/*
 * GE watchdog userspace interface
 *
 * Author:  Martyn Welch <martyn.welch@ge.com>
 *
 * Copyright 2008 GE Intelligent Platforms Embedded Systems, Inc.
 *
 * This program is free software; you can redistribute  it and/or modify it
 * under  the terms of  the GNU General  Public License as published by the
 * Free Software Foundation;  either version 2 of the  License, or (at your
 * option) any later version.
 *
 * Based on: mv64x60_wdt.c (MV64X60 watchdog userspace interface)
 *   Author: James Chapman <jchapman@katalix.com>
 */

/* TODO:
 * This driver does not provide support for the hardwares capability of sending
 * an interrupt at a programmable threshold.
 *
 * This driver currently can only support 1 watchdog - there are 2 in the
 * hardware that this driver supports. Thus one could be configured as a
 * process-based watchdog (via /dev/watchdog), the second (using the interrupt
 * capabilities) a kernel-based watchdog.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/compiler.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/miscdevice.h>
#include <linux/watchdog.h>
#include <linux/fs.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_platform.h>
#include <linux/io.h>
#include <linux/uaccess.h>

#include <sysdev/fsl_soc.h>

/*
 * The watchdog configuration register contains a pair of 2-bit fields,
 *   1.  a reload field, bits 27-26, which triggers a reload of
 *       the countdown register, and
 *   2.  an enable field, bits 25-24, which toggles between
 *       enabling and disabling the watchdog timer.
 * Bit 31 is a read-only field which indicates whether the
 * watchdog timer is currently enabled.
 *
 * The low 24 bits contain the timer reload value.
 */
#define GEF_WDC_ENABLE_SHIFT    24
#define GEF_WDC_SERVICE_SHIFT   26
#define GEF_WDC_ENABLED_SHIFT   31

#define GEF_WDC_ENABLED_TRUE    1
#define GEF_WDC_ENABLED_FALSE   0

/* Flags bits */
#define GEF_WDOG_FLAG_OPENED    0

static unsigned long wdt_flags;
static int wdt_status;
static void __iomem *gef_wdt_regs;
static int gef_wdt_timeout;
static int gef_wdt_count;
static unsigned int bus_clk;
static char expect_close;
static DEFINE_SPINLOCK(gef_wdt_spinlock);

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 gef_wdt_toggle_wdc(int enabled_predicate, int field_shift)
{
        u32 data;
        u32 enabled;
        int ret = 0;

        spin_lock(&gef_wdt_spinlock);
        data = ioread32be(gef_wdt_regs);
        enabled = (data >> GEF_WDC_ENABLED_SHIFT) & 1;

        /* only toggle the requested field if enabled state matches predicate */
        if ((enabled ^ enabled_predicate) == 0) {
                /* We write a 1, then a 2 -- to the appropriate field */
                data = (1 << field_shift) | gef_wdt_count;
                iowrite32be(data, gef_wdt_regs);

                data = (2 << field_shift) | gef_wdt_count;
                iowrite32be(data, gef_wdt_regs);
                ret = 1;
        }
        spin_unlock(&gef_wdt_spinlock);

        return ret;
}

static void gef_wdt_service(void)
{
        gef_wdt_toggle_wdc(GEF_WDC_ENABLED_TRUE,
                GEF_WDC_SERVICE_SHIFT);
}

static void gef_wdt_handler_enable(void)
{
        if (gef_wdt_toggle_wdc(GEF_WDC_ENABLED_FALSE,
                                   GEF_WDC_ENABLE_SHIFT)) {
                gef_wdt_service();
                pr_notice("watchdog activated\n");
        }
}

static void gef_wdt_handler_disable(void)
{
        if (gef_wdt_toggle_wdc(GEF_WDC_ENABLED_TRUE,
                                   GEF_WDC_ENABLE_SHIFT))
                pr_notice("watchdog deactivated\n");
}

static void gef_wdt_set_timeout(unsigned int timeout)
{
        /* maximum bus cycle count is 0xFFFFFFFF */
        if (timeout > 0xFFFFFFFF / bus_clk)
                timeout = 0xFFFFFFFF / bus_clk;

        /* Register only holds upper 24 bits, bit shifted into lower 24 */
        gef_wdt_count = (timeout * bus_clk) >> 8;
        gef_wdt_timeout = timeout;
}


static ssize_t gef_wdt_write(struct file *file, const char __user *data,
                                 size_t len, loff_t *ppos)
{
        if (len) {
                if (!nowayout) {
                        size_t i;

                        expect_close = 0;

                        for (i = 0; i != len; i++) {
                                char c;
                                if (get_user(c, data + i))
                                        return -EFAULT;
                                if (c == 'V')
                                        expect_close = 42;
                        }
                }
                gef_wdt_service();
        }

        return len;
}

static long gef_wdt_ioctl(struct file *file, unsigned int cmd,
                                                        unsigned long arg)
{
        int timeout;
        int options;
        void __user *argp = (void __user *)arg;
        static const struct watchdog_info info = {
                .options =      WDIOF_SETTIMEOUT | WDIOF_MAGICCLOSE |
                                WDIOF_KEEPALIVEPING,
                .firmware_version = 0,
                .identity = "GE watchdog",
        };

        switch (cmd) {
        case WDIOC_GETSUPPORT:
                if (copy_to_user(argp, &info, sizeof(info)))
                        return -EFAULT;
                break;

        case WDIOC_GETSTATUS:
        case WDIOC_GETBOOTSTATUS:
                if (put_user(wdt_status, (int __user *)argp))
                        return -EFAULT;
                wdt_status &= ~WDIOF_KEEPALIVEPING;
                break;

        case WDIOC_SETOPTIONS:
                if (get_user(options, (int __user *)argp))
                        return -EFAULT;

                if (options & WDIOS_DISABLECARD)
                        gef_wdt_handler_disable();

                if (options & WDIOS_ENABLECARD)
                        gef_wdt_handler_enable();
                break;

        case WDIOC_KEEPALIVE:
                gef_wdt_service();
                wdt_status |= WDIOF_KEEPALIVEPING;
                break;

        case WDIOC_SETTIMEOUT:
                if (get_user(timeout, (int __user *)argp))
                        return -EFAULT;
                gef_wdt_set_timeout(timeout);
                /* Fall through */

        case WDIOC_GETTIMEOUT:
                if (put_user(gef_wdt_timeout, (int __user *)argp))
                        return -EFAULT;
                break;

        default:
                return -ENOTTY;
        }

        return 0;
}

static int gef_wdt_open(struct inode *inode, struct file *file)
{
        if (test_and_set_bit(GEF_WDOG_FLAG_OPENED, &wdt_flags))
                return -EBUSY;

        if (nowayout)
                __module_get(THIS_MODULE);

        gef_wdt_handler_enable();

        return nonseekable_open(inode, file);
}

static int gef_wdt_release(struct inode *inode, struct file *file)
{
        if (expect_close == 42)
                gef_wdt_handler_disable();
        else {
                pr_crit("unexpected close, not stopping timer!\n");
                gef_wdt_service();
        }
        expect_close = 0;

        clear_bit(GEF_WDOG_FLAG_OPENED, &wdt_flags);

        return 0;
}

static const struct file_operations gef_wdt_fops = {
        .owner = THIS_MODULE,
        .llseek = no_llseek,
        .write = gef_wdt_write,
        .unlocked_ioctl = gef_wdt_ioctl,
        .open = gef_wdt_open,
        .release = gef_wdt_release,
};

static struct miscdevice gef_wdt_miscdev = {
        .minor = WATCHDOG_MINOR,
        .name = "watchdog",
        .fops = &gef_wdt_fops,
};


static int gef_wdt_probe(struct platform_device *dev)
{
        int timeout = 10;
        u32 freq;

        bus_clk = 133; /* in MHz */

        freq = fsl_get_sys_freq();
        if (freq != -1)
                bus_clk = freq;

        /* Map devices registers into memory */
        gef_wdt_regs = of_iomap(dev->dev.of_node, 0);
        if (gef_wdt_regs == NULL)
                return -ENOMEM;

        gef_wdt_set_timeout(timeout);

        gef_wdt_handler_disable();      /* in case timer was already running */

        return misc_register(&gef_wdt_miscdev);
}

static int gef_wdt_remove(struct platform_device *dev)
{
        misc_deregister(&gef_wdt_miscdev);

        gef_wdt_handler_disable();

        iounmap(gef_wdt_regs);

        return 0;
}

static const struct of_device_id gef_wdt_ids[] = {
        {
                .compatible = "gef,fpga-wdt",
        },
        {},
};
MODULE_DEVICE_TABLE(of, gef_wdt_ids);

static struct platform_driver gef_wdt_driver = {
        .driver = {
                .name = "gef_wdt",
                .of_match_table = gef_wdt_ids,
        },
        .probe          = gef_wdt_probe,
        .remove         = gef_wdt_remove,
};

static int __init gef_wdt_init(void)
{
        pr_info("GE watchdog driver\n");
        return platform_driver_register(&gef_wdt_driver);
}

static void __exit gef_wdt_exit(void)
{
        platform_driver_unregister(&gef_wdt_driver);
}

module_init(gef_wdt_init);
module_exit(gef_wdt_exit);

MODULE_AUTHOR("Martyn Welch <martyn.welch@ge.com>");
MODULE_DESCRIPTION("GE watchdog driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:gef_wdt");