linux-kernel - Re: [RFC PATCH 19/77] dtc: Introduce export symbols

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Message-ID: <20260116172735.757c1872@bootlin.com>
Date: Fri, 16 Jan 2026 17:27:35 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: David Gibson <david@...son.dropbear.id.au>
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 19/77] dtc: Introduce export symbols

Hi David,

On Thu, 15 Jan 2026 16:52:26 +1100
David Gibson <david@...son.dropbear.id.au> wrote:

> On Mon, Jan 12, 2026 at 03:19:09PM +0100, Herve Codina wrote:
> > Export symbols allow to define a list of symbols exported at a given
> > node level. Those exported symbols can be used by an addon when the
> > addon is applied on the node exporting the symbols.  
> 
> This seems to imply an addon always applies at a single node location.
> I'm not sure that's a good design choice, since I don't see how it
> covers the case of something that connects to several connectors.

Apply the addon on a node that knows about those connectors.

> 
> > In order to perform
> > its symbol resolution. Any unresolved phandle value will be resolved
> > using those exported symbols.
> > 
> > The feature is similar to __symbols__ involved with overlay but while
> > all symbols are visible with __symbols__, only specific symbols
> > (exported symbols) are visible with export symbols.  
> 
> This paragraph doesn't make sense to me.  What's a "symbol" if it's
> not something in __symbols__ or export symbols?

An imported symbols ?

/import/ foo "blabla";

from the addon point of view where this /import/ is present, 'foo' is a
symbol.

> 
> > Also an exported symbol has a specific name and this name has to
> > used for symbol resolution. Having this specific name allows to:
> > 
> >   - Have several nodes providing the same exported symbols
> >     name but each of them pointing to different nodes.  
> 
> That's not a property of having a specific name, that's a property of
> being local to a node.

Yes, exactly. I will reword.

Best regards,
Hervé