drivers/usb/core/usb-acpi.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * USB-ACPI glue code
  *
  * Copyright 2012 Red Hat <mjg@redhat.com>
  */
 #include <linux/module.h>
 #include <linux/usb.h>
 #include <linux/device.h>
 #include <linux/errno.h>
 #include <linux/kernel.h>
 #include <linux/acpi.h>
 #include <linux/pci.h>
 #include <linux/usb/hcd.h>

 #include "hub.h"

 /**
  * usb_acpi_power_manageable - check whether usb port has
  * acpi power resource.
  * @hdev: USB device belonging to the usb hub
  * @index: port index based zero
  *
  * Return true if the port has acpi power resource and false if no.
  */
 bool usb_acpi_power_manageable(struct usb_device *hdev, int index)
 {
 	acpi_handle port_handle;
 	int port1 = index + 1;

 	port_handle = usb_get_hub_port_acpi_handle(hdev,
 		port1);
 	if (port_handle)
 		return acpi_bus_power_manageable(port_handle);
 	else
 		return false;
 }
 EXPORT_SYMBOL_GPL(usb_acpi_power_manageable);

 #define UUID_USB_CONTROLLER_DSM "ce2ee385-00e6-48cb-9f05-2edb927c4899"
 #define USB_DSM_DISABLE_U1_U2_FOR_PORT	5

 /**
  * usb_acpi_port_lpm_incapable - check if lpm should be disabled for a port.
  * @hdev: USB device belonging to the usb hub
  * @index: zero based port index
  *
  * Some USB3 ports may not support USB3 link power management U1/U2 states
  * due to different retimer setup. ACPI provides _DSM method which returns 0x01
  * if U1 and U2 states should be disabled. Evaluate _DSM with:
  * Arg0: UUID = ce2ee385-00e6-48cb-9f05-2edb927c4899
  * Arg1: Revision ID = 0
  * Arg2: Function Index = 5
  * Arg3: (empty)
  *
  * Return 1 if USB3 port is LPM incapable, negative on error, otherwise 0
  */

 int usb_acpi_port_lpm_incapable(struct usb_device *hdev, int index)
 {
 	union acpi_object *obj;
 	acpi_handle port_handle;
 	int port1 = index + 1;
 	guid_t guid;
 	int ret;

 	ret = guid_parse(UUID_USB_CONTROLLER_DSM, &guid);
 	if (ret)
 		return ret;

 	port_handle = usb_get_hub_port_acpi_handle(hdev, port1);
 	if (!port_handle) {
 		dev_dbg(&hdev->dev, "port-%d no acpi handle\n", port1);
 		return -ENODEV;
 	}

 	if (!acpi_check_dsm(port_handle, &guid, 0,
 			    BIT(USB_DSM_DISABLE_U1_U2_FOR_PORT))) {
 		dev_dbg(&hdev->dev, "port-%d no _DSM function %d\n",
 			port1, USB_DSM_DISABLE_U1_U2_FOR_PORT);
 		return -ENODEV;
 	}

 	obj = acpi_evaluate_dsm_typed(port_handle, &guid, 0,
 				      USB_DSM_DISABLE_U1_U2_FOR_PORT, NULL,
 				      ACPI_TYPE_INTEGER);
 	if (!obj) {
 		dev_dbg(&hdev->dev, "evaluate port-%d _DSM failed\n", port1);
 		return -EINVAL;
 	}

 	if (obj->integer.value == 0x01)
 		ret = 1;

 	ACPI_FREE(obj);

 	return ret;
 }
 EXPORT_SYMBOL_GPL(usb_acpi_port_lpm_incapable);

 /**
  * usb_acpi_set_power_state - control usb port's power via acpi power
  * resource
  * @hdev: USB device belonging to the usb hub
  * @index: port index based zero
  * @enable: power state expected to be set
  *
  * Notice to use usb_acpi_power_manageable() to check whether the usb port
  * has acpi power resource before invoking this function.
  *
  * Returns 0 on success, else negative errno.
  */
 int usb_acpi_set_power_state(struct usb_device *hdev, int index, bool enable)
 {
 	struct usb_hub *hub = usb_hub_to_struct_hub(hdev);
 	struct usb_port *port_dev;
 	acpi_handle port_handle;
 	unsigned char state;
 	int port1 = index + 1;
 	int error = -EINVAL;

 	if (!hub)
 		return -ENODEV;
 	port_dev = hub->ports[port1 - 1];

 	port_handle = (acpi_handle) usb_get_hub_port_acpi_handle(hdev, port1);
 	if (!port_handle)
 		return error;

 	if (enable)
 		state = ACPI_STATE_D0;
 	else
 		state = ACPI_STATE_D3_COLD;

 	error = acpi_bus_set_power(port_handle, state);
 	if (!error)
 		dev_dbg(&port_dev->dev, "acpi: power was set to %d\n", enable);
 	else
 		dev_dbg(&port_dev->dev, "acpi: power failed to be set\n");

 	return error;
 }
 EXPORT_SYMBOL_GPL(usb_acpi_set_power_state);

 /**
  * usb_acpi_add_usb4_devlink - add device link to USB4 Host Interface for tunneled USB3 devices
  *
  * @udev: Tunneled USB3 device connected to a roothub.
  *
  * Adds a device link between a tunneled USB3 device and the USB4 Host Interface
  * device to ensure correct runtime PM suspend and resume order. This function
  * should only be called for tunneled USB3 devices.
  * The USB4 Host Interface this tunneled device depends on is found from the roothub
  * port ACPI device specific data _DSD entry.
  *
  * Return: negative error code on failure, 0 otherwise
  */
 static int usb_acpi_add_usb4_devlink(struct usb_device *udev)
 {
 	const struct device_link *link;
 	struct usb_port *port_dev;
 	struct usb_hub *hub;

 	if (!udev->parent || udev->parent->parent)
 		return 0;

 	hub = usb_hub_to_struct_hub(udev->parent);
 	port_dev = hub->ports[udev->portnum - 1];

 	struct fwnode_handle *nhi_fwnode __free(fwnode_handle) =
 		fwnode_find_reference(dev_fwnode(&port_dev->dev), "usb4-host-interface", 0);

 	if (IS_ERR(nhi_fwnode) || !nhi_fwnode->dev)
 		return 0;

 	link = device_link_add(&port_dev->child->dev, nhi_fwnode->dev,
 			       DL_FLAG_STATELESS |
 			       DL_FLAG_RPM_ACTIVE |
 			       DL_FLAG_PM_RUNTIME);
 	if (!link) {
 		dev_err(&port_dev->dev, "Failed to created device link from %s to %s\n",
 			dev_name(&port_dev->child->dev), dev_name(nhi_fwnode->dev));
 		return -EINVAL;
 	}

 	dev_dbg(&port_dev->dev, "Created device link from %s to %s\n",
 		dev_name(&port_dev->child->dev), dev_name(nhi_fwnode->dev));

 	return 0;
 }

 /*
  * Private to usb-acpi, all the core needs to know is that
  * port_dev->location is non-zero when it has been set by the firmware.
  */
 #define USB_ACPI_LOCATION_VALID (1 << 31)

 static void
 usb_acpi_get_connect_type(struct usb_port *port_dev, acpi_handle *handle)
 {
 	enum usb_port_connect_type connect_type = USB_PORT_CONNECT_TYPE_UNKNOWN;
 	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
 	union acpi_object *upc = NULL;
 	struct acpi_pld_info *pld = NULL;
 	acpi_status status;

 	/*
 	 * According to 9.14 in ACPI Spec 6.2. _PLD indicates whether usb port
 	 * is user visible and _UPC indicates whether it is connectable. If
 	 * the port was visible and connectable, it could be freely connected
 	 * and disconnected with USB devices. If no visible and connectable,
 	 * a usb device is directly hard-wired to the port. If no visible and
 	 * no connectable, the port would be not used.
 	 */

 	status = acpi_get_physical_device_location(handle, &pld);
 	if (ACPI_SUCCESS(status) && pld)
 		port_dev->location = USB_ACPI_LOCATION_VALID |
 			pld->group_token << 8 | pld->group_position;

 	status = acpi_evaluate_object(handle, "_UPC", NULL, &buffer);
 	if (ACPI_FAILURE(status))
 		goto out;

 	upc = buffer.pointer;
 	if (!upc || (upc->type != ACPI_TYPE_PACKAGE) || upc->package.count != 4)
 		goto out;

 	/* UPC states port is connectable */
 	if (upc->package.elements[0].integer.value)
 		if (!pld)
 			; /* keep connect_type as unknown */
 		else if (pld->user_visible)
 			connect_type = USB_PORT_CONNECT_TYPE_HOT_PLUG;
 		else
 			connect_type = USB_PORT_CONNECT_TYPE_HARD_WIRED;
 	else
 		connect_type = USB_PORT_NOT_USED;
 out:
 	port_dev->connect_type = connect_type;
 	kfree(upc);
 	ACPI_FREE(pld);
 }

 static struct acpi_device *
 usb_acpi_get_companion_for_port(struct usb_port *port_dev)
 {
 	struct usb_device *udev;
 	struct acpi_device *adev;
 	acpi_handle *parent_handle;
 	int port1;

 	/* Get the struct usb_device point of port's hub */
 	udev = to_usb_device(port_dev->dev.parent->parent);

 	/*
 	 * The root hub ports' parent is the root hub. The non-root-hub
 	 * ports' parent is the parent hub port which the hub is
 	 * connected to.
 	 */
 	if (!udev->parent) {
 		adev = ACPI_COMPANION(&udev->dev);
 		port1 = usb_hcd_find_raw_port_number(bus_to_hcd(udev->bus),
 						     port_dev->portnum);
 	} else {
 		parent_handle = usb_get_hub_port_acpi_handle(udev->parent,
 							     udev->portnum);
 		if (!parent_handle)
 			return NULL;

 		adev = acpi_fetch_acpi_dev(parent_handle);
 		port1 = port_dev->portnum;
 	}

 	return acpi_find_child_by_adr(adev, port1);
 }

 static struct acpi_device *
 usb_acpi_find_companion_for_port(struct usb_port *port_dev)
 {
 	struct acpi_device *adev;

 	adev = usb_acpi_get_companion_for_port(port_dev);
 	if (!adev)
 		return NULL;

 	usb_acpi_get_connect_type(port_dev, adev->handle);

 	return adev;
 }

 static struct acpi_device *
 usb_acpi_find_companion_for_device(struct usb_device *udev)
 {
 	struct acpi_device *adev;
 	struct usb_port *port_dev;
 	struct usb_hub *hub;

 	if (!udev->parent) {
 		/*
 		 * root hub is only child (_ADR=0) under its parent, the HC.
 		 * sysdev pointer is the HC as seen from firmware.
 		 */
 		adev = ACPI_COMPANION(udev->bus->sysdev);
 		return acpi_find_child_device(adev, 0, false);
 	}

 	hub = usb_hub_to_struct_hub(udev->parent);
 	if (!hub)
 		return NULL;


 	/* Tunneled USB3 devices depend on USB4 Host Interface, set device link to it */
 	if (udev->speed >= USB_SPEED_SUPER &&
 	    udev->tunnel_mode != USB_LINK_NATIVE)
 		usb_acpi_add_usb4_devlink(udev);

 	/*
 	 * This is an embedded USB device connected to a port and such
 	 * devices share port's ACPI companion.
 	 */
 	port_dev = hub->ports[udev->portnum - 1];
 	return usb_acpi_get_companion_for_port(port_dev);
 }

 static struct acpi_device *usb_acpi_find_companion(struct device *dev)
 {
 	/*
 	 * The USB hierarchy like following:
 	 *
 	 * Device (EHC1)
 	 *	Device (HUBN)
 	 *		Device (PR01)
 	 *			Device (PR11)
 	 *			Device (PR12)
 	 *				Device (FN12)
 	 *				Device (FN13)
 	 *			Device (PR13)
 	 *			...
 	 * where HUBN is root hub, and PRNN are USB ports and devices
 	 * connected to them, and FNNN are individualk functions for
 	 * connected composite USB devices. PRNN and FNNN may contain
 	 * _CRS and other methods describing sideband resources for
 	 * the connected device.
 	 *
 	 * On the kernel side both root hub and embedded USB devices are
 	 * represented as instances of usb_device structure, and ports
 	 * are represented as usb_port structures, so the whole process
 	 * is split into 2 parts: finding companions for devices and
 	 * finding companions for ports.
 	 *
 	 * Note that we do not handle individual functions of composite
 	 * devices yet, for that we would need to assign companions to
 	 * devices corresponding to USB interfaces.
 	 */
 	if (is_usb_device(dev))
 		return usb_acpi_find_companion_for_device(to_usb_device(dev));
 	else if (is_usb_port(dev))
 		return usb_acpi_find_companion_for_port(to_usb_port(dev));

 	return NULL;
 }

 static bool usb_acpi_bus_match(struct device *dev)
 {
 	return is_usb_device(dev) || is_usb_port(dev);
 }

 static struct acpi_bus_type usb_acpi_bus = {
 	.name = "USB",
 	.match = usb_acpi_bus_match,
 	.find_companion = usb_acpi_find_companion,
 };

 int usb_acpi_register(void)
 {
 	return register_acpi_bus_type(&usb_acpi_bus);
 }

 void usb_acpi_unregister(void)
 {
 	unregister_acpi_bus_type(&usb_acpi_bus);
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* USB-ACPI glue code
	*
	* Copyright 2012 Red Hat <mjg@redhat.com>
	*/
	#include <linux/module.h>
	#include <linux/usb.h>
	#include <linux/device.h>
	#include <linux/errno.h>
	#include <linux/kernel.h>
	#include <linux/acpi.h>
	#include <linux/pci.h>
	#include <linux/usb/hcd.h>

	#include "hub.h"

	/**
	* usb_acpi_power_manageable - check whether usb port has
	* acpi power resource.
	* @hdev: USB device belonging to the usb hub
	* @index: port index based zero
	*
	* Return true if the port has acpi power resource and false if no.
	*/
	bool usb_acpi_power_manageable(struct usb_device *hdev, int index)
	{
	acpi_handle port_handle;
	int port1 = index + 1;

	port_handle = usb_get_hub_port_acpi_handle(hdev,
	port1);
	if (port_handle)
	return acpi_bus_power_manageable(port_handle);
	else
	return false;
	}
	EXPORT_SYMBOL_GPL(usb_acpi_power_manageable);

	#define UUID_USB_CONTROLLER_DSM "ce2ee385-00e6-48cb-9f05-2edb927c4899"
	#define USB_DSM_DISABLE_U1_U2_FOR_PORT 5

	/**
	* usb_acpi_port_lpm_incapable - check if lpm should be disabled for a port.
	* @hdev: USB device belonging to the usb hub
	* @index: zero based port index
	*
	* Some USB3 ports may not support USB3 link power management U1/U2 states
	* due to different retimer setup. ACPI provides _DSM method which returns 0x01
	* if U1 and U2 states should be disabled. Evaluate _DSM with:
	* Arg0: UUID = ce2ee385-00e6-48cb-9f05-2edb927c4899
	* Arg1: Revision ID = 0
	* Arg2: Function Index = 5
	* Arg3: (empty)
	*
	* Return 1 if USB3 port is LPM incapable, negative on error, otherwise 0
	*/

	int usb_acpi_port_lpm_incapable(struct usb_device *hdev, int index)
	{
	union acpi_object *obj;
	acpi_handle port_handle;
	int port1 = index + 1;
	guid_t guid;
	int ret;

	ret = guid_parse(UUID_USB_CONTROLLER_DSM, &guid);
	if (ret)
	return ret;

	port_handle = usb_get_hub_port_acpi_handle(hdev, port1);
	if (!port_handle) {
	dev_dbg(&hdev->dev, "port-%d no acpi handle\n", port1);
	return -ENODEV;
	}

	if (!acpi_check_dsm(port_handle, &guid, 0,
	BIT(USB_DSM_DISABLE_U1_U2_FOR_PORT))) {
	dev_dbg(&hdev->dev, "port-%d no _DSM function %d\n",
	port1, USB_DSM_DISABLE_U1_U2_FOR_PORT);
	return -ENODEV;
	}

	obj = acpi_evaluate_dsm_typed(port_handle, &guid, 0,
	USB_DSM_DISABLE_U1_U2_FOR_PORT, NULL,
	ACPI_TYPE_INTEGER);
	if (!obj) {
	dev_dbg(&hdev->dev, "evaluate port-%d _DSM failed\n", port1);
	return -EINVAL;
	}

	if (obj->integer.value == 0x01)
	ret = 1;

	ACPI_FREE(obj);

	return ret;
	}
	EXPORT_SYMBOL_GPL(usb_acpi_port_lpm_incapable);

	/**
	* usb_acpi_set_power_state - control usb port's power via acpi power
	* resource
	* @hdev: USB device belonging to the usb hub
	* @index: port index based zero
	* @enable: power state expected to be set
	*
	* Notice to use usb_acpi_power_manageable() to check whether the usb port
	* has acpi power resource before invoking this function.
	*
	* Returns 0 on success, else negative errno.
	*/
	int usb_acpi_set_power_state(struct usb_device *hdev, int index, bool enable)
	{
	struct usb_hub *hub = usb_hub_to_struct_hub(hdev);
	struct usb_port *port_dev;
	acpi_handle port_handle;
	unsigned char state;
	int port1 = index + 1;
	int error = -EINVAL;

	if (!hub)
	return -ENODEV;
	port_dev = hub->ports[port1 - 1];

	port_handle = (acpi_handle) usb_get_hub_port_acpi_handle(hdev, port1);
	if (!port_handle)
	return error;

	if (enable)
	state = ACPI_STATE_D0;
	else
	state = ACPI_STATE_D3_COLD;

	error = acpi_bus_set_power(port_handle, state);
	if (!error)
	dev_dbg(&port_dev->dev, "acpi: power was set to %d\n", enable);
	else
	dev_dbg(&port_dev->dev, "acpi: power failed to be set\n");

	return error;
	}
	EXPORT_SYMBOL_GPL(usb_acpi_set_power_state);

	/**
	* usb_acpi_add_usb4_devlink - add device link to USB4 Host Interface for tunneled USB3 devices
	*
	* @udev: Tunneled USB3 device connected to a roothub.
	*
	* Adds a device link between a tunneled USB3 device and the USB4 Host Interface
	* device to ensure correct runtime PM suspend and resume order. This function
	* should only be called for tunneled USB3 devices.
	* The USB4 Host Interface this tunneled device depends on is found from the roothub
	* port ACPI device specific data _DSD entry.
	*
	* Return: negative error code on failure, 0 otherwise
	*/
	static int usb_acpi_add_usb4_devlink(struct usb_device *udev)
	{
	const struct device_link *link;
	struct usb_port *port_dev;
	struct usb_hub *hub;

	if (!udev->parent \|\| udev->parent->parent)
	return 0;

	hub = usb_hub_to_struct_hub(udev->parent);
	port_dev = hub->ports[udev->portnum - 1];

	struct fwnode_handle *nhi_fwnode __free(fwnode_handle) =
	fwnode_find_reference(dev_fwnode(&port_dev->dev), "usb4-host-interface", 0);

	if (IS_ERR(nhi_fwnode) \|\| !nhi_fwnode->dev)
	return 0;

	link = device_link_add(&port_dev->child->dev, nhi_fwnode->dev,
	DL_FLAG_STATELESS \|
	DL_FLAG_RPM_ACTIVE \|
	DL_FLAG_PM_RUNTIME);
	if (!link) {
	dev_err(&port_dev->dev, "Failed to created device link from %s to %s\n",
	dev_name(&port_dev->child->dev), dev_name(nhi_fwnode->dev));
	return -EINVAL;
	}

	dev_dbg(&port_dev->dev, "Created device link from %s to %s\n",
	dev_name(&port_dev->child->dev), dev_name(nhi_fwnode->dev));

	return 0;
	}

	/*
	* Private to usb-acpi, all the core needs to know is that
	* port_dev->location is non-zero when it has been set by the firmware.
	*/
	#define USB_ACPI_LOCATION_VALID (1 << 31)

	static void
	usb_acpi_get_connect_type(struct usb_port port_dev, acpi_handle handle)
	{
	enum usb_port_connect_type connect_type = USB_PORT_CONNECT_TYPE_UNKNOWN;
	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
	union acpi_object *upc = NULL;
	struct acpi_pld_info *pld = NULL;
	acpi_status status;

	/*
	* According to 9.14 in ACPI Spec 6.2. _PLD indicates whether usb port
	* is user visible and _UPC indicates whether it is connectable. If
	* the port was visible and connectable, it could be freely connected
	* and disconnected with USB devices. If no visible and connectable,
	* a usb device is directly hard-wired to the port. If no visible and
	* no connectable, the port would be not used.
	*/

	status = acpi_get_physical_device_location(handle, &pld);
	if (ACPI_SUCCESS(status) && pld)
	port_dev->location = USB_ACPI_LOCATION_VALID \|
	pld->group_token << 8 \| pld->group_position;

	status = acpi_evaluate_object(handle, "_UPC", NULL, &buffer);
	if (ACPI_FAILURE(status))
	goto out;

	upc = buffer.pointer;
	if (!upc \|\| (upc->type != ACPI_TYPE_PACKAGE) \|\| upc->package.count != 4)
	goto out;

	/* UPC states port is connectable */
	if (upc->package.elements[0].integer.value)
	if (!pld)
	; /* keep connect_type as unknown */
	else if (pld->user_visible)
	connect_type = USB_PORT_CONNECT_TYPE_HOT_PLUG;
	else
	connect_type = USB_PORT_CONNECT_TYPE_HARD_WIRED;
	else
	connect_type = USB_PORT_NOT_USED;
	out:
	port_dev->connect_type = connect_type;
	kfree(upc);
	ACPI_FREE(pld);
	}

	static struct acpi_device *
	usb_acpi_get_companion_for_port(struct usb_port *port_dev)
	{
	struct usb_device *udev;
	struct acpi_device *adev;
	acpi_handle *parent_handle;
	int port1;

	/* Get the struct usb_device point of port's hub */
	udev = to_usb_device(port_dev->dev.parent->parent);

	/*
	* The root hub ports' parent is the root hub. The non-root-hub
	* ports' parent is the parent hub port which the hub is
	* connected to.
	*/
	if (!udev->parent) {
	adev = ACPI_COMPANION(&udev->dev);
	port1 = usb_hcd_find_raw_port_number(bus_to_hcd(udev->bus),
	port_dev->portnum);
	} else {
	parent_handle = usb_get_hub_port_acpi_handle(udev->parent,
	udev->portnum);
	if (!parent_handle)
	return NULL;

	adev = acpi_fetch_acpi_dev(parent_handle);
	port1 = port_dev->portnum;
	}

	return acpi_find_child_by_adr(adev, port1);
	}

	static struct acpi_device *
	usb_acpi_find_companion_for_port(struct usb_port *port_dev)
	{
	struct acpi_device *adev;

	adev = usb_acpi_get_companion_for_port(port_dev);
	if (!adev)
	return NULL;

	usb_acpi_get_connect_type(port_dev, adev->handle);

	return adev;
	}

	static struct acpi_device *
	usb_acpi_find_companion_for_device(struct usb_device *udev)
	{
	struct acpi_device *adev;
	struct usb_port *port_dev;
	struct usb_hub *hub;

	if (!udev->parent) {
	/*
	* root hub is only child (_ADR=0) under its parent, the HC.
	* sysdev pointer is the HC as seen from firmware.
	*/
	adev = ACPI_COMPANION(udev->bus->sysdev);
	return acpi_find_child_device(adev, 0, false);
	}

	hub = usb_hub_to_struct_hub(udev->parent);
	if (!hub)
	return NULL;


	/* Tunneled USB3 devices depend on USB4 Host Interface, set device link to it */
	if (udev->speed >= USB_SPEED_SUPER &&
	udev->tunnel_mode != USB_LINK_NATIVE)
	usb_acpi_add_usb4_devlink(udev);

	/*
	* This is an embedded USB device connected to a port and such
	* devices share port's ACPI companion.
	*/
	port_dev = hub->ports[udev->portnum - 1];
	return usb_acpi_get_companion_for_port(port_dev);
	}

	static struct acpi_device usb_acpi_find_companion(struct device dev)
	{
	/*
	* The USB hierarchy like following:
	*
	* Device (EHC1)
	* Device (HUBN)
	* Device (PR01)
	* Device (PR11)
	* Device (PR12)
	* Device (FN12)
	* Device (FN13)
	* Device (PR13)
	* ...
	* where HUBN is root hub, and PRNN are USB ports and devices
	* connected to them, and FNNN are individualk functions for
	* connected composite USB devices. PRNN and FNNN may contain
	* _CRS and other methods describing sideband resources for
	* the connected device.
	*
	* On the kernel side both root hub and embedded USB devices are
	* represented as instances of usb_device structure, and ports
	* are represented as usb_port structures, so the whole process
	* is split into 2 parts: finding companions for devices and
	* finding companions for ports.
	*
	* Note that we do not handle individual functions of composite
	* devices yet, for that we would need to assign companions to
	* devices corresponding to USB interfaces.
	*/
	if (is_usb_device(dev))
	return usb_acpi_find_companion_for_device(to_usb_device(dev));
	else if (is_usb_port(dev))
	return usb_acpi_find_companion_for_port(to_usb_port(dev));

	return NULL;
	}

	static bool usb_acpi_bus_match(struct device *dev)
	{
	return is_usb_device(dev) \|\| is_usb_port(dev);
	}

	static struct acpi_bus_type usb_acpi_bus = {
	.name = "USB",
	.match = usb_acpi_bus_match,
	.find_companion = usb_acpi_find_companion,
	};

	int usb_acpi_register(void)
	{
	return register_acpi_bus_type(&usb_acpi_bus);
	}

	void usb_acpi_unregister(void)
	{
	unregister_acpi_bus_type(&usb_acpi_bus);
	}