The first thing one needs to do is be sure the firmware is loaded.
The firmware can be extracted from the Drivers folder on the CD shipped with the HVR-1950 using the script found at http://www.isely.net/downloads/fwextract.pl. The firmware gets placed in the /lib/firmware directory. There are four files v4l-cx2341x-enc.fw
v4l-pvrusb2-29xxx-01.fw
v4l-cx25840.fw
v4l-pvrusb2-73xxx-01.fw
More info can be found at http://www.isely.net/pvrusb2/pvrusb2.html