QSerialPort::waitForReadyRead always returns false

QSerialPort::waitForReadyRead always returns false even if bytes are available to be read.

Additional weird fact is that if you call QIODevice::readAll to retrieve the bytes you get nothing, while if you call QSerialPort::waitForReadyRead ignoring the return code followed by QIODevice::readAll you actually get the bytes.

To clarify, the following code DOES NOT WORK because execution never enters the block

if (m_serialPort->waitForReadyRead(TOUT_MS))

{

    buff.append(m_serialPort->readAll());

}

The following code DOES NOT WORK as well

buff.append(m_serialPort->readAll());

To make things work you have to do

m_serialPort->waitForReadyRead(TOUT_MS))

buff.append(m_serialPort->readAll());

 It seems that calling waitForReadyRead triggers some mechanism that make things work.