From: Thierry Reding <treding@xxxxxxxxxx> The device tree specification (v0.4) suggests that #address-cells is mandatory for interrupt parent nodes. If this property is missing, Linux will default to the value of 0.
Just to clarify, this relates to interrupt-map specifically. In that scenario the device tree spec requires that both the child node and parent node specify #address-cells and #interrupt-cells. It further specifies if a unit address component is not needed then it must be explicitly defined as zero. In other words, this does not seem to be just a suggestion, but more of a firm requirement.
A number of device tree files rely on Linux' fallback and don't specify an explicit #address-cells as suggested by the specification. This can cause issues when these device trees are passed to software with a more pedantic interpretation of the DT spec.
The device tree spec also says that in the case where #address-cells is not specified that a value of 2 should be assumed. So in this context, I find the kernel's current practice of assuming #address-cells = <0> also violates the spec.
Add a warning when this case is detected so that device tree files can be fixed.
I think a warning is reasonable, but perhaps we should consider making it an outright error. Though given the number of impacted device trees, perhaps that needs to be done in a couple of steps.
