Re: Device tree overlays

[Jason Thorpe <thorpej%me.com@localhost>]

> On Jan 10, 2024, at 1:36 PM, Lloyd Parkes <lloyd%must-have-coffee.gen.nz@localhost> wrote:
> 
> Kia ora Jason,
> 
> On Wed, 2024-01-10 at 09:42 -0800, Jason Thorpe wrote:
>> 
>> 
>> If you have documentation on the hardware, I would encourage writing
>> the overlays from scratch, using the conventions documented in the
>> FDT bindings.  That’s what I do.
> 
> I was helping Brook with this and I am aware that I cannot write
> overlays from scratch. The lack of documentation on how to do this is
> main problem, compounded by the fact that the multiple alternate
> syntaxes makes my head spin.

The main thing is the *bindings*.  There are different bindings for different SoCs and device and bus types.

> Searching the web for some of the syntax I saw in your source code lead
> me to a pretty useful web page, so I'm slightly less confused now than
> I was first thing today. I'm still expecting to need to decompile a few
> examples to see how the variant syntaxes translate to one another
> though.

https://www.devicetree.org/ is a great place to start for the basic theory, how references work, etc., and you can find the bindings here:

https://github.com/devicetree-org/devicetree-source/tree/master/Bindings

-- thorpej