Caveats: haven't bought any hardware yet, just reading documentation. Please provide pointers/correction as needed.
Linux (kernel >2.6.3x) has a direct "driver" level gpio service /linux/gpio.h, /linux/drivers/gpio/gpiolib.c, etc) which seems fairly easy to use. Does anyone know if the Olimex images come with the full kernel source trees?
For those of you looking for RK3188 GPIO information similar to Dr. Guido Pelz's awesome "GPIO on the Olimex A20" pdf (A20-GPIO.pdf), Section 6.5.1->6.6 of the Olimex RK3188-SOM-UM has the Pin#-Signal_Name-Processor_Pin mappings.