Re: [PATCH v1 1/2] dt-bindings: trivial-devices: add toradex,lava-hat-spi

[Francesco Dolcini <francesco@dolcini.it>]

On Tue, Apr 21, 2026 at 12:05:45PM +0200, Krzysztof Kozlowski wrote:
> On 21/04/2026 11:59, Francesco Dolcini wrote:
> > 
> >> Toradex LAVA hat is way too generic. No, single compatible string is not
> >> sufficient, please read writing bindings.
> >>
> >> Please define exact model and variants.
> >>
> >>>
> >>> The need is to be able to test SPI with a mainline Linux kernel, so I am
> >>> looking for a solution that works in mainline Linux.
> >>
> >> incomplete devices do not stop you from that.
> > 
> > Do this sentence means that I can send a DT file for inclusion in the
> > Linux kernel using a compatible documented in incomplete-devices?
> 
> No. You will be testing a mainline DTS + load non-mainline overlay. So
> your requirements of "mainline Linux" are fully solved. Overlay is
> loaded by bootloader for example and thus your kernel is fully mainline.

Ok, I was not clear enough, I am looking to have a solution that is 100% in
mainline.

> >> But you don't get exceptions because you want to mainline your DTS. Your
> >> need detailed hardware description and precise compatible per each exact
> >> hat ("exists in multiple variants").
> > 
> > Let me get into more details here, before sending a new patch version.
> > 
> > We have various LAVA HAT devices, the difference is that they provide
> > different features and a different layout, based on the actual carrier
> > board they are mated with.
> > 
> > We have an "Aquila LAVA HAT", that can be mated with the "Aquila
> > Development Board", and a "Verdin LAVA HAT", that can be mated with a
> > "Verdin Dahlia Board".
> 
> Of course, because each device is specific so even the hat must be
> specific, unless you have a standard connector like Arduino or RPi.
> 
> > 
> > As an example, you can find the Verdin Dahlia DTS here,
> > ti/k3-am625-verdin-wifi-dahlia.dts, that can be mated with the "Verdin
> > LAVA HAT".
> > 
> > The SPI device on both "Aquila LAVA HAT" and "Verdin LAVA HAT", is the
> > same, no differences. On the Aquila variant we
> > have two instances of it, while on the Verdin we have only one instance
> > of it.
> > 
> > So, would we need a compatible like this? 
> > 
> > compatible = "toradex,aquila-lava-hat-spi", "toradex,lava-hat-spi";
> > 
> > or
> > 
> > compatible = "toradex,verdin-lava-hat-spi", "toradex,lava-hat-spi";
> 
> Yes, assuming that verdin/aquila hat works for EVERY verdin/aquila
> board, regardless what SoM or SoC you have there.

This is correct, it's exactly like that.

> Verdin is a SoM family according to:
> https://www.toradex.com/computer-on-modules/verdin-arm-family
> 
> and I doubt you can attach hat to a SoM. There is no connector on SoM
> for the hat... so probably you have a board, like Dahlia.

Correct, the HAT is for the carrier, and the carrier is for the family.

With that clarified I plan to send a v2, with something like
"toradex,verdin-dahlia-lava-hat-spi", "toradex,lava-hat-spi" (for each
carrier board we have) and DTS files where this is used, and properly
documenting the compatibility between the various HW devices.

Thanks,
Francesco