virtio_rpmsg_bus.c

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/*
 * Virtio-based remote processor messaging bus
 *
 * Copyright (C) 2011 Texas Instruments, Inc.
 * Copyright (C) 2011 Google, Inc.
 *
 * Ohad Ben-Cohen <[email protected]>
 * Brian Swetland <[email protected]>
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * 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.
 */

#define pr_fmt(fmt) "%s: " fmt, __func__

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/virtio.h>
#include <linux/virtio_ids.h>
#include <linux/virtio_config.h>
#include <linux/scatterlist.h>
#include <linux/dma-mapping.h>
#include <linux/slab.h>
#include <linux/idr.h>
#include <linux/jiffies.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/rpmsg.h>
#include <linux/mutex.h>

struct virtproc_info {
    struct virtio_device *vdev;
    struct virtqueue *rvq, *svq;
    void *rbufs, *sbufs;
    int last_sbuf;
    dma_addr_t bufs_dma;
    struct mutex tx_lock;
    struct idr endpoints;
    struct mutex endpoints_lock;
    wait_queue_head_t sendq;
    atomic_t sleepers;
    struct rpmsg_endpoint *ns_ept;
};

struct rpmsg_channel_info {
    char name[RPMSG_NAME_SIZE];
    u32 src;
    u32 dst;
};

#define to_rpmsg_channel(d) container_of(d, struct rpmsg_channel, dev)
#define to_rpmsg_driver(d) container_of(d, struct rpmsg_driver, drv)

/*
 * We're allocating 512 buffers of 512 bytes for communications, and then
 * using the first 256 buffers for RX, and the last 256 buffers for TX.
 *
 * Each buffer will have 16 bytes for the msg header and 496 bytes for
 * the payload.
 *
 * This will require a total space of 256KB for the buffers.
 *
 * We might also want to add support for user-provided buffers in time.
 * This will allow bigger buffer size flexibility, and can also be used
 * to achieve zero-copy messaging.
 *
 * Note that these numbers are purely a decision of this driver - we
 * can change this without changing anything in the firmware of the remote
 * processor.
 */
#define RPMSG_NUM_BUFS      (512)
#define RPMSG_BUF_SIZE      (512)
#define RPMSG_TOTAL_BUF_SPACE   (RPMSG_NUM_BUFS * RPMSG_BUF_SIZE)

/*
 * Local addresses are dynamically allocated on-demand.
 * We do not dynamically assign addresses from the low 1024 range,
 * in order to reserve that address range for predefined services.
 */
#define RPMSG_RESERVED_ADDRESSES    (1024)

/* Address 53 is reserved for advertising remote services */
#define RPMSG_NS_ADDR           (53)

/* sysfs show configuration fields */
#define rpmsg_show_attr(field, path, format_string)         \
static ssize_t                              \
field##_show(struct device *dev,                    \
            struct device_attribute *attr, char *buf)   \
{                                   \
    struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);        \
                                    \
    return sprintf(buf, format_string, rpdev->path);        \
}

/* for more info, see Documentation/ABI/testing/sysfs-bus-rpmsg */
rpmsg_show_attr(name, id.name, "%s\n");
rpmsg_show_attr(src, src, "0x%x\n");
rpmsg_show_attr(dst, dst, "0x%x\n");
rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n");

/*
 * Unique (and free running) index for rpmsg devices.
 *
 * Yeah, we're not recycling those numbers (yet?). will be easy
 * to change if/when we want to.
 */
static unsigned int rpmsg_dev_index;

static ssize_t modalias_show(struct device *dev,
                 struct device_attribute *attr, char *buf)
{
    struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);

    return sprintf(buf, RPMSG_DEVICE_MODALIAS_FMT "\n", rpdev->id.name);
}

static struct device_attribute rpmsg_dev_attrs[] = {
    __ATTR_RO(name),
    __ATTR_RO(modalias),
    __ATTR_RO(dst),
    __ATTR_RO(src),
    __ATTR_RO(announce),
    __ATTR_NULL
};

/* rpmsg devices and drivers are matched using the service name */
static inline int rpmsg_id_match(const struct rpmsg_channel *rpdev,
                  const struct rpmsg_device_id *id)
{
    return strncmp(id->name, rpdev->id.name, RPMSG_NAME_SIZE) == 0;
}

/* match rpmsg channel and rpmsg driver */
static int rpmsg_dev_match(struct device *dev, struct device_driver *drv)
{
    struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);
    struct rpmsg_driver *rpdrv = to_rpmsg_driver(drv);
    const struct rpmsg_device_id *ids = rpdrv->id_table;
    unsigned int i;

    for (i = 0; ids[i].name[0]; i++)
        if (rpmsg_id_match(rpdev, &ids[i]))
            return 1;

    return 0;
}

static int rpmsg_uevent(struct device *dev, struct kobj_uevent_env *env)
{
    struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);

    return add_uevent_var(env, "MODALIAS=" RPMSG_DEVICE_MODALIAS_FMT,
                    rpdev->id.name);
}

static void __ept_release(struct kref *kref)
{
    struct rpmsg_endpoint *ept = container_of(kref, struct rpmsg_endpoint,
                          refcount);
    /*
     * At this point no one holds a reference to ept anymore,
     * so we can directly free it
     */
    kfree(ept);
}

/* for more info, see below documentation of rpmsg_create_ept() */
static struct rpmsg_endpoint *__rpmsg_create_ept(struct virtproc_info *vrp,
        struct rpmsg_channel *rpdev, rpmsg_rx_cb_t cb,
        void *priv, u32 addr)
{
    int err, tmpaddr, request;
    struct rpmsg_endpoint *ept;
    struct device *dev = rpdev ? &rpdev->dev : &vrp->vdev->dev;

    if (!idr_pre_get(&vrp->endpoints, GFP_KERNEL))
        return NULL;

    ept = kzalloc(sizeof(*ept), GFP_KERNEL);
    if (!ept) {
        dev_err(dev, "failed to kzalloc a new ept\n");
        return NULL;
    }

    kref_init(&ept->refcount);
    mutex_init(&ept->cb_lock);

    ept->rpdev = rpdev;
    ept->cb = cb;
    ept->priv = priv;

    /* do we need to allocate a local address ? */
    request = addr == RPMSG_ADDR_ANY ? RPMSG_RESERVED_ADDRESSES : addr;

    mutex_lock(&vrp->endpoints_lock);

    /* bind the endpoint to an rpmsg address (and allocate one if needed) */
    err = idr_get_new_above(&vrp->endpoints, ept, request, &tmpaddr);
    if (err) {
        dev_err(dev, "idr_get_new_above failed: %d\n", err);
        goto free_ept;
    }

    /* make sure the user's address request is fulfilled, if relevant */
    if (addr != RPMSG_ADDR_ANY && tmpaddr != addr) {
        dev_err(dev, "address 0x%x already in use\n", addr);
        goto rem_idr;
    }

    ept->addr = tmpaddr;

    mutex_unlock(&vrp->endpoints_lock);

    return ept;

rem_idr:
    idr_remove(&vrp->endpoints, request);
free_ept:
    mutex_unlock(&vrp->endpoints_lock);
    kref_put(&ept->refcount, __ept_release);
    return NULL;
}

struct rpmsg_endpoint *rpmsg_create_ept(struct rpmsg_channel *rpdev,
                rpmsg_rx_cb_t cb, void *priv, u32 addr)
{
    return __rpmsg_create_ept(rpdev->vrp, rpdev, cb, priv, addr);
}
EXPORT_SYMBOL(rpmsg_create_ept);

static void
__rpmsg_destroy_ept(struct virtproc_info *vrp, struct rpmsg_endpoint *ept)
{
    /* make sure new inbound messages can't find this ept anymore */
    mutex_lock(&vrp->endpoints_lock);
    idr_remove(&vrp->endpoints, ept->addr);
    mutex_unlock(&vrp->endpoints_lock);

    /* make sure in-flight inbound messages won't invoke cb anymore */
    mutex_lock(&ept->cb_lock);
    ept->cb = NULL;
    mutex_unlock(&ept->cb_lock);

    kref_put(&ept->refcount, __ept_release);
}

void rpmsg_destroy_ept(struct rpmsg_endpoint *ept)
{
    __rpmsg_destroy_ept(ept->rpdev->vrp, ept);
}
EXPORT_SYMBOL(rpmsg_destroy_ept);

/*
 * when an rpmsg driver is probed with a channel, we seamlessly create
 * it an endpoint, binding its rx callback to a unique local rpmsg
 * address.
 *
 * if we need to, we also announce about this channel to the remote
 * processor (needed in case the driver is exposing an rpmsg service).
 */
static int rpmsg_dev_probe(struct device *dev)
{
    struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);
    struct rpmsg_driver *rpdrv = to_rpmsg_driver(rpdev->dev.driver);
    struct virtproc_info *vrp = rpdev->vrp;
    struct rpmsg_endpoint *ept;
    int err;

    ept = rpmsg_create_ept(rpdev, rpdrv->callback, NULL, rpdev->src);
    if (!ept) {
        dev_err(dev, "failed to create endpoint\n");
        err = -ENOMEM;
        goto out;
    }

    rpdev->ept = ept;
    rpdev->src = ept->addr;

    err = rpdrv->probe(rpdev);
    if (err) {
        dev_err(dev, "%s: failed: %d\n", __func__, err);
        rpmsg_destroy_ept(ept);
        goto out;
    }

    /* need to tell remote processor's name service about this channel ? */
    if (rpdev->announce &&
            virtio_has_feature(vrp->vdev, VIRTIO_RPMSG_F_NS)) {
        struct rpmsg_ns_msg nsm;

        strncpy(nsm.name, rpdev->id.name, RPMSG_NAME_SIZE);
        nsm.addr = rpdev->src;
        nsm.flags = RPMSG_NS_CREATE;

        err = rpmsg_sendto(rpdev, &nsm, sizeof(nsm), RPMSG_NS_ADDR);
        if (err)
            dev_err(dev, "failed to announce service %d\n", err);
    }

out:
    return err;
}

static int rpmsg_dev_remove(struct device *dev)
{
    struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);
    struct rpmsg_driver *rpdrv = to_rpmsg_driver(rpdev->dev.driver);
    struct virtproc_info *vrp = rpdev->vrp;
    int err = 0;

    /* tell remote processor's name service we're removing this channel */
    if (rpdev->announce &&
            virtio_has_feature(vrp->vdev, VIRTIO_RPMSG_F_NS)) {
        struct rpmsg_ns_msg nsm;

        strncpy(nsm.name, rpdev->id.name, RPMSG_NAME_SIZE);
        nsm.addr = rpdev->src;
        nsm.flags = RPMSG_NS_DESTROY;

        err = rpmsg_sendto(rpdev, &nsm, sizeof(nsm), RPMSG_NS_ADDR);
        if (err)
            dev_err(dev, "failed to announce service %d\n", err);
    }

    rpdrv->remove(rpdev);

    rpmsg_destroy_ept(rpdev->ept);

    return err;
}

static struct bus_type rpmsg_bus = {
    .name       = "rpmsg",
    .match      = rpmsg_dev_match,
    .dev_attrs  = rpmsg_dev_attrs,
    .uevent     = rpmsg_uevent,
    .probe      = rpmsg_dev_probe,
    .remove     = rpmsg_dev_remove,
};

int register_rpmsg_driver(struct rpmsg_driver *rpdrv)
{
    rpdrv->drv.bus = &rpmsg_bus;
    return driver_register(&rpdrv->drv);
}
EXPORT_SYMBOL(register_rpmsg_driver);

void unregister_rpmsg_driver(struct rpmsg_driver *rpdrv)
{
    driver_unregister(&rpdrv->drv);
}
EXPORT_SYMBOL(unregister_rpmsg_driver);

static void rpmsg_release_device(struct device *dev)
{
    struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);

    kfree(rpdev);
}

/*
 * match an rpmsg channel with a channel info struct.
 * this is used to make sure we're not creating rpmsg devices for channels
 * that already exist.
 */
static int rpmsg_channel_match(struct device *dev, void *data)
{
    struct rpmsg_channel_info *chinfo = data;
    struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);

    if (chinfo->src != RPMSG_ADDR_ANY && chinfo->src != rpdev->src)
        return 0;

    if (chinfo->dst != RPMSG_ADDR_ANY && chinfo->dst != rpdev->dst)
        return 0;

    if (strncmp(chinfo->name, rpdev->id.name, RPMSG_NAME_SIZE))
        return 0;

    /* found a match ! */
    return 1;
}

/*
 * create an rpmsg channel using its name and address info.
 * this function will be used to create both static and dynamic
 * channels.
 */
static struct rpmsg_channel *rpmsg_create_channel(struct virtproc_info *vrp,
                struct rpmsg_channel_info *chinfo)
{
    struct rpmsg_channel *rpdev;
    struct device *tmp, *dev = &vrp->vdev->dev;
    int ret;

    /* make sure a similar channel doesn't already exist */
    tmp = device_find_child(dev, chinfo, rpmsg_channel_match);
    if (tmp) {
        /* decrement the matched device's refcount back */
        put_device(tmp);
        dev_err(dev, "channel %s:%x:%x already exist\n",
                chinfo->name, chinfo->src, chinfo->dst);
        return NULL;
    }

    rpdev = kzalloc(sizeof(struct rpmsg_channel), GFP_KERNEL);
    if (!rpdev) {
        pr_err("kzalloc failed\n");
        return NULL;
    }

    rpdev->vrp = vrp;
    rpdev->src = chinfo->src;
    rpdev->dst = chinfo->dst;

    /*
     * rpmsg server channels has predefined local address (for now),
     * and their existence needs to be announced remotely
     */
    rpdev->announce = rpdev->src != RPMSG_ADDR_ANY ? true : false;

    strncpy(rpdev->id.name, chinfo->name, RPMSG_NAME_SIZE);

    /* very simple device indexing plumbing which is enough for now */
    dev_set_name(&rpdev->dev, "rpmsg%d", rpmsg_dev_index++);

    rpdev->dev.parent = &vrp->vdev->dev;
    rpdev->dev.bus = &rpmsg_bus;
    rpdev->dev.release = rpmsg_release_device;

    ret = device_register(&rpdev->dev);
    if (ret) {
        dev_err(dev, "device_register failed: %d\n", ret);
        put_device(&rpdev->dev);
        return NULL;
    }

    return rpdev;
}

/*
 * find an existing channel using its name + address properties,
 * and destroy it
 */
static int rpmsg_destroy_channel(struct virtproc_info *vrp,
                    struct rpmsg_channel_info *chinfo)
{
    struct virtio_device *vdev = vrp->vdev;
    struct device *dev;

    dev = device_find_child(&vdev->dev, chinfo, rpmsg_channel_match);
    if (!dev)
        return -EINVAL;

    device_unregister(dev);

    put_device(dev);

    return 0;
}

/* super simple buffer "allocator" that is just enough for now */
static void *get_a_tx_buf(struct virtproc_info *vrp)
{
    unsigned int len;
    void *ret;

    /* support multiple concurrent senders */
    mutex_lock(&vrp->tx_lock);

    /*
     * either pick the next unused tx buffer
     * (half of our buffers are used for sending messages)
     */
    if (vrp->last_sbuf < RPMSG_NUM_BUFS / 2)
        ret = vrp->sbufs + RPMSG_BUF_SIZE * vrp->last_sbuf++;
    /* or recycle a used one */
    else
        ret = virtqueue_get_buf(vrp->svq, &len);

    mutex_unlock(&vrp->tx_lock);

    return ret;
}

static void rpmsg_upref_sleepers(struct virtproc_info *vrp)
{
    /* support multiple concurrent senders */
    mutex_lock(&vrp->tx_lock);

    /* are we the first sleeping context waiting for tx buffers ? */
    if (atomic_inc_return(&vrp->sleepers) == 1)
        /* enable "tx-complete" interrupts before dozing off */
        virtqueue_enable_cb(vrp->svq);

    mutex_unlock(&vrp->tx_lock);
}

static void rpmsg_downref_sleepers(struct virtproc_info *vrp)
{
    /* support multiple concurrent senders */
    mutex_lock(&vrp->tx_lock);

    /* are we the last sleeping context waiting for tx buffers ? */
    if (atomic_dec_and_test(&vrp->sleepers))
        /* disable "tx-complete" interrupts */
        virtqueue_disable_cb(vrp->svq);

    mutex_unlock(&vrp->tx_lock);
}

int rpmsg_send_offchannel_raw(struct rpmsg_channel *rpdev, u32 src, u32 dst,
                    void *data, int len, bool wait)
{
    struct virtproc_info *vrp = rpdev->vrp;
    struct device *dev = &rpdev->dev;
    struct scatterlist sg;
    struct rpmsg_hdr *msg;
    int err;

    /* bcasting isn't allowed */
    if (src == RPMSG_ADDR_ANY || dst == RPMSG_ADDR_ANY) {
        dev_err(dev, "invalid addr (src 0x%x, dst 0x%x)\n", src, dst);
        return -EINVAL;
    }

    /*
     * We currently use fixed-sized buffers, and therefore the payload
     * length is limited.
     *
     * One of the possible improvements here is either to support
     * user-provided buffers (and then we can also support zero-copy
     * messaging), or to improve the buffer allocator, to support
     * variable-length buffer sizes.
     */
    if (len > RPMSG_BUF_SIZE - sizeof(struct rpmsg_hdr)) {
        dev_err(dev, "message is too big (%d)\n", len);
        return -EMSGSIZE;
    }

    /* grab a buffer */
    msg = get_a_tx_buf(vrp);
    if (!msg && !wait)
        return -ENOMEM;

    /* no free buffer ? wait for one (but bail after 15 seconds) */
    while (!msg) {
        /* enable "tx-complete" interrupts, if not already enabled */
        rpmsg_upref_sleepers(vrp);

        /*
         * sleep until a free buffer is available or 15 secs elapse.
         * the timeout period is not configurable because there's
         * little point in asking drivers to specify that.
         * if later this happens to be required, it'd be easy to add.
         */
        err = wait_event_interruptible_timeout(vrp->sendq,
                    (msg = get_a_tx_buf(vrp)),
                    msecs_to_jiffies(15000));

        /* disable "tx-complete" interrupts if we're the last sleeper */
        rpmsg_downref_sleepers(vrp);

        /* timeout ? */
        if (!err) {
            dev_err(dev, "timeout waiting for a tx buffer\n");
            return -ERESTARTSYS;
        }
    }

    msg->len = len;
    msg->flags = 0;
    msg->src = src;
    msg->dst = dst;
    msg->reserved = 0;
    memcpy(msg->data, data, len);

    dev_dbg(dev, "TX From 0x%x, To 0x%x, Len %d, Flags %d, Reserved %d\n",
                    msg->src, msg->dst, msg->len,
                    msg->flags, msg->reserved);
    print_hex_dump(KERN_DEBUG, "rpmsg_virtio TX: ", DUMP_PREFIX_NONE, 16, 1,
                    msg, sizeof(*msg) + msg->len, true);

    sg_init_one(&sg, msg, sizeof(*msg) + len);

    mutex_lock(&vrp->tx_lock);

    /* add message to the remote processor's virtqueue */
    err = virtqueue_add_buf(vrp->svq, &sg, 1, 0, msg, GFP_KERNEL);
    if (err < 0) {
        /*
         * need to reclaim the buffer here, otherwise it's lost
         * (memory won't leak, but rpmsg won't use it again for TX).
         * this will wait for a buffer management overhaul.
         */
        dev_err(dev, "virtqueue_add_buf failed: %d\n", err);
        goto out;
    }

    /* tell the remote processor it has a pending message to read */
    virtqueue_kick(vrp->svq);

    err = 0;
out:
    mutex_unlock(&vrp->tx_lock);
    return err;
}
EXPORT_SYMBOL(rpmsg_send_offchannel_raw);

/* called when an rx buffer is used, and it's time to digest a message */
static void rpmsg_recv_done(struct virtqueue *rvq)
{
    struct rpmsg_hdr *msg;
    unsigned int len;
    struct rpmsg_endpoint *ept;
    struct scatterlist sg;
    struct virtproc_info *vrp = rvq->vdev->priv;
    struct device *dev = &rvq->vdev->dev;
    int err;

    msg = virtqueue_get_buf(rvq, &len);
    if (!msg) {
        dev_err(dev, "uhm, incoming signal, but no used buffer ?\n");
        return;
    }

    dev_dbg(dev, "From: 0x%x, To: 0x%x, Len: %d, Flags: %d, Reserved: %d\n",
                    msg->src, msg->dst, msg->len,
                    msg->flags, msg->reserved);
    print_hex_dump(KERN_DEBUG, "rpmsg_virtio RX: ", DUMP_PREFIX_NONE, 16, 1,
                    msg, sizeof(*msg) + msg->len, true);

    /*
     * We currently use fixed-sized buffers, so trivially sanitize
     * the reported payload length.
     */
    if (len > RPMSG_BUF_SIZE ||
        msg->len > (len - sizeof(struct rpmsg_hdr))) {
        dev_warn(dev, "inbound msg too big: (%d, %d)\n", len, msg->len);
        return;
    }

    /* use the dst addr to fetch the callback of the appropriate user */
    mutex_lock(&vrp->endpoints_lock);

    ept = idr_find(&vrp->endpoints, msg->dst);

    /* let's make sure no one deallocates ept while we use it */
    if (ept)
        kref_get(&ept->refcount);

    mutex_unlock(&vrp->endpoints_lock);

    if (ept) {
        /* make sure ept->cb doesn't go away while we use it */
        mutex_lock(&ept->cb_lock);

        if (ept->cb)
            ept->cb(ept->rpdev, msg->data, msg->len, ept->priv,
                msg->src);

        mutex_unlock(&ept->cb_lock);

        /* farewell, ept, we don't need you anymore */
        kref_put(&ept->refcount, __ept_release);
    } else
        dev_warn(dev, "msg received with no recepient\n");

    /* publish the real size of the buffer */
    sg_init_one(&sg, msg, RPMSG_BUF_SIZE);

    /* add the buffer back to the remote processor's virtqueue */
    err = virtqueue_add_buf(vrp->rvq, &sg, 0, 1, msg, GFP_KERNEL);
    if (err < 0) {
        dev_err(dev, "failed to add a virtqueue buffer: %d\n", err);
        return;
    }

    /* tell the remote processor we added another available rx buffer */
    virtqueue_kick(vrp->rvq);
}

/*
 * This is invoked whenever the remote processor completed processing
 * a TX msg we just sent it, and the buffer is put back to the used ring.
 *
 * Normally, though, we suppress this "tx complete" interrupt in order to
 * avoid the incurred overhead.
 */
static void rpmsg_xmit_done(struct virtqueue *svq)
{
    struct virtproc_info *vrp = svq->vdev->priv;

    dev_dbg(&svq->vdev->dev, "%s\n", __func__);

    /* wake up potential senders that are waiting for a tx buffer */
    wake_up_interruptible(&vrp->sendq);
}

/* invoked when a name service announcement arrives */
static void rpmsg_ns_cb(struct rpmsg_channel *rpdev, void *data, int len,
                            void *priv, u32 src)
{
    struct rpmsg_ns_msg *msg = data;
    struct rpmsg_channel *newch;
    struct rpmsg_channel_info chinfo;
    struct virtproc_info *vrp = priv;
    struct device *dev = &vrp->vdev->dev;
    int ret;

    print_hex_dump(KERN_DEBUG, "NS announcement: ",
            DUMP_PREFIX_NONE, 16, 1,
            data, len, true);

    if (len != sizeof(*msg)) {
        dev_err(dev, "malformed ns msg (%d)\n", len);
        return;
    }

    /*
     * the name service ept does _not_ belong to a real rpmsg channel,
     * and is handled by the rpmsg bus itself.
     * for sanity reasons, make sure a valid rpdev has _not_ sneaked
     * in somehow.
     */
    if (rpdev) {
        dev_err(dev, "anomaly: ns ept has an rpdev handle\n");
        return;
    }

    /* don't trust the remote processor for null terminating the name */
    msg->name[RPMSG_NAME_SIZE - 1] = '\0';

    dev_info(dev, "%sing channel %s addr 0x%x\n",
            msg->flags & RPMSG_NS_DESTROY ? "destroy" : "creat",
            msg->name, msg->addr);

    strncpy(chinfo.name, msg->name, sizeof(chinfo.name));
    chinfo.src = RPMSG_ADDR_ANY;
    chinfo.dst = msg->addr;

    if (msg->flags & RPMSG_NS_DESTROY) {
        ret = rpmsg_destroy_channel(vrp, &chinfo);
        if (ret)
            dev_err(dev, "rpmsg_destroy_channel failed: %d\n", ret);
    } else {
        newch = rpmsg_create_channel(vrp, &chinfo);
        if (!newch)
            dev_err(dev, "rpmsg_create_channel failed\n");
    }
}

static int rpmsg_probe(struct virtio_device *vdev)
{
    vq_callback_t *vq_cbs[] = { rpmsg_recv_done, rpmsg_xmit_done };
    const char *names[] = { "input", "output" };
    struct virtqueue *vqs[2];
    struct virtproc_info *vrp;
    void *bufs_va;
    int err = 0, i;

    vrp = kzalloc(sizeof(*vrp), GFP_KERNEL);
    if (!vrp)
        return -ENOMEM;

    vrp->vdev = vdev;

    idr_init(&vrp->endpoints);
    mutex_init(&vrp->endpoints_lock);
    mutex_init(&vrp->tx_lock);
    init_waitqueue_head(&vrp->sendq);

    /* We expect two virtqueues, rx and tx (and in this order) */
    err = vdev->config->find_vqs(vdev, 2, vqs, vq_cbs, names);
    if (err)
        goto free_vrp;

    vrp->rvq = vqs[0];
    vrp->svq = vqs[1];

    /* allocate coherent memory for the buffers */
    bufs_va = dma_alloc_coherent(vdev->dev.parent->parent,
                RPMSG_TOTAL_BUF_SPACE,
                &vrp->bufs_dma, GFP_KERNEL);
    if (!bufs_va)
        goto vqs_del;

    dev_dbg(&vdev->dev, "buffers: va %p, dma 0x%llx\n", bufs_va,
                    (unsigned long long)vrp->bufs_dma);

    /* half of the buffers is dedicated for RX */
    vrp->rbufs = bufs_va;

    /* and half is dedicated for TX */
    vrp->sbufs = bufs_va + RPMSG_TOTAL_BUF_SPACE / 2;

    /* set up the receive buffers */
    for (i = 0; i < RPMSG_NUM_BUFS / 2; i++) {
        struct scatterlist sg;
        void *cpu_addr = vrp->rbufs + i * RPMSG_BUF_SIZE;

        sg_init_one(&sg, cpu_addr, RPMSG_BUF_SIZE);

        err = virtqueue_add_buf(vrp->rvq, &sg, 0, 1, cpu_addr,
                                GFP_KERNEL);
        WARN_ON(err < 0); /* sanity check; this can't really happen */
    }

    /* suppress "tx-complete" interrupts */
    virtqueue_disable_cb(vrp->svq);

    vdev->priv = vrp;

    /* if supported by the remote processor, enable the name service */
    if (virtio_has_feature(vdev, VIRTIO_RPMSG_F_NS)) {
        /* a dedicated endpoint handles the name service msgs */
        vrp->ns_ept = __rpmsg_create_ept(vrp, NULL, rpmsg_ns_cb,
                        vrp, RPMSG_NS_ADDR);
        if (!vrp->ns_ept) {
            dev_err(&vdev->dev, "failed to create the ns ept\n");
            err = -ENOMEM;
            goto free_coherent;
        }
    }

    /* tell the remote processor it can start sending messages */
    virtqueue_kick(vrp->rvq);

    dev_info(&vdev->dev, "rpmsg host is online\n");

    return 0;

free_coherent:
    dma_free_coherent(vdev->dev.parent->parent, RPMSG_TOTAL_BUF_SPACE,
                    bufs_va, vrp->bufs_dma);
vqs_del:
    vdev->config->del_vqs(vrp->vdev);
free_vrp:
    kfree(vrp);
    return err;
}

static int rpmsg_remove_device(struct device *dev, void *data)
{
    device_unregister(dev);

    return 0;
}

static void __devexit rpmsg_remove(struct virtio_device *vdev)
{
    struct virtproc_info *vrp = vdev->priv;
    int ret;

    vdev->config->reset(vdev);

    ret = device_for_each_child(&vdev->dev, NULL, rpmsg_remove_device);
    if (ret)
        dev_warn(&vdev->dev, "can't remove rpmsg device: %d\n", ret);

    if (vrp->ns_ept)
        __rpmsg_destroy_ept(vrp, vrp->ns_ept);

    idr_remove_all(&vrp->endpoints);
    idr_destroy(&vrp->endpoints);

    vdev->config->del_vqs(vrp->vdev);

    dma_free_coherent(vdev->dev.parent->parent, RPMSG_TOTAL_BUF_SPACE,
                    vrp->rbufs, vrp->bufs_dma);

    kfree(vrp);
}

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

static unsigned int features[] = {
    VIRTIO_RPMSG_F_NS,
};

static struct virtio_driver virtio_ipc_driver = {
    .feature_table  = features,
    .feature_table_size = ARRAY_SIZE(features),
    .driver.name    = KBUILD_MODNAME,
    .driver.owner   = THIS_MODULE,
    .id_table   = id_table,
    .probe      = rpmsg_probe,
    .remove     = __devexit_p(rpmsg_remove),
};

static int __init rpmsg_init(void)
{
    int ret;

    ret = bus_register(&rpmsg_bus);
    if (ret) {
        pr_err("failed to register rpmsg bus: %d\n", ret);
        return ret;
    }

    ret = register_virtio_driver(&virtio_ipc_driver);
    if (ret) {
        pr_err("failed to register virtio driver: %d\n", ret);
        bus_unregister(&rpmsg_bus);
    }

    return ret;
}
subsys_initcall(rpmsg_init);

static void __exit rpmsg_fini(void)
{
    unregister_virtio_driver(&virtio_ipc_driver);
    bus_unregister(&rpmsg_bus);
}
module_exit(rpmsg_fini);

MODULE_DEVICE_TABLE(virtio, id_table);
MODULE_DESCRIPTION("Virtio-based remote processor messaging bus");
MODULE_LICENSE("GPL v2");