/*
 * USB Network driver infrastructure
 * Copyright (C) 2000-2005 by David Brownell
 * Copyright (C) 2003-2005 David Hollis <dhollis@davehollis.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

/*
 * This is a generic "USB networking" framework that works with several
 * kinds of full and high speed networking devices:  host-to-host cables,
 * smart usb peripherals, and actual Ethernet adapters.
 *
 * These devices usually differ in terms of control protocols (if they
 * even have one!) and sometimes they define new framing to wrap or batch
 * Ethernet packets.  Otherwise, they talk to USB pretty much the same,
 * so interface (un)binding, endpoint I/O queues, fault handling, and other
 * issues can usefully be addressed by this framework.
 */

// #define      DEBUG                   // error path messages, extra info
// #define      VERBOSE                 // more; success messages

#include <linux/module.h>
#include <linux/init.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/ctype.h>
#include <linux/ethtool.h>
#include <linux/workqueue.h>
#include <linux/mii.h>
#include <linux/usb.h>
#include <linux/usb/usbnet.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/pm_runtime.h>

#define DRIVER_VERSION          "22-Aug-2005"


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

/*
 * Nineteen USB 1.1 max size bulk transactions per frame (ms), max.
 * Several dozen bytes of IPv4 data can fit in two such transactions.
 * One maximum size Ethernet packet takes twenty four of them.
 * For high speed, each frame comfortably fits almost 36 max size
 * Ethernet packets (so queues should be bigger).
 *
 * The goal is to let the USB host controller be busy for 5msec or
 * more before an irq is required, under load.  Jumbograms change
 * the equation.
 */
#define MAX_QUEUE_MEMORY        (60 * 1518)
#define RX_QLEN(dev)            ((dev)->rx_qlen)
#define TX_QLEN(dev)            ((dev)->tx_qlen)

// reawaken network queue this soon after stopping; else watchdog barks
#define TX_TIMEOUT_JIFFIES      (5*HZ)

/* throttle rx/tx briefly after some faults, so hub_wq might disconnect()
 * us (it polls at HZ/4 usually) before we report too many false errors.
 */
#define THROTTLE_JIFFIES        (HZ/8)

// between wakeups
#define UNLINK_TIMEOUT_MS       3

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

// randomly generated ethernet address
static u8       node_id [ETH_ALEN];

static const char driver_name [] = "usbnet";

/* use ethtool to change the level for any given device */
static int msg_level = -1;
module_param (msg_level, int, 0);
MODULE_PARM_DESC (msg_level, "Override default message level");

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

/* handles CDC Ethernet and many other network "bulk data" interfaces */
int usbnet_get_endpoints(struct usbnet *dev, struct usb_interface *intf)
{
        int                             tmp;
        struct usb_host_interface       *alt = NULL;
        struct usb_host_endpoint        *in = NULL, *out = NULL;
        struct usb_host_endpoint        *status = NULL;

        for (tmp = 0; tmp < intf->num_altsetting; tmp++) {
                unsigned        ep;

                in = out = status = NULL;
                alt = intf->altsetting + tmp;

                /* take the first altsetting with in-bulk + out-bulk;
                 * remember any status endpoint, just in case;
                 * ignore other endpoints and altsettings.
                 */
                for (ep = 0; ep < alt->desc.bNumEndpoints; ep++) {
                        struct usb_host_endpoint        *e;
                        int                             intr = 0;

                        e = alt->endpoint + ep;
                        switch (e->desc.bmAttributes) {
                        case USB_ENDPOINT_XFER_INT:
                                if (!usb_endpoint_dir_in(&e->desc))
                                        continue;
                                intr = 1;
                                /* FALLTHROUGH */
                        case USB_ENDPOINT_XFER_BULK:
                                break;
                        default:
                                continue;
                        }
                        if (usb_endpoint_dir_in(&e->desc)) {
                                if (!intr && !in)
                                        in = e;
                                else if (intr && !status)
                                        status = e;
                        } else {
                                if (!out)
                                        out = e;
                        }
                }
                if (in && out)
                        break;
        }
        if (!alt || !in || !out)
                return -EINVAL;

        if (alt->desc.bAlternateSetting != 0 ||
            !(dev->driver_info->flags & FLAG_NO_SETINT)) {
                tmp = usb_set_interface (dev->udev, alt->desc.bInterfaceNumber,
                                alt->desc.bAlternateSetting);
                if (tmp < 0)
                        return tmp;
        }

        dev->in = usb_rcvbulkpipe (dev->udev,
                        in->desc.bEndpointAddress & USB_ENDPOINT_NUMBER_MASK);
        dev->out = usb_sndbulkpipe (dev->udev,
                        out->desc.bEndpointAddress & USB_ENDPOINT_NUMBER_MASK);
        dev->status = status;
        return 0;
}
EXPORT_SYMBOL_GPL(usbnet_get_endpoints);

int usbnet_get_ethernet_addr(struct usbnet *dev, int iMACAddress)
{
        int             tmp = -1, ret;
        unsigned char   buf [13];

        ret = usb_string(dev->udev, iMACAddress, buf, sizeof buf);
        if (ret == 12)
                tmp = hex2bin(dev->net->dev_addr, buf, 6);
        if (tmp < 0) {
                dev_dbg(&dev->udev->dev,
                        "bad MAC string %d fetch, %d\n", iMACAddress, tmp);
                if (ret >= 0)
                        ret = -EINVAL;
                return ret;
        }
        return 0;
}
EXPORT_SYMBOL_GPL(usbnet_get_ethernet_addr);

static void intr_complete (struct urb *urb)
{
        struct usbnet   *dev = urb->context;
        int             status = urb->status;

        switch (status) {
        /* success */
        case 0:
                dev->driver_info->status(dev, urb);
                break;

        /* software-driven interface shutdown */
        case -ENOENT:           /* urb killed */
        case -ESHUTDOWN:        /* hardware gone */
                netif_dbg(dev, ifdown, dev->net,
                          "intr shutdown, code %d\n", status);
                return;

        /* NOTE:  not throttling like RX/TX, since this endpoint
         * already polls infrequently
         */
        default:
                netdev_dbg(dev->net, "intr status %d\n", status);
                break;
        }

        status = usb_submit_urb (urb, GFP_ATOMIC);
        if (status != 0)
                netif_err(dev, timer, dev->net,
                          "intr resubmit --> %d\n", status);
}

static int init_status (struct usbnet *dev, struct usb_interface *intf)
{
        char            *buf = NULL;
        unsigned        pipe = 0;
        unsigned        maxp;
        unsigned        period;

        if (!dev->driver_info->status)
                return 0;

        pipe = usb_rcvintpipe (dev->udev,
                        dev->status->desc.bEndpointAddress
                                & USB_ENDPOINT_NUMBER_MASK);
        maxp = usb_maxpacket (dev->udev, pipe, 0);

        /* avoid 1 msec chatter:  min 8 msec poll rate */
        period = max ((int) dev->status->desc.bInterval,
                (dev->udev->speed == USB_SPEED_HIGH) ? 7 : 3);

        buf = kmalloc (maxp, GFP_KERNEL);
        if (buf) {
                dev->interrupt = usb_alloc_urb (0, GFP_KERNEL);
                if (!dev->interrupt) {
                        kfree (buf);
                        return -ENOMEM;
                } else {
                        usb_fill_int_urb(dev->interrupt, dev->udev, pipe,
                                buf, maxp, intr_complete, dev, period);
                        dev->interrupt->transfer_flags |= URB_FREE_BUFFER;
                        dev_dbg(&intf->dev,
                                "status ep%din, %d bytes period %d\n",
                                usb_pipeendpoint(pipe), maxp, period);
                }
        }
        return 0;
}

/* Submit the interrupt URB if not previously submitted, increasing refcount */
int usbnet_status_start(struct usbnet *dev, gfp_t mem_flags)
{
        int ret = 0;

        WARN_ON_ONCE(dev->interrupt == NULL);
        if (dev->interrupt) {
                mutex_lock(&dev->interrupt_mutex);

                if (++dev->interrupt_count == 1)
                        ret = usb_submit_urb(dev->interrupt, mem_flags);

                dev_dbg(&dev->udev->dev, "incremented interrupt URB count to %d\n",
                        dev->interrupt_count);
                mutex_unlock(&dev->interrupt_mutex);
        }
        return ret;
}
EXPORT_SYMBOL_GPL(usbnet_status_start);

/* For resume; submit interrupt URB if previously submitted */
static int __usbnet_status_start_force(struct usbnet *dev, gfp_t mem_flags)
{
        int ret = 0;

        mutex_lock(&dev->interrupt_mutex);
        if (dev->interrupt_count) {
                ret = usb_submit_urb(dev->interrupt, mem_flags);
                dev_dbg(&dev->udev->dev,
                        "submitted interrupt URB for resume\n");
        }
        mutex_unlock(&dev->interrupt_mutex);
        return ret;
}

/* Kill the interrupt URB if all submitters want it killed */
void usbnet_status_stop(struct usbnet *dev)
{
        if (dev->interrupt) {
                mutex_lock(&dev->interrupt_mutex);
                WARN_ON(dev->interrupt_count == 0);

                if (dev->interrupt_count && --dev->interrupt_count == 0)
                        usb_kill_urb(dev->interrupt);

                dev_dbg(&dev->udev->dev,
                        "decremented interrupt URB count to %d\n",
                        dev->interrupt_count);
                mutex_unlock(&dev->interrupt_mutex);
        }
}
EXPORT_SYMBOL_GPL(usbnet_status_stop);

/* For suspend; always kill interrupt URB */
static void __usbnet_status_stop_force(struct usbnet *dev)
{
        if (dev->interrupt) {
                mutex_lock(&dev->interrupt_mutex);
                usb_kill_urb(dev->interrupt);
                dev_dbg(&dev->udev->dev, "killed interrupt URB for suspend\n");
                mutex_unlock(&dev->interrupt_mutex);
        }
}

/* Passes this packet up the stack, updating its accounting.
 * Some link protocols batch packets, so their rx_fixup paths
 * can return clones as well as just modify the original skb.
 */
void usbnet_skb_return (struct usbnet *dev, struct sk_buff *skb)
{
        int     status;

        if (test_bit(EVENT_RX_PAUSED, &dev->flags)) {
                skb_queue_tail(&dev->rxq_pause, skb);
                return;
        }

        /* only update if unset to allow minidriver rx_fixup override */
        if (skb->protocol == 0)
                skb->protocol = eth_type_trans (skb, dev->net);

        dev->net->stats.rx_packets++;
        dev->net->stats.rx_bytes += skb->len;

        netif_dbg(dev, rx_status, dev->net, "< rx, len %zu, type 0x%x\n",
                  skb->len + sizeof (struct ethhdr), skb->protocol);
        memset (skb->cb, 0, sizeof (struct skb_data));

        if (skb_defer_rx_timestamp(skb))
                return;

        status = netif_rx (skb);
        if (status != NET_RX_SUCCESS)
                netif_dbg(dev, rx_err, dev->net,
                          "netif_rx status %d\n", status);
}
EXPORT_SYMBOL_GPL(usbnet_skb_return);

/* must be called if hard_mtu or rx_urb_size changed */
void usbnet_update_max_qlen(struct usbnet *dev)
{
        enum usb_device_speed speed = dev->udev->speed;

        switch (speed) {
        case USB_SPEED_HIGH:
                dev->rx_qlen = MAX_QUEUE_MEMORY / dev->rx_urb_size;
                dev->tx_qlen = MAX_QUEUE_MEMORY / dev->hard_mtu;
                break;
        case USB_SPEED_SUPER:
        case USB_SPEED_SUPER_PLUS:
                /*
                 * Not take default 5ms qlen for super speed HC to
                 * save memory, and iperf tests show 2.5ms qlen can
                 * work well
                 */
                dev->rx_qlen = 5 * MAX_QUEUE_MEMORY / dev->rx_urb_size;
                dev->tx_qlen = 5 * MAX_QUEUE_MEMORY / dev->hard_mtu;
                break;
        default:
                dev->rx_qlen = dev->tx_qlen = 4;
        }
}
EXPORT_SYMBOL_GPL(usbnet_update_max_qlen);


/*-------------------------------------------------------------------------
 *
 * Network Device Driver (peer link to "Host Device", from USB host)
 *
 *-------------------------------------------------------------------------*/

int usbnet_change_mtu (struct net_device *net, int new_mtu)
{
        struct usbnet   *dev = netdev_priv(net);
        int             ll_mtu = new_mtu + net->hard_header_len;
        int             old_hard_mtu = dev->hard_mtu;
        int             old_rx_urb_size = dev->rx_urb_size;

        if (new_mtu <= 0)
                return -EINVAL;
        // no second zero-length packet read wanted after mtu-sized packets
        if ((ll_mtu % dev->maxpacket) == 0)
                return -EDOM;
        net->mtu = new_mtu;

        dev->hard_mtu = net->mtu + net->hard_header_len;
        if (dev->rx_urb_size == old_hard_mtu) {
                dev->rx_urb_size = dev->hard_mtu;
                if (dev->rx_urb_size > old_rx_urb_size) {
                        usbnet_pause_rx(dev);
                        usbnet_unlink_rx_urbs(dev);
                        usbnet_resume_rx(dev);
                }
        }

        /* max qlen depend on hard_mtu and rx_urb_size */
        usbnet_update_max_qlen(dev);

        return 0;
}
EXPORT_SYMBOL_GPL(usbnet_change_mtu);

/* The caller must hold list->lock */
static void __usbnet_queue_skb(struct sk_buff_head *list,
                        struct sk_buff *newsk, enum skb_state state)
{
        struct skb_data *entry = (struct skb_data *) newsk->cb;

        __skb_queue_tail(list, newsk);
        entry->state = state;
}

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

/* some LK 2.4 HCDs oopsed if we freed or resubmitted urbs from
 * completion callbacks.  2.5 should have fixed those bugs...
 */

static enum skb_state defer_bh(struct usbnet *dev, struct sk_buff *skb,
                struct sk_buff_head *list, enum skb_state state)
{
        unsigned long           flags;
        enum skb_state          old_state;
        struct skb_data *entry = (struct skb_data *) skb->cb;

        spin_lock_irqsave(&list->lock, flags);
        old_state = entry->state;
        entry->state = state;
        __skb_unlink(skb, list);

        /* defer_bh() is never called with list == &dev->done.
         * spin_lock_nested() tells lockdep that it is OK to take
         * dev->done.lock here with list->lock held.
         */
        spin_lock_nested(&dev->done.lock, SINGLE_DEPTH_NESTING);

        __skb_queue_tail(&dev->done, skb);
        if (dev->done.qlen == 1)
                tasklet_schedule(&dev->bh);
        spin_unlock(&dev->done.lock);
        spin_unlock_irqrestore(&list->lock, flags);
        return old_state;
}

/* some work can't be done in tasklets, so we use keventd
 *
 * NOTE:  annoying asymmetry:  if it's active, schedule_work() fails,
 * but tasklet_schedule() doesn't.  hope the failure is rare.
 */
void usbnet_defer_kevent (struct usbnet *dev, int work)
{
        set_bit (work, &dev->flags);
        if (!schedule_work (&dev->kevent)) {
                if (net_ratelimit())
                        netdev_err(dev->net, "kevent %d may have been dropped\n", work);
        } else {
                netdev_dbg(dev->net, "kevent %d scheduled\n", work);
        }
}
EXPORT_SYMBOL_GPL(usbnet_defer_kevent);

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

static void rx_complete (struct urb *urb);

static int rx_submit (struct usbnet *dev, struct urb *urb, gfp_t flags)
{
        struct sk_buff          *skb;
        struct skb_data         *entry;
        int                     retval = 0;
        unsigned long           lockflags;
        size_t                  size = dev->rx_urb_size;

        /* prevent rx skb allocation when error ratio is high */
        if (test_bit(EVENT_RX_KILL, &dev->flags)) {
                usb_free_urb(urb);
                return -ENOLINK;
        }

        skb = __netdev_alloc_skb_ip_align(dev->net, size, flags);
        if (!skb) {
                netif_dbg(dev, rx_err, dev->net, "no rx skb\n");
                usbnet_defer_kevent (dev, EVENT_RX_MEMORY);
                usb_free_urb (urb);
                return -ENOMEM;
        }

        entry = (struct skb_data *) skb->cb;
        entry->urb = urb;
        entry->dev = dev;
        entry->length = 0;

        usb_fill_bulk_urb (urb, dev->udev, dev->in,
                skb->data, size, rx_complete, skb);

        spin_lock_irqsave (&dev->rxq.lock, lockflags);

        if (netif_running (dev->net) &&
            netif_device_present (dev->net) &&
            !test_bit (EVENT_RX_HALT, &dev->flags) &&
            !test_bit (EVENT_DEV_ASLEEP, &dev->flags)) {
                switch (retval = usb_submit_urb (urb, GFP_ATOMIC)) {
                case -EPIPE:
                        usbnet_defer_kevent (dev, EVENT_RX_HALT);
                        break;
                case -ENOMEM:
                        usbnet_defer_kevent (dev, EVENT_RX_MEMORY);
                        break;
                case -ENODEV:
                        netif_dbg(dev, ifdown, dev->net, "device gone\n");
                        netif_device_detach (dev->net);
                        break;
                case -EHOSTUNREACH:
                        retval = -ENOLINK;
                        break;
                default:
                        netif_dbg(dev, rx_err, dev->net,
                                  "rx submit, %d\n", retval);
                        tasklet_schedule (&dev->bh);
                        break;
                case 0:
                        __usbnet_queue_skb(&dev->rxq, skb, rx_start);
                }
        } else {
                netif_dbg(dev, ifdown, dev->net, "rx: stopped\n");
                retval = -ENOLINK;
        }
        spin_unlock_irqrestore (&dev->rxq.lock, lockflags);
        if (retval) {
                dev_kfree_skb_any (skb);
                usb_free_urb (urb);
        }
        return retval;
}


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

static inline void rx_process (struct usbnet *dev, struct sk_buff *skb)
{
        if (dev->driver_info->rx_fixup &&
            !dev->driver_info->rx_fixup (dev, skb)) {
                /* With RX_ASSEMBLE, rx_fixup() must update counters */
                if (!(dev->driver_info->flags & FLAG_RX_ASSEMBLE))
                        dev->net->stats.rx_errors++;
                goto done;
        }
        // else network stack removes extra byte if we forced a short packet

        /* all data was already cloned from skb inside the driver */
        if (dev->driver_info->flags & FLAG_MULTI_PACKET)
                goto done;

        if (skb->len < ETH_HLEN) {
                dev->net->stats.rx_errors++;
                dev->net->stats.rx_length_errors++;
                netif_dbg(dev, rx_err, dev->net, "rx length %d\n", skb->len);
        } else {
                usbnet_skb_return(dev, skb);
                return;
        }

done:
        skb_queue_tail(&dev->done, skb);
}

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

static void rx_complete (struct urb *urb)
{
        struct sk_buff          *skb = (struct sk_buff *) urb->context;
        struct skb_data         *entry = (struct skb_data *) skb->cb;
        struct usbnet           *dev = entry->dev;
        int                     urb_status = urb->status;
        enum skb_state          state;

        skb_put (skb, urb->actual_length);
        state = rx_done;
        entry->urb = NULL;

        switch (urb_status) {
        /* success */
        case 0:
                break;

        /* stalls need manual reset. this is rare ... except that
         * when going through USB 2.0 TTs, unplug appears this way.
         * we avoid the highspeed version of the ETIMEDOUT/EILSEQ
         * storm, recovering as needed.
         */
        case -EPIPE:
                dev->net->stats.rx_errors++;
                usbnet_defer_kevent (dev, EVENT_RX_HALT);
                // FALLTHROUGH

        /* software-driven interface shutdown */
        case -ECONNRESET:               /* async unlink */
        case -ESHUTDOWN:                /* hardware gone */
                netif_dbg(dev, ifdown, dev->net,
                          "rx shutdown, code %d\n", urb_status);
                goto block;

        /* we get controller i/o faults during hub_wq disconnect() delays.
         * throttle down resubmits, to avoid log floods; just temporarily,
         * so we still recover when the fault isn't a hub_wq delay.
         */
        case -EPROTO:
        case -ETIME:
        case -EILSEQ:
                dev->net->stats.rx_errors++;
                if (!timer_pending (&dev->delay)) {
                        mod_timer (&dev->delay, jiffies + THROTTLE_JIFFIES);
                        netif_dbg(dev, link, dev->net,
                                  "rx throttle %d\n", urb_status);
                }
block:
                state = rx_cleanup;
                entry->urb = urb;
                urb = NULL;
                break;

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

        default:
                state = rx_cleanup;
                dev->net->stats.rx_errors++;
                netif_dbg(dev, rx_err, dev->net, "rx status %d\n", urb_status);
                break;
        }

        /* stop rx if packet error rate is high */
        if (++dev->pkt_cnt > 30) {
                dev->pkt_cnt = 0;
                dev->pkt_err = 0;
        } else {
                if (state == rx_cleanup)
                        dev->pkt_err++;
                if (dev->pkt_err > 20)
                        set_bit(EVENT_RX_KILL, &dev->flags);
        }

        state = defer_bh(dev, skb, &dev->rxq, state);

        if (urb) {
                if (netif_running (dev->net) &&
                    !test_bit (EVENT_RX_HALT, &dev->flags) &&
                    state != unlink_start) {
                        rx_submit (dev, urb, GFP_ATOMIC);
                        usb_mark_last_busy(dev->udev);
                        return;
                }
                usb_free_urb (urb);
        }
        netif_dbg(dev, rx_err, dev->net, "no read resubmitted\n");
}

/*-------------------------------------------------------------------------*/
void usbnet_pause_rx(struct usbnet *dev)
{
        set_bit(EVENT_RX_PAUSED, &dev->flags);

        netif_dbg(dev, rx_status, dev->net, "paused rx queue enabled\n");
}
EXPORT_SYMBOL_GPL(usbnet_pause_rx);

void usbnet_resume_rx(struct usbnet *dev)
{
        struct sk_buff *skb;
        int num = 0;

        clear_bit(EVENT_RX_PAUSED, &dev->flags);

        while ((skb = skb_dequeue(&dev->rxq_pause)) != NULL) {
                usbnet_skb_return(dev, skb);
                num++;
        }

        tasklet_schedule(&dev->bh);

        netif_dbg(dev, rx_status, dev->net,
                  "paused rx queue disabled, %d skbs requeued\n", num);
}
EXPORT_SYMBOL_GPL(usbnet_resume_rx);

void usbnet_purge_paused_rxq(struct usbnet *dev)
{
        skb_queue_purge(&dev->rxq_pause);
}
EXPORT_SYMBOL_GPL(usbnet_purge_paused_rxq);

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

// unlink pending rx/tx; completion handlers do all other cleanup

static int unlink_urbs (struct usbnet *dev, struct sk_buff_head *q)
{
        unsigned long           flags;
        struct sk_buff          *skb;
        int                     count = 0;

        spin_lock_irqsave (&q->lock, flags);
        while (!skb_queue_empty(q)) {
                struct skb_data         *entry;
                struct urb              *urb;
                int                     retval;

                skb_queue_walk(q, skb) {
                        entry = (struct skb_data *) skb->cb;
                        if (entry->state != unlink_start)
                                goto found;
                }
                break;
found:
                entry->state = unlink_start;
                urb = entry->urb;

                /*
                 * Get reference count of the URB to avoid it to be
                 * freed during usb_unlink_urb, which may trigger
                 * use-after-free problem inside usb_unlink_urb since
                 * usb_unlink_urb is always racing with .complete
                 * handler(include defer_bh).
                 */
                usb_get_urb(urb);
                spin_unlock_irqrestore(&q->lock, flags);
                // during some PM-driven resume scenarios,
                // these (async) unlinks complete immediately
                retval = usb_unlink_urb (urb);
                if (retval != -EINPROGRESS && retval != 0)
                        netdev_dbg(dev->net, "unlink urb err, %d\n", retval);
                else
                        count++;
                usb_put_urb(urb);
                spin_lock_irqsave(&q->lock, flags);
        }
        spin_unlock_irqrestore (&q->lock, flags);
        return count;
}

// Flush all pending rx urbs
// minidrivers may need to do this when the MTU changes

void usbnet_unlink_rx_urbs(struct usbnet *dev)
{
        if (netif_running(dev->net)) {
                (void) unlink_urbs (dev, &dev->rxq);
                tasklet_schedule(&dev->bh);
        }
}
EXPORT_SYMBOL_GPL(usbnet_unlink_rx_urbs);

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

static void wait_skb_queue_empty(struct sk_buff_head *q)
{
        unsigned long flags;

        spin_lock_irqsave(&q->lock, flags);
        while (!skb_queue_empty(q)) {
                spin_unlock_irqrestore(&q->lock, flags);
                schedule_timeout(msecs_to_jiffies(UNLINK_TIMEOUT_MS));
                set_current_state(TASK_UNINTERRUPTIBLE);
                spin_lock_irqsave(&q->lock, flags);
        }
        spin_unlock_irqrestore(&q->lock, flags);
}

// precondition: never called in_interrupt
static void usbnet_terminate_urbs(struct usbnet *dev)
{
        DECLARE_WAITQUEUE(wait, current);
        int temp;

        /* ensure there are no more active urbs */
        add_wait_queue(&dev->wait, &wait);
        set_current_state(TASK_UNINTERRUPTIBLE);
        temp = unlink_urbs(dev, &dev->txq) +
                unlink_urbs(dev, &dev->rxq);

        /* maybe wait for deletions to finish. */
        wait_skb_queue_empty(&dev->rxq);
        wait_skb_queue_empty(&dev->txq);
        wait_skb_queue_empty(&dev->done);
        netif_dbg(dev, ifdown, dev->net,
                  "waited for %d urb completions\n", temp);
        set_current_state(TASK_RUNNING);
        remove_wait_queue(&dev->wait, &wait);
}

int usbnet_stop (struct net_device *net)
{
        struct usbnet           *dev = netdev_priv(net);
        struct driver_info      *info = dev->driver_info;
        int                     retval, pm, mpn;

        clear_bit(EVENT_DEV_OPEN, &dev->flags);
        netif_stop_queue (net);

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

        /* to not race resume */
        pm = usb_autopm_get_interface(dev->intf);
        /* allow minidriver to stop correctly (wireless devices to turn off
         * radio etc) */
        if (info->stop) {
                retval = info->stop(dev);
                if (retval < 0)
                        netif_info(dev, ifdown, dev->net,
                                   "stop fail (%d) usbnet usb-%s-%s, %s\n",
                                   retval,
                                   dev->udev->bus->bus_name, dev->udev->devpath,
                                   info->description);
        }

        if (!(info->flags & FLAG_AVOID_UNLINK_URBS))
                usbnet_terminate_urbs(dev);

        usbnet_status_stop(dev);

        usbnet_purge_paused_rxq(dev);

        mpn = !test_and_clear_bit(EVENT_NO_RUNTIME_PM, &dev->flags);

        /* deferred work (task, timer, softirq) must also stop.
         * can't flush_scheduled_work() until we drop rtnl (later),
         * else workers could deadlock; so make workers a NOP.
         */
        dev->flags = 0;
        del_timer_sync (&dev->delay);
        tasklet_kill (&dev->bh);
        if (!pm)
                usb_autopm_put_interface(dev->intf);

        if (info->manage_power && mpn)
                info->manage_power(dev, 0);
        else
                usb_autopm_put_interface(dev->intf);

        return 0;
}
EXPORT_SYMBOL_GPL(usbnet_stop);

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

// posts reads, and enables write queuing

// precondition: never called in_interrupt

int usbnet_open (struct net_device *net)
{
        struct usbnet           *dev = netdev_priv(net);
        int                     retval;
        struct driver_info      *info = dev->driver_info;

        if ((retval = usb_autopm_get_interface(dev->intf)) < 0) {
                netif_info(dev, ifup, dev->net,
                           "resumption fail (%d) usbnet usb-%s-%s, %s\n",
                           retval,
                           dev->udev->bus->bus_name,
                           dev->udev->devpath,
                           info->description);
                goto done_nopm;
        }

        // put into "known safe" state
        if (info->reset && (retval = info->reset (dev)) < 0) {
                netif_info(dev, ifup, dev->net,
                           "open reset fail (%d) usbnet usb-%s-%s, %s\n",
                           retval,
                           dev->udev->bus->bus_name,
                           dev->udev->devpath,
                           info->description);
                goto done;
        }

        /* hard_mtu or rx_urb_size may change in reset() */
        usbnet_update_max_qlen(dev);

        // insist peer be connected
        if (info->check_connect && (retval = info->check_connect (dev)) < 0) {
                netif_dbg(dev, ifup, dev->net, "can't open; %d\n", retval);
                goto done;
        }

        /* start any status interrupt transfer */
        if (dev->interrupt) {
                retval = usbnet_status_start(dev, GFP_KERNEL);
                if (retval < 0) {
                        netif_err(dev, ifup, dev->net,
                                  "intr submit %d\n", retval);
                        goto done;
                }
        }

        set_bit(EVENT_DEV_OPEN, &dev->flags);
        netif_start_queue (net);
        netif_info(dev, ifup, dev->net,
                   "open: enable queueing (rx %d, tx %d) mtu %d %s framing\n",
                   (int)RX_QLEN(dev), (int)TX_QLEN(dev),
                   dev->net->mtu,
                   (dev->driver_info->flags & FLAG_FRAMING_NC) ? "NetChip" :
                   (dev->driver_info->flags & FLAG_FRAMING_GL) ? "GeneSys" :
                   (dev->driver_info->flags & FLAG_FRAMING_Z) ? "Zaurus" :
                   (dev->driver_info->flags & FLAG_FRAMING_RN) ? "RNDIS" :
                   (dev->driver_info->flags & FLAG_FRAMING_AX) ? "ASIX" :
                   "simple");

        /* reset rx error state */
        dev->pkt_cnt = 0;
        dev->pkt_err = 0;
        clear_bit(EVENT_RX_KILL, &dev->flags);

        // delay posting reads until we're fully open
        tasklet_schedule (&dev->bh);
        if (info->manage_power) {
                retval = info->manage_power(dev, 1);
                if (retval < 0) {
                        retval = 0;
                        set_bit(EVENT_NO_RUNTIME_PM, &dev->flags);
                } else {
                        usb_autopm_put_interface(dev->intf);
                }
        }
        return retval;
done:
        usb_autopm_put_interface(dev->intf);
done_nopm:
        return retval;
}
EXPORT_SYMBOL_GPL(usbnet_open);

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

/* ethtool methods; minidrivers may need to add some more, but
 * they'll probably want to use this base set.
 */

int usbnet_get_settings (struct net_device *net, struct ethtool_cmd *cmd)
{
        struct usbnet *dev = netdev_priv(net);

        if (!dev->mii.mdio_read)
                return -EOPNOTSUPP;

        return mii_ethtool_gset(&dev->mii, cmd);
}
EXPORT_SYMBOL_GPL(usbnet_get_settings);

int usbnet_set_settings (struct net_device *net, struct ethtool_cmd *cmd)
{
        struct usbnet *dev = netdev_priv(net);
        int retval;

        if (!dev->mii.mdio_write)
                return -EOPNOTSUPP;

        retval = mii_ethtool_sset(&dev->mii, cmd);

        /* link speed/duplex might have changed */
        if (dev->driver_info->link_reset)
                dev->driver_info->link_reset(dev);

        /* hard_mtu or rx_urb_size may change in link_reset() */
        usbnet_update_max_qlen(dev);

        return retval;

}
EXPORT_SYMBOL_GPL(usbnet_set_settings);

u32 usbnet_get_link (struct net_device *net)
{
        struct usbnet *dev = netdev_priv(net);

        /* If a check_connect is defined, return its result */
        if (dev->driver_info->check_connect)
                return dev->driver_info->check_connect (dev) == 0;

        /* if the device has mii operations, use those */
        if (dev->mii.mdio_read)
                return mii_link_ok(&dev->mii);

        /* Otherwise, dtrt for drivers calling netif_carrier_{on,off} */
        return ethtool_op_get_link(net);
}
EXPORT_SYMBOL_GPL(usbnet_get_link);

int usbnet_nway_reset(struct net_device *net)
{
        struct usbnet *dev = netdev_priv(net);

        if (!dev->mii.mdio_write)
                return -EOPNOTSUPP;

        return mii_nway_restart(&dev->mii);
}
EXPORT_SYMBOL_GPL(usbnet_nway_reset);

void usbnet_get_drvinfo (struct net_device *net, struct ethtool_drvinfo *info)
{
        struct usbnet *dev = netdev_priv(net);

        strlcpy (info->driver, dev->driver_name, sizeof info->driver);
        strlcpy (info->version, DRIVER_VERSION, sizeof info->version);
        strlcpy (info->fw_version, dev->driver_info->description,
                sizeof info->fw_version);
        usb_make_path (dev->udev, info->bus_info, sizeof info->bus_info);
}
EXPORT_SYMBOL_GPL(usbnet_get_drvinfo);

u32 usbnet_get_msglevel (struct net_device *net)
{
        struct usbnet *dev = netdev_priv(net);

        return dev->msg_enable;
}
EXPORT_SYMBOL_GPL(usbnet_get_msglevel);

void usbnet_set_msglevel (struct net_device *net, u32 level)
{
        struct usbnet *dev = netdev_priv(net);

        dev->msg_enable = level;
}
EXPORT_SYMBOL_GPL(usbnet_set_msglevel);

/* drivers may override default ethtool_ops in their bind() routine */
static const struct ethtool_ops usbnet_ethtool_ops = {
        .get_settings           = usbnet_get_settings,
        .set_settings           = usbnet_set_settings,
        .get_link               = usbnet_get_link,
        .nway_reset             = usbnet_nway_reset,
        .get_drvinfo            = usbnet_get_drvinfo,
        .get_msglevel           = usbnet_get_msglevel,
        .set_msglevel           = usbnet_set_msglevel,
        .get_ts_info            = ethtool_op_get_ts_info,
};

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

static void __handle_link_change(struct usbnet *dev)
{
        if (!test_bit(EVENT_DEV_OPEN, &dev->flags))
                return;

        if (!netif_carrier_ok(dev->net)) {
                /* kill URBs for reading packets to save bus bandwidth */
                unlink_urbs(dev, &dev->rxq);

                /*
                 * tx_timeout will unlink URBs for sending packets and
                 * tx queue is stopped by netcore after link becomes off
                 */
        } else {
                /* submitting URBs for reading packets */
                tasklet_schedule(&dev->bh);
        }

        /* hard_mtu or rx_urb_size may change during link change */
        usbnet_update_max_qlen(dev);

        clear_bit(EVENT_LINK_CHANGE, &dev->flags);
}

static void usbnet_set_rx_mode(struct net_device *net)
{
        struct usbnet           *dev = netdev_priv(net);

        usbnet_defer_kevent(dev, EVENT_SET_RX_MODE);
}

static void __handle_set_rx_mode(struct usbnet *dev)
{
        if (dev->driver_info->set_rx_mode)
                (dev->driver_info->set_rx_mode)(dev);

        clear_bit(EVENT_SET_RX_MODE, &dev->flags);
}

/* work that cannot be done in interrupt context uses keventd.
 *
 * NOTE:  with 2.5 we could do more of this using completion callbacks,
 * especially now that control transfers can be queued.
 */
static void
usbnet_deferred_kevent (struct work_struct *work)
{
        struct usbnet           *dev =
                container_of(work, struct usbnet, kevent);
        int                     status;

        /* usb_clear_halt() needs a thread context */
        if (test_bit (EVENT_TX_HALT, &dev->flags)) {
                unlink_urbs (dev, &dev->txq);
                status = usb_autopm_get_interface(dev->intf);
                if (status < 0)
                        goto fail_pipe;
                status = usb_clear_halt (dev->udev, dev->out);
                usb_autopm_put_interface(dev->intf);
                if (status < 0 &&
                    status != -EPIPE &&
                    status != -ESHUTDOWN) {
                        if (netif_msg_tx_err (dev))
fail_pipe:
                                netdev_err(dev->net, "can't clear tx halt, status %d\n",
                                           status);
                } else {
                        clear_bit (EVENT_TX_HALT, &dev->flags);
                        if (status != -ESHUTDOWN)
                                netif_wake_queue (dev->net);
                }
        }
        if (test_bit (EVENT_RX_HALT, &dev->flags)) {
                unlink_urbs (dev, &dev->rxq);
                status = usb_autopm_get_interface(dev->intf);
                if (status < 0)
                        goto fail_halt;
                status = usb_clear_halt (dev->udev, dev->in);
                usb_autopm_put_interface(dev->intf);
                if (status < 0 &&
                    status != -EPIPE &&
                    status != -ESHUTDOWN) {
                        if (netif_msg_rx_err (dev))
fail_halt:
                                netdev_err(dev->net, "can't clear rx halt, status %d\n",
                                           status);
                } else {
                        clear_bit (EVENT_RX_HALT, &dev->flags);
                        tasklet_schedule (&dev->bh);
                }
        }

        /* tasklet could resubmit itself forever if memory is tight */
        if (test_bit (EVENT_RX_MEMORY, &dev->flags)) {
                struct urb      *urb = NULL;
                int resched = 1;

                if (netif_running (dev->net))
                        urb = usb_alloc_urb (0, GFP_KERNEL);
                else
                        clear_bit (EVENT_RX_MEMORY, &dev->flags);
                if (urb != NULL) {
                        clear_bit (EVENT_RX_MEMORY, &dev->flags);
                        status = usb_autopm_get_interface(dev->intf);
                        if (status < 0) {
                                usb_free_urb(urb);
                                goto fail_lowmem;
                        }
                        if (rx_submit (dev, urb, GFP_KERNEL) == -ENOLINK)
                                resched = 0;
                        usb_autopm_put_interface(dev->intf);
fail_lowmem:
                        if (resched)
                                tasklet_schedule (&dev->bh);
                }
        }

        if (test_bit (EVENT_LINK_RESET, &dev->flags)) {
                struct driver_info      *info = dev->driver_info;
                int                     retval = 0;

                clear_bit (EVENT_LINK_RESET, &dev->flags);
                status = usb_autopm_get_interface(dev->intf);
                if (status < 0)
                        goto skip_reset;
                if(info->link_reset && (retval = info->link_reset(dev)) < 0) {
                        usb_autopm_put_interface(dev->intf);
skip_reset:
                        netdev_info(dev->net, "link reset failed (%d) usbnet usb-%s-%s, %s\n",
                                    retval,
                                    dev->udev->bus->bus_name,
                                    dev->udev->devpath,
                                    info->description);
                } else {
                        usb_autopm_put_interface(dev->intf);
                }

                /* handle link change from link resetting */
                __handle_link_change(dev);
        }

        if (test_bit (EVENT_LINK_CHANGE, &dev->flags))
                __handle_link_change(dev);

        if (test_bit (EVENT_SET_RX_MODE, &dev->flags))
                __handle_set_rx_mode(dev);


        if (dev->flags)
                netdev_dbg(dev->net, "kevent done, flags = 0x%lx\n", dev->flags);
}

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

static void tx_complete (struct urb *urb)
{
        struct sk_buff          *skb = (struct sk_buff *) urb->context;
        struct skb_data         *entry = (struct skb_data *) skb->cb;
        struct usbnet           *dev = entry->dev;

        if (urb->status == 0) {
                dev->net->stats.tx_packets += entry->packets;
                dev->net->stats.tx_bytes += entry->length;
        } else {
                dev->net->stats.tx_errors++;

                switch (urb->status) {
                case -EPIPE:
                        usbnet_defer_kevent (dev, EVENT_TX_HALT);
                        break;

                /* software-driven interface shutdown */
                case -ECONNRESET:               // async unlink
                case -ESHUTDOWN:                // hardware gone
                        break;

                /* like rx, tx gets controller i/o faults during hub_wq
                 * delays and so it uses the same throttling mechanism.
                 */
                case -EPROTO:
                case -ETIME:
                case -EILSEQ:
                        usb_mark_last_busy(dev->udev);
                        if (!timer_pending (&dev->delay)) {
                                mod_timer (&dev->delay,
                                        jiffies + THROTTLE_JIFFIES);
                                netif_dbg(dev, link, dev->net,
                                          "tx throttle %d\n", urb->status);
                        }
                        netif_stop_queue (dev->net);
                        break;
                default:
                        netif_dbg(dev, tx_err, dev->net,
                                  "tx err %d\n", entry->urb->status);
                        break;
                }
        }

        usb_autopm_put_interface_async(dev->intf);
        (void) defer_bh(dev, skb, &dev->txq, tx_done);
}

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

void usbnet_tx_timeout (struct net_device *net)
{
        struct usbnet           *dev = netdev_priv(net);

        unlink_urbs (dev, &dev->txq);
        tasklet_schedule (&dev->bh);
        /* this needs to be handled individually because the generic layer
         * doesn't know what is sufficient and could not restore private
         * information if a remedy of an unconditional reset were used.
         */
        if (dev->driver_info->recover)
                (dev->driver_info->recover)(dev);
}
EXPORT_SYMBOL_GPL(usbnet_tx_timeout);

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

static int build_dma_sg(const struct sk_buff *skb, struct urb *urb)
{
        unsigned num_sgs, total_len = 0;
        int i, s = 0;

        num_sgs = skb_shinfo(skb)->nr_frags + 1;
        if (num_sgs == 1)
                return 0;

        /* reserve one for zero packet */
        urb->sg = kmalloc((num_sgs + 1) * sizeof(struct scatterlist),
                          GFP_ATOMIC);
        if (!urb->sg)
                return -ENOMEM;

        urb->num_sgs = num_sgs;
        sg_init_table(urb->sg, urb->num_sgs + 1);

        sg_set_buf(&urb->sg[s++], skb->data, skb_headlen(skb));
        total_len += skb_headlen(skb);

        for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
                struct skb_frag_struct *f = &skb_shinfo(skb)->frags[i];

                total_len += skb_frag_size(f);
                sg_set_page(&urb->sg[i + s], f->page.p, f->size,
                                f->page_offset);
        }
        urb->transfer_buffer_length = total_len;

        return 1;
}

netdev_tx_t usbnet_start_xmit (struct sk_buff *skb,
                                     struct net_device *net)
{
        struct usbnet           *dev = netdev_priv(net);
        unsigned int                    length;
        struct urb              *urb = NULL;
        struct skb_data         *entry;
        struct driver_info      *info = dev->driver_info;
        unsigned long           flags;
        int retval;

        if (skb)
                skb_tx_timestamp(skb);

        // some devices want funky USB-level framing, for
        // win32 driver (usually) and/or hardware quirks
        if (info->tx_fixup) {
                skb = info->tx_fixup (dev, skb, GFP_ATOMIC);
                if (!skb) {
                        /* packet collected; minidriver waiting for more */
                        if (info->flags & FLAG_MULTI_PACKET)
                                goto not_drop;
                        netif_dbg(dev, tx_err, dev->net, "can't tx_fixup skb\n");
                        goto drop;
                }
        }

        if (!(urb = usb_alloc_urb (0, GFP_ATOMIC))) {
                netif_dbg(dev, tx_err, dev->net, "no urb\n");
                goto drop;
        }

        entry = (struct skb_data *) skb->cb;
        entry->urb = urb;
        entry->dev = dev;

        usb_fill_bulk_urb (urb, dev->udev, dev->out,
                        skb->data, skb->len, tx_complete, skb);
        if (dev->can_dma_sg) {
                if (build_dma_sg(skb, urb) < 0)
                        goto drop;
        }
        length = urb->transfer_buffer_length;

        /* don't assume the hardware handles USB_ZERO_PACKET
         * NOTE:  strictly conforming cdc-ether devices should expect
         * the ZLP here, but ignore the one-byte packet.
         * NOTE2: CDC NCM specification is different from CDC ECM when
         * handling ZLP/short packets, so cdc_ncm driver will make short
         * packet itself if needed.
         */
        if (length % dev->maxpacket == 0) {
                if (!(info->flags & FLAG_SEND_ZLP)) {
                        if (!(info->flags & FLAG_MULTI_PACKET)) {
                                length++;
                                if (skb_tailroom(skb) && !urb->num_sgs) {
                                        skb->data[skb->len] = 0;
                                        __skb_put(skb, 1);
                                } else if (urb->num_sgs)
                                        sg_set_buf(&urb->sg[urb->num_sgs++],
                                                        dev->padding_pkt, 1);
                        }
                } else
                        urb->transfer_flags |= URB_ZERO_PACKET;
        }
        urb->transfer_buffer_length = length;

        if (info->flags & FLAG_MULTI_PACKET) {
                /* Driver has set number of packets and a length delta.
                 * Calculate the complete length and ensure that it's
                 * positive.
                 */
                entry->length += length;
                if (WARN_ON_ONCE(entry->length <= 0))
                        entry->length = length;
        } else {
                usbnet_set_skb_tx_stats(skb, 1, length);
        }

        spin_lock_irqsave(&dev->txq.lock, flags);
        retval = usb_autopm_get_interface_async(dev->intf);
        if (retval < 0) {
                spin_unlock_irqrestore(&dev->txq.lock, flags);
                goto drop;
        }

#ifdef CONFIG_PM
        /* if this triggers the device is still a sleep */
        if (test_bit(EVENT_DEV_ASLEEP, &dev->flags)) {
                /* transmission will be done in resume */
                usb_anchor_urb(urb, &dev->deferred);
                /* no use to process more packets */
                netif_stop_queue(net);
                usb_put_urb(urb);
                spin_unlock_irqrestore(&dev->txq.lock, flags);
                netdev_dbg(dev->net, "Delaying transmission for resumption\n");
                goto deferred;
        }
#endif

        switch ((retval = usb_submit_urb (urb, GFP_ATOMIC))) {
        case -EPIPE:
                netif_stop_queue (net);
                usbnet_defer_kevent (dev, EVENT_TX_HALT);
                usb_autopm_put_interface_async(dev->intf);
                break;
        default:
                usb_autopm_put_interface_async(dev->intf);
                netif_dbg(dev, tx_err, dev->net,
                          "tx: submit urb err %d\n", retval);
                break;
        case 0:
                netif_trans_update(net);
                __usbnet_queue_skb(&dev->txq, skb, tx_start);
                if (dev->txq.qlen >= TX_QLEN (dev))
                        netif_stop_queue (net);
        }
        spin_unlock_irqrestore (&dev->txq.lock, flags);

        if (retval) {
                netif_dbg(dev, tx_err, dev->net, "drop, code %d\n", retval);
drop:
                dev->net->stats.tx_dropped++;
not_drop:
                if (skb)
                        dev_kfree_skb_any (skb);
                if (urb) {
                        kfree(urb->sg);
                        usb_free_urb(urb);
                }
        } else
                netif_dbg(dev, tx_queued, dev->net,
                          "> tx, len %u, type 0x%x\n", length, skb->protocol);
#ifdef CONFIG_PM
deferred:
#endif
        return NETDEV_TX_OK;
}
EXPORT_SYMBOL_GPL(usbnet_start_xmit);

static int rx_alloc_submit(struct usbnet *dev, gfp_t flags)
{
        struct urb      *urb;
        int             i;
        int             ret = 0;

        /* don't refill the queue all at once */
        for (i = 0; i < 10 && dev->rxq.qlen < RX_QLEN(dev); i++) {
                urb = usb_alloc_urb(0, flags);
                if (urb != NULL) {
                        ret = rx_submit(dev, urb, flags);
                        if (ret)
                                goto err;
                } else {
                        ret = -ENOMEM;
                        goto err;
                }
        }
err:
        return ret;
}

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

// tasklet (work deferred from completions, in_irq) or timer

static void usbnet_bh (unsigned long param)
{
        struct usbnet           *dev = (struct usbnet *) param;
        struct sk_buff          *skb;
        struct skb_data         *entry;

        while ((skb = skb_dequeue (&dev->done))) {
                entry = (struct skb_data *) skb->cb;
                switch (entry->state) {
                case rx_done:
                        entry->state = rx_cleanup;
                        rx_process (dev, skb);
                        continue;
                case tx_done:
                        kfree(entry->urb->sg);
                case rx_cleanup:
                        usb_free_urb (entry->urb);
                        dev_kfree_skb (skb);
                        continue;
                default:
                        netdev_dbg(dev->net, "bogus skb state %d\n", entry->state);
                }
        }

        /* restart RX again after disabling due to high error rate */
        clear_bit(EVENT_RX_KILL, &dev->flags);

        /* waiting for all pending urbs to complete?
         * only then can we forgo submitting anew
         */
        if (waitqueue_active(&dev->wait)) {
                if (dev->txq.qlen + dev->rxq.qlen + dev->done.qlen == 0)
                        wake_up_all(&dev->wait);

        // or are we maybe short a few urbs?
        } else if (netif_running (dev->net) &&
                   netif_device_present (dev->net) &&
                   netif_carrier_ok(dev->net) &&
                   !timer_pending(&dev->delay) &&
                   !test_bit(EVENT_RX_PAUSED, &dev->flags) &&
                   !test_bit(EVENT_RX_HALT, &dev->flags)) {
                int     temp = dev->rxq.qlen;

                if (temp < RX_QLEN(dev)) {
                        if (rx_alloc_submit(dev, GFP_ATOMIC) == -ENOLINK)
                                return;
                        if (temp != dev->rxq.qlen)
                                netif_dbg(dev, link, dev->net,
                                          "rxqlen %d --> %d\n",
                                          temp, dev->rxq.qlen);
                        if (dev->rxq.qlen < RX_QLEN(dev))
                                tasklet_schedule (&dev->bh);
                }
                if (dev->txq.qlen < TX_QLEN (dev))
                        netif_wake_queue (dev->net);
        }
}


/*-------------------------------------------------------------------------
 *
 * USB Device Driver support
 *
 *-------------------------------------------------------------------------*/

// precondition: never called in_interrupt

void usbnet_disconnect (struct usb_interface *intf)
{
        struct usbnet           *dev;
        struct usb_device       *xdev;
        struct net_device       *net;

        dev = usb_get_intfdata(intf);
        usb_set_intfdata(intf, NULL);
        if (!dev)
                return;

        xdev = interface_to_usbdev (intf);

        netif_info(dev, probe, dev->net, "unregister '%s' usb-%s-%s, %s\n",
                   intf->dev.driver->name,
                   xdev->bus->bus_name, xdev->devpath,
                   dev->driver_info->description);

        net = dev->net;
        unregister_netdev (net);

        cancel_work_sync(&dev->kevent);

        usb_scuttle_anchored_urbs(&dev->deferred);

        if (dev->driver_info->unbind)
                dev->driver_info->unbind (dev, intf);

        usb_kill_urb(dev->interrupt);
        usb_free_urb(dev->interrupt);
        kfree(dev->padding_pkt);

        free_netdev(net);
}
EXPORT_SYMBOL_GPL(usbnet_disconnect);

static const struct net_device_ops usbnet_netdev_ops = {
        .ndo_open               = usbnet_open,
        .ndo_stop               = usbnet_stop,
        .ndo_start_xmit         = usbnet_start_xmit,
        .ndo_tx_timeout         = usbnet_tx_timeout,
        .ndo_set_rx_mode        = usbnet_set_rx_mode,
        .ndo_change_mtu_rh74    = usbnet_change_mtu,
        .ndo_set_mac_address    = eth_mac_addr,
        .ndo_validate_addr      = eth_validate_addr,
};

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

// precondition: never called in_interrupt

static struct device_type wlan_type = {
        .name   = "wlan",
};

static struct device_type wwan_type = {
        .name   = "wwan",
};

int
usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
{
        struct usbnet                   *dev;
        struct net_device               *net;
        struct usb_host_interface       *interface;
        struct driver_info              *info;
        struct usb_device               *xdev;
        int                             status;
        const char                      *name;
        struct usb_driver       *driver = to_usb_driver(udev->dev.driver);

        /* usbnet already took usb runtime pm, so have to enable the feature
         * for usb interface, otherwise usb_autopm_get_interface may return
         * failure if RUNTIME_PM is enabled.
         */
        if (!driver->supports_autosuspend) {
                driver->supports_autosuspend = 1;
                pm_runtime_enable(&udev->dev);
        }

        name = udev->dev.driver->name;
        info = (struct driver_info *) prod->driver_info;
        if (!info) {
                dev_dbg (&udev->dev, "blacklisted by %s\n", name);
                return -ENODEV;
        }
        xdev = interface_to_usbdev (udev);
        interface = udev->cur_altsetting;

        status = -ENOMEM;

        // set up our own records
        net = alloc_etherdev(sizeof(*dev));
        if (!net)
                goto out;

        /* netdev_printk() needs this so do it as early as possible */
        SET_NETDEV_DEV(net, &udev->dev);

        dev = netdev_priv(net);
        dev->udev = xdev;
        dev->intf = udev;
        dev->driver_info = info;
        dev->driver_name = name;
        dev->msg_enable = netif_msg_init (msg_level, NETIF_MSG_DRV
                                | NETIF_MSG_PROBE | NETIF_MSG_LINK);
        init_waitqueue_head(&dev->wait);
        skb_queue_head_init (&dev->rxq);
        skb_queue_head_init (&dev->txq);
        skb_queue_head_init (&dev->done);
        skb_queue_head_init(&dev->rxq_pause);
        dev->bh.func = usbnet_bh;
        dev->bh.data = (unsigned long) dev;
        INIT_WORK (&dev->kevent, usbnet_deferred_kevent);
        init_usb_anchor(&dev->deferred);
        dev->delay.function = usbnet_bh;
        dev->delay.data = (unsigned long) dev;
        init_timer (&dev->delay);
        mutex_init (&dev->phy_mutex);
        mutex_init(&dev->interrupt_mutex);
        dev->interrupt_count = 0;

        dev->net = net;
        strcpy (net->name, "usb%d");
        memcpy (net->dev_addr, node_id, sizeof node_id);

        /* rx and tx sides can use different message sizes;
         * bind() should set rx_urb_size in that case.
         */
        dev->hard_mtu = net->mtu + net->hard_header_len;

        net->netdev_ops = &usbnet_netdev_ops;
        net->watchdog_timeo = TX_TIMEOUT_JIFFIES;
        net->ethtool_ops = &usbnet_ethtool_ops;

        // allow device-specific bind/init procedures
        // NOTE net->name still not usable ...
        if (info->bind) {
                status = info->bind (dev, udev);
                if (status < 0)
                        goto out1;

                // heuristic:  "usb%d" for links we know are two-host,
                // else "eth%d" when there's reasonable doubt.  userspace
                // can rename the link if it knows better.
                if ((dev->driver_info->flags & FLAG_ETHER) != 0 &&
                    ((dev->driver_info->flags & FLAG_POINTTOPOINT) == 0 ||
                     (net->dev_addr [0] & 0x02) == 0))
                        strcpy (net->name, "eth%d");
                /* WLAN devices should always be named "wlan%d" */
                if ((dev->driver_info->flags & FLAG_WLAN) != 0)
                        strcpy(net->name, "wlan%d");
                /* WWAN devices should always be named "wwan%d" */
                if ((dev->driver_info->flags & FLAG_WWAN) != 0)
                        strcpy(net->name, "wwan%d");

                /* devices that cannot do ARP */
                if ((dev->driver_info->flags & FLAG_NOARP) != 0)
                        net->flags |= IFF_NOARP;

                /* maybe the remote can't receive an Ethernet MTU */
                if (net->mtu > (dev->hard_mtu - net->hard_header_len))
                        net->mtu = dev->hard_mtu - net->hard_header_len;
        } else if (!info->in || !info->out)
                status = usbnet_get_endpoints (dev, udev);
        else {
                dev->in = usb_rcvbulkpipe (xdev, info->in);
                dev->out = usb_sndbulkpipe (xdev, info->out);
                if (!(info->flags & FLAG_NO_SETINT))
                        status = usb_set_interface (xdev,
                                interface->desc.bInterfaceNumber,
                                interface->desc.bAlternateSetting);
                else
                        status = 0;

        }
        if (status >= 0 && dev->status)
                status = init_status (dev, udev);
        if (status < 0)
                goto out3;

        if (!dev->rx_urb_size)
                dev->rx_urb_size = dev->hard_mtu;
        dev->maxpacket = usb_maxpacket (dev->udev, dev->out, 1);

        /* let userspace know we have a random address */
        if (ether_addr_equal(net->dev_addr, node_id))
                net->addr_assign_type = NET_ADDR_RANDOM;

        if ((dev->driver_info->flags & FLAG_WLAN) != 0)
                SET_NETDEV_DEVTYPE(net, &wlan_type);
        if ((dev->driver_info->flags & FLAG_WWAN) != 0)
                SET_NETDEV_DEVTYPE(net, &wwan_type);

        /* initialize max rx_qlen and tx_qlen */
        usbnet_update_max_qlen(dev);

        if (dev->can_dma_sg && !(info->flags & FLAG_SEND_ZLP) &&
                !(info->flags & FLAG_MULTI_PACKET)) {
                dev->padding_pkt = kzalloc(1, GFP_KERNEL);
                if (!dev->padding_pkt) {
                        status = -ENOMEM;
                        goto out4;
                }
        }

        status = register_netdev (net);
        if (status)
                goto out5;
        netif_info(dev, probe, dev->net,
                   "register '%s' at usb-%s-%s, %s, %pM\n",
                   udev->dev.driver->name,
                   xdev->bus->bus_name, xdev->devpath,
                   dev->driver_info->description,
                   net->dev_addr);

        // ok, it's ready to go.
        usb_set_intfdata (udev, dev);

        netif_device_attach (net);

        if (dev->driver_info->flags & FLAG_LINK_INTR)
                usbnet_link_change(dev, 0, 0);

        return 0;

out5:
        kfree(dev->padding_pkt);
out4:
        usb_free_urb(dev->interrupt);
out3:
        if (info->unbind)
                info->unbind (dev, udev);
out1:
        /* subdrivers must undo all they did in bind() if they
         * fail it, but we may fail later and a deferred kevent
         * may trigger an error resubmitting itself and, worse,
         * schedule a timer. So we kill it all just in case.
         */
        cancel_work_sync(&dev->kevent);
        del_timer_sync(&dev->delay);
        free_netdev(net);
out:
        return status;
}
EXPORT_SYMBOL_GPL(usbnet_probe);

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

/*
 * suspend the whole driver as soon as the first interface is suspended
 * resume only when the last interface is resumed
 */

int usbnet_suspend (struct usb_interface *intf, pm_message_t message)
{
        struct usbnet           *dev = usb_get_intfdata(intf);

        if (!dev->suspend_count++) {
                spin_lock_irq(&dev->txq.lock);
                /* don't autosuspend while transmitting */
                if (dev->txq.qlen && PMSG_IS_AUTO(message)) {
                        dev->suspend_count--;
                        spin_unlock_irq(&dev->txq.lock);
                        return -EBUSY;
                } else {
                        set_bit(EVENT_DEV_ASLEEP, &dev->flags);
                        spin_unlock_irq(&dev->txq.lock);
                }
                /*
                 * accelerate emptying of the rx and queues, to avoid
                 * having everything error out.
                 */
                netif_device_detach (dev->net);
                usbnet_terminate_urbs(dev);
                __usbnet_status_stop_force(dev);

                /*
                 * reattach so runtime management can use and
                 * wake the device
                 */
                netif_device_attach (dev->net);
        }
        return 0;
}
EXPORT_SYMBOL_GPL(usbnet_suspend);

int usbnet_resume (struct usb_interface *intf)
{
        struct usbnet           *dev = usb_get_intfdata(intf);
        struct sk_buff          *skb;
        struct urb              *res;
        int                     retval;

        if (!--dev->suspend_count) {
                /* resume interrupt URB if it was previously submitted */
                __usbnet_status_start_force(dev, GFP_NOIO);

                spin_lock_irq(&dev->txq.lock);
                while ((res = usb_get_from_anchor(&dev->deferred))) {

                        skb = (struct sk_buff *)res->context;
                        retval = usb_submit_urb(res, GFP_ATOMIC);
                        if (retval < 0) {
                                dev_kfree_skb_any(skb);
                                kfree(res->sg);
                                usb_free_urb(res);
                                usb_autopm_put_interface_async(dev->intf);
                        } else {
                                netif_trans_update(dev->net);
                                __skb_queue_tail(&dev->txq, skb);
                        }
                }

                smp_mb();
                clear_bit(EVENT_DEV_ASLEEP, &dev->flags);
                spin_unlock_irq(&dev->txq.lock);

                if (test_bit(EVENT_DEV_OPEN, &dev->flags)) {
                        /* handle remote wakeup ASAP
                         * we cannot race against stop
                         */
                        if (netif_device_present(dev->net) &&
                                !timer_pending(&dev->delay) &&
                                !test_bit(EVENT_RX_HALT, &dev->flags))
                                        rx_alloc_submit(dev, GFP_NOIO);

                        if (!(dev->txq.qlen >= TX_QLEN(dev)))
                                netif_tx_wake_all_queues(dev->net);
                        tasklet_schedule (&dev->bh);
                }
        }

        if (test_and_clear_bit(EVENT_DEVICE_REPORT_IDLE, &dev->flags))
                usb_autopm_get_interface_no_resume(intf);

        return 0;
}
EXPORT_SYMBOL_GPL(usbnet_resume);

/*
 * Either a subdriver implements manage_power, then it is assumed to always
 * be ready to be suspended or it reports the readiness to be suspended
 * explicitly
 */
void usbnet_device_suggests_idle(struct usbnet *dev)
{
        if (!test_and_set_bit(EVENT_DEVICE_REPORT_IDLE, &dev->flags)) {
                dev->intf->needs_remote_wakeup = 1;
                usb_autopm_put_interface_async(dev->intf);
        }
}
EXPORT_SYMBOL(usbnet_device_suggests_idle);

/*
 * For devices that can do without special commands
 */
int usbnet_manage_power(struct usbnet *dev, int on)
{
        dev->intf->needs_remote_wakeup = on;
        return 0;
}
EXPORT_SYMBOL(usbnet_manage_power);

void usbnet_link_change(struct usbnet *dev, bool link, bool need_reset)
{
        /* update link after link is reseted */
        if (link && !need_reset)
                netif_carrier_on(dev->net);
        else
                netif_carrier_off(dev->net);

        if (need_reset && link)
                usbnet_defer_kevent(dev, EVENT_LINK_RESET);
        else
                usbnet_defer_kevent(dev, EVENT_LINK_CHANGE);
}
EXPORT_SYMBOL(usbnet_link_change);

/*-------------------------------------------------------------------------*/
static int __usbnet_read_cmd(struct usbnet *dev, u8 cmd, u8 reqtype,
                             u16 value, u16 index, void *data, u16 size)
{
        void *buf = NULL;
        int err = -ENOMEM;

        netdev_dbg(dev->net, "usbnet_read_cmd cmd=0x%02x reqtype=%02x"
                   " value=0x%04x index=0x%04x size=%d\n",
                   cmd, reqtype, value, index, size);

        if (size) {
                buf = kmalloc(size, GFP_KERNEL);
                if (!buf)
                        goto out;
        }

        err = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0),
                              cmd, reqtype, value, index, buf, size,
                              USB_CTRL_GET_TIMEOUT);
        if (err > 0 && err <= size) {
        if (data)
            memcpy(data, buf, err);
        else
            netdev_dbg(dev->net,
                "Huh? Data requested but thrown away.\n");
    }
        kfree(buf);
out:
        return err;
}

static int __usbnet_write_cmd(struct usbnet *dev, u8 cmd, u8 reqtype,
                              u16 value, u16 index, const void *data,
                              u16 size)
{
        void *buf = NULL;
        int err = -ENOMEM;

        netdev_dbg(dev->net, "usbnet_write_cmd cmd=0x%02x reqtype=%02x"
                   " value=0x%04x index=0x%04x size=%d\n",
                   cmd, reqtype, value, index, size);

        if (data) {
                buf = kmemdup(data, size, GFP_KERNEL);
                if (!buf)
                        goto out;
        } else {
        if (size) {
            WARN_ON_ONCE(1);
            err = -EINVAL;
            goto out;
        }
    }

        err = usb_control_msg(dev->udev, usb_sndctrlpipe(dev->udev, 0),
                              cmd, reqtype, value, index, buf, size,
                              USB_CTRL_SET_TIMEOUT);
        kfree(buf);

out:
        return err;
}

/*
 * The function can't be called inside suspend/resume callback,
 * otherwise deadlock will be caused.
 */
int usbnet_read_cmd(struct usbnet *dev, u8 cmd, u8 reqtype,
                    u16 value, u16 index, void *data, u16 size)
{
        int ret;

        if (usb_autopm_get_interface(dev->intf) < 0)
                return -ENODEV;
        ret = __usbnet_read_cmd(dev, cmd, reqtype, value, index,
                                data, size);
        usb_autopm_put_interface(dev->intf);
        return ret;
}

EXPORT_SYMBOL_GPL(usbnet_read_cmd);

/*
 * The function can't be called inside suspend/resume callback,
 * otherwise deadlock will be caused.
 */
int usbnet_write_cmd(struct usbnet *dev, u8 cmd, u8 reqtype,
                     u16 value, u16 index, const void *data, u16 size)
{
        int ret;

        if (usb_autopm_get_interface(dev->intf) < 0)
                return -ENODEV;
        ret = __usbnet_write_cmd(dev, cmd, reqtype, value, index,
                                 data, size);
        usb_autopm_put_interface(dev->intf);
        return ret;
}
EXPORT_SYMBOL_GPL(usbnet_write_cmd);

/*
 * The function can be called inside suspend/resume callback safely
 * and should only be called by suspend/resume callback generally.
 */
int usbnet_read_cmd_nopm(struct usbnet *dev, u8 cmd, u8 reqtype,
                          u16 value, u16 index, void *data, u16 size)
{
        return __usbnet_read_cmd(dev, cmd, reqtype, value, index,
                                 data, size);
}
EXPORT_SYMBOL_GPL(usbnet_read_cmd_nopm);

/*
 * The function can be called inside suspend/resume callback safely
 * and should only be called by suspend/resume callback generally.
 */
int usbnet_write_cmd_nopm(struct usbnet *dev, u8 cmd, u8 reqtype,
                          u16 value, u16 index, const void *data,
                          u16 size)
{
        return __usbnet_write_cmd(dev, cmd, reqtype, value, index,
                                  data, size);
}
EXPORT_SYMBOL_GPL(usbnet_write_cmd_nopm);

static void usbnet_async_cmd_cb(struct urb *urb)
{
        struct usb_ctrlrequest *req = (struct usb_ctrlrequest *)urb->context;
        int status = urb->status;

        if (status < 0)
                dev_dbg(&urb->dev->dev, "%s failed with %d",
                        __func__, status);

        kfree(req);
        usb_free_urb(urb);
}

/*
 * The caller must make sure that device can't be put into suspend
 * state until the control URB completes.
 */
int usbnet_write_cmd_async(struct usbnet *dev, u8 cmd, u8 reqtype,
                           u16 value, u16 index, const void *data, u16 size)
{
        struct usb_ctrlrequest *req = NULL;
        struct urb *urb;
        int err = -ENOMEM;
        void *buf = NULL;

        netdev_dbg(dev->net, "usbnet_write_cmd cmd=0x%02x reqtype=%02x"
                   " value=0x%04x index=0x%04x size=%d\n",
                   cmd, reqtype, value, index, size);

        urb = usb_alloc_urb(0, GFP_ATOMIC);
        if (!urb)
                goto fail;

        if (data) {
                buf = kmemdup(data, size, GFP_ATOMIC);
                if (!buf) {
                        netdev_err(dev->net, "Error allocating buffer"
                                   " in %s!\n", __func__);
                        goto fail_free;
                }
        }

        req = kmalloc(sizeof(struct usb_ctrlrequest), GFP_ATOMIC);
        if (!req)
                goto fail_free_buf;

        req->bRequestType = reqtype;
        req->bRequest = cmd;
        req->wValue = cpu_to_le16(value);
        req->wIndex = cpu_to_le16(index);
        req->wLength = cpu_to_le16(size);

        usb_fill_control_urb(urb, dev->udev,
                             usb_sndctrlpipe(dev->udev, 0),
                             (void *)req, buf, size,
                             usbnet_async_cmd_cb, req);
        urb->transfer_flags |= URB_FREE_BUFFER;

        err = usb_submit_urb(urb, GFP_ATOMIC);
        if (err < 0) {
                netdev_err(dev->net, "Error submitting the control"
                           " message: status=%d\n", err);
                goto fail_free;
        }
        return 0;

fail_free_buf:
        kfree(buf);
fail_free:
        kfree(req);
        usb_free_urb(urb);
fail:
        return err;

}
EXPORT_SYMBOL_GPL(usbnet_write_cmd_async);
/*-------------------------------------------------------------------------*/

static int __init usbnet_init(void)
{
        /* Compiler should optimize this out. */
        BUILD_BUG_ON(
                FIELD_SIZEOF(struct sk_buff, cb) < sizeof(struct skb_data));

        eth_random_addr(node_id);
        return 0;
}
module_init(usbnet_init);

static void __exit usbnet_exit(void)
{
}
module_exit(usbnet_exit);

MODULE_AUTHOR("David Brownell");
MODULE_DESCRIPTION("USB network driver framework");
MODULE_LICENSE("GPL");