/*
 *
 * Copyright (c) 2009, Microsoft Corporation.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope 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., 59 Temple
 * Place - Suite 330, Boston, MA 02111-1307 USA.
 *
 * Authors:
 *   Haiyang Zhang <haiyangz@microsoft.com>
 *   Hank Janssen  <hjanssen@microsoft.com>
 *   K. Y. Srinivasan <kys@microsoft.com>
 *
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/hyperv.h>
#include <linux/uio.h>

#include "hyperv_vmbus.h"

void hv_begin_read(struct hv_ring_buffer_info *rbi)
{
        rbi->ring_buffer->interrupt_mask = 1;
        mb();
}

u32 hv_end_read(struct hv_ring_buffer_info *rbi)
{
        u32 read;
        u32 write;

        rbi->ring_buffer->interrupt_mask = 0;
        mb();

        /*
         * Now check to see if the ring buffer is still empty.
         * If it is not, we raced and we need to process new
         * incoming messages.
         */
        hv_get_ringbuffer_availbytes(rbi, &read, &write);

        return read;
}

/*
 * When we write to the ring buffer, check if the host needs to
 * be signaled. Here is the details of this protocol:
 *
 *      1. The host guarantees that while it is draining the
 *         ring buffer, it will set the interrupt_mask to
 *         indicate it does not need to be interrupted when
 *         new data is placed.
 *
 *      2. The host guarantees that it will completely drain
 *         the ring buffer before exiting the read loop. Further,
 *         once the ring buffer is empty, it will clear the
 *         interrupt_mask and re-check to see if new data has
 *         arrived.
 */

static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
{
        mb();
        if (rbi->ring_buffer->interrupt_mask)
                return false;

        /* check interrupt_mask before read_index */
        rmb();
        /*
         * This is the only case we need to signal when the
         * ring transitions from being empty to non-empty.
         */
        if (old_write == rbi->ring_buffer->read_index)
                return true;

        return false;
}

/*
 * To optimize the flow management on the send-side,
 * when the sender is blocked because of lack of
 * sufficient space in the ring buffer, potential the
 * consumer of the ring buffer can signal the producer.
 * This is controlled by the following parameters:
 *
 * 1. pending_send_sz: This is the size in bytes that the
 *    producer is trying to send.
 * 2. The feature bit feat_pending_send_sz set to indicate if
 *    the consumer of the ring will signal when the ring
 *    state transitions from being full to a state where
 *    there is room for the producer to send the pending packet.
 */

static bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi)
{
        u32 cur_write_sz;
        u32 r_size;
        u32 write_loc;
        u32 read_loc = rbi->ring_buffer->read_index;
        u32 pending_sz;

        /*
         * Issue a full memory barrier before making the signaling decision.
         * Here is the reason for having this barrier:
         * If the reading of the pend_sz (in this function)
         * were to be reordered and read before we commit the new read
         * index (in the calling function)  we could
         * have a problem. If the host were to set the pending_sz after we
         * have sampled pending_sz and go to sleep before we commit the
         * read index, we could miss sending the interrupt. Issue a full
         * memory barrier to address this.
         */
        mb();

        pending_sz = rbi->ring_buffer->pending_send_sz;
        write_loc = rbi->ring_buffer->write_index;
        /* If the other end is not blocked on write don't bother. */
        if (pending_sz == 0)
                return false;

        r_size = rbi->ring_datasize;
        cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
                        read_loc - write_loc;

        if (cur_write_sz >= pending_sz)
                return true;

        return false;
}

/* Get the next write location for the specified ring buffer. */
static inline u32
hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
{
        u32 next = ring_info->ring_buffer->write_index;

        return next;
}

/* Set the next write location for the specified ring buffer. */
static inline void
hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
                     u32 next_write_location)
{
        ring_info->ring_buffer->write_index = next_write_location;
}

/* Get the next read location for the specified ring buffer. */
static inline u32
hv_get_next_read_location(struct hv_ring_buffer_info *ring_info)
{
        u32 next = ring_info->ring_buffer->read_index;

        return next;
}

/*
 * Get the next read location + offset for the specified ring buffer.
 * This allows the caller to skip.
 */
static inline u32
hv_get_next_readlocation_withoffset(struct hv_ring_buffer_info *ring_info,
                                 u32 offset)
{
        u32 next = ring_info->ring_buffer->read_index;

        next += offset;
        next %= ring_info->ring_datasize;

        return next;
}

/* Set the next read location for the specified ring buffer. */
static inline void
hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
                    u32 next_read_location)
{
        ring_info->ring_buffer->read_index = next_read_location;
}


/* Get the start of the ring buffer. */
static inline void *
hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
{
        return (void *)ring_info->ring_buffer->buffer;
}


/* Get the size of the ring buffer. */
static inline u32
hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
{
        return ring_info->ring_datasize;
}

/* Get the read and write indices as u64 of the specified ring buffer. */
static inline u64
hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
{
        return (u64)ring_info->ring_buffer->write_index << 32;
}

/*
 * Helper routine to copy to source from ring buffer.
 * Assume there is enough room. Handles wrap-around in src case only!!
 */
static u32 hv_copyfrom_ringbuffer(
        struct hv_ring_buffer_info      *ring_info,
        void                            *dest,
        u32                             destlen,
        u32                             start_read_offset)
{
        void *ring_buffer = hv_get_ring_buffer(ring_info);
        u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);

        u32 frag_len;

        /* wrap-around detected at the src */
        if (destlen > ring_buffer_size - start_read_offset) {
                frag_len = ring_buffer_size - start_read_offset;

                memcpy(dest, ring_buffer + start_read_offset, frag_len);
                memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
        } else

                memcpy(dest, ring_buffer + start_read_offset, destlen);


        start_read_offset += destlen;
        start_read_offset %= ring_buffer_size;

        return start_read_offset;
}


/*
 * Helper routine to copy from source to ring buffer.
 * Assume there is enough room. Handles wrap-around in dest case only!!
 */
static u32 hv_copyto_ringbuffer(
        struct hv_ring_buffer_info      *ring_info,
        u32                             start_write_offset,
        void                            *src,
        u32                             srclen)
{
        void *ring_buffer = hv_get_ring_buffer(ring_info);
        u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
        u32 frag_len;

        /* wrap-around detected! */
        if (srclen > ring_buffer_size - start_write_offset) {
                frag_len = ring_buffer_size - start_write_offset;
                memcpy(ring_buffer + start_write_offset, src, frag_len);
                memcpy(ring_buffer, src + frag_len, srclen - frag_len);
        } else
                memcpy(ring_buffer + start_write_offset, src, srclen);

        start_write_offset += srclen;
        start_write_offset %= ring_buffer_size;

        return start_write_offset;
}

/* Get various debug metrics for the specified ring buffer. */
void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
                            struct hv_ring_buffer_debug_info *debug_info)
{
        u32 bytes_avail_towrite;
        u32 bytes_avail_toread;

        if (ring_info->ring_buffer) {
                hv_get_ringbuffer_availbytes(ring_info,
                                        &bytes_avail_toread,
                                        &bytes_avail_towrite);

                debug_info->bytes_avail_toread = bytes_avail_toread;
                debug_info->bytes_avail_towrite = bytes_avail_towrite;
                debug_info->current_read_index =
                        ring_info->ring_buffer->read_index;
                debug_info->current_write_index =
                        ring_info->ring_buffer->write_index;
                debug_info->current_interrupt_mask =
                        ring_info->ring_buffer->interrupt_mask;
        }
}

/* Initialize the ring buffer. */
int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
                   void *buffer, u32 buflen)
{
        if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
                return -EINVAL;

        memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));

        ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
        ring_info->ring_buffer->read_index =
                ring_info->ring_buffer->write_index = 0;

        /* Set the feature bit for enabling flow control. */
        ring_info->ring_buffer->feature_bits.value = 1;

        ring_info->ring_size = buflen;
        ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);

        spin_lock_init(&ring_info->ring_lock);

        return 0;
}

/* Cleanup the ring buffer. */
void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
{
}

/* Write to the ring buffer. */
int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
                    struct kvec *kv_list, u32 kv_count, bool *signal, bool lock)
{
        int i = 0;
        u32 bytes_avail_towrite;
        u32 bytes_avail_toread;
        u32 totalbytes_towrite = 0;

        u32 next_write_location;
        u32 old_write;
        u64 prev_indices = 0;
        unsigned long flags = 0;

        for (i = 0; i < kv_count; i++)
                totalbytes_towrite += kv_list[i].iov_len;

        totalbytes_towrite += sizeof(u64);

        if (lock)
                spin_lock_irqsave(&outring_info->ring_lock, flags);

        hv_get_ringbuffer_availbytes(outring_info,
                                &bytes_avail_toread,
                                &bytes_avail_towrite);

        /*
         * If there is only room for the packet, assume it is full.
         * Otherwise, the next time around, we think the ring buffer
         * is empty since the read index == write index.
         */
        if (bytes_avail_towrite <= totalbytes_towrite) {
                if (lock)
                        spin_unlock_irqrestore(&outring_info->ring_lock, flags);
                return -EAGAIN;
        }

        /* Write to the ring buffer */
        next_write_location = hv_get_next_write_location(outring_info);

        old_write = next_write_location;

        for (i = 0; i < kv_count; i++) {
                next_write_location = hv_copyto_ringbuffer(outring_info,
                                                     next_write_location,
                                                     kv_list[i].iov_base,
                                                     kv_list[i].iov_len);
        }

        /* Set previous packet start */
        prev_indices = hv_get_ring_bufferindices(outring_info);

        next_write_location = hv_copyto_ringbuffer(outring_info,
                                             next_write_location,
                                             &prev_indices,
                                             sizeof(u64));

        /* Issue a full memory barrier before updating the write index */
        mb();

        /* Now, update the write location */
        hv_set_next_write_location(outring_info, next_write_location);


        if (lock)
                spin_unlock_irqrestore(&outring_info->ring_lock, flags);

        *signal = hv_need_to_signal(old_write, outring_info);
        return 0;
}

int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
                       void *buffer, u32 buflen, u32 *buffer_actual_len,
                       u64 *requestid, bool *signal, bool raw)
{
        u32 bytes_avail_towrite;
        u32 bytes_avail_toread;
        u32 next_read_location = 0;
        u64 prev_indices = 0;
        struct vmpacket_descriptor desc;
        u32 offset;
        u32 packetlen;
        int ret = 0;

        if (buflen <= 0)
                return -EINVAL;


        *buffer_actual_len = 0;
        *requestid = 0;

        hv_get_ringbuffer_availbytes(inring_info,
                                &bytes_avail_toread,
                                &bytes_avail_towrite);

        /* Make sure there is something to read */
        if (bytes_avail_toread < sizeof(desc)) {
                /*
                 * No error is set when there is even no header, drivers are
                 * supposed to analyze buffer_actual_len.
                 */
                return ret;
        }

        next_read_location = hv_get_next_read_location(inring_info);
        next_read_location = hv_copyfrom_ringbuffer(inring_info, &desc,
                                                    sizeof(desc),
                                                    next_read_location);

        offset = raw ? 0 : (desc.offset8 << 3);
        packetlen = (desc.len8 << 3) - offset;
        *buffer_actual_len = packetlen;
        *requestid = desc.trans_id;

        if (bytes_avail_toread < packetlen + offset)
                return -EAGAIN;

        if (packetlen > buflen)
                return -ENOBUFS;

        next_read_location =
                hv_get_next_readlocation_withoffset(inring_info, offset);

        next_read_location = hv_copyfrom_ringbuffer(inring_info,
                                                buffer,
                                                packetlen,
                                                next_read_location);

        next_read_location = hv_copyfrom_ringbuffer(inring_info,
                                                &prev_indices,
                                                sizeof(u64),
                                                next_read_location);

        /*
         * Make sure all reads are done before we update the read index since
         * the writer may start writing to the read area once the read index
         * is updated.
         */
        mb();

        /* Update the read index */
        hv_set_next_read_location(inring_info, next_read_location);

        *signal = hv_need_to_signal_on_read(inring_info);

        return ret;
}