/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2013, Bryan Venteicher <bryanv@FreeBSD.org>
 * 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.
 */

/* Driver for VirtIO entropy device. */

#include <sys/param.h>
#include <sys/types.h>
#include <sys/eventhandler.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/sglist.h>
#include <sys/random.h>
#include <sys/stdatomic.h>

#include <machine/bus.h>
#include <machine/resource.h>
#include <sys/bus.h>

#include <dev/random/randomdev.h>
#include <dev/random/random_harvestq.h>
#include <dev/virtio/virtio.h>
#include <dev/virtio/virtqueue.h>

struct vtrnd_softc {
        device_t                 vtrnd_dev;
        uint64_t                 vtrnd_features;
        struct virtqueue        *vtrnd_vq;
        eventhandler_tag         eh;
        bool                     inactive;
        struct sglist            *vtrnd_sg;
        uint32_t                 *vtrnd_value;
};

static int      vtrnd_modevent(module_t, int, void *);

static int      vtrnd_probe(device_t);
static int      vtrnd_attach(device_t);
static int      vtrnd_detach(device_t);
static int      vtrnd_shutdown(device_t);

static int      vtrnd_negotiate_features(struct vtrnd_softc *);
static int      vtrnd_setup_features(struct vtrnd_softc *);
static int      vtrnd_alloc_virtqueue(struct vtrnd_softc *);
static int      vtrnd_harvest(struct vtrnd_softc *, void *, size_t *);
static void     vtrnd_enqueue(struct vtrnd_softc *sc);
static unsigned vtrnd_read(void *, unsigned);

#define VTRND_FEATURES  0

static struct virtio_feature_desc vtrnd_feature_desc[] = {
        { 0, NULL }
};

static const struct random_source random_vtrnd = {
        .rs_ident = "VirtIO Entropy Adapter",
        .rs_source = RANDOM_PURE_VIRTIO,
        .rs_read = vtrnd_read,
};

/* Kludge for API limitations of random(4). */
static _Atomic(struct vtrnd_softc *) g_vtrnd_softc;

static device_method_t vtrnd_methods[] = {
        /* Device methods. */
        DEVMETHOD(device_probe,         vtrnd_probe),
        DEVMETHOD(device_attach,        vtrnd_attach),
        DEVMETHOD(device_detach,        vtrnd_detach),
        DEVMETHOD(device_shutdown,      vtrnd_shutdown),

        DEVMETHOD_END
};

static driver_t vtrnd_driver = {
        "vtrnd",
        vtrnd_methods,
        sizeof(struct vtrnd_softc)
};

VIRTIO_DRIVER_MODULE(virtio_random, vtrnd_driver, vtrnd_modevent, NULL);
MODULE_VERSION(virtio_random, 1);
MODULE_DEPEND(virtio_random, virtio, 1, 1, 1);
MODULE_DEPEND(virtio_random, random_device, 1, 1, 1);

VIRTIO_SIMPLE_PNPINFO(virtio_random, VIRTIO_ID_ENTROPY,
    "VirtIO Entropy Adapter");

static int
vtrnd_modevent(module_t mod, int type, void *unused)
{
        int error;

        switch (type) {
        case MOD_LOAD:
        case MOD_QUIESCE:
        case MOD_UNLOAD:
        case MOD_SHUTDOWN:
                error = 0;
                break;
        default:
                error = EOPNOTSUPP;
                break;
        }

        return (error);
}

static int
vtrnd_probe(device_t dev)
{
        return (VIRTIO_SIMPLE_PROBE(dev, virtio_random));
}

static int
vtrnd_attach(device_t dev)
{
        struct vtrnd_softc *sc, *exp;
        size_t len;
        int error;

        sc = device_get_softc(dev);
        sc->vtrnd_dev = dev;
        virtio_set_feature_desc(dev, vtrnd_feature_desc);

        len = sizeof(*sc->vtrnd_value) * HARVESTSIZE;
        sc->vtrnd_value = malloc_aligned(len, len, M_DEVBUF, M_WAITOK);
        sc->vtrnd_sg = sglist_build(sc->vtrnd_value, len, M_WAITOK);

        error = vtrnd_setup_features(sc);
        if (error) {
                device_printf(dev, "cannot setup features\n");
                goto fail;
        }

        error = vtrnd_alloc_virtqueue(sc);
        if (error) {
                device_printf(dev, "cannot allocate virtqueue\n");
                goto fail;
        }

        exp = NULL;
        if (!atomic_compare_exchange_strong_explicit(&g_vtrnd_softc, &exp, sc,
            memory_order_release, memory_order_acquire)) {
                error = EEXIST;
                goto fail;
        }

        sc->eh = EVENTHANDLER_REGISTER(shutdown_post_sync,
                vtrnd_shutdown, dev, SHUTDOWN_PRI_LAST + 1); /* ??? */
        if (sc->eh == NULL) {
                device_printf(dev, "Shutdown event registration failed\n");
                error = ENXIO;
                goto fail;
        }

        sc->inactive = false;
        random_source_register(&random_vtrnd);

        vtrnd_enqueue(sc);

fail:
        if (error)
                vtrnd_detach(dev);

        return (error);
}

static int
vtrnd_detach(device_t dev)
{
        struct vtrnd_softc *sc;
        uint32_t rdlen;

        sc = device_get_softc(dev);
        KASSERT(
            atomic_load_explicit(&g_vtrnd_softc, memory_order_acquire) == sc,
            ("only one global instance at a time"));

        sc->inactive = true;
        if (sc->eh != NULL) {
                EVENTHANDLER_DEREGISTER(shutdown_post_sync, sc->eh);
                sc->eh = NULL;
        }
        random_source_deregister(&random_vtrnd);

        /* clear the queue */
        virtqueue_poll(sc->vtrnd_vq, &rdlen);

        atomic_store_explicit(&g_vtrnd_softc, NULL, memory_order_release);
        sglist_free(sc->vtrnd_sg);
        zfree(sc->vtrnd_value, M_DEVBUF);
        return (0);
}

static int
vtrnd_shutdown(device_t dev)
{
        struct vtrnd_softc *sc;

        sc = device_get_softc(dev);
        sc->inactive = true;

        return(0);
}

static int
vtrnd_negotiate_features(struct vtrnd_softc *sc)
{
        device_t dev;
        uint64_t features;

        dev = sc->vtrnd_dev;
        features = VTRND_FEATURES;

        sc->vtrnd_features = virtio_negotiate_features(dev, features);
        return (virtio_finalize_features(dev));
}

static int
vtrnd_setup_features(struct vtrnd_softc *sc)
{
        int error;

        error = vtrnd_negotiate_features(sc);
        if (error)
                return (error);

        return (0);
}

static int
vtrnd_alloc_virtqueue(struct vtrnd_softc *sc)
{
        device_t dev;
        struct vq_alloc_info vq_info;

        dev = sc->vtrnd_dev;

        VQ_ALLOC_INFO_INIT(&vq_info, 0, NULL, sc, &sc->vtrnd_vq,
            "%s request", device_get_nameunit(dev));

        return (virtio_alloc_virtqueues(dev, 1, &vq_info));
}

static void
vtrnd_enqueue(struct vtrnd_softc *sc)
{
        struct virtqueue *vq;
        int error __diagused;

        vq = sc->vtrnd_vq;

        KASSERT(virtqueue_empty(vq), ("%s: non-empty queue", __func__));

        error = virtqueue_enqueue(vq, sc, sc->vtrnd_sg, 0, 1);
        KASSERT(error == 0, ("%s: virtqueue_enqueue returned error: %d",
            __func__, error));

        virtqueue_notify(vq);
}

static int
vtrnd_harvest(struct vtrnd_softc *sc, void *buf, size_t *sz)
{
        struct virtqueue *vq;
        void *cookie;
        uint32_t rdlen;

        if (sc->inactive)
                return (EDEADLK);

        vq = sc->vtrnd_vq;

        cookie = virtqueue_dequeue(vq, &rdlen);
        if (cookie == NULL)
                return (EAGAIN);
        KASSERT(cookie == sc, ("%s: cookie mismatch", __func__));

        *sz = MIN(rdlen, *sz);
        memcpy(buf, sc->vtrnd_value, *sz);

        vtrnd_enqueue(sc);

        return (0);
}

static unsigned
vtrnd_read(void *buf, unsigned usz)
{
        struct vtrnd_softc *sc;
        size_t sz;
        int error;

        sc = g_vtrnd_softc;
        if (sc == NULL)
                return (0);

        sz = usz;
        error = vtrnd_harvest(sc, buf, &sz);
        if (error != 0)
                return (0);

        return (sz);
}