Linux设备驱动之USB hub驱动

Linux设备驱动之USB hub驱动2012-07-24 14:06:49

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原文地址：Linux设备驱动之USB hub驱动 作者：xgr180

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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.

四: hub的驱动分析

4.1: usb_bus_type->match()的匹配过程

usb_bus_type->match()用来判断驱动和设备是否匹配,它的代码如下:

static int usb_device_match(struct device *dev, struct device_driver *drv)

{

/* devices and interfaces are handled separately */

//usb device的情况

if (is_usb_device(dev)) {

/* interface drivers never match devices */

if (!is_usb_device_driver(drv))

return 0;

/* TODO: Add real matching code */

return 1;

}

//interface的情况

else {

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 0;

intf = to_usb_interface(dev);

usb_drv = to_usb_driver(drv);

id = usb_match_id(intf, usb_drv->id_table);

if (id)

return 1;

id = usb_match_dynamic_id(intf, usb_drv);

if (id)

return 1;

}

return 0;

}

这里的match会区分上面所说的两种驱动,即设备的驱动和接口的驱动.

is_usb_device()的代码如下:

static inline int is_usb_device(const struct device *dev)

{

return dev->type == &usb_device_type;

}

很明显,对于root hub来说,这个判断是肯定会满足的.

static inline int is_usb_device_driver(struct device_driver *drv)

{

return container_of(drv, struct usbdrv_wrap, driver)->

for_devices;

}

回忆一下,我们在分析usb_register_device_driver()的时候,不是将new_udriver->drvwrap.for_devices置为了1么?所以对于usb_register_device_driver()注册的驱动来说,这里也是会满足的.

因此,对应root hub的情况,从第一个if就会匹配到usb_register_device_driver()注册的驱动.

对于接口的驱动,我们等遇到的时候再来进行分析.

4.2:root hub的驱动入口

既然我们知道,root hub会匹配到usb_bus_type->match()的驱动,那这个驱动到底是什么呢?我们从usb子系统的初始化开始说起.

在linux-2.6.25/drivers/usb/core/usb.c中.有这样的一段代码:

subsys_initcall(usb_init);

对于subsys_initcall()我们已经不陌生了,在很多地方都会遇到它.在系统初始化的时候,会调用到它对应的函数.在这里,即为usb_init().

在usb_init()中,有这样的代码片段:

static int __init usb_init(void)

{

……

……

retval = usb_register_device_driver(&usb_generic_driver, THIS_MODULE);

if (!retval)

goto out;

……

}

在这里终于看到usb_register_device_driver()了. usb_generic_driver会匹配到所有usb 设备.定义如下:

struct usb_device_driver usb_generic_driver = {

.name = "usb",

.probe = generic_probe,

.disconnect = generic_disconnect,

#ifdef CONFIG_PM

.suspend = generic_suspend,

.resume = generic_resume,

#endif

.supports_autosuspend = 1,

};

现在是到分析probe()的时候了.我们这里说的并不是usb_generic_driver中的probe,而是封装在struct usb_device_driver中的driver对应的probe函数.

在上面的分析, usb_register_device_driver()将封装的driver的probe()函数设置为了usb_probe_device().代码如下:

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__);

//再次判断dev是否是usb device

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.

*/

//pm_usage_cnt: autosuspend计数.如果此计数为1,则不允许autosuspend

udev->pm_usage_cnt = !(udriver->supports_autosuspend);

error = udriver->probe(udev);

return error;

}

首先,可以通过container_of()将封装的struct device, struct device_driver转换为struct usb_device和struct usb_device_driver.

然后,再执行一次安全检查,判断dev是否是属于一个usb device.

在这里,我们首次接触到了hub suspend.如果不支持suspend(udriver->supports_autosuspend为0),则udev->pm_usage_cnt被设为1,也就是说,它不允许设备suspend.否则,将其初始化为0.

最后,正如你所看到的,流程转入到了usb_device_driver->probe().

对应到root hub,流程会转入到generic_probe().代码如下:

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.

*/

if (udev->authorized == 0)

dev_err(&udev->dev, "Device is not authorized for usage\n");

else {

//选择和设定一个配置

c = usb_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;

}

usb_create_sysfs_dev_files()是在sysfs中显示几个属性文件,不进行详细分析,有兴趣的可以结合之前分析的<<linux设备模型详解>>来看下代码.

usb_notify_add_device()是有关notify链表的操作,这里也不做详细分析.

至于udev->authorized,在root hub的初始化中,是会将其初始化为1的.后面的逻辑就更简单了.为root hub 选择一个配置然后再设定这个配置.

还记得我们在分析root hub的时候,在usb_new_device()中,会将设备的所有配置都取出来,然后将它们放到了usb_device-> config.现在这些信息终于会派上用场了.不太熟悉的,可以看下本站之前有关usb控制器驱动的文档.

Usb2.0 spec上规定,对于hub设备,只能有一个config,一个interface,一个endpoint.实际上,在这里,对hub的选择约束不大,反正就一个配置,不管怎么样,选择和设定都是这个配置.

不过,为了方便以后的分析,我们还是跟进去看下usb_choose_configuration()和usb_set_configuration()的实现.

实际上,经过这两个函数之后,设备的probe()过程也就会结束了.

4.2.1:usb_choose_configuration()函数分析

usb_choose_configuration()的代码如下:

//为usb device选择一个合适的配置

int usb_choose_configuration(struct usb_device *udev)

{

int i;

int num_configs;

int insufficient_power = 0;

struct usb_host_config *c, *best;

best = NULL;

//config数组

c = udev->config;

//config项数

num_configs = udev->descriptor.bNumConfigurations;

//遍历所有配置项

for (i = 0; i < num_configs; (i++, c++)) {

struct usb_interface_descriptor *desc = NULL;

/* It's possible that a config has no interfaces! */

//配置项的接口数目

//取配置项的第一个接口

if (c->desc.bNumInterfaces > 0)

desc = &c->intf_cache[0]->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 */

//电源不足.配置描述符中的电力是所需电力的1/2

if (c->desc.bMaxPower * 2 > 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.

*/

if (i == 0 && 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. */

//选择一个不是USB_CLASS_VENDOR_SPEC的配置

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 > 0)

dev_info(&udev->dev, "rejected %d configuration%s "

"due to insufficient available bus power\n",

insufficient_power, plural(insufficient_power));

//如果选择好了配置,返回配置的序号,否则,返回-1

if (best) {

i = best->desc.bConfigurationValue;

dev_info(&udev->dev,

"configuration #%d chosen from %d choice%s\n",

i, num_configs, plural(num_configs));

} else {

i = -1;

dev_warn(&udev->dev,

"no configuration chosen from %d choice%s\n",

num_configs, plural(num_configs));

}

return i;

}

Linux按照自己的喜好选择好了配置之后,返回配置的序号.不过对于HUB来说,它有且仅有一个配置.

4.2.2:usb_set_configuration()函数分析

既然已经选好配置了,那就告诉设备选好的配置,这个过程是在usb_set_configuration()中完成的.它的代码如下:

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 (dev->authorized == 0 || 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");

首先,根据选择好的配置号找到相应的配置,在这里要注意了, dev->config[]数组中的配置并不是按照配置的序号来存放的,而是按照遍历到顺序来排序的.因为有些设备在发送配置描述符的时候,并不是按照配置序号来发送的,例如,配置2可能在第一次GET_CONFIGURATION就被发送了,而配置1可能是在第二次GET_CONFIGURATION才能发送.

取得配置描述信息之后,要对它进行有效性判断,注意一下本段代码的最后几行代码:usb2.0 spec上规定,0号配置是无效配置,但是可能有些厂商的设备并末按照这一约定,所以在linux中,遇到这种情况只是打印出警告信息,然后尝试使用这一配置.

/* 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) {

//接口总数

nintf = cp->desc.bNumInterfaces;

//interface指针数组,

new_interfaces = kmalloc(nintf * sizeof(*new_interfaces),

GFP_KERNEL);

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_KERNEL);

if (!new_interfaces[n]) {

dev_err(&dev->dev, "Out of memory\n");

ret = -ENOMEM;

free_interfaces:

while (--n >= 0)

kfree(new_interfaces[n]);

kfree(new_interfaces);

return ret;

}

}

//如果总电源小于所需电流,打印警告信息

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);

}

在这里,注要是为new_interfaces分配空间,要这意的是, new_interfaces是一个二级指针,它的最终指向是struct usb_interface结构.特别的,如果总电流数要小于配置所需电流,则打印出警告消息.实际上,这种情况在usb_choose_configuration()中已经进行了过滤.

/* Wake up the device so we can send it the Set-Config request */

//要对设备进行配置了,先唤醒它

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.

*/

//不是处于ADDRESS状态,先清除设备的状态

if (dev->state != USB_STATE_ADDRESS)

usb_disable_device(dev, 1); /* Skip ep0 */

//发送控制消息,选取配置

ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),

USB_REQ_SET_CONFIGURATION, 0, configuration, 0,

NULL, 0, USB_CTRL_SET_TIMEOUT);

if (ret < 0) {

/* All the old state is gone, so what else can we do?

* The device is probably useless now anyway.

*/

cp = NULL;

}

//dev->actconfig存放的是当前设备选取的配置

dev->actconfig = cp;

if (!cp) {

usb_set_device_state(dev, USB_STATE_ADDRESS);

usb_autosuspend_device(dev);

goto free_interfaces;

}

//将状态设为CONFIGURED

usb_set_device_state(dev, USB_STATE_CONFIGURED);

接下来,就要对设备进行配置了,首先,将设备唤醒.回忆一下我们在分析UHCI驱动时,列出来的设备状态图.只有在ADDRESS状态才能转入到CONFIG状态.(SUSPEND状态除外). 所以,如果设备当前不是处于ADDRESS状态,就需要将设备的状态初始化.usb_disable_device()函数是个比较重要的操作,在接下来再对它进行详细分析.

接着,发送SET_CONFIGURATION的Control消息给设备,用来选择配置

最后,将dev->actconfig指向选定的配置,将设备状态设为CONFIG

/* Initialize the new interface structures and the

* hc/hcd/usbcore interface/endpoint state.

*/

//遍历所有的接口

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;

//是否关联的接口描述符,定义在minor usb 2.0 spec中

intf->intf_assoc = find_iad(dev, cp, i);

kref_get(&intfc->ref);

//选择0号设置

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.

*/

//如果0号设置不存在,选排在第一个设置

if (!alt)

alt = &intf->altsetting[0];

//当前的配置

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);

之前初始化的new_interfaces在这里终于要派上用场了.初始化各接口,从上面的初始化过程中,我们可以看出:

Intf->altsetting,表示接口的各种设置

Intf->num_altsetting:表示接口的设置数目

Intf->intf_assoc:接口的关联接口(定义于minor usb 2.0 spec)

Intf->cur_altsetting:接口的当前设置.

结合之前在UHCI中的分析,我们总结一下:

Usb_dev->config,其实是一个数组,存放设备的配置.usb_dev->config[m]-> interface[n]表示第m个配置的第n个接口的intercace结构.(m,n不是配置序号和接口序号 *^_^*).

注意这个地方对intf内嵌的struct devcie结构赋值,它的type被赋值为了usb_if_device_type.bus还是usb_bus_type.可能你已经反应过来了,要和这个device匹配的设备是interface的驱动.

特别的,这里的device的命名:

sprintf(&intf->dev.bus_id[0], "%d-%s:%d.%d",

dev->bus->busnum, dev->devpath,

configuration, alt->desc.bInterfaceNumber);

dev指的是这个接口所属的usb_dev,结合我们之前在UHCI中关于usb设备命名方式的描述.可得出它的命令方式如下:

USB总线号-设备路径:配置号.接口号.

例如,在我的虚拟机上:

[root@localhost devices]# pwd

/sys/bus/usb/devices

[root@localhost devices]# ls

1-0:1.0 usb1

[root@localhost devices]#

可以得知,系统只有一个usb control.

1-0:1.0:表示,第一个usb control下的root hub的1号配置的0号接口.

那在插入U盘之后,会发生什么变化呢?不着急,我们等着往下面看,待分析到的时候,我自然就会列出来了 ^_^

usb_enable_interface()用来启用接口,也就是启用接口中的每一个endpoint.这个接口比较简单,其中调用的子函数usb_enable_endpoint()在分析UHCI的时候已经详细分析过了.在这里就不再赘述了.

在这里,还涉及到一个很有意思的函数, mark_quiesced().从字面意思上看来,它是标记接口为停止状态.它的”反函数”是mark_active().两个函数如下示:

static inline void mark_active(struct usb_interface *f)

{

f->is_active = 1;

f->dev.power.power_state.event = PM_EVENT_ON;

}

static inline void mark_quiesced(struct usb_interface *f)

{

f->is_active = 0;

f->dev.power.power_state.event = PM_EVENT_SUSPEND;

}

从代码看来,它只是对接口的活动标志(is_active)进行了设置.

/* 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.

*/

//注册每一个接口?

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);

}

//使设备suspend

usb_autosuspend_device(dev);

return 0;

}

最后,注册intf内嵌的device结构.设备配置完成了,为了省电,可以将设备置为SUSPEND状态.

这个函数中还有几个比较重要的子函数,依次分析如下:

1: usb_disable_device()函数.

顾名思义,这个函数是将设备disable掉.代码如下:

void usb_disable_device(struct usb_device *dev, int skip_ep0)

{

int i;

dev_dbg(&dev->dev, "%s nuking %s URBs\n", __FUNCTION__,

skip_ep0 ? "non-ep0" : "all");

for (i = skip_ep0; i < 16; ++i) {

usb_disable_endpoint(dev, i);

usb_disable_endpoint(dev, i + USB_DIR_IN);

}

dev->toggle[0] = dev->toggle[1] = 0;

/* getting rid of interfaces will disconnect

* any drivers bound to them (a key side effect)

*/

if (dev->actconfig) {

for (i = 0; i < dev->actconfig->desc.bNumInterfaces; i++) {

struct usb_interface *interface;

/* remove this interface if it has been registered */

interface = dev->actconfig->interface[i];

if (!device_is_registered(&interface->dev))

continue;

dev_dbg(&dev->dev, "unregistering interface %s\n",

interface->dev.bus_id);

usb_remove_sysfs_intf_files(interface);

device_del(&interface->dev);

}

/* Now that the interfaces are unbound, nobody should

* try to access them.

*/

for (i = 0; i < dev->actconfig->desc.bNumInterfaces; i++) {

put_device(&dev->actconfig->interface[i]->dev);

dev->actconfig->interface[i] = NULL;

}

dev->actconfig = NULL;

if (dev->state == USB_STATE_CONFIGURED)

usb_set_device_state(dev, USB_STATE_ADDRESS);

}

}

第二个参数是skip_ep0.是表示是否跳过ep0.为1表示跳过,为0表示清除掉设备中的所有endpoint.

这个函数可以分为两个部份,一部份是对usb_dev中的endpoint进行操作,一方面是释放usb_dev的选定配置项.

对于第一部份:

从代码中可能看到,如果skip_ep0为1,那就是从1开始循环,所以,就跳过了ep0.另外,一个端点号对应了两个端点,一个IN,一个OUT.IN端点比OUT端点要大USB_DIR_IN.

另外,既然设备都已经被禁用了,那toggle也应该回归原位了.因些将两个方向的toggle都设为0. usb_disable_endpoint()是一个很有意思的处理.它的代码如下:

void usb_disable_endpoint(struct usb_device *dev, unsigned int epaddr)

{

unsigned int epnum = epaddr & USB_ENDPOINT_NUMBER_MASK;

struct usb_host_endpoint *ep;

if (!dev)

return;

//在dev->ep_out和dev->ep_in删除endpoint

if (usb_endpoint_out(epaddr)) {

ep = dev->ep_out[epnum];

dev->ep_out[epnum] = NULL;

} else {

ep = dev->ep_in[epnum];

dev->ep_in[epnum] = NULL;

}

//禁用掉此ep.包括删除ep上提交的urb 和ep上的QH

if (ep) {

ep->enabled = 0;

usb_hcd_flush_endpoint(dev, ep);

usb_hcd_disable_endpoint(dev, ep);

}

}

在dev->ep_in[]/dev->ep_out[]中删除endpoint,这点很好理解.比较难以理解的是后面的两个操作,即usb_hcd_flush_endpoint()和usb_hcd_disable_endpoint().根据之前分析的UHCI的驱动,我们得知,对于每个endpoint都有一个传输的qh,这个qh上又挂上了要传输的urb.因此,这两个函数一个是删除urb,一个是删除qh.

usb_hcd_flush_endpoint()的代码如下:

void usb_hcd_flush_endpoint(struct usb_device *udev,

struct usb_host_endpoint *ep)

{

struct usb_hcd *hcd;

struct urb *urb;

if (!ep)

return;

might_sleep();

hcd = bus_to_hcd(udev->bus);

/* No more submits can occur */

//在提交urb时,将urb加到ep->urb_list上的时候要持锁

//因此,这里持锁的话,无法发生中断和提交urb

spin_lock_irq(&hcd_urb_list_lock);

rescan:

//将挂在ep->urb_list上的所有urb unlink.注意这里unlink一般只会设置urb->unlinked的

//值,不会将urb从ep->urb_list上删除.只有在UHCI的中断处理的时候,才会调用

//uhci_giveback_urb()将其从ep->urb_list中删除

list_for_each_entry (urb, &ep->urb_list, urb_list) {

int is_in;

if (urb->unlinked)

continue;

usb_get_urb (urb);

is_in = usb_urb_dir_in(urb);

spin_unlock(&hcd_urb_list_lock);

/* kick hcd */

unlink1(hcd, urb, -ESHUTDOWN);

dev_dbg (hcd->self.controller,

"shutdown urb %p ep%d%s%s\n",

urb, usb_endpoint_num(&ep->desc),

is_in ? "in" : "out",

({ char *s;

switch (usb_endpoint_type(&ep->desc)) {

case USB_ENDPOINT_XFER_CONTROL:

s = ""; break;

case USB_ENDPOINT_XFER_BULK:

s = "-bulk"; break;

case USB_ENDPOINT_XFER_INT:

s = "-intr"; break;

default:

s = "-iso"; break;

};

s;

}));

usb_put_urb (urb);

/* list contents may have changed */

//在这里解开锁了,对应ep->urb_list上又可以提交urb.

//这里释放释的话,主要是为了能够产生中断

spin_lock(&hcd_urb_list_lock);

goto rescan;

}

spin_unlock_irq(&hcd_urb_list_lock);

/* Wait until the endpoint queue is completely empty */

//等待urb被调度完

while (!list_empty (&ep->urb_list)) {

spin_lock_irq(&hcd_urb_list_lock);

/* The list may have changed while we acquired the spinlock */

urb = NULL;

if (!list_empty (&ep->urb_list)) {

urb = list_entry (ep->urb_list.prev, struct urb,

urb_list);

usb_get_urb (urb);

}

spin_unlock_irq(&hcd_urb_list_lock);

if (urb) {

usb_kill_urb (urb);

usb_put_urb (urb);

}

}

}

仔细体会这里的代码,为什么在前一个循环中,要使用goto rescan重新开始这个循环呢?这是因为在后面已经将自旋锁释放了,因此,就会有这样的可能,在函数中操作的urb,可能已经被调度完释放了.因此,再对这个urb操作就会产生错误.所以,需要重新开始这个循环.

那后一个循环又是干什么的呢?后一个循环就是等待urb被调度完.有人就会有这样的疑问了,这里一边等待,然后endpoint一边还提交urb,那这个函数岂不是要耗掉很长时间?

在这里,不要忘记了前面的操作,在调这个函数之前, usb_disable_endpoint()已经将这个endpoint禁用了,也就是说该endpoint不会产生新的urb.因为,在后一个循环中,只需要等待那些被unlink的urb调度完即可.在usb_kill_urb()中,会一直等待,直到这个urb被调度完成为止.

可能有人又会有这样的疑问:

Usb_kill_urb()中也有unlink urb的操作,为什么这里要分做两个循环呢?

另外的一个函数是usb_hcd_disable_endpoint().代码如下:

void usb_hcd_disable_endpoint(struct usb_device *udev,

struct usb_host_endpoint *ep)

{

struct usb_hcd *hcd;

might_sleep();

hcd = bus_to_hcd(udev->bus);

if (hcd->driver->endpoint_disable)

hcd->driver->endpoint_disable(hcd, ep);

}

从上面的代码可以看到,操作转向了hcd->driver的endpoint_disable()接口.

以UHCI为例.在UHCI中,对应的接口为:

static void uhci_hcd_endpoint_disable(struct usb_hcd *hcd,

struct usb_host_endpoint *hep)

{

struct uhci_hcd *uhci = hcd_to_uhci(hcd);

struct uhci_qh *qh;

spin_lock_irq(&uhci->lock);

qh = (struct uhci_qh *) hep->hcpriv;

if (qh == NULL)

goto done;

while (qh->state != QH_STATE_IDLE) {

++uhci->num_waiting;

spin_unlock_irq(&uhci->lock);

wait_event_interruptible(uhci->waitqh,

qh->state == QH_STATE_IDLE);

spin_lock_irq(&uhci->lock);

--uhci->num_waiting;

}

uhci_free_qh(uhci, qh);

done:

spin_unlock_irq(&uhci->lock);

}

这个函数没啥好说的,就是在uhci->waitqh上等待队列状态变为QH_STATE_IDLE.来回忆一下,qh在什么情况下才会变为QH_STATE_IDLE呢? 是在qh没有待传输的urb的时候.

然后,将qh释放.

现在我们来接着看usb_disable_device()的第二个部份.

第二部份主要是针对dev->actconfig进行的操作, dev->actconfig存放的是设备当前的配置,现在要将设备设回Address状态.就些东西当然是用不了上的了.释放dev->actconfig->interface[]中的各元素,注意不要将dev->actconfig->interface[]所指向的信息释放了,它都是指向dev->config[]-> intf_cache[]中的东西,这些东西一释放,usb device在Get_ Configure所获得的信息就会部丢失了.

就这样, usb_disable_device()函数也走到了尾声.

2: usb_cache_string()函数

这个函数我们在分析UHCI的时候已经接触过,但末做详细的分析.

首先了解一下这个函数的作用,有时候,为了形象的说明,会提供一个字符串形式的说明.例如,对于配置描述符来说,它的iConfiguration就表示一个字符串索引,然后用Get_String就可以取得这个索引所对应的字串了.不过,事情并不是这么简单.因为字符串对应不同的编码,所以这里还会对应有编码的处理.来看具体的代码:

char *usb_cache_string(struct usb_device *udev, int index)

{

char *buf;

char *smallbuf = NULL;

int len;

if (index <= 0)

return NULL;

//不知道字符到底有多长,就按最长256字节处理

buf = kmalloc(256, GFP_KERNEL);

if (buf) {

len = usb_string(udev, index, buf, 256);

//取到字符了,分配合适的长度

if (len > 0) {

smallbuf = kmalloc(++len, GFP_KERNEL);

if (!smallbuf)

return buf;

//将字符copy过去

memcpy(smallbuf, buf, len);

}

//释放旧空间

kfree(buf);

}

return smallbuf;

}

这个函数没啥好说的,流程转入到usb_string中.代码如下:

int usb_string(struct usb_device *dev, int index, char *buf, size_t size)

{

unsigned char *tbuf;

int err;

unsigned int u, idx;

if (dev->state == USB_STATE_SUSPENDED)

return -EHOSTUNREACH;

if (size <= 0 || !buf || !index)

return -EINVAL;

buf[0] = 0;

tbuf = kmalloc(256, GFP_KERNEL);

if (!tbuf)

return -ENOMEM;

/* get langid for strings if it's not yet known */

//先取得设备支持的编码ID

if (!dev->have_langid) {

//以0号序号和编码0,Get_String就可得到设备所支持的编码列表

err = usb_string_sub(dev, 0, 0, tbuf);

//如果发生了错误,或者是取得的数据超短(最短为4字节)

if (err < 0) {

dev_err(&dev->dev,

"string descriptor 0 read error: %d\n",

err);

goto errout;

} else if (err < 4) {

dev_err(&dev->dev, "string descriptor 0 too short\n");

err = -EINVAL;

goto errout;

}

//取设备支持的第一个编码

else {

dev->have_langid = 1;

dev->string_langid = tbuf[2] | (tbuf[3] << 8);

/* always use the first langid listed */

dev_dbg(&dev->dev, "default language 0x%04x\n",

dev->string_langid);

}

}

//以编码ID和序号Index作为参数Get_String取得序号对应的字串

err = usb_string_sub(dev, dev->string_langid, index, tbuf);

if (err < 0)

goto errout;

//空一个字符来用来存放结束符

size--; /* leave room for trailing NULL char in output buffer */

//两字节一组,(Unicode编码的)

for (idx = 0, u = 2; u < err; u += 2) {

if (idx >= size)

break;

//如果高字节有值,说明它不是ISO-8859-1编码的,将它置为?

//否则,就将低位的值存放到buf中

if (tbuf[u+1]) /* high byte */

buf[idx++] = '?'; /* non ISO-8859-1 character */

else

buf[idx++] = tbuf[u];

}

//在最后一位赋0,字串结尾

buf[idx] = 0;

//返回字串的长度,(算上了最后的结尾字符)

err = idx;

//如果该描述符不是STRING描述符,打印出错误提示

if (tbuf[1] != USB_DT_STRING)

dev_dbg(&dev->dev,

"wrong descriptor type %02x for string %d (\"%s\")\n",

tbuf[1], index, buf);

errout:

//释放空间,返回长度

kfree(tbuf);

return err;

}

结合代码中的注释,就很容易理解这一函数了,在此不对这一函数做详细分析.

跟踪进usb_string_sub().代码如下:

static int usb_string_sub(struct usb_device *dev, unsigned int langid,

unsigned int index, unsigned char *buf)

{

int rc;

/* Try to read the string descriptor by asking for the maximum

* possible number of bytes */

//如果设备不需要Fixup 就发出Get_String

if (dev->quirks & USB_QUIRK_STRING_FETCH_255)

rc = -EIO;

else

rc = usb_get_string(dev, langid, index, buf, 255);

/* If that failed try to read the descriptor length, then

* ask for just that many bytes */

//如果Get_String失败或者取得长度有问题.就先取字符描述符的头部

//再以实际的长度和参数,再次Get_String

if (rc < 2) {

rc = usb_get_string(dev, langid, index, buf, 2);

if (rc == 2)

rc = usb_get_string(dev, langid, index, buf, buf[0]);

}

//如果成功

if (rc >= 2) {

//如果前两个字节为空.则需要找到数据的有效起始位置

if (!buf[0] && !buf[1])

usb_try_string_workarounds(buf, &rc);

/* There might be extra junk at the end of the descriptor */

//整调一下描述符的长度

if (buf[0] < rc)

rc = buf[0];

//将rc置为了一个偶数.

rc = rc - (rc & 1); /* force a multiple of two */

}

//长度最终小于2.返回错误值

if (rc < 2)

rc = (rc < 0 ? rc : -EINVAL);

return rc;

}

在这个地方,有个错误处理,可能有的设备你一次用255的长度去取它对字符串会返回一个错误,所以,在用255长度返回错误的时候,先以2为长度取它的描述符头度,再以描述符的实际长度去取字符串描述符串.

另外,在描述符的前两个字节都为空的情况下,就需要计算它的有效长度.在代码中,这一工作是由usb_try_string_workarounds()完成的.

static void usb_try_string_workarounds(unsigned char *buf, int *length)

{

int newlength, oldlength = *length;

//前两个字节是描述符头部,所以从2开始循环.

//Unicode编码用两个字节来表示一个字符. 所以每次循环完了之后要+2

for (newlength = 2; newlength + 1 < oldlength; newlength += 2)

//低字节是不可打印字符,或者高字节不为空(不是ISO-8859-1), 就退出循环.

if (!isprint(buf[newlength]) || buf[newlength + 1])

break;

//修正字符串描述符的实际长度.

//如果newlength 等于2.说明字符中描述符没有带字串

if (newlength > 2) {

buf[0] = newlength;

*length = newlength;

}

}

这个函数涉及到编码方面的东东,建议参阅fudan_abc的<< Linux那些事儿之我是USB core >>,上面的较详细的描述.

至此, usb_cache_string()完分析完了.

到这里,usb device driver的probe过程也就完成了.

五:hub接口驱动分析

5.1:接口驱动架构

是时候来分析接口驱动的架构了.

我们在上面看到了接口设备的注册.在开篇的时候分析了接口驱动的注册.我们首先来分析接口驱备和接口驱动的匹配.

代码还是在usb_bus_type->match().只不过是对应另外的一种情况了.将相关代码列出:

static int usb_device_match(struct device *dev, struct device_driver *drv)

{

……

if (is_usb_device(dev)) {

……

}

//interface的情况

else {

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 0;

intf = to_usb_interface(dev);

usb_drv = to_usb_driver(drv);

id = usb_match_id(intf, usb_drv->id_table);

if (id)

return 1;

id = usb_match_dynamic_id(intf, usb_drv);

if (id)

return 1;

}

return 0;

}

经过前面的分析,因为在注册接口设备的时候,是将type设为usb_if_device_type,因此,这个函数第一个if是不会满足的.

首先,将struct device和struct device_driver转换为被封装的struct usb_interface和struct usb_driver.紧接着,我们看到了两个匹配,一个是usb_match_id().另外一个是usb_match_dynamic_id().后者只有在前者没有匹配成功的情况下才能调用.我们也可以看到, struct usb_driver中一个struct usb_device_id类型的数组(id_table字段)和一个dynids链表.哪id和dyname_id有什么区别呢?

一般来说,id_table是usb 接口驱动静态定义的可以和此驱动匹配设备的一些参数.而dyname_id是可以动态调整的.

你可以通过写/sys/bus/usb/drivers/XXX/new_id来设置驱动的dyname_id.其中,XXX表示驱动的名称.

这两个函数的逻辑都差不多,我们以usb_match_id()为例进行分析.代码如下:

const struct usb_device_id *usb_match_id(struct usb_interface *interface,

const struct usb_device_id *id)

{

/* proc_connectinfo in devio.c may call us with id == NULL. */

//如果driver中没有定义符合条件的id_talbe.则不能静态匹配所有设备

if (id == NULL)

return NULL;

/* It is important to check that id->driver_info is nonzero,

since an entry that is all zeroes except for a nonzero

id->driver_info is the way to create an entry that

indicates that the driver want to examine every

device and interface. */

//如果id_talbe中,有定义的匹配项,则调用usb_match_one_id()进行匹配测试

//如果成功,则返回匹配成功的id_talbe 项数.否则,继续下一项

for (; id->idVendor || id->idProduct || id->bDeviceClass ||

id->bInterfaceClass || id->driver_info; id++) {

if (usb_match_one_id(interface, id))

return id;

}

//如果没有匹配成功,则返回NULL

return NULL;

}

Id_talbe所属的结构如下示:

struct usb_device_id {

/* which fields to match against? */

__u16 match_flags;

/* Used for product specific matches; range is inclusive */

__u16 idVendor;

__u16 idProduct;

__u16 bcdDevice_lo;

__u16 bcdDevice_hi;

/* Used for device class matches */

__u8 bDeviceClass;

__u8 bDeviceSubClass;

__u8 bDeviceProtocol;

/* Used for interface class matches */

__u8 bInterfaceClass;

__u8 bInterfaceSubClass;

__u8 bInterfaceProtocol;

/* not matched against */

kernel_ulong_t driver_info;

};

match_flags是一个匹配标志,表示要匹配哪一项.而后面的成员,例如idVendor, idProduct.表示具体要匹配项的值.

usb_match_one_id()的代码如下:

int usb_match_one_id(struct usb_interface *interface,

const struct usb_device_id *id)

{

struct usb_host_interface *intf;

struct usb_device *dev;

/* proc_connectinfo in devio.c may call us with id == NULL. */

//再次判断id是否为空

if (id == NULL)

return 0;

//接口听当前匹配

intf = interface->cur_altsetting;

//转换为所属的usb_dev

dev = interface_to_usbdev(interface);

//关于设备参数的匹配.只有在设备参数符合的情况下,才会进行接口

//参数的匹配.

if (!usb_match_device(dev, id))

return 0;

//下面是关于接口参数的匹配

/* The interface class, subclass, and protocol should never be

* checked for a match if the device class is Vendor Specific,

* unless the match record specifies the Vendor ID. */

//当设备是厂商自定义类型时(Vendor Specific).除非定义了//USB_DEVICE_ID_MATCH_VENDOR

//否则是不需要匹配的

if (dev->descriptor.bDeviceClass == USB_CLASS_VENDOR_SPEC &&

!(id->match_flags & USB_DEVICE_ID_MATCH_VENDOR) &&

(id->match_flags & (USB_DEVICE_ID_MATCH_INT_CLASS |

USB_DEVICE_ID_MATCH_INT_SUBCLASS |

USB_DEVICE_ID_MATCH_INT_PROTOCOL)))

return 0;

//如果要匹配interface class

if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_CLASS) &&

(id->bInterfaceClass != intf->desc.bInterfaceClass))

return 0;

//如果要匹配interface subclass

if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_SUBCLASS) &&

(id->bInterfaceSubClass != intf->desc.bInterfaceSubClass))

return 0;

//如果要匹配interface protocol

if ((id->match_flags & USB_DEVICE_ID_MATCH_INT_PROTOCOL) &&

(id->bInterfaceProtocol != intf->desc.bInterfaceProtocol))

return 0;

return 1;

}

这个函数逻辑比较简单.它先检测所属设备参数的匹配项.再检查接口参数的匹配项.由于这个函数比较简单,就不对它多费舌去解释了.

简单的说一下关于Vendor Specific class的设备,这个类型在USB Class Codes被定义如下:

This base class is defined for vendors to use as they please. These class codes can be used in both Device and Interface Descriptors.

也就是说,这个类型是被厂商自定义的.它主要是靠SubClass和protocol来区分设备的.这些都是非标准定义的.

如果被这个match匹配成功的话,就会转入probe()了,由于bus中没有probe()函数,因此,流程转入到了与之匹配的驱动的probe函数.

记得在开篇的时候,分析过接口驱动,它的probe函数被设置为了usb_cache_string().代码如下:

static int usb_probe_interface(struct device *dev)

{

struct usb_driver *driver = to_usb_driver(dev->driver);

struct usb_interface *intf;

struct usb_device *udev;

const struct usb_device_id *id;

int error = -ENODEV;

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

//如果是一个usb 设备,退出

if (is_usb_device(dev)) /* Sanity check */

return error;

intf = to_usb_interface(dev);

udev = interface_to_usbdev(intf);

//如果所属设备的authorized 为0.错误,退出

if (udev->authorized == 0) {

dev_err(&intf->dev, "Device is not authorized for usage\n");

return -ENODEV;

}

//再确认一下设备和驱动是否匹配

id = usb_match_id(intf, driver->id_table);

if (!id)

id = usb_match_dynamic_id(intf, driver);

//如果匹配

if (id) {

dev_dbg(dev, "%s - got id\n", __FUNCTION__);

//使设备resume

error = usb_autoresume_device(udev);

if (error)

return error;

/* Interface "power state" doesn't correspond to any hardware

* state whatsoever. We use it to record when it's bound to

* a driver that may start I/0: it's not frozen/quiesced.

*/

//将接口标志为active

mark_active(intf);

//intf->condition:接口的状态

//USB_INTERFACE_BINDING:正在绑定

intf->condition = USB_INTERFACE_BINDING;

/* The interface should always appear to be in use

* unless the driver suports autosuspend.

*/

//intf->pm_usage_cnt:如果为1,接口不会autosuspend

intf->pm_usage_cnt = !(driver->supports_autosuspend);

//调用挂装结构的probe

error = driver->probe(intf, id);

//如果发生了错误,将接口标记成不活动的,接口状态设为USB_INTERFACE_UNBOUND

if (error) {

mark_quiesced(intf);

intf->needs_remote_wakeup = 0;

intf->condition = USB_INTERFACE_UNBOUND;

}

//如果成功,将接口状态设为USB_INTERFACE_BOUND

else

intf->condition = USB_INTERFACE_BOUND;

//使设备suspend

usb_autosuspend_device(udev);

}

return error;

}

至此为至,我们遇到了大量的usb_autoresume_device()/usb_autosuspend_device().先将它们放到一边,等以后再来详细分析他们的操作.

还记得,在usb_set_configuration()中,为每一个接口调用了mark_quiesced().所以在这个probe里,将正确匹配的接口调用mark_active(),将其标记为Active.

另外,我们来看一下,intf-> condition的几种情况,在代码中, condition属于enum usb_interface_condition结构.如下示:

enum usb_interface_condition {

USB_INTERFACE_UNBOUND = 0,

USB_INTERFACE_BINDING,

USB_INTERFACE_BOUND,

USB_INTERFACE_UNBINDING,

};

分别表示,没有绑定,正在绑定,已经绑定,正在解除绑定.

从上面的代码中可以看出.最后的流程会回溯到usb_driver的probe.

5.2:hub的接口驱动

经过上面的分析,我们知道,接口驱动和接口的匹配主要是根据接口的一些信息来判断的.那对于hub的接口,它的标志信息是什么呢?

在usb2.0 spec上,规定了hub的设备class和接口class都为0x9.也就是代码中定义的USB_CLASS_HUB.

同时,我们注意到,在usb_init()àusb_hub_init()中:

int usb_hub_init(void)

{

if (usb_register(&hub_driver) < 0) {

printk(KERN_ERR "%s: can't register hub driver\n",

usbcore_name);

return -1;

}

khubd_task = kthread_run(hub_thread, NULL, "khubd");

if (!IS_ERR(khubd_task))

return 0;

/* Fall through if kernel_thread failed */

usb_deregister(&hub_driver);

printk(KERN_ERR "%s: can't start khubd\n", usbcore_name);

return -1;

}

这个函数注册了hub_driver对应的接口驱动,还启动了一个内核线程.在这里,我们注意到, hub_driver的定义如下:

static struct usb_driver hub_driver = {

.name = "hub",

.probe = hub_probe,

.disconnect = hub_disconnect,

.suspend = hub_suspend,

.resume = hub_resume,

.reset_resume = hub_reset_resume,

.pre_reset = hub_pre_reset,

.post_reset = hub_post_reset,

.ioctl = hub_ioctl,

.id_table = hub_id_table,

.supports_autosuspend = 1,

};

Hub_id_talbe被定义为:

static struct usb_device_id hub_id_table [] = {

{ .match_flags = USB_DEVICE_ID_MATCH_DEV_CLASS,

.bDeviceClass = USB_CLASS_HUB},

{ .match_flags = USB_DEVICE_ID_MATCH_INT_CLASS,

.bInterfaceClass = USB_CLASS_HUB},

{ } /* Terminating entry */

};

看到了没,这些信息就是hub 的接口class信息.

也就是说, hub_driver就是为们要找的hub 接口的驱动.

根据上面的分析,流程最终会到hub_driver->probe中,对应的接口为hub_probe().

5.2.1:接口驱动的probe过程

Hub_probe()的代码如下:

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);

#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 */

//spec上规定接口的subclass为0.但为1时,也能工作

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? */

//spec上规定hub interface的endpoint数目为1,这里的数目没有包括ep0

if (desc->desc.bNumEndpoints != 1)

goto descriptor_error;

//端点描述符

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

/* If it's not an interrupt in endpoint, we'd better punt! */

//不是IN方向的中断传输端点,有错误

if (!usb_endpoint_is_int_in(endpoint))

goto descriptor_error;

/* We found a hub */

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

//初始化一个struct usb_hub结构

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);

//初始化event_list

INIT_LIST_HEAD(&hub->event_list);

//hub->intfdev:指向接口封装的dev

hub->intfdev = &intf->dev;

//hub->hdev:hub所属的usb_dev

hub->hdev = hdev;

//初始化一个延时工作队列,用来管理hub LED的

INIT_DELAYED_WORK(&hub->leds, led_work);

//增加intf->dev的引用计数

usb_get_intf(intf);

//intf->dev的私有结构指和hub

usb_set_intfdata (intf, hub);

//接口需要远程唤醒

intf->needs_remote_wakeup = 1;

//如果是一个高速设备,增加highspeed_hubs 计数

if (hdev->speed == USB_SPEED_HIGH)

highspeed_hubs++;

//配置hub

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

return 0;

hub_disconnect (intf);

return -ENODEV;

}

这个函数前一部份进行一些有效性检查,后半部份分配并初始化一个struct usb_hub结构.然后流程就转入了hub_configure().

hub_configure()函数是一个很重要的操作,它的代码如下:

static int hub_configure(struct usb_hub *hub,

struct usb_endpoint_descriptor *endpoint)

{

struct usb_device *hdev = hub->hdev;

struct device *hub_dev = hub->intfdev;

u16 hubstatus, hubchange;

u16 wHubCharacteristics;

unsigned int pipe;

int maxp, ret;

char *message;

//为buffer分配空间,DMA分配,其物理地址存放在hub->buffer_dma中

//buffer是一个指向数组的指针

hub->buffer = usb_buffer_alloc(hdev, sizeof(*hub->buffer), GFP_KERNEL,

&hub->buffer_dma);

if (!hub->buffer) {

message = "can't allocate hub irq buffer";

ret = -ENOMEM;

goto fail;

}

//为status分配空间

hub->status = kmalloc(sizeof(*hub->status), GFP_KERNEL);

if (!hub->status) {

message = "can't kmalloc hub status buffer";

ret = -ENOMEM;

goto fail;

}

mutex_init(&hub->status_mutex);

//为hub->descriptor分配空间

hub->descriptor = kmalloc(sizeof(*hub->descriptor), GFP_KERNEL);

if (!hub->descriptor) {

message = "can't kmalloc 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.

*/

//取得hub描述符

ret = get_hub_descriptor(hdev, hub->descriptor,

sizeof(*hub->descriptor));

//如果Get_Descriptor失败或者hub端口超多

if (ret < 0) {

message = "can't read hub descriptor";

goto fail;

}

//协议上规定hub最多有255个接口,但Linux认为31个接口已经够多了

else if (hub->descriptor->bNbrPorts > USB_MAXCHILDREN) {

message = "hub has too many ports!";

ret = -ENODEV;

goto fail;

}

//hdev->maxchild: hub的端口数目

hdev->maxchild = hub->descriptor->bNbrPorts;

dev_info (hub_dev, "%d port%s detected\n", hdev->maxchild,

(hdev->maxchild == 1) ? "" : "s");

//wHubCharacteristics字段

wHubCharacteristics = le16_to_cpu(hub->descriptor->wHubCharacteristics);

//是否是一个复合设备

if (wHubCharacteristics & HUB_CHAR_COMPOUND) {

int i;

char portstr [USB_MAXCHILDREN + 1];

for (i = 0; i < hdev->maxchild; i++)

//找到数组中的所在项和数组项中的位置

portstr[i] = hub->descriptor->DeviceRemovable

[((i + 1) / 8)] & (1 << ((i + 1) % 8))

? 'F' : 'R';

//以\0 结尾

portstr[hdev->maxchild] = 0;

dev_dbg(hub_dev, "compound device; port removable status: %s\n", portstr);

} else

dev_dbg(hub_dev, "standalone hub\n");

//电源开关模式

switch (wHubCharacteristics & HUB_CHAR_LPSM) {

//ganged 电源开关,所有连接端口同时开机

case 0x00:

dev_dbg(hub_dev, "ganged power switching\n");

break;

//端口有单独的电源开关

case 0x01:

dev_dbg(hub_dev, "individual port power switching\n");

break;

//1X:保留, 表示没有电源开关

case 0x02:

case 0x03:

dev_dbg(hub_dev, "no power switching (usb 1.0)\n");

break;

}

//过电流保护模式

switch (wHubCharacteristics & HUB_CHAR_OCPM) {

//全部电流保护

case 0x00:

dev_dbg(hub_dev, "global over-current protection\n");

break;

//个别连接端口电源保护

case 0x08:

dev_dbg(hub_dev, "individual port over-current protection\n");

break;

//没有过电流保护

case 0x10:

case 0x18:

dev_dbg(hub_dev, "no over-current protection\n");

break;

}

//初始化TT相关的东西

spin_lock_init (&hub->tt.lock);

INIT_LIST_HEAD (&hub->tt.clear_list);

INIT_WORK (&hub->tt.kevent, hub_tt_kevent);

//设备描述符的bDeviceProtocol 字段

switch (hdev->descriptor.bDeviceProtocol) {

//HUB是一个低速/全速设备

case 0:

break;

//只有一个TT

case 1:

dev_dbg(hub_dev, "Single TT\n");

hub->tt.hub = hdev;

break;

//多个TT

case 2:

//为接口选取1号设置

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;

default:

dev_dbg(hub_dev, "Unrecognized hub protocol %d\n",

hdev->descriptor.bDeviceProtocol);

break;

}

/* Note 8 FS bit times == (8 bits / 12000000 bps) ~= 666ns */

//TT think time,

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[] */

//是否支持连接端口LED

if (wHubCharacteristics & HUB_CHAR_PORTIND) {

hub->has_indicators = 1;

dev_dbg(hub_dev, "Port indicators are supported\n");

}

//bPwrOn2PwrGood字段表示连接端口从开机到准备好的时间

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).

*/

//Get_Status 设备

ret = usb_get_status(hdev, USB_RECIP_DEVICE, 0, &hubstatus);

//Get_Status失败

if (ret < 2) {

message = "can't get hub status";

goto fail;

}

//设备的status包含两个部份:bit 0 表示使用自身电源bit 1是远程唤醒字段

le16_to_cpus(&hubstatus);

//如果是root hub

if (hdev == hdev->bus->root_hub) {

//如果电流没有限制

if (hdev->bus_mA == 0 || hdev->bus_mA >= 500)

hub->mA_per_port = 500;

//有限制的情况下

else {

hub->mA_per_port = hdev->bus_mA;

hub->limited_power = 1;

}

}

//如果使用总线电流

else if ((hubstatus & (1 << USB_DEVICE_SELF_POWERED)) == 0) {

dev_dbg(hub_dev, "hub controller current requirement: %dmA\n",

hub->descriptor->bHubContrCurrent);

hub->limited_power = 1;

if (hdev->maxchild > 0) {

int remaining = hdev->bus_mA -

hub->descriptor->bHubContrCurrent;

if (remaining < hdev->maxchild * 100)

dev_warn(hub_dev,

"insufficient power available "

"to use all downstream ports\n");

hub->mA_per_port = 100; /* 7.2.1.1 */

}

}

// 如果使用本身电流

else { /* Self-powered external hub */

/* FIXME: What about battery-powered external hubs that

* provide less current per port? */

hub->mA_per_port = 500;

}

if (hub->mA_per_port < 500)

dev_dbg(hub_dev, "%umA bus power budget for each child\n",

hub->mA_per_port);

//Get hub status

//hub 状态位和改变位

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 */

//自身供电

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");

//不支持过电流保护

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. */

//设备中断控制传输的urb

//通道和最大包长度

pipe = usb_rcvintpipe(hdev, endpoint->bEndpointAddress);

maxp = usb_maxpacket(hdev, pipe, usb_pipeout(pipe));

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

maxp = sizeof(*hub->buffer);

//分配urb

hub->urb = usb_alloc_urb(0, GFP_KERNEL);

if (!hub->urb) {

message = "couldn't allocate interrupt urb";

ret = -ENOMEM;

goto fail;

}

//填充urb

usb_fill_int_urb(hub->urb, hdev, pipe, *hub->buffer, maxp, hub_irq,

hub, endpoint->bInterval);

hub->urb->transfer_dma = hub->buffer_dma;

hub->urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;

/* maybe cycle the hub leds */

if (hub->has_indicators && blinkenlights)

hub->indicator [0] = INDICATOR_CYCLE;

//驱动hub

hub_power_on(hub);

//激活hub

hub_activate(hub);

return 0;

fail:

dev_err (hub_dev, "config failed, %s (err %d)\n",

message, ret);

/* hub_disconnect() frees urb and descriptor */

return ret;

}

这个函数先初始化struct usb_hub中的几个指针,为之分配空间,然后,取得hub的描述符,再根据取得的描述符信息再初始化和显示一些调试信息.其中的一些成员赋值等我们用到的时候再来进行分析.这个函数的后面关于urb部份和后面调用的两个子函数才是我们要分析的重点.

在这里,顺带提一下HUB的指示灯问题.

Hub描述符的wHubCharacteristics的bit7来描述设备是否支持显示灯.为1表示在下游的连接端口上支持显示灯,为0则不支持.

如果Hub支持指示灯,则将hub->has_indicators置为1.另外,HUB的指示灯是否起作用,还由一个参数决定,在代码中,大家也看到,这个参数是blinkenlights.这个参数定义如下:

static int blinkenlights = 0;

module_param (blinkenlights, bool, S_IRUGO);

MODULE_PARM_DESC (blinkenlights, "true to cycle leds on hubs");

这是一个可调的模块参数.如果要显示灯起作用,必须要将其置为1才可以.我们可以用下面两种方法来设置这个参数:

1:如果模块没有编译进kernel,可以在插入模块的时候,加上这个参数:

modprobe usbcore blinkenlights=1

2:如果模块已经编进kernel,那在kernel的启动参数上加上如下参数:

usbcore.blinkenlights=1

在usb2.0 spec中,对不同情况下的灯颜色都做了定义.

在代码中,灯的显示交给了一延迟的工作队列进行处理,初始化如下所示:

INIT_DELAYED_WORK(&hub->leds, led_work); (在hub_probe()函数中)

在这里,并不打算详细分析这一部份,有兴趣的可以跟踪下去看下.

那函数后面初始化的URB是用来干什么的呢?我们将这个URB的初始化部份单独列出如下:

pipe = usb_rcvintpipe(hdev, endpoint->bEndpointAddress);

maxp = usb_maxpacket(hdev, pipe, usb_pipeout(pipe));

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

maxp = sizeof(*hub->buffer);

我们从此可以看出,这个URB是作用于ep0之外的另一个端点,而且传输数据的长度最大为sizeof(*hub->buffer)

Hub->buffer被定义如下:

struct usb_hub {

……

char (*buffer)[8];

……

}

由此可以看出buffer是指向一个8元素字符数组的指针,sizeof(*hub->buffer)等于0.

关于传输的数据长度,代码中有一段注释,这段注释说,spec上规定的长度是(PORTS+1+7)/8.而linux中,对每个hub上挂有认为最多的端口进行处理,因些,就是(31+1+7)/8 = 5

为什么这里要是8呢?

因为usb2.0 spec上规定,ep0的最大发包长度,可能为8.16.32.64.512.所以选择比5要大的最小值8.

另外,我们注意到,URB完成之后,所要调用的函数是hub_irq().如下所示:

usb_fill_int_urb(hub->urb, hdev, pipe, *hub->buffer, maxp, hub_irq,

hub, endpoint->bInterval);

UHCI必须要知道HUB的端口的一些连接状态,因此,需要HUB周期性的上报它的端口连接状态.这个URB就是用来做这个用途的.UHCI周期性的发送IN方向中断传输传输给HUB.HUB就会通过这个URB将端口信息发送给HUB.

那这个轮询周期是多长呢?根据我们之前分析的UHCI的知识,它的调度周期是由endpoint的bInterval 字段所决定的.

现在,我们慢慢来接触到hub的一些核心处理了.整理一下心情,继续看代码.^_^

接下来,我们要看到的第一个函数是hub_power_on().代码如下:

static void hub_power_on(struct usb_hub *hub)

{

int port1;

//从连接端口从开机到准备好的时间

unsigned pgood_delay = hub->descriptor->bPwrOn2PwrGood * 2;

//wHubCharacteristics字段

u16 wHubCharacteristics =

le16_to_cpu(hub->descriptor->wHubCharacteristics);

/* Enable power on each port. Some hubs have reserved values

* of LPSM (> 2) in their descriptors, even though they are

* USB 2.0 hubs. Some hubs do not implement port-power switching

* but only emulate it. In all cases, the ports won't work

* unless we send these messages to the hub.

*/

//开关模式

if ((wHubCharacteristics & HUB_CHAR_LPSM) < 2)

dev_dbg(hub->intfdev, "enabling power on all ports\n");

else

dev_dbg(hub->intfdev, "trying to enable port power on "

"non-switchable hub\n");

//给每一个端口发送PORT_POWER的Set_Feature消息

for (port1 = 1; port1 <= hub->descriptor->bNbrPorts; port1++)

set_port_feature(hub->hdev, port1, USB_PORT_FEAT_POWER);

/* Wait at least 100 msec for power to become stable */

//等待端口可以正常工作,至少100 ms

msleep(max(pgood_delay, (unsigned) 100));

}

这里就是给每个接口发送PORT_POWER的Set_Feature消息,告之可起来工作了,然后等待端口可以工作.

另外要分析的函数是hub_activate().代码如下:

static void hub_activate(struct usb_hub *hub)

{

int status;

hub->quiescing = 0;

hub->activating = 1;

//提交urb

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 ASAP */

kick_khubd(hub);

}

首先,是在hub的两个字段进行赋值操作,hub-> quiescing 和 hub->activating表示分别表示hub处理暂停和活跃状态.注意,在这里,不要和接口的mark_active()设置的intf->is_active相混淆.

然后,将hub->urb提交.开始调度Led的工作队列.

最后,流程转入kick_khubd().代码如下:

static void kick_khubd(struct usb_hub *hub)

{

unsigned long flags;

/* Suppress autosuspend until khubd runs */

//pm_usage_cnt设置为1，防止autosuspend

to_usb_interface(hub->intfdev)->pm_usage_cnt = 1;

spin_lock_irqsave(&hub_event_lock, flags);

if (!hub->disconnected && list_empty(&hub->event_list)) {

list_add_tail(&hub->event_list, &hub_event_list);

wake_up(&khubd_wait);

}

spin_unlock_irqrestore(&hub_event_lock, flags);

}

在这个函数中,先将接口的pm_usage_cnt置1,此后,该接口就不能SUSPEND.

然后,将该hub添加进hub_event_list链表,并唤醒Khubd_wait等待队列.

hub_event_list和Khubd_wait到底代表着什么呢?它后面的参数又是什么呢?接着往下看…

 

 

Linux设备驱动之USB hub驱动(续)2012-07-24 14:06:54

分类：

原文地址：Linux设备驱动之USB hub驱动(续) 作者：xgr180

5.2.2:接口驱动中的hub_thread()函数

我们之前在分析usb_hub_init()的代码的时候,忽略掉了一部份.

代码片段如下所示:

int usb_hub_init(void)

{

……

khubd_task = kthread_run(hub_thread, NULL, "khubd");

……

}

Kthread_run()是kernel中用来启动一个新kernel线程的接口,它所要执行的函数就是后面跟的第一个参数.在这里,也就是hub_thread().另外,顺带提一句,要终止kthread_run()创建的线程,可以调用kthread_stop().

Hub_thread()的代码如下:

static int hub_thread(void *__unused)

{

set_freezable();

do {

hub_events();

wait_event_freezable(khubd_wait,

!list_empty(&hub_event_list) ||

kthread_should_stop());

} while (!kthread_should_stop() || !list_empty(&hub_event_list));

pr_debug("%s: khubd exiting\n", usbcore_name);

return 0;

}

在上面的代码中, kthread_should_stop()用来判断是否有kthread_stop()将其终止.

在这里,我们终止看到,我们在前面要唤醒的等待队列khubd_wait,也就是在这个地方了.

这个函数的核心处理是hub_events().分段分析代码,如下:

static void hub_events(void)

{

struct list_head *tmp;

struct usb_device *hdev;

struct usb_interface *intf;

struct usb_hub *hub;

struct device *hub_dev;

u16 hubstatus;

u16 hubchange;

u16 portstatus;

u16 portchange;

int i, ret;

int connect_change;

/*

* We restart the list every time to avoid a deadlock with

* deleting hubs downstream from this one. This should be

* safe since we delete the hub from the event list.

* Not the most efficient, but avoids deadlocks.

*/

while (1) {

/* Grab the first entry at the beginning of the list */

//如果hub_event_list为空，退出

spin_lock_irq(&hub_event_lock);

if (list_empty(&hub_event_list)) {

spin_unlock_irq(&hub_event_lock);

break;

}

//取hub_event_list中的后一个元素，并将其断链

tmp = hub_event_list.next;

list_del_init(tmp);

hub = list_entry(tmp, struct usb_hub, event_list);

kref_get(&hub->kref);

spin_unlock_irq(&hub_event_lock);

hdev = hub->hdev;

hub_dev = hub->intfdev;

intf = to_usb_interface(hub_dev);

dev_dbg(hub_dev, "state %d ports %d chg %04x evt %04x\n",

hdev->state, hub->descriptor

? hub->descriptor->bNbrPorts

: 0,

/* NOTE: expects max 15 ports... */

(u16) hub->change_bits[0],

(u16) hub->event_bits[0]);

/* Lock the device, then check to see if we were

* disconnected while waiting for the lock to succeed. */

usb_lock_device(hdev);

//如果hub断开了,继续hub_event_list中的下一个

if (unlikely(hub->disconnected))

goto loop;

/* If the hub has died, clean up after it */

//设备没有连接上

if (hdev->state == USB_STATE_NOTATTACHED) {

hub->error = -ENODEV;

//将下面的子设备全部disable

hub_pre_reset(intf);

goto loop;

}

/* Autoresume */

ret = usb_autopm_get_interface(intf);

if (ret) {

dev_dbg(hub_dev, "Can't autoresume: %d\n", ret);

goto loop;

}

/* If this is an inactive hub, do nothing */

//hub 暂停

if (hub->quiescing)

goto loop_autopm;

//hub 有错误发生？

if (hub->error) {

dev_dbg (hub_dev, "resetting for error %d\n",

hub->error);

ret = usb_reset_composite_device(hdev, intf);

if (ret) {

dev_dbg (hub_dev,

"error resetting hub: %d\n", ret);

goto loop_autopm;

}

hub->nerrors = 0;

hub->error = 0;

}

首先,从hub_event_list摘下第一个元素,根据我们之前在接口驱动probe过程的kick_khubd()函数分析中,有将hub->event_list添加到hub_event_list.因此,就可以顺藤摸瓜找到hub,再根据hub结构,找到接口结构和所属的usb 设备结构.

然后,进行第一个重要的判断.如果hub被断开了,则,断开hub下面所连接的所有端口,这是在hub_pre_reset()中完成的.

最后,进行第二个重要的判断,如果hub发生了错误,则reset它下面的所有端口,这是在usb_reset_composite_device()中完成的.

/* deal with port status changes */

//遍历hub中的每一个port

for (i = 1; i <= hub->descriptor->bNbrPorts; i++) {

{

if (test_bit(i, hub->busy_bits))

continue;

connect_change = test_bit(i, hub->change_bits);

if (!test_and_clear_bit(i, hub->event_bits) &&

!connect_change && !hub->activating)

continue;

//Get_Port_Status:取得端口状态.

//会取得port的改变值和状态值

ret = hub_port_status(hub, i,

&portstatus, &portchange);

if (ret < 0)

continue;

//如果对应端口没有在设备树上,且端口显示已经连接上

//将connect_change置为1

if (hub->activating && !hdev->children[i-1] &&

(portstatus &

USB_PORT_STAT_CONNECTION))

connect_change = 1;

//端口的连接状态发生了改变.需要发送Clear_Feature

if (portchange & USB_PORT_STAT_C_CONNECTION) {

clear_port_feature(hdev, i,

USB_PORT_FEAT_C_CONNECTION);

connect_change = 1;

}

//端口的状态从enable 变为了disable

if (portchange & USB_PORT_STAT_C_ENABLE) {

if (!connect_change)

dev_dbg (hub_dev,

"port %d enable change, "

"status %08x\n",

i, portstatus);

clear_port_feature(hdev, i,

USB_PORT_FEAT_C_ENABLE);

/*

* EM interference sometimes causes badly

* shielded USB devices to be shutdown by

* the hub, this hack enables them again.

* Works at least with mouse driver.

*/

//端口已经被停止了,且端口已经被连在设备树中.

//需要重启一下此端口

if (!(portstatus & USB_PORT_STAT_ENABLE)

&& !connect_change

&& hdev->children[i-1]) {

dev_err (hub_dev,

"port %i "

"disabled by hub (EMI?), "

"re-enabling...\n",

i);

connect_change = 1;

}

}

//Resume完成

if (portchange & USB_PORT_STAT_C_SUSPEND) {

clear_port_feature(hdev, i,

USB_PORT_FEAT_C_SUSPEND);

//如果端口连接了设备,就将设备唤醒

if (hdev->children[i-1]) {

ret = remote_wakeup(hdev->

children[i-1]);

if (ret < 0)

connect_change = 1;

}

//如果端口没有连接设备,就将端口禁用

else {

ret = -ENODEV;

hub_port_disable(hub, i, 1);

}

dev_dbg (hub_dev,

"resume on port %d, status %d\n",

i, ret);

}

//有过流保护,需要对hub power on

if (portchange & USB_PORT_STAT_C_OVERCURRENT) {

dev_err (hub_dev,

"over-current change on port %d\n",

i);

clear_port_feature(hdev, i,

USB_PORT_FEAT_C_OVER_CURRENT);

hub_power_on(hub);

}

//Reset状态已经完成了

if (portchange & USB_PORT_STAT_C_RESET) {

dev_dbg (hub_dev,

"reset change on port %d\n",

i);

clear_port_feature(hdev, i,

USB_PORT_FEAT_C_RESET);

}

if (connect_change)

hub_port_connect_change(hub, i,

portstatus, portchange);

}

这段代码就是最核心的操作了,首先要说明的是,在struct usb_dev中,有一个struct usb_device *children[USB_MAXCHILDREN]的成员,它是表示对应端口序号上所连接的usb设备.

在这里,它遍历hub上的每一个端口,如果端口的连接会生了改变(connect_change等于1)的情况,就会调用hub_port_connect_change().我们来看一下,什么情况下, hub_port_connect_change才会被设为1.

1:端口在hub->change_bits中被置位.搜索整个代码树,发生在设置hub->change_bits的地方,只有在hub_port_logical_disconnect()中手动将端口禁用,会将对应位置1.

2:hub上没有这个设备树上没有这个端口上的设备.但显示端口已经连上了设备

3:hub这个端口上的连接发生了改变,从端口有设备连接变为无设备连接,或者从无设备连接变为有设备连接.

4:hub的端口变为了disable,此时这个端口上连接了设备,但被显示该端口已经变禁用,需要将connect_change设为1.

5:端口状态从SUSPEND变成了RESUME,远程唤醒端口上的设备失败,就需要将connect_change设为1.

另外hub_port_connect_change()函数我们放在后面再来讨论

//对HUB的处理

/* deal with hub status changes */

//如果hub状态末变化，不需要做任何处理

if (test_and_clear_bit(0, hub->event_bits) == 0)

; /* do nothing */

//Get_hub_status 失败?

else if (hub_hub_status(hub, &hubstatus, &hubchange) < 0)

dev_err (hub_dev, "get_hub_status failed\n");

else {

//这里是对应hub 状态发生了改变,且Get_hub_status正常返回的情况

//如果hub的本地电源供电发生了改变

if (hubchange & HUB_CHANGE_LOCAL_POWER) {

dev_dbg (hub_dev, "power change\n");

clear_hub_feature(hdev, C_HUB_LOCAL_POWER);

//如果是本地电源供电

if (hubstatus & HUB_STATUS_LOCAL_POWER)

/* FIXME: Is this always true? */

hub->limited_power = 1;

//如果本电源不供电

else

hub->limited_power = 0;

}

//如果hub 发生过电源保护,需要对hub power on

if (hubchange & HUB_CHANGE_OVERCURRENT) {

dev_dbg (hub_dev, "overcurrent change\n");

msleep(500); /* Cool down */

clear_hub_feature(hdev, C_HUB_OVER_CURRENT);

hub_power_on(hub);

}

}

hub->activating = 0;

/* If this is a root hub, tell the HCD it's okay to

* re-enable port-change interrupts now. */

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);

kref_put(&hub->kref, hub_release);

} /* end while (1) */

}

处理完hub上的port之后,就要来处理hub本身的状态改变了,结合代码中的注释应该很容易看懂,在这里主要是清除hub的对应Feature.

之后,将 hub->activating设为了0,如果hub是root hub,需要重新打开root hub的中断.

这个函数到这里就完成了.不过,其中的几个子函数,涉及到的操作很重要,现分析如下:

1: hub_pre_reset()函数.

该函数在设备断开连接的时候,将其下挂载的所有子设备全部注销掉,代码如下所示:

static int hub_pre_reset(struct usb_interface *intf)

{

struct usb_hub *hub = usb_get_intfdata(intf);

struct usb_device *hdev = hub->hdev;

int i;

/* Disconnect all the children */

for (i = 0; i < hdev->maxchild; ++i) {

if (hdev->children[i])

usb_disconnect(&hdev->children[i]);

}

hub_quiesce(hub);

return 0;

}

它将设备上所挂载的所有设备全部都调用usb_disconnect()来断开联接.之后,再对hub调用hub_quiesce().

hub_quiesce()是和hub_activate()相对应的一个函数, hub_activate()在前面已经分析过了,现在来对hub_quiesce()进行分析.

代码如下:

static void hub_quiesce(struct usb_hub *hub)

{

/* (nonblocking) khubd and related activity won't re-trigger */

hub->quiescing = 1;

hub->activating = 0;

/* (blocking) stop khubd and related activity */

usb_kill_urb(hub->urb);

if (hub->has_indicators)

cancel_delayed_work_sync(&hub->leds);

if (hub->tt.hub)

cancel_work_sync(&hub->tt.kevent);

}

首先,它调hub->quiescing置为1,而activating置为0.这和hub_activate()刚好是相反的动作.之后,取消hub的中断传输出URB.取得TT和LED的工作队列.

我们在后面分析的HUB中断URB传输,可以知道,如果将这个URB禁用,那么,就不会将hub->event_list添加到hub_event_list.因此,也不会进入到hub_events()函数.

usb_disconnect()用来断开某个设备,代码如下:

void usb_disconnect(struct usb_device **pdev)

{

struct usb_device *udev = *pdev;

int i;

if (!udev) {

pr_debug ("%s nodev\n", __FUNCTION__);

return;

}

/* mark the device as inactive, so any further urb submissions for

* this device (and any of its children) will fail immediately.

* this quiesces everyting except pending urbs.

*/

usb_set_device_state(udev, USB_STATE_NOTATTACHED);

dev_info (&udev->dev, "USB disconnect, address %d\n", udev->devnum);

usb_lock_device(udev);

/* Free up all the children before we remove this device */

for (i = 0; i < USB_MAXCHILDREN; i++) {

if (udev->children[i])

usb_disconnect(&udev->children[i]);

}

/* deallocate hcd/hardware state ... nuking all pending urbs and

* cleaning up all state associated with the current configuration

* so that the hardware is now fully quiesced.

*/

dev_dbg (&udev->dev, "unregistering device\n");

usb_disable_device(udev, 0);

usb_unlock_device(udev);

/* Unregister the device. The device driver is responsible

* for removing the device files from usbfs and sysfs and for

* de-configuring the device.

*/

device_del(&udev->dev);

/* Free the device number and delete the parent's children[]

* (or root_hub) pointer.

*/

release_address(udev);

/* Avoid races with recursively_mark_NOTATTACHED() */

spin_lock_irq(&device_state_lock);

*pdev = NULL;

spin_unlock_irq(&device_state_lock);

usb_stop_pm(udev);

put_device(&udev->dev);

}

很容易看出.这个函数采用深度遍历算法,它依次遍历udev->children[]下的子设备,然后依然调用usb_disconnect().

这个函数中的另外几个子函数有的在前面已经分析过,有的是设备模型中的基础函数.很有是跟PM相关的,在这里就不做详细分析,来看一下release_address()函数,顾名思意,它用来释放设备的地址,如下示:

static void release_address(struct usb_device *udev)

{

if (udev->devnum > 0) {

clear_bit(udev->devnum, udev->bus->devmap.devicemap);

udev->devnum = -1;

}

}

我们在分析UHCI中,有关root hub的初始化时说明,设各号都是保存在bus->devmap数组中的.在这里,只需要将该设备号在数组中的某位清了即可.

hub_pre_reset()函数就分析到这里了.

注意到这里调用的put_device(&udev->dev)没.根据Linux设备模型的分析,这时它会调用跟它绑定的driver的remove()接口,对应的,这个函数会将操作回溯到usb_driver->disconnect().可以自行查阅这个过程.

或许,有人的疑问又来了?要是这个usb_dev没有跟usb_driver绑定怎么办呢?

不要忘记我们之前的分析了,对于usb_generic_driver这个驱动是会适用所有的usb_dev的.^_^,也是说,无论如何,usb_dev都会绑定到usb_generic_driver.

2: hub_port_connect_change()函数

这个函数是一个很核心的操作,它的代码如下:

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;

struct usb_hcd *hcd = bus_to_hcd(hdev->bus);

u16 wHubCharacteristics = le16_to_cpu(hub->descriptor->wHubCharacteristics);

int status, i;

dev_dbg (hub_dev,

"port %d, status %04x, change %04x, %s\n",

port1, portstatus, portchange, portspeed (portstatus));

//HUB LED

if (hub->has_indicators) {

set_port_led(hub, port1, HUB_LED_AUTO);

hub->indicator[port1-1] = INDICATOR_AUTO;

}

/* Disconnect any existing devices under this port */

//如果对应端口已经有设备连接,先将其断开

if (hdev->children[port1-1])

usb_disconnect(&hdev->children[port1-1]);

//将hub_change_bits中的对应位清零,以免下次进来的时候,还会检测到

//hub_port_logical_disconnect()对该值的设置

clear_bit(port1, hub->change_bits);

#ifdef CONFIG_USB_OTG

/* during HNP, don't repeat the debounce */

if (hdev->bus->is_b_host)

portchange &= ~USB_PORT_STAT_C_CONNECTION;

#endif

//连接发生改变

//连接反弹的处理,实际上就是除抖动

if (portchange & USB_PORT_STAT_C_CONNECTION) {

status = hub_port_debounce(hub, port1);

if (status < 0) {

if (printk_ratelimit())

dev_err (hub_dev, "connect-debounce failed, "

"port %d disabled\n", port1);

goto done;

}

portstatus = status;

}

在这里,我们忽略掉HUB LED灯的操作,然后,将HUB对应端口下面挂载的设备断开.经过前面的分析,进入到这个函数的可能有多种情况(在hub_events()中分析的五种情况).可以分为三大类:

一类是之前有连接之后没联接的,在这里,将hub 对应端口下的设备全部断开是无可非议的.

第二类是之前没有,之后有连接的,在这里,if(hdev->children[port-1])的判断是不会满足的.

第三类是需要重置的端口,在这里先将设备断开,然后再将它联连上去好了.

接下来,将hub->change_bits的对应位清掉,该位是在函数hub_port_logical_disconnect()中被置的,在这里将其清除,免得下次在进入hub_events()的时候,再次检测到这个位发生改变.

忽略掉CONFIG_USB_OTG的处理,这个宏我们在前面分析过很多次了,这里不再赘述.

如果该端口的连接发生改变(从有连接到无接接,或者从无连接到有连接),就有一个除抖动的过程,usb2.0 spec上规定,除抖动的时间为100ms.

也许有人会有这样的想法: 那检测到移除了一个设备,但它在100ms又插上去了,这里适不适合这里的抖动检测的情况呢?

我们先从代码的流程看,检测到连接发生改变,进入到hub_port_connect_change(),它首先就会将端口上的设备移除.这样,就算你在100ms上连接上去了,也得要再次建立.

从usb2.0的协议看来,设备移除后,usb设备里保存的信息(例如选择的配置,给它分配的地址)全部都丢失了,必须要重新进行配置过程才能够使用.

在这里,顺便将hub_port_debounce()列出,来看一下具体的除抖过程是怎么样实现的.

static int hub_port_debounce(struct usb_hub *hub, int port1)

{

int ret;

int total_time, stable_time = 0;

u16 portchange, portstatus;

unsigned connection = 0xffff;

for (total_time = 0; ; total_time += HUB_DEBOUNCE_STEP) {

ret = hub_port_status(hub, port1, &portstatus, &portchange);

if (ret < 0)

return ret;

if (!(portchange & USB_PORT_STAT_C_CONNECTION) &&

(portstatus & USB_PORT_STAT_CONNECTION) == connection) {

stable_time += HUB_DEBOUNCE_STEP;

if (stable_time >= HUB_DEBOUNCE_STABLE)

break;

} else {

stable_time = 0;

connection = portstatus & USB_PORT_STAT_CONNECTION;

}

if (portchange & USB_PORT_STAT_C_CONNECTION) {

clear_port_feature(hub->hdev, port1,

USB_PORT_FEAT_C_CONNECTION);

}

if (total_time >= HUB_DEBOUNCE_TIMEOUT)

break;

msleep(HUB_DEBOUNCE_STEP);

}

dev_dbg (hub->intfdev,

"debounce: port %d: total %dms stable %dms status 0x%x\n",

port1, total_time, stable_time, portstatus);

if (stable_time < HUB_DEBOUNCE_STABLE)

return -ETIMEDOUT;

return portstatus;

}

函数中的stable_time表示隐定的时间.在hub_events()的代码分析时,我们看到了,在检测到连接状态发生改变的时候,会发送Clear_Feature.因此,如果在这里检测到有USB_PORT_STAT_C_CONNECTION,就说明之后又有一次连接状态发生改变了.

分析这个函数的时候,要注意有这样的情况,端口的连接状态,一直在波动,即时有连接,时末有连接.

还有注意, connection的初始值是0xffff,所以(portstatus & USB_PORT_STAT_CONNECTION) == connection这个判断是肯定不会满足的,因为hub_port_status()取得的portstatus里面还有一些保留位.所以,在第一次进入这个循环的时候,就会进入到else中,就会将stable_time置0,而connection也保存了这一次的连接信息.

如果端口维持前一个状态,那循环中的流程就会满足第一个if,在这个if的操作里,会增加stable_time的值.

如果端口的状态发生了改变,那循环中的流程就会满足else,又将stable_time和connection初始化了.另外,要记得在状态发生改变的时候,要发送Clear_Feature,将状态清除.

在函数里,定义的测试时间是1500ms.如果在这个时间内,端口还末处于稳定状态,就会返回-ETIMEDOUT.

如果已经处于稳定状态了,就会返回稳定状态下的portstatus.

/* Return now if nothing is connected */

//如果接口上没有连接了,可以直接退出了

if (!(portstatus & USB_PORT_STAT_CONNECTION)) {

/* maybe switch power back on (e.g. root hub was reset) */

if ((wHubCharacteristics & HUB_CHAR_LPSM) < 2

&& !(portstatus & (1 << USB_PORT_FEAT_POWER)))

set_port_feature(hdev, port1, USB_PORT_FEAT_POWER);

if (portstatus & USB_PORT_STAT_ENABLE)

goto done;

return;

}

经过去抖后,端口稳定的处于断开连接状态.说明端口已经没有设备了.然后,再判断hub是否有电源开关((wHubCharacteristics & HUB_CHAR_LPSM) < 2),portstatus 的 USB_PORT_FEAT_POWER位是否被设置,如果没有被设置,则说明该端口断电了.如果hub有电源开关,且端口没有上电,则需要发送POWER的Set_Feature来为之上电.

如果端口依然处理enable状态,就会跳转到标号done处,就端口disalbe.

//如果接口上面有了联接,需要为联接在端口上设备建立连接

for (i = 0; i < SET_CONFIG_TRIES; i++) {

struct usb_device *udev;

/* reallocate for each attempt, since references

* to the previous one can escape in various ways

*/

udev = usb_alloc_dev(hdev, hdev->bus, port1);

if (!udev) {

dev_err (hub_dev,

"couldn't allocate port %d usb_device\n",

port1);

goto done;

}

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;

/* set the address */

choose_address(udev);

if (udev->devnum <= 0) {

status = -ENOTCONN; /* Don't retry */

goto loop;

}

/* reset and get descriptor */

status = hub_port_init(hub, udev, port1, i);

if (status < 0)

goto loop;

/* consecutive bus-powered hubs aren't reliable; they can

* violate the voltage drop budget. if the new child has

* a "powered" LED, users should notice we didn't enable it

* (without reading syslog), even without per-port LEDs

* on the parent.

*/

if (udev->descriptor.bDeviceClass == USB_CLASS_HUB

&& udev->bus_mA <= 100) {

u16 devstat;

status = usb_get_status(udev, USB_RECIP_DEVICE, 0,

&devstat);

if (status < 2) {

dev_dbg(&udev->dev, "get status %d ?\n", status);

goto loop_disable;

}

le16_to_cpus(&devstat);

if ((devstat & (1 << USB_DEVICE_SELF_POWERED)) == 0) {

dev_err(&udev->dev,

"can't connect bus-powered hub "

"to this port\n");

if (hub->has_indicators) {

hub->indicator[port1-1] =

INDICATOR_AMBER_BLINK;

schedule_delayed_work (&hub->leds, 0);

}

status = -ENOTCONN; /* Don't retry */

goto loop_disable;

}

}

/* check for devices running slower than they could */

if (le16_to_cpu(udev->descriptor.bcdUSB) >= 0x0200

&& udev->speed == USB_SPEED_FULL

&& highspeed_hubs != 0)

check_highspeed (hub, udev, port1);

/* Store the parent's children[] pointer. At this point

* udev becomes globally accessible, although presumably

* no one will look at it until hdev is unlocked.

*/

status = 0;

/* We mustn't add new devices if the parent hub has

* been disconnected; we would race with the

* recursively_mark_NOTATTACHED() routine.

*/

spin_lock_irq(&device_state_lock);

if (hdev->state == USB_STATE_NOTATTACHED)

status = -ENOTCONN;

else

hdev->children[port1-1] = udev;

spin_unlock_irq(&device_state_lock);

/* Run it through the hoops (find a driver, etc) */

if (!status) {

status = usb_new_device(udev);

if (status) {

spin_lock_irq(&device_state_lock);

hdev->children[port1-1] = NULL;

spin_unlock_irq(&device_state_lock);

}

}

if (status)

goto loop_disable;

status = hub_power_remaining(hub);

if (status)

dev_dbg(hub_dev, "%dmA power budget left\n", status);

return;

loop_disable:

hub_port_disable(hub, port1, 1);

loop:

ep0_reinit(udev);

release_address(udev);

usb_put_dev(udev);

if ((status == -ENOTCONN) || (status == -ENOTSUPP))

break;

}

如果端口隐定处于连接状态,那就需要连接端口下的设备了.首先看到的是一个for循环,是用来配置设备的两种方式.我们知道,在配置设备的时候,首先要去取设备的描述符,这个过程是在ep0上完成的.而这个ep0支持的最大传输出数据又是在设备描述符的bMaxPacketSize0中所定义的.

因此就对应有两种处理方式:

第一种是传输8个字节,取得描述符的前面一部份,从而就可以取得bMaxPacketSize0.此后再reset设备,再根据这个bMaxPacketSize0的长度去取它的设备描述符.

第二种是一次传输64字节,取得设备描述符的bMaxPacketSize0字段

关于这两种方式的描述,详见fudan_abc的<< Linux那些事儿之我是Hub>>.

有关这个for循环的作用就解释到这里.

在这段代码里,它首先分配一个usb_dev的结构,然后将其置为USB_STATE_POWERED状态.接着,为设备指定一个地址.

然后就调用hub_port_init()对这个usb_dev结构进行一系的初始化,在这个函数中会处理:Get_Description,Set_address.等操作,这个函数接下来我们再详细分析.

接着,将分配的struct usb_dev结构跟他的父结构关联起来,也就是说添加到它的父结构的usb_dev->children[]数组.

最后再调用usb_new_device()来取这个设备的配置项.这个函数我们在分析UHCI的时候已经分析过了.

中间是关于一些电流的判断处理,这部份比较简单,自行查看就可以看懂,这里不再分析.

注意,这里在分配usb_dev结构的时候,跟root hub是不相同的,如下示:

udev = usb_alloc_dev(hdev, hdev->bus, port1)

在为root hub分配struct usb_dev的时候,它的第一个参数,也就是它的父结点是为NULL.

我们来观察一下它在sysfs中的命名方式:

如下所示:

在没有插入U盘之前:

[root@localhost devices]# pwd

/sys/bus/usb/devices

[root@localhost devices]# ls

1-0:1.0 usb1

[root@localhost devices]#

插入U盘之后:

[root@localhost devices]# ls

1-0:1.0 1-1 1-1:1.0 usb1

增加的两个目是:

1-1和1-1:1.0

表示,U盘对应的设备目录是1-1.结合之前UHCI分析中,对usb_alloc_dev()应该很容易理解.

1-1:1.0 :只有这样的目录,表示该U盘只有一个接口,当前选取的是第0号设置项.

done:

hub_port_disable(hub, port1, 1);

if (hcd->driver->relinquish_port && !hub->hdev->parent)

hcd->driver->relinquish_port(hcd, port1);

}

Done标号是对应上述处理失败的处理,它禁用掉该端口(因为该端口没有连接设备或者是端口上的设备配置失败),如果是root hub,且USB控制器器驱动中又定义了relinquish_port.调用它.

照例,还是分析一下这个函数中涉及到的重要的子函数.

第一个要分析的函数是choose_address()

该函数用来为设备选择一个地址,代码如下所示:

static void choose_address(struct usb_device *udev)

{

int devnum;

struct usb_bus *bus = udev->bus;

/* If khubd ever becomes multithreaded, this will need a lock */

/* Try to allocate the next devnum beginning at bus->devnum_next. */

//从bus->devnum_next开始找到一个末被使用的位

devnum = find_next_zero_bit(bus->devmap.devicemap, 128,

bus->devnum_next);

//如果搜索到了最末尾,(128是不能被占用的),则从1起开始搜索

if (devnum >= 128)

devnum = find_next_zero_bit(bus->devmap.devicemap, 128, 1);

//更新bus->devnum_next

bus->devnum_next = ( devnum >= 127 ? 1 : devnum + 1);

//如果找到了合适位,将该位设为占用,然后更新udev->devnum为找到的设备号

if (devnum < 128) {

set_bit(devnum, bus->devmap.devicemap);

udev->devnum = devnum;

}

}

这个函数的原理我们在之前说过了多次,它是到所属的usb bus的bus->devmap中找到没有使用的那一位.在这里设置bus->devnum_next项是一个搜索的优化,它不必每次都从第1位起开始搜索.最后将找到的值存放在udev->devnum中.

第二个要分析的函数是hub_port_disable().

这个函数将hub对应的端口禁用,代码如下:

static int hub_port_disable(struct usb_hub *hub, int port1, int set_state)

{

struct usb_device *hdev = hub->hdev;

int ret = 0;

//将接在该端口下的设备设为末连接

if (hdev->children[port1-1] && set_state)

usb_set_device_state(hdev->children[port1-1],

USB_STATE_NOTATTACHED);

//发送enable 的Clear_Feature请求.

if (!hub->error)

ret = clear_port_feature(hdev, port1, USB_PORT_FEAT_ENABLE);

if (ret)

dev_err(hub->intfdev, "cannot disable port %d (err = %d)\n",

port1, ret);

return ret;

}

该函数的逻辑很简单,就是该端点下的联接设备断开,如果端口有设备连接的话.然后清除端口的enable.

第三个要分析的函数是hub_port_init().

将它列到最后,并不是因为它最轻微,而是因为它太复杂.^_^

代码分段分析如下:

static int

hub_port_init (struct usb_hub *hub, struct usb_device *udev, int port1,

int retry_counter)

{

static DEFINE_MUTEX(usb_address0_mutex);

struct usb_device *hdev = hub->hdev;

int i, j, retval;

unsigned delay = HUB_SHORT_RESET_TIME;

enum usb_device_speed oldspeed = udev->speed;

char *speed, *type;

int devnum = udev->devnum;

/* root hub ports have a slightly longer reset period

* (from USB 2.0 spec, section 7.1.7.5)

*/

//设置port 的重置等待时间

if (!hdev->parent) {

delay = HUB_ROOT_RESET_TIME;

if (port1 == hdev->bus->otg_port)

hdev->bus->b_hnp_enable = 0;

}

/* Some low speed devices have problems with the quick delay, so */

/* be a bit pessimistic with those devices. RHbug #23670 */

if (oldspeed == USB_SPEED_LOW)

delay = HUB_LONG_RESET_TIME;

mutex_lock(&usb_address0_mutex);

/* Reset the device; full speed may morph to high speed */

//将port reset

retval = hub_port_reset(hub, port1, udev, delay);

if (retval < 0) /* error or disconnect */

goto fail;

/* success, speed is known */

retval = -ENODEV;

//在设备之前的设速已经确定的情况下

//如果设备的速度发生了改变,肯定是发生了错误

if (oldspeed != USB_SPEED_UNKNOWN && oldspeed != udev->speed) {

dev_dbg(&udev->dev, "device reset changed speed!\n");

goto fail;

}

oldspeed = udev->speed;

首先为端口重置选择一个合适的延时,即在这个延时过后,端口的Reset应该完成了.usb2.0 spec上规定,root hub的延时值是50ms,高速设备是10ms,而低速设备是100ms.从代码上看,这个延时都是从udev参数中来的,这个参数就是表示在端口上连接的设备.其实,所谓的Reset端口,就是Reset端口上连接的设备.

由于我们现在要对这个设备进行配置,因此,先将它复原成初始值.

另外,如果重置之后,设备的speed发生了变化,这肯定是错误的.

/* USB 2.0 section 5.5.3 talks about ep0 maxpacket ...

* it's fixed size except for full speed devices.

* For Wireless USB devices, ep0 max packet is always 512 (tho

* reported as 0xff in the device descriptor). WUSB1.0[4.8.1].

*/

switch (udev->speed) {

case USB_SPEED_VARIABLE: /* fixed at 512 */

udev->ep0.desc.wMaxPacketSize = __constant_cpu_to_le16(512);

break;

case USB_SPEED_HIGH: /* fixed at 64 */

udev->ep0.desc.wMaxPacketSize = __constant_cpu_to_le16(64);

break;

case USB_SPEED_FULL: /* 8, 16, 32, or 64 */

/* to determine the ep0 maxpacket size, try to read

* the device descriptor to get bMaxPacketSize0 and

* then correct our initial guess.

*/

udev->ep0.desc.wMaxPacketSize = __constant_cpu_to_le16(64);

break;

case USB_SPEED_LOW: /* fixed at 8 */

udev->ep0.desc.wMaxPacketSize = __constant_cpu_to_le16(8);

break;

default:

goto fail;

}

根据设备的speed来设定ep0的MaxPacketSize.这个只是spec上规定的值.另外对于Full Speed的设来说,它的MaxPacketSize有四种情况,即8.16.32和64实际的值要在设备描述符的bMaxPacketSize0字段才能知道.

type = "";

switch (udev->speed) {

case USB_SPEED_LOW: speed = "low"; break;

case USB_SPEED_FULL: speed = "full"; break;

case USB_SPEED_HIGH: speed = "high"; break;

case USB_SPEED_VARIABLE:

speed = "variable";

type = "Wireless ";

break;

default: speed = "?"; break;

}

dev_info (&udev->dev,

"%s %s speed %sUSB device using %s and address %d\n",

(udev->config) ? "reset" : "new", speed, type,

udev->bus->controller->driver->name, devnum);

这段代码无关紧要,只是打印出了一个Debug信息，

/* Set up TT records, if needed */

if (hdev->tt) {

udev->tt = hdev->tt;

udev->ttport = hdev->ttport;

} else if (udev->speed != USB_SPEED_HIGH

&& hdev->speed == USB_SPEED_HIGH) {

udev->tt = &hub->tt;

udev->ttport = port1;

}

/* Why interleave GET_DESCRIPTOR and SET_ADDRESS this way?

* Because device hardware and firmware is sometimes buggy in

* this area, and this is how Linux has done it for ages.

* Change it cautiously.

*

* NOTE: If USE_NEW_SCHEME() is true we will start by issuing

* a 64-byte GET_DESCRIPTOR request. This is what Windows does,

* so it may help with some non-standards-compliant devices.

* Otherwise we start with SET_ADDRESS and then try to read the

* first 8 bytes of the device descriptor to get the ep0 maxpacket

* value.

*/

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 64

buf = kmalloc(GET_DESCRIPTOR_BUFSIZE, GFP_NOIO);

if (!buf) {

retval = -ENOMEM;

continue;

}

/* Retry on all errors; some devices are flakey.

* 255 is for WUSB devices, we actually need to use

* 512 (WUSB1.0[4.8.1]).

*/

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);

switch (buf->bMaxPacketSize0) {

case 8: case 16: case 32: case 64: case 255:

if (buf->bDescriptorType ==

USB_DT_DEVICE) {

r = 0;

break;

}

/* FALL THROUGH */

default:

if (r == 0)

r = -EPROTO;

break;

}

if (r == 0)

break;

}

udev->descriptor.bMaxPacketSize0 =

buf->bMaxPacketSize0;

kfree(buf);

retval = hub_port_reset(hub, port1, udev, delay);

if (retval < 0) /* error or disconnect */

goto fail;

if (oldspeed != udev->speed) {

dev_dbg(&udev->dev,

"device reset changed speed!\n");

retval = -ENODEV;

goto fail;

}

if (r) {

dev_err(&udev->dev, "device descriptor "

"read/%s, error %d\n",

"64", r);

retval = -EMSGSIZE;

continue;

}

#undef GET_DESCRIPTOR_BUFSIZE

}

for (j = 0; j < SET_ADDRESS_TRIES; ++j) {

retval = hub_set_address(udev, devnum);

if (retval >= 0)

break;

msleep(200);

}

if (retval < 0) {

dev_err(&udev->dev,

"device not accepting address %d, error %d\n",

devnum, retval);

goto fail;

}

/* cope with hardware quirkiness:

* - let SET_ADDRESS settle, some device hardware wants it

* - read ep0 maxpacket even for high and low speed,

*/

msleep(10);

if (USE_NEW_SCHEME(retry_counter))

break;

retval = usb_get_device_descriptor(udev, 8);

if (retval < 8) {

dev_err(&udev->dev, "device descriptor "

"read/%s, error %d\n",

"8", retval);

if (retval >= 0)

retval = -EMSGSIZE;

} else {

retval = 0;

break;

}

}

这个for循环是一个很重要的操作,首先,我们来看一下USE_NEW_SCHEME宏的定义.如下示:

((i) / 2 == old_scheme_first), old_scheme_first默认为0,也就是说,当i为0,1的时候,这个宏会返回1.那就是说,对于之前分析的两种机制,每种机制尝试两次.

区分一下这两种机制的不同:

对于第一种机制,它先用64的buffer去取设备描述符.而第二种机制,是以长度8的缓存区,取设备描述符的前半部份.

另外,第一种机制,去取设备描述符之前没有设置设备的地址,因此使用地址0来表示设备的地址,在代码中,用usb_rcvaddr0pipe()表示.而在第二种机制中,它在取设备描述符之前已经设置了设备的地址.

疑问:可能有人就有这样的疑问,既然地址0可以表示没有设置地址的设备地址,那如果有多个没有set address的设备,这个地址0到底是表示那个设备呢?

实际上,从代码上看,Linux是每打开一个hub的端口就初始连在这个端口上的设备.之后这连接上的设备设置好地址之后再打开hub的另外的端口进行配置,因此,在同一条usb bus上,不会出现多个末配置的活动设备.

if (retval)

goto fail;

i = udev->descriptor.bMaxPacketSize0 == 0xff?

512 : udev->descriptor.bMaxPacketSize0;

if (le16_to_cpu(udev->ep0.desc.wMaxPacketSize) != i) {

if (udev->speed != USB_SPEED_FULL ||

!(i == 8 || i == 16 || i == 32 || i == 64)) {

dev_err(&udev->dev, "ep0 maxpacket = %d\n", i);

retval = -EMSGSIZE;

goto fail;

}

dev_dbg(&udev->dev, "ep0 maxpacket = %d\n", i);

udev->ep0.desc.wMaxPacketSize = cpu_to_le16(i);

ep0_reinit(udev);

}

retval = usb_get_device_descriptor(udev, USB_DT_DEVICE_SIZE);

if (retval < (signed)sizeof(udev->descriptor)) {

dev_err(&udev->dev, "device descriptor read/%s, error %d\n",

"all", retval);

if (retval >= 0)

retval = -ENOMSG;

goto fail;

}

retval = 0;

fail:

if (retval) {

hub_port_disable(hub, port1, 0);

udev->devnum = devnum; /* for disconnect processing */

}

mutex_unlock(&usb_address0_mutex);

return retval;

}

在上面获得的设备描述符的bMaxPacketSize0字段,也就是ep0的MaxPacketSize.但如果这个值不和我们之前根据spec为ep0设定的MaxPacketSize值相等,且不是Full speed的话,就会有错误了.因为只有Full Speed的设备的ep0 的MaxPacketSize在spec上并没有一个明确的定义值.

有了确定的ep0 的MaxPacketSize值,就可以取得完整的设备描述符了.

第四个要分析的函数是hub_port_reset().

这个函数将端口重置并等待端口重置完成.代码如下:

static int hub_port_reset(struct usb_hub *hub, int port1,

struct usb_device *udev, unsigned int delay)

{

int i, status;

/* Block EHCI CF initialization during the port reset.

* Some companion controllers don't like it when they mix.

*/

down_read(&ehci_cf_port_reset_rwsem);

/* Reset the port */

//尝试5次

for (i = 0; i < PORT_RESET_TRIES; i++) {

//发送Reset 的Set_Feature

status = set_port_feature(hub->hdev,

port1, USB_PORT_FEAT_RESET);

//发送错误

if (status)

dev_err(hub->intfdev,

"cannot reset port %d (err = %d)\n",

port1, status);

else {

//发送Clear_Feature成功,等待端口重置完成

status = hub_port_wait_reset(hub, port1, udev, delay);

if (status && status != -ENOTCONN)

dev_dbg(hub->intfdev,

"port_wait_reset: err = %d\n",

status);

}

/* return on disconnect or reset */

switch (status) {

//成功

case 0:

/* TRSTRCY = 10 ms; plus some extra */

msleep(10 + 40);

udev->devnum = 0; /* Device now at address 0 */

/* FALL THROUGH */

//端口没有连接

case -ENOTCONN:

//要发送的设备不存在

case -ENODEV:

clear_port_feature(hub->hdev,

port1, USB_PORT_FEAT_C_RESET);

/* FIXME need disconnect() for NOTATTACHED device */

usb_set_device_state(udev, status

? USB_STATE_NOTATTACHED

: USB_STATE_DEFAULT);

goto done;

}

dev_dbg (hub->intfdev,

"port %d not enabled, trying reset again...\n",

port1);

//将延迟设至最长,再试一次

delay = HUB_LONG_RESET_TIME;

}

dev_err (hub->intfdev,

"Cannot enable port %i. Maybe the USB cable is bad?\n",

port1);

done:

up_read(&ehci_cf_port_reset_rwsem);

return status;

}

这个函数的代码看清淅,首先将端口重置,然后等待端口重置完成.在成功返回或者是发错致命错误的时候就会在清除掉RESET Feature,设置设备状态之后返回.这个所谓的致命包括:

1:发送Clear_Feature时,返回-ENODEV,表示设备不存在

2:在hub_port_wait_reset()后返回的-ENOTCONN,表示端口上末连接设备.

另外,在这里哆嗦的重复一句,只有在设备有这个Feature的时候,才能Clear_Feature.在上面的代码中,只有代码中,如果Reset不成功,是不需要Clear USB_PORT_FEAT_C_RESET 这个Feature的.只有在已经设置成功的情况,才能将其Clear(-ENODEV的情况,无所谓,这个错误在submit urb前期就能测检出来,不会跟硬件交互,而-ENOTCONN则表示端口Reset完成,但尚末检测到连接设备,这种情况下,也是需要Clear_Feature的).

另外,里面还调用了一个子函数, hub_port_wait_reset().代码如下:

static int hub_port_wait_reset(struct usb_hub *hub, int port1,

struct usb_device *udev, unsigned int delay)

{

int delay_time, ret;

u16 portstatus;

u16 portchange;

//最长等待时间是500

for (delay_time = 0;

delay_time < HUB_RESET_TIMEOUT;

delay_time += delay) {

/* wait to give the device a chance to reset */

msleep(delay);

/* read and decode port status */

ret = hub_port_status(hub, port1, &portstatus, &portchange);

if (ret < 0)

return ret;

/* Device went away? */

//端口已经没有连接了,说明连接的设备在某个时刻被拨下来了

if (!(portstatus & USB_PORT_STAT_CONNECTION))

return -ENOTCONN;

/* bomb out completely if the connection bounced */

//连接状态发生了改变,则说明连接状态不稳定.因为断开之后,再联上是需要重新配置的

//退出

if ((portchange & USB_PORT_STAT_C_CONNECTION))

return -ENOTCONN;

/* if we`ve finished resetting, then break out of the loop */

//如果Reset已经完成,且端口处于enable状态,设置speed成员就可以返回了

if (!(portstatus & USB_PORT_STAT_RESET) &&

(portstatus & USB_PORT_STAT_ENABLE)) {

if (hub_is_wusb(hub))

udev->speed = USB_SPEED_VARIABLE;

else if (portstatus & USB_PORT_STAT_HIGH_SPEED)

udev->speed = USB_SPEED_HIGH;

else if (portstatus & USB_PORT_STAT_LOW_SPEED)

udev->speed = USB_SPEED_LOW;

else

udev->speed = USB_SPEED_FULL;

return 0;

}

/* switch to the long delay after two short delay failures */

//失败两次,将延时时间设为最长的时间

if (delay_time >= 2 * HUB_SHORT_RESET_TIME)

delay = HUB_LONG_RESET_TIME;

dev_dbg (hub->intfdev,

"port %d not reset yet, waiting %dms\n",

port1, delay);

}

return -EBUSY;

}

注意到在上面为speed成员赋值的时候,出现了一个hub_is_wusb().该宏用来判断hcd是否是一个无线的USB主机控制器.如果hcd 是一个无线的,那其下的所有设备的speed均为USB_SPEED_VARIABLE.这个是属于usb2.5 spec里面定义的.

到这里,hub_thread()函数已经分析完了.它已经将hub下连接的所有新设备都初始化并添加进了设备模型.

5.2.3:HUB中断URB传输完成的处理

在之前分析中断URB初始化的时候,曾分析到,如果中断URB传输完成,就会调用hub_irq().在分析这个函数之前,我们先从spec上了解一下,对于hub的中断传输到底会传些什么样的东西:

如下图所示:

Bit0表示hub的连接状态发生了改变,而bit1~bitN表示的是各端口连接状态的改变.如果1表示改变,为0表示末改变.

现在可以看该函数的代码了,如下:

static void hub_irq(struct urb *urb)

{

struct usb_hub *hub = urb->context;

int status = urb->status;

int i;

unsigned long bits;

switch (status) {

case -ENOENT: /* synchronous unlink */

case -ECONNRESET: /* async unlink */

case -ESHUTDOWN: /* hardware going away */

return;

default: /* presumably an error */

/* Cause a hub reset after 10 consecutive errors */

dev_dbg (hub->intfdev, "transfer --> %d\n", status);

if ((++hub->nerrors < 10) || hub->error)

goto resubmit;

hub->error = status;

/* FALL THROUGH */

/* let khubd handle things */

case 0: /* we got data: port status changed */

bits = 0;

for (i = 0; i < urb->actual_length; ++i)

bits |= ((unsigned long) ((*hub->buffer)[i]))

<< (i*8);

hub->event_bits[0] = bits;

break;

}

hub->nerrors = 0;

/* Something happened, let khubd figure it out */

kick_khubd(hub);

resubmit:

if (hub->quiescing)

return;

if ((status = usb_submit_urb (hub->urb, GFP_ATOMIC)) != 0

&& status != -ENODEV && status != -EPERM)

dev_err (hub->intfdev, "resubmit --> %d\n", status);

}

从上面的代码可以看出,就将是设HUB中断传输的信息保存在hub->event_bits中,然后又将此URB再次提交,再次提交的结果是,可以轮询获得hub的状态,另外,还会调用kick_khubd().这样,hub_events()就又会调用,又可以处理HUB端口的状态改变.