Working with device tree cause the two question bothers me: How does the interrupt number relate to the physical interrupt from the device? How to know which interrupt number choose describing node in device tree? For example below is a node for gpio expander:
expander: max7325@6d {
compatible = "maxim,max7325";
reg = <0x6d>;
gpio-controller;
#gpio-cells = <2>;
interrupt-controller;
#interrupt-cells = <2>;
interrupt-parent = <&gpio4>;
interrupts = <29 IRQ_TYPE_EDGE_FALLING>;
};
How author knew that magic 29 interrupt number will be appropriate for this device?