1. 根目录:
2. include
3. linux
4. usb
5. ch9.h

/*
 * This file holds USB constants and structures that are needed for
 * USB device APIs.  These are used by the USB device model, which is
 * defined in chapter 9 of the USB 2.0 specification and in the
 * Wireless USB 1.0 (spread around).  Linux has several APIs in C that
 * need these:
 *
 * - the master/host side Linux-USB kernel driver API;
 * - the "usbfs" user space API; and
 * - the Linux "gadget" slave/device/peripheral side driver API.
 *
 * USB 2.0 adds an additional "On The Go" (OTG) mode, which lets systems
 * act either as a USB master/host or as a USB slave/device.  That means
 * the master and slave side APIs benefit from working well together.
 *
 * There's also "Wireless USB", using low power short range radios for
 * peripheral interconnection but otherwise building on the USB framework.
 *
 * Note all descriptors are declared '__attribute__((packed))' so that:
 *
 * [a] they never get padded, either internally (USB spec writers
 *     probably handled that) or externally;
 *
 * [b] so that accessing bigger-than-a-bytes fields will never
 *     generate bus errors on any platform, even when the location of
 *     its descriptor inside a bundle isn't "naturally aligned", and
 *
 * [c] for consistency, removing all doubt even when it appears to
 *     someone that the two other points are non-issues for that
 *     particular descriptor type.
 */
#ifndef __LINUX_USB_CH9_H
#define __LINUX_USB_CH9_H

#include <uapi/linux/usb/ch9.h>


/**
 * usb_speed_string() - Returns human readable-name of the speed.
 * @speed: The speed to return human-readable name for.  If it's not
 *   any of the speeds defined in usb_device_speed enum, string for
 *   USB_SPEED_UNKNOWN will be returned.
 */
extern const char *usb_speed_string(enum usb_device_speed speed);


/**
 * usb_state_string - Returns human readable name for the state.
 * @state: The state to return a human-readable name for. If it's not
 *	any of the states devices in usb_device_state_string enum,
 *	the string UNKNOWN will be returned.
 */
extern const char *usb_state_string(enum usb_device_state state);

#endif /* __LINUX_USB_CH9_H */