Linux下的USB HUB驱动

Linux下的USB HUB驱动

一:前言
继UHCI的驱动之后,我们对USB Control的运作有了一定的了解.在接下来的分析中,我们对USB设备的驱动做一个全面的分析,我们先从HUB的驱动说起.关于HUB,usb2.0 spec上有详细的定义,基于这部份的代码位于linux-2.6.25/drivers/usb/core下,也就是说,这部份代码是位于core下,和具体设备是无关的,因为各厂商的hub都是按照spec的要求来设计的.
二:UHCI驱动中的root hub
记得在分析UHCI驱动的时候,曾详细分析过root hub的初始化操作.为了分析方便,将代码片段列出如下:
usb_add_hcd() à usb_alloc_dev():
struct usb_device *usb_alloc_dev(struct usb_device *parent,
               struct usb_bus *bus, unsigned port1)
{
    ……
    ……
    //usb_device,内嵌有struct device结构,对这个结构进行初始化
    device_initialize(&dev->dev);
    dev->dev.bus = &usb_bus_type;
    dev->dev.type = &usb_device_type;
    ……
    ……
}
一看到前面对dev的赋值,根据我们对设备模型的理解,一旦这个device进行注册,就会发生driver和device的匹配过程了.
不过,现在还不是分析这个过程的时候,我们先来看一下,USB子系统中的两种驱动.
 
三:USB子系统中的两种驱动
linux-2.6.25/drivers/usb/core/driver.c中,我们可以找到两种register driver的方式,分别为usb_register_driver()和usb_register_device_driver().分别来分析一下这两个接口.
 
usb_register_device_driver()接口的代码如下:
int usb_register_device_driver(struct usb_device_driver *new_udriver,
        struct module *owner)
{
    int retval = 0;
 
    if (usb_disabled())
        return -ENODEV;
 
    new_udriver->drvwrap.for_devices = 1;
    new_udriver->drvwrap.driver.name = (char *) new_udriver->name;
    new_udriver->drvwrap.driver.bus = &usb_bus_type;
    new_udriver->drvwrap.driver.probe = usb_probe_device;
    new_udriver->drvwrap.driver.remove = usb_unbind_device;
    new_udriver->drvwrap.driver.owner = owner;
 
    retval = driver_register(&new_udriver->drvwrap.driver);
 
    if (!retval) {
        pr_info("%s: registered new device driver %s\n",
            usbcore_name, new_udriver->name);
        usbfs_update_special();
    } else {
        printk(KERN_ERR "%s: error %d registering device "
            "   driver %s\n",
            usbcore_name, retval, new_udriver->name);
    }
 
    return retval;
}
首先,通过usb_disabled()来判断一下usb是否被禁用,如果被禁用,当然就不必执行下面的流程了,直接退出即可.
从上面的代码,很明显可以看到, struct usb_device_driver 对struct device_driver进行了一次封装,我们注意一下这里的赋值操作:new_udriver->drvwrap.for_devices = 1.等等.这些在后面都是用派上用场的.
 
usb_register_driver()的代码如下:
int usb_register_driver(struct usb_driver *new_driver, struct module *owner,
            const char *mod_name)
{
    int retval = 0;
 
    if (usb_disabled())
        return -ENODEV;
 
    new_driver->drvwrap.for_devices = 0;
    new_driver->drvwrap.driver.name = (char *) new_driver->name;
    new_driver->drvwrap.driver.bus = &usb_bus_type;
    new_driver->drvwrap.driver.probe = usb_probe_interface;
    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);
 
    if (!retval) {
        pr_info("%s: registered new interface driver %s\n",
            usbcore_name, new_driver->name);
        usbfs_update_special();
        usb_create_newid_file(new_driver);
    } else {
        printk(KERN_ERR "%s: error %d registering interface "
            "   driver %s\n",
            usbcore_name, retval, new_driver->name);
    }
 
    return retval;
}
很明显,在这里接口里,将new_driver->drvwrap.for_devices设为了0.而且两个接口的porbe()函数也不一样.
其实,对于usb_register_driver()可以看作是usb设备中的接口驱动,而usb_register_device_driver()是一个单纯的USB设备驱动.