[RFC][PATCH] kbuild: Produce diff between base DT and U-Boot augmented DT if DEVICE_TREE_DEBUG=1

[Simon Glass]

Hi Marek,

On Fri, 7 Nov 2025 at 17:44, Marek Vasut <marek.vasut at mailbox.org> wrote:
>
> On 11/7/25 4:56 PM, Tom Rini wrote:
> > On Fri, Nov 07, 2025 at 03:06:47PM +0100, Marek Vasut wrote:
> >> On 11/7/25 10:12 AM, Heinrich Schuchardt wrote:
> >>> On 11/6/25 22:08, Marek Vasut wrote:
> >>>> In case DEVICE_TREE_DEBUG is set, produce a diff between the base DT and
> >>>> DT with U-Boot extras, to show how much does the U-Boot DT differ from
> >>>> the base DT. This is particularly useful together with OF_UPSTREAM, to
> >>>> minimize the diff between upstream DTs and U-Boot DTs.
> >>>>
> >>>> Example usage:
> >>>> $ make r8a779g3_sparrowhawk_defconfig && make DEVICE_TREE_DEBUG=1
> >>>> $ cat ./dts/upstream/src/arm64/renesas/r8a779g3-sparrow-hawk.dtb.diff
> >>>>
> >>>> This still has a downside. Even 'dtc -I dts -O dts ...' applied on
> >>>> base DT and U-Boot augmented DT can produce different phandle IDs
> >>>> for the same node in those two DTs, which results in a lot of noise
> >>>> in the resulting diff. The only way I can think of is to patch DTC
> >>>> to emit full paths in those phandles instead, something like a
> >>>> phandle = <&{/full/path/to/remote/end} ...>;
> >>
> >> What bothers me is ^ this part.
> >>
> >> Hello Heinrich,
> >>
> >>> Without documentation developers will not know about the new feature.
> >>> Could you, please, add a doc/build/ change in the next iteration.
> >> Sure, although I am not convinced it should go in in its current form.
> >> Please see my first line of comment.
> >
> > Maybe we put it in the u-boot-extras repo for now as a standalone
> > script, so people can be asked to run it and look at the output?
> I'd say no, because the output is full of noise unless the phandle
> non-resolution gets somehow improved.

Another idea would be to create an fdtdiff tool which does this. We
already have fdtgrep[1]

Regards,
Simon

[1] https://github.com/devicetree-org/fdt-tools