/*      $OpenBSD: viornd.c,v 1.13 2025/09/16 12:18:10 hshoexer Exp $    */

/*
 * Copyright (c) 2014 Stefan Fritsch <sf@sfritsch.de>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/timeout.h>
#include <machine/bus.h>
#include <sys/device.h>
#include <sys/pool.h>
#include <dev/pv/virtioreg.h>
#include <dev/pv/virtiovar.h>

/*
 * The host may not have an unlimited supply of entropy. Therefore, we must
 * not blindly get as much entropy as we can. Instead, we just request
 * VIORND_BUFSIZE bytes at boot and every 15 * (1 << interval_shift) seconds.
 * XXX There should be an API to check if we actually need more entropy.
 *
 * The lowest byte in the flags is used for transport specific settings.
 * Therefore we use the second byte.
 */
#define VIORND_INTERVAL_SHIFT(f)        ((f >> 8) & 0xf)
#define VIORND_INTERVAL_SHIFT_DEFAULT   5
#define VIORND_ONESHOT                  0x1000
#define VIORND_BUFSIZE                  16

#define VIORND_DEBUG 0

struct viornd_softc {
        struct device            sc_dev;
        struct virtio_softc     *sc_virtio;

        struct virtqueue         sc_vq;
        int                     *sc_buf;
        bus_dmamap_t             sc_dmamap;

        unsigned int             sc_interval;
        struct timeout           sc_tick;
};

int     viornd_match(struct device *, void *, void *);
void    viornd_attach(struct device *, struct device *, void *);
int     viornd_vq_done(struct virtqueue *);
void    viornd_tick(void *);

const struct cfattach viornd_ca = {
        sizeof(struct viornd_softc),
        viornd_match,
        viornd_attach,
        NULL
};

struct cfdriver viornd_cd = {
        NULL, "viornd", DV_DULL, CD_COCOVM
};

int
viornd_match(struct device *parent, void *match, void *aux)
{
        struct virtio_attach_args *va = aux;
        if (va->va_devid == PCI_PRODUCT_VIRTIO_ENTROPY)
                return 1;
        return 0;
}

void
viornd_attach(struct device *parent, struct device *self, void *aux)
{
        struct viornd_softc *sc = (struct viornd_softc *)self;
        struct virtio_softc *vsc = (struct virtio_softc *)parent;
        struct virtio_attach_args *va = aux;
        unsigned int shift;

        vsc->sc_vqs = &sc->sc_vq;
        vsc->sc_nvqs = 1;
        if (vsc->sc_child != NULL)
                panic("already attached to something else");
        vsc->sc_child = self;
        vsc->sc_ipl = IPL_NET;
        sc->sc_virtio = vsc;

        if (virtio_negotiate_features(vsc, NULL) != 0)
                goto err;

        if (sc->sc_dev.dv_cfdata->cf_flags & VIORND_ONESHOT) {
                sc->sc_interval = 0;
        } else {
                shift = VIORND_INTERVAL_SHIFT(sc->sc_dev.dv_cfdata->cf_flags);
                if (shift == 0)
                        shift = VIORND_INTERVAL_SHIFT_DEFAULT;
                sc->sc_interval = 15 * (1 << shift);
        }
#if VIORND_DEBUG
        printf(": request interval: %us\n", sc->sc_interval);
#endif

        sc->sc_buf = dma_alloc(VIORND_BUFSIZE, PR_NOWAIT|PR_ZERO);
        if (sc->sc_buf == NULL) {
                printf(": Can't alloc dma buffer\n");
                goto err;
        }
        if (bus_dmamap_create(sc->sc_virtio->sc_dmat, VIORND_BUFSIZE, 1,
            VIORND_BUFSIZE, 0, BUS_DMA_NOWAIT|BUS_DMA_ALLOCNOW,
            &sc->sc_dmamap)) {
                printf(": Can't alloc dmamap\n");
                goto err;
        }
        if (bus_dmamap_load(sc->sc_virtio->sc_dmat, sc->sc_dmamap,
            sc->sc_buf, VIORND_BUFSIZE, NULL, BUS_DMA_NOWAIT|BUS_DMA_READ)) {
                printf(": Can't load dmamap\n");
                goto err2;
        }

        if (virtio_alloc_vq(vsc, &sc->sc_vq, 0, 1, "Entropy request") != 0) {
                printf(": Can't alloc virtqueue\n");
                goto err2;
        }

        sc->sc_vq.vq_done = viornd_vq_done;
        virtio_start_vq_intr(vsc, &sc->sc_vq);
        timeout_set(&sc->sc_tick, viornd_tick, sc);
        timeout_add(&sc->sc_tick, 1);

        printf("\n");
        if (virtio_attach_finish(vsc, va) != 0)
                goto err2;
        return;
err2:
        bus_dmamap_destroy(vsc->sc_dmat, sc->sc_dmamap);
err:
        vsc->sc_child = VIRTIO_CHILD_ERROR;
        if (sc->sc_buf != NULL) {
                dma_free(sc->sc_buf, VIORND_BUFSIZE);
                sc->sc_buf = NULL;
        }
        return;
}

int
viornd_vq_done(struct virtqueue *vq)
{
        struct virtio_softc *vsc = vq->vq_owner;
        struct viornd_softc *sc = (struct viornd_softc *)vsc->sc_child;
        int slot, len, i;

        if (virtio_dequeue(vsc, vq, &slot, &len) != 0)
                return 0;
        bus_dmamap_sync(vsc->sc_dmat, sc->sc_dmamap, 0, VIORND_BUFSIZE,
            BUS_DMASYNC_POSTREAD);
        if (len > VIORND_BUFSIZE) {
                printf("%s: inconsistent descriptor length %d > %d\n",
                    sc->sc_dev.dv_xname, len, VIORND_BUFSIZE);
                goto out;
        }

#if VIORND_DEBUG
        printf("%s: got %d bytes of entropy\n", __func__, len);
#endif
        for (i = 0; (i + 1) * sizeof(int) <= len; i++)
                enqueue_randomness(sc->sc_buf[i]);

        if (sc->sc_interval)
                timeout_add_sec(&sc->sc_tick, sc->sc_interval);

out:
        virtio_dequeue_commit(vq, slot);
        return 1;
}

void
viornd_tick(void *arg)
{
        struct viornd_softc *sc = arg;
        struct virtio_softc *vsc = sc->sc_virtio;
        struct virtqueue *vq = &sc->sc_vq;
        int slot;

        bus_dmamap_sync(vsc->sc_dmat, sc->sc_dmamap, 0, VIORND_BUFSIZE,
            BUS_DMASYNC_PREREAD);
        if (virtio_enqueue_prep(vq, &slot) != 0 ||
            virtio_enqueue_reserve(vq, slot, 1) != 0) {
                panic("%s: virtqueue enqueue failed", sc->sc_dev.dv_xname);
        }
        virtio_enqueue(vq, slot, sc->sc_dmamap, 0);
        virtio_enqueue_commit(vsc, vq, slot, 1);
}