drivers: introduce rpmsg, a remote-processor messaging virtio bus

Add a virtio IPC bus, which enables kernel users to communicate
with remote processors over shared memory using a simple messaging
protocol.

Assign a local address for every local endpoint that is created,
and bind it to the user's callback. Invoke that callback when a message
is received carrying the user's address as the destination addr.

Change-Id: I0c6804859c2344bdddd433075d4116d88eea67e4
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>

8 files changed, 1012 insertions, 0 deletions

diff --git a/drivers/Kconfig b/drivers/Kconfig
index 72175f3..85ac967 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -127,4 +127,8 @@ source "drivers/hwspinlock/Kconfig"
 source "drivers/clocksource/Kconfig"
 
 source "drivers/remoteproc/Kconfig"
+
+source "drivers/virtio/Kconfig"
+
+source "drivers/rpmsg/Kconfig"
 endmenu
diff --git a/drivers/Makefile b/drivers/Makefile
index 4d53a18..2980a15 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -22,6 +22,7 @@ obj-$(CONFIG_ARM_AMBA)		+= amba/
 obj-$(CONFIG_DMA_ENGINE)	+= dma/
 
 obj-$(CONFIG_VIRTIO)		+= virtio/
+obj-$(CONFIG_RPMSG)		+= rpmsg/
 obj-$(CONFIG_XEN)		+= xen/
 
 # regulators early, since some subsystems rely on them to initialize
diff --git a/drivers/rpmsg/Kconfig b/drivers/rpmsg/Kconfig
new file mode 100644
index 0000000..d4d39bf
--- /dev/null
+++ b/drivers/rpmsg/Kconfig
@@ -0,0 +1,15 @@
+config RPMSG
+	tristate "Virtio-based remote processor messaging bus"
+	select VIRTIO
+	select VIRTIO_RING
+	depends on OMAP_RPMSG
+	---help---
+	  This virtio driver provides support for shared-memory-based
+          remote processor messaging, by registering the RPMSG bus which
+          in turn enables a handful of IPC drivers.
+
+	  Such support is usually required to offload cpu-intensive
+          or latency-sensitive tasks to specialized remote processors with
+          dedicated hardware accelerators and/or real-time properties.
+
+	  If unsure, say N.
diff --git a/drivers/rpmsg/Makefile b/drivers/rpmsg/Makefile
new file mode 100644
index 0000000..7617fcb
--- /dev/null
+++ b/drivers/rpmsg/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_RPMSG)	+= virtio_rpmsg_bus.o
diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
new file mode 100644
index 0000000..5dde5fc
--- /dev/null
+++ b/drivers/rpmsg/virtio_rpmsg_bus.c
@@ -0,0 +1,789 @@
+/*
+ * 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/slab.h>
+#include <linux/idr.h>
+#include <linux/jiffies.h>
+#include <linux/sched.h>
+#include <linux/wait.h>
+#include <linux/rpmsg.h>
+
+/**
+ * struct virtproc_info - virtual remote processor info
+ *
+ * @vdev:	the virtio device
+ * @rvq:	rx virtqueue (from pov of local processor)
+ * @svq:	tx virtqueue (from pov of local processor)
+ * @rbufs:	address of rx buffers
+ * @sbufs:	address of tx buffers
+ * @last_rbuf:	index of last rx buffer used
+ * @last_sbuf:	index of last tx buffer used
+ * @sim_base:	simulated base addr base to make virtio's virt_to_page happy
+ * @svq_lock:	protects the tx virtqueue, to allow several concurrent senders
+ * @num_bufs:	total number of buffers allocated for communicating with this
+ *		virtual remote processor. half is used for rx and half for tx.
+ * @buf_size:	size of buffers allocated for communications
+ * @endpoints:	the set of local endpoints
+ * @endpoints_lock: lock of the endpoints set
+ * @sendq:	wait queue of sending contexts waiting for free rpmsg 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 rproc devices for each physical
+ * remote processor).
+ */
+struct virtproc_info {
+	struct virtio_device *vdev;
+	struct virtqueue *rvq, *svq;
+	void *rbufs, *sbufs;
+	int last_rbuf, last_sbuf;
+	void *sim_base;
+	spinlock_t svq_lock;
+	int num_bufs;
+	int buf_size;
+	struct idr endpoints;
+	spinlock_t endpoints_lock;
+	wait_queue_head_t sendq;
+	struct rpmsg_endpoint *ns_ept;
+};
+
+#define to_rpmsg_channel(d) container_of(d, struct rpmsg_channel, dev)
+#define to_rpmsg_driver(d) container_of(d, struct rpmsg_driver, drv)
+
+/*
+ * 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)
+
+/* 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);		\
+}
+
+rpmsg_show_attr(name, id.name, "%s\n");
+rpmsg_show_attr(dst, dst, "0x%x\n");
+rpmsg_show_attr(src, src, "0x%x\n");
+rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n");
+
+/* unique (free running) numbering for rpmsg devices */
+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
+};
+
+static inline int rpmsg_id_match(const struct rpmsg_channel *rpdev,
+				  const struct rpmsg_device_id *id)
+{
+	if (strncmp(id->name, rpdev->id.name, RPMSG_NAME_SIZE))
+		return 0;
+
+	return 1;
+}
+
+/* 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 struct rpmsg_endpoint *__rpmsg_create_ept(struct virtproc_info *vrp,
+		struct rpmsg_channel *rpdev,
+		void (*cb)(struct rpmsg_channel *, void *, int, void *, u32),
+		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;
+
+	spin_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;
+	}
+
+	if (addr != RPMSG_ADDR_ANY && tmpaddr != addr) {
+		dev_err(dev, "address 0x%x already in use\n", addr);
+		goto rem_idr;
+	}
+
+	ept->addr = tmpaddr;
+
+	spin_unlock(&vrp->endpoints_lock);
+
+	return ept;
+
+rem_idr:
+	idr_remove(&vrp->endpoints, request);
+free_ept:
+	spin_unlock(&vrp->endpoints_lock);
+	kfree(ept);
+	return NULL;
+}
+
+struct rpmsg_endpoint *rpmsg_create_ept(struct rpmsg_channel *rpdev,
+		void (*cb)(struct rpmsg_channel *, void *, int, void *, u32),
+		void *priv, u32 addr)
+{
+	return __rpmsg_create_ept(rpdev->vrp, rpdev, cb, priv, addr);
+}
+EXPORT_SYMBOL(rpmsg_create_ept);
+
+void rpmsg_destroy_ept(struct rpmsg_endpoint *ept)
+{
+	struct virtproc_info *vrp = ept->rpdev->vrp;
+
+	spin_lock(&vrp->endpoints_lock);
+	idr_remove(&vrp->endpoints, ept->addr);
+	spin_unlock(&vrp->endpoints_lock);
+
+	kfree(ept);
+}
+EXPORT_SYMBOL(rpmsg_destroy_ept);
+
+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 channel info structs */
+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;
+
+	return 1;
+}
+
+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) {
+		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, 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 just works (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);
+		kfree(rpdev);
+		return NULL;
+	}
+
+	return rpdev;
+}
+
+static void rpmsg_destroy_channel(struct rpmsg_channel *rpdev)
+{
+	device_unregister(&rpdev->dev);
+}
+
+static int rpmsg_destroy_channel_by_info(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;
+
+	rpmsg_destroy_channel(to_rpmsg_channel(dev));
+
+	return 0;
+}
+
+/* minimal buf "allocator" that is just enough for now */
+static void *get_a_buf(struct virtproc_info *vrp)
+{
+	unsigned int len;
+
+	/* either pick the next unused buffer */
+	if (vrp->last_sbuf < vrp->num_bufs / 2)
+		return vrp->sbufs + vrp->buf_size * vrp->last_sbuf++;
+	/* or recycle a used one */
+	else
+		return virtqueue_get_buf(vrp->svq, &len);
+}
+
+/* XXX: the blocking 'wait' mechanism hasn't been tested yet */
+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;
+	unsigned long offset;
+	void *sim_addr;
+
+	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;
+	}
+
+	/* the payload's size is currently limited */
+	if (len > vrp->buf_size - sizeof(struct rpmsg_hdr)) {
+		dev_err(dev, "message is too big (%d)\n", len);
+		return -EMSGSIZE;
+	}
+
+	/* grab a buffer */
+	msg = get_a_buf(vrp);
+	if (!msg && !wait)
+		return -ENOMEM;
+
+	/* no free buffer ? wait for one (but bail after 15 seconds) */
+	while (!msg) {
+		/* enable "tx-complete" interrupts before dozing off */
+		virtqueue_enable_cb(vrp->svq);
+		/*
+		 * sleep until a free buffer is available or 15 secs elapse.
+		 * the timeout period is not configurable because frankly
+		 * i don't see why drivers need to deal with that.
+		 * if later this happens to be required, it'd be easy to add.
+		 */
+		if (wait_event_interruptible_timeout(vrp->sendq,
+					(msg = get_a_buf(vrp)),
+					msecs_to_jiffies(15000)))
+			return -ERESTARTSYS;
+		/* on success, suppress "tx-complete" interrupts again */
+		if (msg)
+			virtqueue_disable_cb(vrp->svq);
+	}
+
+	msg->len = len;
+	msg->flags = 0;
+	msg->src = src;
+	msg->dst = dst;
+	msg->unused = 0;
+	memcpy(msg->data, data, len);
+
+	dev_dbg(dev, "TX From 0x%x, To 0x%x, Len %d, Flags %d, Unused %d\n",
+					msg->src, msg->dst, msg->len,
+					msg->flags, msg->unused);
+	print_hex_dump(KERN_DEBUG, "rpmsg_virtio TX: ", DUMP_PREFIX_NONE, 16, 1,
+					msg, sizeof(*msg) + msg->len, true);
+
+	offset = ((unsigned long) msg) - ((unsigned long) vrp->rbufs);
+	sim_addr = vrp->sim_base + offset;
+	sg_init_one(&sg, sim_addr, sizeof(*msg) + len);
+
+	/* protect svq from simultaneous concurrent manipulations */
+	spin_lock(&vrp->svq_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) {
+		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:
+	spin_unlock(&vrp->svq_lock);
+	return err;
+}
+EXPORT_SYMBOL(rpmsg_send_offchannel_raw);
+
+static void rpmsg_recv_done(struct virtqueue *rvq)
+{
+	struct rpmsg_hdr *msg;
+	unsigned int len;
+	struct rpmsg_endpoint *ept;
+	struct scatterlist sg;
+	unsigned long offset;
+	void *sim_addr;
+	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, Unused: %d\n",
+					msg->src, msg->dst, msg->len,
+					msg->flags, msg->unused);
+	print_hex_dump(KERN_DEBUG, "rpmsg_virtio RX: ", DUMP_PREFIX_NONE, 16, 1,
+					msg, sizeof(*msg) + msg->len, true);
+
+	/* fetch the callback of the appropriate user */
+	spin_lock(&vrp->endpoints_lock);
+	ept = idr_find(&vrp->endpoints, msg->dst);
+	spin_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");
+
+	/* add the buffer back to the remote processor's virtqueue */
+	offset = ((unsigned long) msg) - ((unsigned long) vrp->rbufs);
+	sim_addr = vrp->sim_base + offset;
+	sg_init_one(&sg, sim_addr, sizeof(*msg) + len);
+
+	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);
+}
+
+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 processes that are waiting for a buffer */
+	wake_up_interruptible(&vrp->sendq);
+}
+
+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, __func__, 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_by_info(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 *addr;
+	int err, i, num_bufs, buf_size, total_buf_size;
+	struct rpmsg_channel_info *ch;
+
+	vrp = kzalloc(sizeof(*vrp), GFP_KERNEL);
+	if (!vrp)
+		return -ENOMEM;
+
+	vrp->vdev = vdev;
+
+	idr_init(&vrp->endpoints);
+	spin_lock_init(&vrp->endpoints_lock);
+	spin_lock_init(&vrp->svq_lock);
+	init_waitqueue_head(&vrp->sendq);
+
+	/* We expect two virtqueues, rx and tx (in this order) */
+	err = vdev->config->find_vqs(vdev, 2, vqs, vq_cbs, names);
+	if (err)
+		goto free_vi;
+
+	vrp->rvq = vqs[0];
+	vrp->svq = vqs[1];
+
+	/* Platform must supply pre-allocated uncached buffers for now */
+	vdev->config->get(vdev, VPROC_BUF_ADDR, &addr, sizeof(addr));
+	vdev->config->get(vdev, VPROC_BUF_NUM, &num_bufs,
+							sizeof(num_bufs));
+	vdev->config->get(vdev, VPROC_BUF_SZ, &buf_size, sizeof(buf_size));
+
+	total_buf_size = num_bufs * buf_size;
+
+	dev_dbg(&vdev->dev, "%d buffers, size %d, addr 0x%x, total 0x%x\n",
+		num_bufs, buf_size, (unsigned int) addr, total_buf_size);
+
+	vrp->num_bufs = num_bufs;
+	vrp->buf_size = buf_size;
+	vrp->rbufs = addr;
+	vrp->sbufs = addr + total_buf_size / 2;
+
+	/* simulated addr base to make virt_to_page happy */
+	vdev->config->get(vdev, VPROC_SIM_BASE, &vrp->sim_base,
+							sizeof(vrp->sim_base));
+
+	/* set up the receive buffers */
+	for (i = 0; i < num_bufs / 2; i++) {
+		struct scatterlist sg;
+		void *tmpaddr = vrp->rbufs + i * buf_size;
+		void *simaddr = vrp->sim_base + i * buf_size;
+
+		sg_init_one(&sg, simaddr, buf_size);
+		err = virtqueue_add_buf_gfp(vrp->rvq, &sg, 0, 1, tmpaddr,
+								GFP_KERNEL);
+		WARN_ON(err < 0); /* sanity check; this can't really happen */
+	}
+
+	/* tell the remote processor it can start sending data */
+	virtqueue_kick(vrp->rvq);
+
+	/* suppress "tx-complete" interrupts */
+	virtqueue_disable_cb(vrp->svq);
+
+	vdev->priv = vrp;
+
+	dev_info(&vdev->dev, "rpmsg backend virtproc probed successfully\n");
+
+	/* if supported by the remote processor, enable the name service */
+	if (virtio_has_feature(vdev, VIRTIO_RPMSG_F_NS)) {
+		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 vqs_del;
+		}
+	}
+
+	/* look for platform-specific static channels */
+	vdev->config->get(vdev, VPROC_STATIC_CHANNELS, &ch, sizeof(ch));
+
+	for (i = 0; ch && ch[i].name[0]; i++)
+		rpmsg_create_channel(vrp, &ch[i]);
+
+	return 0;
+
+vqs_del:
+	vdev->config->del_vqs(vrp->vdev);
+free_vi:
+	kfree(vrp);
+	return err;
+}
+
+static int rpmsg_remove_device(struct device *dev, void *data)
+{
+	struct rpmsg_channel *rpdev = to_rpmsg_channel(dev);
+
+	rpmsg_destroy_channel(rpdev);
+
+	return 0;
+}
+
+static void __devexit rpmsg_remove(struct virtio_device *vdev)
+{
+	struct virtproc_info *vrp = vdev->priv;
+	int ret;
+
+	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);
+
+	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 init(void)
+{
+	int ret;
+
+	ret = bus_register(&rpmsg_bus);
+	if (ret) {
+		pr_err("failed to register rpmsg bus: %d\n", ret);
+		return ret;
+	}
+
+	return register_virtio_driver(&virtio_ipc_driver);
+}
+module_init(init);
+
+static void __exit fini(void)
+{
+	unregister_virtio_driver(&virtio_ipc_driver);
+	bus_unregister(&rpmsg_bus);
+}
+module_exit(fini);
+
+MODULE_DEVICE_TABLE(virtio, id_table);
+MODULE_DESCRIPTION("Virtio-based remote processor messaging bus");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index ae28e93..561567e 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -533,4 +533,14 @@ struct isapnp_device_id {
 	kernel_ulong_t driver_data;	/* data private to the driver */
 };
 
+/* rpmsg */
+
+#define RPMSG_NAME_SIZE			32
+#define RPMSG_DEVICE_MODALIAS_FMT	"rpmsg:%s"
+
+struct rpmsg_device_id {
+	char name[RPMSG_NAME_SIZE];
+	kernel_ulong_t driver_data	/* Data private to the driver */
+			__attribute__((aligned(sizeof(kernel_ulong_t))));
+};
 #endif /* LINUX_MOD_DEVICETABLE_H */
diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
new file mode 100644
index 0000000..1f7ba09
--- /dev/null
+++ b/include/linux/rpmsg.h
@@ -0,0 +1,191 @@
+/*
+ * Remote processor messaging
+ *
+ * Copyright(c) 2011 Texas Instruments. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * * Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * * 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.
+ * * Neither the name Texas Instruments nor the names of its
+ *   contributors may be used to endorse or promote products derived
+ *   from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "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 COPYRIGHT
+ * OWNER OR CONTRIBUTORS 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.
+ */
+
+#ifndef _LINUX_RPMSG_H
+#define _LINUX_RPMSG_H
+
+#include <linux/types.h>
+#include <linux/device.h>
+#include <linux/mod_devicetable.h>
+
+/* The feature bitmap for virtio rpmsg */
+#define VIRTIO_RPMSG_F_NS	0 /* RP supports name service notifications */
+
+/**
+ * struct rpmsg_hdr -
+ *
+ * ... keep documenting ...
+ */
+struct rpmsg_hdr {
+	u16 len;
+	u16 flags;
+	u32 src;
+	u32 dst;
+	u32 unused;
+	u8 data[0];
+} __packed;
+
+enum rpmsg_ns_flags {
+	RPMSG_NS_CREATE		= 0,
+	RPMSG_NS_DESTROY	= 1,
+};
+
+struct rpmsg_ns_msg {
+	char name[RPMSG_NAME_SIZE];
+	u32 addr;
+	u32 flags;
+} __packed;
+
+/* driver requests */
+enum {
+	VPROC_BUF_ADDR,
+	VPROC_BUF_NUM,
+	VPROC_BUF_SZ,
+	VPROC_SIM_BASE,
+	VPROC_STATIC_CHANNELS,
+};
+
+#define RPMSG_ADDR_ANY		0xFFFFFFFF
+
+struct virtproc_info;
+
+/**
+ * rpmsg_channel - rpmsg channels are the devices of the rpmsg bus
+ *
+ * @vrp: the remote processor this channel connects to
+ * @dev: underlying device
+ * @id: the device type identification (used to match an rpmsg driver)
+ * @src: local address of this channel
+ * @dst: destination address of the remote service
+ * @priv: private pointer for the driver's use.
+ * @ept: local rpmsg endpoint of this channel
+ * @announce: need to tell remoteproc about channel creation/removal
+ */
+struct rpmsg_channel {
+	struct virtproc_info *vrp;
+	struct device dev;
+	struct rpmsg_device_id id;
+	u32 src;
+	u32 dst;
+	void *priv;
+	struct rpmsg_endpoint *ept;
+	bool announce;
+};
+
+struct rpmsg_channel_info {
+	char name[RPMSG_NAME_SIZE];
+	u32 src;
+	u32 dst;
+};
+
+/**
+ * struct rpmsg_endpoint
+ *
+ * @rpdev:
+ * @cb:
+ * @src: local rpmsg address
+ * @priv:
+ */
+struct rpmsg_endpoint {
+	struct rpmsg_channel *rpdev;
+	void (*cb)(struct rpmsg_channel *, void *, int, void *, u32);
+	u32 addr;
+	void *priv;
+};
+
+/**
+ * rpmsg_driver - operations for a rpmsg I/O driver
+ * @driver: underlying device driver (populate name and owner).
+ * @id_table: the ids serviced by this driver.
+ * @probe: the function to call when a device is found.  Returns 0 or -errno.
+ * @remove: the function when a device is removed.
+ * @callback: invoked when a message is received on the channel
+ */
+struct rpmsg_driver {
+	struct device_driver drv;
+	const struct rpmsg_device_id *id_table;
+	int (*probe)(struct rpmsg_channel *dev);
+	void (*remove)(struct rpmsg_channel *dev);
+	void (*callback)(struct rpmsg_channel *, void *, int, void *, u32);
+};
+
+int register_rpmsg_device(struct rpmsg_channel *dev);
+void unregister_rpmsg_device(struct rpmsg_channel *dev);
+int register_rpmsg_driver(struct rpmsg_driver *drv);
+void unregister_rpmsg_driver(struct rpmsg_driver *drv);
+void rpmsg_destroy_ept(struct rpmsg_endpoint *);
+struct rpmsg_endpoint *rpmsg_create_ept(struct rpmsg_channel *,
+		void (*cb)(struct rpmsg_channel *, void *, int, void *, u32),
+		void *priv, u32 addr);
+
+int
+rpmsg_send_offchannel_raw(struct rpmsg_channel *, u32, u32, void *, int, bool);
+
+static inline
+int rpmsg_send_offchannel(struct rpmsg_channel *rpdev, u32 src, u32 dst,
+							void *data, int len)
+{
+	return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, true);
+}
+
+static inline int rpmsg_send(struct rpmsg_channel *rpdev, void *data, int len)
+{
+	return rpmsg_send_offchannel(rpdev, rpdev->src, rpdev->dst, data, len);
+}
+
+static inline
+int rpmsg_sendto(struct rpmsg_channel *rpdev, void *data, int len, u32 dst)
+{
+	return rpmsg_send_offchannel(rpdev, rpdev->src, dst, data, len);
+}
+
+static inline
+int rpmsg_trysend_offchannel(struct rpmsg_channel *rpdev, u32 src, u32 dst,
+							void *data, int len)
+{
+	return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, false);
+}
+
+static inline
+int rpmsg_trysend(struct rpmsg_channel *rpdev, void *data, int len)
+{
+	return rpmsg_trysend_offchannel(rpdev, rpdev->src, rpdev->dst,
+								data, len);
+}
+
+static inline
+int rpmsg_trysendto(struct rpmsg_channel *rpdev, void *data, int len, u32 dst)
+{
+	return rpmsg_trysend_offchannel(rpdev, rpdev->src, dst, data, len);
+}
+
+#endif /* _LINUX_RPMSG_H */
diff --git a/include/linux/virtio_ids.h b/include/linux/virtio_ids.h
index 85bb0bb..1520c06 100644
--- a/include/linux/virtio_ids.h
+++ b/include/linux/virtio_ids.h
@@ -35,5 +35,6 @@
 #define VIRTIO_ID_RNG		4 /* virtio ring */
 #define VIRTIO_ID_BALLOON	5 /* virtio balloon */
 #define VIRTIO_ID_9P		9 /* 9p virtio console */
+#define VIRTIO_ID_RPMSG		10 /* virtio remote processor messaging */
 
 #endif /* _LINUX_VIRTIO_IDS_H */