Re: [RFC PATCH 15/15] Introduce v18 dtb version

Luca Ceresoli
2026-04-08T07:55:45Z

On Tue Apr 7, 2026 at 6:44 PM CEST, Herve Codina wrote:
> Hi Luca,
>
> On Wed, 01 Apr 2026 17:19:09 +0200
> "Luca Ceresoli" <luca.ceresoli@bootlin.com> wrote:
>
>> On Tue Feb 10, 2026 at 6:33 PM CET, Herve Codina wrote:
>> > This v18 version will add support for
>> > - Structured tags.
>> > Those tags value definition will allow old libfdt, dtc and other
>> > tools to skip unknown tags if encountered in future dtb version.
>>
>> "old" seems to imply that versions released before today will be able to
>> wkip unknown tags. I think this should be clarified along the lines of:
>>
>> libfdt, dtc and other tools implementing version v18 will be able to wkip
>> unknown tags in dtbs generated with later versions of dtc
>
> Yes, I will add this clarification in the next iteration.
>
>>
>> > - dt_flags header field.
>> > For now this flag field is set to 0. It is a placeholder for future
>> > dtb version and could be used to store some dtb related information
>> > such as the kind of dtb.
>>
>> Is this intended for DT addons?
>>
>> You may mention a realistiv use case here.
>
> Intended, maybe not. Used by addons, yes, for sure.
>
> What do you think if I add the following:
> For instance, the future addons format will use this field to
> clearly identify that the dtb is an addon dtb.

This clarifies a lot to me, so I think it can be added to the commit
message.

>> > Compared to previous version, it is worth noting that the dtb is not
>> ^
>> "dtb version"
>>
>> > downgrade for all modification but only when unknown tags are removed
>> ^
>> downgraded for any
>>
>>
>> > due a property modification.
>> ^
>> "due to a ..."
>>
>> I'm not sure I got what you mean by the initial "Compared to previous
>> version". Version(s) of what?
>>
>> If I just remove those 4 words the sentence seems OK to me BTW.
>
> Is the following clearer?
>
> It is worth noting that with this v18 version, the dtb version is not
> downgraded for any modification but only when unknown tags are removed
> due to a property modification. In v17 or older version any modification
> led to a dtb version downgrade.

Yes, totally clear now, thanks!

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering