Device tree for Atmel SAMA5D31

This isn't strictly a U-Boot issue but I am hoping that there are appropriately knowledgeable people here who will be able to help!

I am working on a Linux driver for an I2C RTC device and need to add the correct definitions into the device tree for the SAMA5D31 to be passed to the kernel at boot time. I have added:

i2c0: i2c at f0014000 {
        status = "okay";

        rv8523c3 at 68 {
                compatible = "mc,rv8523c3";
                reg = <0x68>;
        };
};

This sets up enough to allow the basic clock functions within the RTC to work correctly and the hwclock command within Busybox to work correctly. I need to add in the definitions for a GPIO (PE31) to be used as the alarm interrupt pin and can't get my head around the definitions needed within the device tree. I have tried adding the following

interrupt-parent = <&pioE>;
interrupts = <31>;

When the RTC driver is loaded by Linux the client->irq variable in the probe function doesn't contain a value > 0 and so doesn't setup an interrupt.

Any ideas on the correct definitions needed?

Thanks (and apologies for the noise),

Andy.