Merge master.kernel.org:/pub/scm/linux/kernel/git/gregkh/pci-2.6

[linux-2.6] / drivers / usb / core / usb.c

/*
 * 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/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/smp_lock.h>
#include <linux/usb.h>
#include <linux/mutex.h>
#include <linux/workqueue.h>

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

#include "hcd.h"
#include "usb.h"


const char *usbcore_name = "usbcore";

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

struct workqueue_struct *ksuspend_usb_wq;       /* For autosuspend */


/**
 * usb_ifnum_to_if - get the interface object with a given interface number
 * @dev: the device whose current configuration is considered
 * @ifnum: the desired interface
 *
 * This walks the device descriptor for the currently active configuration
 * and returns a pointer to the interface with that particular interface
 * number, or null.
 *
 * Note that configuration descriptors are not required to assign interface
 * numbers sequentially, so that it would be incorrect to assume that
 * the first interface in that descriptor corresponds to interface zero.
 * This routine helps device drivers avoid such mistakes.
 * However, you should make sure that you do the right thing with any
 * alternate settings available for this interfaces.
 *
 * Don't call this function unless you are bound to one of the interfaces
 * on this device or you have locked the device!
 */
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;
}

/**
 * usb_altnum_to_altsetting - get the altsetting structure with a given
 *      alternate setting number.
 * @intf: the interface containing the altsetting in question
 * @altnum: the desired alternate setting number
 *
 * This searches the altsetting array of the specified interface for
 * an entry with the correct bAlternateSetting value and returns a pointer
 * to that entry, or null.
 *
 * Note that altsettings need not be stored sequentially by number, so
 * it would be incorrect to assume that the first altsetting entry in
 * the array corresponds to altsetting zero.  This routine helps device
 * drivers avoid such mistakes.
 *
 * Don't call this function unless you are bound to the intf interface
 * or you have locked the device!
 */
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;
}

struct find_interface_arg {
        int minor;
        struct usb_interface *interface;
};

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

        /* can't look at usb devices, only interfaces */
        if (is_usb_device(dev))
                return 0;

        intf = to_usb_interface(dev);
        if (intf->minor != -1 && intf->minor == arg->minor) {
                arg->interface = intf;
                return 1;
        }
        return 0;
}

/**
 * usb_find_interface - find usb_interface pointer for driver and device
 * @drv: the driver whose current configuration is considered
 * @minor: the minor number of the desired device
 *
 * This walks the driver device list and returns a pointer to the interface 
 * with the matching minor.  Note, this only works for devices that share the
 * USB major number.
 */
struct usb_interface *usb_find_interface(struct usb_driver *drv, int minor)
{
        struct find_interface_arg argb;
        int retval;

        argb.minor = minor;
        argb.interface = NULL;
        /* eat the error, it will be in argb.interface */
        retval = driver_for_each_device(&drv->drvwrap.driver, NULL, &argb,
                                        __find_interface);
        return argb.interface;
}

/**
 * usb_release_dev - free a usb device structure when all users of it are finished.
 * @dev: device that's been disconnected
 *
 * Will be called only by the device core when all users of this usb device are
 * done.
 */
static void usb_release_dev(struct device *dev)
{
        struct usb_device *udev;

        udev = to_usb_device(dev);

#ifdef  CONFIG_USB_SUSPEND
        cancel_delayed_work(&udev->autosuspend);
        flush_workqueue(ksuspend_usb_wq);
#endif
        usb_destroy_configuration(udev);
        usb_put_hcd(bus_to_hcd(udev->bus));
        kfree(udev->product);
        kfree(udev->manufacturer);
        kfree(udev->serial);
        kfree(udev);
}

#ifdef  CONFIG_PM

static int ksuspend_usb_init(void)
{
        ksuspend_usb_wq = create_singlethread_workqueue("ksuspend_usbd");
        if (!ksuspend_usb_wq)
                return -ENOMEM;
        return 0;
}

static void ksuspend_usb_cleanup(void)
{
        destroy_workqueue(ksuspend_usb_wq);
}

#ifdef  CONFIG_USB_SUSPEND

/* usb_autosuspend_work - callback routine to autosuspend a USB device */
static void usb_autosuspend_work(struct work_struct *work)
{
        struct usb_device *udev =
                container_of(work, struct usb_device, autosuspend.work);

        usb_pm_lock(udev);
        udev->auto_pm = 1;
        usb_suspend_both(udev, PMSG_SUSPEND);
        usb_pm_unlock(udev);
}

#else

static void usb_autosuspend_work(struct work_struct *work)
{}

#endif  /* CONFIG_USB_SUSPEND */

#else

#define ksuspend_usb_init()     0
#define ksuspend_usb_cleanup()  do {} while (0)

#endif  /* CONFIG_PM */

/**
 * usb_alloc_dev - usb device constructor (usbcore-internal)
 * @parent: hub to which device is connected; null to allocate a root hub
 * @bus: bus used to access the device
 * @port1: one-based index of port; ignored for root hubs
 * Context: !in_interrupt()
 *
 * Only hub drivers (including virtual root hub drivers for host
 * controllers) should ever call this.
 *
 * This call may not be used in a non-sleeping context.
 */
struct usb_device *
usb_alloc_dev(struct usb_device *parent, struct usb_bus *bus, unsigned port1)
{
        struct usb_device *dev;

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

        if (!usb_get_hcd(bus_to_hcd(bus))) {
                kfree(dev);
                return NULL;
        }

        device_initialize(&dev->dev);
        dev->dev.bus = &usb_bus_type;
        dev->dev.dma_mask = bus->controller->dma_mask;
        dev->dev.release = usb_release_dev;
        dev->state = USB_STATE_ATTACHED;

        /* This magic assignment distinguishes devices from interfaces */
        dev->dev.platform_data = &usb_generic_driver;

        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 */
        dev->ep_in[0] = dev->ep_out[0] = &dev->ep0;

        /* 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 bus_id 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->dev.parent = bus->controller;
                sprintf(&dev->dev.bus_id[0], "usb%d", bus->busnum);
        } else {
                /* match any labeling on the hubs; it's one-based */
                if (parent->devpath[0] == '0')
                        snprintf(dev->devpath, sizeof dev->devpath,
                                "%d", port1);
                else
                        snprintf(dev->devpath, sizeof dev->devpath,
                                "%s.%d", parent->devpath, port1);

                dev->dev.parent = &parent->dev;
                sprintf(&dev->dev.bus_id[0], "%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
        mutex_init(&dev->pm_mutex);
        INIT_DELAYED_WORK(&dev->autosuspend, usb_autosuspend_work);
#endif
        return dev;
}

/**
 * usb_get_dev - increments the reference count of the usb device structure
 * @dev: the device being referenced
 *
 * Each live reference to a device should be refcounted.
 *
 * Drivers for USB interfaces should normally record such references in
 * their probe() methods, when they bind to an interface, and release
 * them by calling usb_put_dev(), in their disconnect() methods.
 *
 * A pointer to the device with the incremented reference counter is returned.
 */
struct usb_device *usb_get_dev(struct usb_device *dev)
{
        if (dev)
                get_device(&dev->dev);
        return dev;
}

/**
 * usb_put_dev - release a use of the usb device structure
 * @dev: device that's been disconnected
 *
 * Must be called when a user of a device is finished with it.  When the last
 * user of the device calls this function, the memory of the device is freed.
 */
void usb_put_dev(struct usb_device *dev)
{
        if (dev)
                put_device(&dev->dev);
}

/**
 * usb_get_intf - increments the reference count of the usb interface structure
 * @intf: the interface being referenced
 *
 * Each live reference to a interface must be refcounted.
 *
 * Drivers for USB interfaces should normally record such references in
 * their probe() methods, when they bind to an interface, and release
 * them by calling usb_put_intf(), in their disconnect() methods.
 *
 * A pointer to the interface with the incremented reference counter is
 * returned.
 */
struct usb_interface *usb_get_intf(struct usb_interface *intf)
{
        if (intf)
                get_device(&intf->dev);
        return intf;
}

/**
 * usb_put_intf - release a use of the usb interface structure
 * @intf: interface that's been decremented
 *
 * Must be called when a user of an interface is finished with it.  When the
 * last user of the interface calls this function, the memory of the interface
 * is freed.
 */
void usb_put_intf(struct usb_interface *intf)
{
        if (intf)
                put_device(&intf->dev);
}


/*                      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.
 */

/**
 * usb_lock_device_for_reset - cautiously acquire the lock for a
 *      usb device structure
 * @udev: device that's being locked
 * @iface: interface bound to the driver making the request (optional)
 *
 * Attempts to acquire the device lock, but fails if the device is
 * NOTATTACHED or SUSPENDED, or if iface is specified and the interface
 * is neither BINDING nor BOUND.  Rather than sleeping to wait for the
 * lock, the routine polls repeatedly.  This is to prevent deadlock with
 * disconnect; in some drivers (such as usb-storage) the disconnect()
 * or suspend() method will block waiting for a device reset to complete.
 *
 * Returns a negative error code for failure, otherwise 1 or 0 to indicate
 * that the device will or will not have to be unlocked.  (0 can be
 * returned when an interface is given and is BINDING, because in that
 * case the driver already owns the device lock.)
 */
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) {
                switch (iface->condition) {
                  case USB_INTERFACE_BINDING:
                        return 0;
                  case USB_INTERFACE_BOUND:
                        break;
                  default:
                        return -EINTR;
                }
        }

        while (usb_trylock_device(udev) != 0) {

                /* 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_BOUND)
                        return -EINTR;
        }
        return 1;
}


static struct usb_device *match_device(struct usb_device *dev,
                                       u16 vendor_id, u16 product_id)
{
        struct usb_device *ret_dev = NULL;
        int child;

        dev_dbg(&dev->dev, "check for vendor %04x, product %04x ...\n",
            le16_to_cpu(dev->descriptor.idVendor),
            le16_to_cpu(dev->descriptor.idProduct));

        /* see if this device matches */
        if ((vendor_id == le16_to_cpu(dev->descriptor.idVendor)) &&
            (product_id == le16_to_cpu(dev->descriptor.idProduct))) {
                dev_dbg(&dev->dev, "matched this device!\n");
                ret_dev = usb_get_dev(dev);
                goto exit;
        }

        /* look through all of the children of this device */
        for (child = 0; child < dev->maxchild; ++child) {
                if (dev->children[child]) {
                        usb_lock_device(dev->children[child]);
                        ret_dev = match_device(dev->children[child],
                                               vendor_id, product_id);
                        usb_unlock_device(dev->children[child]);
                        if (ret_dev)
                                goto exit;
                }
        }
exit:
        return ret_dev;
}

/**
 * usb_find_device - find a specific usb device in the system
 * @vendor_id: the vendor id of the device to find
 * @product_id: the product id of the device to find
 *
 * Returns a pointer to a struct usb_device if such a specified usb
 * device is present in the system currently.  The usage count of the
 * device will be incremented if a device is found.  Make sure to call
 * usb_put_dev() when the caller is finished with the device.
 *
 * If a device with the specified vendor and product id is not found,
 * NULL is returned.
 */
struct usb_device *usb_find_device(u16 vendor_id, u16 product_id)
{
        struct list_head *buslist;
        struct usb_bus *bus;
        struct usb_device *dev = NULL;
        
        mutex_lock(&usb_bus_list_lock);
        for (buslist = usb_bus_list.next;
             buslist != &usb_bus_list; 
             buslist = buslist->next) {
                bus = container_of(buslist, struct usb_bus, bus_list);
                if (!bus->root_hub)
                        continue;
                usb_lock_device(bus->root_hub);
                dev = match_device(bus->root_hub, vendor_id, product_id);
                usb_unlock_device(bus->root_hub);
                if (dev)
                        goto exit;
        }
exit:
        mutex_unlock(&usb_bus_list_lock);
        return dev;
}

/**
 * usb_get_current_frame_number - return current bus frame number
 * @dev: the device whose bus is being queried
 *
 * Returns the current frame number for the USB host controller
 * used with the given USB device.  This can be used when scheduling
 * isochronous requests.
 *
 * Note that different kinds of host controller have different
 * "scheduling horizons".  While one type might support scheduling only
 * 32 frames into the future, others could support scheduling up to
 * 1024 frames into the future.
 */
int usb_get_current_frame_number(struct usb_device *dev)
{
        return usb_hcd_get_frame_number(dev);
}

/*-------------------------------------------------------------------*/
/*
 * __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;
}

/**
 * usb_buffer_alloc - allocate dma-consistent buffer for URB_NO_xxx_DMA_MAP
 * @dev: device the buffer will be used with
 * @size: requested buffer size
 * @mem_flags: affect whether allocation may block
 * @dma: used to return DMA address of buffer
 *
 * Return value is either null (indicating no buffer could be allocated), or
 * the cpu-space pointer to a buffer that may be used to perform DMA to the
 * specified device.  Such cpu-space buffers are returned along with the DMA
 * address (through the pointer provided).
 *
 * These buffers are used with URB_NO_xxx_DMA_MAP set in urb->transfer_flags
 * to avoid behaviors like using "DMA bounce buffers", or tying down I/O
 * mapping hardware for long idle periods.  The implementation varies between
 * platforms, depending on details of how DMA will work to this device.
 * Using these buffers also helps prevent cacheline sharing problems on
 * architectures where CPU caches are not DMA-coherent.
 *
 * When the buffer is no longer used, free it with usb_buffer_free().
 */
void *usb_buffer_alloc(
        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);
}

/**
 * usb_buffer_free - free memory allocated with usb_buffer_alloc()
 * @dev: device the buffer was used with
 * @size: requested buffer size
 * @addr: CPU address of buffer
 * @dma: DMA address of buffer
 *
 * This reclaims an I/O buffer, letting it be reused.  The memory must have
 * been allocated using usb_buffer_alloc(), and the parameters must match
 * those provided in that allocation request. 
 */
void usb_buffer_free(
        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);
}

/**
 * usb_buffer_map - create DMA mapping(s) for an urb
 * @urb: urb whose transfer_buffer/setup_packet will be mapped
 *
 * Return value is either null (indicating no buffer could be mapped), or
 * the parameter.  URB_NO_TRANSFER_DMA_MAP and URB_NO_SETUP_DMA_MAP are
 * added to urb->transfer_flags if the operation succeeds.  If the device
 * is connected to this system through a non-DMA controller, this operation
 * always succeeds.
 *
 * This call would normally be used for an urb which is reused, perhaps
 * as the target of a large periodic transfer, with usb_buffer_dmasync()
 * calls to synchronize memory and dma state.
 *
 * Reverse the effect of this call with usb_buffer_unmap().
 */
#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);
                if (usb_pipecontrol(urb->pipe))
                        urb->setup_dma = dma_map_single(controller,
                                        urb->setup_packet,
                                        sizeof(struct usb_ctrlrequest),
                                        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
                                | URB_NO_SETUP_DMA_MAP);
        return urb;
}
#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

/**
 * usb_buffer_dmasync - synchronize DMA and CPU view of buffer(s)
 * @urb: urb whose transfer_buffer/setup_packet will be synchronized
 */
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(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(controller,
                                        urb->setup_dma,
                                        sizeof(struct usb_ctrlrequest),
                                        DMA_TO_DEVICE);
        }
}
#endif

/**
 * usb_buffer_unmap - free DMA mapping(s) for an urb
 * @urb: urb whose transfer_buffer will be unmapped
 *
 * Reverses the effect of usb_buffer_map().
 */
#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);
                if (usb_pipecontrol(urb->pipe))
                        dma_unmap_single(controller,
                                        urb->setup_dma,
                                        sizeof(struct usb_ctrlrequest),
                                        DMA_TO_DEVICE);
        }
        urb->transfer_flags &= ~(URB_NO_TRANSFER_DMA_MAP
                                | URB_NO_SETUP_DMA_MAP);
}
#endif  /*  0  */

/**
 * usb_buffer_map_sg - create scatterlist DMA mapping(s) for an endpoint
 * @dev: device to which the scatterlist will be mapped
 * @pipe: endpoint defining the mapping direction
 * @sg: the scatterlist to map
 * @nents: the number of entries in the scatterlist
 *
 * Return value is either < 0 (indicating no buffers could be mapped), or
 * the number of DMA mapping array entries in the scatterlist.
 *
 * The caller is responsible for placing the resulting DMA addresses from
 * the scatterlist into URB transfer buffer pointers, and for setting the
 * URB_NO_TRANSFER_DMA_MAP transfer flag in each of those URBs.
 *
 * Top I/O rates come from queuing URBs, instead of waiting for each one
 * to complete before starting the next I/O.   This is particularly easy
 * to do with scatterlists.  Just allocate and submit one URB for each DMA
 * mapping entry returned, stopping on the first error or when all succeed.
 * Better yet, use the usb_sg_*() calls, which do that (and more) for you.
 *
 * This call would normally be used when translating scatterlist requests,
 * rather than usb_buffer_map(), since on some hardware (with IOMMUs) it
 * may be able to coalesce mappings for improved I/O efficiency.
 *
 * Reverse the effect of this call with usb_buffer_unmap_sg().
 */
int usb_buffer_map_sg(const struct usb_device *dev, unsigned pipe,
                      struct scatterlist *sg, int nents)
{
        struct usb_bus          *bus;
        struct device           *controller;

        if (!dev
                        || usb_pipecontrol(pipe)
                        || !(bus = dev->bus)
                        || !(controller = bus->controller)
                        || !controller->dma_mask)
                return -1;

        // FIXME generic api broken like pci, can't report errors
        return dma_map_sg(controller, sg, nents,
                        usb_pipein(pipe) ? DMA_FROM_DEVICE : DMA_TO_DEVICE);
}

/* 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

/**
 * usb_buffer_dmasync_sg - synchronize DMA and CPU view of scatterlist buffer(s)
 * @dev: device to which the scatterlist will be mapped
 * @pipe: endpoint defining the mapping direction
 * @sg: the scatterlist to synchronize
 * @n_hw_ents: the positive return value from usb_buffer_map_sg
 *
 * Use this when you are re-using a scatterlist's data buffers for
 * another USB request.
 */
void usb_buffer_dmasync_sg(const struct usb_device *dev, unsigned pipe,
                           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(controller, sg, n_hw_ents,
                        usb_pipein(pipe) ? DMA_FROM_DEVICE : DMA_TO_DEVICE);
}
#endif

/**
 * usb_buffer_unmap_sg - free DMA mapping(s) for a scatterlist
 * @dev: device to which the scatterlist will be mapped
 * @pipe: endpoint defining the mapping direction
 * @sg: the scatterlist to unmap
 * @n_hw_ents: the positive return value from usb_buffer_map_sg
 *
 * Reverses the effect of usb_buffer_map_sg().
 */
void usb_buffer_unmap_sg(const struct usb_device *dev, unsigned pipe,
                         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,
                        usb_pipein(pipe) ? DMA_FROM_DEVICE : DMA_TO_DEVICE);
}

/* format to disable USB on kernel command line is: nousb */
__module_param_call("", nousb, param_set_bool, param_get_bool, &nousb, 0444);

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

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

        retval = ksuspend_usb_init();
        if (retval)
                goto out;
        retval = bus_register(&usb_bus_type);
        if (retval) 
                goto bus_register_failed;
        retval = usb_host_init();
        if (retval)
                goto host_init_failed;
        retval = usb_major_init();
        if (retval)
                goto major_init_failed;
        retval = usb_register(&usbfs_driver);
        if (retval)
                goto driver_register_failed;
        retval = usbdev_init();
        if (retval)
                goto usbdevice_init_failed;
        retval = usbfs_init();
        if (retval)
                goto fs_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:
        usbfs_cleanup();
fs_init_failed:
        usbdev_cleanup();
usbdevice_init_failed:
        usb_deregister(&usbfs_driver);
driver_register_failed:
        usb_major_cleanup();
major_init_failed:
        usb_host_cleanup();
host_init_failed:
        bus_unregister(&usb_bus_type);
bus_register_failed:
        ksuspend_usb_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();
        usbfs_cleanup();
        usb_deregister(&usbfs_driver);
        usbdev_cleanup();
        usb_hub_cleanup();
        usb_host_cleanup();
        bus_unregister(&usb_bus_type);
        ksuspend_usb_cleanup();
}

subsys_initcall(usb_init);
module_exit(usb_exit);

/*
 * USB may be built into the kernel or be built as modules.
 * These symbols are exported for device (or host controller)
 * driver modules to use.
 */

EXPORT_SYMBOL(usb_disabled);

EXPORT_SYMBOL_GPL(usb_get_intf);
EXPORT_SYMBOL_GPL(usb_put_intf);

EXPORT_SYMBOL(usb_put_dev);
EXPORT_SYMBOL(usb_get_dev);
EXPORT_SYMBOL(usb_hub_tt_clear_buffer);

EXPORT_SYMBOL(usb_lock_device_for_reset);

EXPORT_SYMBOL(usb_find_interface);
EXPORT_SYMBOL(usb_ifnum_to_if);
EXPORT_SYMBOL(usb_altnum_to_altsetting);

EXPORT_SYMBOL(__usb_get_extra_descriptor);

EXPORT_SYMBOL(usb_find_device);
EXPORT_SYMBOL(usb_get_current_frame_number);

EXPORT_SYMBOL(usb_buffer_alloc);
EXPORT_SYMBOL(usb_buffer_free);

#if 0
EXPORT_SYMBOL(usb_buffer_map);
EXPORT_SYMBOL(usb_buffer_dmasync);
EXPORT_SYMBOL(usb_buffer_unmap);
#endif

EXPORT_SYMBOL(usb_buffer_map_sg);
#if 0
EXPORT_SYMBOL(usb_buffer_dmasync_sg);
#endif
EXPORT_SYMBOL(usb_buffer_unmap_sg);

MODULE_LICENSE("GPL");