/*
 * Watchdog implementation based on z/VM Watchdog Timer API
 *
 * Copyright IBM Corp. 2004,2009
 *
 * The user space watchdog daemon can use this driver as
 * /dev/vmwatchdog to have z/VM execute the specified CP
 * command when the timeout expires. The default command is
 * "IPL", which which cause an immediate reboot.
 */
#define KMSG_COMPONENT "vmwatchdog"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt

#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/suspend.h>
#include <linux/watchdog.h>
#include <linux/smp_lock.h>

#include <asm/ebcdic.h>
#include <asm/io.h>
#include <asm/uaccess.h>

#define MAX_CMDLEN 240
#define MIN_INTERVAL 15
static char vmwdt_cmd[MAX_CMDLEN] = "IPL";
static int vmwdt_conceal;

static int vmwdt_nowayout = WATCHDOG_NOWAYOUT;

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Arnd Bergmann <arndb@de.ibm.com>");
MODULE_DESCRIPTION("z/VM Watchdog Timer");
module_param_string(cmd, vmwdt_cmd, MAX_CMDLEN, 0644);
MODULE_PARM_DESC(cmd, "CP command that is run when the watchdog triggers");
module_param_named(conceal, vmwdt_conceal, bool, 0644);
MODULE_PARM_DESC(conceal, "Enable the CONCEAL CP option while the watchdog "
                " is active");
module_param_named(nowayout, vmwdt_nowayout, bool, 0);
MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started"
                " (default=CONFIG_WATCHDOG_NOWAYOUT)");
MODULE_ALIAS_MISCDEV(WATCHDOG_MINOR);

static unsigned int vmwdt_interval = 60;
static unsigned long vmwdt_is_open;
static int vmwdt_expect_close;

#define VMWDT_OPEN      0       /* devnode is open or suspend in progress */
#define VMWDT_RUNNING   1       /* The watchdog is armed */

enum vmwdt_func {
        /* function codes */
        wdt_init   = 0,
        wdt_change = 1,
        wdt_cancel = 2,
        /* flags */
        wdt_conceal = 0x80000000,
};

static int __diag288(enum vmwdt_func func, unsigned int timeout,
                            char *cmd, size_t len)
{
        register unsigned long __func asm("2") = func;
        register unsigned long __timeout asm("3") = timeout;
        register unsigned long __cmdp asm("4") = virt_to_phys(cmd);
        register unsigned long __cmdl asm("5") = len;
        int err;

        err = -EINVAL;
        asm volatile(
                "       diag    %1,%3,0x288\n"
                "0:     la      %0,0\n"
                "1:\n"
                EX_TABLE(0b,1b)
                : "+d" (err) : "d"(__func), "d"(__timeout),
                  "d"(__cmdp), "d"(__cmdl) : "1", "cc");
        return err;
}

static int vmwdt_keepalive(void)
{
        /* we allocate new memory every time to avoid having
         * to track the state. static allocation is not an
         * option since that might not be contiguous in real
         * storage in case of a modular build */
        static char *ebc_cmd;
        size_t len;
        int ret;
        unsigned int func;

        ebc_cmd = kmalloc(MAX_CMDLEN, GFP_KERNEL);
        if (!ebc_cmd)
                return -ENOMEM;

        len = strlcpy(ebc_cmd, vmwdt_cmd, MAX_CMDLEN);
        ASCEBC(ebc_cmd, MAX_CMDLEN);
        EBC_TOUPPER(ebc_cmd, MAX_CMDLEN);

        func = vmwdt_conceal ? (wdt_init | wdt_conceal) : wdt_init;
        set_bit(VMWDT_RUNNING, &vmwdt_is_open);
        ret = __diag288(func, vmwdt_interval, ebc_cmd, len);
        WARN_ON(ret != 0);
        kfree(ebc_cmd);
        return ret;
}

static int vmwdt_disable(void)
{
        int ret = __diag288(wdt_cancel, 0, "", 0);
        WARN_ON(ret != 0);
        clear_bit(VMWDT_RUNNING, &vmwdt_is_open);
        return ret;
}

static int __init vmwdt_probe(void)
{
        /* there is no real way to see if the watchdog is supported,
         * so we try initializing it with a NOP command ("BEGIN")
         * that won't cause any harm even if the following disable
         * fails for some reason */
        static char __initdata ebc_begin[] = {
                194, 197, 199, 201, 213
        };
        if (__diag288(wdt_init, 15, ebc_begin, sizeof(ebc_begin)) != 0)
                return -EINVAL;
        return vmwdt_disable();
}

static int vmwdt_open(struct inode *i, struct file *f)
{
        int ret;
        lock_kernel();
        if (test_and_set_bit(VMWDT_OPEN, &vmwdt_is_open)) {
                unlock_kernel();
                return -EBUSY;
        }
        ret = vmwdt_keepalive();
        if (ret)
                clear_bit(VMWDT_OPEN, &vmwdt_is_open);
        unlock_kernel();
        return ret ? ret : nonseekable_open(i, f);
}

static int vmwdt_close(struct inode *i, struct file *f)
{
        if (vmwdt_expect_close == 42)
                vmwdt_disable();
        vmwdt_expect_close = 0;
        clear_bit(VMWDT_OPEN, &vmwdt_is_open);
        return 0;
}

static struct watchdog_info vmwdt_info = {
        .options = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING | WDIOF_MAGICCLOSE,
        .firmware_version = 0,
        .identity = "z/VM Watchdog Timer",
};

static int vmwdt_ioctl(struct inode *i, struct file *f,
                          unsigned int cmd, unsigned long arg)
{
        switch (cmd) {
        case WDIOC_GETSUPPORT:
                if (copy_to_user((void __user *)arg, &vmwdt_info,
                                        sizeof(vmwdt_info)))
                        return -EFAULT;
                return 0;
        case WDIOC_GETSTATUS:
        case WDIOC_GETBOOTSTATUS:
                return put_user(0, (int __user *)arg);
        case WDIOC_GETTEMP:
                return -EINVAL;
        case WDIOC_SETOPTIONS:
                {
                        int options, ret;
                        if (get_user(options, (int __user *)arg))
                                return -EFAULT;
                        ret = -EINVAL;
                        if (options & WDIOS_DISABLECARD) {
                                ret = vmwdt_disable();
                                if (ret)
                                        return ret;
                        }
                        if (options & WDIOS_ENABLECARD) {
                                ret = vmwdt_keepalive();
                        }
                        return ret;
                }
        case WDIOC_GETTIMEOUT:
                return put_user(vmwdt_interval, (int __user *)arg);
        case WDIOC_SETTIMEOUT:
                {
                        int interval;
                        if (get_user(interval, (int __user *)arg))
                                return -EFAULT;
                        if (interval < MIN_INTERVAL)
                                return -EINVAL;
                        vmwdt_interval = interval;
                }
                return vmwdt_keepalive();
        case WDIOC_KEEPALIVE:
                return vmwdt_keepalive();
        }

        return -EINVAL;
}

static ssize_t vmwdt_write(struct file *f, const char __user *buf,
                                size_t count, loff_t *ppos)
{
        if(count) {
                if (!vmwdt_nowayout) {
                        size_t i;

                        /* note: just in case someone wrote the magic character
                         * five months ago... */
                        vmwdt_expect_close = 0;

                        for (i = 0; i != count; i++) {
                                char c;
                                if (get_user(c, buf+i))
                                        return -EFAULT;
                                if (c == 'V')
                                        vmwdt_expect_close = 42;
                        }
                }
                /* someone wrote to us, we should restart timer */
                vmwdt_keepalive();
        }
        return count;
}

static int vmwdt_resume(void)
{
        clear_bit(VMWDT_OPEN, &vmwdt_is_open);
        return NOTIFY_DONE;
}

/*
 * It makes no sense to go into suspend while the watchdog is running.
 * Depending on the memory size, the watchdog might trigger, while we
 * are still saving the memory.
 * We reuse the open flag to ensure that suspend and watchdog open are
 * exclusive operations
 */
static int vmwdt_suspend(void)
{
        if (test_and_set_bit(VMWDT_OPEN, &vmwdt_is_open)) {
                pr_err("The system cannot be suspended while the watchdog"
                        " is in use\n");
                return NOTIFY_BAD;
        }
        if (test_bit(VMWDT_RUNNING, &vmwdt_is_open)) {
                clear_bit(VMWDT_OPEN, &vmwdt_is_open);
                pr_err("The system cannot be suspended while the watchdog"
                        " is running\n");
                return NOTIFY_BAD;
        }
        return NOTIFY_DONE;
}

/*
 * This function is called for suspend and resume.
 */
static int vmwdt_power_event(struct notifier_block *this, unsigned long event,
                             void *ptr)
{
        switch (event) {
        case PM_POST_HIBERNATION:
        case PM_POST_SUSPEND:
                return vmwdt_resume();
        case PM_HIBERNATION_PREPARE:
        case PM_SUSPEND_PREPARE:
                return vmwdt_suspend();
        default:
                return NOTIFY_DONE;
        }
}

static struct notifier_block vmwdt_power_notifier = {
        .notifier_call = vmwdt_power_event,
};

static const struct file_operations vmwdt_fops = {
        .open    = &vmwdt_open,
        .release = &vmwdt_close,
        .ioctl   = &vmwdt_ioctl,
        .write   = &vmwdt_write,
        .owner   = THIS_MODULE,
};

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

static int __init vmwdt_init(void)
{
        int ret;

        ret = vmwdt_probe();
        if (ret)
                return ret;
        ret = register_pm_notifier(&vmwdt_power_notifier);
        if (ret)
                return ret;
        ret = misc_register(&vmwdt_dev);
        if (ret) {
                unregister_pm_notifier(&vmwdt_power_notifier);
                return ret;
        }
        return 0;
}
module_init(vmwdt_init);

static void __exit vmwdt_exit(void)
{
        unregister_pm_notifier(&vmwdt_power_notifier);
        misc_deregister(&vmwdt_dev);
}
module_exit(vmwdt_exit);