On Tue, Jan 9, 2024 at 12:20 AM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > Hi. > > Sorry for a stupid question. > > > When you get a DTB by using fdtoverlay, there is no way to > know how it was produced later. Correct? > > For instance, this case: > > $ fdtoverlay --input base.dtb ovl.dtbo --output foo.dtb > > Once you get foo.dtb, you will never know whether it was > assembled from base.dtb + ovl.dtbo, or it was directly > generated from a single source, foo.dts. That is correct. If the results are the same, why do you care? > In my understanding, there is no room in DTB to record > such metadata, and it is impossible to disassemble foo.dtb > into the original components, base.dtb and ovl.dtbo. > > Please let me confirm that I did not miss anything. The kernel has the ability to un-apply overlays. I think that only depends on having the original overlay and not any state from having applied the overlay. fdtoverlay could be extended to do something similar if you wanted to get base.dtb from foo.dtb and ovl.dtbo. If you can't un-apply the overlay, then it would be a hint that it wasn't created by applying the overlay. Rob
