linux usb驱动记录（一）

一、linux 下的usb驱动框架

　　在linux系统中，usb驱动可以从两个角度去观察，一个是主机侧，一个是设备侧。linux usb 驱动的总体框架如下图所示：　　　　

　　　　　　

　　  从主机侧看usb驱动可分为四层：usb主机控制器硬件底层、usb主机控制器驱动、usb核心和usb设备驱动。

　　在主机侧要实现的驱动主要分为两类：usb主机控制器驱动和usb设备驱动。主机控制器驱动负责控制插入其中的usb设备，usb设备驱动主要负责usb设备和主机的通信。

　　usb核心向上为设备驱动提供编程接口，向下为usb控制器驱动提供编程口，维护整个usb设备信息，完成设备热插拔控制，总线数据传输控制。

　　可以看到这种设备驱动、核心层、主机控制器驱动这种三层结构的驱动框架，与之前分析过linux系统下i2c子系统的驱动架构有异曲同工之处。linux内核中将主机控制器的驱动和外设端的驱动分离，通过一个核心层将某种总线的协议进行抽象，外设端的驱动调用核心层API间接过渡到主机驱动传输函数的调用。

　　这里借助一张图来对比linux下，i2c、spi、usb三个子系统的相似之处。

　　　　　　

　　这样一对比，就能比较清晰的分析usb主机控制器驱动与usb设备驱动。

二、usb总线驱动程序分析

　　主机控制器中重要的数据结构：

　　usb_hcd：描述了USB主机控制器驱动，包含主机控制器的信息

　　hc_driver：用于操作主机控制器的驱动，该结构体在usb_hcd 中

　   ohci_hcd： 是usb_hcd 结构体中的私有数据

　　在主机控制驱动中还是通过平台设备驱动来注册platform_device和platform_driver，然后用平台总线进行匹配，匹配成功之后调用probe函数，在probe函数中做j进一步的操作。

　　　　　　

　　　　　　

probe函数：

　　　　　　

static int usb_hcd_s3c2410_probe (const struct hc_driver *driver,
                  struct platform_device *dev)
{
    struct usb_hcd *hcd = NULL;
    int retval;
    // dev->dev.platform_data == NULL，因此这里不会不用set_power
    s3c2410_usb_set_power(dev->dev.platform_data, , );
    s3c2410_usb_set_power(dev->dev.platform_data, , );
    // 创建一个hcd结构体，并做一些设置
    hcd = usb_create_hcd(driver, &dev->dev, "s3c24xx");
    if (hcd == NULL)
        return -ENOMEM;
    // 设置内存和IO资源的开始位置
    hcd->rsrc_start = dev->resource[].start;
    //  设置内存和IO资源的长度
    hcd->rsrc_len   = dev->resource[].end - dev->resource[].start + ;
    // 申请一块内存资源
    if (!request_mem_region(hcd->rsrc_start, hcd->rsrc_len, hcd_name)) {
        dev_err(&dev->dev, "request_mem_region failed\n");
        retval = -EBUSY;
        goto err_put;
    }
    //  在clock.c中找到"usb-host"对应的clk结构体
    clk = clk_get(&dev->dev, "usb-host");
    if (IS_ERR(clk)) {
        dev_err(&dev->dev, "cannot get usb-host clock\n");
        retval = -ENOENT;
        goto err_mem;
    }
     //  在clock.c中找到"usb-bus-host"对应的clk结构体
    usb_clk = clk_get(&dev->dev, "usb-bus-host");
    if (IS_ERR(usb_clk)) {
        dev_err(&dev->dev, "cannot get usb-bus-host clock\n");
        retval = -ENOENT;
        goto err_clk;
    }
    //  使能时钟  使能过流检查
    s3c2410_start_hc(dev, hcd);
    //  io端口重映射
    hcd->regs = ioremap(hcd->rsrc_start, hcd->rsrc_len);
    if (!hcd->regs) {
        dev_err(&dev->dev, "ioremap failed\n");
        retval = -ENOMEM;
        goto err_ioremap;
    }
    // 初始化ohci_hcd 结构体ohci->next_statechange = jiffies
    ohci_hcd_init(hcd_to_ohci(hcd));
    // 这个函数下边分析 一个usb主机控制器对应一个usb_hcd，对应一条usb总线，集成一个root_hub
    retval = usb_add_hcd(hcd, dev->resource[].start, IRQF_DISABLED);
    if (retval != )
        goto err_ioremap;

    return ;

 err_ioremap:
    s3c2410_stop_hc(dev);
    iounmap(hcd->regs);
    clk_put(usb_clk);

 err_clk:
    clk_put(clk);

 err_mem:
    release_mem_region(hcd->rsrc_start, hcd->rsrc_len);

 err_put:
    usb_put_hcd(hcd);
    return retval;
}

在probe函数中主要的任务如下：

　　（1）创建一个usb_hcd结构体===>和i2c控制器驱动中的中分配一个i2c_adapter一样

　　（2）设置这个这个usb_hcd结构体（设置操作主机控制器的hc_driver）===>设置i2c_adapter结构体（设置操作i2c_adapter的transfer函数）

　　（3）从platform_device中获取到硬件资源，进行内存映射

　　（4）使能时钟

　　（5）usb_add_hcd

usb_create_hcd函数：

struct usb_hcd *usb_create_hcd (const struct hc_driver *driver,
        struct device *dev, const char *bus_name)
{
    struct usb_hcd *hcd;
    hcd = kzalloc(sizeof(*hcd) + driver->hcd_priv_size, GFP_KERNEL);
    dev_set_drvdata(dev, hcd);
        ...
        // 初始化hcd下边的usb_bus，为后边将其加入到usb_bus 中做准备：
            //bus->devnum_next = 1;  bus->root_hub = NULL;  bus->busnum = -1;
            //bus->bandwidth_allocated = 0;  bus->bandwidth_int_reqs  = 0;
            //bus->bandwidth_isoc_reqs = 0;
    usb_bus_init(&hcd->self);
    hcd->self.controller = dev;
    hcd->self.bus_name = bus_name;
    hcd->self.uses_dma = (dev->dma_mask != NULL);
        // 初始定时器用来轮询控制器的root_hub的状态改变
    init_timer(&hcd->rh_timer);
        // 注册定时器中断服务函数
    hcd->rh_timer.function = rh_timer_func;
    hcd->rh_timer.data = (unsigned long) hcd;
#ifdef CONFIG_USB_SUSPEND
    INIT_WORK(&hcd->wakeup_work, hcd_resume_work);
#endif
    mutex_init(&hcd->bandwidth_mutex);
        // 给hcd添加主机控制器驱动函数    driver==ohci_s3c2410_hc_driver
    hcd->driver = driver;
    hcd->product_desc = (driver->product_desc) ? driver->product_desc :
            "USB Host Controller";
    return hcd;
}

　　 usb_add_hcd函数：一个usb主机控制器对应一条usb总线，集成一个root_hub，对应一个usb_hcd。

int usb_add_hcd(struct usb_hcd *hcd,
        unsigned int irqnum, unsigned long irqflags)
{
        // 初始化缓存池
    if ((retval = hcd_buffer_create(hcd)) != ) {
        dev_dbg(hcd->self.controller, "pool alloc failed\n");
        return retval;
    }
        //设置hcd下usb_bus的busnum并将其挂到usb_bus_list这个链表中 hcd->self 在usb_create_hcd 中已经初始化了  (注册完之后hcd->self.busnum = 1)
    if ((retval = usb_register_bus(&hcd->self)) < )
        goto err_register_bus;
        // 创建一个root_hub
    if ((rhdev = usb_alloc_dev(NULL, &hcd->self, )) == NULL) {
        dev_err(hcd->self.controller, "unable to allocate root hub\n");
        retval = -ENOMEM;
        goto err_allocate_root_hub;
    }
　　　　  // 将上边分配好的usb_device挂在主机控制的usb_bus下
    hcd->self.root_hub = rhdev;
        // 根据ohci_s3c2410_hc_driver(HCD_USB11 | HCD_MEMORY,)下的flag 选择 root_hub 的speed
    switch (hcd->driver->flags & HCD_MASK) {
    case HCD_USB11:
        rhdev->speed = USB_SPEED_FULL;
        break;
    case HCD_USB2:
        rhdev->speed = USB_SPEED_HIGH;
        break;
    case HCD_USB3:
        rhdev->speed = USB_SPEED_SUPER;
        break;
    default:
        goto err_set_rh_speed;
    }
    device_init_wakeup(&rhdev->dev, );
    if (hcd->driver->reset && (retval = hcd->driver->reset(hcd)) < ) {
        dev_err(hcd->self.controller, "can't setup\n");
        goto err_hcd_driver_setup;
    }
    hcd->rh_pollable = ;

    /* NOTE: root hub and controller capabilities may not be the same */
    if (device_can_wakeup(hcd->self.controller)
            && device_can_wakeup(&hcd->self.root_hub->dev))
        dev_dbg(hcd->self.controller, "supports USB remote wakeup\n");

    /* enable irqs just before we start the controller */
    // 接下来使能中断
    // 接下来执行主机控制器的启动函数

    /* starting here, usbcore will pay attention to this root hub */
    rhdev->bus_mA = min(500u, hcd->power_budget);
    if ((retval = register_root_hub(hcd)) != )
        goto err_register_root_hub;

    retval = sysfs_create_group(&rhdev->dev.kobj, &usb_bus_attr_group);
    if (retval < ) {
        printk(KERN_ERR "Cannot register USB bus sysfs attributes: %d\n",
               retval);
        goto error_create_attr_group;
    }
    if (hcd->uses_new_polling && HCD_POLL_RH(hcd))
        usb_hcd_poll_rh_status(hcd);
    return retval;
    ...
} 

　　在usb_add_hcd中，最主要干的一件事是创建一个root_hub，这个root_hub的数据类型是一个usb_device，并将这个root_hub注册到usb总线中。

　　这里大概解释一下什么是root_hub。在我们的电脑上通常有几个usb端口，这些端口可以用来连接一个普通的usb设备，或者一个hub，hub是一个usb设备，可以用来扩展连接usb设备的端口数量。通常情况下主机控制器的物理端口由一个虚拟的root_hub来管理。这个hub是主机控制器的设备驱动虚拟的，用来统一管理总线拓扑。用一张图说明usb系统的拓扑结构。

　　　　　　　　　　　　　　

register_root_hub函数的调用太复杂了，这里先抽象出其函数调用过程如下：

　　　　　　

为了分析清楚root_hub下的dev到底与总线上的哪一个device_driver匹配需要分析usb总线上的match函数

static int usb_device_match(struct device *dev, struct device_driver *drv)
{
    // 需要匹配的是usb_device时的情况
    if (is_usb_device(dev)) {

        /* interface drivers never match devices */
        if (!is_usb_device_driver(drv))
            return ;

        /* TODO: Add real matching code */
        return ;
    }
    // 需要匹配的是接口的情况
　　else if (is_usb_interface(dev)) {
        struct usb_interface *intf;
        struct usb_driver *usb_drv;
        const struct usb_device_id *id;
        /* device drivers never match interfaces */
        if (is_usb_device_driver(drv))
            return ;
        intf = to_usb_interface(dev);
        usb_drv = to_usb_driver(drv);

        id = usb_match_id(intf, usb_drv->id_table);
        if (id)
            return ;
        id = usb_match_dynamic_id(intf, usb_drv);
        if (id)
            return ;
    }
    return ;
}

　　　　　　

　　对于传入的match函数的dev其dev->type是usb_device_type（在分配usb_alloc_dev中已经设置了）。

　　现在看usb总线上有哪些device_driver：在/core/usb.c中我们可以看到已经注册了两个usb_driver结构体 usbfs_driver和hub_driver

一个usb_device_driver结构体  usb_generic_driver

　　（这里跳转的比较突然，这三个结构体的注册是在usb_init函数中进行的）

　　所以match函数中传入的dev会和这三个已经注册到usb_bus上的device_driver进行匹配，这里看哪一个usb_driver下的device_driver会匹配成功，也就是看usbdrv_wrap->for_devices的值，这个值需要在usb_register函数中查看，这里给出结果。其实从driver的名字就可以看出只有usb_device_driver （usb设备驱动）是能够和device（设备）进行匹配的。

　　　　

　　因此root_hub->dev会和usb_generic_driver->drvwrap.driver进行匹配，匹配完成之后会执行probe函数。那么这个probe函数有是哪一个呢？probe函数肯定是usb_generic_driver->drvwrap.driver.probe

这个函数在usb_register_device_driver(&usb_generic_driver, THIS_MODULE)中进行了设置usb_generic_driver->drvwrap.driver.probe = usb_probe_device

usb_probe_device函数的分析：　

static int usb_probe_device(struct device *dev)
{
        // 这里通过container_of 找到usb_device_driver  和 usb_device
        // 注意在really_probe 函数中已经将dev->driver 挂上了 device_driver ，所以这个地方才能找到usb_device_driver
    struct usb_device_driver *udriver = to_usb_device_driver(dev->driver);
    struct usb_device *udev = to_usb_device(dev);
    int error = ;

    dev_dbg(dev, "%s\n", __func__);

    /* TODO: Add real matching code */

    /* The device should always appear to be in use
     * unless the driver suports autosuspend.
     */
    if (!udriver->supports_autosuspend)
        error = usb_autoresume_device(udev);
        // 程序执行到这里可以看到饶了一大圈的probe函数就是usb_generic_driver->probe函数  也就是generic_probe 函数
    if (!error)
        error = udriver->probe(udev);
    return error;
}

因此接下分析generic_probe 函数：

static int generic_probe(struct usb_device *udev)
{
    int err, c;
    if (usb_device_is_owned(udev))
        ;        /* Don't configure if the device is owned */
        // 在创建root_hub 时分配usb_device时已经设置了dev->authorized = 1
    else if (udev->authorized == )
        dev_err(&udev->dev, "Device is not authorized for usage\n");
    else {
        // 因此会执行到这里来配置操作
        c = usb_choose_configuration(udev);
        if (c >= ) {
            err = usb_set_configuration(udev, c);
            if (err) {
                dev_err(&udev->dev, "can't set config #%d, error %d\n",
                    c, err);
            }
        }
    }
    /* USB device state == configured ... usable */
    usb_notify_add_device(udev);
    return ;
}

在这里我们可以看一下到底对着root->hub选择了什么配置，设置了什么配置

int usb_choose_configuration(struct usb_device *udev)
{
    int i;
    int num_configs;
    int insufficient_power = ;
    struct usb_host_config *c, *best;

    best = NULL;
        // root_hub下的一些与配置有关的东西在usb_new_device中都读取出来然后放到了root_hub下的config中
    c = udev->config;
        // 有多少项配置
    num_configs = udev->descriptor.bNumConfigurations;
        //  遍历所有的配置项
    for (i = ; i < num_configs; (i++, c++)) {
        struct usb_interface_descriptor    *desc = NULL;

        /* It's possible that a config has no interfaces! */
                // 有可能一个配置没有接口，所以要做判断
        if (c->desc.bNumInterfaces > )
                //  取出配置下的第一个接口
            desc = &c->intf_cache[]->altsetting->desc;

        /*
         * HP's USB bus-powered keyboard has only one configuration
         * and it claims to be self-powered; other devices may have
         * similar errors in their descriptors.  If the next test
         * were allowed to execute, such configurations would always
         * be rejected and the devices would not work as expected.
         * In the meantime, we run the risk of selecting a config
         * that requires external power at a time when that power
         * isn't available.  It seems to be the lesser of two evils.
         *
         * Bugzilla #6448 reports a device that appears to crash
         * when it receives a GET_DEVICE_STATUS request!  We don't
         * have any other way to tell whether a device is self-powered,
         * but since we don't use that information anywhere but here,
         * the call has been removed.
         *
         * Maybe the GET_DEVICE_STATUS call and the test below can
         * be reinstated when device firmwares become more reliable.
         * Don't hold your breath.
         */
#if 0
        /* Rule out self-powered configs for a bus-powered device */
        if (bus_powered && (c->desc.bmAttributes &
                    USB_CONFIG_ATT_SELFPOWER))
            continue;
#endif

        /*
         * The next test may not be as effective as it should be.
         * Some hubs have errors in their descriptor, claiming
         * to be self-powered when they are really bus-powered.
         * We will overestimate the amount of current such hubs
         * make available for each port.
         *
         * This is a fairly benign sort of failure.  It won't
         * cause us to reject configurations that we should have
         * accepted.
         */

        /* Rule out configs that draw too much bus current */
        if (c->desc.bMaxPower *  > udev->bus_mA) {
            insufficient_power++;
            continue;
        }

        /* When the first config's first interface is one of Microsoft's
         * pet nonstandard Ethernet-over-USB protocols, ignore it unless
         * this kernel has enabled the necessary host side driver.
         * But: Don't ignore it if it's the only config.
         */
        if (i ==  && num_configs >  && desc &&
                (is_rndis(desc) || is_activesync(desc))) {
#if !defined(CONFIG_USB_NET_RNDIS_HOST) && !defined(CONFIG_USB_NET_RNDIS_HOST_MODULE)
            continue;
#else
            best = c;
#endif
        }

        /* From the remaining configs, choose the first one whose
         * first interface is for a non-vendor-specific class.
         * Reason: Linux is more likely to have a class driver
         * than a vendor-specific driver. */
        else if (udev->descriptor.bDeviceClass !=
                        USB_CLASS_VENDOR_SPEC &&
                (desc && desc->bInterfaceClass !=
                        USB_CLASS_VENDOR_SPEC)) {
            best = c;
            break;
        }

        /* If all the remaining configs are vendor-specific,
         * choose the first one. */
        else if (!best)
            best = c;
    }

    if (insufficient_power > )
        dev_info(&udev->dev, "rejected %d configuration%s "
            "due to insufficient available bus power\n",
            insufficient_power, plural(insufficient_power));

    if (best) {
        i = best->desc.bConfigurationValue;
        dev_dbg(&udev->dev,
            "configuration #%d chosen from %d choice%s\n",
            i, num_configs, plural(num_configs));
    } else {
        i = -;
        dev_warn(&udev->dev,
            "no configuration chosen from %d choice%s\n",
            num_configs, plural(num_configs));
    }
    return i;  // 这里返回了一个系统觉得合适的配置项的编号
}

返回的这个最好的配置项的编号传入到usb_set_configuration，猜测要对此项配置进行设置。

int usb_set_configuration(struct usb_device *dev, int configuration)
{
    int i, ret;
    struct usb_host_config *cp = NULL;
    struct usb_interface **new_interfaces = NULL;
    struct usb_hcd *hcd = bus_to_hcd(dev->bus);
    int n, nintf;
        // 首先根据选择的配置项的编号 找到相应的配置
    if (dev->authorized ==  || configuration == -)
        configuration = ;
    else {
        for (i = ; i < dev->descriptor.bNumConfigurations; i++) {
            if (dev->config[i].desc.bConfigurationValue ==
                    configuration) {
                cp = &dev->config[i];
                break;
            }
        }
    }
    if ((!cp && configuration != ))
        return -EINVAL;

    /* The USB spec says configuration 0 means unconfigured.
     * But if a device includes a configuration numbered 0,
     * we will accept it as a correctly configured state.
     * Use -1 if you really want to unconfigure the device.
     */
        //当configuration==0 时发出警告，0是无效的配置，但仍然认为他是正确的
    if (cp && configuration == )
        dev_warn(&dev->dev, "config 0 descriptor??\n");

    /* Allocate memory for new interfaces before doing anything else,
     * so that if we run out then nothing will have changed. */
    n = nintf = ;
        // 得到接口总数，并分配内存
    if (cp) {
        nintf = cp->desc.bNumInterfaces;
        new_interfaces = kmalloc(nintf * sizeof(*new_interfaces),
                GFP_NOIO);
        if (!new_interfaces) {
            dev_err(&dev->dev, "Out of memory\n");
            return -ENOMEM;
        }

        for (; n < nintf; ++n) {
            new_interfaces[n] = kzalloc(
                    sizeof(struct usb_interface),
                    GFP_NOIO);
            if (!new_interfaces[n]) {
                dev_err(&dev->dev, "Out of memory\n");
                ret = -ENOMEM;
free_interfaces:
                while (--n >= )
                    kfree(new_interfaces[n]);
                kfree(new_interfaces);
                return ret;
            }
        }

        i = dev->bus_mA - cp->desc.bMaxPower * ;
        if (i < )
            dev_warn(&dev->dev, "new config #%d exceeds power "
                    "limit by %dmA\n",
                    configuration, -i);
    }

    /* Wake up the device so we can send it the Set-Config request */
        // 配置前唤醒设备
    ret = usb_autoresume_device(dev);
    if (ret)
        goto free_interfaces;

    /* if it's already configured, clear out old state first.
     * getting rid of old interfaces means unbinding their drivers.
     */
    if (dev->state != USB_STATE_ADDRESS)
        usb_disable_device(dev, );    /* Skip ep0 */

    /* Get rid of pending async Set-Config requests for this device */
    cancel_async_set_config(dev);

    /* Make sure we have bandwidth (and available HCD resources) for this
     * configuration.  Remove endpoints from the schedule if we're dropping
     * this configuration to set configuration 0.  After this point, the
     * host controller will not allow submissions to dropped endpoints.  If
     * this call fails, the device state is unchanged.
     */
    mutex_lock(&hcd->bandwidth_mutex);
    ret = usb_hcd_alloc_bandwidth(dev, cp, NULL, NULL);
    if (ret < ) {
        mutex_unlock(&hcd->bandwidth_mutex);
        usb_autosuspend_device(dev);
        goto free_interfaces;
    }
        // 设置配置
    ret = usb_control_msg(dev, usb_sndctrlpipe(dev, ),
                  USB_REQ_SET_CONFIGURATION, , configuration, ,
                  NULL, , USB_CTRL_SET_TIMEOUT);
    if (ret < ) {
        /* All the old state is gone, so what else can we do?
         * The device is probably useless now anyway.
         */
        cp = NULL;
    }

    dev->actconfig = cp;
    if (!cp) {
        usb_set_device_state(dev, USB_STATE_ADDRESS);
        usb_hcd_alloc_bandwidth(dev, NULL, NULL, NULL);
        mutex_unlock(&hcd->bandwidth_mutex);
        usb_autosuspend_device(dev);
        goto free_interfaces;
    }
    mutex_unlock(&hcd->bandwidth_mutex);
    usb_set_device_state(dev, USB_STATE_CONFIGURED);

    /* Initialize the new interface structures and the
     * hc/hcd/usbcore interface/endpoint state.
     */
        // 接下来设置这个配置的接口并将接口注册到usb总线下
    for (i = ; i < nintf; ++i) {
        struct usb_interface_cache *intfc;
        struct usb_interface *intf;
        struct usb_host_interface *alt;

        cp->interface[i] = intf = new_interfaces[i];
        intfc = cp->intf_cache[i];
        intf->altsetting = intfc->altsetting;
        intf->num_altsetting = intfc->num_altsetting;
        intf->intf_assoc = find_iad(dev, cp, i);
        kref_get(&intfc->ref);

        alt = usb_altnum_to_altsetting(intf, );

        /* No altsetting 0?  We'll assume the first altsetting.
         * We could use a GetInterface call, but if a device is
         * so non-compliant that it doesn't have altsetting 0
         * then I wouldn't trust its reply anyway.
         */
        if (!alt)
            alt = &intf->altsetting[];

        intf->cur_altsetting = alt;
        usb_enable_interface(dev, intf, true);
        intf->dev.parent = &dev->dev;
        intf->dev.driver = NULL;
        intf->dev.bus = &usb_bus_type;
        intf->dev.type = &usb_if_device_type;
        intf->dev.groups = usb_interface_groups;
        intf->dev.dma_mask = dev->dev.dma_mask;
        INIT_WORK(&intf->reset_ws, __usb_queue_reset_device);
        intf->minor = -;
        device_initialize(&intf->dev);
        pm_runtime_no_callbacks(&intf->dev);
        dev_set_name(&intf->dev, "%d-%s:%d.%d",
            dev->bus->busnum, dev->devpath,
            configuration, alt->desc.bInterfaceNumber);
    }
    kfree(new_interfaces);

    if (cp->string == NULL &&
            !(dev->quirks & USB_QUIRK_CONFIG_INTF_STRINGS))
        cp->string = usb_cache_string(dev, cp->desc.iConfiguration);

    /* Now that all the interfaces are set up, register them
     * to trigger binding of drivers to interfaces.  probe()
     * routines may install different altsettings and may
     * claim() any interfaces not yet bound.  Many class drivers
     * need that: CDC, audio, video, etc.
     */
    for (i = ; i < nintf; ++i) {
        struct usb_interface *intf = cp->interface[i];

        dev_dbg(&dev->dev,
            "adding %s (config #%d, interface %d)\n",
            dev_name(&intf->dev), configuration,
            intf->cur_altsetting->desc.bInterfaceNumber);
        device_enable_async_suspend(&intf->dev);
        ret = device_add(&intf->dev);
        if (ret != ) {
            dev_err(&dev->dev, "device_add(%s) --> %d\n",
                dev_name(&intf->dev), ret);
            continue;
        }
        create_intf_ep_devs(intf);
    }

    usb_autosuspend_device(dev);
    return ;
}

简单看完usb_set_configuration之后，看一下此刻在/sys/bus/usb/device 路径存在的设备如下：

　　　　　　

usb1这个设备是在之前一次register_root_hub中的device_add中添加的，而1-0:1.0是在sub_set_configuration中device_add添加的，对应表示 总线号-设备路径：配置号-接口号

1-0:1.0表示usb控制器1下的usb_hub下的1号配置的0号接口

　　注意到这里有出现了device_add，这又是一长串的函数调用，但是还是向总线注册设备、与总线上的device_driver进行匹配，匹配成功之后执行probe函数的一系列套路。所以在这里又得分析usb_device_match函数和probe，重点是这个probe函数执行的是哪一个函数？

之前分析过usb_device_match函数，这次传入到usb_device_match中的dev是一个接口类型的，所以应该执行usb_device_match中的第二条分支，通过id来进行匹配。这次与root_hub下的接口匹配的应该是hub_driver->drvwrap.driver，通过静态id_table的匹配成功之后应该执行usb_probe_interface这个函数。

static int usb_probe_interface(struct device *dev)
{
    struct usb_driver *driver = to_usb_driver(dev->driver);
    struct usb_interface *intf = to_usb_interface(dev);
    struct usb_device *udev = interface_to_usbdev(intf);
    const struct usb_device_id *id;
        ....
        // 执行到这里又回到了hub_driver下的hub_probe函数
        // 可以看到这里的probe函数的调用是一层套一层的，但最终都会执行到driver下的probe函数
    error = driver->probe(intf, id);
    if (error)
        goto err;
　　　　  ....
}

hub_probe函数：

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;
    hdev = interface_to_usbdev(intf);

    /* Hubs have proper suspend/resume support */
    usb_enable_autosuspend(hdev);
    // hub 只支持6层嵌套，在前边那张usb系统拓扑图中hub接hub最多接6层
    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 != ) &&
        (desc->desc.bInterfaceSubClass != )) {
descriptor_error:
        dev_err (&intf->dev, "bad descriptor, ignoring hub\n");
        return -EIO;
    }

        //hub interface的endpoint数目为1,这里的数目没有包括ep0
    if (desc->desc.bNumEndpoints != )
        goto descriptor_error;
        //获取端点描述符
    endpoint = &desc->endpoint[].desc;
        //判断端点是不是中断in类型的端点，
    if (!usb_endpoint_is_int_in(endpoint))
        goto descriptor_error;
        // 在上述情况都满足的情况下才说明有一个hub存在
    /* We found a hub */
    dev_info (&intf->dev, "USB hub found\n");
        // 分配一个usb_hub
    hub = kzalloc(sizeof(*hub), GFP_KERNEL);
    if (!hub) {
        dev_dbg (&intf->dev, "couldn't kmalloc hub struct\n");
        return -ENOMEM;
    }
        //初始化引用计数
    kref_init(&hub->kref);
    INIT_LIST_HEAD(&hub->event_list);
    hub->intfdev = &intf->dev;// 接口设备
    hub->hdev = hdev;         // hub实体
    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 = ;

    if (hdev->speed == USB_SPEED_HIGH)
        highspeed_hubs++;
        // 配置hub
    if (hub_configure(hub, endpoint) >= )
        return ;

    hub_disconnect (intf);
    return -ENODEV;
}

在hub_probe函数中创建了一个hub实例后，在hub_configure中配置这个hub。

static int hub_configure(struct usb_hub *hub,
    struct usb_endpoint_descriptor *endpoint)
{
        ...
        // 为hub开辟缓冲区
    hub->buffer = kmalloc(sizeof(*hub->buffer), GFP_KERNEL);
    hub->status = kmalloc(sizeof(*hub->status), GFP_KERNEL);
    hub->descriptor = kmalloc(sizeof(*hub->descriptor), GFP_KERNEL);
        // 获取hub的描述符， 之前说过hub从本质上讲也是一种usb设备，只是其设备描述符与普通的usb设备不同
    ret = get_hub_descriptor(hdev, hub->descriptor,
            sizeof(*hub->descriptor));

    hdev->maxchild = hub->descriptor->bNbrPorts;
    hub->port_owners = kzalloc(hdev->maxchild * sizeof(void *), GFP_KERNEL);
        // 获取描述hub特性的信息
    wHubCharacteristics = le16_to_cpu(hub->descriptor->wHubCharacteristics);
         // 判断hub是不是混合设备
    if (wHubCharacteristics & HUB_CHAR_COMPOUND) {
                  // 如果是混合设备就需要存储其每一个下行端口是否可以被移除
         // 判断hub的电源管理类型
    switch (wHubCharacteristics & HUB_CHAR_LPSM) {
    }
        // 判断hub的过流保护类型
    switch (wHubCharacteristics & HUB_CHAR_OCPM) {
    }

    spin_lock_init (&hub->tt.lock);
    INIT_LIST_HEAD (&hub->tt.clear_list);
    INIT_WORK(&hub->tt.clear_work, hub_tt_work);
        //  根据设备描述符中bDeviceProtocol字段信息设置hub->tt
    switch (hdev->descriptor.bDeviceProtocol) {
    }
        //  设置usb->tt.think_time
    switch (wHubCharacteristics & HUB_CHAR_TTTT) {
    }
        // 判断是否支持指示
    if (wHubCharacteristics & HUB_CHAR_PORTIND) {

    }
        //  获得hub的状态
    ret = usb_get_status(hdev, USB_RECIP_DEVICE, , &hubstatus);
        //  对hub的电源管理
        ...........
    ret = hub_hub_status(hub, &hubstatus, &hubchange);
        ...........
        //  分配一个urb
    hub->urb = usb_alloc_urb(, GFP_KERNEL);
        //  填充这个urb
    usb_fill_int_urb(hub->urb, hdev, pipe, *hub->buffer, maxp, hub_irq,
        hub, endpoint->bInterval);
        //  激活hub
    hub_activate(hub, HUB_INIT);
}

　　在hub_configure中填充了urb后，检测hub端口，如果状态发生变化，那么会调用hub_irq函数（这其中的过程需要后续的发现）