/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * 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.
 *
 * $FreeBSD: head/sys/dev/virtio/random/virtio_random.c 338324 2018-08-26 12:51:46Z markm $
 */

/* Driver for VirtIO entropy device. */

#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/module.h>
#include <sys/thread.h>
#include <sys/sglist.h>
#include <sys/callout.h>
#include <sys/random.h>
#include <sys/systm.h>
#include <sys/bus.h>

#include <dev/virtual/virtio/virtio/virtio.h>
#include <dev/virtual/virtio/virtio/virtqueue.h>

struct vtrnd_softc {
        device_t                 vtrnd_dev;
        uint64_t                 vtrnd_features;
        struct callout           vtrnd_callout;
        struct virtqueue        *vtrnd_vq;
};

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 void     vtrnd_negotiate_features(struct vtrnd_softc *);
static int      vtrnd_alloc_virtqueue(struct vtrnd_softc *);
static void     vtrnd_harvest(struct vtrnd_softc *);
static void     vtrnd_timer(void *);

#define VTRND_FEATURES  0

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

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

        DEVMETHOD_END
};

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

DRIVER_MODULE(virtio_random, virtio_pci, vtrnd_driver, vtrnd_devclass,
    vtrnd_modevent, NULL);
MODULE_VERSION(virtio_random, 1);
MODULE_DEPEND(virtio_random, virtio, 1, 1, 1);

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

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

        return (error);
}

static int
vtrnd_probe(device_t dev)
{

        if (virtio_get_device_type(dev) != VIRTIO_ID_ENTROPY)
                return (ENXIO);

        device_set_desc(dev, "VirtIO Entropy Adapter");

        return (BUS_PROBE_DEFAULT);
}

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

        sc = device_get_softc(dev);
        sc->vtrnd_dev = dev;

        callout_init_mp(&sc->vtrnd_callout);

        virtio_set_feature_desc(dev, vtrnd_feature_desc);
        vtrnd_negotiate_features(sc);

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

        callout_reset(&sc->vtrnd_callout, 5 * hz, vtrnd_timer, sc);

fail:
        if (error)
                vtrnd_detach(dev);

        return (error);
}

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

        sc = device_get_softc(dev);

        callout_terminate(&sc->vtrnd_callout);

        return (0);
}

static void
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);
}

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, &sc->vtrnd_vq,
            "%s request", device_get_nameunit(dev));

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

static void
vtrnd_harvest(struct vtrnd_softc *sc)
{
        struct sglist_seg segs[1];
        struct sglist sg;
        struct virtqueue *vq;
        uint32_t value;
        int error;

        vq = sc->vtrnd_vq;

        sglist_init(&sg, 1, segs);
        error = sglist_append(&sg, &value, sizeof(value));
        KASSERT(error == 0 && sg.sg_nseg == 1,
            ("%s: error %d adding buffer to sglist", __func__, error));

        if (!virtqueue_empty(vq))
                return;
        if (virtqueue_enqueue(vq, &value, &sg, 0, 1) != 0)
                return;

        /*
         * Poll for the response, but the command is likely already
         * done when we return from the notify.
         */
        virtqueue_notify(vq, NULL);
        virtqueue_poll(vq, NULL);

        add_buffer_randomness_src((const char *)&value, sizeof(value),
            RAND_SRC_VIRTIO);
}

static void
vtrnd_timer(void *xsc)
{
        struct vtrnd_softc *sc;

        sc = xsc;

        vtrnd_harvest(sc);
        callout_reset(&sc->vtrnd_callout, 5 * hz, vtrnd_timer, sc);
}