现在开始就沿着usb_generic_driver的生命线继续往下走。设备的生命线你可以为是从你的usb设备连接到hub的某个端口时开始，而驱动的生命线就必须得回溯到usb子系统的初始化函数usb_init了。
if (retval)
goto hub_init_failed;
retval = usb_register_device_driver(&usb_generic_driver, THIS_MODULE);
if (!retval)
goto out;
在usb子系统初始化的时候就调用driver.c里的usb_register_device_driver函数将usb_generic_driver注册给系统了，怀胎十月，嗷嗷一声之后，usb世界里的一个超级大美女诞生了。现在先看看带她来到这个世界上的usb_register_device_driver函数。
/**
* usb_register_device_driver - register a USB device (not interface) driver
* @new_udriver: USB operations for the device driver
* @owner: module owner of this driver.
*
* Registers a USB device driver with the USB core. The list of
* unattached devices will be rescanned whenever a new driver is
* added, allowing the new driver to attach to any recognized devices.
* Returns a negative error code on failure and 0 on success.
*/
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;
}
usb_disabled函数判断一下usb子系统是不是在你启动内核的时候就被禁止了，如果是的话，这个超级大美女的生命也就太短暂了。
看到没，for_devices就是在这儿被初始化为1的，有了它，match里的那个is_usb_device_driver把门儿的才有章可循有凭可依。
下面就是充实了下usb_generic_driver里嵌入的那个struct device_driver结构体，usb_generic_driver就是通过它和设备模型搭上关系的。name就是usb_generic_driver的名字，即usb，所属的总线类型同样被设置为usb_bus_type，然后是指定probe函数和remove函数。
然后调用设备模型的函数driver_register将usb_generic_driver添加到usb总线的那条驱动链表里。
usb_generic_driver和usb设备匹配成功后，就会调用指定的probe函数usb_probe_device()，现在看看driver.c里定义的这个函数。
/* called from driver core with dev locked */
static int usb_probe_device(struct device *dev)
{
struct usb_device_driver *udriver = to_usb_device_driver(dev->driver);
struct usb_device *udev;
int error = -ENODEV;
dev_dbg(dev, "%s\n", __FUNCTION__);
if (!is_usb_device(dev)) /* Sanity check */
return error;
udev = to_usb_device(dev);
/* TODO: Add real matching code */
/* The device should always appear to be in use
* unless the driver suports autosuspend.
*/
udev->pm_usage_cnt = !(udriver->supports_autosuspend);
error = udriver->probe(udev);
return error;
}
首先to_usb_device_driver是include/linux/usb.h里定义的一个宏，和前面遇到的那个to_usb_device有异曲同工之妙，
然后is_usb_device表示 usb_generic_driver是match成功了，但是还需要获得usb_device结构体，所以to_usb_device它这就来了。
pm_usage_cnt和supports_autosuspend两个变量，前面都提到过那么一下，现在将那两个片断给回顾一下。每个struct usb_interface或struct usb_device里都有一个pm_usage_cnt，每个struct usb_driver或struct usb_device_driver里都有一个supports_autosuspend。提到pm_usage_cnt时说只有它为0时才会允许接口autosuspend，提到supports_autosuspend时说如果它为0就不再允许绑定到这个驱动的接口autosuspend。接口乎？设备乎？有些时候需要那么难得糊涂一下。需要的时候，群众的眼睛是雪亮的，接口是接口设备是设备，不需要的时候，群众是不明真相的，接口设备一个样。这里就是不需要的时候，所以将上面的话里的接口换成设备套一下就是：pm_usage_cnt为0时才会允许设备autosuspend，supports_autosuspend为0就不再允许绑定到这个驱动的设备autosuspend。
所有的usb设备都是绑定到usb_generic_driver上面的，usb_generic_driver的supports_autosuspend字段又是为1的，所以这行就是将设备struct usb_device结构体的pm_usage_cnt置为了0，也就是说允许设备autosuspend。但是不是说这里将pm_usage_cnt轻轻松松置为0，设备就能够autosuspend了，什么事都是说起来简单，做起来就不是那么回事儿，驱动必须得实现一对儿suspend/resume函数供PM子系统那块驱使，usb_generic_driver里的这对函数就是generic_suspend/generic_resume，就不多说它们了。
最后调用usb_generic_driver自己私有的probe函数generic_probe()对你的设备进行进一步的审查。
static int generic_probe(struct usb_device *udev)
{
int err, c;
/* put device-specific files into sysfs */
usb_create_sysfs_dev_files(udev);
/* Choose and set the configuration. This registers the interfaces
* with the driver core and lets interface drivers bind to them.
*/
c = choose_configuration(udev);
if (c >= 0) {
err = usb_set_configuration(udev, c);
if (err) {
dev_err(&udev->dev, "can't set config #%d, error %d\n",
c, err);
/* This need not be fatal. The user can try to
* set other configurations. */
}
}
/* USB device state == configured ... usable */
usb_notify_add_device(udev);
return 0;
}
这函数用一句话去概括它的中心思想，就是从设备可能的众多配置中选择一个合适的，然后去配置设备，从而让设备进入期待已久的Configured状态。概括了中心思想，再去看看细节。先看看是怎么选择一个配置的，调用的是generic.c里的choose_configuration函数。注释很详细就不说了。看一下另一个设备配置usb_set_configuration函数。
/*
* usb_set_configuration - Makes a particular device setting be current
* @dev: the device whose configuration is being updated
* @configuration: the configuration being chosen.
* Context: !in_interrupt(), caller owns the device lock
*
* This is used to enable non-default device modes. Not all devices
* use this kind of configurability; many devices only have one
* configuration.
*
* @configuration is the value of the configuration to be installed.
* According to the USB spec (e.g. section 9.1.1.5), configuration values
* must be non-zero; a value of zero indicates that the device in
* unconfigured. However some devices erroneously use 0 as one of their
* configuration values. To help manage such devices, this routine will
* accept @configuration = -1 as indicating the device should be put in
* an unconfigured state.
*
* USB device configurations may affect Linux interoperability,
* power consumption and the functionality available. For example,
* the default configuration is limited to using 100mA of bus power,
* so that when certain device functionality requires more power,
* and the device is bus powered, that functionality should be in some
* non-default device configuration. Other device modes may also be
* reflected as configuration options, such as whether two ISDN
* channels are available independently; and choosing between open
* standard device protocols (like CDC) or proprietary ones.
*
* Note that USB has an additional level of device configurability,
* associated with interfaces. That configurability is accessed using
* usb_set_interface().
*
* This call is synchronous. The calling context must be able to sleep,
* must own the device lock, and must not hold the driver model's USB
* bus mutex; usb device driver probe() methods cannot use this routine.
*
* Returns zero on success, or else the status code returned by the
* underlying call that failed. On successful completion, each interface
* in the original device configuration has been destroyed, and each one
* in the new configuration has been probed by all relevant usb device
* drivers currently known to the kernel.
*/
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;
int n, nintf;
if (configuration == -1)
configuration = 0;
else {
for (i = 0; i < dev->descriptor.bNumConfigurations; i++) {
if (dev->config[i].desc.bConfigurationValue ==
configuration) {
cp = &dev->config[i];
break;
}
}
}
if ((!cp && configuration != 0))
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.
*/
if (cp && configuration == 0)
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 = 0;
if (cp) {
nintf = cp->desc.bNumInterfaces;
new_interfaces = kmalloc(nintf * sizeof(*new_interfaces),
GFP_KERNEL);
if (!new_interfaces) {
dev_err(&dev->dev, "Out of memory");
return -ENOMEM;
}
for (; n < nintf; ++n) {
new_interfaces[n] = kzalloc(
sizeof(struct usb_interface),
GFP_KERNEL);
if (!new_interfaces[n]) {
dev_err(&dev->dev, "Out of memory");
ret = -ENOMEM;
free_interfaces:
while (--n >= 0)
kfree(new_interfaces[n]);
kfree(new_interfaces);
return ret;
}
}
i = dev->bus_mA - cp->desc.bMaxPower * 2;
if (i < 0)
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 */
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, 1); // Skip ep0
if ((ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
USB_REQ_SET_CONFIGURATION, 0, configuration, 0,
NULL, 0, USB_CTRL_SET_TIMEOUT)) < 0) {
/* 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_autosuspend_device(dev);
goto free_interfaces;
}
usb_set_device_state(dev, USB_STATE_CONFIGURED);
/* Initialize the new interface structures and the
* hc/hcd/usbcore interface/endpoint state.
*/
for (i = 0; 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;
kref_get(&intfc->ref);
alt = usb_altnum_to_altsetting(intf, 0);
/* 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[0];
intf->cur_altsetting = alt;
usb_enable_interface(dev, intf);
intf->dev.parent = &dev->dev;
intf->dev.driver = NULL;
intf->dev.bus = &usb_bus_type;
intf->dev.type = &usb_if_device_type;
intf->dev.dma_mask = dev->dev.dma_mask;
device_initialize (&intf->dev);
mark_quiesced(intf);
sprintf (&intf->dev.bus_id[0], "%d-%s:%d.%d",
dev->bus->busnum, dev->devpath,
configuration, alt->desc.bInterfaceNumber);
}
kfree(new_interfaces);
if (cp->string == NULL)
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 = 0; i < nintf; ++i) {
struct usb_interface *intf = cp->interface[i];
dev_dbg (&dev->dev,
"adding %s (config #%d, interface %d)\n",
intf->dev.bus_id, configuration,
intf->cur_altsetting->desc.bInterfaceNumber);
ret = device_add (&intf->dev);
if (ret != 0) {
dev_err(&dev->dev, "device_add(%s) --> %d\n",
intf->dev.bus_id, ret);
continue;
}
usb_create_sysfs_intf_files (intf);
}
usb_autosuspend_device(dev);
return 0;
}
遇到很长的代码，我们总是想说点函数背后的理论，或者聊聊函数背后的人生哲学。走到这里，设备已经和usb_generic_driver这个大美女配对成功了，这并不意味着你可以高枕无忧了，要想保持和她的这种亲密关系，你得想办法让她得到满足，你就要准备着让她去配置，准备着她想让你什么样你就什么样。你要明白，吸引住男人的办法就是让他一直得不到，吸引住女人的办法正好相反，就是让她一直满足。从这个角度看，这个函数就可以泾渭分明的分成三个部分三个阶段。一是准备阶段，做做常规检查啊，申请申请内存啊，搞点前戏什么的。二是设备从Address发展到了Configured，可算是高潮阶段，别看它短，这是事物发展的规律，也是每个男人女人的规律，充实充实设备的每个接口并提交给设备模型，为它们寻找命中注定的接口驱动。最后温存温存，过了这个后戏阶段，usb_generic_driver也就彻底从你设备那儿得到满足了，generic_probe的历史使命也就完成了。事物的发展大体上就脱离不了这三个阶段，再比如股票，买、卖、回味。
先看第一阶段，configuration（函数参数之一）是前边儿choose_configuration()那里返回回来的，找到合意的配置的话，就返回那个配置的bConfigurationValue值，没有找到称心的配置的话，就返回-1，所以这里的configuration值就可能有两种情况，或者为-1，或者为配置的bConfigurationValue值。当configuration为-1时这里为啥又要把它改为0捏？要知道configuration这个值是要在后面的高潮阶段里发送SET_CONFIGURATION请求时用的，关于SET_CONFIGURATION请求，spec里说，这个值必须为0或者与配置描述符的bConfigurationValue一致，如果为0，则设备收到SET_CONFIGURATION请求后，仍然会待在Address状态。这里当configuration为-1也就是没有发现满意的配置时，设备不能进入Configured，所以要把configuration的值改为0，以便满足SET_CONFIGURATION请求的要求。那接下来的问题就出来了，在没有找到合适配置的时候直接给configuration这个参数传个0，也就是让choose_configuration()返回个0不就得了，干吗还这么麻烦先返回个-1再把它改成0，不是脱裤子放屁多此一举么？这归根结底还是那句话，有些设备就是有拿0当配置bConfigurationValue值的毛病，你又不能不让它用，这里妥协一下就是了，想让设备回到Address状态时，usb_set_configuration()就别传递0了，传递个-1，里边儿去处理一下。如果configuration值为0或大于0的值，就从设备struct usb_device结构体的config数组里将相应配置的描述信息，也就是struct usb_host_config结构体给取出来。如果没有拿到配置的内容，configuration值就必须为0了，让设备待在Address那儿别动。这也很好理解，配置的内容都找不到了，还配置个什么劲儿。当然，如果拿到了配置的内容，但同时configuration为0，这就是对应了上面说的那种有毛病的设备的情况，就提出一下警告，告诉你不正常现象出现了。接下来的if判断如果配置是实实在在存在的，就为它使用的那些接口都准备一个struct usb_interface结构体。new_interfaces是开头儿就定义好的一个struct usb_interface结构体指针数组，数组的每一项都指向了一个struct usb_interface结构体，所以这里申请内存也要分两步走，先申请指针数组的，再申请每一项的。
下面的高潮部分，还是抽两支烟的功夫后再看吧。