[Linux-stm32] [PATCH v5 1/2] dt-bindings: arm: stm32: Document st, stm32mp23/25-syscfg subnodes and cells

[Marek Vasut]

On 9/2/26 10:55 AM, Fabrice Gasnier wrote:

Hello Fabrice,

>> @@ -57,10 +68,17 @@ allOf:
>>     - if:
>>         properties:
>>           compatible:
>> -          const: st,stm32mp25-syscfg
>> +          contains:
>> +            enum:
>> +              - st,stm32mp23-syscfg
>> +              - st,stm32mp25-syscfg
>>       then:
>>         required:
>>           - "#clock-cells"
>> +        - "#address-cells"
>> +        - "#size-cells"
>> +        - phy at 2400
>> +        - phy at 2800
> 
> Hi Marek,
> 
> Is just saw the discussing on V4 with Conor. That's mainly a thought:
> I'm not sure USB is required, e.g. mandatory for a product, even if not
> so likely (I don't know if this could exist out there).

I assume you have two use cases in mind:
A) A wall-mount HMI device with only display/touchscreen (No USB plug)
B) A RPi form evaluation kit with all kinds of plugs (Yes USB plug)
?

> Still, the nodes
> could be tweaked (deleted) in a board, to reduce dtb size in such case.
> I'd relax, e.g. let these 4 props as optional. Do you see any drawback ?
> That can also be relaxed later, if the case is seen.
DT is a hardware description. The PHY IP is not removed from the chip 
silicon only because the USB signals are not used on that specific 
product. Therefore, for device type:

A) without USB plug - no action is necessary, the PHYs are already 
disabled by default in SoC DTSI
B) with USB plug - board DT sets status = "okay" on the PHYs and 
controllers.

As for reducing the DT size, removing DT nodes for hardware that is 
present in the silicon negatively impacts the ability to apply DTOs 
outside of the kernel build process, so I would argue against 
preemptively removing any DT nodes from DTs to reduce size.

One exception is U-Boot, which adds additional generic bootph-* 
properties to a subset of DT nodes which should be available early on, 
and also contains a mechanism which reduces DT size for its U-Boot SPL 
which operates in severely size constrained environment. However, this 
is a special case, where removal of nodes from the DT is justified, 
because in that case, it is certain that those nodes would not and could 
not be used, and would only waste time.

On the contrary, the DTs that are used to boot Linux should be complete, 
because the user might enable an IP in there by setting status = "okay" 
after reaching U-Boot shell, and before booting Linux.