作者：刘洪涛，华清远见嵌入式学院讲师。
一、编写计划
通过前面几节的基础，本节计划编写一个简单的gadget驱动。重在让大家快速了解gadget驱动结构。
上节中简单介绍了zero.c程序。这个程序考虑到了多配置、高速传输、USB OTG等因素。应该说写的比较清楚，是我们了解gadget驱动架构的一个非常好的途径。但把这些东西都放在一起，对很多初学人员来说还是不能快速理解。那就再把它简化一些，针对S3C2410平台，只实现一个配置、一个接口、一个端点，不考虑高速及OTG的情况。只完成单向从host端接收数据的功能，但要把字符设备驱动结合在里面。这需要有一个host端的驱动，来完成向device端发送数据。关于在主机端编写一个简单的USB设备驱动程序，有很多的资料。相信大家很快就会完成的。
二、功能展示
1、PC端编写了一个usbtransfer.ko，能够向device端发送数据
2、对目标平台编写一个gadget驱动，名称是g_zero.ko
3、测试步骤
在目标平台（基于S3C2410）上加载gadget驱动
# insmod g_zero.ko
name=ep1-bulk
smdk2410_udc: Pull-up enable
# mknod /dev/usb_rcv c 251 0
#
在PC主机上加载驱动usbtransfer.ko
#insmod usbtransfer.ko
#mknod /dev/usbtransfer c 266 0
连接设备，目标平台的终端显示：
connected
目标平台读取数据
# cat /dev/usb_rcv
PC端发送数据
#echo “12345” > /dev/usbtransfer
#echo “abcd” > /dev/usbtransfer
设备端会显示收到的数据
# cat /dev/usb_rcv
12345
abcd
三、代码分析
下面的代码是在原有的zero.c基础上做了精简、修改的。一些结构的名称还是保留以前的，但含义有所变化。如：loopback_config，不再表示loopback，而只是单向的接收数据。
/*
* zero.c -- Gadget Zero, for simple USB development
*
* All rights reserved.*/
/* #define VERBOSE_DEBUG */
#include
#include
#include
#include
#include
#include "gadget_chips.h"
#include
#include
#include
#include
#include
#include
#include
#include
#include /* size_t */
#include /* error codes */
#include
#include
#include /*-------------------------------------------------------------------------*/
static const char shortname[] = "zero";
static const char loopback[] = "loop input to output";
static const char longname[] = "Gadget Zero";
static const char source_sink[] = "source and sink data";
#define STRING_MANUFACTURER 25
#define STRING_PRODUCT 42
#define STRING_SERIAL 101
#define STRING_SOURCE_SINK 250
#define STRING_LOOPBACK 251
//#define DRIVER_VENDOR_NUM 0x0525 /* NetChip */
//#define DRIVER_PRODUCT_NUM 0xa4a0 /* Linux-USB "Gadget Zero" */
#define DRIVER_VENDOR_NUM 0x5345 /* NetChip */
#define DRIVER_PRODUCT_NUM 0x1234 /* Linux-USB "Gadget Zero" */
static int usb_zero_major = 251;
/*-------------------------------------------------------------------------*/
static const char *EP_OUT_NAME; /* sink */
/*-------------------------------------------------------------------------*/
/* big enough to hold our biggest descriptor */
#define USB_BUFSIZ 256
struct zero_dev { //zero设备结构
spinlock_t lock;
struct usb_gadget *gadget;
struct usb_request *req; /* for control responses */
struct usb_ep *out_ep;
struct cdev cdev;
unsigned char data[128];
unsigned int data_size;
wait_queue_head_t bulkrq;
};
#define CONFIG_LOOPBACK 2
static struct usb_device_descriptor device_desc = { //设备描述符
.bLength = sizeof device_desc,
.bDescriptorType = USB_DT_DEVICE,
.bcdUSB = __constant_cpu_to_le16(0x0110),
.bDeviceClass = USB_CLASS_VENDOR_SPEC,
.idVendor = __constant_cpu_to_le16(DRIVER_VENDOR_NUM),
.idProduct = __constant_cpu_to_le16(DRIVER_PRODUCT_NUM),
.iManufacturer = STRING_MANUFACTURER,
.iProduct = STRING_PRODUCT,
.iSerialNumber = STRING_SERIAL,
.bNumConfigurations = 1,
};
static struct usb_endpoint_descriptor fs_sink_desc = { //端点描述符
.bLength = USB_DT_ENDPOINT_SIZE,
.bDescriptorType = USB_DT_ENDPOINT,
.bEndpointAddress = USB_DIR_OUT, //对主机端来说，输出
.bmAttributes = USB_ENDPOINT_XFER_BULK,
};
static struct usb_config_descriptor loopback_config = { //配置描述符
.bLength = sizeof loopback_config,
.bDescriptorType = USB_DT_CONFIG,
/* compute wTotalLength on the fly */
.bNumInterfaces = 1,
.bConfigurationValue = CONFIG_LOOPBACK,
.iConfiguration = STRING_LOOPBACK,
.bmAttributes = USB_CONFIG_ATT_ONE | USB_CONFIG_ATT_SELFPOWER,
.bMaxPower = 1, /* self-powered */
};
static const struct usb_interface_descriptor loopback_intf = { //接口描述符
.bLength = sizeof loopback_intf,
.bDescriptorType = USB_DT_INTERFACE,
.bNumEndpoints = 1,
.bInterfaceClass = USB_CLASS_VENDOR_SPEC,
.iInterface = STRING_LOOPBACK,
};
/* static strings, in UTF-8 */
#define STRING_MANUFACTURER 25
#define STRING_PRODUCT 42
#define STRING_SERIAL 101
#define STRING_SOURCE_SINK 250
#define STRING_LOOPBACK 251
static char manufacturer[50];
/* default serial number takes at least two packets */
static char serial[] = "0123456789.0123456789.0123456789";
static struct usb_string strings[] = { //字符串描述符
{ STRING_MANUFACTURER, manufacturer, },
{ STRING_PRODUCT, longname, },
{ STRING_SERIAL, serial, },
{ STRING_LOOPBACK, loopback, },
{ STRING_SOURCE_SINK, source_sink, },
{ } /* end of list */
};
static struct usb_gadget_strings stringtab = {
.language = 0x0409, /* en-us */
.strings = strings,
};
static const struct usb_descriptor_header *fs_loopback_function[] = {
(struct usb_descriptor_header *) &loopback_intf,
(struct usb_descriptor_header *) &fs_sink_desc,
NULL,
};
static int
usb_zero_open (struct inode *inode, struct file *file) //打开设备
{
struct zero_dev *dev =
container_of (inode->i_cdev, struct zero_dev, cdev);
file->private_data = dev;
init_waitqueue_head (&dev->bulkrq);
return 0;
}
static int
usb_zero_release (struct inode *inode, struct file *file) //关闭设备
{
return 0;
}
static void free_ep_req(struct usb_ep *ep, struct usb_request *req)
{
kfree(req->buf);
usb_ep_free_request(ep, req);
}
static struct usb_request *alloc_ep_req(struct usb_ep *ep, unsigned length)//分配请求
{
struct usb_request *req;
req = usb_ep_alloc_request(ep, GFP_ATOMIC);
if (req) {
req->length = length;
req->buf = kmalloc(length, GFP_ATOMIC);
if (!req->buf) {
usb_ep_free_request(ep, req);
req = NULL;
}
}
return req;
}
static void source_sink_complete(struct usb_ep *ep, struct usb_request *req)//请求完成函数
{
struct zero_dev *dev = ep->driver_data;
int status = req->status;
switch (status) {
case 0: /* normal completion */
if (ep == dev->out_ep) {
memcpy(dev->data, req->buf, req-> actual);//返回数据拷贝到req->buf中， //dev->data_size=req->length;
dev->data_size=req->actual; //实际长度为req-> actual；需要确认
req –>short_not_ok为0。参考gadget.h中关于usb_request结构的注释
}
break;
/* this endpoint is normally active while we're configured */
case -ECONNABORTED: /* hardware forced ep reset */
case -ECONNRESET: /* request dequeued */
case -ESHUTDOWN: /* disconnect from host */
printk("%s gone (%d), %d/%d\n", ep->name, status,
req->actual, req->length);
case -EOVERFLOW: /* buffer overrun on read means that
* we didn't provide a big enough
* buffer.
*/
default:
#if 1
printk("%s complete --> %d, %d/%d\n", ep->name,
status, req->actual, req->length);
#endif
case -EREMOTEIO: /* short read */
break;
}
free_ep_req(ep, req);
wake_up_interruptible (&dev->bulkrq); //唤醒读函数
}
static struct usb_request *source_sink_start_ep(struct usb_ep *ep)//构造并发送读请求
{
struct usb_request *req;
int status;
//printk("in %s\n",__FUNCTION__);
req = alloc_ep_req(ep, 128);
if (!req)
return NULL;
memset(req->buf, 0, req->length);
req->complete = source_sink_complete; //请求完成函数
status = usb_ep_queue(ep, req, GFP_ATOMIC); //递交请求
if (status) {
struct zero_dev *dev = ep->driver_data;
printk("start %s --> %d\n", ep->name, status);
free_ep_req(ep, req);
req = NULL;
}
return req;
}
ssize_t
usb_zero_read (struct file * file, const char __user * buf, size_t count,loff_t * f_pos) //读设备
{
struct zero_dev *dev =file->private_data;
struct usb_request *req;
int status;
struct usb_ep *ep;
struct usb_gadget *gadget = dev->gadget;
ssize_t ret = 0;
int result;
ep=dev->out_ep;
source_sink_start_ep(ep);//构造、递交读请求
if (count < 0)
return -EINVAL;
interruptible_sleep_on (&dev->bulkrq);//睡眠，等到请求完成
if (copy_to_user (buf,dev->data,dev->data_size)) //拷贝读取的数据到用户空间
{
ret = -EFAULT;
}
else
{
ret = dev->data_size;
}
return ret;
}
struct file_operations usb_zero_fops = {
.owner = THIS_MODULE,
.read = usb_zero_read,
.open = usb_zero_open,
.release = usb_zero_release,
};
static void
usb_zero_setup_cdev (struct zero_dev *dev, int minor)//注册字符设备驱动
{
int err, devno = MKDEV (usb_zero_major, minor);
cdev_init(&dev->cdev, &usb_zero_fops);
dev->cdev.owner = THIS_MODULE;
err = cdev_add (&dev->cdev, devno, 1);
if (err)
printk ("Error adding usb_rcv\n");
}
static void zero_setup_complete(struct usb_ep *ep, struct usb_request *req)//配置端点0的请求
完成处理
{
if (req->status || req->actual != req->length)
printk("setup complete --> %d, %d/%d\n",
req->status, req->actual, req->length);
}
static void zero_reset_config(struct zero_dev *dev) //复位配置
{
usb_ep_disable(dev->out_ep);
dev->out_ep = NULL;
}
static void zero_disconnect(struct usb_gadget *gadget)//卸载驱动时被调用，做一些注销工作
{
struct zero_dev *dev = get_gadget_data(gadget);
unsigned long flags;
unregister_chrdev_region (MKDEV (usb_zero_major, 0), 1);
cdev_del (&(dev->cdev));
zero_reset_config(dev);
printk("in %s\n",__FUNCTION__);
}
static int config_buf(struct usb_gadget *gadget,
u8 *buf, u8 type, unsigned index)
{
//int is_source_sink;
int len;
const struct usb_descriptor_header **function;
int hs = 0;
function =fs_loopback_function;//根据fs_loopback_function，得到长度，
//此处len=配置（9）+1个接口（9）+1个端点（7）=25
len = usb_gadget_config_buf(&loopback_config,
buf, USB_BUFSIZ, function);
if (len < 0)
return len;
((struct usb_config_descriptor *) buf)->bDescriptorType = type;
return len;
}
static int set_loopback_config(struct zero_dev *dev)
{
int result = 0;
struct usb_ep *ep;
struct usb_gadget *gadget = dev->gadget;
ep=dev->out_ep;
const struct usb_endpoint_descriptor *d;
d = &fs_sink_desc;
result = usb_ep_enable(ep, d); //激活端点
//printk("");
if (result == 0) {
printk("connected\n"); //如果成功，打印“connected”
}
else
printk("can't enable %s, result %d\n", ep->name, result);
return result;
}
static int zero_set_config(struct zero_dev *dev, unsigned number)
{
int result = 0;
struct usb_gadget *gadget = dev->gadget;
result = set_loopback_config(dev);//激活设备
if (result)
zero_reset_config(dev); //复位设备
else {
char *speed;
switch (gadget->speed) {
case USB_SPEED_LOW: speed = "low"; break;
case USB_SPEED_FULL: speed = "full"; break;
case USB_SPEED_HIGH: speed = "high"; break;
default: speed = " "; break;
}
}
return result;
}
/***
zero_setup完成USB设置阶段和具体功能相关的交互部分
***/
static int
zero_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
{
struct zero_dev *dev = get_gadget_data(gadget);
struct usb_request *req = dev->req;
int value = -EOPNOTSUPP;
u16 w_index = le16_to_cpu(ctrl->wIndex);
u16 w_value = le16_to_cpu(ctrl->wValue);
u16 w_length = le16_to_cpu(ctrl->wLength);
/* usually this stores reply data in the pre-allocated ep0 buffer,
* but config change events will reconfigure hardware.
*/
req->zero = 0;
switch (ctrl->bRequest) {
case USB_REQ_GET_DESCRIPTOR: //获取描述符
if (ctrl->bRequestType != USB_DIR_IN)
goto unknown;
switch (w_value >> 8) {
case USB_DT_DEVICE: //获取设备描述符
value = min(w_length, (u16) sizeof device_desc);
memcpy(req->buf, &device_desc, value);
break;
case USB_DT_CONFIG: //获取配置，注意：会根据fs_loopback_function读取到接口、端点描述符，注意通过config_buf完成读取数据及数量的统计。
value = config_buf(gadget, req->buf,
w_value >> 8,
w_value & 0xff);
if (value >= 0)
value = min(w_length, (u16) value);
break;
case USB_DT_STRING:
value = usb_gadget_get_string(&stringtab,
w_value & 0xff, req->buf);
if (value >= 0)
value = min(w_length, (u16) value);
break;
}
break;
case USB_REQ_SET_CONFIGURATION:
if (ctrl->bRequestType != 0)
goto unknown;
spin_lock(&dev->lock);
value = zero_set_config(dev, w_value);//激活相应的端点
spin_unlock(&dev->lock);
break;
default:
unknown:
printk(
"unknown control req%02x.%02x v%04x i%04x l%d\n",
ctrl->bRequestType, ctrl->bRequest,
w_value, w_index, w_length);
}
/* respond with data transfer before status phase */
if (value >= 0) {
req->length = value;
req->zero = value < w_length;
value = usb_ep_queue(gadget->ep0, req, GFP_ATOMIC);//通过端点0完成setup
if (value < 0) {
printk("ep_queue --> %d\n", value);
req->status = 0;
zero_setup_complete(gadget->ep0, req);
}
}
/* device either stalls (value < 0) or reports success */
return value;
}
static void zero_unbind(struct usb_gadget *gadget) //解除绑定
{
struct zero_dev *dev = get_gadget_data(gadget);
printk("unbind\n");
unregister_chrdev_region (MKDEV (usb_zero_major, 0), 1);
cdev_del (&(dev->cdev));
/* we've already been disconnected ... no i/o is active */
if (dev->req) {
dev->req->length = USB_BUFSIZ;
free_ep_req(gadget->ep0, dev->req);
}
kfree(dev);
set_gadget_data(gadget, NULL);
}
static int __init zero_bind(struct usb_gadget *gadget) //绑定过程
{
struct zero_dev *dev;
struct usb_ep *ep;
int gcnum;
usb_ep_autoconfig_reset(gadget);
ep = usb_ep_autoconfig(gadget, &fs_sink_desc);//根据端点描述符及控制器端点情况，分配一个合适的端点。
if (!ep)
goto enomem;
EP_OUT_NAME = ep->name; //记录名称
gcnum = usb_gadget_controller_number(gadget);//获得控制器代号
if (gcnum >= 0)
device_desc.bcdDevice = cpu_to_le16(0x0200 + gcnum);//赋值设备描述符
else {
pr_warning("%s: controller '%s' not recognized\n",
shortname, gadget->name);
device_desc.bcdDevice = __constant_cpu_to_le16(0x9999);
}
dev = kzalloc(sizeof(*dev), GFP_KERNEL); //分配设备结构体
if (!dev)
return -ENOMEM;
spin_lock_init(&dev->lock);
dev->gadget = gadget;
set_gadget_data(gadget, dev);
dev->req = usb_ep_alloc_request(gadget->ep0, GFP_KERNEL);//分配一个请求
if (!dev->req)
goto enomem;
dev->req->buf = kmalloc(USB_BUFSIZ, GFP_KERNEL);
if (!dev->req->buf)
goto enomem;
dev->req->complete = zero_setup_complete;
dev->out_ep=ep; //记录端点（就是接收host端数据的端点）
printk("name=%s\n",dev->out_ep->name); //打印出这个端点的名称
ep->driver_data=dev;
device_desc.bMaxPacketSize0 = gadget->ep0->maxpacket;
usb_gadget_set_selfpowered(gadget);
gadget->ep0->driver_data = dev;
snprintf(manufacturer, sizeof manufacturer, "%s %s with %s",
init_utsname()->sysname, init_utsname()->release,
gadget->name);
/**************************字符设备注册*******************/
dev_t usb_zero_dev = MKDEV (usb_zero_major, 0);
int result = register_chrdev_region (usb_zero_dev, 1, "usb_zero");
if (result < 0)
{
printk (KERN_NOTICE "Unable to get usb_transfer region, error %d\n",result);
return 0;
}
usb_zero_setup_cdev (dev, 0);
return 0;
enomem:
zero_unbind(gadget);
return -ENOMEM;
}
/*-------------------------------------------------------------------------*/
static struct usb_gadget_driver zero_driver = { //gadget驱动的核心数据结构
#ifdef CONFIG_USB_GADGET_DUALSPEED
.speed = USB_SPEED_HIGH,
#else
.speed = USB_SPEED_FULL,
#endif
.function = (char *) longname,
.bind = zero_bind,
.unbind = __exit_p(zero_unbind),
.setup = zero_setup,
.disconnect = zero_disconnect,
//.suspend = zero_suspend, //不考虑电源管理的功能
//.resume = zero_resume,
.driver = {
.name = (char *) shortname,
.owner = THIS_MODULE,
},
};
MODULE_AUTHOR("David Brownell");
MODULE_LICENSE("GPL");
static int __init init(void)
{
return usb_gadget_register_driver(&zero_driver); //注册驱动，调用bind绑定到控制器
}
module_init(init);
static void __exit cleanup(void)
{
usb_gadget_unregister_driver(&zero_driver); //注销驱动，通常会调用到unbind解除绑定， //在s3c2410_udc.c中调用的是disconnect方法
}
module_exit(cleanup);
三、总结
时间关系，上面的代码没有做太多的优化，但功能都是测试通过。希望能给大家的学习提供一点帮助。最后想谈谈学习USB驱动的一些方法。
USB驱动比较难掌握，主要原因是：
复杂的USB协议，包括USB基本协议、类规范等
控制器包括主机端、设备端。控制器本身相对复杂，其对应的主、从控制器驱动比较复杂
Hub功能及驱动、管理程序比较复杂
需要专业的硬件测试工具，硬件信号调试较困难
主、从端上层驱动程序本身不难，但由于对硬件不理解，及不好编写测试程序。所以往往望而却步。 我觉得学习USB驱动前应该有一个比较好的思路，个人建议可以按下面的过程学习
熟悉USB协议。不用看完所有的协议，重点关注一些概念、配置过程及数据包格式
