1 files changed, 1026 insertions, 0 deletions

diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
new file mode 100644
index 000000000000..257683e7fe8a
--- /dev/null
+++ b/drivers/rpmsg/virtio_rpmsg_bus.c
@@ -0,0 +1,1026 @@
+/*
+ * Virtio-based remote processor messaging bus
+ *
+ * Copyright (C) 2011 Texas Instruments, Inc.
+ * Copyright (C) 2011 Google, Inc.
+ *
+ * Ohad Ben-Cohen <ohad@wizery.com>
+ * Brian Swetland <swetland@google.com>
+ *
+ * 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 - virtual remote processor state
+ * @vdev:       the virtio device
+ * @rvq:        rx virtqueue
+ * @svq:        tx virtqueue
+ * @rbufs:      kernel address of rx buffers
+ * @sbufs:      kernel address of tx buffers
+ * @last_sbuf:  index of last tx buffer used
+ * @bufs_dma:   dma base addr of the buffers
+ * @tx_lock:    protects svq, sbufs and sleepers, to allow concurrent senders.
+ *              sending a message might require waking up a dozing remote
+ *              processor, which involves sleeping, hence the mutex.
+ * @endpoints:  idr of local endpoints, allows fast retrieval
+ * @endpoints_lock: lock of the endpoints set
+ * @sendq:      wait queue of sending contexts waiting for a tx buffers
+ * @sleepers:   number of senders that are waiting for a tx buffer
+ * @ns_ept:     the bus's name service endpoint
+ *
+ * This structure stores the rpmsg state of a given virtio remote processor
+ * device (there might be several virtio proc devices for each physical
+ * remote processor).
+ */
+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 - internal channel info representation
+ * @name: name of service
+ * @src: local address
+ * @dst: destination address
+ */
+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);
+}
+
+/* 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;
+        }
+
+        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);
+        kfree(ept);
+        return NULL;
+}
+
+/**
+ * rpmsg_create_ept() - create a new rpmsg_endpoint
+ * @rpdev: rpmsg channel device
+ * @cb: rx callback handler
+ * @priv: private data for the driver's use
+ * @addr: local rpmsg address to bind with @cb
+ *
+ * Every rpmsg address in the system is bound to an rx callback (so when
+ * inbound messages arrive, they are dispatched by the rpmsg bus using the
+ * appropriate callback handler) by means of an rpmsg_endpoint struct.
+ *
+ * This function allows drivers to create such an endpoint, and by that,
+ * bind a callback, and possibly some private data too, to an rpmsg address
+ * (either one that is known in advance, or one that will be dynamically
+ * assigned for them).
+ *
+ * Simple rpmsg drivers need not call rpmsg_create_ept, because an endpoint
+ * is already created for them when they are probed by the rpmsg bus
+ * (using the rx callback provided when they registered to the rpmsg bus).
+ *
+ * So things should just work for simple drivers: they already have an
+ * endpoint, their rx callback is bound to their rpmsg address, and when
+ * relevant inbound messages arrive (i.e. messages which their dst address
+ * equals to the src address of their rpmsg channel), the driver's handler
+ * is invoked to process it.
+ *
+ * That said, more complicated drivers might do need to allocate
+ * additional rpmsg addresses, and bind them to different rx callbacks.
+ * To accomplish that, those drivers need to call this function.
+ *
+ * Drivers should provide their @rpdev channel (so the new endpoint would belong
+ * to the same remote processor their channel belongs to), an rx callback
+ * function, an optional private data (which is provided back when the
+ * rx callback is invoked), and an address they want to bind with the
+ * callback. If @addr is RPMSG_ADDR_ANY, then rpmsg_create_ept will
+ * dynamically assign them an available rpmsg address (drivers should have
+ * a very good reason why not to always use RPMSG_ADDR_ANY here).
+ *
+ * Returns a pointer to the endpoint on success, or NULL on error.
+ */
+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);
+
+/**
+ * rpmsg_destroy_ept() - destroy an existing rpmsg endpoint
+ * @ept: endpoing to destroy
+ *
+ * Should be used by drivers to destroy an rpmsg endpoint previously
+ * created with rpmsg_create_ept().
+ */
+void rpmsg_destroy_ept(struct rpmsg_endpoint *ept)
+{
+        struct virtproc_info *vrp = ept->rpdev->vrp;
+
+        mutex_lock(&vrp->endpoints_lock);
+        idr_remove(&vrp->endpoints, ept->addr);
+        mutex_unlock(&vrp->endpoints_lock);
+
+        kfree(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,
+};
+
+/**
+ * register_rpmsg_driver() - register an rpmsg driver with the rpmsg bus
+ * @rpdrv: pointer to a struct rpmsg_driver
+ *
+ * Returns 0 on success, and an appropriate error value on failure.
+ */
+int register_rpmsg_driver(struct rpmsg_driver *rpdrv)
+{
+        rpdrv->drv.bus = &rpmsg_bus;
+        return driver_register(&rpdrv->drv);
+}
+EXPORT_SYMBOL(register_rpmsg_driver);
+
+/**
+ * unregister_rpmsg_driver() - unregister an rpmsg driver from the rpmsg bus
+ * @rpdrv: pointer to a struct rpmsg_driver
+ *
+ * Returns 0 on success, and an appropriate error value on failure.
+ */
+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;
+}
+
+/**
+ * rpmsg_upref_sleepers() - enable "tx-complete" interrupts, if needed
+ * @vrp: virtual remote processor state
+ *
+ * This function is called before a sender is blocked, waiting for
+ * a tx buffer to become available.
+ *
+ * If we already have blocking senders, this function merely increases
+ * the "sleepers" reference count, and exits.
+ *
+ * Otherwise, if this is the first sender to block, we also enable
+ * virtio's tx callbacks, so we'd be immediately notified when a tx
+ * buffer is consumed (we rely on virtio's tx callback in order
+ * to wake up sleeping senders as soon as a tx buffer is used by the
+ * remote processor).
+ */
+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);
+}
+
+/**
+ * rpmsg_downref_sleepers() - disable "tx-complete" interrupts, if needed
+ * @vrp: virtual remote processor state
+ *
+ * This function is called after a sender, that waited for a tx buffer
+ * to become available, is unblocked.
+ *
+ * If we still have blocking senders, this function merely decreases
+ * the "sleepers" reference count, and exits.
+ *
+ * Otherwise, if there are no more blocking senders, we also disable
+ * virtio's tx callbacks, to avoid the overhead incurred with handling
+ * those (now redundant) interrupts.
+ */
+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);
+}
+
+/**
+ * rpmsg_send_offchannel_raw() - send a message across to the remote processor
+ * @rpdev: the rpmsg channel
+ * @src: source address
+ * @dst: destination address
+ * @data: payload of message
+ * @len: length of payload
+ * @wait: indicates whether caller should block in case no TX buffers available
+ *
+ * This function is the base implementation for all of the rpmsg sending API.
+ *
+ * It will send @data of length @len to @dst, and say it's from @src. The
+ * message will be sent to the remote processor which the @rpdev channel
+ * belongs to.
+ *
+ * The message is sent using one of the TX buffers that are available for
+ * communication with this remote processor.
+ *
+ * If @wait is true, the caller will be blocked until either a TX buffer is
+ * available, or 15 seconds elapses (we don't want callers to
+ * sleep indefinitely due to misbehaving remote processors), and in that
+ * case -ERESTARTSYS is returned. The number '15' itself was picked
+ * arbitrarily; there's little point in asking drivers to provide a timeout
+ * value themselves.
+ *
+ * Otherwise, if @wait is false, and there are no TX buffers available,
+ * the function will immediately fail, and -ENOMEM will be returned.
+ *
+ * Normally drivers shouldn't use this function directly; instead, drivers
+ * should use the appropriate rpmsg_{try}send{to, _offchannel} API
+ * (see include/linux/rpmsg.h).
+ *
+ * Returns 0 on success and an appropriate error value on failure.
+ */
+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_gfp(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_gfp 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);
+
+        /* use the dst addr to fetch the callback of the appropriate user */
+        mutex_lock(&vrp->endpoints_lock);
+        ept = idr_find(&vrp->endpoints, msg->dst);
+        mutex_unlock(&vrp->endpoints_lock);
+
+        if (ept && ept->cb)
+                ept->cb(ept->rpdev, msg->data, msg->len, ept->priv, msg->src);
+        else
+                dev_warn(dev, "msg received with no recepient\n");
+
+        sg_init_one(&sg, msg, sizeof(*msg) + len);
+
+        /* add the buffer back to the remote processor's virtqueue */
+        err = virtqueue_add_buf_gfp(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, RPMSG_TOTAL_BUF_SPACE,
+                                &vrp->bufs_dma, GFP_KERNEL);
+        if (!bufs_va)
+                goto vqs_del;
+
+        dev_dbg(&vdev->dev, "buffers: va %p, dma 0x%x\n", bufs_va,
+                                                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_gfp(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, 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);
+
+        idr_remove_all(&vrp->endpoints);
+        idr_destroy(&vrp->endpoints);
+
+        vdev->config->del_vqs(vrp->vdev);
+
+        dma_free_coherent(vdev->dev.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;
+}
+module_init(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");