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

[Marek Vasut]

On 11/7/25 5:44 PM, Marek Vasut 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.

If I run this with "DTC=/usr/bin/dtc make ..." , then the phandles are 
correctly retained. This uses system DTC 1.7.2 instead of in-tree DTC 
1.4.6+ .

Is there still any reason for us to carry our own copy of DTC ?