/* 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_wmb(); else wmb(); } 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\n",               \
                              (_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\n",
                         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\n", 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);
        /* We need to expose available array entries before checking avail
         * event. */
        virtio_mb(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\n");
                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\n", i);
                return NULL;
        }
        if (unlikely(!vq->data[i])) {
                BAD_RING(vq, "id %u is not a head!\n", 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\n", vq);
                return IRQ_NONE;
        }

        if (unlikely(vq->broken))
                return IRQ_HANDLED;

        pr_debug("virtqueue callback for %p (%p)\n", 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\n", 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");