/*-
 * Copyright (c) 2017 Hans Petter Selasky
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice unmodified, this list of conditions, and the following
 *    disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/malloc.h>
#include <sys/gtaskqueue.h>
#include <sys/proc.h>
#include <sys/sched.h>

#include <linux/compiler.h>
#include <linux/interrupt.h>
#include <linux/compat.h>

#define TASKLET_ST_IDLE 0
#define TASKLET_ST_BUSY 1
#define TASKLET_ST_EXEC 2
#define TASKLET_ST_LOOP 3

#define TASKLET_ST_CMPSET(ts, old, new) \
        atomic_cmpset_int((volatile u_int *)&(ts)->tasklet_state, old, new)

#define TASKLET_ST_SET(ts, new) \
        WRITE_ONCE(*(volatile u_int *)&(ts)->tasklet_state, new)

#define TASKLET_ST_GET(ts) \
        READ_ONCE(*(volatile u_int *)&(ts)->tasklet_state)

struct tasklet_worker {
        struct mtx mtx;
        TAILQ_HEAD(tasklet_list, tasklet_struct) head;
        struct grouptask gtask;
} __aligned(CACHE_LINE_SIZE);

#define TASKLET_WORKER_LOCK(tw) mtx_lock(&(tw)->mtx)
#define TASKLET_WORKER_UNLOCK(tw) mtx_unlock(&(tw)->mtx)

DPCPU_DEFINE_STATIC(struct tasklet_worker, tasklet_worker);

static void
tasklet_handler(void *arg)
{
        struct tasklet_worker *tw = (struct tasklet_worker *)arg;
        struct tasklet_struct *ts;
        struct tasklet_struct *last;

        linux_set_current(curthread);

        TASKLET_WORKER_LOCK(tw);
        last = TAILQ_LAST(&tw->head, tasklet_list);
        while (1) {
                ts = TAILQ_FIRST(&tw->head);
                if (ts == NULL)
                        break;
                TAILQ_REMOVE(&tw->head, ts, entry);

                if (!atomic_read(&ts->count)) {
                        TASKLET_WORKER_UNLOCK(tw);
                        do {
                                /* reset executing state */
                                TASKLET_ST_SET(ts, TASKLET_ST_EXEC);

                                if (ts->use_callback)
                                        ts->callback(ts);
                                else
                                        ts->func(ts->data);

                        } while (TASKLET_ST_CMPSET(ts, TASKLET_ST_EXEC,
                                TASKLET_ST_IDLE) == 0);
                        TASKLET_WORKER_LOCK(tw);
                } else {
                        TAILQ_INSERT_TAIL(&tw->head, ts, entry);
                }
                if (ts == last)
                        break;
        }
        TASKLET_WORKER_UNLOCK(tw);
}

static void
tasklet_subsystem_init(void *arg __unused)
{
        struct tasklet_worker *tw;
        char buf[32];
        int i;

        CPU_FOREACH(i) {
                if (CPU_ABSENT(i))
                        continue;

                tw = DPCPU_ID_PTR(i, tasklet_worker);

                mtx_init(&tw->mtx, "linux_tasklet", NULL, MTX_DEF);
                TAILQ_INIT(&tw->head);
                GROUPTASK_INIT(&tw->gtask, 0, tasklet_handler, tw);
                snprintf(buf, sizeof(buf), "softirq%d", i);
                taskqgroup_attach_cpu(qgroup_softirq, &tw->gtask,
                    "tasklet", i, NULL, NULL, buf);
       }
}
SYSINIT(linux_tasklet, SI_SUB_TASKQ, SI_ORDER_THIRD, tasklet_subsystem_init, NULL);

static void
tasklet_subsystem_uninit(void *arg __unused)
{
        struct tasklet_worker *tw;
        int i;

        taskqgroup_drain_all(qgroup_softirq);

        CPU_FOREACH(i) {
                if (CPU_ABSENT(i))
                        continue;

                tw = DPCPU_ID_PTR(i, tasklet_worker);

                taskqgroup_detach(qgroup_softirq, &tw->gtask);
                mtx_destroy(&tw->mtx);
        }
}
SYSUNINIT(linux_tasklet, SI_SUB_TASKQ, SI_ORDER_THIRD, tasklet_subsystem_uninit, NULL);

void
tasklet_init(struct tasklet_struct *ts,
    tasklet_func_t *func, unsigned long data)
{
        ts->entry.tqe_prev = NULL;
        ts->entry.tqe_next = NULL;
        ts->func = func;
        ts->callback = NULL;
        ts->data = data;
        atomic_set_int(&ts->tasklet_state, TASKLET_ST_IDLE);
        atomic_set(&ts->count, 0);
        ts->use_callback = false;
}

void
tasklet_setup(struct tasklet_struct *ts, tasklet_callback_t *c)
{
        ts->entry.tqe_prev = NULL;
        ts->entry.tqe_next = NULL;
        ts->func = NULL;
        ts->callback = c;
        ts->data = 0;
        atomic_set_int(&ts->tasklet_state, TASKLET_ST_IDLE);
        atomic_set(&ts->count, 0);
        ts->use_callback = true;
}

void
local_bh_enable(void)
{
        sched_unpin();
}

void
local_bh_disable(void)
{
        sched_pin();
}

void
tasklet_schedule(struct tasklet_struct *ts)
{

        /* tasklet is paused */
        if (atomic_read(&ts->count))
                return;

        if (TASKLET_ST_CMPSET(ts, TASKLET_ST_EXEC, TASKLET_ST_LOOP)) {
                /* tasklet_handler() will loop */
        } else if (TASKLET_ST_CMPSET(ts, TASKLET_ST_IDLE, TASKLET_ST_BUSY)) {
                struct tasklet_worker *tw;

                tw = &DPCPU_GET(tasklet_worker);

                /* tasklet_handler() was not queued */
                TASKLET_WORKER_LOCK(tw);
                /* enqueue tasklet */
                TAILQ_INSERT_TAIL(&tw->head, ts, entry);
                /* schedule worker */
                GROUPTASK_ENQUEUE(&tw->gtask);
                TASKLET_WORKER_UNLOCK(tw);
        } else {
                /*
                 * tasklet_handler() is already executing
                 *
                 * If the state is neither EXEC nor IDLE, it is either
                 * LOOP or BUSY. If the state changed between the two
                 * CMPSET's above the only possible transitions by
                 * elimination are LOOP->EXEC and BUSY->EXEC. If a
                 * EXEC->LOOP transition was missed that is not a
                 * problem because the callback function is then
                 * already about to be called again.
                 */
        }
}

void
tasklet_kill(struct tasklet_struct *ts)
{

        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "tasklet_kill() can sleep");

        /* wait until tasklet is no longer busy */
        while (TASKLET_ST_GET(ts) != TASKLET_ST_IDLE)
                pause("W", 1);
}

void
tasklet_enable(struct tasklet_struct *ts)
{

        atomic_dec(&ts->count);
}

void
tasklet_disable(struct tasklet_struct *ts)
{

        atomic_inc(&ts->count);
        tasklet_unlock_wait(ts);
}

void
tasklet_disable_nosync(struct tasklet_struct *ts)
{
        atomic_inc(&ts->count);
        barrier();
}

int
tasklet_trylock(struct tasklet_struct *ts)
{

        return (TASKLET_ST_CMPSET(ts, TASKLET_ST_IDLE, TASKLET_ST_BUSY));
}

void
tasklet_unlock(struct tasklet_struct *ts)
{

        TASKLET_ST_SET(ts, TASKLET_ST_IDLE);
}

void
tasklet_unlock_wait(struct tasklet_struct *ts)
{

        WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "tasklet_kill() can sleep");

        /* wait until tasklet is no longer busy */
        while (TASKLET_ST_GET(ts) != TASKLET_ST_IDLE)
                pause("W", 1);
}