nuttx/drivers/usbhost/usbhost_skeleton.c

/****************************************************************************
 * drivers/usbhost/usbhost_skeleton.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <errno.h>
#include <debug.h>

#include <nuttx/irq.h>
#include <nuttx/kmalloc.h>
#include <nuttx/fs/fs.h>
#include <nuttx/arch.h>
#include <nuttx/mutex.h>
#include <nuttx/wqueue.h>

#include <nuttx/usb/usb.h>
#include <nuttx/usb/usbhost.h>

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/* Configuration ************************************************************/

#ifndef CONFIG_SCHED_WORKQUEUE
#  warning "Worker thread support is required (CONFIG_SCHED_WORKQUEUE)"
#endif

/* Driver support ***********************************************************/

/* The format used to construct device file path, defined for consistent use
 * from all places.
 */

#define DEV_FORMAT          "/dev/skel%c"
#define DEV_NAMELEN         12

/* Used in usbhost_cfgdesc() */

#define USBHOST_IFFOUND     0x01
#define USBHOST_BINFOUND    0x02
#define USBHOST_BOUTFOUND   0x04
#define USBHOST_ALLFOUND    0x07

#define USBHOST_MAX_CREFS   0x7fff

/****************************************************************************
 * Private Types
 ****************************************************************************/

/* This is the internal, private state of the USB host class driver. */

struct usbhost_state_s
{
  /* This is the externally visible portion of the state */

  struct usbhost_class_s  usbclass;

  /* The remainder of the fields are provide to the class driver */

  char            devchar;      /* char in /dev/skel[n] format name */
  volatile bool   disconnected; /* TRUE: Device has been disconnected */
  uint8_t         ifno;         /* Interface number */
  int16_t         crefs;        /* Reference count on the driver instance */
  mutex_t         lock;         /* Used for mutual exclusive access */
  struct work_s   work;         /* For interacting with the worker thread */
  FAR uint8_t    *tbuffer;      /* The allocated transfer buffer */
  size_t          tbuflen;      /* Size of the allocated transfer buffer */
  usbhost_ep_t    epin;         /* IN endpoint */
  usbhost_ep_t    epout;        /* OUT endpoint */
};

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

/* Memory allocation services */

static inline FAR struct usbhost_state_s *usbhost_allocclass(void);
static inline void usbhost_freeclass(FAR struct usbhost_state_s *usbclass);

/* Device name management */

static int usbhost_allocdevno(FAR struct usbhost_state_s *priv);
static void usbhost_freedevno(FAR struct usbhost_state_s *priv);
static inline void usbhost_mkdevname(FAR struct usbhost_state_s *priv,
                                     FAR char *devname);

/* Worker thread actions */

static void usbhost_destroy(FAR void *arg);

/* Helpers for usbhost_connect() */

static inline int usbhost_cfgdesc(FAR struct usbhost_state_s *priv,
                                  FAR const uint8_t *configdesc,
                                  int desclen);
static inline int usbhost_devinit(FAR struct usbhost_state_s *priv);

/* (Little Endian) Data helpers */

static inline uint16_t usbhost_getle16(const uint8_t *val);
static inline void usbhost_putle16(uint8_t *dest, uint16_t val);
static inline uint32_t usbhost_getle32(const uint8_t *val);
static void usbhost_putle32(uint8_t *dest, uint32_t val);

/* Transfer descriptor memory management */

static inline int usbhost_talloc(FAR struct usbhost_state_s *priv);
static inline int usbhost_tfree(FAR struct usbhost_state_s *priv);

/* struct usbhost_registry_s methods */

static struct usbhost_class_s *
  usbhost_create(FAR struct usbhost_hubport_s *hport,
                 FAR const struct usbhost_id_s *id);

/* struct usbhost_class_s methods */

static int usbhost_connect(FAR struct usbhost_class_s *usbclass,
                           FAR const uint8_t *configdesc, int desclen);
static int usbhost_disconnected(FAR struct usbhost_class_s *usbclass);

/* Driver methods --
 * depend upon the type of NuttX driver interface exported
 */

/****************************************************************************
 * Private Data
 ****************************************************************************/

/* This structure provides the registry entry ID information that will be
 * used to associate the USB host class driver to a connected USB device.
 */

static const struct usbhost_id_s g_id =
{
  0,  /* base -- Must be one of the USB_CLASS_* definitions in usb.h */
  0,  /* subclass -- depends on the device */
  0,  /* proto -- depends on the device    */
  0,  /* vid      */
  0   /* pid      */
};

/* This is the USB host class' registry entry */

static struct usbhost_registry_s g_skeleton =
{
  NULL,                   /* flink    */
  usbhost_create,         /* create   */
  1,                      /* nids     */
  &g_id                   /* id[]     */
};

/* The bitmap depicting allocated device names in "/dev/skel[a-z]". */

static uint32_t g_devinuse;

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: usbhost_allocclass
 *
 * Description:
 *   This is really part of the logic that implements the create() method
 *   of struct usbhost_registry_s.  This function allocates memory for one
 *   new class instance.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   On success, this function will return a non-NULL instance of struct
 *   usbhost_class_s.  NULL is returned on failure; this function will
 *   will fail only if there are insufficient resources to create another
 *   USB host class instance.
 *
 ****************************************************************************/

static inline FAR struct usbhost_state_s *usbhost_allocclass(void)
{
  FAR struct usbhost_state_s *priv;

  DEBUGASSERT(!up_interrupt_context());

  priv = (FAR struct usbhost_state_s *)
    kmm_malloc(sizeof(struct usbhost_state_s));

  uinfo("Allocated: %p\n", priv);
  return priv;
}

/****************************************************************************
 * Name: usbhost_freeclass
 *
 * Description:
 *   Free a class instance previously allocated by usbhost_allocclass().
 *
 * Input Parameters:
 *   usbclass - A reference to the class instance to be freed.
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

static inline void usbhost_freeclass(FAR struct usbhost_state_s *usbclass)
{
  DEBUGASSERT(usbclass != NULL);

  /* Free the class instance (perhaps calling sched_kmm_free() in case we are
   * executing from an interrupt handler.
   */

  uinfo("Freeing: %p\n", usbclass);
  kmm_free(usbclass);
}

/****************************************************************************
 * Name: Device name management
 *
 * Description:
 *   Some tiny functions to coordinate management of device names.
 *
 ****************************************************************************/

static int usbhost_allocdevno(FAR struct usbhost_state_s *priv)
{
  irqstate_t flags;
  int devno;

  flags = enter_critical_section();
  for (devno = 0; devno < 26; devno++)
    {
      uint32_t bitno = 1 << devno;
      if ((g_devinuse & bitno) == 0)
        {
          g_devinuse |= bitno;
          priv->devchar = 'a' + devno;
          leave_critical_section(flags);
          return OK;
        }
    }

  leave_critical_section(flags);
  return -EMFILE;
}

static void usbhost_freedevno(FAR struct usbhost_state_s *priv)
{
  int devno = 'a' - priv->devchar;

  if (devno >= 0 && devno < 26)
    {
      irqstate_t flags = enter_critical_section();
      g_devinuse &= ~(1 << devno);
      leave_critical_section(flags);
    }
}

static inline void usbhost_mkdevname(FAR struct usbhost_state_s *priv,
                                     FAR char *devname)
{
  snprintf(devname, DEV_NAMELEN, DEV_FORMAT, priv->devchar);
}

/****************************************************************************
 * Name: usbhost_destroy
 *
 * Description:
 *   The USB device has been disconnected and the reference count on the USB
 *   host class instance has gone to 1.. Time to destroy the USB host class
 *   instance.
 *
 * Input Parameters:
 *   arg - A reference to the class instance to be destroyed.
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

static void usbhost_destroy(FAR void *arg)
{
  FAR struct usbhost_state_s *priv = (FAR struct usbhost_state_s *)arg;
  FAR struct usbhost_hubport_s *hport;
  FAR struct usbhost_driver_s *drvr;

  DEBUGASSERT(priv != NULL && priv->usbclass.hport != NULL);
  hport = priv->usbclass.hport;

  DEBUGASSERT(hport->drvr);
  drvr = hport->drvr;

  uinfo("crefs: %d\n", priv->crefs);

  /* Unregister the driver */

  /* Release the device name used by this connection */

  usbhost_freedevno(priv);

  /* Free the endpoints */

  /* Free any transfer buffers */

  /* Free the function address assigned to this device */

  usbhost_devaddr_destroy(hport, hport->funcaddr);
  hport->funcaddr = 0;

  /* Destroy the semaphores */

  /* Disconnect the USB host device */

  DRVR_DISCONNECT(drvr, hport);

  /* And free the class instance.  Hmmm.. this may execute on the worker
   * thread and the work structure is part of what is getting freed.  That
   * should be okay because once the work contained is removed from the
   * queue, it should not longer be accessed by the worker thread.
   */

  usbhost_freeclass(priv);
}

/****************************************************************************
 * Name: usbhost_cfgdesc
 *
 * Description:
 *   This function implements the connect() method of struct
 *   usbhost_class_s.  This method is a callback into the class
 *   implementation.  It is used to provide the device's configuration
 *   descriptor to the class so that the class may initialize properly
 *
 * Input Parameters:
 *   priv - The USB host class instance.
 *   configdesc - A pointer to a uint8_t buffer container the configuration
 *     descriptor.
 *   desclen - The length in bytes of the configuration descriptor.
 *
 * Returned Value:
 *   On success, zero (OK) is returned. On a failure, a negated errno value
 *   is returned indicating the nature of the failure
 *
 * Assumptions:
 *   This function will *not* be called from an interrupt handler.
 *
 ****************************************************************************/

static inline int usbhost_cfgdesc(FAR struct usbhost_state_s *priv,
                                  FAR const uint8_t *configdesc, int desclen)
{
  FAR struct usbhost_hubport_s *hport;
  FAR struct usb_cfgdesc_s *cfgdesc;
  FAR struct usb_desc_s *desc;
  FAR struct usbhost_epdesc_s bindesc;
  FAR struct usbhost_epdesc_s boutdesc;
  int remaining;
  uint8_t found = 0;
  int ret;

  DEBUGASSERT(priv != NULL && priv->usbclass.hport &&
              configdesc != NULL && desclen >= sizeof(struct usb_cfgdesc_s));
  hport = priv->usbclass.hport;

  /* Verify that we were passed a configuration descriptor */

  cfgdesc = (FAR struct usb_cfgdesc_s *)configdesc;
  if (cfgdesc->type != USB_DESC_TYPE_CONFIG)
    {
      return -EINVAL;
    }

  /* Get the total length of the configuration descriptor (little endian).
   * It might be a good check to get the number of interfaces here too.
   */

  remaining = (int)usbhost_getle16(cfgdesc->totallen);

  /* Skip to the next entry descriptor */

  configdesc += cfgdesc->len;
  remaining  -= cfgdesc->len;

  /* Loop where there are more dscriptors to examine */

  while (remaining >= sizeof(struct usb_desc_s))
    {
      /* What is the next descriptor? */

      desc = (FAR struct usb_desc_s *)configdesc;
      switch (desc->type)
        {
        /* Interface descriptor. We really should get the number of endpoints
         * from this descriptor too.
         */

        case USB_DESC_TYPE_INTERFACE:
          {
            FAR struct usb_ifdesc_s *ifdesc =
              (FAR struct usb_ifdesc_s *)configdesc;

            uinfo("Interface descriptor\n");
            DEBUGASSERT(remaining >= USB_SIZEOF_IFDESC);

            /* Save the interface number and mark ONLY the interface found */

            priv->ifno = ifdesc->ifno;
            found      = USBHOST_IFFOUND;
          }
          break;

        /* Endpoint descriptor.  Here, we expect two bulk endpoints, an IN
         * and an OUT.
         */

        case USB_DESC_TYPE_ENDPOINT:
          {
            FAR struct usb_epdesc_s *epdesc =
              (FAR struct usb_epdesc_s *)configdesc;

            uinfo("Endpoint descriptor\n");
            DEBUGASSERT(remaining >= USB_SIZEOF_EPDESC);

            /* Check for a bulk endpoint. */

            if ((epdesc->attr & USB_EP_ATTR_XFERTYPE_MASK) ==
                USB_EP_ATTR_XFER_BULK)
              {
                /* Yes.. it is a bulk endpoint.  IN or OUT? */

                if (USB_ISEPOUT(epdesc->addr))
                  {
                    /* It is an OUT bulk endpoint.  There should be only one
                     * bulk OUT endpoint.
                     */

                    if ((found & USBHOST_BOUTFOUND) != 0)
                      {
                        /* Oops.. more than one endpoint.  We don't know
                         * what to do with this.
                         */

                        return -EINVAL;
                      }

                    found |= USBHOST_BOUTFOUND;

                    /* Save the bulk OUT endpoint information */

                    boutdesc.hport        = hport;
                    boutdesc.addr         = epdesc->addr &
                                            USB_EP_ADDR_NUMBER_MASK;
                    boutdesc.in           = false;
                    boutdesc.xfrtype      = USB_EP_ATTR_XFER_BULK;
                    boutdesc.interval     = epdesc->interval;
                    boutdesc.mxpacketsize =
                      usbhost_getle16(epdesc->mxpacketsize);

                    uinfo("Bulk OUT EP addr:%d mxpacketsize:%d\n",
                          boutdesc.addr, boutdesc.mxpacketsize);
                  }
                else
                  {
                    /* It is an IN bulk endpoint.  There should be only one
                     * bulk IN endpoint.
                     */

                    if ((found & USBHOST_BINFOUND) != 0)
                      {
                        /* Oops.. more than one endpoint.  We don't know
                         * what to do with this.
                         */

                        return -EINVAL;
                      }

                    found |= USBHOST_BINFOUND;

                    /* Save the bulk IN endpoint information */

                    bindesc.hport        = hport;
                    bindesc.addr         = epdesc->addr &
                                           USB_EP_ADDR_NUMBER_MASK;
                    bindesc.in           = 1;
                    bindesc.xfrtype      = USB_EP_ATTR_XFER_BULK;
                    bindesc.interval     = epdesc->interval;
                    bindesc.mxpacketsize =
                      usbhost_getle16(epdesc->mxpacketsize);

                    uinfo("Bulk IN EP addr:%d mxpacketsize:%d\n",
                          bindesc.addr, bindesc.mxpacketsize);
                  }
              }
          }
          break;

        /* Other descriptors are just ignored for now */

        default:
          break;
        }

      /* If we found everything we need with this interface, then break out
       * of the loop early.
       */

      if (found == USBHOST_ALLFOUND)
        {
          break;
        }

      /* Increment the address of the next descriptor */

      configdesc += desc->len;
      remaining  -= desc->len;
    }

  /* Sanity checking... did we find all of things that we need? */

  if (found != USBHOST_ALLFOUND)
    {
      uerr("ERROR: Found IF:%s BIN:%s BOUT:%s\n",
           (found & USBHOST_IFFOUND) != 0  ? "YES" : "NO",
           (found & USBHOST_BINFOUND) != 0 ? "YES" : "NO",
           (found & USBHOST_BOUTFOUND) != 0 ? "YES" : "NO");
      return -EINVAL;
    }

  /* We are good... Allocate the endpoints */

  ret = DRVR_EPALLOC(hport->drvr, &boutdesc, &priv->epout);
  if (ret < 0)
    {
      uerr("ERROR: Failed to allocate Bulk OUT endpoint\n");
      return ret;
    }

  ret = DRVR_EPALLOC(hport->drvr, &bindesc, &priv->epin);
  if (ret < 0)
    {
      uerr("ERROR: Failed to allocate Bulk IN endpoint\n");
      DRVR_EPFREE(hport->drvr, priv->epout);
      return ret;
    }

  uinfo("Endpoints allocated\n");
  return OK;
}

/****************************************************************************
 * Name: usbhost_devinit
 *
 * Description:
 *   The USB device has been successfully connected.  This completes the
 *   initialization operations.  It is first called after the
 *   configuration descriptor has been received.
 *
 *   This function is called from the connect() method.  This function always
 *   executes on the thread of the caller of connect().
 *
 * Input Parameters:
 *   priv - A reference to the class instance.
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

static inline int usbhost_devinit(FAR struct usbhost_state_s *priv)
{
  int ret = OK;

  /* Set aside a transfer buffer for exclusive use by the class driver */

  /* Increment the reference count.  This will prevent usbhost_destroy() from
   * being called asynchronously if the device is removed.
   */

  priv->crefs++;
  DEBUGASSERT(priv->crefs == 2);

  /* Configure the device */

  /* Register the driver */

  if (ret >= 0)
    {
      char devname[DEV_NAMELEN];

      uinfo("Register block driver\n");
      usbhost_mkdevname(priv, devname);
#if 0 /* Finish me */
      ret = register_blockdriver(devname, &g_bops, 0, priv);
#endif
    }

  /* Check if we successfully initialized. We now have to be concerned
   * about asynchronous modification of crefs because the block
   * driver has been registered.
   */

  if (ret >= 0)
    {
      ret = nxmutex_lock(&priv->lock);
      if (ret < 0)
        {
          return ret;
        }

      DEBUGASSERT(priv->crefs >= 2);

      /* Handle a corner case where (1) open() has been called so the
       * reference count is > 2, but the device has been disconnected.
       * In this case, the class instance needs to persist until close()
       * is called.
       */

      if (priv->crefs <= 2 && priv->disconnected)
        {
          /* We don't have to give the semaphore because it will be
           * destroyed when usb_destroy is called.
           */

          ret = -ENODEV;
        }
      else
        {
          /* Ready for normal operation as a block device driver */

          uinfo("Successfully initialized\n");
          priv->crefs--;
        }

      nxmutex_unlock(&priv->lock);
    }

  return ret;
}

/****************************************************************************
 * Name: usbhost_getle16
 *
 * Description:
 *   Get a (possibly unaligned) 16-bit little endian value.
 *
 * Input Parameters:
 *   val - A pointer to the first byte of the little endian value.
 *
 * Returned Value:
 *   A uint16_t representing the whole 16-bit integer value
 *
 ****************************************************************************/

static inline uint16_t usbhost_getle16(const uint8_t *val)
{
  return (uint16_t)val[1] << 8 | (uint16_t)val[0];
}

/****************************************************************************
 * Name: usbhost_putle16
 *
 * Description:
 *   Put a (possibly unaligned) 16-bit little endian value.
 *
 * Input Parameters:
 *   dest - A pointer to the first byte to save the little endian value.
 *   val - The 16-bit value to be saved.
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

static void usbhost_putle16(uint8_t *dest, uint16_t val)
{
  dest[0] = val & 0xff; /* Little endian means LS byte first in byte stream */
  dest[1] = val >> 8;
}

/****************************************************************************
 * Name: usbhost_getle32
 *
 * Description:
 *   Get a (possibly unaligned) 32-bit little endian value.
 *
 * Input Parameters:
 *   dest - A pointer to the first byte to save the big endian value.
 *   val - The 32-bit value to be saved.
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

static inline uint32_t usbhost_getle32(const uint8_t *val)
{
  /* Little endian means LS halfword first in byte stream */

  return (uint32_t)usbhost_getle16(&val[2]) << 16 |
         (uint32_t)usbhost_getle16(val);
}

/****************************************************************************
 * Name: usbhost_putle32
 *
 * Description:
 *   Put a (possibly unaligned) 32-bit little endian value.
 *
 * Input Parameters:
 *   dest - A pointer to the first byte to save the little endian value.
 *   val - The 32-bit value to be saved.
 *
 * Returned Value:
 *   None
 *
 ****************************************************************************/

static void usbhost_putle32(uint8_t *dest, uint32_t val)
{
  /* Little endian means LS halfword first in byte stream */

  usbhost_putle16(dest, (uint16_t)(val & 0xffff));
  usbhost_putle16(dest + 2, (uint16_t)(val >> 16));
}

/****************************************************************************
 * Name: usbhost_talloc
 *
 * Description:
 *   Allocate transfer buffer memory.
 *
 * Input Parameters:
 *   priv - A reference to the class instance.
 *
 * Returned Value:
 *   On success, zero (OK) is returned.  On failure, an negated errno value
 *   is returned to indicate the nature of the failure.
 *
 ****************************************************************************/

static inline int usbhost_talloc(FAR struct usbhost_state_s *priv)
{
  FAR struct usbhost_hubport_s *hport;

  DEBUGASSERT(priv != NULL && priv->usbclass.hport != NULL &&
              priv->tbuffer == NULL);
  hport = priv->usbclass.hport;

  return DRVR_ALLOC(hport->drvr, &priv->tbuffer, &priv->tbuflen);
}

/****************************************************************************
 * Name: usbhost_tfree
 *
 * Description:
 *   Free transfer buffer memory.
 *
 * Input Parameters:
 *   priv - A reference to the class instance.
 *
 * Returned Value:
 *   On success, zero (OK) is returned.  On failure, an negated errno value
 *   is returned to indicate the nature of the failure.
 *
 ****************************************************************************/

static inline int usbhost_tfree(FAR struct usbhost_state_s *priv)
{
  FAR struct usbhost_hubport_s *hport;
  int result = OK;

  DEBUGASSERT(priv != NULL && priv->usbclass.hport != NULL);

  if (priv->tbuffer)
    {
      hport          = priv->usbclass.hport;
      result         = DRVR_FREE(hport->drvr, priv->tbuffer);
      priv->tbuffer = NULL;
      priv->tbuflen = 0;
    }

  return result;
}

/****************************************************************************
 * struct usbhost_registry_s methods
 ****************************************************************************/

/****************************************************************************
 * Name: usbhost_create
 *
 * Description:
 *   This function implements the create() method of struct
 *   usbhost_registry_s.  The create() method is a callback into the class
 *   implementation.  It is used to (1) create a new instance of the USB
 *   host class state and to (2) bind a USB host driver "session" to the
 *   class instance.  Use of this create() method will support environments
 *   where there may be multiple USB ports and multiple USB devices
 *   simultaneously connected.
 *
 * Input Parameters:
 *   hport - The hub hat manages the new class instance.
 *   id - In the case where the device supports multiple base classes,
 *     subclasses, or protocols, this specifies which to configure for.
 *
 * Returned Value:
 *   On success, this function will return a non-NULL instance of struct
 *   usbhost_class_s that can be used by the USB host driver to communicate
 *   with the USB host class.  NULL is returned on failure; this function
 *   will fail only if the hport input parameter is NULL or if there are
 *   insufficient resources to create another USB host class instance.
 *
 ****************************************************************************/

static FAR struct usbhost_class_s *
  usbhost_create(FAR struct usbhost_hubport_s *hport,
                 FAR const struct usbhost_id_s *id)
{
  FAR struct usbhost_state_s *priv;

  /* Allocate a USB host class instance */

  priv = usbhost_allocclass();
  if (priv)
    {
      /* Initialize the allocated storage class instance */

      memset(priv, 0, sizeof(struct usbhost_state_s));

      /* Assign a device number to this class instance */

      if (usbhost_allocdevno(priv) == OK)
        {
          /* Initialize class method function pointers */

          priv->usbclass.hport        = hport;
          priv->usbclass.connect      = usbhost_connect;
          priv->usbclass.disconnected = usbhost_disconnected;

          /* The initial reference count is 1...
           * One reference is held by the driver
           */

          priv->crefs = 1;

          /* Initialize mutex
           * (this works okay in the interrupt context)
           */

          nxmutex_init(&priv->lock);

          /* Return the instance of the USB class driver */

          return &priv->usbclass;
        }
    }

  /* An error occurred. Free the allocation and return NULL on all failures */

  if (priv)
    {
      usbhost_freeclass(priv);
    }

  return NULL;
}

/****************************************************************************
 * struct usbhost_class_s methods
 ****************************************************************************/

/****************************************************************************
 * Name: usbhost_connect
 *
 * Description:
 *   This function implements the connect() method of struct
 *   usbhost_class_s.  This method is a callback into the class
 *   implementation.  It is used to provide the device's configuration
 *   descriptor to the class so that the class may initialize properly
 *
 * Input Parameters:
 *   usbclass - The USB host class entry previously obtained from a call to
 *     create().
 *   configdesc - A pointer to a uint8_t buffer container the configuration
 *     descriptor.
 *   desclen - The length in bytes of the configuration descriptor.
 *
 * Returned Value:
 *   On success, zero (OK) is returned. On a failure, a negated errno value
 *   is returned indicating the nature of the failure
 *
 *   NOTE that the class instance remains valid upon return with a failure.
 *   It is the responsibility of the higher level enumeration logic to call
 *   CLASS_DISCONNECTED to free up the class driver resources.
 *
 * Assumptions:
 *   - This function will *not* be called from an interrupt handler.
 *   - If this function returns an error, the USB host controller driver
 *     must call to DISCONNECTED method to recover from the error
 *
 ****************************************************************************/

static int usbhost_connect(FAR struct usbhost_class_s *usbclass,
                           FAR const uint8_t *configdesc, int desclen)
{
  FAR struct usbhost_state_s *priv = (FAR struct usbhost_state_s *)usbclass;
  int ret;

  DEBUGASSERT(priv != NULL &&
              configdesc != NULL &&
              desclen >= sizeof(struct usb_cfgdesc_s));

  /* Parse the configuration descriptor to get the endpoints */

  ret = usbhost_cfgdesc(priv, configdesc, desclen);
  if (ret < 0)
    {
      uerr("ERROR: usbhost_cfgdesc() failed: %d\n", ret);
    }
  else
    {
      /* Now configure the device and register the NuttX driver */

      ret = usbhost_devinit(priv);
      if (ret < 0)
        {
          uerr("ERROR: usbhost_devinit() failed: %d\n", ret);
        }
    }

  return ret;
}

/****************************************************************************
 * Name: usbhost_disconnected
 *
 * Description:
 *   This function implements the disconnected() method of struct
 *   usbhost_class_s.  This method is a callback into the class
 *   implementation.  It is used to inform the class that the USB device has
 *   been disconnected.
 *
 * Input Parameters:
 *   usbclass - The USB host class entry previously obtained from a call to
 *     create().
 *
 * Returned Value:
 *   On success, zero (OK) is returned. On a failure, a negated errno value
 *   is returned indicating the nature of the failure
 *
 * Assumptions:
 *   This function may be called from an interrupt handler.
 *
 ****************************************************************************/

static int usbhost_disconnected(struct usbhost_class_s *usbclass)
{
  FAR struct usbhost_state_s *priv = (FAR struct usbhost_state_s *)usbclass;
  irqstate_t flags;

  DEBUGASSERT(priv != NULL);

  /* Set an indication to any users of the device that the device is no
   * longer available.
   */

  flags              = enter_critical_section();
  priv->disconnected = true;

  /* Now check the number of references on the class instance.  If it is one,
   * then we can free the class instance now.  Otherwise, we will have to
   * wait until the holders of the references free them by closing the
   * block driver.
   */

  uinfo("crefs: %d\n", priv->crefs);
  if (priv->crefs == 1)
    {
      /* Destroy the class instance.  If we are executing from an interrupt
       * handler, then defer the destruction to the worker thread.
       * Otherwise, destroy the instance now.
       */

      if (up_interrupt_context())
        {
          /* Destroy the instance on the worker thread. */

          uinfo("Queuing destruction: worker %p->%p\n",
                priv->work.worker, usbhost_destroy);

          DEBUGASSERT(priv->work.worker == NULL);
          work_queue(HPWORK, &priv->work, usbhost_destroy, priv, 0);
        }
      else
        {
          /* Do the work now */

          usbhost_destroy(priv);
        }
    }

  leave_critical_section(flags);
  return OK;
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: usbhost_skelinit
 *
 * Description:
 *   Initialize the USB class driver.  This function should be called
 *   be platform-specific code in order to initialize and register support
 *   for the USB host class device.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   On success this function will return zero (OK);  A negated errno value
 *   will be returned on failure.
 *
 ****************************************************************************/

int usbhost_skelinit(void)
{
  /* Perform any one-time initialization of the class implementation */

  /* Advertise our availability to support (certain) devices */

  return usbhost_registerclass(&g_skeleton);
}