Re: delete-node without label or address from overlay dts

[David Gibson <david@gibson.dropbear.id.au>]

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On Fri, Jan 16, 2026 at 02:39:30PM +0000, Phil Dawson wrote:
> On Fri, 16 Jan 2026 at 13:03, David Gibson <david@gibson.dropbear.id.au> wrote:
> >
> > On Thu, Jan 15, 2026 at 12:00:13PM +0000, Phil Dawson wrote:
> > > Hi,
> > >
> > > Apologies if this is covered in documentation that I've missed.
> > > Is there a way to use /delete-node/ to remove a node with no label or
> > > address from a plugin/overlay dts file?
> >
> > No.  /delete-node/ has no representation within overlay files.  One of
> > several examples of how plugin/overlays are misleading in that they
> > sort of resemble dtc's older build-time overlays, but not really.
> >
> Just to be clear as my understanding is a bit muddy:
> 
> I know you cannot use an overlay to remove a node from the base tree
> at runtime.

Oh, sorry, I misunderstood your question.

> But is it correct that when constructing an overlay with dtc you can
> only use /delete-node/ if the node you wish to remove has a label
> or address?

I think that's correct, though kind of by accident.

> > > I have a device tree overlay file pl.dtsi that is auto generated by
> > > vendor tools. Unfortunately many nodes in this file are generated
> > > wrong and the overlay fails to apply.
> > > I've been removing the broken nodes with /delete-node/ &label; syntax
> > > in a second dtsi file and then compiling the two together with a
> > > wrapper dts file and the commands:
> > > gcc -E -nostdinc -undef -D__DTS__ -x assembler-with-cpp -o pl.dts.pp
> > > <path redacted>/pl.dts
> > > dtc -R 8 -b 0 -p 0 -@ -H epapr -o pl.dtbo -I dts -O dtb pl.dts.pp
> > > (These are run as part of a larger yocto build so there may be some
> > > other work around this I'm missing!)
> > >
> > > The auto generated pl.dtsi also has a few broken nodes without labels
> > > or addresses like this:
> > >
> > > /dts-v1/;
> > > /plugin/;
> > > &amba {
> > >     vcap_hdmi_input_1_v_proc_ss_1 {
> > > <contents removed for brevity>
> > >     };
> > > };
> > >
> > > I am unable to figure out the syntax to remove these nodes with
> > > /delete-node/, should this be possible?
> > >
> > > I've tried using the below syntax:
> > > &amba {
> > >     /delete-node/ vcap_hdmi_input_1_v_proc_ss_1;
> > > };
> > >
> > > But while dtc doesn't complain, the nodes are not removed from the
> > > resulting dtbo.

Right.  So this happens because when compiling a plugin each top-level
chunk is compiled into a separate "fragment" in the plugin.  The
/delete-node/ here would remove anything already defined in the same
fragment, but not things in earlier fragments.

In non-/plugin/ mode we merge all the chunks together, so
/delete-node/ (and /delete-property/ for that matter) will apply
properly regardless of which chunks everything appears in.

This is another ugly consequence of the rather haphazard ways
plugins/overlays are designed / implemented.  I think we could fix it
by not merging everything during the parse: instead generating a list
of chunks, then merging them in a later, explicit step.  We'd always
do that for full trees, and merge only those pieces that we can
resolve for plugins.

I think that would be a good fix, but I'm certainly not going to have
time to implement it in the forseeable future.

> > Hm, we probably should make this generate an error.  I'm unlikely to
> > get to that any time soon, though.
> >
> > > I also can't remove using the full path as there is no root node/full
> > > path in the generated dtsi file.
> > >
> > > According to this discussion on an unrelated project
> > > (https://github.com/zephyrproject-rtos/zephyr/discussions/67228)
> > > trying to delete a node with a name and address without using the
> > > address won't work. But in my case the node has no address.
> > >
> > > I can work around my issue by hacking the auto generated files (while
> > > I try to persuade the vendor to fix them!) to add a label for these
> > > nodes and then removing them using the label. But is there a correct
> > > way of doing this just using my separate dtsi file and dtc?
> > >
> > > Best Regards,
> > > Phil Dawson
> > >
> >
> > --
> > David Gibson (he or they)       | 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
> 
> Thanks,
> Phil
> 

-- 
David Gibson (he or they)	| 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

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