GPIO controllers and the DT

Every GPIO controller declared in the DT must have the Boolean property gpio-controller set. Some controllers provide IRQs mapped to the GPIO. In that case, the interrupt-cells property should be set too; usually you use2, but it depends on the need. The first cell is thepinnumber, and the second represents the interrupt flag.

gpio-cells should be set to identify how many cells are used to describe a GPIO specifier. You usually use <2>, the first cell to identify the GPIO number, and the second for flags. Actually, most non-memory mapped GPIO controllers do not use flags:

expander_1: mcp23016@27 { 
    compatible = "microchip,mcp23016"; 
    interrupt-controller; 
    gpio-controller; 
    #gpio-cells = <2>; 
    interrupt-parent = <&gpio6>; 
    interrupts = <31 IRQ_TYPE_LEVEL_LOW>; 
    reg = <0x27>; 
    #interrupt-cells=<2>; 
}; 

The preceding sample is the node of our GPIO-controller device, and the complete device driver...