In doing a super quick scan of Device::SerialPort, I didn't see documentation on those methods. Since the module is described as "Linux/POSIX emulation of Win32::SerialPort functions", I did a super quick scan of Win32::SerialPort, but again didn't find much. Perhaps my super quick scans were too fast and I overlooked the information.

If you're ok with adding a layer of abstraction, you could check out Control::CLI, which will use Win32::SerialPort or Device::SerialPort for serial port communication. It's read and readwait methods are definitely documented.

I'm not necessarily advocating using Control::CLI over directly using Device::SerialPort. Just tossing out a suggestion on another module that you might find easier to use in your code.