@User I'm guessing that the GPIOs configured with all zeros or all ones doesn't give you a useful configuration?

All zeros would have both input and output digital buffers cut off and would be effectively high-impedence unless a project had connected an analog signal to that pad. All ones disables the output through OEB and disables the input through INP_DIS, so it's effectively the same thing. But the housekeeping SDO pin has its OEB driven by housekeeping, so if the housekeeping SPI (which is known to work) were to be set to a state where it is driving SDO, then a configuration of all 1s would be a weak-drive output and could be distinguished from the normal strong-drive output state.