Re: SoC-specific device tree aliases?

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hello Krzysztof,

On 11/17/25 5:29 PM, Krzysztof Kozlowski wrote:
> On 17/11/2025 17:06, Rob Herring wrote:
>>> So you want it to be an ABI for barebox, sure, just make it a binding.
>>
>> What do you have in mind? Other than standard names for the aliases,
>> what can we check here? That a specific alias points to a specific
>> path? That would be a bit too much IMO. That would be equivalent to
>> specifying possible values in 'reg' for all devices.
> 
> Binding with pattern or list of needed alias names, referenced by given
> soc-platform top-level schema.
> 
> One of the points is to make it explicit and obvious (e.g. to Arnd or to
> me if I forget, because I follow the same logic of aliases per board)
> that these aliases are used outside of kernel.
> 
> Just because ufs/mmc/spi can be used that way, does not mean we should
> accept any possible alias into soc.dtsi.

I can't see how this could work. A number of boards renumber MMC devices
in a different manner than the SoC reference manual:

- Changing the alias numbering is an ABI break, because Linux derives
its /dev/mmcblkX numbering from it

- Leaving them as-is means they are not usable for boot source determination

That's why I am suggesting a separate node that reflects only the SoC
reference manual's numbering. I don't see how a schema for the existing
/aliases would remove the need for this.

Thanks,
Ahmad

> 
> Best regards,
> Krzysztof
> 

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