/*
 * Randomness driver for virtio
 *  Copyright (C) 2007, 2008 Rusty Russell IBM Corporation
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#include <linux/err.h>
#include <linux/hw_random.h>
#include <linux/scatterlist.h>
#include <linux/spinlock.h>
#include <linux/virtio.h>
#include <linux/virtio_rng.h>
#include <linux/module.h>

static DEFINE_IDA(rng_index_ida);

struct virtrng_info {
        struct virtio_device *vdev;
        struct hwrng hwrng;
        struct virtqueue *vq;
        unsigned int data_avail;
        struct completion have_data;
        bool busy;
        char name[25];
        int index;
};

static bool probe_done;

static void random_recv_done(struct virtqueue *vq)
{
        struct virtrng_info *vi = vq->vdev->priv;

        /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */
        if (!virtqueue_get_buf(vi->vq, &vi->data_avail))
                return;

        complete(&vi->have_data);
}

/* The host will fill any buffer we give it with sweet, sweet randomness. */
static void register_buffer(struct virtrng_info *vi, u8 *buf, size_t size)
{
        struct scatterlist sg;

        sg_init_one(&sg, buf, size);

        /* There should always be room for one buffer. */
        virtqueue_add_inbuf(vi->vq, &sg, 1, buf, GFP_KERNEL);

        virtqueue_kick(vi->vq);
}

static int virtio_read(struct hwrng *rng, void *buf, size_t size, bool wait)
{
        int ret;
        struct virtrng_info *vi = (struct virtrng_info *)rng->priv;

        /*
         * Don't ask host for data till we're setup.  This call can
         * happen during hwrng_register(), after commit d9e7972619.
         */
        if (unlikely(!probe_done))
                return 0;

        if (!vi->busy) {
                vi->busy = true;
                init_completion(&vi->have_data);
                register_buffer(vi, buf, size);
        }

        if (!wait)
                return 0;

        ret = wait_for_completion_killable(&vi->have_data);
        if (ret < 0)
                return ret;

        vi->busy = false;

        return vi->data_avail;
}

static void virtio_cleanup(struct hwrng *rng)
{
        struct virtrng_info *vi = (struct virtrng_info *)rng->priv;

        if (vi->busy)
                wait_for_completion(&vi->have_data);
}

static int probe_common(struct virtio_device *vdev)
{
        int err, index;
        struct virtrng_info *vi = NULL;

        vi = kzalloc(sizeof(struct virtrng_info), GFP_KERNEL);
        if (!vi)
                return -ENOMEM;

        vi->index = index = ida_simple_get(&rng_index_ida, 0, 0, GFP_KERNEL);
        if (index < 0) {
                kfree(vi);
                return index;
        }
        sprintf(vi->name, "virtio_rng.%d", index);
        init_completion(&vi->have_data);

        vi->hwrng = (struct hwrng) {
                .read = virtio_read,
                .cleanup = virtio_cleanup,
                .priv = (unsigned long)vi,
                .name = vi->name,
        };
        vdev->priv = vi;

        /* We expect a single virtqueue. */
        vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input");
        if (IS_ERR(vi->vq)) {
                err = PTR_ERR(vi->vq);
                vi->vq = NULL;
                kfree(vi);
                ida_simple_remove(&rng_index_ida, index);
                return err;
        }

        err = hwrng_register(&vi->hwrng);
        if (err) {
                vdev->config->del_vqs(vdev);
                vi->vq = NULL;
                kfree(vi);
                ida_simple_remove(&rng_index_ida, index);
                return err;
        }

        probe_done = true;
        return 0;
}

static void remove_common(struct virtio_device *vdev)
{
        struct virtrng_info *vi = vdev->priv;
        vdev->config->reset(vdev);
        vi->busy = false;
        hwrng_unregister(&vi->hwrng);
        vdev->config->del_vqs(vdev);
        ida_simple_remove(&rng_index_ida, vi->index);
        kfree(vi);
}

static int virtrng_probe(struct virtio_device *vdev)
{
        return probe_common(vdev);
}

static void virtrng_remove(struct virtio_device *vdev)
{
        remove_common(vdev);
}

#ifdef CONFIG_PM_SLEEP
static int virtrng_freeze(struct virtio_device *vdev)
{
        remove_common(vdev);
        return 0;
}

static int virtrng_restore(struct virtio_device *vdev)
{
        return probe_common(vdev);
}
#endif

static struct virtio_device_id id_table[] = {
        { VIRTIO_ID_RNG, VIRTIO_DEV_ANY_ID },
        { 0 },
};

static struct virtio_driver virtio_rng_driver = {
        .driver.name =  KBUILD_MODNAME,
        .driver.owner = THIS_MODULE,
        .id_table =     id_table,
        .probe =        virtrng_probe,
        .remove =       virtrng_remove,
#ifdef CONFIG_PM_SLEEP
        .freeze =       virtrng_freeze,
        .restore =      virtrng_restore,
#endif
};

module_virtio_driver(virtio_rng_driver);
MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio random number driver");
MODULE_LICENSE("GPL");