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USB Hub 检测设备

news 来源：原创 2025/5/18 17:50:09

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系列文章目录

xHCI 简单分析
USB Root Hub 分析
USB Hub 检测设备

文章目录

系列文章目录
一、引言
二、hub_events
- hub_port_connect_change
- usb_alloc_dev
- usb_set_device_state
- hub_port_init
- usb_new_device

一、引言

USB Hub 检测设备一文中讲到，当有 USB 插入时，它会激活 hub_events 函数。

static int hub_thread(void *__unused)
{do {hub_events();wait_event_interruptible(khubd_wait,!list_empty(&hub_event_list) ||kthread_should_stop());try_to_freeze();} while (!kthread_should_stop() || !list_empty(&hub_event_list));pr_debug("%s: khubd exiting\n", usbcore_name);return 0;
}

二、hub_events

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static void hub_events(void)
{// ...while (1) {// ...tmp = hub_event_list.next;list_del_init(tmp);hub = list_entry(tmp, struct usb_hub, event_list);// 描述 usb 设备（Hub，整体，不是接口）hdev = hub->hdev;intf = to_usb_interface(hub->intfdev);// hub 接口设备hub_dev = &intf->dev;// .../* Lock the device, then check to see if we were* disconnected while waiting for the lock to succeed. */if (locktree(hdev) < 0) {// .../* Autoresume */ret = usb_autopm_get_interface(intf);// .../* deal with port status changes */for (i = 1; i <= hub->descriptor->bNbrPorts; i++) {// ...ret = hub_port_status(hub, i,&portstatus, &portchange);// ...if (connect_change)hub_port_connect_change(hub, i,portstatus, portchange);} /* end for i */// ...if (!hdev->parent && !hub->busy_bits[0])usb_enable_root_hub_irq(hdev->bus);loop_autopm:/* Allow autosuspend if we're not going to run again */if (list_empty(&hub->event_list))usb_autopm_enable(intf);
loop:usb_unlock_device(hdev);usb_put_intf(intf);} /* end while (1) */
}

在这个循环中，检测 Hub 的每个端口是否有变化，有变化则调用 hub_port_connect_change 进行处理。

hub_port_connect_change

static void hub_port_connect_change(struct usb_hub *hub, int port1,u16 portstatus, u16 portchange)
{struct usb_device *hdev = hub->hdev;struct device *hub_dev = hub->intfdev;// .../* Disconnect any existing devices under this port */if (hdev->children[port1-1])usb_disconnect(&hdev->children[port1-1]);clear_bit(port1, hub->change_bits);// ...for (i = 0; i < SET_CONFIG_TRIES; i++) {struct usb_device *udev;// ...udev = usb_alloc_dev(hdev, hdev->bus, port1);// ...usb_set_device_state(udev, USB_STATE_POWERED);udev->speed = USB_SPEED_UNKNOWN;udev->bus_mA = hub->mA_per_port;udev->level = hdev->level + 1;// ...choose_address(udev);// .../* reset and get descriptor */status = hub_port_init(hub, udev, port1, i);// ...if (!status) {status = usb_new_device(udev);// ...}// ...status = hub_power_remaining(hub);// ...
}

在这个循环中，主要涉及 8 个重量级函数，先点明它们的角色分工。

第一个函数，usb_alloc_dev()，一个 struct usb_device 结构体指针，申请内存，这个结构体指针可不是为 Hub 准备的，它正是为了 Hub 这个端口所接的设备而申请的，别忘了我们此时此刻的上下文，之所以进入这个循环，是因为我们的 Hub 检测到某个端口有设备连接，所以，Hub 驱动就义不容辞地要为该设备做点什么。

第二个函数，usb_set_device_state()，这个函数用来设置设备的状态，在 struct usb_device 结构体中，有一个成员 enum usb_device_state state，这一刻会把这个设备的状态设置为 USB_STATE_POWERED，即上电状态。

第三个函数，choose_address()，为设备选择一个地址。后面会用实例来查看效果。

第四个函数，hub_port_init()，端口初始化，主要就是前面所讲的获取设备的描述符。

第五个函数，usb_get_status()，这个函数是专门为 Hub 准备的，不是为当前的这个 Hub，而是说当前 Hub 的这个端口上连接的如果又是 Hub，那么和连接普通设备就不一样。

第六个函数，check_highspeed()，不同速度的设备，当然待遇不一样。

第七个函数，usb_new_device()。寻找驱动程序，调用驱动程序的 probe，跟踪这个函数就能一直到设备驱动程序的 probe() 函数的调用。

第八个函数，hub_power_remaining()，电源管理。

usb_alloc_dev

struct usb_device *
usb_alloc_dev(struct usb_device *parent, struct usb_bus *bus, unsigned port1)
{struct usb_device *dev;// ...device_initialize(&dev->dev);dev->dev.bus = &usb_bus_type;dev->dev.type = &usb_device_type;dev->dev.dma_mask = bus->controller->dma_mask;dev->state = USB_STATE_ATTACHED;INIT_LIST_HEAD(&dev->ep0.urb_list);dev->ep0.desc.bLength = USB_DT_ENDPOINT_SIZE;dev->ep0.desc.bDescriptorType = USB_DT_ENDPOINT;/* ep0 maxpacket comes later, from device descriptor */dev->ep_in[0] = dev->ep_out[0] = &dev->ep0;// ...dev->portnum = port1;dev->bus = bus;dev->parent = parent;INIT_LIST_HEAD(&dev->filelist);#ifdef	CONFIG_PMmutex_init(&dev->pm_mutex);INIT_DELAYED_WORK(&dev->autosuspend, usb_autosuspend_work);dev->autosuspend_delay = usb_autosuspend_delay * HZ;
#endifreturn dev;
}

usb_set_device_state

void usb_set_device_state(struct usb_device *udev,enum usb_device_state new_state)
{unsigned long flags;spin_lock_irqsave(&device_state_lock, flags);if (udev->state == USB_STATE_NOTATTACHED);	/* do nothing */else if (new_state != USB_STATE_NOTATTACHED) {/* root hub wakeup capabilities are managed out-of-band* and may involve silicon errata ... ignore them here.*/if (udev->parent) {if (udev->state == USB_STATE_SUSPENDED|| new_state == USB_STATE_SUSPENDED);	/* No change to wakeup settings */else if (new_state == USB_STATE_CONFIGURED)device_init_wakeup(&udev->dev,(udev->actconfig->desc.bmAttributes& USB_CONFIG_ATT_WAKEUP));elsedevice_init_wakeup(&udev->dev, 0);}udev->state = new_state;} elserecursively_mark_NOTATTACHED(udev);spin_unlock_irqrestore(&device_state_lock, flags);
}

hub_port_init

static int
hub_port_init (struct usb_hub *hub, struct usb_device *udev, int port1,int retry_counter)
{// .../* Reset the device; full speed may morph to high speed */retval = hub_port_reset(hub, port1, udev, delay);// ...for (i = 0; i < GET_DESCRIPTOR_TRIES; (++i, msleep(100))) {if (USE_NEW_SCHEME(retry_counter)) {struct usb_device_descriptor *buf;int r = 0;#define GET_DESCRIPTOR_BUFSIZE	64buf = kmalloc(GET_DESCRIPTOR_BUFSIZE, GFP_NOIO);// ...for (j = 0; j < 3; ++j) {buf->bMaxPacketSize0 = 0;r = usb_control_msg(udev, usb_rcvaddr0pipe(),USB_REQ_GET_DESCRIPTOR, USB_DIR_IN,USB_DT_DEVICE << 8, 0,buf, GET_DESCRIPTOR_BUFSIZE,USB_CTRL_GET_TIMEOUT);// ...}udev->descriptor.bMaxPacketSize0 =buf->bMaxPacketSize0;kfree(buf);retval = hub_port_reset(hub, port1, udev, delay);// ...}for (j = 0; j < SET_ADDRESS_TRIES; ++j) {retval = hub_set_address(udev);if (retval >= 0)break;msleep(200);}// ...retval = usb_get_device_descriptor(udev, 8);// ...
}

usb_new_device

int usb_new_device(struct usb_device *udev)
{// ...usb_detect_quirks(udev);err = usb_get_configuration(udev);// .../* read the standard strings and cache them if present */udev->product = usb_cache_string(udev, udev->descriptor.iProduct);udev->manufacturer = usb_cache_string(udev,udev->descriptor.iManufacturer);udev->serial = usb_cache_string(udev, udev->descriptor.iSerialNumber);// .../* export the usbdev device-node for libusb */udev->dev.devt = MKDEV(USB_DEVICE_MAJOR,(((udev->bus->busnum-1) * 128) + (udev->devnum-1)));// ...err = device_add(&udev->dev);// ...if (udev->parent)usb_autoresume_device(udev->parent);// ...			
}

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