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.
六:小结
在本小结里,对HUB的处理过程做了一个详尽的分析,在这一节里,也了解到了USB的驱动架构以及USB设备的枚举过程.
在下一节里,我们以特定的USB设备分例,来分析USB驱动程序的架构.
