1. 根目录:
2. drivers
3. usb
4. usb-common.c

/*
 * Provides code common for host and device side USB.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, version 2.
 *
 * If either host side (ie. CONFIG_USB=y) or device side USB stack
 * (ie. CONFIG_USB_GADGET=y) is compiled in the kernel, this module is
 * compiled-in as well.  Otherwise, if either of the two stacks is
 * compiled as module, this file is compiled as module as well.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/usb/ch9.h>
#include <linux/usb/otg.h>

const char *usb_otg_state_string(enum usb_otg_state state)
{
	static const char *const names[] = {
		[OTG_STATE_A_IDLE] = "a_idle",
		[OTG_STATE_A_WAIT_VRISE] = "a_wait_vrise",
		[OTG_STATE_A_WAIT_BCON] = "a_wait_bcon",
		[OTG_STATE_A_HOST] = "a_host",
		[OTG_STATE_A_SUSPEND] = "a_suspend",
		[OTG_STATE_A_PERIPHERAL] = "a_peripheral",
		[OTG_STATE_A_WAIT_VFALL] = "a_wait_vfall",
		[OTG_STATE_A_VBUS_ERR] = "a_vbus_err",
		[OTG_STATE_B_IDLE] = "b_idle",
		[OTG_STATE_B_SRP_INIT] = "b_srp_init",
		[OTG_STATE_B_PERIPHERAL] = "b_peripheral",
		[OTG_STATE_B_WAIT_ACON] = "b_wait_acon",
		[OTG_STATE_B_HOST] = "b_host",
	};

	if (state < 0 || state >= ARRAY_SIZE(names))
		return "UNDEFINED";

	return names[state];
}
EXPORT_SYMBOL_GPL(usb_otg_state_string);

const char *usb_speed_string(enum usb_device_speed speed)
{
	static const char *const names[] = {
		[USB_SPEED_UNKNOWN] = "UNKNOWN",
		[USB_SPEED_LOW] = "low-speed",
		[USB_SPEED_FULL] = "full-speed",
		[USB_SPEED_HIGH] = "high-speed",
		[USB_SPEED_WIRELESS] = "wireless",
		[USB_SPEED_SUPER] = "super-speed",
	};

	if (speed < 0 || speed >= ARRAY_SIZE(names))
		speed = USB_SPEED_UNKNOWN;
	return names[speed];
}
EXPORT_SYMBOL_GPL(usb_speed_string);

const char *usb_state_string(enum usb_device_state state)
{
	static const char *const names[] = {
		[USB_STATE_NOTATTACHED] = "not attached",
		[USB_STATE_ATTACHED] = "attached",
		[USB_STATE_POWERED] = "powered",
		[USB_STATE_RECONNECTING] = "reconnecting",
		[USB_STATE_UNAUTHENTICATED] = "unauthenticated",
		[USB_STATE_DEFAULT] = "default",
		[USB_STATE_ADDRESS] = "addresssed",
		[USB_STATE_CONFIGURED] = "configured",
		[USB_STATE_SUSPENDED] = "suspended",
	};

	if (state < 0 || state >= ARRAY_SIZE(names))
		return "UNKNOWN";

	return names[state];
}
EXPORT_SYMBOL_GPL(usb_state_string);

MODULE_LICENSE("GPL");