reading pwm signal input parallel port

Good morning, do you know how I can read a pwm entry in linuxcnc? I have a bit input that will work with a variable frequency, I need some component that reads this frequency and transforms it to floating point, I didn't find anything like that in the manual, does anyone have an idea?

PWM probably not, frequency yes for sure, use encoder
linuxcnc.org/docs/2.9/html/man/man9/encoder.9.html