linux设备驱动之USB主机控制器驱动分析（二）
首先来看一下这个函数要做什么事情:
我们在前面说过,int128,int64,int32……int4,int2,int1这样8个QH.我们在后面看到.会将 uhci->frame的物理地址存放到UHCI控制器的Frame List Base Address Register中.所以现在要做的事情就是将这些QH与uhci->frame[ ]关联起来.必须要按照相应的时间间隔将QH插入到uhci->frame[]中.例如,例如如果frame[]的n存放int128的QH,那么 下一个int128的QH就必须要放到n+128的位置.很明显,对于int1是可以随便放的,也可放可不放.因为int1链接在所有的间隔的QH后面. 同时int1又可以单独存放到frame[]中.
另外,从skelqh[2]~skelqh[9]分别表示int128~int1.对于skelqh[0]和skelqh[1]是不需要用到 的,而且8- (int) __ffs(frame | UHCI_NUMFRAMES)不可能大于9.所以,将用到skelqh[0]和skelqh[1]的地方.用间隔1ms的skelqh[9]代替.
经过这个函数这后,uhci->frame[]中的各个QH都按照对应的间隔存放到一起了.
接着看下面的configure_hc()函数:
static void configure_hc(struct uhci_hcd *uhci)
{
/* Set the frame length to the default: 1 ms exactly */
outb(USBSOF_DEFAULT, uhci->io_addr + USBSOF);
/* Store the frame list base address */
//将frame指针地址写入基地址寄存器
outl(uhci->frame_dma_handle, uhci->io_addr + USBFLBASEADD);
/* Set the current frame number */
//当前的frame number
outw(uhci->frame_number & UHCI_MAX_SOF_NUMBER,
uhci->io_addr + USBFRNUM);
/* Mark controller as not halted before we enable interrupts */
uhci_to_hcd(uhci)->state = HC_STATE_SUSPENDED;
mb();
/* Enable PIRQ */
pci_write_config_word(to_pci_dev(uhci_dev(uhci)), USBLEGSUP,
USBLEGSUP_DEFAULT);
}
这个函数比较简单.首先将uhci->frame[ ]的物理地址写到FRBASEADD寄存器中.再将起始帧号写入到FRNUM寄存器.再将状态置为HC_STATE_SUSPENDED.最后到USBLEGSUP中启用PIRQ.这样UHCI就可以产生中断了.
到这里,UHCI已经初始化完成了.现在到了启用它的时候了.
返回到uhci_start().流程转入到uhci_start().代码如下:
static void start_rh(struct uhci_hcd *uhci)
{
//将UHCI的状态置为HC_STATE_RUNNING
uhci_to_hcd(uhci)->state = HC_STATE_RUNNING;
uhci->is_stopped = 0;
/* Mark it configured and running with a 64-byte max packet.
* All interrupts are enabled, even though RESUME won't do anything.
*/
//启用UHCI,设置CF位,表示已经配置好了,指定最大的包长为64 byte
outw(USBCMD_RS | USBCMD_CF | USBCMD_MAXP, uhci->io_addr + USBCMD);
//启用各种中断.包括传输超时或者CRC检验错误,RESUME状态中断.传输完成时产生中断
//短包中断
outw(USBINTR_TIMEOUT | USBINTR_RESUME | USBINTR_IOC | USBINTR_SP,
uhci->io_addr + USBINTR);
mb();
//然后将UHCI的状态置为UHCI_RH_RUNNING状态.
uhci->rh_state = UHCI_RH_RUNNING;
uhci_to_hcd(uhci)->poll_rh = 1;
}
对照代码中的注释和UHCI spec,理解这段代码比较容易.在这里要特别提示一下,什么叫短包中断.
在发送包的时候,如果一次不能够打包完.那就需要将包截短成小包. 一个个传输传输出去.另外,最后一个包可能传输数据会小于允许包大小的最大值.这个的包叫短包.我们在后面的中断处理函数中会有对于短包的处理.到时再详细分析它的处理.
到这里.UHCI就开始调度了.不过这时候.整个调度系统中就只含有一个term_td.然而这个td的初始化如下(在uhci_start[ ]函数中):
uhci_fill_td(uhci->term_td, 0, uhci_explen(0) |
(0x7f << TD_TOKEN_DEVADDR_SHIFT) | USB_PID_IN, 0);
也就是它的status为空,也就是说,这个TD是一个INACTIVE的.实际这个UHCI是空负荷运行.
运行到这里,hcd->start()运行完了.流程会返回到usb_add_hcd()到.的重要操作只剩余register_root_hub().probe过程也要接近尾声了.
2.4:register_root_hub()的操作
这个函数主要是对UHCI的root hub进行处理.代码如下:
static int register_root_hub(struct usb_hcd *hcd)
{
struct device *parent_dev = hcd->self.controller;
struct usb_device *usb_dev = hcd->self.root_hub;
const int devnum = 1;
int retval;
//root hub的devnum为1.下一个设备号从2开始.devnum也即设备地址
usb_dev->devnum = devnum;
usb_dev->bus->devnum_next = devnum + 1;
//usb_bus->devmap是一个位图.表示设备号的分配情况
memset (&usb_dev->bus->devmap.devicemap, 0,
sizeof usb_dev->bus->devmap.devicemap);
//将root hub占用位置1
set_bit (devnum, usb_dev->bus->devmap.devicemap);
//设置成Address 状态
usb_set_device_state(usb_dev, USB_STATE_ADDRESS);
mutex_lock(&usb_bus_list_lock);
//端点0的最大发送或者接收值
usb_dev->ep0.desc.wMaxPacketSize = __constant_cpu_to_le16(64);
//取得root hub的设备描述符
retval = usb_get_device_descriptor(usb_dev, USB_DT_DEVICE_SIZE);
if (retval != sizeof usb_dev->descriptor) {
mutex_unlock(&usb_bus_list_lock);
dev_dbg (parent_dev, "can't read %s device descriptor %d\n",
usb_dev->dev.bus_id, retval);
return (retval < 0) ? retval : -EMSGSIZE;
}
//进一步初始化这个设备
retval = usb_new_device (usb_dev);
if (retval) {
dev_err (parent_dev, "can't register root hub for %s, %d\n",
usb_dev->dev.bus_id, retval);
}
mutex_unlock(&usb_bus_list_lock);
if (retval == 0) {
spin_lock_irq (&hcd_root_hub_lock);
//root hub注册成功,将rh_registered设为1
hcd->rh_registered = 1;
spin_unlock_irq (&hcd_root_hub_lock);
/* Did the HC die before the root hub was registered? */
//如果hcd被人为置为了HALT
if (hcd->state == HC_STATE_HALT)
usb_hc_died (hcd); /* This time clean up */
}
return retval;
}
对于代码中较简单部份,结合注释应该就能看懂了.详细分析一下里面涉及到的几个子函数.
第一个是usb_set_device_state().
在分析代码之前,先来看一下USB设备的状态机.在USB2.0的spec上.有一副这样的图:
上图表示USB设备的各种状态的转变.
1:如果设备末连接,对应状态为USB_STATE_NOTATTACHED. 这个状态在spec上末表示.是linux中自定义的.实际上它就是表示Attached的一个对立状态.
2:如果设备连上了,但是没有打开电源,处于Attached状态.USB检测到一个设备的时候,会将它初始化这个状态(道理很简单,因为要连上才能检测到 ^_^).可以查看下usb_alloc_dev()函数对状态的初始化.在代码,这个状态对应为:
USB_STATE_ATTACHED.
3:如果在上个状态中打开了设备此时打开了电源,设备处于Rowered.在代码中对应USB_STATE_POWERED.
4:如果在上一个状态中,设备被重置,也即初始化,就会转入Default.代码中对应USB_STATE_DEFAULT.
5:如果在上一个状态中,USB为设备分配了地址,就会转入到Address.代码中对应USB_STATE_ADDRESS.
6:如果在上一个状态中,USB完成了设备的配置.就会转入Configured.代码中对应USB_STATE_CONFIGURED.
7:上面除NoAttached和Attached外的所有状态,如果设备被挂起,就会转入Suspended.代码中对应USB_STATE_SUSPENDED.
特别说明:UHCI本身带有root hub功能.hub是一个特殊的USB设备.它的设备地址被固定为1.
对应到上面的代码中:
指定root hub的devnum之后,就将其状态设为Address.这个devnum也即设备的地址.设备状态函数为usb_set_device_state().代码如下:
void usb_set_device_state(struct usb_device *udev,
enum usb_device_state new_state)
{
unsigned long flags;
spin_lock_irqsave(&device_state_lock, flags);
//如果设备末连接.不做任何处理
if (udev->state == USB_STATE_NOTATTACHED)
; /* do nothing */
else if (new_state != USB_STATE_NOTATTACHED) {
/* root hub wakeup capabilities are managed out-of-band
* and may involve silicon errata ... ignore them here.
*/
//如果不是root hub
if (udev->parent) {
if (udev->state == USB_STATE_SUSPENDED
|| new_state == USB_STATE_SUSPENDED)
; /* No change to wakeup settings */
else if (new_state == USB_STATE_CONFIGURED)
device_init_wakeup(&udev->dev,
(udev->actconfig->desc.bmAttributes
& USB_CONFIG_ATT_WAKEUP));
else
device_init_wakeup(&udev->dev, 0);
}
//如果是从Suspended转到其它状态或者是转到Suspended状态
//更新active_duration计数
if (udev->state == USB_STATE_SUSPENDED &&
new_state != USB_STATE_SUSPENDED)
udev->active_duration -= jiffies;
else if (new_state == USB_STATE_SUSPENDED &&
udev->state != USB_STATE_SUSPENDED)
udev->active_duration += jiffies;
//设置状态
udev->state = new_state;
}
else
//这里是多余的吧?
recursively_mark_NOTATTACHED(udev);
spin_unlock_irqrestore(&device_state_lock, flags);
}
这段代码没有什么好多讲的.就是设置状态而已.对于不是root hub的情况,还涉及到了电源管理的情况,在这里不做分析.
设置完设备状态之后,调用usb_get_device_descriptor()来取得设备描述符.这个函数涉及到数据的传输实现.在接下来的章节中再做详细分析.在这里只需知道,完成之后会将设备描述符存放在usb_dev->descriptor.
获取到设备描述符之后,就可以获得设备的详细信息了.具体的详细可考阅USB2.0 spec.在这些信息里会包括设备的配置项数目.因此在接下来的操作中,就会将设备所支持的所有配置取出来.这是在usb_new_device()中完成的.代码如下所示:
int usb_new_device(struct usb_device *udev)
{
int err;
//一些设备的fixup
usb_detect_quirks(udev); /* Determine quirks */
//取得配置描述符
err = usb_configure_device(udev); /* detect & probe dev/intfs */
if (err < 0)
goto fail;
/* export the usbdev device-node for libusb */
//指定设备的设备号
udev->dev.devt = MKDEV(USB_DEVICE_MAJOR,
(((udev->bus->busnum-1) * 128) + (udev->devnum-1)));
/* Increment the parent's count of unsuspended children */
if (udev->parent)
usb_autoresume_device(udev->parent);
/* Register the device. The device driver is responsible
* for adding the device files to sysfs and for configuring
* the device.
*/
//注册usb_dev中内嵌的struct device
err = device_add(&udev->dev);
if (err) {
dev_err(&udev->dev, "can't device_add, error %d\n", err);
goto fail;
}
/* Tell the world! */
//输出一些该设备的信息
announce_device(udev);
return err;
fail:
usb_set_device_state(udev, USB_STATE_NOTATTACHED);
return err;
}
这个代码的逻辑比较清淅.首先是usb_detect_quirks()函数,为个函数较简单,不打算进行详细分析,只是简单提一下.有些设备 可能在设计存在一些问题.比如说,有的设备在Reset的时候会出现问题,或者在取string描述符的时候对buffer长度有要求.这样的设备都会在 linux内核中形成一个链表,即usb_quirk_list.然后将设备的厂商ID,版本等信息与usb_quirk_list上的设备匹配.如果匹 配到了,就在usb_dev添上相应的标识,不允许设备进行限制的功能.或者是设备驱动根据修改信息调整相关的操作.
然后是usb_configure_device()函数.这个函数比较重要,跟踪进去分析一下 :
static int usb_configure_device(struct usb_device *udev)
{
int err;
//取得设备的配置
if (udev->config == NULL) {
err = usb_get_configuration(udev);
if (err < 0) {
dev_err(&udev->dev, "can't read configurations, error %d\n",
err);
goto fail;
}
}
//如果是无线设备
if (udev->wusb == 1 && udev->authorized == 0) {
udev->product = kstrdup("n/a (unauthorized)", GFP_KERNEL);
udev->manufacturer = kstrdup("n/a (unauthorized)", GFP_KERNEL);
udev->serial = kstrdup("n/a (unauthorized)", GFP_KERNEL);
}
else {
//usb_cache_string:会将其关的字串存进一个缓冲,用户空间如果要取设备信息的话
//只要从缓存区取就可以了
/* read the standard strings and cache them if present */
udev->product = usb_cache_string(udev, udev->descriptor.iProduct);
udev->manufacturer = usb_cache_string(udev,
udev->descriptor.iManufacturer);
udev->serial = usb_cache_string(udev, udev->descriptor.iSerialNumber);
}
//OTG: On-The-GO.表示设备有主机控制器的功能
err = usb_configure_device_otg(udev);
fail:
return err;
}
首先解释一下CONFIG_USB_OTG的配置选项.一般来说,系统中只能有一个主机控制器.但有时候设备也可以带一个host control的功能.举个例子,数码相机.它接在PC上,做为一般的USB设备使用.它也可以连接在打印上直接打印,这时就会做会一个HC使用.
关于OTG的选择编译代码,这里不做深入研究,忽略掉.
其次要解释的是关于usb_cache_string()的操作.这个函数在取字串的时候还会将字符信息保存到一个缓存区.这样一些读USB信息的工具,就只要从指定的缓存区里取值就可以了.
重点放在usb_get_configuration()函数上.这个函数很烦锁.在分析之前.先来了解一下相关的部份.
USB设备有时候会用做多种用途.比如上面的一个例如.数码相机中的USB,可以用做视频存储,也可以当做U盘来使用.那做为驱动程序.它必须 要知道设备有多少种功能.在USB2.0 spec中,用配置表示功能.也就是说,对于上在的例子来说,数码相机的USB设备至少应该有两个配置,一个是视频存储的配置,另外的是U盘的配置.由驱 动程序来决定应用哪种配置来使用对应的功能.
接口是USB提供的单元组件.因此,有可能一个配置要使用到多个接口,也有可能一个接口也被多个配置使用的情况,不过不使用接口的配置是不存在的.
根据USB的spec有关设备的检测过程中描述,USB控制器先取得设备描述符,这个描述符里包含了配置的个数.然后再以长度9做为参数去取设 备配置描述符头部,这个描述符里包含了描述符的实际长际.最后再以实际长度做参数去取完整的配置描述符.取得的配置描述符不仅包含配置描述符信息,还包括 了接口信息和接口所使用的端口信息.
将代码中的有关数据结构如下所示 :
大概说一下,usb_dev中的config数组对应每一项配置.config数组的数据结构为struct usb_host_config.这个数据结构中又包含Inft_cache[ ]数组,这个数组用来表示存放接口信息.由于一个接口可能属于同一配置的不同设置,用接口描述符的bAlternateSetting字段来区别接口所属 的接口描述符.所以在inft_cache[]对应的usb_host_cache中又有一个扩展项来存放每一个接口描述符.
以注释的方式列出usb_get_configuration(),就不做详细分析了,结合上面的说明和代码中的注释来分析这段代码应该没什么问题了.如下:
int usb_get_configuration(struct usb_device *dev)
{
struct device *ddev = &dev->dev;
int ncfg = dev->descriptor.bNumConfigurations;
int result = 0;
unsigned int cfgno, length;
unsigned char *buffer;
unsigned char *bigbuffer;
struct usb_config_descriptor *desc;
cfgno = 0;
if (dev->authorized == 0) /* Not really an error */
goto out_not_authorized;
result = -ENOMEM;
//如果配置项数目超过允许的最大数.将其强制设为最大数
if (ncfg > USB_MAXCONFIG) {
dev_warn(ddev, "too many configurations: %d, "
"using maximum allowed: %d\n", ncfg, USB_MAXCONFIG);
dev->descriptor.bNumConfigurations = ncfg = USB_MAXCONFIG;
}
//如果一个配置都没有.错误
if (ncfg < 1) {
dev_err(ddev, "no configurations\n");
return -EINVAL;
}
//dev->config所占内存大小.总共有ncfg个配置项
length = ncfg * sizeof(struct usb_host_config);
//为dev->config分存内存
dev->config = kzalloc(length, GFP_KERNEL);
if (!dev->config)
goto err2;
length = ncfg * sizeof(char *);
dev->rawdescriptors = kzalloc(length, GFP_KERNEL);
if (!dev->rawdescriptors)
goto err2;
buffer = kmalloc(USB_DT_CONFIG_SIZE, GFP_KERNEL);
if (!buffer)
goto err2;
desc = (struct usb_config_descriptor *)buffer;
result = 0;
//从设备中依次取出各配置.
for (; cfgno < ncfg; cfgno++) {
//这里有两次取CONFIG的过程.第一次是9为size取得配置的长度.然后
//再以特定长度做为size去取完整的config
/* We grab just the first descriptor so we know how long
* the whole configuration is */
result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno,
buffer, USB_DT_CONFIG_SIZE);
if (result < 0) {
dev_err(ddev, "unable to read config index %d "
"descriptor/%s: %d\n", cfgno, "start", result);
dev_err(ddev, "chopping to %d config(s)\n", cfgno);
dev->descriptor.bNumConfigurations = cfgno;
break;
} else if (result < 4) {
dev_err(ddev, "config index %d descriptor too short "
"(expected %i, got %i)\n", cfgno,
USB_DT_CONFIG_SIZE, result);
result = -EINVAL;
goto err;
}
//取config长度
length = max((int) le16_to_cpu(desc->wTotalLength),
USB_DT_CONFIG_SIZE);
/* Now that we know the length, get the whole thing */
bigbuffer = kmalloc(length, GFP_KERNEL);
if (!bigbuffer) {
result = -ENOMEM;
goto err;
}
//取完整的config,并将其存放在bigbuffer中
result = usb_get_descriptor(dev, USB_DT_CONFIG, cfgno,
bigbuffer, length);
if (result < 0) {
dev_err(ddev, "unable to read config index %d "
"descriptor/%s\n", cfgno, "all");
kfree(bigbuffer);
goto err;
}
if (result < length) {
dev_warn(ddev, "config index %d descriptor too short "
"(expected %i, got %i)\n", cfgno, length, result);
length = result;
}
//dev->rawdescriptors中存放了取得的CONFIG
dev->rawdescriptors[cfgno] = bigbuffer;
//解析取得的config信息
result = usb_parse_configuration(&dev->dev, cfgno,
&dev->config[cfgno], bigbuffer, length);
if (result < 0) {
++cfgno;
goto err;
}
}
result = 0;
err:
kfree(buffer);
out_not_authorized:
dev->descriptor.bNumConfigurations = cfgno;
err2:
if (result == -ENOMEM)
dev_err(ddev, "out of memory\n");
return result;
}
对每个配置都会调用usb_parse_configuration()对它进行解析.代码如下:
static int usb_parse_configuration(struct device *ddev, int cfgidx,
struct usb_host_config *config, unsigned char *buffer, int size)
{
unsigned char *buffer0 = buffer;
int cfgno;
int nintf, nintf_orig;
int i, j, n;
struct usb_interface_cache *intfc;
unsigned char *buffer2;
int size2;
struct usb_descriptor_header *header;
int len, retval;
u8 inums[USB_MAXINTERFACES], nalts[USB_MAXINTERFACES];
unsigned iad_num = 0;
//配置描述符信息.这个信息在后面还会修正的
memcpy(&config->desc, buffer, USB_DT_CONFIG_SIZE);
if (config->desc.bDescriptorType != USB_DT_CONFIG ||
config->desc.bLength < USB_DT_CONFIG_SIZE) {
dev_err(ddev, "invalid descriptor for config index %d: "
"type = 0x%X, length = %d\n", cfgidx,
config->desc.bDescriptorType, config->desc.bLength);
return -EINVAL;
}
//CONFIG序号
cfgno = config->desc.bConfigurationValue;
//完整的配置信息除了标准头部处,还会带上接口和端口描述符信息
//bLength: 描述符长度
buffer += config->desc.bLength;
//接口描述符大小
size -= config->desc.bLength;
//接口数目
nintf = nintf_orig = config->desc.bNumInterfaces;
//接口数目太多
if (nintf > USB_MAXINTERFACES) {
dev_warn(ddev, "config %d has too many interfaces: %d, "
"using maximum allowed: %d\n",
cfgno, nintf, USB_MAXINTERFACES);
nintf = USB_MAXINTERFACES;
}
/* Go through the descriptors, checking their length and counting the
* number of altsettings for each interface */
n = 0;
for ((buffer2 = buffer, size2 = size);
size2 > 0;
(buffer2 += header->bLength, size2 -= header->bLength)) {
if (size2 < sizeof(struct usb_descriptor_header)) {
dev_warn(ddev, "config %d descriptor has %d excess "
"byte%s, ignoring\n",
cfgno, size2, plural(size2));
break;
}
header = (struct usb_descriptor_header *) buffer2;
if ((header->bLength > size2) || (header->bLength < 2)) {
dev_warn(ddev, "config %d has an invalid descriptor "
"of length %d, skipping remainder of the config\n",
cfgno, header->bLength);
break;
}
//如果后面跟的是INTERFACE的描述符
if (header->bDescriptorType == USB_DT_INTERFACE) {
struct usb_interface_descriptor *d;
int inum;
d = (struct usb_interface_descriptor *) header;
//如果长度太短,不合法.继续下一个interface config
if (d->bLength < USB_DT_INTERFACE_SIZE) {
dev_warn(ddev, "config %d has an invalid "
"interface descriptor of length %d, "
"skipping\n", cfgno, d->bLength);
continue;
}
//接号序号
inum = d->bInterfaceNumber;
//接口序号超过了最大值
if (inum >= nintf_orig)
dev_warn(ddev, "config %d has an invalid "
"interface number: %d but max is %d\n",
cfgno, inum, nintf_orig - 1);
/* Have we already encountered this interface?
* Count its altsettings */
//nalts[ ]是相同端口出现次数的统计
//如果在inums[ ]中已经包含这个接口了.
for (i = 0; i < n; ++i) {
if (inums[i] == inum)
break;
}
//如果已经在inums[ ]了,增加nalts[]相应项的统计计数
if (i < n) {
if (nalts[i] < 255)
++nalts[i];
}
//否则将序号设置进inums[ ]中,nalts[]相应项为1.因为还是第一次出现
else if (n < USB_MAXINTERFACES) {
inums[n] = inum;
nalts[n] = 1;
++n;
}
}
//minor usb only
else if (header->bDescriptorType ==
USB_DT_INTERFACE_ASSOCIATION) {
if (iad_num == USB_MAXIADS) {
dev_warn(ddev, "found more Interface "
"Association Descriptors "
"than allocated for in "
"configuration %d\n", cfgno);
} else {
config->intf_assoc[iad_num] =
(struct usb_interface_assoc_descriptor
*)header;
iad_num++;
}
} else if (header->bDescriptorType == USB_DT_DEVICE ||
header->bDescriptorType == USB_DT_CONFIG)
dev_warn(ddev, "config %d contains an unexpected "
"descriptor of type 0x%X, skipping\n",
cfgno, header->bDescriptorType);
} /* for ((buffer2 = buffer, size2 = size); ...) */
//size是有效的interface config数据部份的长度
size = buffer2 - buffer;
config->desc.wTotalLength = cpu_to_le16(buffer2 - buffer0);
//n是inums[ ]数组的有效项数,也即端口个数.
//更新n,使表示实际的端口个数
if (n != nintf)
dev_warn(ddev, "config %d has %d interface%s, different from "
"the descriptor's value: %d\n",
cfgno, n, plural(n), nintf_orig);
else if (n == 0)
dev_warn(ddev, "config %d has no interfaces?\n", cfgno);
config->desc.bNumInterfaces = nintf = n;
/* Check for missing interface numbers */
//检查inums[ ]是否准确.如果有异常,打印出警告信息
for (i = 0; i < nintf; ++i) {
for (j = 0; j < nintf; ++j) {
if (inums[j] == i)
break;
}
if (j >= nintf)
dev_warn(ddev, "config %d has no interface number "
"%d\n", cfgno, i);
}
/* Allocate the usb_interface_caches and altsetting arrays */
//每一个接口号对应intf_cache[ ]一项.然nals[ ]表示该接口号的个数
for (i = 0; i < nintf; ++i) {
j = nalts[i];
//
if (j > USB_MAXALTSETTING) {
dev_warn(ddev, "too many alternate settings for "
"config %d interface %d: %d, "
"using maximum allowed: %d\n",
cfgno, inums[i], j, USB_MAXALTSETTING);
nalts[i] = j = USB_MAXALTSETTING;
}
len = sizeof(*intfc) + sizeof(struct usb_host_interface) * j;
config->intf_cache[i] = intfc = kzalloc(len, GFP_KERNEL);
if (!intfc)
return -ENOMEM;
kref_init(&intfc->ref);
}
/* Skip over any Class Specific or Vendor Specific descriptors;
* find the first interface descriptor */
//config->extar:config的扩展部份,即interface config的那部份
config->extra = buffer;
//找到一下个USB_DT_INTERFACE项.返回跳过去的数据长度和描述符项
i = find_next_descriptor(buffer, size, USB_DT_INTERFACE,
USB_DT_INTERFACE, &n);
config->extralen = i;
//到现在为止,config->extra返回的是下一个配置描述符起始地址
//config->extralen下一个配置描述符地址和config->extra的偏移值
if (n > 0)
dev_dbg(ddev, "skipped %d descriptor%s after %s\n",
n, plural(n), "configuration");
//现在interface config有效的起点位置,size有效大小
buffer += i;
size -= i;
/* Parse all the interface/altsetting descriptors */
while (size > 0) {
retval = usb_parse_interface(ddev, cfgno, config,
buffer, size, inums, nalts);
if (retval < 0)
return retval;
buffer += retval;
size -= retval;
}
/* Check for missing altsettings */
//检查config->inft)cache[]中是否有异常
for (i = 0; i < nintf; ++i) {
intfc = config->intf_cache[i];
for (j = 0; j < intfc->num_altsetting; ++j) {
for (n = 0; n < intfc->num_altsetting; ++n) {
if (intfc->altsetting[n].desc.
bAlternateSetting == j)
break;
}
if (n >= intfc->num_altsetting)
dev_warn(ddev, "config %d interface %d has no "
"altsetting %d\n", cfgno, inums[i], j);
}
}
return 0;
}
usb_parse_interface()代码如下:
static int usb_parse_interface(struct device *ddev, int cfgno,
struct usb_host_config *config, unsigned char *buffer, int size,
u8 inums[], u8 nalts[])
{
unsigned char *buffer0 = buffer;
struct usb_interface_descriptor *d;
int inum, asnum;
struct usb_interface_cache *intfc;
struct usb_host_interface *alt;
int i, n;
int len, retval;
int num_ep, num_ep_orig;
d = (struct usb_interface_descriptor *) buffer;
buffer += d->bLength;
size -= d->bLength;
if (d->bLength < USB_DT_INTERFACE_SIZE)
goto skip_to_next_interface_descriptor;
/* Which interface entry is this? */
intfc = NULL;
inum = d->bInterfaceNumber;
//config->intf_cache保存着端点的相关信息
for (i = 0; i < config->desc.bNumInterfaces; ++i) {
if (inums[i] == inum) {
intfc = config->intf_cache[i];
break;
}
}
//保存的端口总数超过了最大值,非法
if (!intfc || intfc->num_altsetting >= nalts[i])
goto skip_to_next_interface_descriptor;
/* Check for duplicate altsetting entries */
//标识字段
asnum = d->bAlternateSetting;
//如果存在相同的.非法
for ((i = 0, alt = &intfc->altsetting[0]);
i < intfc->num_altsetting;
(++i, ++alt)) {
if (alt->desc.bAlternateSetting == asnum) {
dev_warn(ddev, "Duplicate descriptor for config %d "
"interface %d altsetting %d, skipping\n",
cfgno, inum, asnum);
goto skip_to_next_interface_descriptor;
}
}
//更新计数
++intfc->num_altsetting;
//如果合法的话,那alt就是指向一个空的接点描述符
memcpy(&alt->desc, d, USB_DT_INTERFACE_SIZE);
/* Skip over any Class Specific or Vendor Specific descriptors;
* find the first endpoint or interface descriptor */
//下一个endpoint descriptors的地址
alt->extra = buffer;
i = find_next_descriptor(buffer, size, USB_DT_ENDPOINT,
USB_DT_INTERFACE, &n);
//alt->extar+alt->extralen表示下一个描述符地址
alt->extralen = i;
if (n > 0)
dev_dbg(ddev, "skipped %d descriptor%s after %s\n",
n, plural(n), "interface");
//下个intreface desp的地址
buffer += i;
size -= i;
//接口中端点描述符的个数.
注意在这里将alt->desc.bNumEndpoints清0了
/* Allocate space for the right(?) number of endpoints */
num_ep = num_ep_orig = alt->desc.bNumEndpoints;
alt->desc.bNumEndpoints = 0; /* Use as a counter */
if (num_ep > USB_MAXENDPOINTS) {
dev_warn(ddev, "too many endpoints for config %d interface %d "
"altsetting %d: %d, using maximum allowed: %d\n",
cfgno, inum, asnum, num_ep, USB_MAXENDPOINTS);
num_ep = USB_MAXENDPOINTS;
}
if (num_ep > 0) {
/* Can't allocate 0 bytes */
len = sizeof(struct usb_host_endpoint) * num_ep;
alt->endpoint = kzalloc(len, GFP_KERNEL);
if (!alt->endpoint)
return -ENOMEM;
}
/* Parse all the endpoint descriptors */
n = 0;
while (size > 0) {
if (((struct usb_descriptor_header *) buffer)->bDescriptorType
== USB_DT_INTERFACE)
break;
retval = usb_parse_endpoint(ddev, cfgno, inum, asnum, alt,
num_ep, buffer, size);
if (retval < 0)
return retval;
++n;
buffer += retval;
size -= retval;
}
if (n != num_ep_orig)
dev_warn(ddev, "config %d interface %d altsetting %d has %d "
"endpoint descriptor%s, different from the interface "
"descriptor's value: %d\n",
cfgno, inum, asnum, n, plural(n), num_ep_orig);
return buffer - buffer0;
skip_to_next_interface_descriptor:
i = find_next_descriptor(buffer, size, USB_DT_INTERFACE,
USB_DT_INTERFACE, NULL);
return buffer - buffer0 + i;
}
usb_parse_endpoint()代码如下:
static int usb_parse_endpoint(struct device *ddev, int cfgno, int inum,
int asnum, struct usb_host_interface *ifp, int num_ep,
unsigned char *buffer, int size)
{
unsigned char *buffer0 = buffer;
struct usb_endpoint_descriptor *d;
struct usb_host_endpoint *endpoint;
int n, i, j;
d = (struct usb_endpoint_descriptor *) buffer;
buffer += d->bLength;
size -= d->bLength;
//判断长度是否合法
if (d->bLength >= USB_DT_ENDPOINT_AUDIO_SIZE)
n = USB_DT_ENDPOINT_AUDIO_SIZE;
else if (d->bLength >= USB_DT_ENDPOINT_SIZE)
n = USB_DT_ENDPOINT_SIZE;
else {
dev_warn(ddev, "config %d interface %d altsetting %d has an "
"invalid endpoint descriptor of length %d, skipping\n",
cfgno, inum, asnum, d->bLength);
goto skip_to_next_endpoint_or_interface_descriptor;
}
//取得端点的地址,也就是端口号
i = d->bEndpointAddress & ~USB_ENDPOINT_DIR_MASK;
//不可能会超16个端点,也不可能
if (i >= 16 || i == 0) {
dev_warn(ddev, "config %d interface %d altsetting %d has an "
"invalid endpoint with address 0x%X, skipping\n",
cfgno, inum, asnum, d->bEndpointAddress);
goto skip_to_next_endpoint_or_interface_descriptor;
}
/* Only store as many endpoints as we have room for */
//注意在前面调用函数中已经将ifp->desc.bNumEndpoints清0了,以后每处理
//一个端点描述符,都会将这个成员值+1
if (ifp->desc.bNumEndpoints >= num_ep)
goto skip_to_next_endpoint_or_interface_descriptor;
//保存端点描述符信息,并更新端点数目
endpoint = &ifp->endpoint[ifp->desc.bNumEndpoints];
++ifp->desc.bNumEndpoints;
memcpy(&endpoint->desc, d, n);
INIT_LIST_HEAD(&endpoint->urb_list);
/* Fix up bInterval values outside the legal range. Use 32 ms if no
* proper value can be guessed. */
i = 0; /* i = min, j = max, n = default */
j = 255;
//根据不同的传输类型,计算间隔时间
if (usb_endpoint_xfer_int(d)) {
i = 1;
switch (to_usb_device(ddev)->speed) {
case USB_SPEED_HIGH:
/* Many device manufacturers are using full-speed
* bInterval values in high-speed interrupt endpoint
* descriptors. Try to fix those and fall back to a
* 32 ms default value otherwise. */
n = fls(d->bInterval*8);
if (n == 0)
n = 9; /* 32 ms = 2^(9-1) uframes */
j = 16;
break;
default: /* USB_SPEED_FULL or _LOW */
/* For low-speed, 10 ms is the official minimum.
* But some "overclocked" devices might want faster
* polling so we'll allow it. */
n = 32;
break;
}
} else if (usb_endpoint_xfer_isoc(d)) {
i = 1;
j = 16;
switch (to_usb_device(ddev)->speed) {
case USB_SPEED_HIGH:
n = 9; /* 32 ms = 2^(9-1) uframes */
break;
default: /* USB_SPEED_FULL */
n = 6; /* 32 ms = 2^(6-1) frames */
break;
}
}
if (d->bInterval < i || d->bInterval > j) {
dev_warn(ddev, "config %d interface %d altsetting %d "
"endpoint 0x%X has an invalid bInterval %d, "
"changing to %d\n",
cfgno, inum, asnum,
d->bEndpointAddress, d->bInterval, n);
endpoint->desc.bInterval = n;
}
/* Some buggy low-speed devices have Bulk endpoints, which is
* explicitly forbidden by the USB spec. In an attempt to make
* them usable, we will try treating them as Interrupt endpoints.
*/
if (to_usb_device(ddev)->speed == USB_SPEED_LOW &&
usb_endpoint_xfer_bulk(d)) {
dev_warn(ddev, "config %d interface %d altsetting %d "
"endpoint 0x%X is Bulk; changing to Interrupt\n",
cfgno, inum, asnum, d->bEndpointAddress);
endpoint->desc.bmAttributes = USB_ENDPOINT_XFER_INT;
endpoint->desc.bInterval = 1;
if (le16_to_cpu(endpoint->desc.wMaxPacketSize) > 8)
endpoint->desc.wMaxPacketSize = cpu_to_le16(8);
}
/* Skip over any Class Specific or Vendor Specific descriptors;
* find the next endpoint or interface descriptor */
//同之前分析的一样,下一个描述符的有效地址和偏移
endpoint->extra = buffer;
i = find_next_descriptor(buffer, size, USB_DT_ENDPOINT,
USB_DT_INTERFACE, &n);
endpoint->extralen = i;
if (n > 0)
dev_dbg(ddev, "skipped %d descriptor%s after %s\n",
n, plural(n), "endpoint");
return buffer - buffer0 + i;
skip_to_next_endpoint_or_interface_descriptor:
i = find_next_descriptor(buffer, size, USB_DT_ENDPOINT,
USB_DT_INTERFACE, NULL);
return buffer - buffer0 + i;
}
到这里,root hub对应的配置,接口,端点信息都可以在usb_dev中找到了.UHCI的初始化工作就全部完成了.在之后的分析中,会经常涉及到具体的信息传输过 程.在前面的代码中遇到也一笔代过了.为了以后的分析方便,在下一节里,对每个类型的传输过程做一个全面的分析.