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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/scatterlist.h>
#include <linux/usb/quirks.h>
#include <asm/byteorder.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_endpoint_num(&urb->ep->desc),
                  usb_urb_dir_in(urb) ? "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, usb_pipein(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_endpoint_num(&urb->ep->desc),
                  usb_urb_dir_in(urb) ? "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, usb_pipein(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_GART_IOMMU)
                  io->urbs[i]->transfer_buffer = NULL;
#else
                  io->urbs[i]->transfer_buffer = sg_virt(&sg[i]);
#endif
            } else {
                  /* hc may use _only_ transfer_buffer */
                  io->urbs [i]->transfer_buffer = sg_virt(&sg[i]);
                  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) {
            ep->enabled = 0;
            usb_hcd_flush_endpoint(dev, ep);
            usb_hcd_disable_endpoint(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.
 */
void usb_enable_endpoint(struct usb_device *dev, struct usb_host_endpoint *ep)
{
      int epnum = usb_endpoint_num(&ep->desc);
      int is_out = usb_endpoint_dir_out(&ep->desc);
      int is_control = usb_endpoint_xfer_control(&ep->desc);

      if (is_out || is_control) {
            usb_settoggle(dev, epnum, 1, 0);
            dev->ep_out[epnum] = ep;
      }
      if (!is_out || is_control) {
            usb_settoggle(dev, epnum, 0, 0);
            dev->ep_in[epnum] = ep;
      }
      ep->enabled = 1;
}

/*
 * 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 (iface->cur_altsetting != alt && 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;
}

static 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, struct kobj_uevent_env *env)
{
      struct usb_device *usb_dev;
      struct usb_interface *intf;
      struct usb_host_interface *alt;

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

      if (add_uevent_var(env, "INTERFACE=%d/%d/%d",
               alt->desc.bInterfaceClass,
               alt->desc.bInterfaceSubClass,
               alt->desc.bInterfaceProtocol))
            return -ENOMEM;

      if (add_uevent_var(env,
               "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;

      return 0;
}

#else

static int usb_if_uevent(struct device *dev, struct kobj_uevent_env *env)
{
      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 a non-authorized device (dev->authorized == 0) will only
 * be put in unconfigured mode.
 *
 * 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 (dev->authorized == 0 || 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\n");
                  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\n");
                        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);


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