I wrote a kernel module to demonstrate the problems I am having with the Venus chipset. The module writes a value to the interrupt enable register (IER) on one's modem. It then immediately reads the value stored in the IER. Reading a value from the IER that does not equal the value written to it seems to represent a bug in the chipset. Theodore Ts'o's serial driver makes extensive use of a modem's IER when it performs detection operations; thus detecting a Venus-based modem often fails.
To try this test on your own machine, download the kernel module and read the directions included in the source file.