USB: allow retry on descriptor fetch errors

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / drivers / usb / core / message.c

/*
 * message.c - synchronous message handling
 */

#include <linux/pci.h>  /* for scatterlist macros */
#include <linux/usb.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/timer.h>
#include <linux/ctype.h>
#include <linux/device.h>
#include <linux/usb/quirks.h>
#include <asm/byteorder.h>
#include <asm/scatterlist.h>

#include "hcd.h"        /* for usbcore internals */
#include "usb.h"

struct api_context {
        struct completion       done;
        int                     status;
};

static void usb_api_blocking_completion(struct urb *urb)
{
        struct api_context *ctx = urb->context;

        ctx->status = urb->status;
        complete(&ctx->done);
}


/*
 * Starts urb and waits for completion or timeout. Note that this call
 * is NOT interruptible. Many device driver i/o requests should be
 * interruptible and therefore these drivers should implement their
 * own interruptible routines.
 */
static int usb_start_wait_urb(struct urb *urb, int timeout, int *actual_length)
{ 
        struct api_context ctx;
        unsigned long expire;
        int retval;

        init_completion(&ctx.done);
        urb->context = &ctx;
        urb->actual_length = 0;
        retval = usb_submit_urb(urb, GFP_NOIO);
        if (unlikely(retval))
                goto out;

        expire = timeout ? msecs_to_jiffies(timeout) : MAX_SCHEDULE_TIMEOUT;
        if (!wait_for_completion_timeout(&ctx.done, expire)) {
                usb_kill_urb(urb);
                retval = (ctx.status == -ENOENT ? -ETIMEDOUT : ctx.status);

                dev_dbg(&urb->dev->dev,
                        "%s timed out on ep%d%s len=%d/%d\n",
                        current->comm,
                        usb_pipeendpoint(urb->pipe),
                        usb_pipein(urb->pipe) ? "in" : "out",
                        urb->actual_length,
                        urb->transfer_buffer_length);
        } else
                retval = ctx.status;
out:
        if (actual_length)
                *actual_length = urb->actual_length;

        usb_free_urb(urb);
        return retval;
}

/*-------------------------------------------------------------------*/
// returns status (negative) or length (positive)
static int usb_internal_control_msg(struct usb_device *usb_dev,
                                    unsigned int pipe, 
                                    struct usb_ctrlrequest *cmd,
                                    void *data, int len, int timeout)
{
        struct urb *urb;
        int retv;
        int length;

        urb = usb_alloc_urb(0, GFP_NOIO);
        if (!urb)
                return -ENOMEM;
  
        usb_fill_control_urb(urb, usb_dev, pipe, (unsigned char *)cmd, data,
                             len, usb_api_blocking_completion, NULL);

        retv = usb_start_wait_urb(urb, timeout, &length);
        if (retv < 0)
                return retv;
        else
                return length;
}

/**
 *      usb_control_msg - Builds a control urb, sends it off and waits for completion
 *      @dev: pointer to the usb device to send the message to
 *      @pipe: endpoint "pipe" to send the message to
 *      @request: USB message request value
 *      @requesttype: USB message request type value
 *      @value: USB message value
 *      @index: USB message index value
 *      @data: pointer to the data to send
 *      @size: length in bytes of the data to send
 *      @timeout: time in msecs to wait for the message to complete before
 *              timing out (if 0 the wait is forever)
 *      Context: !in_interrupt ()
 *
 *      This function sends a simple control message to a specified endpoint
 *      and waits for the message to complete, or timeout.
 *      
 *      If successful, it returns the number of bytes transferred, otherwise a negative error number.
 *
 *      Don't use this function from within an interrupt context, like a
 *      bottom half handler.  If you need an asynchronous message, or need to send
 *      a message from within interrupt context, use usb_submit_urb()
 *      If a thread in your driver uses this call, make sure your disconnect()
 *      method can wait for it to complete.  Since you don't have a handle on
 *      the URB used, you can't cancel the request.
 */
int usb_control_msg(struct usb_device *dev, unsigned int pipe, __u8 request, __u8 requesttype,
                         __u16 value, __u16 index, void *data, __u16 size, int timeout)
{
        struct usb_ctrlrequest *dr = kmalloc(sizeof(struct usb_ctrlrequest), GFP_NOIO);
        int ret;
        
        if (!dr)
                return -ENOMEM;

        dr->bRequestType= requesttype;
        dr->bRequest = request;
        dr->wValue = cpu_to_le16p(&value);
        dr->wIndex = cpu_to_le16p(&index);
        dr->wLength = cpu_to_le16p(&size);

        //dbg("usb_control_msg");       

        ret = usb_internal_control_msg(dev, pipe, dr, data, size, timeout);

        kfree(dr);

        return ret;
}


/**
 * usb_interrupt_msg - Builds an interrupt urb, sends it off and waits for completion
 * @usb_dev: pointer to the usb device to send the message to
 * @pipe: endpoint "pipe" to send the message to
 * @data: pointer to the data to send
 * @len: length in bytes of the data to send
 * @actual_length: pointer to a location to put the actual length transferred in bytes
 * @timeout: time in msecs to wait for the message to complete before
 *      timing out (if 0 the wait is forever)
 * Context: !in_interrupt ()
 *
 * This function sends a simple interrupt message to a specified endpoint and
 * waits for the message to complete, or timeout.
 *
 * If successful, it returns 0, otherwise a negative error number.  The number
 * of actual bytes transferred will be stored in the actual_length paramater.
 *
 * Don't use this function from within an interrupt context, like a bottom half
 * handler.  If you need an asynchronous message, or need to send a message
 * from within interrupt context, use usb_submit_urb() If a thread in your
 * driver uses this call, make sure your disconnect() method can wait for it to
 * complete.  Since you don't have a handle on the URB used, you can't cancel
 * the request.
 */
int usb_interrupt_msg(struct usb_device *usb_dev, unsigned int pipe,
                      void *data, int len, int *actual_length, int timeout)
{
        return usb_bulk_msg(usb_dev, pipe, data, len, actual_length, timeout);
}
EXPORT_SYMBOL_GPL(usb_interrupt_msg);

/**
 *      usb_bulk_msg - Builds a bulk urb, sends it off and waits for completion
 *      @usb_dev: pointer to the usb device to send the message to
 *      @pipe: endpoint "pipe" to send the message to
 *      @data: pointer to the data to send
 *      @len: length in bytes of the data to send
 *      @actual_length: pointer to a location to put the actual length transferred in bytes
 *      @timeout: time in msecs to wait for the message to complete before
 *              timing out (if 0 the wait is forever)
 *      Context: !in_interrupt ()
 *
 *      This function sends a simple bulk message to a specified endpoint
 *      and waits for the message to complete, or timeout.
 *      
 *      If successful, it returns 0, otherwise a negative error number.
 *      The number of actual bytes transferred will be stored in the 
 *      actual_length paramater.
 *
 *      Don't use this function from within an interrupt context, like a
 *      bottom half handler.  If you need an asynchronous message, or need to
 *      send a message from within interrupt context, use usb_submit_urb()
 *      If a thread in your driver uses this call, make sure your disconnect()
 *      method can wait for it to complete.  Since you don't have a handle on
 *      the URB used, you can't cancel the request.
 *
 *      Because there is no usb_interrupt_msg() and no USBDEVFS_INTERRUPT
 *      ioctl, users are forced to abuse this routine by using it to submit
 *      URBs for interrupt endpoints.  We will take the liberty of creating
 *      an interrupt URB (with the default interval) if the target is an
 *      interrupt endpoint.
 */
int usb_bulk_msg(struct usb_device *usb_dev, unsigned int pipe, 
                        void *data, int len, int *actual_length, int timeout)
{
        struct urb *urb;
        struct usb_host_endpoint *ep;

        ep = (usb_pipein(pipe) ? usb_dev->ep_in : usb_dev->ep_out)
                        [usb_pipeendpoint(pipe)];
        if (!ep || len < 0)
                return -EINVAL;

        urb = usb_alloc_urb(0, GFP_KERNEL);
        if (!urb)
                return -ENOMEM;

        if ((ep->desc.bmAttributes & USB_ENDPOINT_XFERTYPE_MASK) ==
                        USB_ENDPOINT_XFER_INT) {
                pipe = (pipe & ~(3 << 30)) | (PIPE_INTERRUPT << 30);
                usb_fill_int_urb(urb, usb_dev, pipe, data, len,
                                usb_api_blocking_completion, NULL,
                                ep->desc.bInterval);
        } else
                usb_fill_bulk_urb(urb, usb_dev, pipe, data, len,
                                usb_api_blocking_completion, NULL);

        return usb_start_wait_urb(urb, timeout, actual_length);
}

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

static void sg_clean (struct usb_sg_request *io)
{
        if (io->urbs) {
                while (io->entries--)
                        usb_free_urb (io->urbs [io->entries]);
                kfree (io->urbs);
                io->urbs = NULL;
        }
        if (io->dev->dev.dma_mask != NULL)
                usb_buffer_unmap_sg (io->dev, io->pipe, io->sg, io->nents);
        io->dev = NULL;
}

static void sg_complete (struct urb *urb)
{
        struct usb_sg_request   *io = urb->context;
        int status = urb->status;

        spin_lock (&io->lock);

        /* In 2.5 we require hcds' endpoint queues not to progress after fault
         * reports, until the completion callback (this!) returns.  That lets
         * device driver code (like this routine) unlink queued urbs first,
         * if it needs to, since the HC won't work on them at all.  So it's
         * not possible for page N+1 to overwrite page N, and so on.
         *
         * That's only for "hard" faults; "soft" faults (unlinks) sometimes
         * complete before the HCD can get requests away from hardware,
         * though never during cleanup after a hard fault.
         */
        if (io->status
                        && (io->status != -ECONNRESET
                                || status != -ECONNRESET)
                        && urb->actual_length) {
                dev_err (io->dev->bus->controller,
                        "dev %s ep%d%s scatterlist error %d/%d\n",
                        io->dev->devpath,
                        usb_pipeendpoint (urb->pipe),
                        usb_pipein (urb->pipe) ? "in" : "out",
                        status, io->status);
                // BUG ();
        }

        if (io->status == 0 && status && status != -ECONNRESET) {
                int i, found, retval;

                io->status = status;

                /* the previous urbs, and this one, completed already.
                 * unlink pending urbs so they won't rx/tx bad data.
                 * careful: unlink can sometimes be synchronous...
                 */
                spin_unlock (&io->lock);
                for (i = 0, found = 0; i < io->entries; i++) {
                        if (!io->urbs [i] || !io->urbs [i]->dev)
                                continue;
                        if (found) {
                                retval = usb_unlink_urb (io->urbs [i]);
                                if (retval != -EINPROGRESS &&
                                    retval != -ENODEV &&
                                    retval != -EBUSY)
                                        dev_err (&io->dev->dev,
                                                "%s, unlink --> %d\n",
                                                __FUNCTION__, retval);
                        } else if (urb == io->urbs [i])
                                found = 1;
                }
                spin_lock (&io->lock);
        }
        urb->dev = NULL;

        /* on the last completion, signal usb_sg_wait() */
        io->bytes += urb->actual_length;
        io->count--;
        if (!io->count)
                complete (&io->complete);

        spin_unlock (&io->lock);
}


/**
 * usb_sg_init - initializes scatterlist-based bulk/interrupt I/O request
 * @io: request block being initialized.  until usb_sg_wait() returns,
 *      treat this as a pointer to an opaque block of memory,
 * @dev: the usb device that will send or receive the data
 * @pipe: endpoint "pipe" used to transfer the data
 * @period: polling rate for interrupt endpoints, in frames or
 *      (for high speed endpoints) microframes; ignored for bulk
 * @sg: scatterlist entries
 * @nents: how many entries in the scatterlist
 * @length: how many bytes to send from the scatterlist, or zero to
 *      send every byte identified in the list.
 * @mem_flags: SLAB_* flags affecting memory allocations in this call
 *
 * Returns zero for success, else a negative errno value.  This initializes a
 * scatter/gather request, allocating resources such as I/O mappings and urb
 * memory (except maybe memory used by USB controller drivers).
 *
 * The request must be issued using usb_sg_wait(), which waits for the I/O to
 * complete (or to be canceled) and then cleans up all resources allocated by
 * usb_sg_init().
 *
 * The request may be canceled with usb_sg_cancel(), either before or after
 * usb_sg_wait() is called.
 */
int usb_sg_init (
        struct usb_sg_request   *io,
        struct usb_device       *dev,
        unsigned                pipe, 
        unsigned                period,
        struct scatterlist      *sg,
        int                     nents,
        size_t                  length,
        gfp_t                   mem_flags
)
{
        int                     i;
        int                     urb_flags;
        int                     dma;

        if (!io || !dev || !sg
                        || usb_pipecontrol (pipe)
                        || usb_pipeisoc (pipe)
                        || nents <= 0)
                return -EINVAL;

        spin_lock_init (&io->lock);
        io->dev = dev;
        io->pipe = pipe;
        io->sg = sg;
        io->nents = nents;

        /* not all host controllers use DMA (like the mainstream pci ones);
         * they can use PIO (sl811) or be software over another transport.
         */
        dma = (dev->dev.dma_mask != NULL);
        if (dma)
                io->entries = usb_buffer_map_sg (dev, pipe, sg, nents);
        else
                io->entries = nents;

        /* initialize all the urbs we'll use */
        if (io->entries <= 0)
                return io->entries;

        io->count = io->entries;
        io->urbs = kmalloc (io->entries * sizeof *io->urbs, mem_flags);
        if (!io->urbs)
                goto nomem;

        urb_flags = URB_NO_TRANSFER_DMA_MAP | URB_NO_INTERRUPT;
        if (usb_pipein (pipe))
                urb_flags |= URB_SHORT_NOT_OK;

        for (i = 0; i < io->entries; i++) {
                unsigned                len;

                io->urbs [i] = usb_alloc_urb (0, mem_flags);
                if (!io->urbs [i]) {
                        io->entries = i;
                        goto nomem;
                }

                io->urbs [i]->dev = NULL;
                io->urbs [i]->pipe = pipe;
                io->urbs [i]->interval = period;
                io->urbs [i]->transfer_flags = urb_flags;

                io->urbs [i]->complete = sg_complete;
                io->urbs [i]->context = io;

                /*
                 * Some systems need to revert to PIO when DMA is temporarily
                 * unavailable.  For their sakes, both transfer_buffer and
                 * transfer_dma are set when possible.  However this can only
                 * work on systems without:
                 *
                 *  - HIGHMEM, since DMA buffers located in high memory are
                 *    not directly addressable by the CPU for PIO;
                 *
                 *  - IOMMU, since dma_map_sg() is allowed to use an IOMMU to
                 *    make virtually discontiguous buffers be "dma-contiguous"
                 *    so that PIO and DMA need diferent numbers of URBs.
                 *
                 * So when HIGHMEM or IOMMU are in use, transfer_buffer is NULL
                 * to prevent stale pointers and to help spot bugs.
                 */
                if (dma) {
                        io->urbs [i]->transfer_dma = sg_dma_address (sg + i);
                        len = sg_dma_len (sg + i);
#if defined(CONFIG_HIGHMEM) || defined(CONFIG_IOMMU)
                        io->urbs[i]->transfer_buffer = NULL;
#else
                        io->urbs[i]->transfer_buffer =
                                page_address(sg[i].page) + sg[i].offset;
#endif
                } else {
                        /* hc may use _only_ transfer_buffer */
                        io->urbs [i]->transfer_buffer =
                                page_address (sg [i].page) + sg [i].offset;
                        len = sg [i].length;
                }

                if (length) {
                        len = min_t (unsigned, len, length);
                        length -= len;
                        if (length == 0)
                                io->entries = i + 1;
                }
                io->urbs [i]->transfer_buffer_length = len;
        }
        io->urbs [--i]->transfer_flags &= ~URB_NO_INTERRUPT;

        /* transaction state */
        io->status = 0;
        io->bytes = 0;
        init_completion (&io->complete);
        return 0;

nomem:
        sg_clean (io);
        return -ENOMEM;
}


/**
 * usb_sg_wait - synchronously execute scatter/gather request
 * @io: request block handle, as initialized with usb_sg_init().
 *      some fields become accessible when this call returns.
 * Context: !in_interrupt ()
 *
 * This function blocks until the specified I/O operation completes.  It
 * leverages the grouping of the related I/O requests to get good transfer
 * rates, by queueing the requests.  At higher speeds, such queuing can
 * significantly improve USB throughput.
 *
 * There are three kinds of completion for this function.
 * (1) success, where io->status is zero.  The number of io->bytes
 *     transferred is as requested.
 * (2) error, where io->status is a negative errno value.  The number
 *     of io->bytes transferred before the error is usually less
 *     than requested, and can be nonzero.
 * (3) cancellation, a type of error with status -ECONNRESET that
 *     is initiated by usb_sg_cancel().
 *
 * When this function returns, all memory allocated through usb_sg_init() or
 * this call will have been freed.  The request block parameter may still be
 * passed to usb_sg_cancel(), or it may be freed.  It could also be
 * reinitialized and then reused.
 *
 * Data Transfer Rates:
 *
 * Bulk transfers are valid for full or high speed endpoints.
 * The best full speed data rate is 19 packets of 64 bytes each
 * per frame, or 1216 bytes per millisecond.
 * The best high speed data rate is 13 packets of 512 bytes each
 * per microframe, or 52 KBytes per millisecond.
 *
 * The reason to use interrupt transfers through this API would most likely
 * be to reserve high speed bandwidth, where up to 24 KBytes per millisecond
 * could be transferred.  That capability is less useful for low or full
 * speed interrupt endpoints, which allow at most one packet per millisecond,
 * of at most 8 or 64 bytes (respectively).
 */
void usb_sg_wait (struct usb_sg_request *io)
{
        int             i, entries = io->entries;

        /* queue the urbs.  */
        spin_lock_irq (&io->lock);
        i = 0;
        while (i < entries && !io->status) {
                int     retval;

                io->urbs [i]->dev = io->dev;
                retval = usb_submit_urb (io->urbs [i], GFP_ATOMIC);

                /* after we submit, let completions or cancelations fire;
                 * we handshake using io->status.
                 */
                spin_unlock_irq (&io->lock);
                switch (retval) {
                        /* maybe we retrying will recover */
                case -ENXIO:    // hc didn't queue this one
                case -EAGAIN:
                case -ENOMEM:
                        io->urbs[i]->dev = NULL;
                        retval = 0;
                        yield ();
                        break;

                        /* no error? continue immediately.
                         *
                         * NOTE: to work better with UHCI (4K I/O buffer may
                         * need 3K of TDs) it may be good to limit how many
                         * URBs are queued at once; N milliseconds?
                         */
                case 0:
                        ++i;
                        cpu_relax ();
                        break;

                        /* fail any uncompleted urbs */
                default:
                        io->urbs [i]->dev = NULL;
                        io->urbs [i]->status = retval;
                        dev_dbg (&io->dev->dev, "%s, submit --> %d\n",
                                __FUNCTION__, retval);
                        usb_sg_cancel (io);
                }
                spin_lock_irq (&io->lock);
                if (retval && (io->status == 0 || io->status == -ECONNRESET))
                        io->status = retval;
        }
        io->count -= entries - i;
        if (io->count == 0)
                complete (&io->complete);
        spin_unlock_irq (&io->lock);

        /* OK, yes, this could be packaged as non-blocking.
         * So could the submit loop above ... but it's easier to
         * solve neither problem than to solve both!
         */
        wait_for_completion (&io->complete);

        sg_clean (io);
}

/**
 * usb_sg_cancel - stop scatter/gather i/o issued by usb_sg_wait()
 * @io: request block, initialized with usb_sg_init()
 *
 * This stops a request after it has been started by usb_sg_wait().
 * It can also prevents one initialized by usb_sg_init() from starting,
 * so that call just frees resources allocated to the request.
 */
void usb_sg_cancel (struct usb_sg_request *io)
{
        unsigned long   flags;

        spin_lock_irqsave (&io->lock, flags);

        /* shut everything down, if it didn't already */
        if (!io->status) {
                int     i;

                io->status = -ECONNRESET;
                spin_unlock (&io->lock);
                for (i = 0; i < io->entries; i++) {
                        int     retval;

                        if (!io->urbs [i]->dev)
                                continue;
                        retval = usb_unlink_urb (io->urbs [i]);
                        if (retval != -EINPROGRESS && retval != -EBUSY)
                                dev_warn (&io->dev->dev, "%s, unlink --> %d\n",
                                        __FUNCTION__, retval);
                }
                spin_lock (&io->lock);
        }
        spin_unlock_irqrestore (&io->lock, flags);
}

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

/**
 * usb_get_descriptor - issues a generic GET_DESCRIPTOR request
 * @dev: the device whose descriptor is being retrieved
 * @type: the descriptor type (USB_DT_*)
 * @index: the number of the descriptor
 * @buf: where to put the descriptor
 * @size: how big is "buf"?
 * Context: !in_interrupt ()
 *
 * Gets a USB descriptor.  Convenience functions exist to simplify
 * getting some types of descriptors.  Use
 * usb_get_string() or usb_string() for USB_DT_STRING.
 * Device (USB_DT_DEVICE) and configuration descriptors (USB_DT_CONFIG)
 * are part of the device structure.
 * In addition to a number of USB-standard descriptors, some
 * devices also use class-specific or vendor-specific descriptors.
 *
 * This call is synchronous, and may not be used in an interrupt context.
 *
 * Returns the number of bytes received on success, or else the status code
 * returned by the underlying usb_control_msg() call.
 */
int usb_get_descriptor(struct usb_device *dev, unsigned char type, unsigned char index, void *buf, int size)
{
        int i;
        int result;
        
        memset(buf,0,size);     // Make sure we parse really received data

        for (i = 0; i < 3; ++i) {
                /* retry on length 0 or error; some devices are flakey */
                result = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
                                USB_REQ_GET_DESCRIPTOR, USB_DIR_IN,
                                (type << 8) + index, 0, buf, size,
                                USB_CTRL_GET_TIMEOUT);
                if (result <= 0 && result != -ETIMEDOUT)
                        continue;
                if (result > 1 && ((u8 *)buf)[1] != type) {
                        result = -EPROTO;
                        continue;
                }
                break;
        }
        return result;
}

/**
 * usb_get_string - gets a string descriptor
 * @dev: the device whose string descriptor is being retrieved
 * @langid: code for language chosen (from string descriptor zero)
 * @index: the number of the descriptor
 * @buf: where to put the string
 * @size: how big is "buf"?
 * Context: !in_interrupt ()
 *
 * Retrieves a string, encoded using UTF-16LE (Unicode, 16 bits per character,
 * in little-endian byte order).
 * The usb_string() function will often be a convenient way to turn
 * these strings into kernel-printable form.
 *
 * Strings may be referenced in device, configuration, interface, or other
 * descriptors, and could also be used in vendor-specific ways.
 *
 * This call is synchronous, and may not be used in an interrupt context.
 *
 * Returns the number of bytes received on success, or else the status code
 * returned by the underlying usb_control_msg() call.
 */
static int usb_get_string(struct usb_device *dev, unsigned short langid,
                          unsigned char index, void *buf, int size)
{
        int i;
        int result;

        for (i = 0; i < 3; ++i) {
                /* retry on length 0 or stall; some devices are flakey */
                result = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
                        USB_REQ_GET_DESCRIPTOR, USB_DIR_IN,
                        (USB_DT_STRING << 8) + index, langid, buf, size,
                        USB_CTRL_GET_TIMEOUT);
                if (!(result == 0 || result == -EPIPE))
                        break;
        }
        return result;
}

static void usb_try_string_workarounds(unsigned char *buf, int *length)
{
        int newlength, oldlength = *length;

        for (newlength = 2; newlength + 1 < oldlength; newlength += 2)
                if (!isprint(buf[newlength]) || buf[newlength + 1])
                        break;

        if (newlength > 2) {
                buf[0] = newlength;
                *length = newlength;
        }
}

static int usb_string_sub(struct usb_device *dev, unsigned int langid,
                unsigned int index, unsigned char *buf)
{
        int rc;

        /* Try to read the string descriptor by asking for the maximum
         * possible number of bytes */
        if (dev->quirks & USB_QUIRK_STRING_FETCH_255)
                rc = -EIO;
        else
                rc = usb_get_string(dev, langid, index, buf, 255);

        /* If that failed try to read the descriptor length, then
         * ask for just that many bytes */
        if (rc < 2) {
                rc = usb_get_string(dev, langid, index, buf, 2);
                if (rc == 2)
                        rc = usb_get_string(dev, langid, index, buf, buf[0]);
        }

        if (rc >= 2) {
                if (!buf[0] && !buf[1])
                        usb_try_string_workarounds(buf, &rc);

                /* There might be extra junk at the end of the descriptor */
                if (buf[0] < rc)
                        rc = buf[0];

                rc = rc - (rc & 1); /* force a multiple of two */
        }

        if (rc < 2)
                rc = (rc < 0 ? rc : -EINVAL);

        return rc;
}

/**
 * usb_string - returns ISO 8859-1 version of a string descriptor
 * @dev: the device whose string descriptor is being retrieved
 * @index: the number of the descriptor
 * @buf: where to put the string
 * @size: how big is "buf"?
 * Context: !in_interrupt ()
 * 
 * This converts the UTF-16LE encoded strings returned by devices, from
 * usb_get_string_descriptor(), to null-terminated ISO-8859-1 encoded ones
 * that are more usable in most kernel contexts.  Note that all characters
 * in the chosen descriptor that can't be encoded using ISO-8859-1
 * are converted to the question mark ("?") character, and this function
 * chooses strings in the first language supported by the device.
 *
 * The ASCII (or, redundantly, "US-ASCII") character set is the seven-bit
 * subset of ISO 8859-1. ISO-8859-1 is the eight-bit subset of Unicode,
 * and is appropriate for use many uses of English and several other
 * Western European languages.  (But it doesn't include the "Euro" symbol.)
 *
 * This call is synchronous, and may not be used in an interrupt context.
 *
 * Returns length of the string (>= 0) or usb_control_msg status (< 0).
 */
int usb_string(struct usb_device *dev, int index, char *buf, size_t size)
{
        unsigned char *tbuf;
        int err;
        unsigned int u, idx;

        if (dev->state == USB_STATE_SUSPENDED)
                return -EHOSTUNREACH;
        if (size <= 0 || !buf || !index)
                return -EINVAL;
        buf[0] = 0;
        tbuf = kmalloc(256, GFP_KERNEL);
        if (!tbuf)
                return -ENOMEM;

        /* get langid for strings if it's not yet known */
        if (!dev->have_langid) {
                err = usb_string_sub(dev, 0, 0, tbuf);
                if (err < 0) {
                        dev_err (&dev->dev,
                                "string descriptor 0 read error: %d\n",
                                err);
                        goto errout;
                } else if (err < 4) {
                        dev_err (&dev->dev, "string descriptor 0 too short\n");
                        err = -EINVAL;
                        goto errout;
                } else {
                        dev->have_langid = 1;
                        dev->string_langid = tbuf[2] | (tbuf[3]<< 8);
                                /* always use the first langid listed */
                        dev_dbg (&dev->dev, "default language 0x%04x\n",
                                dev->string_langid);
                }
        }
        
        err = usb_string_sub(dev, dev->string_langid, index, tbuf);
        if (err < 0)
                goto errout;

        size--;         /* leave room for trailing NULL char in output buffer */
        for (idx = 0, u = 2; u < err; u += 2) {
                if (idx >= size)
                        break;
                if (tbuf[u+1])                  /* high byte */
                        buf[idx++] = '?';  /* non ISO-8859-1 character */
                else
                        buf[idx++] = tbuf[u];
        }
        buf[idx] = 0;
        err = idx;

        if (tbuf[1] != USB_DT_STRING)
                dev_dbg(&dev->dev, "wrong descriptor type %02x for string %d (\"%s\")\n", tbuf[1], index, buf);

 errout:
        kfree(tbuf);
        return err;
}

/**
 * usb_cache_string - read a string descriptor and cache it for later use
 * @udev: the device whose string descriptor is being read
 * @index: the descriptor index
 *
 * Returns a pointer to a kmalloc'ed buffer containing the descriptor string,
 * or NULL if the index is 0 or the string could not be read.
 */
char *usb_cache_string(struct usb_device *udev, int index)
{
        char *buf;
        char *smallbuf = NULL;
        int len;

        if (index > 0 && (buf = kmalloc(256, GFP_KERNEL)) != NULL) {
                if ((len = usb_string(udev, index, buf, 256)) > 0) {
                        if ((smallbuf = kmalloc(++len, GFP_KERNEL)) == NULL)
                                return buf;
                        memcpy(smallbuf, buf, len);
                }
                kfree(buf);
        }
        return smallbuf;
}

/*
 * usb_get_device_descriptor - (re)reads the device descriptor (usbcore)
 * @dev: the device whose device descriptor is being updated
 * @size: how much of the descriptor to read
 * Context: !in_interrupt ()
 *
 * Updates the copy of the device descriptor stored in the device structure,
 * which dedicates space for this purpose.
 *
 * Not exported, only for use by the core.  If drivers really want to read
 * the device descriptor directly, they can call usb_get_descriptor() with
 * type = USB_DT_DEVICE and index = 0.
 *
 * This call is synchronous, and may not be used in an interrupt context.
 *
 * Returns the number of bytes received on success, or else the status code
 * returned by the underlying usb_control_msg() call.
 */
int usb_get_device_descriptor(struct usb_device *dev, unsigned int size)
{
        struct usb_device_descriptor *desc;
        int ret;

        if (size > sizeof(*desc))
                return -EINVAL;
        desc = kmalloc(sizeof(*desc), GFP_NOIO);
        if (!desc)
                return -ENOMEM;

        ret = usb_get_descriptor(dev, USB_DT_DEVICE, 0, desc, size);
        if (ret >= 0) 
                memcpy(&dev->descriptor, desc, size);
        kfree(desc);
        return ret;
}

/**
 * usb_get_status - issues a GET_STATUS call
 * @dev: the device whose status is being checked
 * @type: USB_RECIP_*; for device, interface, or endpoint
 * @target: zero (for device), else interface or endpoint number
 * @data: pointer to two bytes of bitmap data
 * Context: !in_interrupt ()
 *
 * Returns device, interface, or endpoint status.  Normally only of
 * interest to see if the device is self powered, or has enabled the
 * remote wakeup facility; or whether a bulk or interrupt endpoint
 * is halted ("stalled").
 *
 * Bits in these status bitmaps are set using the SET_FEATURE request,
 * and cleared using the CLEAR_FEATURE request.  The usb_clear_halt()
 * function should be used to clear halt ("stall") status.
 *
 * This call is synchronous, and may not be used in an interrupt context.
 *
 * Returns the number of bytes received on success, or else the status code
 * returned by the underlying usb_control_msg() call.
 */
int usb_get_status(struct usb_device *dev, int type, int target, void *data)
{
        int ret;
        u16 *status = kmalloc(sizeof(*status), GFP_KERNEL);

        if (!status)
                return -ENOMEM;

        ret = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
                USB_REQ_GET_STATUS, USB_DIR_IN | type, 0, target, status,
                sizeof(*status), USB_CTRL_GET_TIMEOUT);

        *(u16 *)data = *status;
        kfree(status);
        return ret;
}

/**
 * usb_clear_halt - tells device to clear endpoint halt/stall condition
 * @dev: device whose endpoint is halted
 * @pipe: endpoint "pipe" being cleared
 * Context: !in_interrupt ()
 *
 * This is used to clear halt conditions for bulk and interrupt endpoints,
 * as reported by URB completion status.  Endpoints that are halted are
 * sometimes referred to as being "stalled".  Such endpoints are unable
 * to transmit or receive data until the halt status is cleared.  Any URBs
 * queued for such an endpoint should normally be unlinked by the driver
 * before clearing the halt condition, as described in sections 5.7.5
 * and 5.8.5 of the USB 2.0 spec.
 *
 * Note that control and isochronous endpoints don't halt, although control
 * endpoints report "protocol stall" (for unsupported requests) using the
 * same status code used to report a true stall.
 *
 * This call is synchronous, and may not be used in an interrupt context.
 *
 * Returns zero on success, or else the status code returned by the
 * underlying usb_control_msg() call.
 */
int usb_clear_halt(struct usb_device *dev, int pipe)
{
        int result;
        int endp = usb_pipeendpoint(pipe);
        
        if (usb_pipein (pipe))
                endp |= USB_DIR_IN;

        /* we don't care if it wasn't halted first. in fact some devices
         * (like some ibmcam model 1 units) seem to expect hosts to make
         * this request for iso endpoints, which can't halt!
         */
        result = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
                USB_REQ_CLEAR_FEATURE, USB_RECIP_ENDPOINT,
                USB_ENDPOINT_HALT, endp, NULL, 0,
                USB_CTRL_SET_TIMEOUT);

        /* don't un-halt or force to DATA0 except on success */
        if (result < 0)
                return result;

        /* NOTE:  seems like Microsoft and Apple don't bother verifying
         * the clear "took", so some devices could lock up if you check...
         * such as the Hagiwara FlashGate DUAL.  So we won't bother.
         *
         * NOTE:  make sure the logic here doesn't diverge much from
         * the copy in usb-storage, for as long as we need two copies.
         */

        /* toggle was reset by the clear */
        usb_settoggle(dev, usb_pipeendpoint(pipe), usb_pipeout(pipe), 0);

        return 0;
}

/**
 * usb_disable_endpoint -- Disable an endpoint by address
 * @dev: the device whose endpoint is being disabled
 * @epaddr: the endpoint's address.  Endpoint number for output,
 *      endpoint number + USB_DIR_IN for input
 *
 * Deallocates hcd/hardware state for this endpoint ... and nukes all
 * pending urbs.
 *
 * If the HCD hasn't registered a disable() function, this sets the
 * endpoint's maxpacket size to 0 to prevent further submissions.
 */
void usb_disable_endpoint(struct usb_device *dev, unsigned int epaddr)
{
        unsigned int epnum = epaddr & USB_ENDPOINT_NUMBER_MASK;
        struct usb_host_endpoint *ep;

        if (!dev)
                return;

        if (usb_endpoint_out(epaddr)) {
                ep = dev->ep_out[epnum];
                dev->ep_out[epnum] = NULL;
        } else {
                ep = dev->ep_in[epnum];
                dev->ep_in[epnum] = NULL;
        }
        if (ep && dev->bus)
                usb_hcd_endpoint_disable(dev, ep);
}

/**
 * usb_disable_interface -- Disable all endpoints for an interface
 * @dev: the device whose interface is being disabled
 * @intf: pointer to the interface descriptor
 *
 * Disables all the endpoints for the interface's current altsetting.
 */
void usb_disable_interface(struct usb_device *dev, struct usb_interface *intf)
{
        struct usb_host_interface *alt = intf->cur_altsetting;
        int i;

        for (i = 0; i < alt->desc.bNumEndpoints; ++i) {
                usb_disable_endpoint(dev,
                                alt->endpoint[i].desc.bEndpointAddress);
        }
}

/*
 * usb_disable_device - Disable all the endpoints for a USB device
 * @dev: the device whose endpoints are being disabled
 * @skip_ep0: 0 to disable endpoint 0, 1 to skip it.
 *
 * Disables all the device's endpoints, potentially including endpoint 0.
 * Deallocates hcd/hardware state for the endpoints (nuking all or most
 * pending urbs) and usbcore state for the interfaces, so that usbcore
 * must usb_set_configuration() before any interfaces could be used.
 */
void usb_disable_device(struct usb_device *dev, int skip_ep0)
{
        int i;

        dev_dbg(&dev->dev, "%s nuking %s URBs\n", __FUNCTION__,
                        skip_ep0 ? "non-ep0" : "all");
        for (i = skip_ep0; i < 16; ++i) {
                usb_disable_endpoint(dev, i);
                usb_disable_endpoint(dev, i + USB_DIR_IN);
        }
        dev->toggle[0] = dev->toggle[1] = 0;

        /* getting rid of interfaces will disconnect
         * any drivers bound to them (a key side effect)
         */
        if (dev->actconfig) {
                for (i = 0; i < dev->actconfig->desc.bNumInterfaces; i++) {
                        struct usb_interface    *interface;

                        /* remove this interface if it has been registered */
                        interface = dev->actconfig->interface[i];
                        if (!device_is_registered(&interface->dev))
                                continue;
                        dev_dbg (&dev->dev, "unregistering interface %s\n",
                                interface->dev.bus_id);
                        usb_remove_sysfs_intf_files(interface);
                        device_del (&interface->dev);
                }

                /* Now that the interfaces are unbound, nobody should
                 * try to access them.
                 */
                for (i = 0; i < dev->actconfig->desc.bNumInterfaces; i++) {
                        put_device (&dev->actconfig->interface[i]->dev);
                        dev->actconfig->interface[i] = NULL;
                }
                dev->actconfig = NULL;
                if (dev->state == USB_STATE_CONFIGURED)
                        usb_set_device_state(dev, USB_STATE_ADDRESS);
        }
}


/*
 * usb_enable_endpoint - Enable an endpoint for USB communications
 * @dev: the device whose interface is being enabled
 * @ep: the endpoint
 *
 * Resets the endpoint toggle, and sets dev->ep_{in,out} pointers.
 * For control endpoints, both the input and output sides are handled.
 */
static void
usb_enable_endpoint(struct usb_device *dev, struct usb_host_endpoint *ep)
{
        unsigned int epaddr = ep->desc.bEndpointAddress;
        unsigned int epnum = epaddr & USB_ENDPOINT_NUMBER_MASK;
        int is_control;

        is_control = ((ep->desc.bmAttributes & USB_ENDPOINT_XFERTYPE_MASK)
                        == USB_ENDPOINT_XFER_CONTROL);
        if (usb_endpoint_out(epaddr) || is_control) {
                usb_settoggle(dev, epnum, 1, 0);
                dev->ep_out[epnum] = ep;
        }
        if (!usb_endpoint_out(epaddr) || is_control) {
                usb_settoggle(dev, epnum, 0, 0);
                dev->ep_in[epnum] = ep;
        }
}

/*
 * usb_enable_interface - Enable all the endpoints for an interface
 * @dev: the device whose interface is being enabled
 * @intf: pointer to the interface descriptor
 *
 * Enables all the endpoints for the interface's current altsetting.
 */
static void usb_enable_interface(struct usb_device *dev,
                                 struct usb_interface *intf)
{
        struct usb_host_interface *alt = intf->cur_altsetting;
        int i;

        for (i = 0; i < alt->desc.bNumEndpoints; ++i)
                usb_enable_endpoint(dev, &alt->endpoint[i]);
}

/**
 * usb_set_interface - Makes a particular alternate setting be current
 * @dev: the device whose interface is being updated
 * @interface: the interface being updated
 * @alternate: the setting being chosen.
 * Context: !in_interrupt ()
 *
 * This is used to enable data transfers on interfaces that may not
 * be enabled by default.  Not all devices support such configurability.
 * Only the driver bound to an interface may change its setting.
 *
 * Within any given configuration, each interface may have several
 * alternative settings.  These are often used to control levels of
 * bandwidth consumption.  For example, the default setting for a high
 * speed interrupt endpoint may not send more than 64 bytes per microframe,
 * while interrupt transfers of up to 3KBytes per microframe are legal.
 * Also, isochronous endpoints may never be part of an
 * interface's default setting.  To access such bandwidth, alternate
 * interface settings must be made current.
 *
 * Note that in the Linux USB subsystem, bandwidth associated with
 * an endpoint in a given alternate setting is not reserved until an URB
 * is submitted that needs that bandwidth.  Some other operating systems
 * allocate bandwidth early, when a configuration is chosen.
 *
 * This call is synchronous, and may not be used in an interrupt context.
 * Also, drivers must not change altsettings while urbs are scheduled for
 * endpoints in that interface; all such urbs must first be completed
 * (perhaps forced by unlinking).
 *
 * Returns zero on success, or else the status code returned by the
 * underlying usb_control_msg() call.
 */
int usb_set_interface(struct usb_device *dev, int interface, int alternate)
{
        struct usb_interface *iface;
        struct usb_host_interface *alt;
        int ret;
        int manual = 0;

        if (dev->state == USB_STATE_SUSPENDED)
                return -EHOSTUNREACH;

        iface = usb_ifnum_to_if(dev, interface);
        if (!iface) {
                dev_dbg(&dev->dev, "selecting invalid interface %d\n",
                        interface);
                return -EINVAL;
        }

        alt = usb_altnum_to_altsetting(iface, alternate);
        if (!alt) {
                warn("selecting invalid altsetting %d", alternate);
                return -EINVAL;
        }

        ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
                                   USB_REQ_SET_INTERFACE, USB_RECIP_INTERFACE,
                                   alternate, interface, NULL, 0, 5000);

        /* 9.4.10 says devices don't need this and are free to STALL the
         * request if the interface only has one alternate setting.
         */
        if (ret == -EPIPE && iface->num_altsetting == 1) {
                dev_dbg(&dev->dev,
                        "manual set_interface for iface %d, alt %d\n",
                        interface, alternate);
                manual = 1;
        } else if (ret < 0)
                return ret;

        /* FIXME drivers shouldn't need to replicate/bugfix the logic here
         * when they implement async or easily-killable versions of this or
         * other "should-be-internal" functions (like clear_halt).
         * should hcd+usbcore postprocess control requests?
         */

        /* prevent submissions using previous endpoint settings */
        if (device_is_registered(&iface->dev))
                usb_remove_sysfs_intf_files(iface);
        usb_disable_interface(dev, iface);

        iface->cur_altsetting = alt;

        /* If the interface only has one altsetting and the device didn't
         * accept the request, we attempt to carry out the equivalent action
         * by manually clearing the HALT feature for each endpoint in the
         * new altsetting.
         */
        if (manual) {
                int i;

                for (i = 0; i < alt->desc.bNumEndpoints; i++) {
                        unsigned int epaddr =
                                alt->endpoint[i].desc.bEndpointAddress;
                        unsigned int pipe =
        __create_pipe(dev, USB_ENDPOINT_NUMBER_MASK & epaddr)
        | (usb_endpoint_out(epaddr) ? USB_DIR_OUT : USB_DIR_IN);

                        usb_clear_halt(dev, pipe);
                }
        }

        /* 9.1.1.5: reset toggles for all endpoints in the new altsetting
         *
         * Note:
         * Despite EP0 is always present in all interfaces/AS, the list of
         * endpoints from the descriptor does not contain EP0. Due to its
         * omnipresence one might expect EP0 being considered "affected" by
         * any SetInterface request and hence assume toggles need to be reset.
         * However, EP0 toggles are re-synced for every individual transfer
         * during the SETUP stage - hence EP0 toggles are "don't care" here.
         * (Likewise, EP0 never "halts" on well designed devices.)
         */
        usb_enable_interface(dev, iface);
        if (device_is_registered(&iface->dev))
                usb_create_sysfs_intf_files(iface);

        return 0;
}

/**
 * usb_reset_configuration - lightweight device reset
 * @dev: the device whose configuration is being reset
 *
 * This issues a standard SET_CONFIGURATION request to the device using
 * the current configuration.  The effect is to reset most USB-related
 * state in the device, including interface altsettings (reset to zero),
 * endpoint halts (cleared), and data toggle (only for bulk and interrupt
 * endpoints).  Other usbcore state is unchanged, including bindings of
 * usb device drivers to interfaces.
 *
 * Because this affects multiple interfaces, avoid using this with composite
 * (multi-interface) devices.  Instead, the driver for each interface may
 * use usb_set_interface() on the interfaces it claims.  Be careful though;
 * some devices don't support the SET_INTERFACE request, and others won't
 * reset all the interface state (notably data toggles).  Resetting the whole
 * configuration would affect other drivers' interfaces.
 *
 * The caller must own the device lock.
 *
 * Returns zero on success, else a negative error code.
 */
int usb_reset_configuration(struct usb_device *dev)
{
        int                     i, retval;
        struct usb_host_config  *config;

        if (dev->state == USB_STATE_SUSPENDED)
                return -EHOSTUNREACH;

        /* caller must have locked the device and must own
         * the usb bus readlock (so driver bindings are stable);
         * calls during probe() are fine
         */

        for (i = 1; i < 16; ++i) {
                usb_disable_endpoint(dev, i);
                usb_disable_endpoint(dev, i + USB_DIR_IN);
        }

        config = dev->actconfig;
        retval = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
                        USB_REQ_SET_CONFIGURATION, 0,
                        config->desc.bConfigurationValue, 0,
                        NULL, 0, USB_CTRL_SET_TIMEOUT);
        if (retval < 0)
                return retval;

        dev->toggle[0] = dev->toggle[1] = 0;

        /* re-init hc/hcd interface/endpoint state */
        for (i = 0; i < config->desc.bNumInterfaces; i++) {
                struct usb_interface *intf = config->interface[i];
                struct usb_host_interface *alt;

                if (device_is_registered(&intf->dev))
                        usb_remove_sysfs_intf_files(intf);
                alt = usb_altnum_to_altsetting(intf, 0);

                /* No altsetting 0?  We'll assume the first altsetting.
                 * We could use a GetInterface call, but if a device is
                 * so non-compliant that it doesn't have altsetting 0
                 * then I wouldn't trust its reply anyway.
                 */
                if (!alt)
                        alt = &intf->altsetting[0];

                intf->cur_altsetting = alt;
                usb_enable_interface(dev, intf);
                if (device_is_registered(&intf->dev))
                        usb_create_sysfs_intf_files(intf);
        }
        return 0;
}

void usb_release_interface(struct device *dev)
{
        struct usb_interface *intf = to_usb_interface(dev);
        struct usb_interface_cache *intfc =
                        altsetting_to_usb_interface_cache(intf->altsetting);

        kref_put(&intfc->ref, usb_release_interface_cache);
        kfree(intf);
}

#ifdef  CONFIG_HOTPLUG
static int usb_if_uevent(struct device *dev, char **envp, int num_envp,
                 char *buffer, int buffer_size)
{
        struct usb_device *usb_dev;
        struct usb_interface *intf;
        struct usb_host_interface *alt;
        int i = 0;
        int length = 0;

        if (!dev)
                return -ENODEV;

        /* driver is often null here; dev_dbg() would oops */
        pr_debug ("usb %s: uevent\n", dev->bus_id);

        intf = to_usb_interface(dev);
        usb_dev = interface_to_usbdev(intf);
        alt = intf->cur_altsetting;

        if (add_uevent_var(envp, num_envp, &i,
                   buffer, buffer_size, &length,
                   "INTERFACE=%d/%d/%d",
                   alt->desc.bInterfaceClass,
                   alt->desc.bInterfaceSubClass,
                   alt->desc.bInterfaceProtocol))
                return -ENOMEM;

        if (add_uevent_var(envp, num_envp, &i,
                   buffer, buffer_size, &length,
                   "MODALIAS=usb:v%04Xp%04Xd%04Xdc%02Xdsc%02Xdp%02Xic%02Xisc%02Xip%02X",
                   le16_to_cpu(usb_dev->descriptor.idVendor),
                   le16_to_cpu(usb_dev->descriptor.idProduct),
                   le16_to_cpu(usb_dev->descriptor.bcdDevice),
                   usb_dev->descriptor.bDeviceClass,
                   usb_dev->descriptor.bDeviceSubClass,
                   usb_dev->descriptor.bDeviceProtocol,
                   alt->desc.bInterfaceClass,
                   alt->desc.bInterfaceSubClass,
                   alt->desc.bInterfaceProtocol))
                return -ENOMEM;

        envp[i] = NULL;
        return 0;
}

#else

static int usb_if_uevent(struct device *dev, char **envp,
                         int num_envp, char *buffer, int buffer_size)
{
        return -ENODEV;
}
#endif  /* CONFIG_HOTPLUG */

struct device_type usb_if_device_type = {
        .name =         "usb_interface",
        .release =      usb_release_interface,
        .uevent =       usb_if_uevent,
};

static struct usb_interface_assoc_descriptor *find_iad(struct usb_device *dev,
                                                       struct usb_host_config *config,
                                                       u8 inum)
{
        struct usb_interface_assoc_descriptor *retval = NULL;
        struct usb_interface_assoc_descriptor *intf_assoc;
        int first_intf;
        int last_intf;
        int i;

        for (i = 0; (i < USB_MAXIADS && config->intf_assoc[i]); i++) {
                intf_assoc = config->intf_assoc[i];
                if (intf_assoc->bInterfaceCount == 0)
                        continue;

                first_intf = intf_assoc->bFirstInterface;
                last_intf = first_intf + (intf_assoc->bInterfaceCount - 1);
                if (inum >= first_intf && inum <= last_intf) {
                        if (!retval)
                                retval = intf_assoc;
                        else
                                dev_err(&dev->dev, "Interface #%d referenced"
                                        " by multiple IADs\n", inum);
                }
        }

        return retval;
}


/*
 * usb_set_configuration - Makes a particular device setting be current
 * @dev: the device whose configuration is being updated
 * @configuration: the configuration being chosen.
 * Context: !in_interrupt(), caller owns the device lock
 *
 * This is used to enable non-default device modes.  Not all devices
 * use this kind of configurability; many devices only have one
 * configuration.
 *
 * @configuration is the value of the configuration to be installed.
 * According to the USB spec (e.g. section 9.1.1.5), configuration values
 * must be non-zero; a value of zero indicates that the device in
 * unconfigured.  However some devices erroneously use 0 as one of their
 * configuration values.  To help manage such devices, this routine will
 * accept @configuration = -1 as indicating the device should be put in
 * an unconfigured state.
 *
 * USB device configurations may affect Linux interoperability,
 * power consumption and the functionality available.  For example,
 * the default configuration is limited to using 100mA of bus power,
 * so that when certain device functionality requires more power,
 * and the device is bus powered, that functionality should be in some
 * non-default device configuration.  Other device modes may also be
 * reflected as configuration options, such as whether two ISDN
 * channels are available independently; and choosing between open
 * standard device protocols (like CDC) or proprietary ones.
 *
 * Note that USB has an additional level of device configurability,
 * associated with interfaces.  That configurability is accessed using
 * usb_set_interface().
 *
 * This call is synchronous. The calling context must be able to sleep,
 * must own the device lock, and must not hold the driver model's USB
 * bus mutex; usb device driver probe() methods cannot use this routine.
 *
 * Returns zero on success, or else the status code returned by the
 * underlying call that failed.  On successful completion, each interface
 * in the original device configuration has been destroyed, and each one
 * in the new configuration has been probed by all relevant usb device
 * drivers currently known to the kernel.
 */
int usb_set_configuration(struct usb_device *dev, int configuration)
{
        int i, ret;
        struct usb_host_config *cp = NULL;
        struct usb_interface **new_interfaces = NULL;
        int n, nintf;

        if (configuration == -1)
                configuration = 0;
        else {
                for (i = 0; i < dev->descriptor.bNumConfigurations; i++) {
                        if (dev->config[i].desc.bConfigurationValue ==
                                        configuration) {
                                cp = &dev->config[i];
                                break;
                        }
                }
        }
        if ((!cp && configuration != 0))
                return -EINVAL;

        /* The USB spec says configuration 0 means unconfigured.
         * But if a device includes a configuration numbered 0,
         * we will accept it as a correctly configured state.
         * Use -1 if you really want to unconfigure the device.
         */
        if (cp && configuration == 0)
                dev_warn(&dev->dev, "config 0 descriptor??\n");

        /* Allocate memory for new interfaces before doing anything else,
         * so that if we run out then nothing will have changed. */
        n = nintf = 0;
        if (cp) {
                nintf = cp->desc.bNumInterfaces;
                new_interfaces = kmalloc(nintf * sizeof(*new_interfaces),
                                GFP_KERNEL);
                if (!new_interfaces) {
                        dev_err(&dev->dev, "Out of memory");
                        return -ENOMEM;
                }

                for (; n < nintf; ++n) {
                        new_interfaces[n] = kzalloc(
                                        sizeof(struct usb_interface),
                                        GFP_KERNEL);
                        if (!new_interfaces[n]) {
                                dev_err(&dev->dev, "Out of memory");
                                ret = -ENOMEM;
free_interfaces:
                                while (--n >= 0)
                                        kfree(new_interfaces[n]);
                                kfree(new_interfaces);
                                return ret;
                        }
                }

                i = dev->bus_mA - cp->desc.bMaxPower * 2;
                if (i < 0)
                        dev_warn(&dev->dev, "new config #%d exceeds power "
                                        "limit by %dmA\n",
                                        configuration, -i);
        }

        /* Wake up the device so we can send it the Set-Config request */
        ret = usb_autoresume_device(dev);
        if (ret)
                goto free_interfaces;

        /* if it's already configured, clear out old state first.
         * getting rid of old interfaces means unbinding their drivers.
         */
        if (dev->state != USB_STATE_ADDRESS)
                usb_disable_device (dev, 1);    // Skip ep0

        if ((ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
                        USB_REQ_SET_CONFIGURATION, 0, configuration, 0,
                        NULL, 0, USB_CTRL_SET_TIMEOUT)) < 0) {

                /* All the old state is gone, so what else can we do?
                 * The device is probably useless now anyway.
                 */
                cp = NULL;
        }

        dev->actconfig = cp;
        if (!cp) {
                usb_set_device_state(dev, USB_STATE_ADDRESS);
                usb_autosuspend_device(dev);
                goto free_interfaces;
        }
        usb_set_device_state(dev, USB_STATE_CONFIGURED);

        /* Initialize the new interface structures and the
         * hc/hcd/usbcore interface/endpoint state.
         */
        for (i = 0; i < nintf; ++i) {
                struct usb_interface_cache *intfc;
                struct usb_interface *intf;
                struct usb_host_interface *alt;

                cp->interface[i] = intf = new_interfaces[i];
                intfc = cp->intf_cache[i];
                intf->altsetting = intfc->altsetting;
                intf->num_altsetting = intfc->num_altsetting;
                intf->intf_assoc = find_iad(dev, cp, i);
                kref_get(&intfc->ref);

                alt = usb_altnum_to_altsetting(intf, 0);

                /* No altsetting 0?  We'll assume the first altsetting.
                 * We could use a GetInterface call, but if a device is
                 * so non-compliant that it doesn't have altsetting 0
                 * then I wouldn't trust its reply anyway.
                 */
                if (!alt)
                        alt = &intf->altsetting[0];

                intf->cur_altsetting = alt;
                usb_enable_interface(dev, intf);
                intf->dev.parent = &dev->dev;
                intf->dev.driver = NULL;
                intf->dev.bus = &usb_bus_type;
                intf->dev.type = &usb_if_device_type;
                intf->dev.dma_mask = dev->dev.dma_mask;
                device_initialize (&intf->dev);
                mark_quiesced(intf);
                sprintf (&intf->dev.bus_id[0], "%d-%s:%d.%d",
                         dev->bus->busnum, dev->devpath,
                         configuration, alt->desc.bInterfaceNumber);
        }
        kfree(new_interfaces);

        if (cp->string == NULL)
                cp->string = usb_cache_string(dev, cp->desc.iConfiguration);

        /* Now that all the interfaces are set up, register them
         * to trigger binding of drivers to interfaces.  probe()
         * routines may install different altsettings and may
         * claim() any interfaces not yet bound.  Many class drivers
         * need that: CDC, audio, video, etc.
         */
        for (i = 0; i < nintf; ++i) {
                struct usb_interface *intf = cp->interface[i];

                dev_dbg (&dev->dev,
                        "adding %s (config #%d, interface %d)\n",
                        intf->dev.bus_id, configuration,
                        intf->cur_altsetting->desc.bInterfaceNumber);
                ret = device_add (&intf->dev);
                if (ret != 0) {
                        dev_err(&dev->dev, "device_add(%s) --> %d\n",
                                intf->dev.bus_id, ret);
                        continue;
                }
                usb_create_sysfs_intf_files (intf);
        }

        usb_autosuspend_device(dev);
        return 0;
}

struct set_config_request {
        struct usb_device       *udev;
        int                     config;
        struct work_struct      work;
};

/* Worker routine for usb_driver_set_configuration() */
static void driver_set_config_work(struct work_struct *work)
{
        struct set_config_request *req =
                container_of(work, struct set_config_request, work);

        usb_lock_device(req->udev);
        usb_set_configuration(req->udev, req->config);
        usb_unlock_device(req->udev);
        usb_put_dev(req->udev);
        kfree(req);
}

/**
 * usb_driver_set_configuration - Provide a way for drivers to change device configurations
 * @udev: the device whose configuration is being updated
 * @config: the configuration being chosen.
 * Context: In process context, must be able to sleep
 *
 * Device interface drivers are not allowed to change device configurations.
 * This is because changing configurations will destroy the interface the
 * driver is bound to and create new ones; it would be like a floppy-disk
 * driver telling the computer to replace the floppy-disk drive with a
 * tape drive!
 *
 * Still, in certain specialized circumstances the need may arise.  This
 * routine gets around the normal restrictions by using a work thread to
 * submit the change-config request.
 *
 * Returns 0 if the request was succesfully queued, error code otherwise.
 * The caller has no way to know whether the queued request will eventually
 * succeed.
 */
int usb_driver_set_configuration(struct usb_device *udev, int config)
{
        struct set_config_request *req;

        req = kmalloc(sizeof(*req), GFP_KERNEL);
        if (!req)
                return -ENOMEM;
        req->udev = udev;
        req->config = config;
        INIT_WORK(&req->work, driver_set_config_work);

        usb_get_dev(udev);
        schedule_work(&req->work);
        return 0;
}
EXPORT_SYMBOL_GPL(usb_driver_set_configuration);

// synchronous request completion model
EXPORT_SYMBOL(usb_control_msg);
EXPORT_SYMBOL(usb_bulk_msg);

EXPORT_SYMBOL(usb_sg_init);
EXPORT_SYMBOL(usb_sg_cancel);
EXPORT_SYMBOL(usb_sg_wait);

// synchronous control message convenience routines
EXPORT_SYMBOL(usb_get_descriptor);
EXPORT_SYMBOL(usb_get_status);
EXPORT_SYMBOL(usb_string);

// synchronous calls that also maintain usbcore state
EXPORT_SYMBOL(usb_clear_halt);
EXPORT_SYMBOL(usb_reset_configuration);
EXPORT_SYMBOL(usb_set_interface);