpio_flags flags;
  	unsigned int hw_margin;
  	unsigned long f = 0;
  	const char *algo;
  	int ret;
  
  	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
  	if (!priv)
  		return -ENOMEM;
  
  	priv->gpio = of_get_gpio_flags(pdev->dev.of_node, 0, &flags);
  	if (!gpio_is_valid(priv->gpio))
  		return priv->gpio;
  
  	priv->active_low = flags & OF_GPIO_ACTIVE_LOW;
  
  	ret = of_property_read_string(pdev->dev.of_node, "hw_algo", &algo);
  	if (ret)
  		return ret;
  	if (!strncmp(algo, "toggle", 6)) {
  		priv->hw_algo = HW_ALGO_TOGGLE;
  		f = GPIOF_IN;
  	} else if (!strncmp(algo, "level", 5)) {
  		priv->hw_algo = HW_ALGO_LEVEL;
  		f = priv->active_low ? GPIOF_OUT_INIT_HIGH : GPIOF_OUT_INIT_LOW;
  	} else {
  		return -EINVAL;
  	}
  
  	ret = devm_gpio_request_one(&pdev->dev, priv->gpio, f,
  				    dev_name(&pdev->dev));
  	if (ret)
  		return ret;
  
  	ret = of_property_read_u32(pdev->dev.of_node,
  				   "hw_margin_ms", &hw_margin);
  	if (ret)
  		return ret;
  	/* Disallow values lower than 2 and higher than 65535 ms */
  	if (hw_margin < 2 || hw_margin > 65535)
  		return -EINVAL;
  
  	/* Use safe value (1/2 of real timeout) */
  	priv->hw_margin = msecs_to_jiffies(hw_margin / 2);
  
  	watchdog_set_drvdata(&priv->wdd, priv);
  
  	priv->wdd.info		= &gpio_wdt_ident;
  	priv->wdd.ops		= &gpio_wdt_ops;
  	priv->wdd.min_timeout	= SOFT_TIMEOUT_MIN;
  	priv->wdd.max_timeout	= SOFT_TIMEOUT_MAX;
  
  	if (watchdog_init_timeout(&priv->wdd, 0, &pdev->dev) < 0)
  		priv->wdd.timeout = SOFT_TIMEOUT_DEF;
  
  	setup_timer(&priv->timer, gpio_wdt_hwping, (unsigned long)&priv->wdd);
  
  	ret = watchdog_register_device(&priv->wdd);
  	if (ret)
  		return ret;
  
  	priv->notifier.notifier_call = gpio_wdt_notify_sys;
  	ret = register_reboot_notifier(&priv->notifier);
  	if (ret)
  		watchdog_unregister_device(&priv->wdd);
  
  	return ret;
  }
  
  static int gpio_wdt_remove(struct platform_device *pdev)
  {
  	struct gpio_wdt_priv *priv = platform_get_drvdata(pdev);
  
  	del_timer_sync(&priv->timer);
  	unregister_reboot_notifier(&priv->notifier);
  	watchdog_unregister_device(&priv->wdd);
  
  	return 0;
  }
  
  static const struct of_device_id gpio_wdt_dt_ids[] = {
  	{ .compatible = "linux,wdt-gpio", },
  	{ }
  };
  MODULE_DEVICE_TABLE(of, gpio_wdt_dt_ids);
  
  static struct platform_driver gpio_wdt_driver = {
  	.driver	= {
  		.name		= "gpio-wdt",
  		.owner		= THIS_MODULE,
  		.of_match_table	= gpio_wdt_dt_ids,
  	},
  	.probe	= gpio_wdt_probe,
  	.remove	= gpio_wdt_remove,
  };
  module_platform_driver(gpio_wdt_driver);
  
  MODULE_AUTHOR("Alexander Shiyan <shc_work@mail.ru>");
  MODULE_DESCRIPTION("GPIO Watchdog");
  MODULE_LICENSE("GPL");