MPC52xx simple GPIO support

Hi
I still don't quite understand how to use the Flattened Device Tree /
Open Firmware. I see there's a driver (mpc52xx_gpt.c) that supports to
use the Pins on the GPT as simple GPIOs. I activated it by adding these
lines to my dts file:

gpt2: timer@620 {
	compatible = "fsl,mpc5200b-gpt-gpio","fsl,mpc5200-gpt-gpio";
	reg = <0x620 0x10>;
	interrupts = <1 11 0>;
	gpio-controller;
	#gpio-cells = <2>;
};

I can see the appropriate entries in sysfs
(/sys/devices/f0000000.soc5200/f0000620.timer), but how can I actually
use these GPIO's now?

Many thanks
Stefan.