mlx4_en: Add driver for Mellanox ConnectX 10GbE NIC

[deliverable/linux.git] / drivers / net / mlx4 / en_tx.c

/*
 * Copyright (c) 2007 Mellanox Technologies. All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */

#include <asm/page.h>
#include <linux/mlx4/cq.h>
#include <linux/mlx4/qp.h>
#include <linux/skbuff.h>
#include <linux/if_vlan.h>
#include <linux/vmalloc.h>

#include "mlx4_en.h"

enum {
        MAX_INLINE = 104, /* 128 - 16 - 4 - 4 */
};

static int inline_thold __read_mostly = MAX_INLINE;

module_param_named(inline_thold, inline_thold, int, 0444);
MODULE_PARM_DESC(inline_thold, "treshold for using inline data");

int mlx4_en_create_tx_ring(struct mlx4_en_priv *priv,
                           struct mlx4_en_tx_ring *ring, u32 size,
                           u16 stride)
{
        struct mlx4_en_dev *mdev = priv->mdev;
        int tmp;
        int err;

        ring->size = size;
        ring->size_mask = size - 1;
        ring->stride = stride;

        inline_thold = min(inline_thold, MAX_INLINE);

        spin_lock_init(&ring->comp_lock);

        tmp = size * sizeof(struct mlx4_en_tx_info);
        ring->tx_info = vmalloc(tmp);
        if (!ring->tx_info) {
                mlx4_err(mdev, "Failed allocating tx_info ring\n");
                return -ENOMEM;
        }
        mlx4_dbg(DRV, priv, "Allocated tx_info ring at addr:%p size:%d\n",
                 ring->tx_info, tmp);

        ring->bounce_buf = kmalloc(MAX_DESC_SIZE, GFP_KERNEL);
        if (!ring->bounce_buf) {
                mlx4_err(mdev, "Failed allocating bounce buffer\n");
                err = -ENOMEM;
                goto err_tx;
        }
        ring->buf_size = ALIGN(size * ring->stride, MLX4_EN_PAGE_SIZE);

        err = mlx4_alloc_hwq_res(mdev->dev, &ring->wqres, ring->buf_size,
                                 2 * PAGE_SIZE);
        if (err) {
                mlx4_err(mdev, "Failed allocating hwq resources\n");
                goto err_bounce;
        }

        err = mlx4_en_map_buffer(&ring->wqres.buf);
        if (err) {
                mlx4_err(mdev, "Failed to map TX buffer\n");
                goto err_hwq_res;
        }

        ring->buf = ring->wqres.buf.direct.buf;

        mlx4_dbg(DRV, priv, "Allocated TX ring (addr:%p) - buf:%p size:%d "
                 "buf_size:%d dma:%llx\n", ring, ring->buf, ring->size,
                 ring->buf_size, (unsigned long long) ring->wqres.buf.direct.map);

        err = mlx4_qp_reserve_range(mdev->dev, 1, 1, &ring->qpn);
        if (err) {
                mlx4_err(mdev, "Failed reserving qp for tx ring.\n");
                goto err_map;
        }

        err = mlx4_qp_alloc(mdev->dev, ring->qpn, &ring->qp);
        if (err) {
                mlx4_err(mdev, "Failed allocating qp %d\n", ring->qpn);
                goto err_reserve;
        }

        return 0;

err_reserve:
        mlx4_qp_release_range(mdev->dev, ring->qpn, 1);
err_map:
        mlx4_en_unmap_buffer(&ring->wqres.buf);
err_hwq_res:
        mlx4_free_hwq_res(mdev->dev, &ring->wqres, ring->buf_size);
err_bounce:
        kfree(ring->bounce_buf);
        ring->bounce_buf = NULL;
err_tx:
        vfree(ring->tx_info);
        ring->tx_info = NULL;
        return err;
}

void mlx4_en_destroy_tx_ring(struct mlx4_en_priv *priv,
                             struct mlx4_en_tx_ring *ring)
{
        struct mlx4_en_dev *mdev = priv->mdev;
        mlx4_dbg(DRV, priv, "Destroying tx ring, qpn: %d\n", ring->qpn);

        mlx4_qp_remove(mdev->dev, &ring->qp);
        mlx4_qp_free(mdev->dev, &ring->qp);
        mlx4_qp_release_range(mdev->dev, ring->qpn, 1);
        mlx4_en_unmap_buffer(&ring->wqres.buf);
        mlx4_free_hwq_res(mdev->dev, &ring->wqres, ring->buf_size);
        kfree(ring->bounce_buf);
        ring->bounce_buf = NULL;
        vfree(ring->tx_info);
        ring->tx_info = NULL;
}

int mlx4_en_activate_tx_ring(struct mlx4_en_priv *priv,
                             struct mlx4_en_tx_ring *ring,
                             int cq, int srqn)
{
        struct mlx4_en_dev *mdev = priv->mdev;
        int err;

        ring->cqn = cq;
        ring->prod = 0;
        ring->cons = 0xffffffff;
        ring->last_nr_txbb = 1;
        ring->poll_cnt = 0;
        ring->blocked = 0;
        memset(ring->tx_info, 0, ring->size * sizeof(struct mlx4_en_tx_info));
        memset(ring->buf, 0, ring->buf_size);

        ring->qp_state = MLX4_QP_STATE_RST;
        ring->doorbell_qpn = swab32(ring->qp.qpn << 8);

        mlx4_en_fill_qp_context(priv, ring->size, ring->stride, 1, 0, ring->qpn,
                                ring->cqn, srqn, &ring->context);

        err = mlx4_qp_to_ready(mdev->dev, &ring->wqres.mtt, &ring->context,
                               &ring->qp, &ring->qp_state);

        return err;
}

void mlx4_en_deactivate_tx_ring(struct mlx4_en_priv *priv,
                                struct mlx4_en_tx_ring *ring)
{
        struct mlx4_en_dev *mdev = priv->mdev;

        mlx4_qp_modify(mdev->dev, NULL, ring->qp_state,
                       MLX4_QP_STATE_RST, NULL, 0, 0, &ring->qp);
}


static u32 mlx4_en_free_tx_desc(struct mlx4_en_priv *priv,
                                struct mlx4_en_tx_ring *ring,
                                int index, u8 owner)
{
        struct mlx4_en_dev *mdev = priv->mdev;
        struct mlx4_en_tx_info *tx_info = &ring->tx_info[index];
        struct mlx4_en_tx_desc *tx_desc = ring->buf + index * TXBB_SIZE;
        struct mlx4_wqe_data_seg *data = (void *) tx_desc + tx_info->data_offset;
        struct sk_buff *skb = tx_info->skb;
        struct skb_frag_struct *frag;
        void *end = ring->buf + ring->buf_size;
        int frags = skb_shinfo(skb)->nr_frags;
        int i;
        __be32 *ptr = (__be32 *)tx_desc;
        __be32 stamp = cpu_to_be32(STAMP_VAL | (!!owner << STAMP_SHIFT));

        /* Optimize the common case when there are no wraparounds */
        if (likely((void *) tx_desc + tx_info->nr_txbb * TXBB_SIZE <= end)) {
                if (tx_info->linear) {
                        pci_unmap_single(mdev->pdev,
                                         (dma_addr_t) be64_to_cpu(data->addr),
                                         be32_to_cpu(data->byte_count),
                                         PCI_DMA_TODEVICE);
                        ++data;
                }

                for (i = 0; i < frags; i++) {
                        frag = &skb_shinfo(skb)->frags[i];
                        pci_unmap_page(mdev->pdev,
                                       (dma_addr_t) be64_to_cpu(data[i].addr),
                                       frag->size, PCI_DMA_TODEVICE);
                }
                /* Stamp the freed descriptor */
                for (i = 0; i < tx_info->nr_txbb * TXBB_SIZE; i += STAMP_STRIDE) {
                        *ptr = stamp;
                        ptr += STAMP_DWORDS;
                }

        } else {
                if ((void *) data >= end) {
                        data = (struct mlx4_wqe_data_seg *)
                                        (ring->buf + ((void *) data - end));
                }

                if (tx_info->linear) {
                        pci_unmap_single(mdev->pdev,
                                         (dma_addr_t) be64_to_cpu(data->addr),
                                         be32_to_cpu(data->byte_count),
                                         PCI_DMA_TODEVICE);
                        ++data;
                }

                for (i = 0; i < frags; i++) {
                        /* Check for wraparound before unmapping */
                        if ((void *) data >= end)
                                data = (struct mlx4_wqe_data_seg *) ring->buf;
                        frag = &skb_shinfo(skb)->frags[i];
                        pci_unmap_page(mdev->pdev,
                                        (dma_addr_t) be64_to_cpu(data->addr),
                                         frag->size, PCI_DMA_TODEVICE);
                }
                /* Stamp the freed descriptor */
                for (i = 0; i < tx_info->nr_txbb * TXBB_SIZE; i += STAMP_STRIDE) {
                        *ptr = stamp;
                        ptr += STAMP_DWORDS;
                        if ((void *) ptr >= end) {
                                ptr = ring->buf;
                                stamp ^= cpu_to_be32(0x80000000);
                        }
                }

        }
        dev_kfree_skb_any(skb);
        return tx_info->nr_txbb;
}


int mlx4_en_free_tx_buf(struct net_device *dev, struct mlx4_en_tx_ring *ring)
{
        struct mlx4_en_priv *priv = netdev_priv(dev);
        int cnt = 0;

        /* Skip last polled descriptor */
        ring->cons += ring->last_nr_txbb;
        mlx4_dbg(DRV, priv, "Freeing Tx buf - cons:0x%x prod:0x%x\n",
                 ring->cons, ring->prod);

        if ((u32) (ring->prod - ring->cons) > ring->size) {
                if (netif_msg_tx_err(priv))
                        mlx4_warn(priv->mdev, "Tx consumer passed producer!\n");
                return 0;
        }

        while (ring->cons != ring->prod) {
                ring->last_nr_txbb = mlx4_en_free_tx_desc(priv, ring,
                                                ring->cons & ring->size_mask,
                                                !!(ring->cons & ring->size));
                ring->cons += ring->last_nr_txbb;
                cnt++;
        }

        if (cnt)
                mlx4_dbg(DRV, priv, "Freed %d uncompleted tx descriptors\n", cnt);

        return cnt;
}

void mlx4_en_set_prio_map(struct mlx4_en_priv *priv, u16 *prio_map, u32 ring_num)
{
        int block = 8 / ring_num;
        int extra = 8 - (block * ring_num);
        int num = 0;
        u16 ring = 1;
        int prio;

        if (ring_num == 1) {
                for (prio = 0; prio < 8; prio++)
                        prio_map[prio] = 0;
                return;
        }

        for (prio = 0; prio < 8; prio++) {
                if (extra && (num == block + 1)) {
                        ring++;
                        num = 0;
                        extra--;
                } else if (!extra && (num == block)) {
                        ring++;
                        num = 0;
                }
                prio_map[prio] = ring;
                mlx4_dbg(DRV, priv, " prio:%d --> ring:%d\n", prio, ring);
                num++;
        }
}

static void mlx4_en_process_tx_cq(struct net_device *dev, struct mlx4_en_cq *cq)
{
        struct mlx4_en_priv *priv = netdev_priv(dev);
        struct mlx4_cq *mcq = &cq->mcq;
        struct mlx4_en_tx_ring *ring = &priv->tx_ring[cq->ring];
        struct mlx4_cqe *cqe = cq->buf;
        u16 index;
        u16 new_index;
        u32 txbbs_skipped = 0;
        u32 cq_last_sav;

        /* index always points to the first TXBB of the last polled descriptor */
        index = ring->cons & ring->size_mask;
        new_index = be16_to_cpu(cqe->wqe_index) & ring->size_mask;
        if (index == new_index)
                return;

        if (!priv->port_up)
                return;

        /*
         * We use a two-stage loop:
         * - the first samples the HW-updated CQE
         * - the second frees TXBBs until the last sample
         * This lets us amortize CQE cache misses, while still polling the CQ
         * until is quiescent.
         */
        cq_last_sav = mcq->cons_index;
        do {
                do {
                        /* Skip over last polled CQE */
                        index = (index + ring->last_nr_txbb) & ring->size_mask;
                        txbbs_skipped += ring->last_nr_txbb;

                        /* Poll next CQE */
                        ring->last_nr_txbb = mlx4_en_free_tx_desc(
                                                priv, ring, index,
                                                !!((ring->cons + txbbs_skipped) &
                                                   ring->size));
                        ++mcq->cons_index;

                } while (index != new_index);

                new_index = be16_to_cpu(cqe->wqe_index) & ring->size_mask;
        } while (index != new_index);
        AVG_PERF_COUNTER(priv->pstats.tx_coal_avg,
                         (u32) (mcq->cons_index - cq_last_sav));

        /*
         * To prevent CQ overflow we first update CQ consumer and only then
         * the ring consumer.
         */
        mlx4_cq_set_ci(mcq);
        wmb();
        ring->cons += txbbs_skipped;

        /* Wakeup Tx queue if this ring stopped it */
        if (unlikely(ring->blocked)) {
                if (((u32) (ring->prod - ring->cons) <=
                     ring->size - HEADROOM - MAX_DESC_TXBBS) && !cq->armed) {

                        /* TODO: support multiqueue netdevs. Currently, we block
                         * when *any* ring is full. Note that:
                         * - 2 Tx rings can unblock at the same time and call
                         *   netif_wake_queue(), which is OK since this
                         *   operation is idempotent.
                         * - We might wake the queue just after another ring
                         *   stopped it. This is no big deal because the next
                         *   transmission on that ring would stop the queue.
                         */
                        ring->blocked = 0;
                        netif_wake_queue(dev);
                        priv->port_stats.wake_queue++;
                }
        }
}

void mlx4_en_tx_irq(struct mlx4_cq *mcq)
{
        struct mlx4_en_cq *cq = container_of(mcq, struct mlx4_en_cq, mcq);
        struct mlx4_en_priv *priv = netdev_priv(cq->dev);
        struct mlx4_en_tx_ring *ring = &priv->tx_ring[cq->ring];

        spin_lock_irq(&ring->comp_lock);
        cq->armed = 0;
        mlx4_en_process_tx_cq(cq->dev, cq);
        if (ring->blocked)
                mlx4_en_arm_cq(priv, cq);
        else
                mod_timer(&cq->timer, jiffies + 1);
        spin_unlock_irq(&ring->comp_lock);
}


void mlx4_en_poll_tx_cq(unsigned long data)
{
        struct mlx4_en_cq *cq = (struct mlx4_en_cq *) data;
        struct mlx4_en_priv *priv = netdev_priv(cq->dev);
        struct mlx4_en_tx_ring *ring = &priv->tx_ring[cq->ring];
        u32 inflight;

        INC_PERF_COUNTER(priv->pstats.tx_poll);

        netif_tx_lock(priv->dev);
        spin_lock_irq(&ring->comp_lock);
        mlx4_en_process_tx_cq(cq->dev, cq);
        inflight = (u32) (ring->prod - ring->cons - ring->last_nr_txbb);

        /* If there are still packets in flight and the timer has not already
         * been scheduled by the Tx routine then schedule it here to guarantee
         * completion processing of these packets */
        if (inflight && priv->port_up)
                mod_timer(&cq->timer, jiffies + MLX4_EN_TX_POLL_TIMEOUT);

        spin_unlock_irq(&ring->comp_lock);
        netif_tx_unlock(priv->dev);
}

static struct mlx4_en_tx_desc *mlx4_en_bounce_to_desc(struct mlx4_en_priv *priv,
                                                      struct mlx4_en_tx_ring *ring,
                                                      u32 index,
                                                      unsigned int desc_size)
{
        u32 copy = (ring->size - index) * TXBB_SIZE;
        int i;

        for (i = desc_size - copy - 4; i >= 0; i -= 4) {
                if ((i & (TXBB_SIZE - 1)) == 0)
                        wmb();

                *((u32 *) (ring->buf + i)) =
                        *((u32 *) (ring->bounce_buf + copy + i));
        }

        for (i = copy - 4; i >= 4 ; i -= 4) {
                if ((i & (TXBB_SIZE - 1)) == 0)
                        wmb();

                *((u32 *) (ring->buf + index * TXBB_SIZE + i)) =
                        *((u32 *) (ring->bounce_buf + i));
        }

        /* Return real descriptor location */
        return ring->buf + index * TXBB_SIZE;
}

static inline void mlx4_en_xmit_poll(struct mlx4_en_priv *priv, int tx_ind)
{
        struct mlx4_en_cq *cq = &priv->tx_cq[tx_ind];
        struct mlx4_en_tx_ring *ring = &priv->tx_ring[tx_ind];

        /* If we don't have a pending timer, set one up to catch our recent
           post in case the interface becomes idle */
        if (!timer_pending(&cq->timer))
                mod_timer(&cq->timer, jiffies + MLX4_EN_TX_POLL_TIMEOUT);

        /* Poll the CQ every mlx4_en_TX_MODER_POLL packets */
        if ((++ring->poll_cnt & (MLX4_EN_TX_POLL_MODER - 1)) == 0)
                mlx4_en_process_tx_cq(priv->dev, cq);
}

static void *get_frag_ptr(struct sk_buff *skb)
{
        struct skb_frag_struct *frag =  &skb_shinfo(skb)->frags[0];
        struct page *page = frag->page;
        void *ptr;

        ptr = page_address(page);
        if (unlikely(!ptr))
                return NULL;

        return ptr + frag->page_offset;
}

static int is_inline(struct sk_buff *skb, void **pfrag)
{
        void *ptr;

        if (inline_thold && !skb_is_gso(skb) && skb->len <= inline_thold) {
                if (skb_shinfo(skb)->nr_frags == 1) {
                        ptr = get_frag_ptr(skb);
                        if (unlikely(!ptr))
                                return 0;

                        if (pfrag)
                                *pfrag = ptr;

                        return 1;
                } else if (unlikely(skb_shinfo(skb)->nr_frags))
                        return 0;
                else
                        return 1;
        }

        return 0;
}

static int inline_size(struct sk_buff *skb)
{
        if (skb->len + CTRL_SIZE + sizeof(struct mlx4_wqe_inline_seg)
            <= MLX4_INLINE_ALIGN)
                return ALIGN(skb->len + CTRL_SIZE +
                             sizeof(struct mlx4_wqe_inline_seg), 16);
        else
                return ALIGN(skb->len + CTRL_SIZE + 2 *
                             sizeof(struct mlx4_wqe_inline_seg), 16);
}

static int get_real_size(struct sk_buff *skb, struct net_device *dev,
                         int *lso_header_size)
{
        struct mlx4_en_priv *priv = netdev_priv(dev);
        struct mlx4_en_dev *mdev = priv->mdev;
        int real_size;

        if (skb_is_gso(skb)) {
                *lso_header_size = skb_transport_offset(skb) + tcp_hdrlen(skb);
                real_size = CTRL_SIZE + skb_shinfo(skb)->nr_frags * DS_SIZE +
                        ALIGN(*lso_header_size + 4, DS_SIZE);
                if (unlikely(*lso_header_size != skb_headlen(skb))) {
                        /* We add a segment for the skb linear buffer only if
                         * it contains data */
                        if (*lso_header_size < skb_headlen(skb))
                                real_size += DS_SIZE;
                        else {
                                if (netif_msg_tx_err(priv))
                                        mlx4_warn(mdev, "Non-linear headers\n");
                                dev_kfree_skb_any(skb);
                                return 0;
                        }
                }
                if (unlikely(*lso_header_size > MAX_LSO_HDR_SIZE)) {
                        if (netif_msg_tx_err(priv))
                                mlx4_warn(mdev, "LSO header size too big\n");
                        dev_kfree_skb_any(skb);
                        return 0;
                }
        } else {
                *lso_header_size = 0;
                if (!is_inline(skb, NULL))
                        real_size = CTRL_SIZE + (skb_shinfo(skb)->nr_frags + 1) * DS_SIZE;
                else
                        real_size = inline_size(skb);
        }

        return real_size;
}

static void build_inline_wqe(struct mlx4_en_tx_desc *tx_desc, struct sk_buff *skb,
                             int real_size, u16 *vlan_tag, int tx_ind, void *fragptr)
{
        struct mlx4_wqe_inline_seg *inl = &tx_desc->inl;
        int spc = MLX4_INLINE_ALIGN - CTRL_SIZE - sizeof *inl;

        if (skb->len <= spc) {
                inl->byte_count = cpu_to_be32(1 << 31 | skb->len);
                skb_copy_from_linear_data(skb, inl + 1, skb_headlen(skb));
                if (skb_shinfo(skb)->nr_frags)
                        memcpy(((void *)(inl + 1)) + skb_headlen(skb), fragptr,
                               skb_shinfo(skb)->frags[0].size);

        } else {
                inl->byte_count = cpu_to_be32(1 << 31 | spc);
                if (skb_headlen(skb) <= spc) {
                        skb_copy_from_linear_data(skb, inl + 1, skb_headlen(skb));
                        if (skb_headlen(skb) < spc) {
                                memcpy(((void *)(inl + 1)) + skb_headlen(skb),
                                        fragptr, spc - skb_headlen(skb));
                                fragptr +=  spc - skb_headlen(skb);
                        }
                        inl = (void *) (inl + 1) + spc;
                        memcpy(((void *)(inl + 1)), fragptr, skb->len - spc);
                } else {
                        skb_copy_from_linear_data(skb, inl + 1, spc);
                        inl = (void *) (inl + 1) + spc;
                        skb_copy_from_linear_data_offset(skb, spc, inl + 1,
                                        skb_headlen(skb) - spc);
                        if (skb_shinfo(skb)->nr_frags)
                                memcpy(((void *)(inl + 1)) + skb_headlen(skb) - spc,
                                        fragptr, skb_shinfo(skb)->frags[0].size);
                }

                wmb();
                inl->byte_count = cpu_to_be32(1 << 31 | (skb->len - spc));
        }
        tx_desc->ctrl.vlan_tag = cpu_to_be16(*vlan_tag);
        tx_desc->ctrl.ins_vlan = MLX4_WQE_CTRL_INS_VLAN * !!(*vlan_tag);
        tx_desc->ctrl.fence_size = (real_size / 16) & 0x3f;
}

static int get_vlan_info(struct mlx4_en_priv *priv, struct sk_buff *skb,
                         u16 *vlan_tag)
{
        int tx_ind;

        /* Obtain VLAN information if present */
        if (priv->vlgrp && vlan_tx_tag_present(skb)) {
                *vlan_tag = vlan_tx_tag_get(skb);
                /* Set the Tx ring to use according to vlan priority */
                tx_ind = priv->tx_prio_map[*vlan_tag >> 13];
        } else {
                *vlan_tag = 0;
                tx_ind = 0;
        }
        return tx_ind;
}

int mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct mlx4_en_priv *priv = netdev_priv(dev);
        struct mlx4_en_dev *mdev = priv->mdev;
        struct mlx4_en_tx_ring *ring;
        struct mlx4_en_cq *cq;
        struct mlx4_en_tx_desc *tx_desc;
        struct mlx4_wqe_data_seg *data;
        struct skb_frag_struct *frag;
        struct mlx4_en_tx_info *tx_info;
        int tx_ind = 0;
        int nr_txbb;
        int desc_size;
        int real_size;
        dma_addr_t dma;
        u32 index;
        __be32 op_own;
        u16 vlan_tag;
        int i;
        int lso_header_size;
        void *fragptr;

        if (unlikely(!skb->len)) {
                dev_kfree_skb_any(skb);
                return NETDEV_TX_OK;
        }
        real_size = get_real_size(skb, dev, &lso_header_size);
        if (unlikely(!real_size))
                return NETDEV_TX_OK;

        /* Allign descriptor to TXBB size */
        desc_size = ALIGN(real_size, TXBB_SIZE);
        nr_txbb = desc_size / TXBB_SIZE;
        if (unlikely(nr_txbb > MAX_DESC_TXBBS)) {
                if (netif_msg_tx_err(priv))
                        mlx4_warn(mdev, "Oversized header or SG list\n");
                dev_kfree_skb_any(skb);
                return NETDEV_TX_OK;
        }

        tx_ind = get_vlan_info(priv, skb, &vlan_tag);
        ring = &priv->tx_ring[tx_ind];

        /* Check available TXBBs And 2K spare for prefetch */
        if (unlikely(((int)(ring->prod - ring->cons)) >
                     ring->size - HEADROOM - MAX_DESC_TXBBS)) {
                /* every full Tx ring stops queue.
                 * TODO: implement multi-queue support (per-queue stop) */
                netif_stop_queue(dev);
                ring->blocked = 1;
                priv->port_stats.queue_stopped++;

                /* Use interrupts to find out when queue opened */
                cq = &priv->tx_cq[tx_ind];
                mlx4_en_arm_cq(priv, cq);
                return NETDEV_TX_BUSY;
        }

        /* Now that we know what Tx ring to use */
        if (unlikely(!priv->port_up)) {
                if (netif_msg_tx_err(priv))
                        mlx4_warn(mdev, "xmit: port down!\n");
                dev_kfree_skb_any(skb);
                return NETDEV_TX_OK;
        }

        /* Track current inflight packets for performance analysis */
        AVG_PERF_COUNTER(priv->pstats.inflight_avg,
                         (u32) (ring->prod - ring->cons - 1));

        /* Packet is good - grab an index and transmit it */
        index = ring->prod & ring->size_mask;

        /* See if we have enough space for whole descriptor TXBB for setting
         * SW ownership on next descriptor; if not, use a bounce buffer. */
        if (likely(index + nr_txbb <= ring->size))
                tx_desc = ring->buf + index * TXBB_SIZE;
        else
                tx_desc = (struct mlx4_en_tx_desc *) ring->bounce_buf;

        /* Save skb in tx_info ring */
        tx_info = &ring->tx_info[index];
        tx_info->skb = skb;
        tx_info->nr_txbb = nr_txbb;

        /* Prepare ctrl segement apart opcode+ownership, which depends on
         * whether LSO is used */
        tx_desc->ctrl.vlan_tag = cpu_to_be16(vlan_tag);
        tx_desc->ctrl.ins_vlan = MLX4_WQE_CTRL_INS_VLAN * !!vlan_tag;
        tx_desc->ctrl.fence_size = (real_size / 16) & 0x3f;
        tx_desc->ctrl.srcrb_flags = cpu_to_be32(MLX4_WQE_CTRL_CQ_UPDATE |
                                                MLX4_WQE_CTRL_SOLICITED);
        if (likely(skb->ip_summed == CHECKSUM_PARTIAL)) {
                tx_desc->ctrl.srcrb_flags |= cpu_to_be32(MLX4_WQE_CTRL_IP_CSUM |
                                                         MLX4_WQE_CTRL_TCP_UDP_CSUM);
                priv->port_stats.tx_chksum_offload++;
        }

        /* Handle LSO (TSO) packets */
        if (lso_header_size) {
                /* Mark opcode as LSO */
                op_own = cpu_to_be32(MLX4_OPCODE_LSO | (1 << 6)) |
                        ((ring->prod & ring->size) ?
                                cpu_to_be32(MLX4_EN_BIT_DESC_OWN) : 0);

                /* Fill in the LSO prefix */
                tx_desc->lso.mss_hdr_size = cpu_to_be32(
                        skb_shinfo(skb)->gso_size << 16 | lso_header_size);

                /* Copy headers;
                 * note that we already verified that it is linear */
                memcpy(tx_desc->lso.header, skb->data, lso_header_size);
                data = ((void *) &tx_desc->lso +
                        ALIGN(lso_header_size + 4, DS_SIZE));

                priv->port_stats.tso_packets++;
                i = ((skb->len - lso_header_size) / skb_shinfo(skb)->gso_size) +
                        !!((skb->len - lso_header_size) % skb_shinfo(skb)->gso_size);
                ring->bytes += skb->len + (i - 1) * lso_header_size;
                ring->packets += i;
        } else {
                /* Normal (Non LSO) packet */
                op_own = cpu_to_be32(MLX4_OPCODE_SEND) |
                        ((ring->prod & ring->size) ?
                         cpu_to_be32(MLX4_EN_BIT_DESC_OWN) : 0);
                data = &tx_desc->data;
                ring->bytes += max(skb->len, (unsigned int) ETH_ZLEN);
                ring->packets++;

        }
        AVG_PERF_COUNTER(priv->pstats.tx_pktsz_avg, skb->len);


        /* valid only for none inline segments */
        tx_info->data_offset = (void *) data - (void *) tx_desc;

        tx_info->linear = (lso_header_size < skb_headlen(skb) && !is_inline(skb, NULL)) ? 1 : 0;
        data += skb_shinfo(skb)->nr_frags + tx_info->linear - 1;

        if (!is_inline(skb, &fragptr)) {
                /* Map fragments */
                for (i = skb_shinfo(skb)->nr_frags - 1; i >= 0; i--) {
                        frag = &skb_shinfo(skb)->frags[i];
                        dma = pci_map_page(mdev->dev->pdev, frag->page, frag->page_offset,
                                           frag->size, PCI_DMA_TODEVICE);
                        data->addr = cpu_to_be64(dma);
                        data->lkey = cpu_to_be32(mdev->mr.key);
                        wmb();
                        data->byte_count = cpu_to_be32(frag->size);
                        --data;
                }

                /* Map linear part */
                if (tx_info->linear) {
                        dma = pci_map_single(mdev->dev->pdev, skb->data + lso_header_size,
                                             skb_headlen(skb) - lso_header_size, PCI_DMA_TODEVICE);
                        data->addr = cpu_to_be64(dma);
                        data->lkey = cpu_to_be32(mdev->mr.key);
                        wmb();
                        data->byte_count = cpu_to_be32(skb_headlen(skb) - lso_header_size);
                }
        } else
                build_inline_wqe(tx_desc, skb, real_size, &vlan_tag, tx_ind, fragptr);

        ring->prod += nr_txbb;

        /* If we used a bounce buffer then copy descriptor back into place */
        if (tx_desc == (struct mlx4_en_tx_desc *) ring->bounce_buf)
                tx_desc = mlx4_en_bounce_to_desc(priv, ring, index, desc_size);

        /* Run destructor before passing skb to HW */
        if (likely(!skb_shared(skb)))
                skb_orphan(skb);

        /* Ensure new descirptor hits memory
         * before setting ownership of this descriptor to HW */
        wmb();
        tx_desc->ctrl.owner_opcode = op_own;

        /* Ring doorbell! */
        wmb();
        writel(ring->doorbell_qpn, mdev->uar_map + MLX4_SEND_DOORBELL);
        dev->trans_start = jiffies;

        /* Poll CQ here */
        mlx4_en_xmit_poll(priv, tx_ind);

        return 0;
}