Linux USB gadget设备驱动解析（4）--编写一个gadget驱动

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
        * [e-mail]
        * All rights reserved.*/
        /* #define VERBOSE_DEBUG */

#include <linux/kernel.h>
#include <linux/utsname.h>
#include <linux/device.h>
#include <linux/usb/ch9.h>
#include <linux/usb/gadget.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/usb/input.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/types.h> /* size_t */
#include <linux/errno.h> /* error codes */
#include <asm/system.h>
#include <asm/io.h>
#include <linux/sched.h>

#include "gadget_chips.h"
/*-------------------------------------------------------------------------*/
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);