ethernet.c

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/*****************************************************************************
 *
 *  Copyright (C) 2006-2024  Florian Pose, Ingenieurgemeinschaft IgH
 *
 *  This file is part of the IgH EtherCAT Master.
 *
 *  The IgH EtherCAT Master is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License version 2, as
 *  published by the Free Software Foundation.
 *
 *  The IgH EtherCAT Master 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 the IgH EtherCAT Master; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 *
 ****************************************************************************/

/****************************************************************************/

#include <linux/version.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/lockdep.h>
#include <linux/skbuff.h>

#include "globals.h"
#include "master.h"
#include "slave.h"
#include "mailbox.h"
#include "ethernet.h"

#if defined(CONFIG_SUSE_KERNEL) && \
    LINUX_VERSION_CODE >= KERNEL_VERSION(5, 14, 0)
#include <linux/suse_version.h>
#else
#  ifndef SUSE_VERSION
#    define SUSE_VERSION 0
#  endif
#  ifndef SUSE_PATCHLEVEL
#    define SUSE_PATCHLEVEL 0
#  endif
#endif

/****************************************************************************/

#define EOE_DEBUG_LEVEL 1

#define EC_EOE_TX_QUEUE_SIZE 100

#define EC_EOE_TRIES 100

/****************************************************************************/

// prototypes for private methods
void ec_eoe_flush(ec_eoe_t *);
int ec_eoe_send(ec_eoe_t *);

/****************************************************************************/

// state functions
void ec_eoe_state_rx_start(ec_eoe_t *);
void ec_eoe_state_rx_fetch(ec_eoe_t *);
void ec_eoe_state_tx_start(ec_eoe_t *);
void ec_eoe_state_tx_sent(ec_eoe_t *);

// net_device functions
int ec_eoedev_open(struct net_device *);
int ec_eoedev_stop(struct net_device *);
int ec_eoedev_tx(struct sk_buff *, struct net_device *);
struct net_device_stats *ec_eoedev_stats(struct net_device *);

/****************************************************************************/

static const struct net_device_ops ec_eoedev_ops = {
    .ndo_open = ec_eoedev_open,
    .ndo_stop = ec_eoedev_stop,
    .ndo_start_xmit = ec_eoedev_tx,
    .ndo_get_stats = ec_eoedev_stats,
};

/****************************************************************************/

int ec_eoe_init(
        ec_eoe_t *eoe, 
        ec_slave_t *slave 
        )
{
    ec_eoe_t **priv;
    int ret = 0;
    char name[EC_DATAGRAM_NAME_SIZE];
    u8 mac_addr[ETH_ALEN] = {0x00, 0x11, 0x22, 0x33, 0x44, 0x55};

    eoe->slave = slave;

    ec_datagram_init(&eoe->datagram);
    eoe->queue_datagram = 0;
    eoe->state = ec_eoe_state_rx_start;
    ec_fsm_mbox_init(&eoe->fsm_mbox);
    eoe->opened = 0;
    eoe->rx_skb = NULL;
    eoe->rx_expected_fragment = 0;
    INIT_LIST_HEAD(&eoe->tx_queue);
    eoe->tx_frame = NULL;
    eoe->tx_queue_active = 0;
    eoe->tx_queue_size = EC_EOE_TX_QUEUE_SIZE;
    eoe->tx_queued_frames = 0;

    eoe->tx_frame_number = 0xFF;
    memset(&eoe->stats, 0, sizeof(struct net_device_stats));

    eoe->rx_counter = 0;
    eoe->tx_counter = 0;
    eoe->rx_rate = 0;
    eoe->tx_rate = 0;
    eoe->rate_jiffies = 0;
    eoe->rx_idle = 1;
    eoe->tx_idle = 1;

    /* device name eoe<MASTER>[as]<SLAVE>, because networking scripts don't
     * like hyphens etc. in interface names. */
    if (slave->effective_alias) {
        snprintf(name, EC_DATAGRAM_NAME_SIZE,
                "eoe%ua%u", slave->master->index, slave->effective_alias);
    } else {
        snprintf(name, EC_DATAGRAM_NAME_SIZE,
                "eoe%us%u", slave->master->index, slave->ring_position);
    }

    snprintf(eoe->datagram.name, EC_DATAGRAM_NAME_SIZE, name);

#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 17, 0)
    eoe->dev = alloc_netdev(sizeof(ec_eoe_t *), name, NET_NAME_UNKNOWN,
            ether_setup);
#else
    eoe->dev = alloc_netdev(sizeof(ec_eoe_t *), name, ether_setup);
#endif
    if (!eoe->dev) {
        EC_SLAVE_ERR(slave, "Unable to allocate net_device %s"
                " for EoE handler!\n", name);
        ret = -ENODEV;
        goto out_return;
    }

    // initialize net_device
    eoe->dev->netdev_ops = &ec_eoedev_ops;

#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 15, 0) || \
    (SUSE_VERSION == 15 && SUSE_PATCHLEVEL >= 5)
    eth_hw_addr_set(eoe->dev, mac_addr);
#else
    memcpy(eoe->dev->dev_addr, mac_addr, sizeof(mac_addr));
#endif

    // initialize private data
    priv = netdev_priv(eoe->dev);
    *priv = eoe;

    // Usually setting the MTU appropriately makes the upper layers
    // do the frame fragmenting. In some cases this doesn't work
    // so the MTU is left on the Ethernet standard value and fragmenting
    // is done "manually".
#if 0
    eoe->dev->mtu = slave->configured_rx_mailbox_size - ETH_HLEN - 10;
#endif

    // connect the net_device to the kernel
    ret = register_netdev(eoe->dev);
    if (ret) {
        EC_SLAVE_ERR(slave, "Unable to register net_device:"
                " error %i\n", ret);
        goto out_free;
    }

    // make the last address octet unique
    mac_addr[ETH_ALEN - 1] = (uint8_t) eoe->dev->ifindex;
#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 15, 0) || \
    (SUSE_VERSION == 15 && SUSE_PATCHLEVEL >= 5)
    eth_hw_addr_set(eoe->dev, mac_addr);
#else
    memcpy(eoe->dev->dev_addr, mac_addr, sizeof(mac_addr));
#endif

    return 0;

 out_free:
    free_netdev(eoe->dev);
    eoe->dev = NULL;
 out_return:
    return ret;
}

/****************************************************************************/

void ec_eoe_clear(ec_eoe_t *eoe )
{
    unregister_netdev(eoe->dev); // possibly calls close callback

    // empty transmit queue
    ec_eoe_flush(eoe);

    if (eoe->tx_frame) {
        dev_kfree_skb(eoe->tx_frame->skb);
        kfree(eoe->tx_frame);
    }

    if (eoe->rx_skb)
        dev_kfree_skb(eoe->rx_skb);

    free_netdev(eoe->dev);

    ec_fsm_mbox_clear(&eoe->fsm_mbox);
    ec_datagram_clear(&eoe->datagram);
}

/****************************************************************************/

void ec_eoe_flush(ec_eoe_t *eoe )
{
    ec_eoe_frame_t *frame, *next;
    struct list_head tx_queue;

    netif_tx_lock_bh(eoe->dev);

    list_replace_init(&eoe->tx_queue, &tx_queue);
    eoe->tx_queued_frames = 0;

    netif_tx_unlock_bh(eoe->dev);

    list_for_each_entry_safe(frame, next, &tx_queue, queue) {
        list_del(&frame->queue);
        dev_kfree_skb(frame->skb);
        kfree(frame);
    }
}

/****************************************************************************/

int ec_eoe_send(ec_eoe_t *eoe )
{
    size_t remaining_size, current_size, complete_offset;
    unsigned int last_fragment;
    uint8_t *data;
#if EOE_DEBUG_LEVEL >= 3
    unsigned int i;
#endif

    remaining_size = eoe->tx_frame->skb->len - eoe->tx_offset;

    if (remaining_size <= eoe->slave->configured_tx_mailbox_size - 10) {
        current_size = remaining_size;
        last_fragment = 1;
    } else {
        current_size =
            ((eoe->slave->configured_tx_mailbox_size - 10) / 32) * 32;
        last_fragment = 0;
    }

    if (eoe->tx_fragment_number) {
        complete_offset = eoe->tx_offset / 32;
    }
    else {
        // complete size in 32 bit blocks, rounded up.
        complete_offset = remaining_size / 32 + 1;
    }

#if EOE_DEBUG_LEVEL >= 2
    EC_SLAVE_DBG(eoe->slave, 0, "EoE %s TX sending fragment %u%s"
            " with %zu octets (%zu). %u frames queued.\n",
            eoe->dev->name, eoe->tx_fragment_number,
            last_fragment ? "" : "+", current_size, complete_offset,
            eoe->tx_queued_frames);
#endif

#if EOE_DEBUG_LEVEL >= 3
    EC_SLAVE_DBG(eoe->slave, 0, "");
    for (i = 0; i < current_size; i++) {
        printk(KERN_CONT "%02X ",
                eoe->tx_frame->skb->data[eoe->tx_offset + i]);
        if ((i + 1) % 16 == 0) {
            printk(KERN_CONT "\n");
            EC_SLAVE_DBG(eoe->slave, 0, "");
        }
    }
    printk(KERN_CONT "\n");
#endif

    data = ec_slave_mbox_prepare_send(eoe->slave, &eoe->datagram,
            EC_MBOX_TYPE_EOE, current_size + 4);
    if (IS_ERR(data))
        return PTR_ERR(data);

    EC_WRITE_U8 (data, EC_EOE_FRAMETYPE_INIT_REQ); // Initiate EoE Request
    EC_WRITE_U8 (data + 1, last_fragment);
    EC_WRITE_U16(data + 2, ((eoe->tx_fragment_number & 0x3F) |
                            (complete_offset & 0x3F) << 6 |
                            (eoe->tx_frame_number & 0x0F) << 12));

    memcpy(data + 4, eoe->tx_frame->skb->data + eoe->tx_offset, current_size);
    eoe->queue_datagram = 1;

    eoe->tx_offset += current_size;
    eoe->tx_fragment_number++;
    return 0;
}

/****************************************************************************/

void ec_eoe_run(ec_eoe_t *eoe )
{
    if (!eoe->opened) {
        if (!ec_eoe_holds_mbox_lock(eoe))
            return;

        // the device was closed during a receive sequence. release the
        // mailbox read lock, as soon as the datagram is not in use any more.
        if (eoe->queue_datagram) {
            eoe->queue_datagram = 0; // not handed over yet
        } else if (eoe->datagram.state == EC_DATAGRAM_QUEUED ||
                eoe->datagram.state == EC_DATAGRAM_SENT) {
            return;
        }

        ec_fsm_mbox_abort(&eoe->fsm_mbox);
        eoe->state = ec_eoe_state_rx_start;
        return;
    }

    // if the datagram was not sent, or is not yet received, skip this cycle
    if (eoe->queue_datagram || eoe->datagram.state == EC_DATAGRAM_SENT)
        return;

    // call state function
    eoe->state(eoe);

    // update statistics
    if (jiffies - eoe->rate_jiffies > HZ) {
        eoe->rx_rate = eoe->rx_counter;
        eoe->tx_rate = eoe->tx_counter;
        eoe->rx_counter = 0;
        eoe->tx_counter = 0;
        eoe->rate_jiffies = jiffies;
    }

    ec_datagram_output_stats(&eoe->datagram);
}

/****************************************************************************/

void ec_eoe_queue(ec_eoe_t *eoe )
{
    if (eoe->queue_datagram) {
        ec_master_queue_datagram_ext(eoe->slave->master, &eoe->datagram);
        eoe->queue_datagram = 0;
    }
}

/****************************************************************************/

int ec_eoe_is_open(const ec_eoe_t *eoe )
{
    return eoe->opened;
}

/****************************************************************************/

int ec_eoe_holds_mbox_lock(const ec_eoe_t *eoe )
{
    return ec_fsm_mbox_holds_lock(&eoe->fsm_mbox);
}

/****************************************************************************/

int ec_eoe_is_idle(const ec_eoe_t *eoe )
{
    return eoe->rx_idle && eoe->tx_idle;
}

/*****************************************************************************
 *  STATE PROCESSING FUNCTIONS
 ****************************************************************************/

void ec_eoe_state_rx_start(ec_eoe_t *eoe )
{
    if (eoe->slave->error_flag ||
            !eoe->slave->master->devices[EC_DEVICE_MAIN].link_state) {
        eoe->rx_idle = 1;
        eoe->tx_idle = 1;
        return;
    }

    ec_fsm_mbox_poll(&eoe->fsm_mbox, eoe->slave, &eoe->slave->mbox_eoe_data);
    eoe->state = ec_eoe_state_rx_fetch;
    eoe->state(eoe);
}

/****************************************************************************/

void ec_eoe_state_rx_fetch(ec_eoe_t *eoe )
{
    size_t rec_size, data_size;
    uint8_t *data, frame_type, last_fragment, time_appended, mbox_prot;
    uint8_t size_or_offset, fragment_number;
#if EOE_DEBUG_LEVEL >= 2
    uint8_t frame_number;
#endif
#if EOE_DEBUG_LEVEL >= 3
    unsigned int i;
#endif

    if (ec_fsm_mbox_exec(&eoe->fsm_mbox, &eoe->datagram)) {
        if (eoe->datagram.state != EC_DATAGRAM_UNUSED) {
            eoe->queue_datagram = 1;
        }
        return;
    }

    switch (ec_fsm_mbox_result(&eoe->fsm_mbox)) {
        case 0:
            eoe->rx_idle = 0;
            break;
        case -EAGAIN: // no EoE data available
        case -EBUSY: // do not wait for the other read request, but transmit
            eoe->rx_idle = 1;
            eoe->state = ec_eoe_state_tx_start;
            return;
        default:
            eoe->stats.rx_errors++;
#if EOE_DEBUG_LEVEL >= 1
            EC_SLAVE_WARN(eoe->slave, "Failed to receive mailbox"
                    " data for %s.\n", eoe->dev->name);
#endif
            eoe->state = ec_eoe_state_tx_start;
            return;
    }

    data = ec_slave_mbox_fetch(eoe->slave, &eoe->slave->mbox_eoe_data,
            &mbox_prot, &rec_size);
    if (IS_ERR(data)) {
        eoe->stats.rx_errors++;
#if EOE_DEBUG_LEVEL >= 1
        EC_SLAVE_WARN(eoe->slave, "Invalid mailbox response for %s.\n",
                eoe->dev->name);
#endif
        eoe->state = ec_eoe_state_tx_start;
        return;
    }

    if (mbox_prot != EC_MBOX_TYPE_EOE) { // FIXME mailbox handler necessary
        eoe->stats.rx_errors++;
#if EOE_DEBUG_LEVEL >= 1
        EC_SLAVE_WARN(eoe->slave, "Other mailbox protocol response for %s.\n",
                eoe->dev->name);
#endif
        eoe->state = ec_eoe_state_tx_start;
        return;
    }

    frame_type = EC_READ_U16(data) & 0x000F;

    if (frame_type != EC_EOE_FRAMETYPE_INIT_REQ) { // EoE Fragment Data
#if EOE_DEBUG_LEVEL >= 1
        EC_SLAVE_WARN(eoe->slave, "%s: Other frame received."
                " Dropping.\n", eoe->dev->name);
#endif
        eoe->stats.rx_dropped++;
        eoe->state = ec_eoe_state_tx_start;
        return;
    }

    // EoE Fragment Request received

    last_fragment = (EC_READ_U16(data) >> 8) & 0x0001;
    time_appended = (EC_READ_U16(data) >> 9) & 0x0001;
    fragment_number = EC_READ_U16(data + 2) & 0x003F;
    size_or_offset = (EC_READ_U16(data + 2) >> 6) & 0x003F;
#if EOE_DEBUG_LEVEL >= 2
    frame_number = (EC_READ_U16(data + 2) >> 12) & 0x000F;
#endif

    data_size = time_appended ? rec_size - 8 : rec_size - 4;

#if EOE_DEBUG_LEVEL >= 2
    EC_SLAVE_DBG(eoe->slave, 0, "EoE %s RX fragment %u%s, offset %u,"
            " frame %u%s, %zu octets\n", eoe->dev->name, fragment_number,
           last_fragment ? "" : "+", size_or_offset, frame_number,
           time_appended ? ", + timestamp" : "", data_size);
#endif

#if EOE_DEBUG_LEVEL >= 3
    EC_SLAVE_DBG(eoe->slave, 0, "");
    for (i = 0; i < rec_size - 4; i++) {
        printk(KERN_CONT "%02X ", data[i + 4]);
        if ((i + 1) % 16 == 0) {
            printk(KERN_CONT "\n");
            EC_SLAVE_DBG(eoe->slave, 0, "");
        }
    }
    printk(KERN_CONT "\n");
#endif

    if (!fragment_number) {
        size_t complete_size = size_or_offset * 32;

        if (eoe->rx_skb) {
            EC_SLAVE_WARN(eoe->slave, "EoE RX freeing old socket buffer.\n");
            dev_kfree_skb(eoe->rx_skb);
            eoe->rx_skb = NULL;
        }

        if (!complete_size || data_size > complete_size) {
            EC_SLAVE_ERR(eoe->slave, "Received corrupted EoE first fragment"
                    " (%zu of %zu bytes)!\n", data_size, complete_size);
            eoe->stats.rx_errors++;
            eoe->state = ec_eoe_state_tx_start;
            return;
        }

        // new socket buffer
        if (!(eoe->rx_skb = dev_alloc_skb(complete_size))) {
            if (printk_ratelimit()) {
                EC_SLAVE_WARN(eoe->slave, "EoE RX low on mem,"
                        " frame dropped.\n");
            }
            eoe->stats.rx_dropped++;
            eoe->state = ec_eoe_state_tx_start;
            return;
        }

        eoe->rx_skb_offset = 0;
        eoe->rx_skb_size = complete_size;
        eoe->rx_expected_fragment = 0;
    }
    else {
        off_t offset = size_or_offset * 32;

        if (!eoe->rx_skb) {
            eoe->stats.rx_dropped++;
            eoe->state = ec_eoe_state_tx_start;
            return;
        }

        if (offset != eoe->rx_skb_offset ||
            offset + data_size > eoe->rx_skb_size ||
            fragment_number != eoe->rx_expected_fragment) {
            dev_kfree_skb(eoe->rx_skb);
            eoe->rx_skb = NULL;
            eoe->stats.rx_errors++;
#if EOE_DEBUG_LEVEL >= 1
            EC_SLAVE_WARN(eoe->slave, "Fragmenting error at %s.\n",
                    eoe->dev->name);
#endif
            eoe->state = ec_eoe_state_tx_start;
            return;
        }
    }

    // copy fragment into socket buffer
    memcpy(skb_put(eoe->rx_skb, data_size), data + 4, data_size);
    eoe->rx_skb_offset += data_size;

    if (last_fragment) {
        // update statistics
        eoe->stats.rx_packets++;
        eoe->stats.rx_bytes += eoe->rx_skb->len;
        eoe->rx_counter += eoe->rx_skb->len;

#if EOE_DEBUG_LEVEL >= 2
        EC_SLAVE_DBG(eoe->slave, 0, "EoE %s RX frame completed"
                " with %u octets.\n", eoe->dev->name, eoe->rx_skb->len);
#endif

        // pass socket buffer to network stack
        eoe->rx_skb->dev = eoe->dev;
        eoe->rx_skb->protocol = eth_type_trans(eoe->rx_skb, eoe->dev);
        eoe->rx_skb->ip_summed = CHECKSUM_UNNECESSARY;
        if (netif_rx(eoe->rx_skb)) {
            EC_SLAVE_WARN(eoe->slave, "EoE RX netif_rx failed.\n");
        }
        eoe->rx_skb = NULL;

        eoe->state = ec_eoe_state_tx_start;
    }
    else {
        eoe->rx_expected_fragment++;
#if EOE_DEBUG_LEVEL >= 2
        EC_SLAVE_DBG(eoe->slave, 0, "EoE %s RX expecting fragment %u\n",
               eoe->dev->name, eoe->rx_expected_fragment);
#endif
        eoe->state = ec_eoe_state_rx_start;
    }
}

/****************************************************************************/

void ec_eoe_state_tx_start(ec_eoe_t *eoe )
{
#if EOE_DEBUG_LEVEL >= 2
    unsigned int wakeup = 0;
#endif

    if (eoe->slave->error_flag ||
            !eoe->slave->master->devices[EC_DEVICE_MAIN].link_state) {
        eoe->rx_idle = 1;
        eoe->tx_idle = 1;
        return;
    }

    netif_tx_lock_bh(eoe->dev);

    if (!eoe->tx_queued_frames || list_empty(&eoe->tx_queue)) {
        netif_tx_unlock_bh(eoe->dev);
        eoe->tx_idle = 1;
        // no data available.
        // start a new receive immediately.
        ec_eoe_state_rx_start(eoe);
        return;
    }

    // take the first frame out of the queue
    eoe->tx_frame = list_entry(eoe->tx_queue.next, ec_eoe_frame_t, queue);
    list_del(&eoe->tx_frame->queue);
    if (!eoe->tx_queue_active &&
        eoe->tx_queued_frames == eoe->tx_queue_size / 2) {
        netif_wake_queue(eoe->dev);
        eoe->tx_queue_active = 1;
#if EOE_DEBUG_LEVEL >= 2
        wakeup = 1;
#endif
    }

    eoe->tx_queued_frames--;
    netif_tx_unlock_bh(eoe->dev);

    eoe->tx_idle = 0;

    eoe->tx_frame_number++;
    eoe->tx_frame_number %= 16;
    eoe->tx_fragment_number = 0;
    eoe->tx_offset = 0;

    if (ec_eoe_send(eoe)) {
        dev_kfree_skb(eoe->tx_frame->skb);
        kfree(eoe->tx_frame);
        eoe->tx_frame = NULL;
        eoe->stats.tx_errors++;
        eoe->state = ec_eoe_state_rx_start;
#if EOE_DEBUG_LEVEL >= 1
        EC_SLAVE_WARN(eoe->slave, "Send error at %s.\n", eoe->dev->name);
#endif
        return;
    }

#if EOE_DEBUG_LEVEL >= 2
    if (wakeup)
        EC_SLAVE_DBG(eoe->slave, 0, "EoE %s waking up TX queue...\n",
                eoe->dev->name);
#endif

    eoe->tries = EC_EOE_TRIES;
    eoe->state = ec_eoe_state_tx_sent;
}

/****************************************************************************/

void ec_eoe_state_tx_sent(ec_eoe_t *eoe )
{
    if (eoe->datagram.state != EC_DATAGRAM_RECEIVED) {
        if (eoe->tries) {
            eoe->tries--; // try again
            eoe->queue_datagram = 1;
        } else {
            eoe->stats.tx_errors++;
#if EOE_DEBUG_LEVEL >= 1
            EC_SLAVE_WARN(eoe->slave, "Failed to receive send"
                    " datagram for %s after %u tries.\n",
                    eoe->dev->name, EC_EOE_TRIES);
#endif
            eoe->state = ec_eoe_state_rx_start;
        }
        return;
    }

    if (eoe->datagram.working_counter != 1) {
        if (eoe->tries) {
            eoe->tries--; // try again
            eoe->queue_datagram = 1;
        } else {
            eoe->stats.tx_errors++;
#if EOE_DEBUG_LEVEL >= 1
            EC_SLAVE_WARN(eoe->slave, "No sending response"
                    " for %s after %u tries.\n",
                    eoe->dev->name, EC_EOE_TRIES);
#endif
            eoe->state = ec_eoe_state_rx_start;
        }
        return;
    }

    // frame completely sent
    if (eoe->tx_offset >= eoe->tx_frame->skb->len) {
        eoe->stats.tx_packets++;
        eoe->stats.tx_bytes += eoe->tx_frame->skb->len;
        eoe->tx_counter += eoe->tx_frame->skb->len;
        dev_kfree_skb(eoe->tx_frame->skb);
        kfree(eoe->tx_frame);
        eoe->tx_frame = NULL;
        eoe->state = ec_eoe_state_rx_start;
    }
    else { // send next fragment
        if (ec_eoe_send(eoe)) {
            dev_kfree_skb(eoe->tx_frame->skb);
            kfree(eoe->tx_frame);
            eoe->tx_frame = NULL;
            eoe->stats.tx_errors++;
#if EOE_DEBUG_LEVEL >= 1
            EC_SLAVE_WARN(eoe->slave, "Send error at %s.\n", eoe->dev->name);
#endif
            eoe->state = ec_eoe_state_rx_start;
        }
    }
}

/*****************************************************************************
 *  NET_DEVICE functions
 ****************************************************************************/

int ec_eoedev_open(struct net_device *dev )
{
    ec_eoe_t *eoe = *((ec_eoe_t **) netdev_priv(dev));
    ec_eoe_flush(eoe);
    eoe->opened = 1;
    eoe->rx_idle = 0;
    eoe->tx_idle = 0;
    netif_start_queue(dev);
    eoe->tx_queue_active = 1;
#if EOE_DEBUG_LEVEL >= 2
    EC_SLAVE_DBG(eoe->slave, 0, "%s opened.\n", dev->name);
#endif
    return 0;
}

/****************************************************************************/

int ec_eoedev_stop(struct net_device *dev )
{
    ec_eoe_t *eoe = *((ec_eoe_t **) netdev_priv(dev));
    netif_stop_queue(dev);
    eoe->rx_idle = 1;
    eoe->tx_idle = 1;
    eoe->tx_queue_active = 0;
    eoe->opened = 0;
    ec_eoe_flush(eoe);
#if EOE_DEBUG_LEVEL >= 2
    EC_SLAVE_DBG(eoe->slave, 0, "%s stopped.\n", dev->name);
#endif
    return 0;
}

/****************************************************************************/

int ec_eoedev_tx(struct sk_buff *skb, 
                 struct net_device *dev 
                )
{
    ec_eoe_t *eoe = *((ec_eoe_t **) netdev_priv(dev));
    ec_eoe_frame_t *frame;

#if 0
    if (skb->len > eoe->slave->configured_tx_mailbox_size - 10) {
        EC_SLAVE_WARN(eoe->slave, "EoE TX frame (%u octets)"
                " exceeds MTU. dropping.\n", skb->len);
        dev_kfree_skb(skb);
        eoe->stats.tx_dropped++;
        return 0;
    }
#endif

    WARN_ON_ONCE(skb_get_queue_mapping(skb) != 0);
    lockdep_assert_held(&netdev_get_tx_queue(dev, 0)->_xmit_lock);

    if (!(frame =
          (ec_eoe_frame_t *) kmalloc(sizeof(ec_eoe_frame_t), GFP_ATOMIC))) {
        if (printk_ratelimit())
            EC_SLAVE_WARN(eoe->slave, "EoE TX: low on mem. frame dropped.\n");
        return 1;
    }

    frame->skb = skb;

    list_add_tail(&frame->queue, &eoe->tx_queue);
    eoe->tx_queued_frames++;
    if (eoe->tx_queued_frames == eoe->tx_queue_size) {
        netif_stop_queue(dev);
        eoe->tx_queue_active = 0;
    }

#if EOE_DEBUG_LEVEL >= 2
    EC_SLAVE_DBG(eoe->slave, 0, "EoE %s TX queued frame"
            " with %u octets (%u frames queued).\n",
            eoe->dev->name, skb->len, eoe->tx_queued_frames);
    if (!eoe->tx_queue_active)
        EC_SLAVE_WARN(eoe->slave, "EoE TX queue is now full.\n");
#endif

    return 0;
}

/****************************************************************************/

struct net_device_stats *ec_eoedev_stats(
        struct net_device *dev 
        )
{
    ec_eoe_t *eoe = *((ec_eoe_t **) netdev_priv(dev));
    return &eoe->stats;
}

/****************************************************************************/