Linux设备驱动之USB hub驱动
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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…