USB HUB 中的 Linux C++ LibUSB 写寄存器

Question

在 Linux 中，我有一个带有“寄存器”的 USB 集线器，如下图所示。该寄存器应该禁用集线器上某个端口的电源。

我尝试使用 LibUSB（我的代码如下所示）写入寄存器 0x​​0A，使用全零禁用所有端口。问题是，集线器由标准 Linux USB 集线器驱动程序控制，因此内核驱动程序被分离。写入也失败。失败消息如下所示。

错误信息：

$ /mnt/apps/UsbPowerControl
5 Devices in list.
Vendor:Device = 1908:1320
Vendor:Device = 0403:6001
Vendor:Device = 289d:0010
Vendor:Device = 0424:2513
Vendor:Device = 1d6b:0002
Opening Device = 0424:2513
Device Opened
Kernel Driver Active
Kernel Driver Detached!
Claimed Interface
Data-><-
Writing Data...
libusb: error [submit_bulk_transfer] submiturb failed error -1 errno=2
Write Error
Released Interface

如何使用 LibUSB 写入此集线器寄存器，动态禁用和启用端口，而无需取消注册 Linux 驱动程序并导致我的写入失败？

#include <iostream>
#include <cassert>
#include <libusb-1.0/libusb.h>

using namespace std;

#define VENDOR_ID 0x0424
#define PRODUCT_ID 0x2513

int main() {

    libusb_device **devs; //pointer to pointer of device, used to retrieve a list of devices
    libusb_device_handle *dev_handle; //a device handle
    libusb_context *ctx = NULL; //a libusb session
    int r; //for return values
    ssize_t cnt; //holding number of devices in list
    r = libusb_init(&ctx); //initialize the library for the session we just declared
    if(r < 0) {
        cout<<"Init Error "<<r<<endl; //there was an error
        return 1;
    }
    libusb_set_debug(ctx, 3); //set verbosity level to 3, as suggested in the documentation

    cnt = libusb_get_device_list(ctx, &devs); //get the list of devices
    if(cnt < 0) {
        cout<<"Get Device Error"<<endl; //there was an error
        return 1;
    }
    cout<<cnt<<" Devices in list."<<endl;

    for (size_t idx = 0; idx < cnt; ++idx) {
        libusb_device *device = devs[idx];
        libusb_device_descriptor desc = {0};

        int rc = libusb_get_device_descriptor(device, &desc);
        assert(rc == 0);

        printf("Vendor:Device = %04x:%04x\n", desc.idVendor, desc.idProduct);
    }

    printf("Opening Device = %04x:%04x\n", VENDOR_ID, PRODUCT_ID);

    dev_handle = libusb_open_device_with_vid_pid(ctx, VENDOR_ID, PRODUCT_ID); //these are vendorID and productID I found for my usb device
    if(dev_handle == NULL)
        cout<<"Cannot open device"<<endl;
    else
        cout<<"Device Opened"<<endl;
    libusb_free_device_list(devs, 1); //free the list, unref the devices in it

    unsigned char *data = new unsigned char[1]; //data to write
    data[0]=0b00000000;

    int actual; //used to find out how many bytes were written
    if(libusb_kernel_driver_active(dev_handle, 0) == 1) { //find out if kernel driver is attached
        cout<<"Kernel Driver Active"<<endl;
        if(libusb_detach_kernel_driver(dev_handle, 0) == 0) //detach it
            cout<<"Kernel Driver Detached!"<<endl;
    }
    r = libusb_claim_interface(dev_handle, 0); //claim interface 0 (the first) of device (mine had jsut 1)
    if(r < 0) {
        cout<<"Cannot Claim Interface"<<endl;
        return 1;
    }
    cout<<"Claimed Interface"<<endl;
    cout<<"Data->"<<data<<"<-"<<endl; //just to see the data we want to write : abcd
    cout<<"Writing Data..."<<endl;
    r = libusb_bulk_transfer(dev_handle, (0x0A | LIBUSB_ENDPOINT_OUT), data, 1, &actual, 0); //my device's out endpoint was 2, found with trial- the device had 2 endpoints: 2 and 129
    if(r == 0 && actual == 1) //we wrote the 1 bytes successfully
        cout<<"Writing Successful!"<<endl;
    else
        cout<<"Write Error"<<endl;

    r = libusb_release_interface(dev_handle, 0); //release the claimed interface
    if(r!=0) {
        cout<<"Cannot Release Interface"<<endl;
        return 1;
    }
    cout<<"Released Interface"<<endl;

    libusb_close(dev_handle); //close the device we opened
    libusb_exit(ctx); //needs to be called to end the

    delete[] data; //delete the allocated memory for data
    return 0;

}

Answer 1

int libusb_detach_kernel_driver (   libusb_device_handle *  dev,
int     interface_number 
)   
...
If successful, you will then be able to claim the interface and perform I/O.
...



int libusb_kernel_driver_active (   libusb_device_handle *  dev,
int     interface_number 
)   
...
If a kernel driver is active, you cannot claim the interface, and libusb will be unable to perform I/O.
...

由于上面写的内容，“如何在不分离驱动程序的情况下进行 I/O”这个问题的简短回答是“你不能”。

为什么写入失败？这是另一回事。我建议调查一些事情：

1. 查看从 libusb_bulk_transfer 返回的值，也许它会让您了解正在发生的事情。
2. 听起来很愚蠢，但我总是先检查一下：进程权限。

另外，我可以建议另一种解决方案，即 sysfs。

我假设your device(am I right?) 支持 EEPROM 和 SMBus 访问。这意味着这种支持应该体现在 /sys/bus/i2c/devices/[some_device_id]/eeprom 周围的内核中（可能是另一个设备号，另一个目录位置等，因为它是所有驱动程序相关），但如果它可以像任何其他文件一样被找到和读取（这很可能，除非设备有问题），那么它可能也应该能够写入它。如果读取成功，那么我建议将找到的文件的 hexdump -C 与数据表进行比较，如果数据看起来合法，请尝试直接写入您的寄存器（文件偏移量）。

无论如何，访问字符设备文件和sysfs文件是linux中访问驱动程序数据的一般方式。可能你甚至不需要使用 libusb 的 API 来写那个单字节。