Re: Phandles

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

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 ?

Best regards,
Hervé