On Thu, Jan 11, 2024 at 2:48 PM David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, Jan 09, 2024 at 03:20:12PM +0900, Masahiro Yamada 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? > > More or less, yes. Depending on the exact situation there might be > some clues that an overlay has been applied, but there's certainly no > easy or reliable way to tell. > > > 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. > > Correct. > > > 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. > > Yes and no. It would certainly be possible to add special property > into the dtb to record a listing of the overlays applied. However, > that would only be accurate if the tools used to apply updated it > correctly, and of course the current ones don't. > > Even with that, it wouldn't be possible to "unapply" overlays - > overlays can overwrite data in the base tree so it's no longer > available. There's not really any natural way of making that possible > within the dtb + overlay model. Thanks. The answers are what I expected. We can assemble a DTB from a base and overlays, but cannot do the opposite. So, I was thinking that it would be sensible to support installation of base and overlay files instead of assembled ones. https://lore.kernel.org/linux-kbuild/20240109120738.346061-1-masahiroy@xxxxxxxxxx/T/#ma9017aeb05462996177434cd4a1daa1c2fbe09cd There was no comment so far, though. > > Please let me confirm that I did not miss anything. > > > > > > -- > David Gibson | I'll have my music baroque, and my code > david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ > | _way_ _around_! > http://www.ozlabs.org/~dgibson -- Best Regards Masahiro Yamada
