// SPDX-License-Identifier: GPL-2.0
/*
 * Emulate a local clock event device via a pseudo clock device.
 */
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/profile.h>
#include <linux/clockchips.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/module.h>

#include "tick-internal.h"

static struct hrtimer bctimer;

static int bc_shutdown(struct clock_event_device *evt)
{
        /*
         * Note, we cannot cancel the timer here as we might
         * run into the following live lock scenario:
         *
         * cpu 0                cpu1
         * lock(broadcast_lock);
         *                      hrtimer_interrupt()
         *                      bc_handler()
         *                         tick_handle_oneshot_broadcast();
         *                          lock(broadcast_lock);
         * hrtimer_cancel()
         *  wait_for_callback()
         */
        hrtimer_try_to_cancel(&bctimer);
        return 0;
}

/*
 * This is called from the guts of the broadcast code when the cpu
 * which is about to enter idle has the earliest broadcast timer event.
 */
static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
{
        /*
         * This is called either from enter/exit idle code or from the
         * broadcast handler. In all cases tick_broadcast_lock is held.
         *
         * hrtimer_cancel() cannot be called here neither from the
         * broadcast handler nor from the enter/exit idle code. The idle
         * code can run into the problem described in bc_shutdown() and the
         * broadcast handler cannot wait for itself to complete for obvious
         * reasons.
         *
         * Each caller tries to arm the hrtimer on its own CPU, but if the
         * hrtimer callback function is currently running, then
         * hrtimer_start() cannot move it and the timer stays on the CPU on
         * which it is assigned at the moment.
         */
        hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED_HARD);
        /*
         * The core tick broadcast mode expects bc->bound_on to be set
         * correctly to prevent a CPU which has the broadcast hrtimer
         * armed from going deep idle.
         *
         * As tick_broadcast_lock is held, nothing can change the cpu
         * base which was just established in hrtimer_start() above. So
         * the below access is safe even without holding the hrtimer
         * base lock.
         */
        bc->bound_on = bctimer.base->cpu_base->cpu;

        return 0;
}

static struct clock_event_device ce_broadcast_hrtimer = {
        .name                   = "bc_hrtimer",
        .set_state_shutdown     = bc_shutdown,
        .set_next_ktime         = bc_set_next,
        .features               = CLOCK_EVT_FEAT_ONESHOT |
                                  CLOCK_EVT_FEAT_KTIME |
                                  CLOCK_EVT_FEAT_HRTIMER,
        .rating                 = 0,
        .bound_on               = -1,
        .min_delta_ns           = 1,
        .max_delta_ns           = KTIME_MAX,
        .min_delta_ticks        = 1,
        .max_delta_ticks        = ULONG_MAX,
        .mult                   = 1,
        .shift                  = 0,
        .cpumask                = cpu_possible_mask,
};

static enum hrtimer_restart bc_handler(struct hrtimer *t)
{
        ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);

        return HRTIMER_NORESTART;
}

void tick_setup_hrtimer_broadcast(void)
{
        hrtimer_setup(&bctimer, bc_handler, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
        clockevents_register_device(&ce_broadcast_hrtimer);
}