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

  #include <linux/virtio_config.h>

  #include <linux/device.h>

  #include <linux/slab.h>

  #include <linux/module.h>

  #include <linux/hrtimer.h>

  /* virtio guest is communicating with a virtual "device" that actually runs on
   * a host processor.  Memory barriers are used to control SMP effects. */
  #ifdef CONFIG_SMP
  /* Where possible, use SMP barriers which are more lightweight than mandatory
   * barriers, because mandatory barriers control MMIO effects on accesses

   * through relaxed memory I/O windows (which virtio-pci does not use). */
  #define virtio_mb(vq) \
  	do { if ((vq)->weak_barriers) smp_mb(); else mb(); } while(0)
  #define virtio_rmb(vq) \
  	do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0)
  #define virtio_wmb(vq) \
  	do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0)

  #else
  /* We must force memory ordering even if guest is UP since host could be
   * running on another CPU, but SMP barriers are defined to barrier() in that
   * configuration. So fall back to mandatory barriers instead. */

  #define virtio_mb(vq) mb()
  #define virtio_rmb(vq) rmb()
  #define virtio_wmb(vq) wmb()

  #endif

  #ifdef DEBUG
  /* For development, we want to crash whenever the ring is screwed. */

  #define BAD_RING(_vq, fmt, args...)				\
  	do {							\
  		dev_err(&(_vq)->vq.vdev->dev,			\
  			"%s:"fmt, (_vq)->vq.name, ##args);	\
  		BUG();						\
  	} while (0)

  /* Caller is supposed to guarantee no reentry. */
  #define START_USE(_vq)						\
  	do {							\
  		if ((_vq)->in_use)				\

  			panic("%s:in_use = %i
  ",		\
  			      (_vq)->vq.name, (_vq)->in_use);	\

  		(_vq)->in_use = __LINE__;			\

  	} while (0)

  #define END_USE(_vq) \

  	do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)

  #else

  #define BAD_RING(_vq, fmt, args...)				\
  	do {							\
  		dev_err(&_vq->vq.vdev->dev,			\
  			"%s:"fmt, (_vq)->vq.name, ##args);	\
  		(_vq)->broken = true;				\
  	} while (0)

  #define START_USE(vq)
  #define END_USE(vq)
  #endif
  
  struct vring_virtqueue
  {
  	struct virtqueue vq;
  
  	/* Actual memory layout for this queue */
  	struct vring vring;

  	/* Can we use weak barriers? */
  	bool weak_barriers;

  	/* Other side has made a mess, don't try any more. */
  	bool broken;

  	/* Host supports indirect buffers */
  	bool indirect;

  	/* Host publishes avail event idx */
  	bool event;

  	/* Number of free buffers */
  	unsigned int num_free;
  	/* Head of free buffer list. */
  	unsigned int free_head;
  	/* Number we've added since last sync. */
  	unsigned int num_added;
  
  	/* Last used index we've seen. */

  	u16 last_used_idx;

  
  	/* How to notify other side. FIXME: commonalize hcalls! */
  	void (*notify)(struct virtqueue *vq);
  
  #ifdef DEBUG
  	/* They're supposed to lock for us. */
  	unsigned int in_use;

  
  	/* Figure out if their kicks are too delayed. */
  	bool last_add_time_valid;
  	ktime_t last_add_time;

  #endif
  
  	/* Tokens for callbacks. */
  	void *data[];
  };
  
  #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)

  /* Set up an indirect table of descriptors and add it to the queue. */
  static int vring_add_indirect(struct vring_virtqueue *vq,
  			      struct scatterlist sg[],
  			      unsigned int out,

  			      unsigned int in,
  			      gfp_t gfp)

  {
  	struct vring_desc *desc;
  	unsigned head;
  	int i;

  	desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);

  	if (!desc)

  		return -ENOMEM;

  
  	/* Transfer entries from the sg list into the indirect page */
  	for (i = 0; i < out; i++) {
  		desc[i].flags = VRING_DESC_F_NEXT;
  		desc[i].addr = sg_phys(sg);
  		desc[i].len = sg->length;
  		desc[i].next = i+1;
  		sg++;
  	}
  	for (; i < (out + in); i++) {
  		desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
  		desc[i].addr = sg_phys(sg);
  		desc[i].len = sg->length;
  		desc[i].next = i+1;
  		sg++;
  	}
  
  	/* Last one doesn't continue. */
  	desc[i-1].flags &= ~VRING_DESC_F_NEXT;
  	desc[i-1].next = 0;
  
  	/* We're about to use a buffer */
  	vq->num_free--;
  
  	/* Use a single buffer which doesn't continue */
  	head = vq->free_head;
  	vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
  	vq->vring.desc[head].addr = virt_to_phys(desc);
  	vq->vring.desc[head].len = i * sizeof(struct vring_desc);
  
  	/* Update free pointer */
  	vq->free_head = vq->vring.desc[head].next;
  
  	return head;
  }

  /**

   * virtqueue_add_buf - expose buffer to other end

   * @vq: the struct virtqueue we're talking about.
   * @sg: the description of the buffer(s).
   * @out_num: the number of sg readable by other side
   * @in_num: the number of sg which are writable (after readable ones)
   * @data: the token identifying the buffer.
   * @gfp: how to do memory allocations (if necessary).
   *
   * Caller must ensure we don't call this with other virtqueue operations
   * at the same time (except where noted).
   *
   * Returns remaining capacity of queue or a negative error
   * (ie. ENOSPC).  Note that it only really makes sense to treat all
   * positive return values as "available": indirect buffers mean that
   * we can put an entire sg[] array inside a single queue entry.
   */

  int virtqueue_add_buf(struct virtqueue *_vq,
  		      struct scatterlist sg[],
  		      unsigned int out,
  		      unsigned int in,
  		      void *data,
  		      gfp_t gfp)

  {
  	struct vring_virtqueue *vq = to_vvq(_vq);

  	unsigned int i, avail, uninitialized_var(prev);
  	int head;

  	START_USE(vq);

  	BUG_ON(data == NULL);

  #ifdef DEBUG
  	{
  		ktime_t now = ktime_get();
  
  		/* No kick or get, with .1 second between?  Warn. */
  		if (vq->last_add_time_valid)
  			WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time))
  					    > 100);
  		vq->last_add_time = now;
  		vq->last_add_time_valid = true;
  	}
  #endif

  	/* If the host supports indirect descriptor tables, and we have multiple
  	 * buffers, then go indirect. FIXME: tune this threshold */
  	if (vq->indirect && (out + in) > 1 && vq->num_free) {

  		head = vring_add_indirect(vq, sg, out, in, gfp);

  		if (likely(head >= 0))

  			goto add_head;
  	}

  	BUG_ON(out + in > vq->vring.num);
  	BUG_ON(out + in == 0);

  	if (vq->num_free < out + in) {
  		pr_debug("Can't add buf len %i - avail = %i
  ",
  			 out + in, vq->num_free);

  		/* FIXME: for historical reasons, we force a notify here if
  		 * there are outgoing parts to the buffer.  Presumably the
  		 * host should service the ring ASAP. */
  		if (out)
  			vq->notify(&vq->vq);

  		END_USE(vq);
  		return -ENOSPC;
  	}
  
  	/* We're about to use some buffers from the free list. */
  	vq->num_free -= out + in;
  
  	head = vq->free_head;
  	for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
  		vq->vring.desc[i].flags = VRING_DESC_F_NEXT;

  		vq->vring.desc[i].addr = sg_phys(sg);

  		vq->vring.desc[i].len = sg->length;
  		prev = i;
  		sg++;
  	}
  	for (; in; i = vq->vring.desc[i].next, in--) {
  		vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;

  		vq->vring.desc[i].addr = sg_phys(sg);

  		vq->vring.desc[i].len = sg->length;
  		prev = i;
  		sg++;
  	}
  	/* Last one doesn't continue. */
  	vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
  
  	/* Update free pointer */
  	vq->free_head = i;

  add_head:

  	/* Set token. */
  	vq->data[head] = data;
  
  	/* Put entry in available array (but don't update avail->idx until they

  	 * do sync). */

  	avail = (vq->vring.avail->idx & (vq->vring.num-1));

  	vq->vring.avail->ring[avail] = head;

  	/* Descriptors and available array need to be set before we expose the
  	 * new available array entries. */
  	virtio_wmb(vq);
  	vq->vring.avail->idx++;
  	vq->num_added++;
  
  	/* This is very unlikely, but theoretically possible.  Kick
  	 * just in case. */
  	if (unlikely(vq->num_added == (1 << 16) - 1))
  		virtqueue_kick(_vq);

  	pr_debug("Added buffer head %i to %p
  ", head, vq);
  	END_USE(vq);

  	return vq->num_free;

  }

  EXPORT_SYMBOL_GPL(virtqueue_add_buf);

  /**

   * virtqueue_kick_prepare - first half of split virtqueue_kick call.

   * @vq: the struct virtqueue
   *

   * Instead of virtqueue_kick(), you can do:
   *	if (virtqueue_kick_prepare(vq))
   *		virtqueue_notify(vq);

   *

   * This is sometimes useful because the virtqueue_kick_prepare() needs
   * to be serialized, but the actual virtqueue_notify() call does not.

   */

  bool virtqueue_kick_prepare(struct virtqueue *_vq)

  {
  	struct vring_virtqueue *vq = to_vvq(_vq);

  	u16 new, old;

  	bool needs_kick;

  	START_USE(vq);
  	/* Descriptors and available array need to be set before we expose the
  	 * new available array entries. */

  	virtio_wmb(vq);

  	old = vq->vring.avail->idx - vq->num_added;
  	new = vq->vring.avail->idx;

  	vq->num_added = 0;

  #ifdef DEBUG
  	if (vq->last_add_time_valid) {
  		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
  					      vq->last_add_time)) > 100);
  	}
  	vq->last_add_time_valid = false;
  #endif

  	if (vq->event) {
  		needs_kick = vring_need_event(vring_avail_event(&vq->vring),
  					      new, old);
  	} else {
  		needs_kick = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
  	}

  	END_USE(vq);

  	return needs_kick;
  }
  EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
  
  /**
   * virtqueue_notify - second half of split virtqueue_kick call.
   * @vq: the struct virtqueue
   *
   * This does not need to be serialized.
   */
  void virtqueue_notify(struct virtqueue *_vq)
  {
  	struct vring_virtqueue *vq = to_vvq(_vq);
  
  	/* Prod other side to tell it about changes. */
  	vq->notify(_vq);
  }
  EXPORT_SYMBOL_GPL(virtqueue_notify);
  
  /**
   * virtqueue_kick - update after add_buf
   * @vq: the struct virtqueue
   *
   * After one or more virtqueue_add_buf calls, invoke this to kick
   * the other side.
   *
   * Caller must ensure we don't call this with other virtqueue
   * operations at the same time (except where noted).
   */
  void virtqueue_kick(struct virtqueue *vq)
  {
  	if (virtqueue_kick_prepare(vq))
  		virtqueue_notify(vq);

  }

  EXPORT_SYMBOL_GPL(virtqueue_kick);

  
  static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
  {
  	unsigned int i;
  
  	/* Clear data ptr. */
  	vq->data[head] = NULL;
  
  	/* Put back on free list: find end */
  	i = head;

  
  	/* Free the indirect table */
  	if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
  		kfree(phys_to_virt(vq->vring.desc[i].addr));

  	while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
  		i = vq->vring.desc[i].next;
  		vq->num_free++;
  	}
  
  	vq->vring.desc[i].next = vq->free_head;
  	vq->free_head = head;
  	/* Plus final descriptor */
  	vq->num_free++;
  }

  static inline bool more_used(const struct vring_virtqueue *vq)
  {
  	return vq->last_used_idx != vq->vring.used->idx;
  }

  /**
   * virtqueue_get_buf - get the next used buffer
   * @vq: the struct virtqueue we're talking about.
   * @len: the length written into the buffer
   *
   * If the driver wrote data into the buffer, @len will be set to the
   * amount written.  This means you don't need to clear the buffer
   * beforehand to ensure there's no data leakage in the case of short
   * writes.
   *
   * Caller must ensure we don't call this with other virtqueue
   * operations at the same time (except where noted).
   *
   * Returns NULL if there are no used buffers, or the "data" token

   * handed to virtqueue_add_buf().

   */

  void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)

  {
  	struct vring_virtqueue *vq = to_vvq(_vq);
  	void *ret;
  	unsigned int i;

  	u16 last_used;

  
  	START_USE(vq);

  	if (unlikely(vq->broken)) {
  		END_USE(vq);
  		return NULL;
  	}

  	if (!more_used(vq)) {
  		pr_debug("No more buffers in queue
  ");
  		END_USE(vq);
  		return NULL;
  	}

  	/* Only get used array entries after they have been exposed by host. */

  	virtio_rmb(vq);

  	last_used = (vq->last_used_idx & (vq->vring.num - 1));
  	i = vq->vring.used->ring[last_used].id;
  	*len = vq->vring.used->ring[last_used].len;

  
  	if (unlikely(i >= vq->vring.num)) {
  		BAD_RING(vq, "id %u out of range
  ", i);
  		return NULL;
  	}
  	if (unlikely(!vq->data[i])) {
  		BAD_RING(vq, "id %u is not a head!
  ", i);
  		return NULL;
  	}
  
  	/* detach_buf clears data, so grab it now. */
  	ret = vq->data[i];
  	detach_buf(vq, i);
  	vq->last_used_idx++;

  	/* If we expect an interrupt for the next entry, tell host
  	 * by writing event index and flush out the write before
  	 * the read in the next get_buf call. */
  	if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) {
  		vring_used_event(&vq->vring) = vq->last_used_idx;

  		virtio_mb(vq);

  	}

  #ifdef DEBUG
  	vq->last_add_time_valid = false;
  #endif

  	END_USE(vq);
  	return ret;
  }

  EXPORT_SYMBOL_GPL(virtqueue_get_buf);

  /**
   * virtqueue_disable_cb - disable callbacks
   * @vq: the struct virtqueue we're talking about.
   *
   * Note that this is not necessarily synchronous, hence unreliable and only
   * useful as an optimization.
   *
   * Unlike other operations, this need not be serialized.
   */

  void virtqueue_disable_cb(struct virtqueue *_vq)

  {
  	struct vring_virtqueue *vq = to_vvq(_vq);

  	vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;

  }

  EXPORT_SYMBOL_GPL(virtqueue_disable_cb);

  /**
   * virtqueue_enable_cb - restart callbacks after disable_cb.
   * @vq: the struct virtqueue we're talking about.
   *
   * This re-enables callbacks; it returns "false" if there are pending
   * buffers in the queue, to detect a possible race between the driver
   * checking for more work, and enabling callbacks.
   *
   * Caller must ensure we don't call this with other virtqueue
   * operations at the same time (except where noted).
   */

  bool virtqueue_enable_cb(struct virtqueue *_vq)

  {
  	struct vring_virtqueue *vq = to_vvq(_vq);
  
  	START_USE(vq);

  
  	/* We optimistically turn back on interrupts, then check if there was
  	 * more to do. */

  	/* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
  	 * either clear the flags bit or point the event index at the next
  	 * entry. Always do both to keep code simple. */

  	vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;

  	vring_used_event(&vq->vring) = vq->last_used_idx;

  	virtio_mb(vq);

  	if (unlikely(more_used(vq))) {

  		END_USE(vq);
  		return false;
  	}
  
  	END_USE(vq);
  	return true;
  }

  EXPORT_SYMBOL_GPL(virtqueue_enable_cb);

  /**
   * virtqueue_enable_cb_delayed - restart callbacks after disable_cb.
   * @vq: the struct virtqueue we're talking about.
   *
   * This re-enables callbacks but hints to the other side to delay
   * interrupts until most of the available buffers have been processed;
   * it returns "false" if there are many pending buffers in the queue,
   * to detect a possible race between the driver checking for more work,
   * and enabling callbacks.
   *
   * Caller must ensure we don't call this with other virtqueue
   * operations at the same time (except where noted).
   */

  bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
  {
  	struct vring_virtqueue *vq = to_vvq(_vq);
  	u16 bufs;
  
  	START_USE(vq);
  
  	/* We optimistically turn back on interrupts, then check if there was
  	 * more to do. */
  	/* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
  	 * either clear the flags bit or point the event index at the next
  	 * entry. Always do both to keep code simple. */
  	vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
  	/* TODO: tune this threshold */
  	bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4;
  	vring_used_event(&vq->vring) = vq->last_used_idx + bufs;

  	virtio_mb(vq);

  	if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) {
  		END_USE(vq);
  		return false;
  	}
  
  	END_USE(vq);
  	return true;
  }
  EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);

  /**
   * virtqueue_detach_unused_buf - detach first unused buffer
   * @vq: the struct virtqueue we're talking about.
   *

   * Returns NULL or the "data" token handed to virtqueue_add_buf().

   * This is not valid on an active queue; it is useful only for device
   * shutdown.
   */

  void *virtqueue_detach_unused_buf(struct virtqueue *_vq)

  {
  	struct vring_virtqueue *vq = to_vvq(_vq);
  	unsigned int i;
  	void *buf;
  
  	START_USE(vq);
  
  	for (i = 0; i < vq->vring.num; i++) {
  		if (!vq->data[i])
  			continue;
  		/* detach_buf clears data, so grab it now. */
  		buf = vq->data[i];
  		detach_buf(vq, i);

  		vq->vring.avail->idx--;

  		END_USE(vq);
  		return buf;
  	}
  	/* That should have freed everything. */
  	BUG_ON(vq->num_free != vq->vring.num);
  
  	END_USE(vq);
  	return NULL;
  }

  EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);

  irqreturn_t vring_interrupt(int irq, void *_vq)
  {
  	struct vring_virtqueue *vq = to_vvq(_vq);
  
  	if (!more_used(vq)) {
  		pr_debug("virtqueue interrupt with no work for %p
  ", vq);
  		return IRQ_NONE;
  	}
  
  	if (unlikely(vq->broken))
  		return IRQ_HANDLED;
  
  	pr_debug("virtqueue callback for %p (%p)
  ", vq, vq->vq.callback);

  	if (vq->vq.callback)
  		vq->vq.callback(&vq->vq);

  
  	return IRQ_HANDLED;
  }

  EXPORT_SYMBOL_GPL(vring_interrupt);

  struct virtqueue *vring_new_virtqueue(unsigned int num,

  				      unsigned int vring_align,

  				      struct virtio_device *vdev,

  				      bool weak_barriers,

  				      void *pages,
  				      void (*notify)(struct virtqueue *),

  				      void (*callback)(struct virtqueue *),
  				      const char *name)

  {
  	struct vring_virtqueue *vq;
  	unsigned int i;

  	/* We assume num is a power of 2. */
  	if (num & (num - 1)) {
  		dev_warn(&vdev->dev, "Bad virtqueue length %u
  ", num);
  		return NULL;
  	}

  	vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
  	if (!vq)
  		return NULL;

  	vring_init(&vq->vring, num, pages, vring_align);

  	vq->vq.callback = callback;
  	vq->vq.vdev = vdev;

  	vq->vq.name = name;

  	vq->notify = notify;

  	vq->weak_barriers = weak_barriers;

  	vq->broken = false;
  	vq->last_used_idx = 0;
  	vq->num_added = 0;

  	list_add_tail(&vq->vq.list, &vdev->vqs);

  #ifdef DEBUG
  	vq->in_use = false;

  	vq->last_add_time_valid = false;

  #endif

  	vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);

  	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);

  	/* No callback?  Tell other side not to bother us. */
  	if (!callback)
  		vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
  
  	/* Put everything in free lists. */
  	vq->num_free = num;
  	vq->free_head = 0;

  	for (i = 0; i < num-1; i++) {

  		vq->vring.desc[i].next = i+1;

  		vq->data[i] = NULL;
  	}
  	vq->data[i] = NULL;

  
  	return &vq->vq;
  }

  EXPORT_SYMBOL_GPL(vring_new_virtqueue);

  
  void vring_del_virtqueue(struct virtqueue *vq)
  {

  	list_del(&vq->list);

  	kfree(to_vvq(vq));
  }

  EXPORT_SYMBOL_GPL(vring_del_virtqueue);

  /* Manipulates transport-specific feature bits. */
  void vring_transport_features(struct virtio_device *vdev)
  {
  	unsigned int i;
  
  	for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
  		switch (i) {

  		case VIRTIO_RING_F_INDIRECT_DESC:
  			break;

  		case VIRTIO_RING_F_EVENT_IDX:
  			break;

  		default:
  			/* We don't understand this bit. */
  			clear_bit(i, vdev->features);
  		}
  	}
  }
  EXPORT_SYMBOL_GPL(vring_transport_features);

  /**
   * virtqueue_get_vring_size - return the size of the virtqueue's vring
   * @vq: the struct virtqueue containing the vring of interest.
   *
   * Returns the size of the vring.  This is mainly used for boasting to
   * userspace.  Unlike other operations, this need not be serialized.
   */

  unsigned int virtqueue_get_vring_size(struct virtqueue *_vq)
  {
  
  	struct vring_virtqueue *vq = to_vvq(_vq);
  
  	return vq->vring.num;
  }
  EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);

  MODULE_LICENSE("GPL");