hub_probe()

1. 前提：

       在前面这边博客详细介绍了ehci驱动是如何创建usb主机控制器，最终调用hub驱动的hub_probe()探测函数，关于ehci驱动注册感兴趣的可以参考点击打开链接，本文主要讲述接口驱动最终调用hub_probe函数的处理。

2. hub_probe()流程图

3. hub驱动注册

retval = usb_hub_init();

int usb_hub_init(void)
{
	//1. 注册usb hub驱动
	if (usb_register(&hub_driver) < 0) { //注册hub驱动到usb子系统总线上,
		printk(KERN_ERR "%s: can't register hub driver\n",
			usbcore_name);
		return -1;
	}
        ......
}

注意！在usb_register()函数内部会绑定接口驱动：

int usb_register_driver(struct usb_driver *new_driver, struct module *owner,
			const char *mod_name)
{
	int retval = 0;

	if (usb_disabled())
		return -ENODEV;

	//对drvwrap USB驱动包初始化
	new_driver->drvwrap.for_devices = 0;
	new_driver->drvwrap.driver.name = (char *) new_driver->name; //初始化驱动名称为“hub”
	new_driver->drvwrap.driver.bus = &usb_bus_type; //绑定总线类型为子系统usb
	new_driver->drvwrap.driver.probe = usb_probe_interface; //重要，是接口的探针函数！！！该函数内部会调用usb_serial_probe()
	new_driver->drvwrap.driver.remove = usb_unbind_interface;
	new_driver->drvwrap.driver.owner = owner;
	new_driver->drvwrap.driver.mod_name = mod_name;
	spin_lock_init(&new_driver->dynids.lock);
	INIT_LIST_HEAD(&new_driver->dynids.list);

	retval = driver_register(&new_driver->drvwrap.driver); //驱动注册
	if (retval)
		goto out;

	retval = usb_create_newid_files(new_driver);
	if (retval)
		goto out_newid;

	pr_info("%s: registered new interface driver %s\n",
			usbcore_name, new_driver->name);

out:
	return retval;

out_newid:
	driver_unregister(&new_driver->drvwrap.driver);

	printk(KERN_ERR "%s: error %d registering interface "
			"	driver %s\n",
			usbcore_name, retval, new_driver->name);
	goto out;
}
EXPORT_SYMBOL_GPL(usb_register_driver);

hub_driver结构体驱动：

static struct usb_driver hub_driver = {
	.name =		"hub",
	.probe =	hub_probe, //hub探测接口，重要，待分析！
	.disconnect =	hub_disconnect,
	.suspend =	hub_suspend, //hub挂起，涉及到PM电源管理驱动控制
	.resume =	hub_resume, //hub恢复，
	.reset_resume =	hub_reset_resume, //通过对hub复位来引发复位
	.pre_reset =	hub_pre_reset, //与PM电源管理系统相关
	.post_reset =	hub_post_reset, //与PM电源管理系统相关
	.unlocked_ioctl = hub_ioctl,
	.id_table =	hub_id_table, //hub id表，重要，待分析！！
	.supports_autosuspend =	1,
};

在本文“1. 前提”里提到过ehci驱动最终会调用hub_probe探测函数，ok，现在我们开始分析...

4. hub_probe()

static int hub_probe(struct usb_interface *intf, const struct usb_device_id *id)
{
	struct usb_host_interface *desc;
	struct usb_endpoint_descriptor *endpoint;
	struct usb_device *hdev;
	struct usb_hub *hub;

	desc = intf->cur_altsetting; //获取当前设置的主机控制器接口
	hdev = interface_to_usbdev(intf);

	/*
	 * Set default autosuspend delay as 0 to speedup bus suspend,
	 * based on the below considerations:
	 *
	 * - Unlike other drivers, the hub driver does not rely on the
	 *   autosuspend delay to provide enough time to handle a wakeup
	 *   event, and the submitted status URB is just to check future
	 *   change on hub downstream ports, so it is safe to do it.
	 *
	 * - The patch might cause one or more auto supend/resume for
	 *   below very rare devices when they are plugged into hub
	 *   first time:
	 *
	 *   	devices having trouble initializing, and disconnect
	 *   	themselves from the bus and then reconnect a second
	 *   	or so later
	 *
	 *   	devices just for downloading firmware, and disconnects
	 *   	themselves after completing it
	 *
	 *   For these quite rare devices, their drivers may change the
	 *   autosuspend delay of their parent hub in the probe() to one
	 *   appropriate value to avoid the subtle problem if someone
	 *   does care it.
	 *
	 * - The patch may cause one or more auto suspend/resume on
	 *   hub during running 'lsusb', but it is probably too
	 *   infrequent to worry about.
	 *
	 * - Change autosuspend delay of hub can avoid unnecessary auto
	 *   suspend timer for hub, also may decrease power consumption
	 *   of USB bus.
	 */
	pm_runtime_set_autosuspend_delay(&hdev->dev, 0);

	/* Hubs have proper suspend/resume support. */
	usb_enable_autosuspend(hdev);

	if (hdev->level == MAX_TOPO_LEVEL) {
		dev_err(&intf->dev,
			"Unsupported bus topology: hub nested too deep\n");
		return -E2BIG;
	}

#ifdef	CONFIG_USB_OTG_BLACKLIST_HUB
	if (hdev->parent) {
		dev_warn(&intf->dev, "ignoring external hub\n");
		return -ENODEV;
	}
#endif

	/* Some hubs have a subclass of 1, which AFAICT according to the */
	/*  specs is not defined, but it works */
	if ((desc->desc.bInterfaceSubClass != 0) &&
	    (desc->desc.bInterfaceSubClass != 1)) {
descriptor_error:
		dev_err (&intf->dev, "bad descriptor, ignoring hub\n");
		return -EIO;
	}

	/* Multiple endpoints? What kind of mutant ninja-hub is this? */
	if (desc->desc.bNumEndpoints != 1)
		goto descriptor_error;

	endpoint = &desc->endpoint[0].desc;

	/* If it's not an interrupt in endpoint, we'd better punt! */
	if (!usb_endpoint_is_int_in(endpoint))
		goto descriptor_error;

	/* We found a hub */
	dev_info (&intf->dev, "USB hub found\n");

	hub = kzalloc(sizeof(*hub), GFP_KERNEL); //分配一个hub
	if (!hub) {
		dev_dbg (&intf->dev, "couldn't kmalloc hub struct\n");
		return -ENOMEM;
	}

	//初始化一个hub
	kref_init(&hub->kref);
	INIT_LIST_HEAD(&hub->event_list);
	hub->intfdev = &intf->dev;
	hub->hdev = hdev;
	INIT_DELAYED_WORK(&hub->leds, led_work);
	INIT_DELAYED_WORK(&hub->init_work, NULL);
	usb_get_intf(intf);

	usb_set_intfdata (intf, hub);
	intf->needs_remote_wakeup = 1;
	pm_suspend_ignore_children(&intf->dev, true);

	if (hdev->speed == USB_SPEED_HIGH)
		highspeed_hubs++;

	if (id->driver_info & HUB_QUIRK_CHECK_PORT_AUTOSUSPEND)
		hub->quirk_check_port_auto_suspend = 1;

	if (hub_configure(hub, endpoint) >= 0)
		return 0;

	hub_disconnect (intf);
	return -ENODEV;
}

初始化hub，最终调用hub_configure():

5. hub_configure()

static int hub_configure(struct usb_hub *hub,
	struct usb_endpoint_descriptor *endpoint)
{
	struct usb_hcd *hcd;
	struct usb_device *hdev = hub->hdev;
	struct device *hub_dev = hub->intfdev;
	u16 hubstatus, hubchange;
	u16 wHubCharacteristics;
	unsigned int pipe;
	int maxp, ret, i;
	char *message = "out of memory";
	unsigned unit_load;
	unsigned full_load;

	hub->buffer = kmalloc(sizeof(*hub->buffer), GFP_KERNEL);
	if (!hub->buffer) {
		ret = -ENOMEM;
		goto fail;
	}

	hub->status = kmalloc(sizeof(*hub->status), GFP_KERNEL);
	if (!hub->status) {
		ret = -ENOMEM;
		goto fail;
	}
	mutex_init(&hub->status_mutex);

	hub->descriptor = kmalloc(sizeof(*hub->descriptor), GFP_KERNEL);
	if (!hub->descriptor) {
		ret = -ENOMEM;
		goto fail;
	}

	/* Request the entire hub descriptor.
	 * hub->descriptor can handle USB_MAXCHILDREN ports,
	 * but the hub can/will return fewer bytes here.
	 */
	ret = get_hub_descriptor(hdev, hub->descriptor);
	if (ret < 0) {
		message = "can't read hub descriptor";
		goto fail;
	} else if (hub->descriptor->bNbrPorts > USB_MAXCHILDREN) {
		message = "hub has too many ports!";
		ret = -ENODEV;
		goto fail;
	} else if (hub->descriptor->bNbrPorts == 0) {
		message = "hub doesn't have any ports!";
		ret = -ENODEV;
		goto fail;
	}

	hdev->maxchild = hub->descriptor->bNbrPorts; //端口个数
	dev_info (hub_dev, "%d port%s detected\n", hdev->maxchild,
		(hdev->maxchild == 1) ? "" : "s");

	hub->ports = kzalloc(hdev->maxchild * sizeof(struct usb_port *), //给端口分配空间
			     GFP_KERNEL);
	if (!hub->ports) {
		ret = -ENOMEM;
		goto fail;
	}

	wHubCharacteristics = le16_to_cpu(hub->descriptor->wHubCharacteristics);
	if (hub_is_superspeed(hdev)) { //是否是usb3.0？
		unit_load = 150;
		full_load = 900;
	} else {
		unit_load = 100;
		full_load = 500;
	}

	/* FIXME for USB 3.0, skip for now */
	if ((wHubCharacteristics & HUB_CHAR_COMPOUND) &&
			!(hub_is_superspeed(hdev))) {
		int	i;
		char	portstr [USB_MAXCHILDREN + 1];

		for (i = 0; i < hdev->maxchild; i++)
			portstr[i] = hub->descriptor->u.hs.DeviceRemovable
				    [((i + 1) / 8)] & (1 << ((i + 1) % 8))
				? 'F' : 'R';
		portstr[hdev->maxchild] = 0;
		dev_dbg(hub_dev, "compound device; port removable status: %s\n", portstr);
	} else
		dev_dbg(hub_dev, "standalone hub\n");

	switch (wHubCharacteristics & HUB_CHAR_LPSM) {
	case HUB_CHAR_COMMON_LPSM:
		dev_dbg(hub_dev, "ganged power switching\n");
		break;
	case HUB_CHAR_INDV_PORT_LPSM:
		dev_dbg(hub_dev, "individual port power switching\n");
		break;
	case HUB_CHAR_NO_LPSM:
	case HUB_CHAR_LPSM:
		dev_dbg(hub_dev, "no power switching (usb 1.0)\n");
		break;
	}

	switch (wHubCharacteristics & HUB_CHAR_OCPM) {
	case HUB_CHAR_COMMON_OCPM:
		dev_dbg(hub_dev, "global over-current protection\n");
		break;
	case HUB_CHAR_INDV_PORT_OCPM:
		dev_dbg(hub_dev, "individual port over-current protection\n");
		break;
	case HUB_CHAR_NO_OCPM:
	case HUB_CHAR_OCPM:
		dev_dbg(hub_dev, "no over-current protection\n");
		break;
	}

	spin_lock_init (&hub->tt.lock);
	INIT_LIST_HEAD (&hub->tt.clear_list);
	INIT_WORK(&hub->tt.clear_work, hub_tt_work); //初始化一个工作队列，绑定回调函数hub_tt_work
	switch (hdev->descriptor.bDeviceProtocol) { //设备协议转换
	case USB_HUB_PR_FS:
		break;
	case USB_HUB_PR_HS_SINGLE_TT:
		dev_dbg(hub_dev, "Single TT\n");
		hub->tt.hub = hdev;
		break;
	case USB_HUB_PR_HS_MULTI_TT:
		ret = usb_set_interface(hdev, 0, 1);
		if (ret == 0) {
			dev_dbg(hub_dev, "TT per port\n");
			hub->tt.multi = 1;
		} else
			dev_err(hub_dev, "Using single TT (err %d)\n",
				ret);
		hub->tt.hub = hdev;
		break;
	case USB_HUB_PR_SS:
		/* USB 3.0 hubs don't have a TT */
		break;
	default:
		dev_dbg(hub_dev, "Unrecognized hub protocol %d\n",
			hdev->descriptor.bDeviceProtocol);
		break;
	}

	/* Note 8 FS bit times == (8 bits / 12000000 bps) ~= 666ns */
	switch (wHubCharacteristics & HUB_CHAR_TTTT) {
		case HUB_TTTT_8_BITS:
			if (hdev->descriptor.bDeviceProtocol != 0) {
				hub->tt.think_time = 666;
				dev_dbg(hub_dev, "TT requires at most %d "
						"FS bit times (%d ns)\n",
					8, hub->tt.think_time);
			}
			break;
		case HUB_TTTT_16_BITS:
			hub->tt.think_time = 666 * 2;
			dev_dbg(hub_dev, "TT requires at most %d "
					"FS bit times (%d ns)\n",
				16, hub->tt.think_time);
			break;
		case HUB_TTTT_24_BITS:
			hub->tt.think_time = 666 * 3;
			dev_dbg(hub_dev, "TT requires at most %d "
					"FS bit times (%d ns)\n",
				24, hub->tt.think_time);
			break;
		case HUB_TTTT_32_BITS:
			hub->tt.think_time = 666 * 4;
			dev_dbg(hub_dev, "TT requires at most %d "
					"FS bit times (%d ns)\n",
				32, hub->tt.think_time);
			break;
	}

	/* probe() zeroes hub->indicator[] */
	if (wHubCharacteristics & HUB_CHAR_PORTIND) {
		hub->has_indicators = 1;
		dev_dbg(hub_dev, "Port indicators are supported\n");
	}

	dev_dbg(hub_dev, "power on to power good time: %dms\n",
		hub->descriptor->bPwrOn2PwrGood * 2);

	/* power budgeting mostly matters with bus-powered hubs,
	 * and battery-powered root hubs (may provide just 8 mA).
	 */
	ret = usb_get_status(hdev, USB_RECIP_DEVICE, 0, &hubstatus);
	if (ret < 2) {
		message = "can't get hub status";
		goto fail;
	}
	le16_to_cpus(&hubstatus);
	hcd = bus_to_hcd(hdev->bus);
	if (hdev == hdev->bus->root_hub) {
		if (hcd->power_budget > 0)
			hdev->bus_mA = hcd->power_budget;
		else
			hdev->bus_mA = full_load * hdev->maxchild;
		if (hdev->bus_mA >= full_load)
			hub->mA_per_port = full_load;
		else {
			hub->mA_per_port = hdev->bus_mA;
			hub->limited_power = 1;
		}
	} else if ((hubstatus & (1 << USB_DEVICE_SELF_POWERED)) == 0) {
		int remaining = hdev->bus_mA -
			hub->descriptor->bHubContrCurrent;

		dev_dbg(hub_dev, "hub controller current requirement: %dmA\n",
			hub->descriptor->bHubContrCurrent);
		hub->limited_power = 1;

		if (remaining < hdev->maxchild * unit_load)
			dev_warn(hub_dev,
					"insufficient power available "
					"to use all downstream ports\n");
		hub->mA_per_port = unit_load;	/* 7.2.1 */

	} else {	/* Self-powered external hub */
		/* FIXME: What about battery-powered external hubs that
		 * provide less current per port? */
		hub->mA_per_port = full_load;
	}
	if (hub->mA_per_port < full_load)
		dev_dbg(hub_dev, "%umA bus power budget for each child\n",
				hub->mA_per_port);

	/* Update the HCD's internal representation of this hub before khubd
	 * starts getting port status changes for devices under the hub.
	 */
	if (hcd->driver->update_hub_device) {
		ret = hcd->driver->update_hub_device(hcd, hdev,
				&hub->tt, GFP_KERNEL);
		if (ret < 0) {
			message = "can't update HCD hub info";
			goto fail;
		}
	}

	ret = hub_hub_status(hub, &hubstatus, &hubchange);
	if (ret < 0) {
		message = "can't get hub status";
		goto fail;
	}

	/* local power status reports aren't always correct */
	if (hdev->actconfig->desc.bmAttributes & USB_CONFIG_ATT_SELFPOWER)
		dev_dbg(hub_dev, "local power source is %s\n",
			(hubstatus & HUB_STATUS_LOCAL_POWER)
			? "lost (inactive)" : "good");

	if ((wHubCharacteristics & HUB_CHAR_OCPM) == 0)
		dev_dbg(hub_dev, "%sover-current condition exists\n",
			(hubstatus & HUB_STATUS_OVERCURRENT) ? "" : "no ");

	/* set up the interrupt endpoint
	 * We use the EP's maxpacket size instead of (PORTS+1+7)/8
	 * bytes as USB2.0[11.12.3] says because some hubs are known
	 * to send more data (and thus cause overflow). For root hubs,
	 * maxpktsize is defined in hcd.c's fake endpoint descriptors
	 * to be big enough for at least USB_MAXCHILDREN ports. */
	pipe = usb_rcvintpipe(hdev, endpoint->bEndpointAddress);
	maxp = usb_maxpacket(hdev, pipe, usb_pipeout(pipe));

	if (maxp > sizeof(*hub->buffer))
		maxp = sizeof(*hub->buffer);

	hub->urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!hub->urb) {
		ret = -ENOMEM;
		goto fail;
	}

	usb_fill_int_urb(hub->urb, hdev, pipe, *hub->buffer, maxp, hub_irq,
		hub, endpoint->bInterval);

	/* maybe cycle the hub leds */
	if (hub->has_indicators && blinkenlights)
		hub->indicator [0] = INDICATOR_CYCLE;

	for (i = 0; i < hdev->maxchild; i++) {
		ret = usb_hub_create_port_device(hub, i + 1);
		if (ret < 0) {
			dev_err(hub->intfdev,
				"couldn't create port%d device.\n", i + 1);
			hdev->maxchild = i;
			goto fail_keep_maxchild;
		}
	}

	usb_hub_adjust_deviceremovable(hdev, hub->descriptor);

	hub_activate(hub, HUB_INIT);
	return 0;

fail:
	hdev->maxchild = 0;
fail_keep_maxchild:
	dev_err (hub_dev, "config failed, %s (err %d)\n",
			message, ret);
	/* hub_disconnect() frees urb and descriptor */
	return ret;
}

该函数内部所做的工作比较多：

a> 获取hub描述符

b> 获取hub状态

c> 填充一个hub中断 hub_irq()

最终调用hub_activate()激活hub。

6. hub_activate()

static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
{
	struct usb_device *hdev = hub->hdev;
	struct usb_hcd *hcd;
	int ret;
	int port1;
	int status;
	bool need_debounce_delay = false;
	unsigned delay;

	/* Continue a partial initialization */
	if (type == HUB_INIT2)
		goto init2;
	if (type == HUB_INIT3)
		goto init3;

	/* The superspeed hub except for root hub has to use Hub Depth
	 * value as an offset into the route string to locate the bits
	 * it uses to determine the downstream port number. So hub driver
	 * should send a set hub depth request to superspeed hub after
	 * the superspeed hub is set configuration in initialization or
	 * reset procedure.
	 *
	 * After a resume, port power should still be on.
	 * For any other type of activation, turn it on.
	 */
	if (type != HUB_RESUME) {
		if (hdev->parent && hub_is_superspeed(hdev)) {
			ret = usb_control_msg(hdev, usb_sndctrlpipe(hdev, 0),
					HUB_SET_DEPTH, USB_RT_HUB,
					hdev->level - 1, 0, NULL, 0,
					USB_CTRL_SET_TIMEOUT);
			if (ret < 0)
				dev_err(hub->intfdev,
						"set hub depth failed\n");
		}

		/* Speed up system boot by using a delayed_work for the
		 * hub's initial power-up delays.  This is pretty awkward
		 * and the implementation looks like a home-brewed sort of
		 * setjmp/longjmp, but it saves at least 100 ms for each
		 * root hub (assuming usbcore is compiled into the kernel
		 * rather than as a module).  It adds up.
		 *
		 * This can't be done for HUB_RESUME or HUB_RESET_RESUME
		 * because for those activation types the ports have to be
		 * operational when we return.  In theory this could be done
		 * for HUB_POST_RESET, but it's easier not to.
		 */
		if (type == HUB_INIT) { //初始化
			delay = hub_power_on(hub, false); //hub上电
			PREPARE_DELAYED_WORK(&hub->init_work, hub_init_func2); //创建工作队列，同时绑定对应的回调函数hub_init_func2
			schedule_delayed_work(&hub->init_work,
					msecs_to_jiffies(delay));

			/* Suppress autosuspend until init is done */
			usb_autopm_get_interface_no_resume(
					to_usb_interface(hub->intfdev));
			return;		/* Continues at init2: below */
		} else if (type == HUB_RESET_RESUME) {
			/* The internal host controller state for the hub device
			 * may be gone after a host power loss on system resume.
			 * Update the device's info so the HW knows it's a hub.
			 */
			hcd = bus_to_hcd(hdev->bus);
			if (hcd->driver->update_hub_device) {
				ret = hcd->driver->update_hub_device(hcd, hdev,
						&hub->tt, GFP_NOIO);
				if (ret < 0) {
					dev_err(hub->intfdev, "Host not "
							"accepting hub info "
							"update.\n");
					dev_err(hub->intfdev, "LS/FS devices "
							"and hubs may not work "
							"under this hub\n.");
				}
			}
			hub_power_on(hub, true);
		} else {
			hub_power_on(hub, true);
		}
	}
 init2:

	/* Check each port and set hub->change_bits to let khubd know
	 * which ports need attention.
	 */
	for (port1 = 1; port1 <= hdev->maxchild; ++port1) {
		struct usb_device *udev = hub->ports[port1 - 1]->child;
		u16 portstatus, portchange;

		portstatus = portchange = 0;
		status = hub_port_status(hub, port1, &portstatus, &portchange);
		if (udev || (portstatus & USB_PORT_STAT_CONNECTION))
			dev_dbg(hub->intfdev,
					"port %d: status %04x change %04x\n",
					port1, portstatus, portchange);

		/* After anything other than HUB_RESUME (i.e., initialization
		 * or any sort of reset), every port should be disabled.
		 * Unconnected ports should likewise be disabled (paranoia),
		 * and so should ports for which we have no usb_device.
		 */
		if ((portstatus & USB_PORT_STAT_ENABLE) && (
				type != HUB_RESUME ||
				!(portstatus & USB_PORT_STAT_CONNECTION) ||
				!udev ||
				udev->state == USB_STATE_NOTATTACHED)) {
			/*
			 * USB3 protocol ports will automatically transition
			 * to Enabled state when detect an USB3.0 device attach.
			 * Do not disable USB3 protocol ports.
			 */
			if (!hub_is_superspeed(hdev)) {
				usb_clear_port_feature(hdev, port1,
						   USB_PORT_FEAT_ENABLE);
				portstatus &= ~USB_PORT_STAT_ENABLE;
			} else {
				/* Pretend that power was lost for USB3 devs */
				portstatus &= ~USB_PORT_STAT_ENABLE;
			}
		}

		/* Clear status-change flags; we'll debounce later */
		if (portchange & USB_PORT_STAT_C_CONNECTION) {
			need_debounce_delay = true;
			usb_clear_port_feature(hub->hdev, port1,
					USB_PORT_FEAT_C_CONNECTION);
		}
		if (portchange & USB_PORT_STAT_C_ENABLE) {
			need_debounce_delay = true;
			usb_clear_port_feature(hub->hdev, port1,
					USB_PORT_FEAT_C_ENABLE);
		}
		if (portchange & USB_PORT_STAT_C_RESET) {
			need_debounce_delay = true;
			usb_clear_port_feature(hub->hdev, port1,
					USB_PORT_FEAT_C_RESET);
		}
		if ((portchange & USB_PORT_STAT_C_BH_RESET) &&
				hub_is_superspeed(hub->hdev)) {
			need_debounce_delay = true;
			usb_clear_port_feature(hub->hdev, port1,
					USB_PORT_FEAT_C_BH_PORT_RESET);
		}
		/* We can forget about a "removed" device when there's a
		 * physical disconnect or the connect status changes.
		 */
		if (!(portstatus & USB_PORT_STAT_CONNECTION) ||
				(portchange & USB_PORT_STAT_C_CONNECTION))
			clear_bit(port1, hub->removed_bits);

		if (!udev || udev->state == USB_STATE_NOTATTACHED) {
			/* Tell khubd to disconnect the device or
			 * check for a new connection
			 */
			if (udev || (portstatus & USB_PORT_STAT_CONNECTION))
				set_bit(port1, hub->change_bits);

		} else if (portstatus & USB_PORT_STAT_ENABLE) {
			bool port_resumed = (portstatus &
					USB_PORT_STAT_LINK_STATE) ==
				USB_SS_PORT_LS_U0;
			/* The power session apparently survived the resume.
			 * If there was an overcurrent or suspend change
			 * (i.e., remote wakeup request), have khubd
			 * take care of it.  Look at the port link state
			 * for USB 3.0 hubs, since they don't have a suspend
			 * change bit, and they don't set the port link change
			 * bit on device-initiated resume.
			 */
			if (portchange || (hub_is_superspeed(hub->hdev) &&
						port_resumed))
				set_bit(port1, hub->change_bits);

		} else if (udev->persist_enabled) {
			struct usb_port *port_dev = hub->ports[port1 - 1];

#ifdef CONFIG_PM
			udev->reset_resume = 1;
#endif
			/* Don't set the change_bits when the device
			 * was powered off.
			 */
			if (port_dev->power_is_on)
				set_bit(port1, hub->change_bits);

		} else {
			/* The power session is gone; tell khubd */
			usb_set_device_state(udev, USB_STATE_NOTATTACHED);
			set_bit(port1, hub->change_bits);
		}
	}

	/* If no port-status-change flags were set, we don't need any
	 * debouncing.  If flags were set we can try to debounce the
	 * ports all at once right now, instead of letting khubd do them
	 * one at a time later on.
	 *
	 * If any port-status changes do occur during this delay, khubd
	 * will see them later and handle them normally.
	 */
	if (need_debounce_delay) {
		delay = HUB_DEBOUNCE_STABLE;

		/* Don't do a long sleep inside a workqueue routine */
		if (type == HUB_INIT2) {
			PREPARE_DELAYED_WORK(&hub->init_work, hub_init_func3); //初始化工作队列，同时绑定回调函数hub_init_func3
			schedule_delayed_work(&hub->init_work,
					msecs_to_jiffies(delay));
			return;		/* Continues at init3: below */
		} else {
			msleep(delay);
		}
	}
 init3:
	hub->quiescing = 0;

	status = usb_submit_urb(hub->urb, GFP_NOIO);
	if (status < 0)
		dev_err(hub->intfdev, "activate --> %d\n", status);
	if (hub->has_indicators && blinkenlights)
		schedule_delayed_work(&hub->leds, LED_CYCLE_PERIOD);

	/* Scan all ports that need attention */
	kick_khubd(hub);

	/* Allow autosuspend if it was suppressed */
	if (type <= HUB_INIT3)
		usb_autopm_put_interface_async(to_usb_interface(hub->intfdev));
}

该函数内部使用了几个延时工作队列，

PREPARE_DELAYED_WORK(&hub->init_work, hub_init_func2); //创建工作队列，同时绑定对应的回调函数hub_init_func2

static void hub_init_func2(struct work_struct *ws)
{
	struct usb_hub *hub = container_of(ws, struct usb_hub, init_work.work);

	hub_activate(hub, HUB_INIT2); //激活HUB_INIT2
}

PREPARE_DELAYED_WORK(&hub->init_work, hub_init_func3); //初始化工作队列，同时绑定回调函数hub_init_func3

static void hub_init_func3(struct work_struct *ws)
{
	struct usb_hub *hub = container_of(ws, struct usb_hub, init_work.work);

	hub_activate(hub, HUB_INIT3);
}

最终调用kick_khubd()

7. kick_khubd()

kick_khubd(hub);

static void kick_khubd(struct usb_hub *hub)
{
	unsigned long	flags;

	spin_lock_irqsave(&hub_event_lock, flags);
	if (!hub->disconnected && list_empty(&hub->event_list)) {
		list_add_tail(&hub->event_list, &hub_event_list); //将hub添加到hub_event_list链表中，

		/* Suppress autosuspend until khubd runs */
		usb_autopm_get_interface_no_resume(
				to_usb_interface(hub->intfdev));
		wake_up(&khubd_wait); //唤醒等待队列
	}
	spin_unlock_irqrestore(&hub_event_lock, flags);
}

到这里我们见到了熟悉的工作机制，就是将当前hub加入到链表hub_event_list，同时唤醒等待队列wake_up(&khubd_wait)，而该链表和等待队列就是在hub_thread()线程内部完成的，详见 点击打开链接第3点。