// SPDX-License-Identifier: GPL-2.0
/*
 *    Time of day based timer functions.
 *
 *  S390 version
 *    Copyright IBM Corp. 1999, 2008
 *    Author(s): Hartmut Penner (hp@de.ibm.com),
 *               Martin Schwidefsky (schwidefsky@de.ibm.com),
 *               Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com)
 *
 *  Derived from "arch/i386/kernel/time.c"
 *    Copyright (C) 1991, 1992, 1995  Linus Torvalds
 */

#define pr_fmt(fmt) "time: " fmt

#include <linux/kernel_stat.h>
#include <linux/errno.h>
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/kernel.h>
#include <linux/param.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/cpu.h>
#include <linux/stop_machine.h>
#include <linux/time.h>
#include <linux/device.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/types.h>
#include <linux/profile.h>
#include <linux/timex.h>
#include <linux/notifier.h>
#include <linux/clockchips.h>
#include <linux/gfp.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <vdso/vsyscall.h>
#include <vdso/clocksource.h>
#include <vdso/helpers.h>
#include <asm/facility.h>
#include <asm/delay.h>
#include <asm/div64.h>
#include <asm/vdso.h>
#include <asm/irq.h>
#include <asm/irq_regs.h>
#include <asm/vtimer.h>
#include <asm/stp.h>
#include <asm/cio.h>
#include "entry.h"

union tod_clock __bootdata_preserved(tod_clock_base);
EXPORT_SYMBOL_GPL(tod_clock_base);

u64 __bootdata_preserved(clock_comparator_max);
EXPORT_SYMBOL_GPL(clock_comparator_max);

static DEFINE_PER_CPU(struct clock_event_device, comparators);

ATOMIC_NOTIFIER_HEAD(s390_epoch_delta_notifier);
EXPORT_SYMBOL(s390_epoch_delta_notifier);

unsigned char ptff_function_mask[16];

static unsigned long lpar_offset;
static unsigned long initial_leap_seconds;

/*
 * Get time offsets with PTFF
 */
void __init time_early_init(void)
{
        struct ptff_qto qto;
        struct ptff_qui qui;

        vdso_k_time_data->arch_data.tod_delta = tod_clock_base.tod;

        if (!test_facility(28))
                return;

        ptff(&ptff_function_mask, sizeof(ptff_function_mask), PTFF_QAF);

        /* get LPAR offset */
        if (ptff_query(PTFF_QTO) && ptff(&qto, sizeof(qto), PTFF_QTO) == 0)
                lpar_offset = qto.tod_epoch_difference;

        /* get initial leap seconds */
        if (ptff_query(PTFF_QUI) && ptff(&qui, sizeof(qui), PTFF_QUI) == 0)
                initial_leap_seconds = (unsigned long)
                        ((long) qui.old_leap * 4096000000L);
}

unsigned long long noinstr sched_clock_noinstr(void)
{
        return tod_to_ns(__get_tod_clock_monotonic());
}

/*
 * Scheduler clock - returns current time in nanosec units.
 */
unsigned long long notrace sched_clock(void)
{
        return tod_to_ns(get_tod_clock_monotonic());
}
NOKPROBE_SYMBOL(sched_clock);

static void ext_to_timespec64(union tod_clock *clk, struct timespec64 *xt)
{
        unsigned long rem, sec, nsec;

        sec = clk->us;
        rem = do_div(sec, 1000000);
        nsec = ((clk->sus + (rem << 12)) * 125) >> 9;
        xt->tv_sec = sec;
        xt->tv_nsec = nsec;
}

void clock_comparator_work(void)
{
        struct clock_event_device *cd;

        get_lowcore()->clock_comparator = clock_comparator_max;
        cd = this_cpu_ptr(&comparators);
        cd->event_handler(cd);
}

static int s390_next_event(unsigned long delta,
                           struct clock_event_device *evt)
{
        get_lowcore()->clock_comparator = get_tod_clock() + delta;
        set_clock_comparator(get_lowcore()->clock_comparator);
        return 0;
}

/*
 * Set up lowcore and control register of the current cpu to
 * enable TOD clock and clock comparator interrupts.
 */
void init_cpu_timer(void)
{
        struct clock_event_device *cd;
        int cpu;

        get_lowcore()->clock_comparator = clock_comparator_max;
        set_clock_comparator(get_lowcore()->clock_comparator);

        cpu = smp_processor_id();
        cd = &per_cpu(comparators, cpu);
        cd->name                = "comparator";
        cd->features            = CLOCK_EVT_FEAT_ONESHOT;
        cd->mult                = 16777;
        cd->shift               = 12;
        cd->min_delta_ns        = 1;
        cd->min_delta_ticks     = 1;
        cd->max_delta_ns        = LONG_MAX;
        cd->max_delta_ticks     = ULONG_MAX;
        cd->rating              = 400;
        cd->cpumask             = cpumask_of(cpu);
        cd->set_next_event      = s390_next_event;

        clockevents_register_device(cd);

        /* Enable clock comparator timer interrupt. */
        local_ctl_set_bit(0, CR0_CLOCK_COMPARATOR_SUBMASK_BIT);

        /* Always allow the timing alert external interrupt. */
        local_ctl_set_bit(0, CR0_ETR_SUBMASK_BIT);
}

static void clock_comparator_interrupt(struct ext_code ext_code,
                                       unsigned int param32,
                                       unsigned long param64)
{
        inc_irq_stat(IRQEXT_CLK);
        if (get_lowcore()->clock_comparator == clock_comparator_max)
                set_clock_comparator(get_lowcore()->clock_comparator);
}

static void stp_timing_alert(struct stp_irq_parm *);

static void timing_alert_interrupt(struct ext_code ext_code,
                                   unsigned int param32, unsigned long param64)
{
        inc_irq_stat(IRQEXT_TLA);
        if (param32 & 0x00038000)
                stp_timing_alert((struct stp_irq_parm *) &param32);
}

static void stp_reset(void);

void read_persistent_clock64(struct timespec64 *ts)
{
        union tod_clock clk;
        u64 delta;

        delta = initial_leap_seconds + TOD_UNIX_EPOCH;
        store_tod_clock_ext(&clk);
        clk.eitod -= delta;
        ext_to_timespec64(&clk, ts);
}

void __init read_persistent_wall_and_boot_offset(struct timespec64 *wall_time,
                                                 struct timespec64 *boot_offset)
{
        struct timespec64 boot_time;
        union tod_clock clk;
        u64 delta;

        delta = initial_leap_seconds + TOD_UNIX_EPOCH;
        clk = tod_clock_base;
        clk.eitod -= delta;
        ext_to_timespec64(&clk, &boot_time);

        read_persistent_clock64(wall_time);
        *boot_offset = timespec64_sub(*wall_time, boot_time);
}

static u64 read_tod_clock(struct clocksource *cs)
{
        return get_tod_clock_monotonic();
}

static struct clocksource clocksource_tod = {
        .name           = "tod",
        .rating         = 400,
        .read           = read_tod_clock,
        .mask           = CLOCKSOURCE_MASK(64),
        .mult           = 4096000,
        .shift          = 24,
        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
        .vdso_clock_mode = VDSO_CLOCKMODE_TOD,
        .id             = CSID_S390_TOD,
};

struct clocksource * __init clocksource_default_clock(void)
{
        return &clocksource_tod;
}

/*
 * Initialize the TOD clock and the CPU timer of
 * the boot cpu.
 */
void __init time_init(void)
{
        /* Reset time synchronization interfaces. */
        stp_reset();

        /* request the clock comparator external interrupt */
        if (register_external_irq(EXT_IRQ_CLK_COMP, clock_comparator_interrupt))
                panic("Couldn't request external interrupt 0x1004");

        /* request the timing alert external interrupt */
        if (register_external_irq(EXT_IRQ_TIMING_ALERT, timing_alert_interrupt))
                panic("Couldn't request external interrupt 0x1406");

        if (__clocksource_register(&clocksource_tod) != 0)
                panic("Could not register TOD clock source");

        /* Enable TOD clock interrupts on the boot cpu. */
        init_cpu_timer();

        /* Enable cpu timer interrupts on the boot cpu. */
        vtime_init();
}

static DEFINE_PER_CPU(atomic_t, clock_sync_word);
static DEFINE_MUTEX(stp_mutex);
static unsigned long clock_sync_flags;

#define CLOCK_SYNC_HAS_STP              0
#define CLOCK_SYNC_STP                  1
#define CLOCK_SYNC_STPINFO_VALID        2

/*
 * The get_clock function for the physical clock. It will get the current
 * TOD clock, subtract the LPAR offset and write the result to *clock.
 * The function returns 0 if the clock is in sync with the external time
 * source. If the clock mode is local it will return -EOPNOTSUPP and
 * -EAGAIN if the clock is not in sync with the external reference.
 */
int get_phys_clock(unsigned long *clock)
{
        atomic_t *sw_ptr;
        unsigned int sw0, sw1;

        sw_ptr = &get_cpu_var(clock_sync_word);
        sw0 = atomic_read(sw_ptr);
        *clock = get_tod_clock() - lpar_offset;
        sw1 = atomic_read(sw_ptr);
        put_cpu_var(clock_sync_word);
        if (sw0 == sw1 && (sw0 & 0x80000000U))
                /* Success: time is in sync. */
                return 0;
        if (!test_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags))
                return -EOPNOTSUPP;
        if (!test_bit(CLOCK_SYNC_STP, &clock_sync_flags))
                return -EACCES;
        return -EAGAIN;
}
EXPORT_SYMBOL(get_phys_clock);

/*
 * Make get_phys_clock() return -EAGAIN.
 */
static void disable_sync_clock(void *dummy)
{
        atomic_t *sw_ptr = this_cpu_ptr(&clock_sync_word);
        /*
         * Clear the in-sync bit 2^31. All get_phys_clock calls will
         * fail until the sync bit is turned back on. In addition
         * increase the "sequence" counter to avoid the race of an
         * stp event and the complete recovery against get_phys_clock.
         */
        atomic_andnot(0x80000000, sw_ptr);
        atomic_inc(sw_ptr);
}

/*
 * Make get_phys_clock() return 0 again.
 * Needs to be called from a context disabled for preemption.
 */
static void enable_sync_clock(void)
{
        atomic_t *sw_ptr = this_cpu_ptr(&clock_sync_word);
        atomic_or(0x80000000, sw_ptr);
}

/*
 * Function to check if the clock is in sync.
 */
static inline int check_sync_clock(void)
{
        atomic_t *sw_ptr;
        int rc;

        sw_ptr = &get_cpu_var(clock_sync_word);
        rc = (atomic_read(sw_ptr) & 0x80000000U) != 0;
        put_cpu_var(clock_sync_word);
        return rc;
}

/*
 * Apply clock delta to the global data structures.
 * This is called once on the CPU that performed the clock sync.
 */
static void clock_sync_global(long delta)
{
        struct ptff_qto qto;

        /* Fixup the monotonic sched clock. */
        tod_clock_base.eitod += delta;
        vdso_k_time_data->arch_data.tod_delta = tod_clock_base.tod;
        /* Update LPAR offset. */
        if (ptff_query(PTFF_QTO) && ptff(&qto, sizeof(qto), PTFF_QTO) == 0)
                lpar_offset = qto.tod_epoch_difference;
        /* Call the TOD clock change notifier. */
        atomic_notifier_call_chain(&s390_epoch_delta_notifier, 0, &delta);
}

/*
 * Apply clock delta to the per-CPU data structures of this CPU.
 * This is called for each online CPU after the call to clock_sync_global.
 */
static void clock_sync_local(long delta)
{
        /* Add the delta to the clock comparator. */
        if (get_lowcore()->clock_comparator != clock_comparator_max) {
                get_lowcore()->clock_comparator += delta;
                set_clock_comparator(get_lowcore()->clock_comparator);
        }
        /* Adjust the last_update_clock time-stamp. */
        get_lowcore()->last_update_clock += delta;
}

/* Single threaded workqueue used for stp sync events */
static struct workqueue_struct *time_sync_wq;

static void __init time_init_wq(void)
{
        if (time_sync_wq)
                return;
        time_sync_wq = create_singlethread_workqueue("timesync");
}

struct clock_sync_data {
        atomic_t cpus;
        int in_sync;
        long clock_delta;
};

/*
 * Server Time Protocol (STP) code.
 */
static bool stp_online = true;
static struct stp_sstpi stp_info;
static void *stp_page;

static void stp_work_fn(struct work_struct *work);
static DECLARE_WORK(stp_work, stp_work_fn);
static struct timer_list stp_timer;

static int __init early_parse_stp(char *p)
{
        return kstrtobool(p, &stp_online);
}
early_param("stp", early_parse_stp);

/*
 * Reset STP attachment.
 */
static void __init stp_reset(void)
{
        int rc;

        stp_page = (void *) get_zeroed_page(GFP_ATOMIC);
        rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0x0000, NULL);
        if (rc == 0)
                set_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags);
        else if (stp_online) {
                free_page((unsigned long) stp_page);
                stp_page = NULL;
                stp_online = false;
        }
}

bool stp_enabled(void)
{
        return test_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags) && stp_online;
}
EXPORT_SYMBOL(stp_enabled);

static void stp_timeout(struct timer_list *unused)
{
        queue_work(time_sync_wq, &stp_work);
}

static int __init stp_init(void)
{
        if (!test_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags))
                return 0;
        timer_setup(&stp_timer, stp_timeout, 0);
        time_init_wq();
        if (!stp_online)
                return 0;
        queue_work(time_sync_wq, &stp_work);
        return 0;
}

arch_initcall(stp_init);

/*
 * STP timing alert. There are three causes:
 * 1) timing status change
 * 2) link availability change
 * 3) time control parameter change
 * In all three cases we are only interested in the clock source state.
 * If a STP clock source is now available use it.
 */
static void stp_timing_alert(struct stp_irq_parm *intparm)
{
        if (intparm->tsc || intparm->lac || intparm->tcpc)
                queue_work(time_sync_wq, &stp_work);
}

/*
 * STP sync check machine check. This is called when the timing state
 * changes from the synchronized state to the unsynchronized state.
 * After a STP sync check the clock is not in sync. The machine check
 * is broadcasted to all cpus at the same time.
 */
int stp_sync_check(void)
{
        disable_sync_clock(NULL);
        return 1;
}

/*
 * STP island condition machine check. This is called when an attached
 * server  attempts to communicate over an STP link and the servers
 * have matching CTN ids and have a valid stratum-1 configuration
 * but the configurations do not match.
 */
int stp_island_check(void)
{
        disable_sync_clock(NULL);
        return 1;
}

void stp_queue_work(void)
{
        queue_work(time_sync_wq, &stp_work);
}

static int __store_stpinfo(void)
{
        int rc = chsc_sstpi(stp_page, &stp_info, sizeof(struct stp_sstpi));

        if (rc)
                clear_bit(CLOCK_SYNC_STPINFO_VALID, &clock_sync_flags);
        else
                set_bit(CLOCK_SYNC_STPINFO_VALID, &clock_sync_flags);
        return rc;
}

static int stpinfo_valid(void)
{
        return stp_online && test_bit(CLOCK_SYNC_STPINFO_VALID, &clock_sync_flags);
}

static int stp_sync_clock(void *data)
{
        struct clock_sync_data *sync = data;
        long clock_delta, flags;
        static int first;
        int rc;

        enable_sync_clock();
        if (xchg(&first, 1) == 0) {
                /* Wait until all other cpus entered the sync function. */
                while (atomic_read(&sync->cpus) != 0)
                        cpu_relax();
                rc = 0;
                if (stp_info.todoff || stp_info.tmd != 2) {
                        flags = vdso_update_begin();
                        rc = chsc_sstpc(stp_page, STP_OP_SYNC, 0,
                                        &clock_delta);
                        if (rc == 0) {
                                sync->clock_delta = clock_delta;
                                clock_sync_global(clock_delta);
                                rc = __store_stpinfo();
                                if (rc == 0 && stp_info.tmd != 2)
                                        rc = -EAGAIN;
                        }
                        vdso_update_end(flags);
                }
                sync->in_sync = rc ? -EAGAIN : 1;
                xchg(&first, 0);
        } else {
                /* Slave */
                atomic_dec(&sync->cpus);
                /* Wait for in_sync to be set. */
                while (READ_ONCE(sync->in_sync) == 0)
                        ;
        }
        if (sync->in_sync != 1)
                /* Didn't work. Clear per-cpu in sync bit again. */
                disable_sync_clock(NULL);
        /* Apply clock delta to per-CPU fields of this CPU. */
        clock_sync_local(sync->clock_delta);

        return 0;
}

/*
 * STP work. Check for the STP state and take over the clock
 * synchronization if the STP clock source is usable.
 */
static void stp_work_fn(struct work_struct *work)
{
        struct clock_sync_data stp_sync;
        int rc;

        /* prevent multiple execution. */
        mutex_lock(&stp_mutex);

        if (!stp_online) {
                chsc_sstpc(stp_page, STP_OP_CTRL, 0x0000, NULL);
                timer_delete_sync(&stp_timer);
                goto out_unlock;
        }

        rc = chsc_sstpc(stp_page, STP_OP_CTRL, 0xf0e0, NULL);
        if (rc)
                goto out_unlock;

        rc = __store_stpinfo();
        if (rc || stp_info.c == 0)
                goto out_unlock;

        /* Skip synchronization if the clock is already in sync. */
        if (!check_sync_clock()) {
                memset(&stp_sync, 0, sizeof(stp_sync));
                cpus_read_lock();
                atomic_set(&stp_sync.cpus, num_online_cpus() - 1);
                stop_machine_cpuslocked(stp_sync_clock, &stp_sync, cpu_online_mask);
                cpus_read_unlock();
        }

        if (!check_sync_clock())
                /*
                 * There is a usable clock but the synchronization failed.
                 * Retry after a second.
                 */
                mod_timer(&stp_timer, jiffies + msecs_to_jiffies(MSEC_PER_SEC));

out_unlock:
        mutex_unlock(&stp_mutex);
}

/*
 * STP subsys sysfs interface functions
 */
static const struct bus_type stp_subsys = {
        .name           = "stp",
        .dev_name       = "stp",
};

static ssize_t ctn_id_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        ssize_t ret = -ENODATA;

        mutex_lock(&stp_mutex);
        if (stpinfo_valid())
                ret = sysfs_emit(buf, "%016lx\n",
                                 *(unsigned long *)stp_info.ctnid);
        mutex_unlock(&stp_mutex);
        return ret;
}

static DEVICE_ATTR_RO(ctn_id);

static ssize_t ctn_type_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        ssize_t ret = -ENODATA;

        mutex_lock(&stp_mutex);
        if (stpinfo_valid())
                ret = sysfs_emit(buf, "%i\n", stp_info.ctn);
        mutex_unlock(&stp_mutex);
        return ret;
}

static DEVICE_ATTR_RO(ctn_type);

static ssize_t dst_offset_show(struct device *dev,
                                   struct device_attribute *attr,
                                   char *buf)
{
        ssize_t ret = -ENODATA;

        mutex_lock(&stp_mutex);
        if (stpinfo_valid() && (stp_info.vbits & 0x2000))
                ret = sysfs_emit(buf, "%i\n", (int)(s16)stp_info.dsto);
        mutex_unlock(&stp_mutex);
        return ret;
}

static DEVICE_ATTR_RO(dst_offset);

static ssize_t leap_seconds_show(struct device *dev,
                                        struct device_attribute *attr,
                                        char *buf)
{
        ssize_t ret = -ENODATA;

        mutex_lock(&stp_mutex);
        if (stpinfo_valid() && (stp_info.vbits & 0x8000))
                ret = sysfs_emit(buf, "%i\n", (int)(s16)stp_info.leaps);
        mutex_unlock(&stp_mutex);
        return ret;
}

static DEVICE_ATTR_RO(leap_seconds);

static ssize_t leap_seconds_scheduled_show(struct device *dev,
                                                struct device_attribute *attr,
                                                char *buf)
{
        struct stp_stzi stzi;
        ssize_t ret;

        mutex_lock(&stp_mutex);
        if (!stpinfo_valid() || !(stp_info.vbits & 0x8000) || !stp_info.lu) {
                mutex_unlock(&stp_mutex);
                return -ENODATA;
        }

        ret = chsc_stzi(stp_page, &stzi, sizeof(stzi));
        mutex_unlock(&stp_mutex);
        if (ret < 0)
                return ret;

        if (!stzi.lsoib.p)
                return sysfs_emit(buf, "0,0\n");

        return sysfs_emit(buf, "%lu,%d\n",
                          tod_to_ns(stzi.lsoib.nlsout - TOD_UNIX_EPOCH) / NSEC_PER_SEC,
                          stzi.lsoib.nlso - stzi.lsoib.also);
}

static DEVICE_ATTR_RO(leap_seconds_scheduled);

static ssize_t stratum_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        ssize_t ret = -ENODATA;

        mutex_lock(&stp_mutex);
        if (stpinfo_valid())
                ret = sysfs_emit(buf, "%i\n", (int)(s16)stp_info.stratum);
        mutex_unlock(&stp_mutex);
        return ret;
}

static DEVICE_ATTR_RO(stratum);

static ssize_t time_offset_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        ssize_t ret = -ENODATA;

        mutex_lock(&stp_mutex);
        if (stpinfo_valid() && (stp_info.vbits & 0x0800))
                ret = sysfs_emit(buf, "%i\n", (int)stp_info.tto);
        mutex_unlock(&stp_mutex);
        return ret;
}

static DEVICE_ATTR_RO(time_offset);

static ssize_t time_zone_offset_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        ssize_t ret = -ENODATA;

        mutex_lock(&stp_mutex);
        if (stpinfo_valid() && (stp_info.vbits & 0x4000))
                ret = sysfs_emit(buf, "%i\n", (int)(s16)stp_info.tzo);
        mutex_unlock(&stp_mutex);
        return ret;
}

static DEVICE_ATTR_RO(time_zone_offset);

static ssize_t timing_mode_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        ssize_t ret = -ENODATA;

        mutex_lock(&stp_mutex);
        if (stpinfo_valid())
                ret = sysfs_emit(buf, "%i\n", stp_info.tmd);
        mutex_unlock(&stp_mutex);
        return ret;
}

static DEVICE_ATTR_RO(timing_mode);

static ssize_t timing_state_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        ssize_t ret = -ENODATA;

        mutex_lock(&stp_mutex);
        if (stpinfo_valid())
                ret = sysfs_emit(buf, "%i\n", stp_info.tst);
        mutex_unlock(&stp_mutex);
        return ret;
}

static DEVICE_ATTR_RO(timing_state);

static ssize_t online_show(struct device *dev,
                                struct device_attribute *attr,
                                char *buf)
{
        return sysfs_emit(buf, "%i\n", stp_online);
}

static ssize_t online_store(struct device *dev,
                                struct device_attribute *attr,
                                const char *buf, size_t count)
{
        unsigned int value;

        value = simple_strtoul(buf, NULL, 0);
        if (value != 0 && value != 1)
                return -EINVAL;
        if (!test_bit(CLOCK_SYNC_HAS_STP, &clock_sync_flags))
                return -EOPNOTSUPP;
        mutex_lock(&stp_mutex);
        stp_online = value;
        if (stp_online)
                set_bit(CLOCK_SYNC_STP, &clock_sync_flags);
        else
                clear_bit(CLOCK_SYNC_STP, &clock_sync_flags);
        queue_work(time_sync_wq, &stp_work);
        mutex_unlock(&stp_mutex);
        return count;
}

/*
 * Can't use DEVICE_ATTR because the attribute should be named
 * stp/online but dev_attr_online already exists in this file ..
 */
static DEVICE_ATTR_RW(online);

static struct attribute *stp_dev_attrs[] = {
        &dev_attr_ctn_id.attr,
        &dev_attr_ctn_type.attr,
        &dev_attr_dst_offset.attr,
        &dev_attr_leap_seconds.attr,
        &dev_attr_online.attr,
        &dev_attr_leap_seconds_scheduled.attr,
        &dev_attr_stratum.attr,
        &dev_attr_time_offset.attr,
        &dev_attr_time_zone_offset.attr,
        &dev_attr_timing_mode.attr,
        &dev_attr_timing_state.attr,
        NULL
};
ATTRIBUTE_GROUPS(stp_dev);

static int __init stp_init_sysfs(void)
{
        return subsys_system_register(&stp_subsys, stp_dev_groups);
}

device_initcall(stp_init_sysfs);