// SPDX-License-Identifier: GPL-2.0+
/*
 *      exar_wdt.c - Driver for the watchdog present in some
 *                   Exar/MaxLinear UART chips like the XR28V38x.
 *
 *      (c) Copyright 2022 D. Müller <d.mueller@elsoft.ch>.
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/io.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/watchdog.h>

#define DRV_NAME        "exar_wdt"

static const unsigned short sio_config_ports[] = { 0x2e, 0x4e };
static const unsigned char sio_enter_keys[] = { 0x67, 0x77, 0x87, 0xA0 };
#define EXAR_EXIT_KEY   0xAA

#define EXAR_LDN        0x07
#define EXAR_DID        0x20
#define EXAR_VID        0x23
#define EXAR_WDT        0x26
#define EXAR_ACT        0x30
#define EXAR_RTBASE     0x60

#define EXAR_WDT_LDEV   0x08

#define EXAR_VEN_ID     0x13A8
#define EXAR_DEV_382    0x0382
#define EXAR_DEV_384    0x0384

/* WDT runtime registers */
#define WDT_CTRL        0x00
#define WDT_VAL         0x01

#define WDT_UNITS_10MS  0x0     /* the 10 millisec unit of the HW is not used */
#define WDT_UNITS_SEC   0x2
#define WDT_UNITS_MIN   0x4

/* default WDT control for WDTOUT signal activ / rearm by read */
#define EXAR_WDT_DEF_CONF       0

struct wdt_pdev_node {
        struct list_head list;
        struct platform_device *pdev;
        const char name[16];
};

struct wdt_priv {
        /* the lock for WDT io operations */
        spinlock_t io_lock;
        struct resource wdt_res;
        struct watchdog_device wdt_dev;
        unsigned short did;
        unsigned short config_port;
        unsigned char enter_key;
        unsigned char unit;
        unsigned char timeout;
};

#define WATCHDOG_TIMEOUT 60

static int timeout = WATCHDOG_TIMEOUT;
module_param(timeout, int, 0);
MODULE_PARM_DESC(timeout,
                 "Watchdog timeout in seconds. 1<=timeout<=15300, default="
                 __MODULE_STRING(WATCHDOG_TIMEOUT) ".");

static bool nowayout = WATCHDOG_NOWAYOUT;
module_param(nowayout, bool, 0);
MODULE_PARM_DESC(nowayout,
                 "Watchdog cannot be stopped once started (default="
                 __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");

static int exar_sio_enter(const unsigned short config_port,
                          const unsigned char key)
{
        if (!request_muxed_region(config_port, 2, DRV_NAME))
                return -EBUSY;

        /* write the ENTER-KEY twice */
        outb(key, config_port);
        outb(key, config_port);

        return 0;
}

static void exar_sio_exit(const unsigned short config_port)
{
        outb(EXAR_EXIT_KEY, config_port);
        release_region(config_port, 2);
}

static unsigned char exar_sio_read(const unsigned short config_port,
                                   const unsigned char reg)
{
        outb(reg, config_port);
        return inb(config_port + 1);
}

static void exar_sio_write(const unsigned short config_port,
                           const unsigned char reg, const unsigned char val)
{
        outb(reg, config_port);
        outb(val, config_port + 1);
}

static unsigned short exar_sio_read16(const unsigned short config_port,
                                      const unsigned char reg)
{
        unsigned char msb, lsb;

        msb = exar_sio_read(config_port, reg);
        lsb = exar_sio_read(config_port, reg + 1);

        return (msb << 8) | lsb;
}

static void exar_sio_select_wdt(const unsigned short config_port)
{
        exar_sio_write(config_port, EXAR_LDN, EXAR_WDT_LDEV);
}

static void exar_wdt_arm(const struct wdt_priv *priv)
{
        unsigned short rt_base = priv->wdt_res.start;

        /* write timeout value twice to arm watchdog */
        outb(priv->timeout, rt_base + WDT_VAL);
        outb(priv->timeout, rt_base + WDT_VAL);
}

static void exar_wdt_disarm(const struct wdt_priv *priv)
{
        unsigned short rt_base = priv->wdt_res.start;

        /*
         * use two accesses with different values to make sure
         * that a combination of a previous single access and
         * the ones below with the same value are not falsely
         * interpreted as "arm watchdog"
         */
        outb(0xFF, rt_base + WDT_VAL);
        outb(0, rt_base + WDT_VAL);
}

static int exar_wdt_start(struct watchdog_device *wdog)
{
        struct wdt_priv *priv = watchdog_get_drvdata(wdog);
        unsigned short rt_base = priv->wdt_res.start;

        spin_lock(&priv->io_lock);

        exar_wdt_disarm(priv);
        outb(priv->unit, rt_base + WDT_CTRL);
        exar_wdt_arm(priv);

        spin_unlock(&priv->io_lock);
        return 0;
}

static int exar_wdt_stop(struct watchdog_device *wdog)
{
        struct wdt_priv *priv = watchdog_get_drvdata(wdog);

        spin_lock(&priv->io_lock);

        exar_wdt_disarm(priv);

        spin_unlock(&priv->io_lock);
        return 0;
}

static int exar_wdt_keepalive(struct watchdog_device *wdog)
{
        struct wdt_priv *priv = watchdog_get_drvdata(wdog);
        unsigned short rt_base = priv->wdt_res.start;

        spin_lock(&priv->io_lock);

        /* reading the WDT_VAL reg will feed the watchdog */
        inb(rt_base + WDT_VAL);

        spin_unlock(&priv->io_lock);
        return 0;
}

static int exar_wdt_set_timeout(struct watchdog_device *wdog, unsigned int t)
{
        struct wdt_priv *priv = watchdog_get_drvdata(wdog);
        bool unit_min = false;

        /*
         * if new timeout is bigger then 255 seconds, change the
         * unit to minutes and round the timeout up to the next whole minute
         */
        if (t > 255) {
                unit_min = true;
                t = DIV_ROUND_UP(t, 60);
        }

        /* save for later use in exar_wdt_start() */
        priv->unit = unit_min ? WDT_UNITS_MIN : WDT_UNITS_SEC;
        priv->timeout = t;

        wdog->timeout = unit_min ? t * 60 : t;

        if (watchdog_hw_running(wdog))
                exar_wdt_start(wdog);

        return 0;
}

static const struct watchdog_info exar_wdt_info = {
        .options        = WDIOF_KEEPALIVEPING |
                          WDIOF_SETTIMEOUT |
                          WDIOF_MAGICCLOSE,
        .identity       = "Exar XR28V38x Watchdog",
};

static const struct watchdog_ops exar_wdt_ops = {
        .owner          = THIS_MODULE,
        .start          = exar_wdt_start,
        .stop           = exar_wdt_stop,
        .ping           = exar_wdt_keepalive,
        .set_timeout    = exar_wdt_set_timeout,
};

static int exar_wdt_config(struct watchdog_device *wdog,
                           const unsigned char conf)
{
        struct wdt_priv *priv = watchdog_get_drvdata(wdog);
        int ret;

        ret = exar_sio_enter(priv->config_port, priv->enter_key);
        if (ret)
                return ret;

        exar_sio_select_wdt(priv->config_port);
        exar_sio_write(priv->config_port, EXAR_WDT, conf);

        exar_sio_exit(priv->config_port);

        return 0;
}

static int __init exar_wdt_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct wdt_priv *priv = dev->platform_data;
        struct watchdog_device *wdt_dev = &priv->wdt_dev;
        struct resource *res;
        int ret;

        res = platform_get_resource(pdev, IORESOURCE_IO, 0);
        if (!res)
                return -ENXIO;

        spin_lock_init(&priv->io_lock);

        wdt_dev->info = &exar_wdt_info;
        wdt_dev->ops = &exar_wdt_ops;
        wdt_dev->min_timeout = 1;
        wdt_dev->max_timeout = 255 * 60;

        watchdog_init_timeout(wdt_dev, timeout, NULL);
        watchdog_set_nowayout(wdt_dev, nowayout);
        watchdog_stop_on_reboot(wdt_dev);
        watchdog_stop_on_unregister(wdt_dev);
        watchdog_set_drvdata(wdt_dev, priv);

        ret = exar_wdt_config(wdt_dev, EXAR_WDT_DEF_CONF);
        if (ret)
                return ret;

        exar_wdt_set_timeout(wdt_dev, timeout);
        /* Make sure that the watchdog is not running */
        exar_wdt_stop(wdt_dev);

        ret = devm_watchdog_register_device(dev, wdt_dev);
        if (ret)
                return ret;

        dev_info(dev, "XR28V%X WDT initialized. timeout=%d sec (nowayout=%d)\n",
                 priv->did, timeout, nowayout);

        return 0;
}

static unsigned short __init exar_detect(const unsigned short config_port,
                                         const unsigned char key,
                                         unsigned short *rt_base)
{
        int ret;
        unsigned short base = 0;
        unsigned short vid, did;

        ret = exar_sio_enter(config_port, key);
        if (ret)
                return 0;

        vid = exar_sio_read16(config_port, EXAR_VID);
        did = exar_sio_read16(config_port, EXAR_DID);

        /* check for the vendor and device IDs we currently know about */
        if (vid == EXAR_VEN_ID &&
            (did == EXAR_DEV_382 ||
             did == EXAR_DEV_384)) {
                exar_sio_select_wdt(config_port);
                /* is device active? */
                if (exar_sio_read(config_port, EXAR_ACT) == 0x01)
                        base = exar_sio_read16(config_port, EXAR_RTBASE);
        }

        exar_sio_exit(config_port);

        if (base) {
                pr_debug("Found a XR28V%X WDT (conf: 0x%x / rt: 0x%04x)\n",
                         did, config_port, base);
                *rt_base = base;
                return did;
        }

        return 0;
}

static struct platform_driver exar_wdt_driver = {
        .driver = {
                .name = DRV_NAME,
        },
};

static LIST_HEAD(pdev_list);

static int __init exar_wdt_register(struct wdt_priv *priv, const int idx)
{
        struct wdt_pdev_node *n;

        n = kzalloc_obj(*n);
        if (!n)
                return -ENOMEM;

        INIT_LIST_HEAD(&n->list);

        scnprintf((char *)n->name, sizeof(n->name), DRV_NAME ".%d", idx);
        priv->wdt_res.name = n->name;

        n->pdev = platform_device_register_resndata(NULL, DRV_NAME, idx,
                                                    &priv->wdt_res, 1,
                                                    priv, sizeof(*priv));
        if (IS_ERR(n->pdev)) {
                int err = PTR_ERR(n->pdev);

                kfree(n);
                return err;
        }

        list_add_tail(&n->list, &pdev_list);

        return 0;
}

static void exar_wdt_unregister(void)
{
        struct wdt_pdev_node *n, *t;

        list_for_each_entry_safe(n, t, &pdev_list, list) {
                platform_device_unregister(n->pdev);
                list_del(&n->list);
                kfree(n);
        }
}

static int __init exar_wdt_init(void)
{
        int ret, i, j, idx = 0;

        /* search for active Exar watchdogs on all possible locations */
        for (i = 0; i < ARRAY_SIZE(sio_config_ports); i++) {
                for (j = 0; j < ARRAY_SIZE(sio_enter_keys); j++) {
                        unsigned short did, rt_base = 0;

                        did = exar_detect(sio_config_ports[i],
                                          sio_enter_keys[j],
                                          &rt_base);

                        if (did) {
                                struct wdt_priv priv = {
                                        .wdt_res = DEFINE_RES_IO(rt_base, 2),
                                        .did = did,
                                        .config_port = sio_config_ports[i],
                                        .enter_key = sio_enter_keys[j],
                                };

                                ret = exar_wdt_register(&priv, idx);
                                if (!ret)
                                        idx++;
                        }
                }
        }

        if (!idx)
                return -ENODEV;

        ret = platform_driver_probe(&exar_wdt_driver, exar_wdt_probe);
        if (ret)
                exar_wdt_unregister();

        return ret;
}

static void __exit exar_wdt_exit(void)
{
        exar_wdt_unregister();
        platform_driver_unregister(&exar_wdt_driver);
}

module_init(exar_wdt_init);
module_exit(exar_wdt_exit);

MODULE_AUTHOR("David Müller <d.mueller@elsoft.ch>");
MODULE_DESCRIPTION("Exar/MaxLinear Watchdog Driver");
MODULE_LICENSE("GPL");