I did a bit of quick research and found out a couple of things. The cp210x driver seems to not be able to handle TIOCGSERIAL and TIOCSSERIAL ioctl wich happens to be used by all serial communication programs that I have on RPi, to set the non standard baud rate. I have an older version of pyserial on the RPi and it also uses the same ioctl to set the baud rate. pyserial on my VM with ubuntu that I've used to communicate with WMR89 uses other ioctl that seems to be supported by the driver.
This is ofcourse a bit of guessing so I'll try to make it work somehow, either by trying with a newer version of pyserial on the RPi or trying to fix the driver. I've found this patched driver which might work https://github.com/GBert/misc/blob/master/cp2102-dcc/src/cp210x.c but it would be nicer if it worked with a new pyserial and not mess around with the device driver.
