/*
 * Intel Management Engine Interface (Intel MEI) Linux driver
 * Copyright (c) 2015, Intel Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/interrupt.h>
#include <linux/debugfs.h>
#include <linux/completion.h>
#include <linux/watchdog.h>

#include <linux/uuid.h>
#include <linux/mei_cl_bus.h>

/*
 * iAMT Watchdog Device
 */
#define INTEL_AMT_WATCHDOG_ID "iamt_wdt"

#define MEI_WDT_DEFAULT_TIMEOUT   120  /* seconds */
#define MEI_WDT_MIN_TIMEOUT       120  /* seconds */
#define MEI_WDT_MAX_TIMEOUT     65535  /* seconds */

/* Commands */
#define MEI_MANAGEMENT_CONTROL 0x02

/* MEI Management Control version number */
#define MEI_MC_VERSION_NUMBER  0x10

/* Sub Commands */
#define MEI_MC_START_WD_TIMER_REQ  0x13
#define MEI_MC_START_WD_TIMER_RES  0x83
#define   MEI_WDT_STATUS_SUCCESS 0
#define   MEI_WDT_WDSTATE_NOT_REQUIRED 0x1
#define MEI_MC_STOP_WD_TIMER_REQ   0x14

/**
 * enum mei_wdt_state - internal watchdog state
 *
 * @MEI_WDT_PROBE: wd in probing stage
 * @MEI_WDT_IDLE: wd is idle and not opened
 * @MEI_WDT_START: wd was opened, start was called
 * @MEI_WDT_RUNNING: wd is expecting keep alive pings
 * @MEI_WDT_STOPPING: wd is stopping and will move to IDLE
 * @MEI_WDT_NOT_REQUIRED: wd device is not required
 */
enum mei_wdt_state {
        MEI_WDT_PROBE,
        MEI_WDT_IDLE,
        MEI_WDT_START,
        MEI_WDT_RUNNING,
        MEI_WDT_STOPPING,
        MEI_WDT_NOT_REQUIRED,
};

static const char *mei_wdt_state_str(enum mei_wdt_state state)
{
        switch (state) {
        case MEI_WDT_PROBE:
                return "PROBE";
        case MEI_WDT_IDLE:
                return "IDLE";
        case MEI_WDT_START:
                return "START";
        case MEI_WDT_RUNNING:
                return "RUNNING";
        case MEI_WDT_STOPPING:
                return "STOPPING";
        case MEI_WDT_NOT_REQUIRED:
                return "NOT_REQUIRED";
        default:
                return "unknown";
        }
}

/**
 * struct mei_wdt - mei watchdog driver
 * @wdd: watchdog device
 *
 * @cldev: mei watchdog client device
 * @state: watchdog internal state
 * @resp_required: ping required response
 * @response: ping response completion
 * @unregister: unregister worker
 * @reg_lock: watchdog device registration lock
 * @timeout: watchdog current timeout
 *
 * @dbgfs_dir: debugfs dir entry
 */
struct mei_wdt {
        struct watchdog_device wdd;

        struct mei_cl_device *cldev;
        enum mei_wdt_state state;
        bool resp_required;
        struct completion response;
        struct work_struct unregister;
        struct mutex reg_lock;
        u16 timeout;

#if IS_ENABLED(CONFIG_DEBUG_FS)
        struct dentry *dbgfs_dir;
#endif /* CONFIG_DEBUG_FS */
};

/*
 * struct mei_mc_hdr - Management Control Command Header
 *
 * @command: Management Control (0x2)
 * @bytecount: Number of bytes in the message beyond this byte
 * @subcommand: Management Control Subcommand
 * @versionnumber: Management Control Version (0x10)
 */
struct mei_mc_hdr {
        u8 command;
        u8 bytecount;
        u8 subcommand;
        u8 versionnumber;
};

/**
 * struct mei_wdt_start_request watchdog start/ping
 *
 * @hdr: Management Control Command Header
 * @timeout: timeout value
 * @reserved: reserved (legacy)
 */
struct mei_wdt_start_request {
        struct mei_mc_hdr hdr;
        u16 timeout;
        u8 reserved[17];
} __packed;

/**
 * struct mei_wdt_start_response watchdog start/ping response
 *
 * @hdr: Management Control Command Header
 * @status: operation status
 * @wdstate: watchdog status bit mask
 */
struct mei_wdt_start_response {
        struct mei_mc_hdr hdr;
        u8 status;
        u8 wdstate;
} __packed;

/**
 * struct mei_wdt_stop_request - watchdog stop
 *
 * @hdr: Management Control Command Header
 */
struct mei_wdt_stop_request {
        struct mei_mc_hdr hdr;
} __packed;

/**
 * mei_wdt_ping - send wd start/ping command
 *
 * @wdt: mei watchdog device
 *
 * Return: 0 on success,
 *         negative errno code on failure
 */
static int mei_wdt_ping(struct mei_wdt *wdt)
{
        struct mei_wdt_start_request req;
        const size_t req_len = sizeof(req);
        int ret;

        memset(&req, 0, req_len);
        req.hdr.command = MEI_MANAGEMENT_CONTROL;
        req.hdr.bytecount = req_len - offsetof(struct mei_mc_hdr, subcommand);
        req.hdr.subcommand = MEI_MC_START_WD_TIMER_REQ;
        req.hdr.versionnumber = MEI_MC_VERSION_NUMBER;
        req.timeout = wdt->timeout;

        ret = mei_cldev_send(wdt->cldev, (u8 *)&req, req_len);
        if (ret < 0)
                return ret;

        return 0;
}

/**
 * mei_wdt_stop - send wd stop command
 *
 * @wdt: mei watchdog device
 *
 * Return: 0 on success,
 *         negative errno code on failure
 */
static int mei_wdt_stop(struct mei_wdt *wdt)
{
        struct mei_wdt_stop_request req;
        const size_t req_len = sizeof(req);
        int ret;

        memset(&req, 0, req_len);
        req.hdr.command = MEI_MANAGEMENT_CONTROL;
        req.hdr.bytecount = req_len - offsetof(struct mei_mc_hdr, subcommand);
        req.hdr.subcommand = MEI_MC_STOP_WD_TIMER_REQ;
        req.hdr.versionnumber = MEI_MC_VERSION_NUMBER;

        ret = mei_cldev_send(wdt->cldev, (u8 *)&req, req_len);
        if (ret < 0)
                return ret;

        return 0;
}

/**
 * mei_wdt_ops_start - wd start command from the watchdog core.
 *
 * @wdd: watchdog device
 *
 * Return: 0 on success or -ENODEV;
 */
static int mei_wdt_ops_start(struct watchdog_device *wdd)
{
        struct mei_wdt *wdt = watchdog_get_drvdata(wdd);

        wdt->state = MEI_WDT_START;
        wdd->timeout = wdt->timeout;
        return 0;
}

/**
 * mei_wdt_ops_stop - wd stop command from the watchdog core.
 *
 * @wdd: watchdog device
 *
 * Return: 0 if success, negative errno code for failure
 */
static int mei_wdt_ops_stop(struct watchdog_device *wdd)
{
        struct mei_wdt *wdt = watchdog_get_drvdata(wdd);
        int ret;

        if (wdt->state != MEI_WDT_RUNNING)
                return 0;

        wdt->state = MEI_WDT_STOPPING;

        ret = mei_wdt_stop(wdt);
        if (ret)
                return ret;

        wdt->state = MEI_WDT_IDLE;

        return 0;
}

/**
 * mei_wdt_ops_ping - wd ping command from the watchdog core.
 *
 * @wdd: watchdog device
 *
 * Return: 0 if success, negative errno code on failure
 */
static int mei_wdt_ops_ping(struct watchdog_device *wdd)
{
        struct mei_wdt *wdt = watchdog_get_drvdata(wdd);
        int ret;

        if (wdt->state != MEI_WDT_START && wdt->state != MEI_WDT_RUNNING)
                return 0;

        if (wdt->resp_required)
                init_completion(&wdt->response);

        wdt->state = MEI_WDT_RUNNING;
        ret = mei_wdt_ping(wdt);
        if (ret)
                return ret;

        if (wdt->resp_required)
                ret = wait_for_completion_killable(&wdt->response);

        return ret;
}

/**
 * mei_wdt_ops_set_timeout - wd set timeout command from the watchdog core.
 *
 * @wdd: watchdog device
 * @timeout: timeout value to set
 *
 * Return: 0 if success, negative errno code for failure
 */
static int mei_wdt_ops_set_timeout(struct watchdog_device *wdd,
                                   unsigned int timeout)
{

        struct mei_wdt *wdt = watchdog_get_drvdata(wdd);

        /* valid value is already checked by the caller */
        wdt->timeout = timeout;
        wdd->timeout = timeout;

        return 0;
}

static const struct watchdog_ops wd_ops = {
        .owner       = THIS_MODULE,
        .start       = mei_wdt_ops_start,
        .stop        = mei_wdt_ops_stop,
        .ping        = mei_wdt_ops_ping,
        .set_timeout = mei_wdt_ops_set_timeout,
};

/* not const as the firmware_version field need to be retrieved */
static struct watchdog_info wd_info = {
        .identity = INTEL_AMT_WATCHDOG_ID,
        .options  = WDIOF_KEEPALIVEPING |
                    WDIOF_SETTIMEOUT |
                    WDIOF_ALARMONLY,
};

/**
 * __mei_wdt_is_registered - check if wdt is registered
 *
 * @wdt: mei watchdog device
 *
 * Return: true if the wdt is registered with the watchdog subsystem
 * Locking: should be called under wdt->reg_lock
 */
static inline bool __mei_wdt_is_registered(struct mei_wdt *wdt)
{
        return !!watchdog_get_drvdata(&wdt->wdd);
}

/**
 * mei_wdt_unregister - unregister from the watchdog subsystem
 *
 * @wdt: mei watchdog device
 */
static void mei_wdt_unregister(struct mei_wdt *wdt)
{
        mutex_lock(&wdt->reg_lock);

        if (__mei_wdt_is_registered(wdt)) {
                watchdog_unregister_device(&wdt->wdd);
                watchdog_set_drvdata(&wdt->wdd, NULL);
                memset(&wdt->wdd, 0, sizeof(wdt->wdd));
        }

        mutex_unlock(&wdt->reg_lock);
}

/**
 * mei_wdt_register - register with the watchdog subsystem
 *
 * @wdt: mei watchdog device
 *
 * Return: 0 if success, negative errno code for failure
 */
static int mei_wdt_register(struct mei_wdt *wdt)
{
        struct device *dev;
        int ret;

        if (!wdt || !wdt->cldev)
                return -EINVAL;

        dev = &wdt->cldev->dev;

        mutex_lock(&wdt->reg_lock);

        if (__mei_wdt_is_registered(wdt)) {
                ret = 0;
                goto out;
        }

        wdt->wdd.info = &wd_info;
        wdt->wdd.ops = &wd_ops;
        wdt->wdd.parent = dev;
        wdt->wdd.timeout = MEI_WDT_DEFAULT_TIMEOUT;
        wdt->wdd.min_timeout = MEI_WDT_MIN_TIMEOUT;
        wdt->wdd.max_timeout = MEI_WDT_MAX_TIMEOUT;

        watchdog_set_drvdata(&wdt->wdd, wdt);
        watchdog_stop_on_reboot(&wdt->wdd);

        ret = watchdog_register_device(&wdt->wdd);
        if (ret) {
                dev_err(dev, "unable to register watchdog device = %d.\n", ret);
                watchdog_set_drvdata(&wdt->wdd, NULL);
        }

        wdt->state = MEI_WDT_IDLE;

out:
        mutex_unlock(&wdt->reg_lock);
        return ret;
}

static void mei_wdt_unregister_work(struct work_struct *work)
{
        struct mei_wdt *wdt = container_of(work, struct mei_wdt, unregister);

        mei_wdt_unregister(wdt);
}

/**
 * mei_wdt_rx - callback for data receive
 *
 * @cldev: bus device
 */
static void mei_wdt_rx(struct mei_cl_device *cldev)
{
        struct mei_wdt *wdt = mei_cldev_get_drvdata(cldev);
        struct mei_wdt_start_response res;
        const size_t res_len = sizeof(res);
        int ret;

        ret = mei_cldev_recv(wdt->cldev, (u8 *)&res, res_len);
        if (ret < 0) {
                dev_err(&cldev->dev, "failure in recv %d\n", ret);
                return;
        }

        /* Empty response can be sent on stop */
        if (ret == 0)
                return;

        if (ret < sizeof(struct mei_mc_hdr)) {
                dev_err(&cldev->dev, "recv small data %d\n", ret);
                return;
        }

        if (res.hdr.command != MEI_MANAGEMENT_CONTROL ||
            res.hdr.versionnumber != MEI_MC_VERSION_NUMBER) {
                dev_err(&cldev->dev, "wrong command received\n");
                return;
        }

        if (res.hdr.subcommand != MEI_MC_START_WD_TIMER_RES) {
                dev_warn(&cldev->dev, "unsupported command %d :%s[%d]\n",
                         res.hdr.subcommand,
                         mei_wdt_state_str(wdt->state),
                         wdt->state);
                return;
        }

        /* Run the unregistration in a worker as this can be
         * run only after ping completion, otherwise the flow will
         * deadlock on watchdog core mutex.
         */
        if (wdt->state == MEI_WDT_RUNNING) {
                if (res.wdstate & MEI_WDT_WDSTATE_NOT_REQUIRED) {
                        wdt->state = MEI_WDT_NOT_REQUIRED;
                        schedule_work(&wdt->unregister);
                }
                goto out;
        }

        if (wdt->state == MEI_WDT_PROBE) {
                if (res.wdstate & MEI_WDT_WDSTATE_NOT_REQUIRED) {
                        wdt->state = MEI_WDT_NOT_REQUIRED;
                } else {
                        /* stop the watchdog and register watchdog device */
                        mei_wdt_stop(wdt);
                        mei_wdt_register(wdt);
                }
                return;
        }

        dev_warn(&cldev->dev, "not in correct state %s[%d]\n",
                         mei_wdt_state_str(wdt->state), wdt->state);

out:
        if (!completion_done(&wdt->response))
                complete(&wdt->response);
}

/*
 * mei_wdt_notif - callback for event notification
 *
 * @cldev: bus device
 */
static void mei_wdt_notif(struct mei_cl_device *cldev)
{
        struct mei_wdt *wdt = mei_cldev_get_drvdata(cldev);

        if (wdt->state != MEI_WDT_NOT_REQUIRED)
                return;

        mei_wdt_register(wdt);
}

#if IS_ENABLED(CONFIG_DEBUG_FS)

static ssize_t mei_dbgfs_read_activation(struct file *file, char __user *ubuf,
                                        size_t cnt, loff_t *ppos)
{
        struct mei_wdt *wdt = file->private_data;
        const size_t bufsz = 32;
        char buf[32];
        ssize_t pos;

        mutex_lock(&wdt->reg_lock);
        pos = scnprintf(buf, bufsz, "%s\n",
                __mei_wdt_is_registered(wdt) ? "activated" : "deactivated");
        mutex_unlock(&wdt->reg_lock);

        return simple_read_from_buffer(ubuf, cnt, ppos, buf, pos);
}

static const struct file_operations dbgfs_fops_activation = {
        .open    = simple_open,
        .read    = mei_dbgfs_read_activation,
        .llseek  = generic_file_llseek,
};

static ssize_t mei_dbgfs_read_state(struct file *file, char __user *ubuf,
                                    size_t cnt, loff_t *ppos)
{
        struct mei_wdt *wdt = file->private_data;
        const size_t bufsz = 32;
        char buf[bufsz];
        ssize_t pos;

        pos = scnprintf(buf, bufsz, "state: %s\n",
                         mei_wdt_state_str(wdt->state));

        return simple_read_from_buffer(ubuf, cnt, ppos, buf, pos);
}

static const struct file_operations dbgfs_fops_state = {
        .open = simple_open,
        .read = mei_dbgfs_read_state,
        .llseek = generic_file_llseek,
};

static void dbgfs_unregister(struct mei_wdt *wdt)
{
        debugfs_remove_recursive(wdt->dbgfs_dir);
        wdt->dbgfs_dir = NULL;
}

static int dbgfs_register(struct mei_wdt *wdt)
{
        struct dentry *dir, *f;

        dir = debugfs_create_dir(KBUILD_MODNAME, NULL);
        if (!dir)
                return -ENOMEM;

        wdt->dbgfs_dir = dir;
        f = debugfs_create_file("state", S_IRUSR, dir, wdt, &dbgfs_fops_state);
        if (!f)
                goto err;

        f = debugfs_create_file("activation",  S_IRUSR,
                                dir, wdt, &dbgfs_fops_activation);
        if (!f)
                goto err;

        return 0;
err:
        dbgfs_unregister(wdt);
        return -ENODEV;
}

#else

static inline void dbgfs_unregister(struct mei_wdt *wdt) {}

static inline int dbgfs_register(struct mei_wdt *wdt)
{
        return 0;
}
#endif /* CONFIG_DEBUG_FS */

static int mei_wdt_probe(struct mei_cl_device *cldev,
                         const struct mei_cl_device_id *id)
{
        struct mei_wdt *wdt;
        int ret;

        wdt = kzalloc(sizeof(struct mei_wdt), GFP_KERNEL);
        if (!wdt)
                return -ENOMEM;

        wdt->timeout = MEI_WDT_DEFAULT_TIMEOUT;
        wdt->state = MEI_WDT_PROBE;
        wdt->cldev = cldev;
        wdt->resp_required = mei_cldev_ver(cldev) > 0x1;
        mutex_init(&wdt->reg_lock);
        init_completion(&wdt->response);
        INIT_WORK(&wdt->unregister, mei_wdt_unregister_work);

        mei_cldev_set_drvdata(cldev, wdt);

        ret = mei_cldev_enable(cldev);
        if (ret < 0) {
                dev_err(&cldev->dev, "Could not enable cl device\n");
                goto err_out;
        }

        ret = mei_cldev_register_rx_cb(wdt->cldev, mei_wdt_rx);
        if (ret) {
                dev_err(&cldev->dev, "Could not reg rx event ret=%d\n", ret);
                goto err_disable;
        }

        ret = mei_cldev_register_notif_cb(wdt->cldev, mei_wdt_notif);
        /* on legacy devices notification is not supported
         */
        if (ret && ret != -EOPNOTSUPP) {
                dev_err(&cldev->dev, "Could not reg notif event ret=%d\n", ret);
                goto err_disable;
        }

        wd_info.firmware_version = mei_cldev_ver(cldev);

        if (wdt->resp_required)
                ret = mei_wdt_ping(wdt);
        else
                ret = mei_wdt_register(wdt);

        if (ret)
                goto err_disable;

        if (dbgfs_register(wdt))
                dev_warn(&cldev->dev, "cannot register debugfs\n");

        return 0;

err_disable:
        mei_cldev_disable(cldev);

err_out:
        kfree(wdt);

        return ret;
}

static int mei_wdt_remove(struct mei_cl_device *cldev)
{
        struct mei_wdt *wdt = mei_cldev_get_drvdata(cldev);

        /* Free the caller in case of fw initiated or unexpected reset */
        if (!completion_done(&wdt->response))
                complete(&wdt->response);

        cancel_work_sync(&wdt->unregister);

        mei_wdt_unregister(wdt);

        mei_cldev_disable(cldev);

        dbgfs_unregister(wdt);

        kfree(wdt);

        return 0;
}

#define MEI_UUID_WD UUID_LE(0x05B79A6F, 0x4628, 0x4D7F, \
                            0x89, 0x9D, 0xA9, 0x15, 0x14, 0xCB, 0x32, 0xAB)

static struct mei_cl_device_id mei_wdt_tbl[] = {
        { .uuid = MEI_UUID_WD, .version = MEI_CL_VERSION_ANY },
        /* required last entry */
        { }
};
MODULE_DEVICE_TABLE(mei, mei_wdt_tbl);

static struct mei_cl_driver mei_wdt_driver = {
        .id_table = mei_wdt_tbl,
        .name = KBUILD_MODNAME,

        .probe = mei_wdt_probe,
        .remove = mei_wdt_remove,
};

module_mei_cl_driver(mei_wdt_driver);

MODULE_AUTHOR("Intel Corporation");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Device driver for Intel MEI iAMT watchdog");