default or selected kernelversion does not have config value CONFIG_RIO.
Result is shown for kernelversion 5.6.18

Specialix RIO system support

modulename: rio/ generic_serial.ko

configname: CONFIG_RIO

Linux Kernel Configuration
└─>Device Drivers
└─>Staging drivers
└─>Specialix RIO system support
In linux kernel since version 2.6.20 (release Date: 2007-02-04)  
This is a driver for the Specialix RIO, a smart serial card which
drives an outboard box that can support up to 128 ports. Product
information is at <>.
There are both ISA and PCI versions.

source code: