/*
 * u_ether.c -- Ethernet-over-USB link layer utilities for Gadget stack
 *
 * Copyright (C) 2003-2005,2008 David Brownell
 * Copyright (C) 2003-2004 Robert Schwebel, Benedikt Spranger
 * Copyright (C) 2008 Nokia 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.
 */

/* #define VERBOSE_DEBUG */

#include <linux/kernel.h>
#include <linux/gfp.h>
#include <linux/device.h>
#include <linux/ctype.h>
#include <linux/etherdevice.h>
#include <linux/ethtool.h>

#include "u_ether.h"


/*
 * This component encapsulates the Ethernet link glue needed to provide
 * one (!) network link through the USB gadget stack, normally "usb0".
 *
 * The control and data models are handled by the function driver which
 * connects to this code; such as CDC Ethernet (ECM or EEM),
 * "CDC Subset", or RNDIS.  That includes all descriptor and endpoint
 * management.
 *
 * Link level addressing is handled by this component using module
 * parameters; if no such parameters are provided, random link level
 * addresses are used.  Each end of the link uses one address.  The
 * host end address is exported in various ways, and is often recorded
 * in configuration databases.
 *
 * The driver which assembles each configuration using such a link is
 * responsible for ensuring that each configuration includes at most one
 * instance of is network link.  (The network layer provides ways for
 * this single "physical" link to be used by multiple virtual links.)
 */

#define UETH__VERSION   "29-May-2008"

struct eth_dev {
        /* lock is held while accessing port_usb
         * or updating its backlink port_usb->ioport
         */
        spinlock_t              lock;
        struct gether           *port_usb;

        struct net_device       *net;
        struct usb_gadget       *gadget;

        spinlock_t              req_lock;       /* guard {rx,tx}_reqs */
        struct list_head        tx_reqs, rx_reqs;
        atomic_t                tx_qlen;

        struct sk_buff_head     rx_frames;

        unsigned                header_len;
        struct sk_buff          *(*wrap)(struct gether *, struct sk_buff *skb);
        int                     (*unwrap)(struct gether *,
                                                struct sk_buff *skb,
                                                struct sk_buff_head *list);

        struct work_struct      work;

        unsigned long           todo;
#define WORK_RX_MEMORY          0

        bool                    zlp;
        u8                      host_mac[ETH_ALEN];
};

/*-------------------------------------------------------------------------*/

#define RX_EXTRA        20      /* bytes guarding against rx overflows */

#define DEFAULT_QLEN    2       /* double buffering by default */


#ifdef CONFIG_USB_GADGET_DUALSPEED

static unsigned qmult = 5;
module_param(qmult, uint, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(qmult, "queue length multiplier at high/super speed");

#else   /* full speed (low speed doesn't do bulk) */
#define qmult           1
#endif

/* for dual-speed hardware, use deeper queues at high/super speed */
static inline int qlen(struct usb_gadget *gadget)
{
        if (gadget_is_dualspeed(gadget) && (gadget->speed == USB_SPEED_HIGH ||
                                            gadget->speed == USB_SPEED_SUPER))
                return qmult * DEFAULT_QLEN;
        else
                return DEFAULT_QLEN;
}

/*-------------------------------------------------------------------------*/

/* REVISIT there must be a better way than having two sets
 * of debug calls ...
 */

#undef DBG
#undef VDBG
#undef ERROR
#undef INFO

#define xprintk(d, level, fmt, args...) \
        printk(level "%s: " fmt , (d)->net->name , ## args)

#ifdef DEBUG
#undef DEBUG
#define DBG(dev, fmt, args...) \
        xprintk(dev , KERN_DEBUG , fmt , ## args)
#else
#define DBG(dev, fmt, args...) \
        do { } while (0)
#endif /* DEBUG */

#ifdef VERBOSE_DEBUG
#define VDBG    DBG
#else
#define VDBG(dev, fmt, args...) \
        do { } while (0)
#endif /* DEBUG */

#define ERROR(dev, fmt, args...) \
        xprintk(dev , KERN_ERR , fmt , ## args)
#define INFO(dev, fmt, args...) \
        xprintk(dev , KERN_INFO , fmt , ## args)

/*-------------------------------------------------------------------------*/

/* NETWORK DRIVER HOOKUP (to the layer above this driver) */

static int ueth_change_mtu(struct net_device *net, int new_mtu)
{
        struct eth_dev  *dev = netdev_priv(net);
        unsigned long   flags;
        int             status = 0;

        /* don't change MTU on "live" link (peer won't know) */
        spin_lock_irqsave(&dev->lock, flags);
        if (dev->port_usb)
                status = -EBUSY;
        else if (new_mtu <= ETH_HLEN || new_mtu > ETH_FRAME_LEN)
                status = -ERANGE;
        else
                net->mtu = new_mtu;
        spin_unlock_irqrestore(&dev->lock, flags);

        return status;
}

static void eth_get_drvinfo(struct net_device *net, struct ethtool_drvinfo *p)
{
        struct eth_dev  *dev = netdev_priv(net);

        strlcpy(p->driver, "g_ether", sizeof p->driver);
        strlcpy(p->version, UETH__VERSION, sizeof p->version);
        strlcpy(p->fw_version, dev->gadget->name, sizeof p->fw_version);
        strlcpy(p->bus_info, dev_name(&dev->gadget->dev), sizeof p->bus_info);
}

/* REVISIT can also support:
 *   - WOL (by tracking suspends and issuing remote wakeup)
 *   - msglevel (implies updated messaging)
 *   - ... probably more ethtool ops
 */

static const struct ethtool_ops ops = {
        .get_drvinfo = eth_get_drvinfo,
        .get_link = ethtool_op_get_link,
};

static void defer_kevent(struct eth_dev *dev, int flag)
{
        if (test_and_set_bit(flag, &dev->todo))
                return;
        if (!schedule_work(&dev->work))
                ERROR(dev, "kevent %d may have been dropped\n", flag);
        else
                DBG(dev, "kevent %d scheduled\n", flag);
}

static void rx_complete(struct usb_ep *ep, struct usb_request *req);

static int
rx_submit(struct eth_dev *dev, struct usb_request *req, gfp_t gfp_flags)
{
        struct sk_buff  *skb;
        int             retval = -ENOMEM;
        size_t          size = 0;
        struct usb_ep   *out;
        unsigned long   flags;

        spin_lock_irqsave(&dev->lock, flags);
        if (dev->port_usb)
                out = dev->port_usb->out_ep;
        else
                out = NULL;
        spin_unlock_irqrestore(&dev->lock, flags);

        if (!out)
                return -ENOTCONN;


        /* Padding up to RX_EXTRA handles minor disagreements with host.
         * Normally we use the USB "terminate on short read" convention;
         * so allow up to (N*maxpacket), since that memory is normally
         * already allocated.  Some hardware doesn't deal well with short
         * reads (e.g. DMA must be N*maxpacket), so for now don't trim a
         * byte off the end (to force hardware errors on overflow).
         *
         * RNDIS uses internal framing, and explicitly allows senders to
         * pad to end-of-packet.  That's potentially nice for speed, but
         * means receivers can't recover lost synch on their own (because
         * new packets don't only start after a short RX).
         */
        size += sizeof(struct ethhdr) + dev->net->mtu + RX_EXTRA;
        size += dev->port_usb->header_len;
        size += out->maxpacket - 1;
        size -= size % out->maxpacket;

        if (dev->port_usb->is_fixed)
                size = max_t(size_t, size, dev->port_usb->fixed_out_len);

        skb = alloc_skb(size + NET_IP_ALIGN, gfp_flags);
        if (skb == NULL) {
                DBG(dev, "no rx skb\n");
                goto enomem;
        }

        /* Some platforms perform better when IP packets are aligned,
         * but on at least one, checksumming fails otherwise.  Note:
         * RNDIS headers involve variable numbers of LE32 values.
         */
        skb_reserve(skb, NET_IP_ALIGN);

        req->buf = skb->data;
        req->length = size;
        req->complete = rx_complete;
        req->context = skb;

        retval = usb_ep_queue(out, req, gfp_flags);
        if (retval == -ENOMEM)
enomem:
                defer_kevent(dev, WORK_RX_MEMORY);
        if (retval) {
                DBG(dev, "rx submit --> %d\n", retval);
                if (skb)
                        dev_kfree_skb_any(skb);
                spin_lock_irqsave(&dev->req_lock, flags);
                list_add(&req->list, &dev->rx_reqs);
                spin_unlock_irqrestore(&dev->req_lock, flags);
        }
        return retval;
}

static void rx_complete(struct usb_ep *ep, struct usb_request *req)
{
        struct sk_buff  *skb = req->context, *skb2;
        struct eth_dev  *dev = ep->driver_data;
        int             status = req->status;

        switch (status) {

        /* normal completion */
        case 0:
                skb_put(skb, req->actual);

                if (dev->unwrap) {
                        unsigned long   flags;

                        spin_lock_irqsave(&dev->lock, flags);
                        if (dev->port_usb) {
                                status = dev->unwrap(dev->port_usb,
                                                        skb,
                                                        &dev->rx_frames);
                        } else {
                                dev_kfree_skb_any(skb);
                                status = -ENOTCONN;
                        }
                        spin_unlock_irqrestore(&dev->lock, flags);
                } else {
                        skb_queue_tail(&dev->rx_frames, skb);
                }
                skb = NULL;

                skb2 = skb_dequeue(&dev->rx_frames);
                while (skb2) {
                        if (status < 0
                                        || ETH_HLEN > skb2->len
                                        || skb2->len > ETH_FRAME_LEN) {
                                dev->net->stats.rx_errors++;
                                dev->net->stats.rx_length_errors++;
                                DBG(dev, "rx length %d\n", skb2->len);
                                dev_kfree_skb_any(skb2);
                                goto next_frame;
                        }
                        skb2->protocol = eth_type_trans(skb2, dev->net);
                        dev->net->stats.rx_packets++;
                        dev->net->stats.rx_bytes += skb2->len;

                        /* no buffer copies needed, unless hardware can't
                         * use skb buffers.
                         */
                        status = netif_rx(skb2);
next_frame:
                        skb2 = skb_dequeue(&dev->rx_frames);
                }
                break;

        /* software-driven interface shutdown */
        case -ECONNRESET:               /* unlink */
        case -ESHUTDOWN:                /* disconnect etc */
                VDBG(dev, "rx shutdown, code %d\n", status);
                goto quiesce;

        /* for hardware automagic (such as pxa) */
        case -ECONNABORTED:             /* endpoint reset */
                DBG(dev, "rx %s reset\n", ep->name);
                defer_kevent(dev, WORK_RX_MEMORY);
quiesce:
                dev_kfree_skb_any(skb);
                goto clean;

        /* data overrun */
        case -EOVERFLOW:
                dev->net->stats.rx_over_errors++;
                /* FALLTHROUGH */

        default:
                dev->net->stats.rx_errors++;
                DBG(dev, "rx status %d\n", status);
                break;
        }

        if (skb)
                dev_kfree_skb_any(skb);
        if (!netif_running(dev->net)) {
clean:
                spin_lock(&dev->req_lock);
                list_add(&req->list, &dev->rx_reqs);
                spin_unlock(&dev->req_lock);
                req = NULL;
        }
        if (req)
                rx_submit(dev, req, GFP_ATOMIC);
}

static int prealloc(struct list_head *list, struct usb_ep *ep, unsigned n)
{
        unsigned                i;
        struct usb_request      *req;

        if (!n)
                return -ENOMEM;

        /* queue/recycle up to N requests */
        i = n;
        list_for_each_entry(req, list, list) {
                if (i-- == 0)
                        goto extra;
        }
        while (i--) {
                req = usb_ep_alloc_request(ep, GFP_ATOMIC);
                if (!req)
                        return list_empty(list) ? -ENOMEM : 0;
                list_add(&req->list, list);
        }
        return 0;

extra:
        /* free extras */
        for (;;) {
                struct list_head        *next;

                next = req->list.next;
                list_del(&req->list);
                usb_ep_free_request(ep, req);

                if (next == list)
                        break;

                req = container_of(next, struct usb_request, list);
        }
        return 0;
}

static int alloc_requests(struct eth_dev *dev, struct gether *link, unsigned n)
{
        int     status;

        spin_lock(&dev->req_lock);
        status = prealloc(&dev->tx_reqs, link->in_ep, n);
        if (status < 0)
                goto fail;
        status = prealloc(&dev->rx_reqs, link->out_ep, n);
        if (status < 0)
                goto fail;
        goto done;
fail:
        DBG(dev, "can't alloc requests\n");
done:
        spin_unlock(&dev->req_lock);
        return status;
}

static void rx_fill(struct eth_dev *dev, gfp_t gfp_flags)
{
        struct usb_request      *req;
        unsigned long           flags;

        /* fill unused rxq slots with some skb */
        spin_lock_irqsave(&dev->req_lock, flags);
        while (!list_empty(&dev->rx_reqs)) {
                req = container_of(dev->rx_reqs.next,
                                struct usb_request, list);
                list_del_init(&req->list);
                spin_unlock_irqrestore(&dev->req_lock, flags);

                if (rx_submit(dev, req, gfp_flags) < 0) {
                        defer_kevent(dev, WORK_RX_MEMORY);
                        return;
                }

                spin_lock_irqsave(&dev->req_lock, flags);
        }
        spin_unlock_irqrestore(&dev->req_lock, flags);
}

static void eth_work(struct work_struct *work)
{
        struct eth_dev  *dev = container_of(work, struct eth_dev, work);

        if (test_and_clear_bit(WORK_RX_MEMORY, &dev->todo)) {
                if (netif_running(dev->net))
                        rx_fill(dev, GFP_KERNEL);
        }

        if (dev->todo)
                DBG(dev, "work done, flags = 0x%lx\n", dev->todo);
}

static void tx_complete(struct usb_ep *ep, struct usb_request *req)
{
        struct sk_buff  *skb = req->context;
        struct eth_dev  *dev = ep->driver_data;

        switch (req->status) {
        default:
                dev->net->stats.tx_errors++;
                VDBG(dev, "tx err %d\n", req->status);
                /* FALLTHROUGH */
        case -ECONNRESET:               /* unlink */
        case -ESHUTDOWN:                /* disconnect etc */
                break;
        case 0:
                dev->net->stats.tx_bytes += skb->len;
        }
        dev->net->stats.tx_packets++;

        spin_lock(&dev->req_lock);
        list_add(&req->list, &dev->tx_reqs);
        spin_unlock(&dev->req_lock);
        dev_kfree_skb_any(skb);

        atomic_dec(&dev->tx_qlen);
        if (netif_carrier_ok(dev->net))
                netif_wake_queue(dev->net);
}

static inline int is_promisc(u16 cdc_filter)
{
        return cdc_filter & USB_CDC_PACKET_TYPE_PROMISCUOUS;
}

static netdev_tx_t eth_start_xmit(struct sk_buff *skb,
                                        struct net_device *net)
{
        struct eth_dev          *dev = netdev_priv(net);
        int                     length = skb->len;
        int                     retval;
        struct usb_request      *req = NULL;
        unsigned long           flags;
        struct usb_ep           *in;
        u16                     cdc_filter;

        spin_lock_irqsave(&dev->lock, flags);
        if (dev->port_usb) {
                in = dev->port_usb->in_ep;
                cdc_filter = dev->port_usb->cdc_filter;
        } else {
                in = NULL;
                cdc_filter = 0;
        }
        spin_unlock_irqrestore(&dev->lock, flags);

        if (!in) {
                dev_kfree_skb_any(skb);
                return NETDEV_TX_OK;
        }

        /* apply outgoing CDC or RNDIS filters */
        if (!is_promisc(cdc_filter)) {
                u8              *dest = skb->data;

                if (is_multicast_ether_addr(dest)) {
                        u16     type;

                        /* ignores USB_CDC_PACKET_TYPE_MULTICAST and host
                         * SET_ETHERNET_MULTICAST_FILTERS requests
                         */
                        if (is_broadcast_ether_addr(dest))
                                type = USB_CDC_PACKET_TYPE_BROADCAST;
                        else
                                type = USB_CDC_PACKET_TYPE_ALL_MULTICAST;
                        if (!(cdc_filter & type)) {
                                dev_kfree_skb_any(skb);
                                return NETDEV_TX_OK;
                        }
                }
                /* ignores USB_CDC_PACKET_TYPE_DIRECTED */
        }

        spin_lock_irqsave(&dev->req_lock, flags);
        /*
         * this freelist can be empty if an interrupt triggered disconnect()
         * and reconfigured the gadget (shutting down this queue) after the
         * network stack decided to xmit but before we got the spinlock.
         */
        if (list_empty(&dev->tx_reqs)) {
                spin_unlock_irqrestore(&dev->req_lock, flags);
                return NETDEV_TX_BUSY;
        }

        req = container_of(dev->tx_reqs.next, struct usb_request, list);
        list_del(&req->list);

        /* temporarily stop TX queue when the freelist empties */
        if (list_empty(&dev->tx_reqs))
                netif_stop_queue(net);
        spin_unlock_irqrestore(&dev->req_lock, flags);

        /* no buffer copies needed, unless the network stack did it
         * or the hardware can't use skb buffers.
         * or there's not enough space for extra headers we need
         */
        if (dev->wrap) {
                unsigned long   flags;

                spin_lock_irqsave(&dev->lock, flags);
                if (dev->port_usb)
                        skb = dev->wrap(dev->port_usb, skb);
                spin_unlock_irqrestore(&dev->lock, flags);
                if (!skb)
                        goto drop;

                length = skb->len;
        }
        req->buf = skb->data;
        req->context = skb;
        req->complete = tx_complete;

        /* NCM requires no zlp if transfer is dwNtbInMaxSize */
        if (dev->port_usb->is_fixed &&
            length == dev->port_usb->fixed_in_len &&
            (length % in->maxpacket) == 0)
                req->zero = 0;
        else
                req->zero = 1;

        /* use zlp framing on tx for strict CDC-Ether conformance,
         * though any robust network rx path ignores extra padding.
         * and some hardware doesn't like to write zlps.
         */
        if (req->zero && !dev->zlp && (length % in->maxpacket) == 0)
                length++;

        req->length = length;

        /* throttle high/super speed IRQ rate back slightly */
        if (gadget_is_dualspeed(dev->gadget))
                req->no_interrupt = (dev->gadget->speed == USB_SPEED_HIGH ||
                                     dev->gadget->speed == USB_SPEED_SUPER)
                        ? ((atomic_read(&dev->tx_qlen) % qmult) != 0)
                        : 0;

        retval = usb_ep_queue(in, req, GFP_ATOMIC);
        switch (retval) {
        default:
                DBG(dev, "tx queue err %d\n", retval);
                break;
        case 0:
                net->trans_start = jiffies;
                atomic_inc(&dev->tx_qlen);
        }

        if (retval) {
                dev_kfree_skb_any(skb);
drop:
                dev->net->stats.tx_dropped++;
                spin_lock_irqsave(&dev->req_lock, flags);
                if (list_empty(&dev->tx_reqs))
                        netif_start_queue(net);
                list_add(&req->list, &dev->tx_reqs);
                spin_unlock_irqrestore(&dev->req_lock, flags);
        }
        return NETDEV_TX_OK;
}

/*-------------------------------------------------------------------------*/

static void eth_start(struct eth_dev *dev, gfp_t gfp_flags)
{
        DBG(dev, "%s\n", __func__);

        /* fill the rx queue */
        rx_fill(dev, gfp_flags);

        /* and open the tx floodgates */
        atomic_set(&dev->tx_qlen, 0);
        netif_wake_queue(dev->net);
}

static int eth_open(struct net_device *net)
{
        struct eth_dev  *dev = netdev_priv(net);
        struct gether   *link;

        DBG(dev, "%s\n", __func__);
        if (netif_carrier_ok(dev->net))
                eth_start(dev, GFP_KERNEL);

        spin_lock_irq(&dev->lock);
        link = dev->port_usb;
        if (link && link->open)
                link->open(link);
        spin_unlock_irq(&dev->lock);

        return 0;
}

static int eth_stop(struct net_device *net)
{
        struct eth_dev  *dev = netdev_priv(net);
        unsigned long   flags;

        VDBG(dev, "%s\n", __func__);
        netif_stop_queue(net);

        DBG(dev, "stop stats: rx/tx %ld/%ld, errs %ld/%ld\n",
                dev->net->stats.rx_packets, dev->net->stats.tx_packets,
                dev->net->stats.rx_errors, dev->net->stats.tx_errors
                );

        /* ensure there are no more active requests */
        spin_lock_irqsave(&dev->lock, flags);
        if (dev->port_usb) {
                struct gether   *link = dev->port_usb;

                if (link->close)
                        link->close(link);

                /* NOTE:  we have no abort-queue primitive we could use
                 * to cancel all pending I/O.  Instead, we disable then
                 * reenable the endpoints ... this idiom may leave toggle
                 * wrong, but that's a self-correcting error.
                 *
                 * REVISIT:  we *COULD* just let the transfers complete at
                 * their own pace; the network stack can handle old packets.
                 * For the moment we leave this here, since it works.
                 */
                usb_ep_disable(link->in_ep);
                usb_ep_disable(link->out_ep);
                if (netif_carrier_ok(net)) {
                        DBG(dev, "host still using in/out endpoints\n");
                        usb_ep_enable(link->in_ep);
                        usb_ep_enable(link->out_ep);
                }
        }
        spin_unlock_irqrestore(&dev->lock, flags);

        return 0;
}

/*-------------------------------------------------------------------------*/

/* initial value, changed by "ifconfig usb0 hw ether xx:xx:xx:xx:xx:xx" */
static char *dev_addr;
module_param(dev_addr, charp, S_IRUGO);
MODULE_PARM_DESC(dev_addr, "Device Ethernet Address");

/* this address is invisible to ifconfig */
static char *host_addr;
module_param(host_addr, charp, S_IRUGO);
MODULE_PARM_DESC(host_addr, "Host Ethernet Address");

static int get_ether_addr(const char *str, u8 *dev_addr)
{
        if (str) {
                unsigned        i;

                for (i = 0; i < 6; i++) {
                        unsigned char num;

                        if ((*str == '.') || (*str == ':'))
                                str++;
                        num = hex_to_bin(*str++) << 4;
                        num |= hex_to_bin(*str++);
                        dev_addr [i] = num;
                }
                if (is_valid_ether_addr(dev_addr))
                        return 0;
        }
        random_ether_addr(dev_addr);
        return 1;
}

static struct eth_dev *the_dev;

static const struct net_device_ops eth_netdev_ops = {
        .ndo_open               = eth_open,
        .ndo_stop               = eth_stop,
        .ndo_start_xmit         = eth_start_xmit,
        .ndo_change_mtu         = ueth_change_mtu,
        .ndo_set_mac_address    = eth_mac_addr,
        .ndo_validate_addr      = eth_validate_addr,
};

static struct device_type gadget_type = {
        .name   = "gadget",
};

/**
 * gether_setup - initialize one ethernet-over-usb link
 * @g: gadget to associated with these links
 * @ethaddr: NULL, or a buffer in which the ethernet address of the
 *      host side of the link is recorded
 * Context: may sleep
 *
 * This sets up the single network link that may be exported by a
 * gadget driver using this framework.  The link layer addresses are
 * set up using module parameters.
 *
 * Returns negative errno, or zero on success
 */
int gether_setup(struct usb_gadget *g, u8 ethaddr[ETH_ALEN])
{
        struct eth_dev          *dev;
        struct net_device       *net;
        int                     status;

        if (the_dev)
                return -EBUSY;

        net = alloc_etherdev(sizeof *dev);
        if (!net)
                return -ENOMEM;

        dev = netdev_priv(net);
        spin_lock_init(&dev->lock);
        spin_lock_init(&dev->req_lock);
        INIT_WORK(&dev->work, eth_work);
        INIT_LIST_HEAD(&dev->tx_reqs);
        INIT_LIST_HEAD(&dev->rx_reqs);

        skb_queue_head_init(&dev->rx_frames);

        /* network device setup */
        dev->net = net;
        strcpy(net->name, "usb%d");

        if (get_ether_addr(dev_addr, net->dev_addr))
                dev_warn(&g->dev,
                        "using random %s ethernet address\n", "self");
        if (get_ether_addr(host_addr, dev->host_mac))
                dev_warn(&g->dev,
                        "using random %s ethernet address\n", "host");

        if (ethaddr)
                memcpy(ethaddr, dev->host_mac, ETH_ALEN);

        net->netdev_ops = &eth_netdev_ops;

        SET_ETHTOOL_OPS(net, &ops);

        /* two kinds of host-initiated state changes:
         *  - iff DATA transfer is active, carrier is "on"
         *  - tx queueing enabled if open *and* carrier is "on"
         */
        netif_carrier_off(net);

        dev->gadget = g;
        SET_NETDEV_DEV(net, &g->dev);
        SET_NETDEV_DEVTYPE(net, &gadget_type);

        status = register_netdev(net);
        if (status < 0) {
                dev_dbg(&g->dev, "register_netdev failed, %d\n", status);
                free_netdev(net);
        } else {
                INFO(dev, "MAC %pM\n", net->dev_addr);
                INFO(dev, "HOST MAC %pM\n", dev->host_mac);

                the_dev = dev;
        }

        return status;
}

/**
 * gether_cleanup - remove Ethernet-over-USB device
 * Context: may sleep
 *
 * This is called to free all resources allocated by @gether_setup().
 */
void gether_cleanup(void)
{
        if (!the_dev)
                return;

        unregister_netdev(the_dev->net);
        flush_work_sync(&the_dev->work);
        free_netdev(the_dev->net);

        the_dev = NULL;
}


/**
 * gether_connect - notify network layer that USB link is active
 * @link: the USB link, set up with endpoints, descriptors matching
 *      current device speed, and any framing wrapper(s) set up.
 * Context: irqs blocked
 *
 * This is called to activate endpoints and let the network layer know
 * the connection is active ("carrier detect").  It may cause the I/O
 * queues to open and start letting network packets flow, but will in
 * any case activate the endpoints so that they respond properly to the
 * USB host.
 *
 * Verify net_device pointer returned using IS_ERR().  If it doesn't
 * indicate some error code (negative errno), ep->driver_data values
 * have been overwritten.
 */
struct net_device *gether_connect(struct gether *link)
{
        struct eth_dev          *dev = the_dev;
        int                     result = 0;

        if (!dev)
                return ERR_PTR(-EINVAL);

        link->in_ep->driver_data = dev;
        result = usb_ep_enable(link->in_ep);
        if (result != 0) {
                DBG(dev, "enable %s --> %d\n",
                        link->in_ep->name, result);
                goto fail0;
        }

        link->out_ep->driver_data = dev;
        result = usb_ep_enable(link->out_ep);
        if (result != 0) {
                DBG(dev, "enable %s --> %d\n",
                        link->out_ep->name, result);
                goto fail1;
        }

        if (result == 0)
                result = alloc_requests(dev, link, qlen(dev->gadget));

        if (result == 0) {
                dev->zlp = link->is_zlp_ok;
                DBG(dev, "qlen %d\n", qlen(dev->gadget));

                dev->header_len = link->header_len;
                dev->unwrap = link->unwrap;
                dev->wrap = link->wrap;

                spin_lock(&dev->lock);
                dev->port_usb = link;
                link->ioport = dev;
                if (netif_running(dev->net)) {
                        if (link->open)
                                link->open(link);
                } else {
                        if (link->close)
                                link->close(link);
                }
                spin_unlock(&dev->lock);

                netif_carrier_on(dev->net);
                if (netif_running(dev->net))
                        eth_start(dev, GFP_ATOMIC);

        /* on error, disable any endpoints  */
        } else {
                (void) usb_ep_disable(link->out_ep);
fail1:
                (void) usb_ep_disable(link->in_ep);
        }
fail0:
        /* caller is responsible for cleanup on error */
        if (result < 0)
                return ERR_PTR(result);
        return dev->net;
}

/**
 * gether_disconnect - notify network layer that USB link is inactive
 * @link: the USB link, on which gether_connect() was called
 * Context: irqs blocked
 *
 * This is called to deactivate endpoints and let the network layer know
 * the connection went inactive ("no carrier").
 *
 * On return, the state is as if gether_connect() had never been called.
 * The endpoints are inactive, and accordingly without active USB I/O.
 * Pointers to endpoint descriptors and endpoint private data are nulled.
 */
void gether_disconnect(struct gether *link)
{
        struct eth_dev          *dev = link->ioport;
        struct usb_request      *req;

        WARN_ON(!dev);
        if (!dev)
                return;

        DBG(dev, "%s\n", __func__);

        netif_stop_queue(dev->net);
        netif_carrier_off(dev->net);

        /* disable endpoints, forcing (synchronous) completion
         * of all pending i/o.  then free the request objects
         * and forget about the endpoints.
         */
        usb_ep_disable(link->in_ep);
        spin_lock(&dev->req_lock);
        while (!list_empty(&dev->tx_reqs)) {
                req = container_of(dev->tx_reqs.next,
                                        struct usb_request, list);
                list_del(&req->list);

                spin_unlock(&dev->req_lock);
                usb_ep_free_request(link->in_ep, req);
                spin_lock(&dev->req_lock);
        }
        spin_unlock(&dev->req_lock);
        link->in_ep->driver_data = NULL;
        link->in_ep->desc = NULL;

        usb_ep_disable(link->out_ep);
        spin_lock(&dev->req_lock);
        while (!list_empty(&dev->rx_reqs)) {
                req = container_of(dev->rx_reqs.next,
                                        struct usb_request, list);
                list_del(&req->list);

                spin_unlock(&dev->req_lock);
                usb_ep_free_request(link->out_ep, req);
                spin_lock(&dev->req_lock);
        }
        spin_unlock(&dev->req_lock);
        link->out_ep->driver_data = NULL;
        link->out_ep->desc = NULL;

        /* finish forgetting about this USB link episode */
        dev->header_len = 0;
        dev->unwrap = NULL;
        dev->wrap = NULL;

        spin_lock(&dev->lock);
        dev->port_usb = NULL;
        link->ioport = NULL;
        spin_unlock(&dev->lock);
}