Cyclic dependencies in device tree

[benediktibk]

I just ran into an issue with a cyclic dependency in the device tree. Cause is a SPI port expander, which itself provides chip selects for the same bus:

&spi1 {
	cs-gpios = <&gpiod 0 GPIO_ACTIVE_LOW &port_expander 0 GPIO_ACTIVE_LOW>;
	
	port_expander: port_expander@0 {
		gpio-controller;
	};
	
	spi_adc: spi_adc@1 {
	};
};

Technically not an issue, but this represents a cyclic dependency in the devicetree graph. There are some comments in the python script which mention that this is forbidden and therefore the build fails. Just out of curiosity I disabled these checks and the build succeeded. In the end these checks only ensure that based upon the dependencies the device ordinal numbers are in the same order, as they are required by other devices (the __device_dts_ord_X stuff). But as there are sys init levels and priorities within the levels defined anyway, is this really necessary?