ok113i平台——qt+tslib支持usb触摸屏热插拔功能实现

问题：重新插拔设备，需要软件重启才能接收到触摸事件
愿因：是因为qt程序的tslib库的操作逻辑是在构造函数里面连接一次usb触摸设备，具体看如下文件内容：
/home/forlinx/OK113i-linux-sdk/buildroot/buildroot-201902/dl/qt5base/qtbase/src/platformsupport/input/tslib/qtslib.cpp；
所以重新插拔usb后，qt程序并没有重新连接usb触摸设备，导致没有触摸数据接收；
解决方案：
参考：https://blog.csdn.net/alone4together/article/details/115269753
参考方案中的代码需要更改一下，完整的qtslib.cpp更改内容如下：

QTsLibMouseHandler::QTsLibMouseHandler(const QString &key,
                                       const QString &specification,
                                       QObject *parent)
    : QObject(parent),
      m_notify(0), m_x(0), m_y(0), m_pressed(0), m_rawMode(false)
{
    m_dev=0;
    qCDebug(qLcTsLib) << "Initializing tslib plugin" << key << specification;
    setObjectName(QLatin1String("TSLib Mouse Handler"));
    ...
    ...
    else
    {
        qErrnoWarning(errno, "tslib: Cannot open input device %s", device.constData());
    }

    QFileSystemWatcher *m_fileWatcher = new QFileSystemWatcher(this);
    // QString dev_=device;
    m_fileWatcher->addPath(QLatin1String("/dev/input/")); // "dev/input/"
    connect(m_fileWatcher, &QFileSystemWatcher::directoryChanged, this, &QTsLibMouseHandler::handleHotPlugWatch);
}

void QTsLibMouseHandler::handleHotPlugWatch(const QString &path)
{
    QByteArray device = qgetenv("TSLIB_TSDEVICE");
    QFile file(QString::fromLocal8Bit(device)); // shoud be TSLIB_TSDEVICE
    qCDebug(qLcTsLib) << path << "is changing";
    if (file.exists())
    {
        qCDebug(qLcTsLib) << "tslib device disconnected .., try connecting ...";
        disconnect(m_notify, 0, 0, 0);
        if (m_notify){
            delete m_notify;
            m_notify = 0;
        }
        //  QByteArray device = qgetenv("TSLIB_TSDEVICE");
        m_dev = ts_open(device.constData(), 1);
        if (!m_dev)
        {
            qCDebug(qLcTsLib) << " touchscreen doesn't exist";
            qErrnoWarning(errno, "ts_open() failed");
        }
        else
        {
            if (ts_config(m_dev)){
                qErrnoWarning(errno, "ts_config() failed");
            }

            int fd = ts_fd(m_dev);
            if (fd >= 0)
            {
                qCDebug(qLcTsLib) << "tslib device is" << device;
                m_notify = new QSocketNotifier(fd, QSocketNotifier::Read, this);
                connect(m_notify, &QSocketNotifier::activated, this, &QTsLibMouseHandler::readMouseData);
            }
            else
            {
                qErrnoWarning(errno, "tslib: Cannot open input device %s", device.constData());
            }

            return;
        }
        qCDebug(qLcTsLib) << path << "is added";
    }
    else
    {
        if (m_dev){
            ts_close(m_dev);
            m_dev = 0;
        }
        qCDebug(qLcTsLib) << path << "is removed";
    }
}

改完qtslib.cpp需要编译buildroot，编译后的qtslib.cpp会在如下路径：
/home/OK113i-linux-sdk/out/t113_i/ok113i/longan/buildroot/build/qt5base-5.12.5/src/platformsupport/input/tslib/qtslib.cpp
需要注意单独编译的buildroot后，还需要全编译，才会将根文件系统镜像rootfs.ext2更新到系统镜像；