/*
 * Watchdog driver for Alphascale ASM9260.
 *
 * Copyright (c) 2014 Oleksij Rempel <linux@rempel-privat.de>
 *
 * Licensed under GPLv2 or later.
 */

#include <linux/bitops.h>
#include <linux/clk.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/reset.h>
#include <linux/watchdog.h>

#define CLOCK_FREQ      1000000

/* Watchdog Mode register */
#define HW_WDMOD                        0x00
/* Wake interrupt. Set by HW, can't be cleared. */
#define BM_MOD_WDINT                    BIT(3)
/* This bit set if timeout reached. Cleared by SW. */
#define BM_MOD_WDTOF                    BIT(2)
/* HW Reset on timeout */
#define BM_MOD_WDRESET                  BIT(1)
/* WD enable */
#define BM_MOD_WDEN                     BIT(0)

/*
 * Watchdog Timer Constant register
 * Minimal value is 0xff, the meaning of this value
 * depends on used clock: T = WDCLK * (0xff + 1) * 4
 */
#define HW_WDTC                         0x04
#define BM_WDTC_MAX(freq)               (0x7fffffff / (freq))

/* Watchdog Feed register */
#define HW_WDFEED                       0x08

/* Watchdog Timer Value register */
#define HW_WDTV                         0x0c

#define ASM9260_WDT_DEFAULT_TIMEOUT     30

enum asm9260_wdt_mode {
        HW_RESET,
        SW_RESET,
        DEBUG,
};

struct asm9260_wdt_priv {
        struct device           *dev;
        struct watchdog_device  wdd;
        struct clk              *clk;
        struct clk              *clk_ahb;
        struct reset_control    *rst;

        void __iomem            *iobase;
        int                     irq;
        unsigned long           wdt_freq;
        enum asm9260_wdt_mode   mode;
};

static int asm9260_wdt_feed(struct watchdog_device *wdd)
{
        struct asm9260_wdt_priv *priv = watchdog_get_drvdata(wdd);

        iowrite32(0xaa, priv->iobase + HW_WDFEED);
        iowrite32(0x55, priv->iobase + HW_WDFEED);

        return 0;
}

static unsigned int asm9260_wdt_gettimeleft(struct watchdog_device *wdd)
{
        struct asm9260_wdt_priv *priv = watchdog_get_drvdata(wdd);
        u32 counter;

        counter = ioread32(priv->iobase + HW_WDTV);

        return counter / priv->wdt_freq;
}

static int asm9260_wdt_updatetimeout(struct watchdog_device *wdd)
{
        struct asm9260_wdt_priv *priv = watchdog_get_drvdata(wdd);
        u32 counter;

        counter = wdd->timeout * priv->wdt_freq;

        iowrite32(counter, priv->iobase + HW_WDTC);

        return 0;
}

static int asm9260_wdt_enable(struct watchdog_device *wdd)
{
        struct asm9260_wdt_priv *priv = watchdog_get_drvdata(wdd);
        u32 mode = 0;

        if (priv->mode == HW_RESET)
                mode = BM_MOD_WDRESET;

        iowrite32(BM_MOD_WDEN | mode, priv->iobase + HW_WDMOD);

        asm9260_wdt_updatetimeout(wdd);

        asm9260_wdt_feed(wdd);

        return 0;
}

static int asm9260_wdt_disable(struct watchdog_device *wdd)
{
        struct asm9260_wdt_priv *priv = watchdog_get_drvdata(wdd);

        /* The only way to disable WD is to reset it. */
        reset_control_assert(priv->rst);
        reset_control_deassert(priv->rst);

        return 0;
}

static int asm9260_wdt_settimeout(struct watchdog_device *wdd, unsigned int to)
{
        wdd->timeout = to;
        asm9260_wdt_updatetimeout(wdd);

        return 0;
}

static void asm9260_wdt_sys_reset(struct asm9260_wdt_priv *priv)
{
        /* init WD if it was not started */

        iowrite32(BM_MOD_WDEN | BM_MOD_WDRESET, priv->iobase + HW_WDMOD);

        iowrite32(0xff, priv->iobase + HW_WDTC);
        /* first pass correct sequence */
        asm9260_wdt_feed(&priv->wdd);
        /*
         * Then write wrong pattern to the feed to trigger reset
         * ASAP.
         */
        iowrite32(0xff, priv->iobase + HW_WDFEED);

        mdelay(1000);
}

static irqreturn_t asm9260_wdt_irq(int irq, void *devid)
{
        struct asm9260_wdt_priv *priv = devid;
        u32 stat;

        stat = ioread32(priv->iobase + HW_WDMOD);
        if (!(stat & BM_MOD_WDINT))
                return IRQ_NONE;

        if (priv->mode == DEBUG) {
                dev_info(priv->dev, "Watchdog Timeout. Do nothing.\n");
        } else {
                dev_info(priv->dev, "Watchdog Timeout. Doing SW Reset.\n");
                asm9260_wdt_sys_reset(priv);
        }

        return IRQ_HANDLED;
}

static int asm9260_restart(struct watchdog_device *wdd, unsigned long action,
                           void *data)
{
        struct asm9260_wdt_priv *priv = watchdog_get_drvdata(wdd);

        asm9260_wdt_sys_reset(priv);

        return 0;
}

static const struct watchdog_info asm9260_wdt_ident = {
        .options          =     WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING
                                | WDIOF_MAGICCLOSE,
        .identity         =     "Alphascale asm9260 Watchdog",
};

static const struct watchdog_ops asm9260_wdt_ops = {
        .owner          = THIS_MODULE,
        .start          = asm9260_wdt_enable,
        .stop           = asm9260_wdt_disable,
        .get_timeleft   = asm9260_wdt_gettimeleft,
        .ping           = asm9260_wdt_feed,
        .set_timeout    = asm9260_wdt_settimeout,
        .restart        = asm9260_restart,
};

static int asm9260_wdt_get_dt_clks(struct asm9260_wdt_priv *priv)
{
        int err;
        unsigned long clk;

        priv->clk = devm_clk_get(priv->dev, "mod");
        if (IS_ERR(priv->clk)) {
                dev_err(priv->dev, "Failed to get \"mod\" clk\n");
                return PTR_ERR(priv->clk);
        }

        /* configure AHB clock */
        priv->clk_ahb = devm_clk_get(priv->dev, "ahb");
        if (IS_ERR(priv->clk_ahb)) {
                dev_err(priv->dev, "Failed to get \"ahb\" clk\n");
                return PTR_ERR(priv->clk_ahb);
        }

        err = clk_prepare_enable(priv->clk_ahb);
        if (err) {
                dev_err(priv->dev, "Failed to enable ahb_clk!\n");
                return err;
        }

        err = clk_set_rate(priv->clk, CLOCK_FREQ);
        if (err) {
                clk_disable_unprepare(priv->clk_ahb);
                dev_err(priv->dev, "Failed to set rate!\n");
                return err;
        }

        err = clk_prepare_enable(priv->clk);
        if (err) {
                clk_disable_unprepare(priv->clk_ahb);
                dev_err(priv->dev, "Failed to enable clk!\n");
                return err;
        }

        /* wdt has internal divider */
        clk = clk_get_rate(priv->clk);
        if (!clk) {
                clk_disable_unprepare(priv->clk);
                clk_disable_unprepare(priv->clk_ahb);
                dev_err(priv->dev, "Failed, clk is 0!\n");
                return -EINVAL;
        }

        priv->wdt_freq = clk / 2;

        return 0;
}

static void asm9260_wdt_get_dt_mode(struct asm9260_wdt_priv *priv)
{
        const char *tmp;
        int ret;

        /* default mode */
        priv->mode = HW_RESET;

        ret = of_property_read_string(priv->dev->of_node,
                                      "alphascale,mode", &tmp);
        if (ret < 0)
                return;

        if (!strcmp(tmp, "hw"))
                priv->mode = HW_RESET;
        else if (!strcmp(tmp, "sw"))
                priv->mode = SW_RESET;
        else if (!strcmp(tmp, "debug"))
                priv->mode = DEBUG;
        else
                dev_warn(priv->dev, "unknown reset-type: %s. Using default \"hw\" mode.",
                         tmp);
}

static int asm9260_wdt_probe(struct platform_device *pdev)
{
        struct asm9260_wdt_priv *priv;
        struct watchdog_device *wdd;
        struct resource *res;
        int ret;
        const char * const mode_name[] = { "hw", "sw", "debug", };

        priv = devm_kzalloc(&pdev->dev, sizeof(struct asm9260_wdt_priv),
                            GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        priv->dev = &pdev->dev;

        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        priv->iobase = devm_ioremap_resource(&pdev->dev, res);
        if (IS_ERR(priv->iobase))
                return PTR_ERR(priv->iobase);

        ret = asm9260_wdt_get_dt_clks(priv);
        if (ret)
                return ret;

        priv->rst = devm_reset_control_get_exclusive(&pdev->dev, "wdt_rst");
        if (IS_ERR(priv->rst))
                return PTR_ERR(priv->rst);

        wdd = &priv->wdd;
        wdd->info = &asm9260_wdt_ident;
        wdd->ops = &asm9260_wdt_ops;
        wdd->min_timeout = 1;
        wdd->max_timeout = BM_WDTC_MAX(priv->wdt_freq);
        wdd->parent = &pdev->dev;

        watchdog_set_drvdata(wdd, priv);

        /*
         * If 'timeout-sec' unspecified in devicetree, assume a 30 second
         * default, unless the max timeout is less than 30 seconds, then use
         * the max instead.
         */
        wdd->timeout = ASM9260_WDT_DEFAULT_TIMEOUT;
        watchdog_init_timeout(wdd, 0, &pdev->dev);

        asm9260_wdt_get_dt_mode(priv);

        if (priv->mode != HW_RESET)
                priv->irq = platform_get_irq(pdev, 0);

        if (priv->irq > 0) {
                /*
                 * Not all supported platforms specify an interrupt for the
                 * watchdog, so let's make it optional.
                 */
                ret = devm_request_irq(&pdev->dev, priv->irq,
                                       asm9260_wdt_irq, 0, pdev->name, priv);
                if (ret < 0)
                        dev_warn(&pdev->dev, "failed to request IRQ\n");
        }

        watchdog_set_restart_priority(wdd, 128);

        ret = watchdog_register_device(wdd);
        if (ret)
                goto clk_off;

        platform_set_drvdata(pdev, priv);

        dev_info(&pdev->dev, "Watchdog enabled (timeout: %d sec, mode: %s)\n",
                 wdd->timeout, mode_name[priv->mode]);
        return 0;

clk_off:
        clk_disable_unprepare(priv->clk);
        clk_disable_unprepare(priv->clk_ahb);
        return ret;
}

static void asm9260_wdt_shutdown(struct platform_device *pdev)
{
        struct asm9260_wdt_priv *priv = platform_get_drvdata(pdev);

        asm9260_wdt_disable(&priv->wdd);
}

static int asm9260_wdt_remove(struct platform_device *pdev)
{
        struct asm9260_wdt_priv *priv = platform_get_drvdata(pdev);

        asm9260_wdt_disable(&priv->wdd);

        watchdog_unregister_device(&priv->wdd);

        clk_disable_unprepare(priv->clk);
        clk_disable_unprepare(priv->clk_ahb);

        return 0;
}

static const struct of_device_id asm9260_wdt_of_match[] = {
        { .compatible = "alphascale,asm9260-wdt"},
        {},
};
MODULE_DEVICE_TABLE(of, asm9260_wdt_of_match);

static struct platform_driver asm9260_wdt_driver = {
        .driver = {
                .name = "asm9260-wdt",
                .of_match_table = asm9260_wdt_of_match,
        },
        .probe = asm9260_wdt_probe,
        .remove = asm9260_wdt_remove,
        .shutdown = asm9260_wdt_shutdown,
};
module_platform_driver(asm9260_wdt_driver);

MODULE_DESCRIPTION("asm9260 WatchDog Timer Driver");
MODULE_AUTHOR("Oleksij Rempel <linux@rempel-privat.de>");
MODULE_LICENSE("GPL");