// SPDX-License-Identifier: GPL-2.0

  /*
   * 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>

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

  #include <linux/dma-mapping.h>
  #include <linux/idr.h>
  #include <linux/jiffies.h>

  #include <linux/kernel.h>
  #include <linux/module.h>

  #include <linux/mutex.h>
  #include <linux/of_device.h>
  #include <linux/rpmsg.h>

  #include <linux/scatterlist.h>

  #include <linux/slab.h>

  #include <linux/sched.h>

  #include <linux/virtio.h>

  #include <linux/virtio_byteorder.h>

  #include <linux/virtio_ids.h>
  #include <linux/virtio_config.h>

  #include <linux/wait.h>

  #include "rpmsg_internal.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

   * @num_bufs:	total number of buffers for rx and tx

   * @buf_size:   size of one rx or tx buffer

   * @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;

  	unsigned int num_bufs;

  	unsigned int buf_size;

  	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;
  };

  /* The feature bitmap for virtio rpmsg */
  #define VIRTIO_RPMSG_F_NS	0 /* RP supports name service notifications */
  
  /**
   * struct rpmsg_hdr - common header for all rpmsg messages
   * @src: source address
   * @dst: destination address
   * @reserved: reserved for future use
   * @len: length of payload (in bytes)
   * @flags: message flags
   * @data: @len bytes of message payload data
   *
   * Every message sent(/received) on the rpmsg bus begins with this header.
   */
  struct rpmsg_hdr {

  	__virtio32 src;
  	__virtio32 dst;
  	__virtio32 reserved;
  	__virtio16 len;
  	__virtio16 flags;

  	u8 data[];

  } __packed;
  
  /**
   * struct rpmsg_ns_msg - dynamic name service announcement message
   * @name: name of remote service that is published
   * @addr: address of remote service that is published
   * @flags: indicates whether service is created or destroyed
   *
   * This message is sent across to publish a new service, or announce
   * about its removal. When we receive these messages, an appropriate
   * rpmsg channel (i.e device) is created/destroyed. In turn, the ->probe()
   * or ->remove() handler of the appropriate rpmsg driver will be invoked
   * (if/as-soon-as one is registered).
   */
  struct rpmsg_ns_msg {
  	char name[RPMSG_NAME_SIZE];

  	__virtio32 addr;
  	__virtio32 flags;

  } __packed;
  
  /**
   * enum rpmsg_ns_flags - dynamic name service announcement flags
   *
   * @RPMSG_NS_CREATE: a new remote service was just created
   * @RPMSG_NS_DESTROY: a known remote service was just destroyed
   */
  enum rpmsg_ns_flags {
  	RPMSG_NS_CREATE		= 0,
  	RPMSG_NS_DESTROY	= 1,
  };

  /**

   * struct virtio_rpmsg_channel - rpmsg channel descriptor
   * @rpdev: the rpmsg channel device
   * @vrp: the virtio remote processor device this channel belongs to
   *
   * This structure stores the channel that links the rpmsg device to the virtio
   * remote processor device.

   */
  struct virtio_rpmsg_channel {
  	struct rpmsg_device rpdev;
  
  	struct virtproc_info *vrp;
  };
  
  #define to_virtio_rpmsg_channel(_rpdev) \
  	container_of(_rpdev, struct virtio_rpmsg_channel, rpdev)

  /*

   * We're allocating buffers of 512 bytes each for communications. The
   * number of buffers will be computed from the number of buffers supported
   * by the vring, upto a maximum of 512 buffers (256 in each direction).

   *
   * Each buffer will have 16 bytes for the msg header and 496 bytes for
   * the payload.
   *

   * This will utilize a maximum 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 MAX_RPMSG_NUM_BUFS	(512)

  #define MAX_RPMSG_BUF_SIZE	(512)

  
  /*
   * 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)

  static void virtio_rpmsg_destroy_ept(struct rpmsg_endpoint *ept);
  static int virtio_rpmsg_send(struct rpmsg_endpoint *ept, void *data, int len);
  static int virtio_rpmsg_sendto(struct rpmsg_endpoint *ept, void *data, int len,
  			       u32 dst);
  static int virtio_rpmsg_send_offchannel(struct rpmsg_endpoint *ept, u32 src,
  					u32 dst, void *data, int len);
  static int virtio_rpmsg_trysend(struct rpmsg_endpoint *ept, void *data, int len);
  static int virtio_rpmsg_trysendto(struct rpmsg_endpoint *ept, void *data,
  				  int len, u32 dst);
  static int virtio_rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src,
  					   u32 dst, void *data, int len);

  static const struct rpmsg_endpoint_ops virtio_endpoint_ops = {
  	.destroy_ept = virtio_rpmsg_destroy_ept,
  	.send = virtio_rpmsg_send,
  	.sendto = virtio_rpmsg_sendto,
  	.send_offchannel = virtio_rpmsg_send_offchannel,
  	.trysend = virtio_rpmsg_trysend,
  	.trysendto = virtio_rpmsg_trysendto,
  	.trysend_offchannel = virtio_rpmsg_trysend_offchannel,
  };

  /**

   * rpmsg_sg_init - initialize scatterlist according to cpu address location
   * @sg: scatterlist to fill
   * @cpu_addr: virtual address of the buffer
   * @len: buffer length
   *
   * An internal function filling scatterlist according to virtual address
   * location (in vmalloc or in kernel).
   */
  static void
  rpmsg_sg_init(struct scatterlist *sg, void *cpu_addr, unsigned int len)
  {
  	if (is_vmalloc_addr(cpu_addr)) {
  		sg_init_table(sg, 1);
  		sg_set_page(sg, vmalloc_to_page(cpu_addr), len,
  			    offset_in_page(cpu_addr));
  	} else {
  		WARN_ON(!virt_addr_valid(cpu_addr));
  		sg_init_one(sg, cpu_addr, len);
  	}
  }
  
  /**

   * __ept_release() - deallocate an rpmsg endpoint
   * @kref: the ept's reference count
   *
   * This function deallocates an ept, and is invoked when its @kref refcount
   * drops to zero.
   *
   * Never invoke this function directly!
   */
  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_device *rpdev,

  						 rpmsg_rx_cb_t cb,
  						 void *priv, u32 addr)

  {

  	int id_min, id_max, id;

  	struct rpmsg_endpoint *ept;
  	struct device *dev = rpdev ? &rpdev->dev : &vrp->vdev->dev;

  	ept = kzalloc(sizeof(*ept), GFP_KERNEL);

  	if (!ept)

  		return NULL;

  	kref_init(&ept->refcount);

  	mutex_init(&ept->cb_lock);

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

  	ept->ops = &virtio_endpoint_ops;

  
  	/* do we need to allocate a local address ? */

  	if (addr == RPMSG_ADDR_ANY) {
  		id_min = RPMSG_RESERVED_ADDRESSES;
  		id_max = 0;
  	} else {
  		id_min = addr;
  		id_max = addr + 1;
  	}

  
  	mutex_lock(&vrp->endpoints_lock);
  
  	/* bind the endpoint to an rpmsg address (and allocate one if needed) */

  	id = idr_alloc(&vrp->endpoints, ept, id_min, id_max, GFP_KERNEL);
  	if (id < 0) {
  		dev_err(dev, "idr_alloc failed: %d
  ", id);

  		goto free_ept;
  	}

  	ept->addr = id;

  
  	mutex_unlock(&vrp->endpoints_lock);
  
  	return ept;

  free_ept:
  	mutex_unlock(&vrp->endpoints_lock);

  	kref_put(&ept->refcount, __ept_release);

  	return NULL;
  }

  static struct rpmsg_endpoint *virtio_rpmsg_create_ept(struct rpmsg_device *rpdev,
  						      rpmsg_rx_cb_t cb,
  						      void *priv,
  						      struct rpmsg_channel_info chinfo)
  {

  	struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
  
  	return __rpmsg_create_ept(vch->vrp, rpdev, cb, priv, chinfo.src);

  }

  /**

   * __rpmsg_destroy_ept() - destroy an existing rpmsg endpoint
   * @vrp: virtproc which owns this ept

   * @ept: endpoing to destroy
   *

   * An internal function which destroy an ept without assuming it is
   * bound to an rpmsg channel. This is needed for handling the internal
   * name service endpoint, which isn't bound to an rpmsg channel.
   * See also __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);

  }

  static void virtio_rpmsg_destroy_ept(struct rpmsg_endpoint *ept)
  {

  	struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(ept->rpdev);
  
  	__rpmsg_destroy_ept(vch->vrp, ept);

  }

  static int virtio_rpmsg_announce_create(struct rpmsg_device *rpdev)
  {

  	struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
  	struct virtproc_info *vrp = vch->vrp;

  	struct device *dev = &rpdev->dev;
  	int err = 0;

  	/* need to tell remote processor's name service about this channel ? */

  	if (rpdev->announce && rpdev->ept &&

  	    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 = cpu_to_virtio32(vrp->vdev, rpdev->ept->addr);
  		nsm.flags = cpu_to_virtio32(vrp->vdev, RPMSG_NS_CREATE);

  		err = rpmsg_sendto(rpdev->ept, &nsm, sizeof(nsm), RPMSG_NS_ADDR);

  		if (err)
  			dev_err(dev, "failed to announce service %d
  ", err);
  	}

  	return err;
  }

  static int virtio_rpmsg_announce_destroy(struct rpmsg_device *rpdev)

  {

  	struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
  	struct virtproc_info *vrp = vch->vrp;

  	struct device *dev = &rpdev->dev;

  	int err = 0;
  
  	/* tell remote processor's name service we're removing this channel */

  	if (rpdev->announce && rpdev->ept &&

  	    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 = cpu_to_virtio32(vrp->vdev, rpdev->ept->addr);
  		nsm.flags = cpu_to_virtio32(vrp->vdev, RPMSG_NS_DESTROY);

  		err = rpmsg_sendto(rpdev->ept, &nsm, sizeof(nsm), RPMSG_NS_ADDR);

  		if (err)
  			dev_err(dev, "failed to announce service %d
  ", err);
  	}

  	return err;
  }

  static const struct rpmsg_device_ops virtio_rpmsg_ops = {
  	.create_ept = virtio_rpmsg_create_ept,
  	.announce_create = virtio_rpmsg_announce_create,
  	.announce_destroy = virtio_rpmsg_announce_destroy,
  };

  static void virtio_rpmsg_release_device(struct device *dev)
  {
  	struct rpmsg_device *rpdev = to_rpmsg_device(dev);
  	struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
  
  	kfree(vch);
  }

  /*
   * 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_device *rpmsg_create_channel(struct virtproc_info *vrp,
  						 struct rpmsg_channel_info *chinfo)

  {

  	struct virtio_rpmsg_channel *vch;

  	struct rpmsg_device *rpdev;

  	struct device *tmp, *dev = &vrp->vdev->dev;
  	int ret;
  
  	/* make sure a similar channel doesn't already exist */

  	tmp = rpmsg_find_device(dev, chinfo);

  	if (tmp) {
  		/* decrement the matched device's refcount back */
  		put_device(tmp);
  		dev_err(dev, "channel %s:%x:%x already exist
  ",
  				chinfo->name, chinfo->src, chinfo->dst);
  		return NULL;
  	}

  	vch = kzalloc(sizeof(*vch), GFP_KERNEL);
  	if (!vch)

  		return NULL;

  	/* Link the channel to our vrp */
  	vch->vrp = vrp;

  	/* Assign public information to the rpmsg_device */
  	rpdev = &vch->rpdev;

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

  	rpdev->ops = &virtio_rpmsg_ops;

  
  	/*
  	 * rpmsg server channels has predefined local address (for now),
  	 * and their existence needs to be announced remotely
  	 */

  	rpdev->announce = rpdev->src != RPMSG_ADDR_ANY;

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

  	rpdev->dev.parent = &vrp->vdev->dev;

  	rpdev->dev.release = virtio_rpmsg_release_device;

  	ret = rpmsg_register_device(rpdev);
  	if (ret)
  		return NULL;
  
  	return rpdev;
  }

  /* 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 < vrp->num_bufs / 2)

  		ret = vrp->sbufs + vrp->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.
   */

  static int rpmsg_send_offchannel_raw(struct rpmsg_device *rpdev,
  				     u32 src, u32 dst,
  				     void *data, int len, bool wait)

  {

  	struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
  	struct virtproc_info *vrp = vch->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)
  ", 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 > vrp->buf_size - sizeof(struct rpmsg_hdr)) {

  		dev_err(dev, "message is too big (%d)
  ", 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
  ");
  			return -ERESTARTSYS;
  		}
  	}

  	msg->len = cpu_to_virtio16(vrp->vdev, len);

  	msg->flags = 0;

  	msg->src = cpu_to_virtio32(vrp->vdev, src);
  	msg->dst = cpu_to_virtio32(vrp->vdev, 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
  ",

  		src, dst, len, msg->flags, msg->reserved);

  #if defined(CONFIG_DYNAMIC_DEBUG)
  	dynamic_hex_dump("rpmsg_virtio TX: ", DUMP_PREFIX_NONE, 16, 1,

  			 msg, sizeof(*msg) + len, true);

  #endif

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

  
  	mutex_lock(&vrp->tx_lock);
  
  	/* add message to the remote processor's virtqueue */

  	err = virtqueue_add_outbuf(vrp->svq, &sg, 1, msg, GFP_KERNEL);

  	if (err) {

  		/*
  		 * 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_outbuf failed: %d
  ", err);

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

  out:
  	mutex_unlock(&vrp->tx_lock);
  	return err;
  }

  static int virtio_rpmsg_send(struct rpmsg_endpoint *ept, void *data, int len)
  {
  	struct rpmsg_device *rpdev = ept->rpdev;
  	u32 src = ept->addr, dst = rpdev->dst;
  
  	return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, true);
  }
  
  static int virtio_rpmsg_sendto(struct rpmsg_endpoint *ept, void *data, int len,
  			       u32 dst)
  {
  	struct rpmsg_device *rpdev = ept->rpdev;
  	u32 src = ept->addr;
  
  	return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, true);
  }
  
  static int virtio_rpmsg_send_offchannel(struct rpmsg_endpoint *ept, u32 src,
  					u32 dst, void *data, int len)
  {
  	struct rpmsg_device *rpdev = ept->rpdev;
  
  	return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, true);
  }
  
  static int virtio_rpmsg_trysend(struct rpmsg_endpoint *ept, void *data, int len)
  {
  	struct rpmsg_device *rpdev = ept->rpdev;
  	u32 src = ept->addr, dst = rpdev->dst;
  
  	return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, false);
  }
  
  static int virtio_rpmsg_trysendto(struct rpmsg_endpoint *ept, void *data,
  				  int len, u32 dst)
  {
  	struct rpmsg_device *rpdev = ept->rpdev;
  	u32 src = ept->addr;
  
  	return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, false);
  }
  
  static int virtio_rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src,
  					   u32 dst, void *data, int len)
  {
  	struct rpmsg_device *rpdev = ept->rpdev;
  
  	return rpmsg_send_offchannel_raw(rpdev, src, dst, data, len, false);
  }

  static int rpmsg_recv_single(struct virtproc_info *vrp, struct device *dev,
  			     struct rpmsg_hdr *msg, unsigned int len)

  {

  	struct rpmsg_endpoint *ept;
  	struct scatterlist sg;

  	unsigned int msg_len = virtio16_to_cpu(vrp->vdev, msg->len);

  	int err;

  	dev_dbg(dev, "From: 0x%x, To: 0x%x, Len: %d, Flags: %d, Reserved: %d
  ",

  		virtio32_to_cpu(vrp->vdev, msg->src),
  		virtio32_to_cpu(vrp->vdev, msg->dst), msg_len,
  		virtio16_to_cpu(vrp->vdev, msg->flags),
  		virtio32_to_cpu(vrp->vdev, msg->reserved));

  #if defined(CONFIG_DYNAMIC_DEBUG)
  	dynamic_hex_dump("rpmsg_virtio RX: ", DUMP_PREFIX_NONE, 16, 1,

  			 msg, sizeof(*msg) + msg_len, true);

  #endif

  	/*
  	 * We currently use fixed-sized buffers, so trivially sanitize
  	 * the reported payload length.
  	 */

  	if (len > vrp->buf_size ||

  	    msg_len > (len - sizeof(struct rpmsg_hdr))) {
  		dev_warn(dev, "inbound msg too big: (%d, %d)
  ", len, msg_len);

  		return -EINVAL;

  	}

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

  	ept = idr_find(&vrp->endpoints, virtio32_to_cpu(vrp->vdev, 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,
  				virtio32_to_cpu(vrp->vdev, 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 recipient
  ");

  	/* publish the real size of the buffer */

  	rpmsg_sg_init(&sg, msg, vrp->buf_size);

  
  	/* add the buffer back to the remote processor's virtqueue */

  	err = virtqueue_add_inbuf(vrp->rvq, &sg, 1, msg, GFP_KERNEL);

  	if (err < 0) {
  		dev_err(dev, "failed to add a virtqueue buffer: %d
  ", err);

  		return err;
  	}
  
  	return 0;
  }
  
  /* called when an rx buffer is used, and it's time to digest a message */
  static void rpmsg_recv_done(struct virtqueue *rvq)
  {
  	struct virtproc_info *vrp = rvq->vdev->priv;
  	struct device *dev = &rvq->vdev->dev;
  	struct rpmsg_hdr *msg;
  	unsigned int len, msgs_received = 0;
  	int err;
  
  	msg = virtqueue_get_buf(rvq, &len);
  	if (!msg) {
  		dev_err(dev, "uhm, incoming signal, but no used buffer ?
  ");

  		return;
  	}

  	while (msg) {
  		err = rpmsg_recv_single(vrp, dev, msg, len);
  		if (err)
  			break;
  
  		msgs_received++;
  
  		msg = virtqueue_get_buf(rvq, &len);

  	}

  
  	dev_dbg(dev, "Received %u messages
  ", msgs_received);

  	/* tell the remote processor we added another available rx buffer */

  	if (msgs_received)
  		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
  ", __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 int rpmsg_ns_cb(struct rpmsg_device *rpdev, void *data, int len,
  		       void *priv, u32 src)

  {
  	struct rpmsg_ns_msg *msg = data;

  	struct rpmsg_device *newch;

  	struct rpmsg_channel_info chinfo;
  	struct virtproc_info *vrp = priv;
  	struct device *dev = &vrp->vdev->dev;
  	int ret;

  #if defined(CONFIG_DYNAMIC_DEBUG)
  	dynamic_hex_dump("NS announcement: ", DUMP_PREFIX_NONE, 16, 1,
  			 data, len, true);
  #endif

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

  		return -EINVAL;

  	}
  
  	/*
  	 * 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
  ");

  		return -EINVAL;

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

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

  	chinfo.dst = virtio32_to_cpu(vrp->vdev, msg->addr);
  
  	dev_info(dev, "%sing channel %s addr 0x%x
  ",
  		 virtio32_to_cpu(vrp->vdev, msg->flags) & RPMSG_NS_DESTROY ?
  		 "destroy" : "creat", msg->name, chinfo.dst);

  	if (virtio32_to_cpu(vrp->vdev, msg->flags) & RPMSG_NS_DESTROY) {

  		ret = rpmsg_unregister_device(&vrp->vdev->dev, &chinfo);

  		if (ret)
  			dev_err(dev, "rpmsg_destroy_channel failed: %d
  ", ret);
  	} else {
  		newch = rpmsg_create_channel(vrp, &chinfo);
  		if (!newch)
  			dev_err(dev, "rpmsg_create_channel failed
  ");
  	}

  
  	return 0;

  }
  
  static int rpmsg_probe(struct virtio_device *vdev)
  {
  	vq_callback_t *vq_cbs[] = { rpmsg_recv_done, rpmsg_xmit_done };

  	static const char * const names[] = { "input", "output" };

  	struct virtqueue *vqs[2];
  	struct virtproc_info *vrp;
  	void *bufs_va;
  	int err = 0, i;

  	size_t total_buf_space;

  	bool notify;

  
  	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 = virtio_find_vqs(vdev, 2, vqs, vq_cbs, names, NULL);

  	if (err)
  		goto free_vrp;
  
  	vrp->rvq = vqs[0];
  	vrp->svq = vqs[1];

  	/* we expect symmetric tx/rx vrings */
  	WARN_ON(virtqueue_get_vring_size(vrp->rvq) !=
  		virtqueue_get_vring_size(vrp->svq));
  
  	/* we need less buffers if vrings are small */
  	if (virtqueue_get_vring_size(vrp->rvq) < MAX_RPMSG_NUM_BUFS / 2)
  		vrp->num_bufs = virtqueue_get_vring_size(vrp->rvq) * 2;
  	else
  		vrp->num_bufs = MAX_RPMSG_NUM_BUFS;

  	vrp->buf_size = MAX_RPMSG_BUF_SIZE;
  
  	total_buf_space = vrp->num_bufs * vrp->buf_size;

  	/* allocate coherent memory for the buffers */

  	bufs_va = dma_alloc_coherent(vdev->dev.parent,

  				     total_buf_space, &vrp->bufs_dma,
  				     GFP_KERNEL);

  	if (!bufs_va) {
  		err = -ENOMEM;

  		goto vqs_del;

  	}

  	dev_dbg(&vdev->dev, "buffers: va %pK, dma %pad
  ",

  		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 + total_buf_space / 2;

  
  	/* set up the receive buffers */

  	for (i = 0; i < vrp->num_bufs / 2; i++) {

  		struct scatterlist sg;

  		void *cpu_addr = vrp->rbufs + i * vrp->buf_size;

  		rpmsg_sg_init(&sg, cpu_addr, vrp->buf_size);

  		err = virtqueue_add_inbuf(vrp->rvq, &sg, 1, cpu_addr,

  					  GFP_KERNEL);

  		WARN_ON(err); /* 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
  ");
  			err = -ENOMEM;
  			goto free_coherent;
  		}
  	}

  	/*
  	 * Prepare to kick but don't notify yet - we can't do this before
  	 * device is ready.
  	 */
  	notify = virtqueue_kick_prepare(vrp->rvq);
  
  	/* From this point on, we can notify and get callbacks. */
  	virtio_device_ready(vdev);

  	/* tell the remote processor it can start sending messages */

  	/*
  	 * this might be concurrent with callbacks, but we are only
  	 * doing notify, not a full kick here, so that's ok.
  	 */
  	if (notify)
  		virtqueue_notify(vrp->rvq);

  
  	dev_info(&vdev->dev, "rpmsg host is online
  ");
  
  	return 0;
  
  free_coherent:

  	dma_free_coherent(vdev->dev.parent, 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 rpmsg_remove(struct virtio_device *vdev)

  {
  	struct virtproc_info *vrp = vdev->priv;

  	size_t total_buf_space = vrp->num_bufs * vrp->buf_size;

  	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
  ", ret);

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

  	idr_destroy(&vrp->endpoints);
  
  	vdev->config->del_vqs(vrp->vdev);

  	dma_free_coherent(vdev->dev.parent, 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		= rpmsg_remove,

  };
  
  static int __init rpmsg_init(void)
  {
  	int ret;

  	ret = register_virtio_driver(&virtio_ipc_driver);

  	if (ret)

  		pr_err("failed to register virtio driver: %d
  ", ret);

  
  	return ret;
  }

  subsys_initcall(rpmsg_init);

  
  static void __exit rpmsg_fini(void)
  {
  	unregister_virtio_driver(&virtio_ipc_driver);

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