Re: [PATCH] checks: Warn about missing #address-cells for interrupt parents

> From: Thierry Reding <[email protected]>
> 
> 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.