# /etc/udev/rules.d/97-gpio.rules
SUBSYSTEM=="gpio*", PROGRAM="/bin/sh -c '\
     chown -R root:gpio /sys/class/gpio && chmod -R 0770 /sys/class/gpio &&\
     chown -R root:gpio /sys/devices/platform/soc && chmod -R 0770 /sys/devices/platform/soc'"