On Wed, Dec 18, 2024 at 09:50:27AM -0600, Rob Herring wrote: > On Tue, Dec 17, 2024 at 8:01 PM Brad Griffis <bgriffis@xxxxxxxxxx> wrote: > > > > > 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. > > Yes. That is the only case that really cares and needs it. We used to > warn on all interrupt-controller nodes if #address-cells was missing. > But that turns out to be way too many cases to fix, so we dropped that > part. > > > 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. > > unit-address being 0 and #address-cells being 0 are 2 different > things. It's poorly phrased, but I think that was meaning to say that if the unit address is not needed then #address-cells must be explicitlyzero, which makes sense. > > > 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. > > Relying on defaults is not good practice and deprecated for longer > than we've had DT support on Arm. The default for the kernel on PPC is > 1 which doesn't agree with dtc nor OpenFirmware. The kernel walking up > all parents to find #address-cells/#size-cells is not behavior defined > in any spec either. Yes, although I believe that behaviour is *very* old, and copied from / made to work with old Apple Open Firmwares. > 6.13 now warns if parent nodes or defaults are used, but not in the > case of interrupt parsing. > > > > 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. > > I'm more inclined to change the spec if needed. We only need > #address-cells if we have interrupt-map, so that's all we should > check. > > If a given binding wants to be stricter, we can do that in its schema. > > Rob > -- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson
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