// SPDX-License-Identifier: GPL-2.0
/*
 * Driver for the Renesas Window Watchdog Timer (WWDT)
 *
 * The WWDT can only be setup once after boot. Because we cannot know if this
 * already happened in early boot stages, it is mandated that the firmware
 * configures the watchdog. Linux then adapts according to the given setup.
 * Note that this watchdog reports in the default configuration an overflow to
 * the Error Control Module which then decides further actions. Or the WWDT is
 * configured to generate an interrupt.
 */

#include <linux/bitfield.h>
#include <linux/clk.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/watchdog.h>

#define WDTA0WDTE       0x00
#define WDTA0RUN        BIT(7)
#define WDTA0_KEY       0x2c

#define WDTA0MD         0x0c
#define WDTA0OVF(x)     FIELD_GET(GENMASK(6, 4), x)
#define WDTA0WIE        BIT(3)
#define WDTA0ERM        BIT(2)
#define WDTA0WS(x)      FIELD_GET(GENMASK(1, 0), x)

struct wwdt_priv {
        void __iomem *base;
        struct watchdog_device wdev;
};

static int wwdt_start(struct watchdog_device *wdev)
{
        struct wwdt_priv *priv = container_of(wdev, struct wwdt_priv, wdev);

        writeb(WDTA0RUN | WDTA0_KEY, priv->base + WDTA0WDTE);
        return 0;
}

static const struct watchdog_info wwdt_ident = {
        .options = WDIOF_KEEPALIVEPING | WDIOF_ALARMONLY,
        .identity = "Renesas Window Watchdog",
};

static const struct watchdog_ops wwdt_ops = {
        .owner = THIS_MODULE,
        .start = wwdt_start,
};

static irqreturn_t wwdt_error_irq(int irq, void *dev_id)
{
        struct device *dev = dev_id;

        dev_warn(dev, "Watchdog timed out\n");
        return IRQ_HANDLED;
}

static irqreturn_t wwdt_pretimeout_irq(int irq, void *dev_id)
{
        struct watchdog_device *wdev = dev_id;

        watchdog_notify_pretimeout(wdev);
        return IRQ_HANDLED;
}

static int wwdt_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct wwdt_priv *priv;
        struct watchdog_device *wdev;
        struct clk *clk;
        unsigned long rate;
        unsigned int interval, window_size;
        int ret;
        u8 val;

        priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        priv->base = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(priv->base))
                return PTR_ERR(priv->base);

        clk = devm_clk_get(dev, "cnt");
        if (IS_ERR(clk))
                return PTR_ERR(clk);

        rate = clk_get_rate(clk);
        if (!rate)
                return -EINVAL;

        wdev = &priv->wdev;

        val = readb(priv->base + WDTA0WDTE);
        if (val & WDTA0RUN)
                set_bit(WDOG_HW_RUNNING, &wdev->status);

        val = readb(priv->base + WDTA0MD);
        interval = 1 << (9 + WDTA0OVF(val));
        /* size of the closed(!) window per mille */
        window_size = 250 * (3 - WDTA0WS(val));

        wdev->info = &wwdt_ident;
        wdev->ops = &wwdt_ops;
        wdev->parent = dev;
        wdev->min_hw_heartbeat_ms = window_size * interval / rate;
        wdev->max_hw_heartbeat_ms = 1000 * interval / rate;
        wdev->timeout = DIV_ROUND_UP(wdev->max_hw_heartbeat_ms, 1000);
        watchdog_set_nowayout(wdev, true);

        if (!(val & WDTA0ERM)) {
                ret = platform_get_irq_byname(pdev, "error");
                if (ret < 0)
                        return ret;

                ret = devm_request_threaded_irq(dev, ret, NULL, wwdt_error_irq,
                                                IRQF_ONESHOT, NULL, dev);
                if (ret < 0)
                        return ret;
        }

        if (val & WDTA0WIE) {
                ret = platform_get_irq_byname(pdev, "pretimeout");
                if (ret < 0)
                        return ret;

                ret = devm_request_threaded_irq(dev, ret, NULL, wwdt_pretimeout_irq,
                                                IRQF_ONESHOT, NULL, wdev);
                if (ret < 0)
                        return ret;
        }

        devm_watchdog_register_device(dev, wdev);

        return 0;
}

static const struct of_device_id renesas_wwdt_ids[] = {
        { .compatible = "renesas,rcar-gen3-wwdt", },
        { .compatible = "renesas,rcar-gen4-wwdt", },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, renesas_wwdt_ids);

static struct platform_driver renesas_wwdt_driver = {
        .driver = {
                .name = "renesas_wwdt",
                .of_match_table = renesas_wwdt_ids,
        },
        .probe = wwdt_probe,
};
module_platform_driver(renesas_wwdt_driver);

MODULE_DESCRIPTION("Renesas Window Watchdog (WWDT) Driver");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Wolfram Sang <wsa+renesas@sang-engineering.com>");