[PATCH v3 1/3] dt-bindings: mfd: syscon: Disallow simple-bus with syscon

[Rob Herring (Arm)]

On Mon, 08 Jun 2026 22:44:24 +0200, Krzysztof Kozlowski wrote:
> "syscon" is a system controller with registers having their own
> functions, thus not really a trivial MMIO simple bus.  "simple-bus" on
> the other hand is just a bus on which multiple devices sit and the
> "simple" means no functions are allowed here.
> 
> Combination of both "syscon" and "simple-bus" is abuse of DT for easier
> instantiating of Linux device drivers so add a schema to disallow that.
> 
> Unfortunately there are a few old cases of that patterns, so add
> exceptions:
> 
> 1. "cznic,turris1x-cpld" and "img,pistachio-cr-periph" are already used
>    in upstream DTS.
> 
> 2. TI has several DTSI with a child of SCM device (e.g. "ti,am3-scm")
>    using "syscon" and "simple-bus" but without a dedicated compatible
>    documented anywhere.  Add new compatibles for such cases.
> 
> Additionally, add comments around code enforcing two or three
> compatibles: it is similar safeguard detecting incorrect bindings.
> 
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski at oss.qualcomm.com>
> 
> ---
> 
> Changes in v3:
> 1. s/ti,omap5-scm-conf/ti,omap5-sysc-padconf-global/ because it is more
>    appropriate (specific)
> 2. Add comments, why simple-mfd+syscon has dedicated if:then:
> 
> Changes in v2:
> 1. Complete patch. I accidentally sent only part of it, built on top of
>    internal WIP which I forgot to squash.
>    I received Ack from Rob, but change is significant, so please kindly
>    re-review.
> ---
>  .../devicetree/bindings/mfd/syscon-common.yaml     | 34 ++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 

Acked-by: Rob Herring (Arm) <robh at kernel.org>