[PATCH 2/3] arm64: dts: sophgo: add initial Milk-V Duo S board support

[Inochi Amaoto]

On Sun, Oct 26, 2025 at 10:48:50PM +0000, Michael Opdenacker wrote:
> Hi Joshua
> 
> Thanks a lot for working on support for Milk-V Duo S. I'll be happy to test
> your V3 :)
> 
> On 10/26/25 22:35, Joshua Milas wrote:
> > Inochi,
> > 
> > Thanks for pointing me twards duo-pinmux. I was able to use it to get
> > the default config which is uart0, spi3, and i2c4. I can change the
> > dts to match, but...
> > 
> > > I suggest enabling devices that are accessed by default
> > Would we rather enable anything that can be accessed by the pinmux?
> 
> If I understand correctly, you can't do that because there will be
> conflicts.

> From the Duo S pinout diagram (https://milkv.io/duo-s/duos-pinout.webp), on
> headers 41 and 39, you have to choose between MIPI, I2C2, PWM12/13 or SD1.
> If at least 2 of these are selected at the same time, there will be a
> conflict, and I assume that the pinctrl controller driver will flag it.
> 

Yes, that's true. Boards with CV18XX always require setting pinctrl.

> Then it sounds complicated to define a default combination for the whole
> board, because it's like a default use model. Who gets to choose? What
> Inochi suggests is to follow the vendor kernel choice, which would
> correspond to the way the vendor intended the board to be used. However the
> community could choose another default way to use the board, so the choice
> may be up to the first contributor to the mainline kernel for this board,
> possibly revised through later discussions.
> 

In fact, I see the maintainers do not agree adding every possible
configuration to the DTS, (especially without "omit-if-unused" flag).
And in many case, it is impossible to add all possibility. As a
result, I prefer to use DTS overlay if there is something custom,
and keep the mainline DTS minimum.

> I guess there are cases when the choice is easy:
> 
> - When only one configuration is available for a set of pins
> - When there are important devices on I2C or SPI buses on the board. Then,
> you want to find a way to prioritize such buses. Fortunately, I guess the
> board design also guides you to the right choice.
> 

In fact the priority is the thing that is hard to decide. This is why
I suggesting keeping compatible with the vendor kernel, as many people
starts with vendor kernel and it is a good thing to refer.

>
> I was facing the the same question today on another board, and that's why
> I'm happy it's raised here. As thousands of DTS files have been written
> before, I'd love to hear from people with experience on this topic. Are
> guidelines written anywhere for board DTS creators?
> 
> Cheers
> Michael.
> 
> -- 
> Michael Opdenacker
> Root Commit
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>