From: Masahiro Yamada <masahiroy@kernel.org>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: Devicetree Compiler <devicetree-compiler@vger.kernel.org>
Subject: Re: Record of original components for fdtoverlay
Date: Wed, 17 Jan 2024 10:51:09 +0900 [thread overview]
Message-ID: <CAK7LNAQUBuxYwPUQc4_o=+Jj3b+CTH+-KNRym-FgrM-fU5dyjw@mail.gmail.com> (raw)
In-Reply-To: <ZZ0lJMxKeD-TGyEr@zatzit>
On Thu, Jan 11, 2024 at 2:48 PM David Gibson
<david@gibson.dropbear.id.au> 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@kernel.org/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
next prev parent reply other threads:[~2024-01-17 1:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-09 6:20 Record of original components for fdtoverlay Masahiro Yamada
2024-01-09 10:51 ` David Gibson
2024-01-17 1:51 ` Masahiro Yamada [this message]
2024-01-09 20:23 ` Rob Herring
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