Permission error while locking the device when writing to QSerialPort

Hi,
I'm working on a Qt5.7 application cross-compiled for my device. I added the serialport module to read and write to the serialport.
After opening the QSerialPort, when I try to write to it, the following error message (attached to the thread) appears in the GUI: "Permission error while locking the device", and the message is not sent to the serial port.
This is the way I open and try to write to the serial port:

Code:

---

serialport->setPortName("/dev/ttymxc2");
    serialport->setBaudRate(QSerialPort::Baud9600);
    serialport->setDataBits(QSerialPort::Data8);
    serialport->setParity(QSerialPort::NoParity);
    serialport->setStopBits(QSerialPort::OneStop);
    serialport->setFlowControl(QSerialPort::NoFlowControl);
    //serial->setFlowControl(QSerialPort::HardwareControl);
    if (serialport->open(QIODevice::ReadWrite))
        //opened

---

...

The write section:

Code:

---

QByteArray ba;
ba.resize(50);
...
 const qint64 bytesWritten = serialport->write(ba);

---

Could anyone help to find the solution? What am I missing?
Thank you!

Try in system console this command : ls /dev/tty*
Here is output from my system :

Code:

---

crw-rw-rw- 1 root tty     5,  0 06-01 22:06 /dev/tty
crw--w---- 1 root tty     4,  0 06-01 22:06 /dev/tty0
crw------- 1 root root    4,  1 06-01 22:08 /dev/tty1
crw--w---- 1 root tty     4, 10 06-01 22:06 /dev/tty10
crw--w---- 1 root tty     4, 11 06-01 22:06 /dev/tty11
crw--w---- 1 root tty     4, 12 06-01 22:06 /dev/tty12

---

As You see only root and tty group have permision to use tty devices.
A problem with system configuration not with application.