usb.c

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/*
 * drivers/usb/core/usb.c
 *
 * (C) Copyright Linus Torvalds 1999
 * (C) Copyright Johannes Erdfelt 1999-2001
 * (C) Copyright Andreas Gal 1999
 * (C) Copyright Gregory P. Smith 1999
 * (C) Copyright Deti Fliegl 1999 (new USB architecture)
 * (C) Copyright Randy Dunlap 2000
 * (C) Copyright David Brownell 2000-2004
 * (C) Copyright Yggdrasil Computing, Inc. 2000
 *     (usb_device_id matching changes by Adam J. Richter)
 * (C) Copyright Greg Kroah-Hartman 2002-2003
 *
 * NOTE! This is not actually a driver at all, rather this is
 * just a collection of helper routines that implement the
 * generic USB things that the real drivers can use..
 *
 * Think of this as a "USB library" rather than anything else.
 * It should be considered a slave, with no callbacks. Callbacks
 * are evil.
 */

#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/string.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/interrupt.h>  /* for in_interrupt() */
#include <linux/kmod.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/errno.h>
#include <linux/usb.h>
#include <linux/usb/hcd.h>
#include <linux/mutex.h>
#include <linux/workqueue.h>
#include <linux/debugfs.h>

#include <asm/io.h>
#include <linux/scatterlist.h>
#include <linux/mm.h>
#include <linux/dma-mapping.h>

#include "usb.h"


const char *usbcore_name = "usbcore";

static bool nousb;  /* Disable USB when built into kernel image */

#ifdef  CONFIG_USB_SUSPEND
static int usb_autosuspend_delay = 2;       /* Default delay value,
                         * in seconds */
module_param_named(autosuspend, usb_autosuspend_delay, int, 0644);
MODULE_PARM_DESC(autosuspend, "default autosuspend delay");

#else
#define usb_autosuspend_delay       0
#endif


struct usb_host_interface *usb_find_alt_setting(
        struct usb_host_config *config,
        unsigned int iface_num,
        unsigned int alt_num)
{
    struct usb_interface_cache *intf_cache = NULL;
    int i;

    for (i = 0; i < config->desc.bNumInterfaces; i++) {
        if (config->intf_cache[i]->altsetting[0].desc.bInterfaceNumber
                == iface_num) {
            intf_cache = config->intf_cache[i];
            break;
        }
    }
    if (!intf_cache)
        return NULL;
    for (i = 0; i < intf_cache->num_altsetting; i++)
        if (intf_cache->altsetting[i].desc.bAlternateSetting == alt_num)
            return &intf_cache->altsetting[i];

    printk(KERN_DEBUG "Did not find alt setting %u for intf %u, "
            "config %u\n", alt_num, iface_num,
            config->desc.bConfigurationValue);
    return NULL;
}
EXPORT_SYMBOL_GPL(usb_find_alt_setting);

struct usb_interface *usb_ifnum_to_if(const struct usb_device *dev,
                      unsigned ifnum)
{
    struct usb_host_config *config = dev->actconfig;
    int i;

    if (!config)
        return NULL;
    for (i = 0; i < config->desc.bNumInterfaces; i++)
        if (config->interface[i]->altsetting[0]
                .desc.bInterfaceNumber == ifnum)
            return config->interface[i];

    return NULL;
}
EXPORT_SYMBOL_GPL(usb_ifnum_to_if);

struct usb_host_interface *usb_altnum_to_altsetting(
                    const struct usb_interface *intf,
                    unsigned int altnum)
{
    int i;

    for (i = 0; i < intf->num_altsetting; i++) {
        if (intf->altsetting[i].desc.bAlternateSetting == altnum)
            return &intf->altsetting[i];
    }
    return NULL;
}
EXPORT_SYMBOL_GPL(usb_altnum_to_altsetting);

struct find_interface_arg {
    int minor;
    struct device_driver *drv;
};

static int __find_interface(struct device *dev, void *data)
{
    struct find_interface_arg *arg = data;
    struct usb_interface *intf;

    if (!is_usb_interface(dev))
        return 0;

    if (dev->driver != arg->drv)
        return 0;
    intf = to_usb_interface(dev);
    return intf->minor == arg->minor;
}

struct usb_interface *usb_find_interface(struct usb_driver *drv, int minor)
{
    struct find_interface_arg argb;
    struct device *dev;

    argb.minor = minor;
    argb.drv = &drv->drvwrap.driver;

    dev = bus_find_device(&usb_bus_type, NULL, &argb, __find_interface);

    /* Drop reference count from bus_find_device */
    put_device(dev);

    return dev ? to_usb_interface(dev) : NULL;
}
EXPORT_SYMBOL_GPL(usb_find_interface);

static void usb_release_dev(struct device *dev)
{
    struct usb_device *udev;
    struct usb_hcd *hcd;

    udev = to_usb_device(dev);
    hcd = bus_to_hcd(udev->bus);

    usb_destroy_configuration(udev);
    usb_release_bos_descriptor(udev);
    usb_put_hcd(hcd);
    kfree(udev->product);
    kfree(udev->manufacturer);
    kfree(udev->serial);
    kfree(udev);
}

#ifdef  CONFIG_HOTPLUG
static int usb_dev_uevent(struct device *dev, struct kobj_uevent_env *env)
{
    struct usb_device *usb_dev;

    usb_dev = to_usb_device(dev);

    if (add_uevent_var(env, "BUSNUM=%03d", usb_dev->bus->busnum))
        return -ENOMEM;

    if (add_uevent_var(env, "DEVNUM=%03d", usb_dev->devnum))
        return -ENOMEM;

    return 0;
}

#else

static int usb_dev_uevent(struct device *dev, struct kobj_uevent_env *env)
{
    return -ENODEV;
}
#endif  /* CONFIG_HOTPLUG */

#ifdef  CONFIG_PM

/* USB device Power-Management thunks.
 * There's no need to distinguish here between quiescing a USB device
 * and powering it down; the generic_suspend() routine takes care of
 * it by skipping the usb_port_suspend() call for a quiesce.  And for
 * USB interfaces there's no difference at all.
 */

static int usb_dev_prepare(struct device *dev)
{
    return 0;       /* Implement eventually? */
}

static void usb_dev_complete(struct device *dev)
{
    /* Currently used only for rebinding interfaces */
    usb_resume_complete(dev);
}

static int usb_dev_suspend(struct device *dev)
{
    return usb_suspend(dev, PMSG_SUSPEND);
}

static int usb_dev_resume(struct device *dev)
{
    return usb_resume(dev, PMSG_RESUME);
}

static int usb_dev_freeze(struct device *dev)
{
    return usb_suspend(dev, PMSG_FREEZE);
}

static int usb_dev_thaw(struct device *dev)
{
    return usb_resume(dev, PMSG_THAW);
}

static int usb_dev_poweroff(struct device *dev)
{
    return usb_suspend(dev, PMSG_HIBERNATE);
}

static int usb_dev_restore(struct device *dev)
{
    return usb_resume(dev, PMSG_RESTORE);
}

static const struct dev_pm_ops usb_device_pm_ops = {
    .prepare =  usb_dev_prepare,
    .complete = usb_dev_complete,
    .suspend =  usb_dev_suspend,
    .resume =   usb_dev_resume,
    .freeze =   usb_dev_freeze,
    .thaw =     usb_dev_thaw,
    .poweroff = usb_dev_poweroff,
    .restore =  usb_dev_restore,
#ifdef CONFIG_USB_SUSPEND
    .runtime_suspend =  usb_runtime_suspend,
    .runtime_resume =   usb_runtime_resume,
    .runtime_idle =     usb_runtime_idle,
#endif
};

#endif  /* CONFIG_PM */


static char *usb_devnode(struct device *dev, umode_t *mode)
{
    struct usb_device *usb_dev;

    usb_dev = to_usb_device(dev);
    return kasprintf(GFP_KERNEL, "bus/usb/%03d/%03d",
             usb_dev->bus->busnum, usb_dev->devnum);
}

struct device_type usb_device_type = {
    .name =     "usb_device",
    .release =  usb_release_dev,
    .uevent =   usb_dev_uevent,
    .devnode =  usb_devnode,
#ifdef CONFIG_PM
    .pm =       &usb_device_pm_ops,
#endif
};


/* Returns 1 if @usb_bus is WUSB, 0 otherwise */
static unsigned usb_bus_is_wusb(struct usb_bus *bus)
{
    struct usb_hcd *hcd = container_of(bus, struct usb_hcd, self);
    return hcd->wireless;
}


struct usb_device *usb_alloc_dev(struct usb_device *parent,
                 struct usb_bus *bus, unsigned port1)
{
    struct usb_device *dev;
    struct usb_hcd *usb_hcd = container_of(bus, struct usb_hcd, self);
    unsigned root_hub = 0;

    dev = kzalloc(sizeof(*dev), GFP_KERNEL);
    if (!dev)
        return NULL;

    if (!usb_get_hcd(bus_to_hcd(bus))) {
        kfree(dev);
        return NULL;
    }
    /* Root hubs aren't true devices, so don't allocate HCD resources */
    if (usb_hcd->driver->alloc_dev && parent &&
        !usb_hcd->driver->alloc_dev(usb_hcd, dev)) {
        usb_put_hcd(bus_to_hcd(bus));
        kfree(dev);
        return NULL;
    }

    device_initialize(&dev->dev);
    dev->dev.bus = &usb_bus_type;
    dev->dev.type = &usb_device_type;
    dev->dev.groups = usb_device_groups;
    dev->dev.dma_mask = bus->controller->dma_mask;
    set_dev_node(&dev->dev, dev_to_node(bus->controller));
    dev->state = USB_STATE_ATTACHED;
    dev->lpm_disable_count = 1;
    atomic_set(&dev->urbnum, 0);

    INIT_LIST_HEAD(&dev->ep0.urb_list);
    dev->ep0.desc.bLength = USB_DT_ENDPOINT_SIZE;
    dev->ep0.desc.bDescriptorType = USB_DT_ENDPOINT;
    /* ep0 maxpacket comes later, from device descriptor */
    usb_enable_endpoint(dev, &dev->ep0, false);
    dev->can_submit = 1;

    /* Save readable and stable topology id, distinguishing devices
     * by location for diagnostics, tools, driver model, etc.  The
     * string is a path along hub ports, from the root.  Each device's
     * dev->devpath will be stable until USB is re-cabled, and hubs
     * are often labeled with these port numbers.  The name isn't
     * as stable:  bus->busnum changes easily from modprobe order,
     * cardbus or pci hotplugging, and so on.
     */
    if (unlikely(!parent)) {
        dev->devpath[0] = '0';
        dev->route = 0;

        dev->dev.parent = bus->controller;
        dev_set_name(&dev->dev, "usb%d", bus->busnum);
        root_hub = 1;
    } else {
        /* match any labeling on the hubs; it's one-based */
        if (parent->devpath[0] == '0') {
            snprintf(dev->devpath, sizeof dev->devpath,
                "%d", port1);
            /* Root ports are not counted in route string */
            dev->route = 0;
        } else {
            snprintf(dev->devpath, sizeof dev->devpath,
                "%s.%d", parent->devpath, port1);
            /* Route string assumes hubs have less than 16 ports */
            if (port1 < 15)
                dev->route = parent->route +
                    (port1 << ((parent->level - 1)*4));
            else
                dev->route = parent->route +
                    (15 << ((parent->level - 1)*4));
        }

        dev->dev.parent = &parent->dev;
        dev_set_name(&dev->dev, "%d-%s", bus->busnum, dev->devpath);

        /* hub driver sets up TT records */
    }

    dev->portnum = port1;
    dev->bus = bus;
    dev->parent = parent;
    INIT_LIST_HEAD(&dev->filelist);

#ifdef  CONFIG_PM
    pm_runtime_set_autosuspend_delay(&dev->dev,
            usb_autosuspend_delay * 1000);
    dev->connect_time = jiffies;
    dev->active_duration = -jiffies;
#endif
    if (root_hub)   /* Root hub always ok [and always wired] */
        dev->authorized = 1;
    else {
        dev->authorized = usb_hcd->authorized_default;
        dev->wusb = usb_bus_is_wusb(bus)? 1 : 0;
    }
    return dev;
}

struct usb_device *usb_get_dev(struct usb_device *dev)
{
    if (dev)
        get_device(&dev->dev);
    return dev;
}
EXPORT_SYMBOL_GPL(usb_get_dev);

void usb_put_dev(struct usb_device *dev)
{
    if (dev)
        put_device(&dev->dev);
}
EXPORT_SYMBOL_GPL(usb_put_dev);

struct usb_interface *usb_get_intf(struct usb_interface *intf)
{
    if (intf)
        get_device(&intf->dev);
    return intf;
}
EXPORT_SYMBOL_GPL(usb_get_intf);

void usb_put_intf(struct usb_interface *intf)
{
    if (intf)
        put_device(&intf->dev);
}
EXPORT_SYMBOL_GPL(usb_put_intf);

/*          USB device locking
 *
 * USB devices and interfaces are locked using the semaphore in their
 * embedded struct device.  The hub driver guarantees that whenever a
 * device is connected or disconnected, drivers are called with the
 * USB device locked as well as their particular interface.
 *
 * Complications arise when several devices are to be locked at the same
 * time.  Only hub-aware drivers that are part of usbcore ever have to
 * do this; nobody else needs to worry about it.  The rule for locking
 * is simple:
 *
 *  When locking both a device and its parent, always lock the
 *  the parent first.
 */

int usb_lock_device_for_reset(struct usb_device *udev,
                  const struct usb_interface *iface)
{
    unsigned long jiffies_expire = jiffies + HZ;

    if (udev->state == USB_STATE_NOTATTACHED)
        return -ENODEV;
    if (udev->state == USB_STATE_SUSPENDED)
        return -EHOSTUNREACH;
    if (iface && (iface->condition == USB_INTERFACE_UNBINDING ||
            iface->condition == USB_INTERFACE_UNBOUND))
        return -EINTR;

    while (!usb_trylock_device(udev)) {

        /* If we can't acquire the lock after waiting one second,
         * we're probably deadlocked */
        if (time_after(jiffies, jiffies_expire))
            return -EBUSY;

        msleep(15);
        if (udev->state == USB_STATE_NOTATTACHED)
            return -ENODEV;
        if (udev->state == USB_STATE_SUSPENDED)
            return -EHOSTUNREACH;
        if (iface && (iface->condition == USB_INTERFACE_UNBINDING ||
                iface->condition == USB_INTERFACE_UNBOUND))
            return -EINTR;
    }
    return 0;
}
EXPORT_SYMBOL_GPL(usb_lock_device_for_reset);

int usb_get_current_frame_number(struct usb_device *dev)
{
    return usb_hcd_get_frame_number(dev);
}
EXPORT_SYMBOL_GPL(usb_get_current_frame_number);

/*-------------------------------------------------------------------*/
/*
 * __usb_get_extra_descriptor() finds a descriptor of specific type in the
 * extra field of the interface and endpoint descriptor structs.
 */

int __usb_get_extra_descriptor(char *buffer, unsigned size,
                   unsigned char type, void **ptr)
{
    struct usb_descriptor_header *header;

    while (size >= sizeof(struct usb_descriptor_header)) {
        header = (struct usb_descriptor_header *)buffer;

        if (header->bLength < 2) {
            printk(KERN_ERR
                "%s: bogus descriptor, type %d length %d\n",
                usbcore_name,
                header->bDescriptorType,
                header->bLength);
            return -1;
        }

        if (header->bDescriptorType == type) {
            *ptr = header;
            return 0;
        }

        buffer += header->bLength;
        size -= header->bLength;
    }
    return -1;
}
EXPORT_SYMBOL_GPL(__usb_get_extra_descriptor);

void *usb_alloc_coherent(struct usb_device *dev, size_t size, gfp_t mem_flags,
             dma_addr_t *dma)
{
    if (!dev || !dev->bus)
        return NULL;
    return hcd_buffer_alloc(dev->bus, size, mem_flags, dma);
}
EXPORT_SYMBOL_GPL(usb_alloc_coherent);

void usb_free_coherent(struct usb_device *dev, size_t size, void *addr,
               dma_addr_t dma)
{
    if (!dev || !dev->bus)
        return;
    if (!addr)
        return;
    hcd_buffer_free(dev->bus, size, addr, dma);
}
EXPORT_SYMBOL_GPL(usb_free_coherent);

#if 0
struct urb *usb_buffer_map(struct urb *urb)
{
    struct usb_bus      *bus;
    struct device       *controller;

    if (!urb
            || !urb->dev
            || !(bus = urb->dev->bus)
            || !(controller = bus->controller))
        return NULL;

    if (controller->dma_mask) {
        urb->transfer_dma = dma_map_single(controller,
            urb->transfer_buffer, urb->transfer_buffer_length,
            usb_pipein(urb->pipe)
                ? DMA_FROM_DEVICE : DMA_TO_DEVICE);
    /* FIXME generic api broken like pci, can't report errors */
    /* if (urb->transfer_dma == DMA_ADDR_INVALID) return 0; */
    } else
        urb->transfer_dma = ~0;
    urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
    return urb;
}
EXPORT_SYMBOL_GPL(usb_buffer_map);
#endif  /*  0  */

/* XXX DISABLED, no users currently.  If you wish to re-enable this
 * XXX please determine whether the sync is to transfer ownership of
 * XXX the buffer from device to cpu or vice verse, and thusly use the
 * XXX appropriate _for_{cpu,device}() method.  -DaveM
 */
#if 0

void usb_buffer_dmasync(struct urb *urb)
{
    struct usb_bus      *bus;
    struct device       *controller;

    if (!urb
            || !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)
            || !urb->dev
            || !(bus = urb->dev->bus)
            || !(controller = bus->controller))
        return;

    if (controller->dma_mask) {
        dma_sync_single_for_cpu(controller,
            urb->transfer_dma, urb->transfer_buffer_length,
            usb_pipein(urb->pipe)
                ? DMA_FROM_DEVICE : DMA_TO_DEVICE);
        if (usb_pipecontrol(urb->pipe))
            dma_sync_single_for_cpu(controller,
                    urb->setup_dma,
                    sizeof(struct usb_ctrlrequest),
                    DMA_TO_DEVICE);
    }
}
EXPORT_SYMBOL_GPL(usb_buffer_dmasync);
#endif

#if 0
void usb_buffer_unmap(struct urb *urb)
{
    struct usb_bus      *bus;
    struct device       *controller;

    if (!urb
            || !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)
            || !urb->dev
            || !(bus = urb->dev->bus)
            || !(controller = bus->controller))
        return;

    if (controller->dma_mask) {
        dma_unmap_single(controller,
            urb->transfer_dma, urb->transfer_buffer_length,
            usb_pipein(urb->pipe)
                ? DMA_FROM_DEVICE : DMA_TO_DEVICE);
    }
    urb->transfer_flags &= ~URB_NO_TRANSFER_DMA_MAP;
}
EXPORT_SYMBOL_GPL(usb_buffer_unmap);
#endif  /*  0  */

#if 0

int usb_buffer_map_sg(const struct usb_device *dev, int is_in,
              struct scatterlist *sg, int nents)
{
    struct usb_bus      *bus;
    struct device       *controller;

    if (!dev
            || !(bus = dev->bus)
            || !(controller = bus->controller)
            || !controller->dma_mask)
        return -EINVAL;

    /* FIXME generic api broken like pci, can't report errors */
    return dma_map_sg(controller, sg, nents,
            is_in ? DMA_FROM_DEVICE : DMA_TO_DEVICE) ? : -ENOMEM;
}
EXPORT_SYMBOL_GPL(usb_buffer_map_sg);
#endif

/* XXX DISABLED, no users currently.  If you wish to re-enable this
 * XXX please determine whether the sync is to transfer ownership of
 * XXX the buffer from device to cpu or vice verse, and thusly use the
 * XXX appropriate _for_{cpu,device}() method.  -DaveM
 */
#if 0

void usb_buffer_dmasync_sg(const struct usb_device *dev, int is_in,
               struct scatterlist *sg, int n_hw_ents)
{
    struct usb_bus      *bus;
    struct device       *controller;

    if (!dev
            || !(bus = dev->bus)
            || !(controller = bus->controller)
            || !controller->dma_mask)
        return;

    dma_sync_sg_for_cpu(controller, sg, n_hw_ents,
                is_in ? DMA_FROM_DEVICE : DMA_TO_DEVICE);
}
EXPORT_SYMBOL_GPL(usb_buffer_dmasync_sg);
#endif

#if 0

void usb_buffer_unmap_sg(const struct usb_device *dev, int is_in,
             struct scatterlist *sg, int n_hw_ents)
{
    struct usb_bus      *bus;
    struct device       *controller;

    if (!dev
            || !(bus = dev->bus)
            || !(controller = bus->controller)
            || !controller->dma_mask)
        return;

    dma_unmap_sg(controller, sg, n_hw_ents,
            is_in ? DMA_FROM_DEVICE : DMA_TO_DEVICE);
}
EXPORT_SYMBOL_GPL(usb_buffer_unmap_sg);
#endif

/* To disable USB, kernel command line is 'nousb' not 'usbcore.nousb' */
#ifdef MODULE
module_param(nousb, bool, 0444);
#else
core_param(nousb, nousb, bool, 0444);
#endif

/*
 * for external read access to <nousb>
 */
int usb_disabled(void)
{
    return nousb;
}
EXPORT_SYMBOL_GPL(usb_disabled);

/*
 * Notifications of device and interface registration
 */
static int usb_bus_notify(struct notifier_block *nb, unsigned long action,
        void *data)
{
    struct device *dev = data;

    switch (action) {
    case BUS_NOTIFY_ADD_DEVICE:
        if (dev->type == &usb_device_type)
            (void) usb_create_sysfs_dev_files(to_usb_device(dev));
        else if (dev->type == &usb_if_device_type)
            usb_create_sysfs_intf_files(to_usb_interface(dev));
        break;

    case BUS_NOTIFY_DEL_DEVICE:
        if (dev->type == &usb_device_type)
            usb_remove_sysfs_dev_files(to_usb_device(dev));
        else if (dev->type == &usb_if_device_type)
            usb_remove_sysfs_intf_files(to_usb_interface(dev));
        break;
    }
    return 0;
}

static struct notifier_block usb_bus_nb = {
    .notifier_call = usb_bus_notify,
};

struct dentry *usb_debug_root;
EXPORT_SYMBOL_GPL(usb_debug_root);

static struct dentry *usb_debug_devices;

static int usb_debugfs_init(void)
{
    usb_debug_root = debugfs_create_dir("usb", NULL);
    if (!usb_debug_root)
        return -ENOENT;

    usb_debug_devices = debugfs_create_file("devices", 0444,
                        usb_debug_root, NULL,
                        &usbfs_devices_fops);
    if (!usb_debug_devices) {
        debugfs_remove(usb_debug_root);
        usb_debug_root = NULL;
        return -ENOENT;
    }

    return 0;
}

static void usb_debugfs_cleanup(void)
{
    debugfs_remove(usb_debug_devices);
    debugfs_remove(usb_debug_root);
}

/*
 * Init
 */
static int __init usb_init(void)
{
    int retval;
    if (nousb) {
        pr_info("%s: USB support disabled\n", usbcore_name);
        return 0;
    }

    retval = usb_debugfs_init();
    if (retval)
        goto out;

    usb_acpi_register();
    retval = bus_register(&usb_bus_type);
    if (retval)
        goto bus_register_failed;
    retval = bus_register_notifier(&usb_bus_type, &usb_bus_nb);
    if (retval)
        goto bus_notifier_failed;
    retval = usb_major_init();
    if (retval)
        goto major_init_failed;
    retval = usb_register(&usbfs_driver);
    if (retval)
        goto driver_register_failed;
    retval = usb_devio_init();
    if (retval)
        goto usb_devio_init_failed;
    retval = usb_hub_init();
    if (retval)
        goto hub_init_failed;
    retval = usb_register_device_driver(&usb_generic_driver, THIS_MODULE);
    if (!retval)
        goto out;

    usb_hub_cleanup();
hub_init_failed:
    usb_devio_cleanup();
usb_devio_init_failed:
    usb_deregister(&usbfs_driver);
driver_register_failed:
    usb_major_cleanup();
major_init_failed:
    bus_unregister_notifier(&usb_bus_type, &usb_bus_nb);
bus_notifier_failed:
    bus_unregister(&usb_bus_type);
bus_register_failed:
    usb_acpi_unregister();
    usb_debugfs_cleanup();
out:
    return retval;
}

/*
 * Cleanup
 */
static void __exit usb_exit(void)
{
    /* This will matter if shutdown/reboot does exitcalls. */
    if (nousb)
        return;

    usb_deregister_device_driver(&usb_generic_driver);
    usb_major_cleanup();
    usb_deregister(&usbfs_driver);
    usb_devio_cleanup();
    usb_hub_cleanup();
    bus_unregister_notifier(&usb_bus_type, &usb_bus_nb);
    bus_unregister(&usb_bus_type);
    usb_acpi_unregister();
    usb_debugfs_cleanup();
}

subsys_initcall(usb_init);
module_exit(usb_exit);
MODULE_LICENSE("GPL");