/******************************************************************************
 * arch/ia64/xen/time.c
 *
 * Copyright (c) 2008 Isaku Yamahata <yamahata at valinux co jp>
 *                    VA Linux Systems Japan K.K.
 *
 * 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.
 *
 * This program is distributed in the hope that 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.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#include <linux/delay.h>
#include <linux/kernel_stat.h>
#include <linux/posix-timers.h>
#include <linux/irq.h>
#include <linux/clocksource.h>

#include <asm/timex.h>

#include <asm/xen/hypervisor.h>

#include <xen/interface/vcpu.h>

#include "../kernel/fsyscall_gtod_data.h"

static DEFINE_PER_CPU(struct vcpu_runstate_info, xen_runstate);
static DEFINE_PER_CPU(unsigned long, xen_stolen_time);
static DEFINE_PER_CPU(unsigned long, xen_blocked_time);

/* taken from i386/kernel/time-xen.c */
static void xen_init_missing_ticks_accounting(int cpu)
{
        struct vcpu_register_runstate_memory_area area;
        struct vcpu_runstate_info *runstate = &per_cpu(xen_runstate, cpu);
        int rc;

        memset(runstate, 0, sizeof(*runstate));

        area.addr.v = runstate;
        rc = HYPERVISOR_vcpu_op(VCPUOP_register_runstate_memory_area, cpu,
                                &area);
        WARN_ON(rc && rc != -ENOSYS);

        per_cpu(xen_blocked_time, cpu) = runstate->time[RUNSTATE_blocked];
        per_cpu(xen_stolen_time, cpu) = runstate->time[RUNSTATE_runnable]
                                            + runstate->time[RUNSTATE_offline];
}

/*
 * Runstate accounting
 */
/* stolen from arch/x86/xen/time.c */
static void get_runstate_snapshot(struct vcpu_runstate_info *res)
{
        u64 state_time;
        struct vcpu_runstate_info *state;

        BUG_ON(preemptible());

        state = &__get_cpu_var(xen_runstate);

        /*
         * The runstate info is always updated by the hypervisor on
         * the current CPU, so there's no need to use anything
         * stronger than a compiler barrier when fetching it.
         */
        do {
                state_time = state->state_entry_time;
                rmb();
                *res = *state;
                rmb();
        } while (state->state_entry_time != state_time);
}

#define NS_PER_TICK (1000000000LL/HZ)

static unsigned long
consider_steal_time(unsigned long new_itm)
{
        unsigned long stolen, blocked;
        unsigned long delta_itm = 0, stolentick = 0;
        int cpu = smp_processor_id();
        struct vcpu_runstate_info runstate;
        struct task_struct *p = current;

        get_runstate_snapshot(&runstate);

        /*
         * Check for vcpu migration effect
         * In this case, itc value is reversed.
         * This causes huge stolen value.
         * This function just checks and reject this effect.
         */
        if (!time_after_eq(runstate.time[RUNSTATE_blocked],
                           per_cpu(xen_blocked_time, cpu)))
                blocked = 0;

        if (!time_after_eq(runstate.time[RUNSTATE_runnable] +
                           runstate.time[RUNSTATE_offline],
                           per_cpu(xen_stolen_time, cpu)))
                stolen = 0;

        if (!time_after(delta_itm + new_itm, ia64_get_itc()))
                stolentick = ia64_get_itc() - new_itm;

        do_div(stolentick, NS_PER_TICK);
        stolentick++;

        do_div(stolen, NS_PER_TICK);

        if (stolen > stolentick)
                stolen = stolentick;

        stolentick -= stolen;
        do_div(blocked, NS_PER_TICK);

        if (blocked > stolentick)
                blocked = stolentick;

        if (stolen > 0 || blocked > 0) {
                account_steal_ticks(stolen);
                account_idle_ticks(blocked);
                run_local_timers();

                rcu_check_callbacks(cpu, user_mode(get_irq_regs()));

                scheduler_tick();
                run_posix_cpu_timers(p);
                delta_itm += local_cpu_data->itm_delta * (stolen + blocked);

                if (cpu == time_keeper_id)
                        xtime_update(stolen + blocked);

                local_cpu_data->itm_next = delta_itm + new_itm;

                per_cpu(xen_stolen_time, cpu) += NS_PER_TICK * stolen;
                per_cpu(xen_blocked_time, cpu) += NS_PER_TICK * blocked;
        }
        return delta_itm;
}

static int xen_do_steal_accounting(unsigned long *new_itm)
{
        unsigned long delta_itm;
        delta_itm = consider_steal_time(*new_itm);
        *new_itm += delta_itm;
        if (time_after(*new_itm, ia64_get_itc()) && delta_itm)
                return 1;

        return 0;
}

static void xen_itc_jitter_data_reset(void)
{
        u64 lcycle, ret;

        do {
                lcycle = itc_jitter_data.itc_lastcycle;
                ret = cmpxchg(&itc_jitter_data.itc_lastcycle, lcycle, 0);
        } while (unlikely(ret != lcycle));
}

/* based on xen_sched_clock() in arch/x86/xen/time.c. */
/*
 * This relies on HAVE_UNSTABLE_SCHED_CLOCK. If it can't be defined,
 * something similar logic should be implemented here.
 */
/*
 * Xen sched_clock implementation.  Returns the number of unstolen
 * nanoseconds, which is nanoseconds the VCPU spent in RUNNING+BLOCKED
 * states.
 */
static unsigned long long xen_sched_clock(void)
{
        struct vcpu_runstate_info runstate;

        unsigned long long now;
        unsigned long long offset;
        unsigned long long ret;

        /*
         * Ideally sched_clock should be called on a per-cpu basis
         * anyway, so preempt should already be disabled, but that's
         * not current practice at the moment.
         */
        preempt_disable();

        /*
         * both ia64_native_sched_clock() and xen's runstate are
         * based on mAR.ITC. So difference of them makes sense.
         */
        now = ia64_native_sched_clock();

        get_runstate_snapshot(&runstate);

        WARN_ON(runstate.state != RUNSTATE_running);

        offset = 0;
        if (now > runstate.state_entry_time)
                offset = now - runstate.state_entry_time;
        ret = runstate.time[RUNSTATE_blocked] +
                runstate.time[RUNSTATE_running] +
                offset;

        preempt_enable();

        return ret;
}

struct pv_time_ops xen_time_ops __initdata = {
        .init_missing_ticks_accounting  = xen_init_missing_ticks_accounting,
        .do_steal_accounting            = xen_do_steal_accounting,
        .clocksource_resume             = xen_itc_jitter_data_reset,
        .sched_clock                    = xen_sched_clock,
};

/* Called after suspend, to resume time.  */
static void xen_local_tick_resume(void)
{
        /* Just trigger a tick.  */
        ia64_cpu_local_tick();
        touch_softlockup_watchdog();
}

void
xen_timer_resume(void)
{
        unsigned int cpu;

        xen_local_tick_resume();

        for_each_online_cpu(cpu)
                xen_init_missing_ticks_accounting(cpu);
}

static void ia64_cpu_local_tick_fn(void *unused)
{
        xen_local_tick_resume();
        xen_init_missing_ticks_accounting(smp_processor_id());
}

void
xen_timer_resume_on_aps(void)
{
        smp_call_function(&ia64_cpu_local_tick_fn, NULL, 1);
}