Re: Phandles

[Herve Codina <herve.codina@bootlin.com>]

Hi Krzysztof

On Mon, 13 Apr 2026 08:33:49 +0200
Krzysztof Kozlowski <krzk@kernel.org> wrote:

> On 12/04/2026 17:40, Herve Codina wrote:
> > Hi Kyle,
> > 
> > +Cc Kernel device-tree maintainers
> > 
> > On Sun, 12 Apr 2026 13:51:35 +0000
> > Kyle Bonnici <kylebonnici@hotmail.com> wrote:
> >   
> >>> On 12 Apr 2026, at 14:51, Herve Codina <herve.codina@bootlin.com> wrote:
> >>>
> >>> Hi Kyle,
> >>>
> >>> On Sat, 11 Apr 2026 18:33:33 +0000
> >>> Kyle Bonnici <kylebonnici@hotmail.com> wrote:
> >>>     
> >>>> Hi
> >>>>
> >>>> I have been looking at the the code for the compiler and I am wondering which specifications marks the below properties MUST BE Nexus Properties hence the validation.
> >>>>
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(clocks, "clocks", "#clock-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(cooling_device, "cooling-device", "#cooling-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(dmas, "dmas", "#dma-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(hwlocks, "hwlocks", "#hwlock-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(interrupts_extended, "interrupts-extended", "#interrupt-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(io_channels, "io-channels", "#io-channel-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(iommus, "iommus", "#iommu-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(mboxes, "mboxes", "#mbox-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(msi_parent, "msi-parent", "#msi-cells", true);
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(mux_controls, "mux-controls", "#mux-control-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(phys, "phys", "#phy-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(power_domains, "power-domains", "#power-domain-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(pwms, "pwms", "#pwm-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(resets, "resets", "#reset-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(sound_dai, "sound-dai", "#sound-dai-cells");
> >>>> WARNING_PROPERTY_PHANDLE_CELLS(thermal_sensors, "thermal-sensors", "#thermal-sensor-cells");    
> >>>
> >>> All of those properties are defined as phandles.
> >>>
> >>> For instance, the 'pwms' property available in a node means the the node is
> >>> a pwm consumer. It must follow the pwm consumer binding [1] and so a phandle
> >>> is involved.
> >>>
> >>> This phandle can have arguments and the number of argument is defined by the
> >>> #pwm-cells property set in the pwm provider node [2], [3].
> >>>
> >>> [1] https://elixir.bootlin.com/zephyr/v4.4.0-rc3/source/dts/bindings/pwm/pwm-controller.yaml
> >>> [2] https://github.com/zephyrproject-rtos/zephyr/blob/main/dts/bindings/pwm/pwm-controller.yaml
> >>> [3] https://elixir.bootlin.com/linux/v7.0-rc7/source/Documentation/devicetree/bindings/pwm/pwm.yaml
> >>>     
> >>>>
> >>>>
> >>>> These can be found here: https://github.com/dgibson/dtc/blob/main/checks.c#L1498 this is relevant for https://github.com/zephyrproject-rtos/zephyr/issues/107066    
> >>>
> >>> Examples provided in the zephyrproject issue link are, in my opinion, incorrect.
> >>>
> >>>  Case 1:
> >>>  / {
> >>>      node1 {
> >>>           pwms = <1 &pwm0 1 20 PWM_POLARITY_NORMAL>;
> >>>
> >>>           Here the first cell '1' is not a phandle.    
> >>
> >> Here the compiler is making an assumption here that all `pwms` properties must be specifier properties and all use `pwm` specifier.  
> > 
> > I think the purpose of 'select: true' is to have the binding always applied:
> >   https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/pwm/pwm-consumer.yaml#L15
> > 
> > If this is confirmed, DTC performs correct checks as this binding must always
> > be applied and so the 'pwms' property must be a phandle-array property.
> > 
> > Device-tree maintainers, can you confirm the purpose of 'select: true' set
> > in a DT binding ?  
> 
> The quoted parts were mentioning Zephyr. Here you mentioned DTC, but ask
> about "select: true", so dtschema. I don't get the context... dtschema
> has nothing to do with DTC and Zephyr.

I wanted be sure about checks done by DTC itself.

My feeling was that if a binding defined in dtschema has to be always applied
(i.e. select: true) it is a legit case to have DTC performing some checks
according to this binding.

Kyle seems to define the 'pwms' property to be something other than a phandle.
IMHO, this is wrong but the 'pwms' property is only defined in dtschema.

Best regards,
Hervé