For all the claims that the hardware is made for Linux, the system I looked at and the two I own do not have detailed information on how to program the register

For all the claims that the hardware is made for Linux, the system I looked at and the two I own do not have detailed information on how to program the registers in some of the hardware. I do not know if it is the chip makers or the system makers but the systems are not 100% open if you want to bit bang all the hardware.