Index: uspace/drv/bus/usb/usbmid/usbmid.c
===================================================================
--- uspace/drv/bus/usb/usbmid/usbmid.c	(revision 26e7d6da331e8d35b5e83880a9740de5e9e4bd99)
+++ uspace/drv/bus/usb/usbmid/usbmid.c	(revision 26e7d6da331e8d35b5e83880a9740de5e9e4bd99)
@@ -0,0 +1,152 @@
+/*
+ * Copyright (c) 2011 Vojtech Horky
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ * - The name of the author may not be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/** @addtogroup drvusbmid
+ * @{
+ */
+/**
+ * @file
+ * Helper functions.
+ */
+#include <errno.h>
+#include <str_error.h>
+#include <stdlib.h>
+#include <usb_iface.h>
+#include <usb/ddfiface.h>
+#include <usb/dev/pipes.h>
+#include <usb/classes/classes.h>
+#include <usb/dev/recognise.h>
+#include "usbmid.h"
+
+/** Callback for DDF USB interface. */
+static int usb_iface_get_address_impl(ddf_fun_t *fun, devman_handle_t handle,
+    usb_address_t *address)
+{
+	return usb_iface_get_address_hub_impl(fun, handle, address);
+}
+
+/** Callback for DDF USB interface. */
+static int usb_iface_get_interface_impl(ddf_fun_t *fun, devman_handle_t handle,
+    int *iface_no)
+{
+	assert(fun);
+
+	usbmid_interface_t *iface = fun->driver_data;
+	assert(iface);
+
+	if (iface_no != NULL) {
+		*iface_no = iface->interface_no;
+	}
+
+	return EOK;
+}
+
+/** DDF interface of the child - interface function. */
+static usb_iface_t child_usb_iface = {
+	.get_hc_handle = usb_iface_get_hc_handle_hub_child_impl,
+	.get_address = usb_iface_get_address_impl,
+	.get_interface = usb_iface_get_interface_impl
+};
+
+/** Operations for children - interface functions. */
+static ddf_dev_ops_t child_device_ops = {
+	.interfaces[USB_DEV_IFACE] = &child_usb_iface
+};
+
+
+/** Spawn new child device from one interface.
+ *
+ * @param parent Parent MID device.
+ * @param iface Interface information.
+ * @param device_descriptor Device descriptor.
+ * @param interface_descriptor Interface descriptor.
+ * @return Error code.
+ */
+int usbmid_spawn_interface_child(usb_device_t *parent,
+    usbmid_interface_t *iface,
+    const usb_standard_device_descriptor_t *device_descriptor,
+    const usb_standard_interface_descriptor_t *interface_descriptor)
+{
+	ddf_fun_t *child = NULL;
+	char *child_name = NULL;
+	int rc;
+
+	/*
+	 * Name is class name followed by interface number.
+	 * The interface number shall provide uniqueness while the
+	 * class name something humanly understandable.
+	 */
+	rc = asprintf(&child_name, "%s%d",
+	    usb_str_class(interface_descriptor->interface_class),
+	    (int) interface_descriptor->interface_number);
+	if (rc < 0) {
+		goto error_leave;
+	}
+
+	/* Create the device. */
+	child = ddf_fun_create(parent->ddf_dev, fun_inner, child_name);
+	if (child == NULL) {
+		rc = ENOMEM;
+		goto error_leave;
+	}
+
+	iface->fun = child;
+
+	child->driver_data = iface;
+	child->ops = &child_device_ops;
+
+	rc = usb_device_create_match_ids_from_interface(device_descriptor,
+	    interface_descriptor,
+	    &child->match_ids);
+	if (rc != EOK) {
+		goto error_leave;
+	}
+
+	rc = ddf_fun_bind(child);
+	if (rc != EOK) {
+		goto error_leave;
+	}
+
+	return EOK;
+
+error_leave:
+	if (child != NULL) {
+		child->name = NULL;
+		/* This takes care of match_id deallocation as well. */
+		ddf_fun_destroy(child);
+	}
+	if (child_name != NULL) {
+		free(child_name);
+	}
+
+	return rc;
+}
+
+/**
+ * @}
+ */
