// SPDX-License-Identifier: GPL-2.0
/*
 * Renesas RZ/A Series WDT Driver
 *
 * Copyright (C) 2017 Renesas Electronics America, Inc.
 * Copyright (C) 2017 Chris Brandt
 */

#include <linux/bitops.h>
#include <linux/clk.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/of_address.h>
#include <linux/of_device.h>
#include <linux/platform_device.h>
#include <linux/watchdog.h>

#define DEFAULT_TIMEOUT         30

/* Watchdog Timer Registers */
#define WTCSR                   0
#define WTCSR_MAGIC             0xA500
#define WTSCR_WT                BIT(6)
#define WTSCR_TME               BIT(5)
#define WTSCR_CKS(i)            (i)

#define WTCNT                   2
#define WTCNT_MAGIC             0x5A00

#define WRCSR                   4
#define WRCSR_MAGIC             0x5A00
#define WRCSR_RSTE              BIT(6)
#define WRCSR_CLEAR_WOVF        0xA500  /* special value */

/* The maximum CKS register setting value to get the longest timeout */
#define CKS_3BIT                0x7
#define CKS_4BIT                0xF

#define DIVIDER_3BIT            16384   /* Clock divider when CKS = 0x7 */
#define DIVIDER_4BIT            4194304 /* Clock divider when CKS = 0xF */

struct rza_wdt {
        struct watchdog_device wdev;
        void __iomem *base;
        struct clk *clk;
        u8 count;
        u8 cks;
};

static void rza_wdt_calc_timeout(struct rza_wdt *priv, int timeout)
{
        unsigned long rate = clk_get_rate(priv->clk);
        unsigned int ticks;

        if (priv->cks == CKS_4BIT) {
                ticks = DIV_ROUND_UP(timeout * rate, DIVIDER_4BIT);

                /*
                 * Since max_timeout was set in probe, we know that the timeout
                 * value passed will never calculate to a tick value greater
                 * than 256.
                 */
                priv->count = 256 - ticks;

        } else {
                /* Start timer with longest timeout */
                priv->count = 0;
        }

        pr_debug("%s: timeout set to %u (WTCNT=%d)\n", __func__,
                 timeout, priv->count);
}

static int rza_wdt_start(struct watchdog_device *wdev)
{
        struct rza_wdt *priv = watchdog_get_drvdata(wdev);

        /* Stop timer */
        writew(WTCSR_MAGIC | 0, priv->base + WTCSR);

        /* Must dummy read WRCSR:WOVF at least once before clearing */
        readb(priv->base + WRCSR);
        writew(WRCSR_CLEAR_WOVF, priv->base + WRCSR);

        rza_wdt_calc_timeout(priv, wdev->timeout);

        writew(WRCSR_MAGIC | WRCSR_RSTE, priv->base + WRCSR);
        writew(WTCNT_MAGIC | priv->count, priv->base + WTCNT);
        writew(WTCSR_MAGIC | WTSCR_WT | WTSCR_TME |
               WTSCR_CKS(priv->cks), priv->base + WTCSR);

        return 0;
}

static int rza_wdt_stop(struct watchdog_device *wdev)
{
        struct rza_wdt *priv = watchdog_get_drvdata(wdev);

        writew(WTCSR_MAGIC | 0, priv->base + WTCSR);

        return 0;
}

static int rza_wdt_ping(struct watchdog_device *wdev)
{
        struct rza_wdt *priv = watchdog_get_drvdata(wdev);

        writew(WTCNT_MAGIC | priv->count, priv->base + WTCNT);

        pr_debug("%s: timeout = %u\n", __func__, wdev->timeout);

        return 0;
}

static int rza_set_timeout(struct watchdog_device *wdev, unsigned int timeout)
{
        wdev->timeout = timeout;
        rza_wdt_start(wdev);
        return 0;
}

static int rza_wdt_restart(struct watchdog_device *wdev, unsigned long action,
                            void *data)
{
        struct rza_wdt *priv = watchdog_get_drvdata(wdev);

        /* Stop timer */
        writew(WTCSR_MAGIC | 0, priv->base + WTCSR);

        /* Must dummy read WRCSR:WOVF at least once before clearing */
        readb(priv->base + WRCSR);
        writew(WRCSR_CLEAR_WOVF, priv->base + WRCSR);

        /*
         * Start timer with fastest clock source and only 1 clock left before
         * overflow with reset option enabled.
         */
        writew(WRCSR_MAGIC | WRCSR_RSTE, priv->base + WRCSR);
        writew(WTCNT_MAGIC | 255, priv->base + WTCNT);
        writew(WTCSR_MAGIC | WTSCR_WT | WTSCR_TME, priv->base + WTCSR);

        /*
         * Actually make sure the above sequence hits hardware before sleeping.
         */
        wmb();

        /* Wait for WDT overflow (reset) */
        udelay(20);

        return 0;
}

static const struct watchdog_info rza_wdt_ident = {
        .options = WDIOF_MAGICCLOSE | WDIOF_KEEPALIVEPING | WDIOF_SETTIMEOUT,
        .identity = "Renesas RZ/A WDT Watchdog",
};

static const struct watchdog_ops rza_wdt_ops = {
        .owner = THIS_MODULE,
        .start = rza_wdt_start,
        .stop = rza_wdt_stop,
        .ping = rza_wdt_ping,
        .set_timeout = rza_set_timeout,
        .restart = rza_wdt_restart,
};

static int rza_wdt_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct rza_wdt *priv;
        unsigned long rate;
        int ret;

        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);

        priv->clk = devm_clk_get(dev, NULL);
        if (IS_ERR(priv->clk))
                return PTR_ERR(priv->clk);

        rate = clk_get_rate(priv->clk);
        if (rate < 16384) {
                dev_err(dev, "invalid clock rate (%ld)\n", rate);
                return -ENOENT;
        }

        priv->wdev.info = &rza_wdt_ident,
        priv->wdev.ops = &rza_wdt_ops,
        priv->wdev.parent = dev;

        priv->cks = (u8)(uintptr_t) of_device_get_match_data(dev);
        if (priv->cks == CKS_4BIT) {
                /* Assume slowest clock rate possible (CKS=0xF) */
                priv->wdev.max_timeout = (DIVIDER_4BIT * U8_MAX) / rate;

        } else if (priv->cks == CKS_3BIT) {
                /* Assume slowest clock rate possible (CKS=7) */
                rate /= DIVIDER_3BIT;

                /*
                 * Since the max possible timeout of our 8-bit count
                 * register is less than a second, we must use
                 * max_hw_heartbeat_ms.
                 */
                priv->wdev.max_hw_heartbeat_ms = (1000 * U8_MAX) / rate;
                dev_dbg(dev, "max hw timeout of %dms\n",
                        priv->wdev.max_hw_heartbeat_ms);
        }

        priv->wdev.min_timeout = 1;
        priv->wdev.timeout = DEFAULT_TIMEOUT;

        watchdog_init_timeout(&priv->wdev, 0, dev);
        watchdog_set_drvdata(&priv->wdev, priv);

        ret = devm_watchdog_register_device(dev, &priv->wdev);
        if (ret)
                dev_err(dev, "Cannot register watchdog device\n");

        return ret;
}

static const struct of_device_id rza_wdt_of_match[] = {
        { .compatible = "renesas,r7s9210-wdt",  .data = (void *)CKS_4BIT, },
        { .compatible = "renesas,rza-wdt",      .data = (void *)CKS_3BIT, },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, rza_wdt_of_match);

static struct platform_driver rza_wdt_driver = {
        .probe = rza_wdt_probe,
        .driver = {
                .name = "rza_wdt",
                .of_match_table = rza_wdt_of_match,
        },
};

module_platform_driver(rza_wdt_driver);

MODULE_DESCRIPTION("Renesas RZ/A WDT Driver");
MODULE_AUTHOR("Chris Brandt <chris.brandt@renesas.com>");
MODULE_LICENSE("GPL v2");