@TDK,
The exact effect of GPIO clock is not very clear from the documentation. I've seen hinted somewhere (in relationship to power consumption reduction), that you need it only to access the registers (which implies also that you need it to be able to read pins set as Input and change state of those set as Output), but once those are set e.g. to AF, you can switch the GPIO clock off - the muxes are set and the peripherals to which signals are connected use their own clock to sample or drive the signals.
JW
