/*
 * 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/of_gpio.h>
#include <linux/platform_device.h>
#include <linux/watchdog.h>

#define SOFT_TIMEOUT_MIN        1
#define SOFT_TIMEOUT_DEF        60

enum {
        HW_ALGO_TOGGLE,
        HW_ALGO_LEVEL,
};

struct gpio_wdt_priv {
        int                     gpio;
        bool                    active_low;
        bool                    state;
        bool                    always_running;
        unsigned int            hw_algo;
        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_ping(struct watchdog_device *wdd)
{
        struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);

        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;
        }
        return 0;
}

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);

        set_bit(WDOG_HW_RUNNING, &wdd->status);

        return gpio_wdt_ping(wdd);
}

static int gpio_wdt_stop(struct watchdog_device *wdd)
{
        struct gpio_wdt_priv *priv = watchdog_get_drvdata(wdd);

        if (!priv->always_running) {
                gpio_wdt_disable(priv);
                clear_bit(WDOG_HW_RUNNING, &wdd->status);
        }

        return 0;
}

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,
};

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;

        platform_set_drvdata(pdev, priv);

        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 (!strcmp(algo, "toggle")) {
                priv->hw_algo = HW_ALGO_TOGGLE;
                f = GPIOF_IN;
        } else if (!strcmp(algo, "level")) {
                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;

        priv->always_running = of_property_read_bool(pdev->dev.of_node,
                                                     "always-running");

        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_hw_heartbeat_ms = hw_margin;
        priv->wdd.parent        = &pdev->dev;

        if (watchdog_init_timeout(&priv->wdd, 0, &pdev->dev) < 0)
                priv->wdd.timeout = SOFT_TIMEOUT_DEF;

        watchdog_stop_on_reboot(&priv->wdd);

        if (priv->always_running)
                gpio_wdt_start(&priv->wdd);

        ret = watchdog_register_device(&priv->wdd);

        return ret;
}

static int gpio_wdt_remove(struct platform_device *pdev)
{
        struct gpio_wdt_priv *priv = platform_get_drvdata(pdev);

        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",
                .of_match_table = gpio_wdt_dt_ids,
        },
        .probe  = gpio_wdt_probe,
        .remove = gpio_wdt_remove,
};

#ifdef CONFIG_GPIO_WATCHDOG_ARCH_INITCALL
static int __init gpio_wdt_init(void)
{
        return platform_driver_register(&gpio_wdt_driver);
}
arch_initcall(gpio_wdt_init);
#else
module_platform_driver(gpio_wdt_driver);
#endif

MODULE_AUTHOR("Alexander Shiyan <shc_work@mail.ru>");
MODULE_DESCRIPTION("GPIO Watchdog");
MODULE_LICENSE("GPL");