linux-kernel - Re: [RFC PATCH 64/77] dtc: Add support for references by path involving orphan nodes

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Message-ID: <aXCXAwm34LobcW1h@zatzit>
Date: Wed, 21 Jan 2026 20:06:11 +1100
From: David Gibson <david@...son.dropbear.id.au>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Ayush Singh <ayush@...gleboard.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	devicetree-compiler@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree-spec@...r.kernel.org,
	Hui Pu <hui.pu@...ealthcare.com>,
	Ian Ray <ian.ray@...ealthcare.com>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [RFC PATCH 64/77] dtc: Add support for references by path
 involving orphan nodes

On Mon, Jan 19, 2026 at 05:38:31PM +0100, Herve Codina wrote:
> On Thu, 15 Jan 2026 18:01:39 +1100
> David Gibson <david@...son.dropbear.id.au> wrote:
> 
> > On Mon, Jan 12, 2026 at 03:19:54PM +0100, Herve Codina wrote:
> > > Referencing a sub-node from an orphan node using a path is needed.
> > > 
> > > Indeed, using the following snippet:
> > > --- 8< ---
> > > /addon/;
> > > 
> > > &node1 {
> > > 	subnode {
> > > 		foo-phandle = <&foo_label>;
> > > 	};
> > > };
> > > 
> > > &node2 {
> > > 	foo_label: foo {
> > > 		prop = <1>;
> > > 	};
> > > };
> > > --- 8< ---
> > > 
> > > Even if node2 is an orphan node, foo is a local node. foo-phandle
> > > references the foo node using a label.  
> > 
> > Another option would be to eliminate the idea of local references, and
> > require a symbol be attached to things that you want to reference by
> > label.
> 
> Hum, new kind of references.

No, I'm trying to remove a type of reference: I'm suggesting using the
same format as for external references on local references as well.
That might mean things referenced need to be both exported and
imported by the tree creating them.  That might be worth it to reduce
the number of cases.

> We have reference by phandle to local nodes. Reference by symbol for
> external nodes (i.e. nodes not present in current dtb).
> 
> Now new kind of reference for node available in the current dtb but
> in a different tree (orphan tree).
> 
> For that we need to:
>   - Mark the phandle value in the property as a cross-tree phandle
>     reference
>   - Add the symbol label in the referenced node.
> 
> When the addon is applied, this new kind of reference need to be taken
> into account in a new way:
>   - The phandle value in the referenced node need to be updated in the
>     same way as all other phandle value in nodes to avoid collisions.
>   - The cross-tree reference needs to be resolved.
> 
> This adds an unneeded complexity.
> 
> IMHO, we shouldn't eliminate local references.
> 
> We need to reference all possible local nodes by path even if cross-tree
> due to orphan tree is involved.
> 
> Best regards,
> Hervé
> 

-- 
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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