linux-kernel - Re: [PATCH v2 1/7] dt-bindings: Add support for export-symbols node

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Message-ID: <20250502163311.1e23aa9a@booty>
Date: Fri, 2 May 2025 16:33:19 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Herve Codina <herve.codina@...tlin.com>
Cc: David Gibson <david@...son.dropbear.id.au>, Andrew Davis <afd@...com>,
 Ayush Singh <ayush@...gleboard.org>, Geert Uytterhoeven
 <geert@...ux-m68k.org>, Rob Herring <robh@...nel.org>, Krzysztof Kozlowski
 <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Arnd Bergmann
 <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Saravana
 Kannan <saravanak@...gle.com>, devicetree@...r.kernel.org,
 devicetree-compiler@...r.kernel.org, linux-kernel@...r.kernel.org, Thomas
 Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 1/7] dt-bindings: Add support for export-symbols node

On Wed, 30 Apr 2025 14:51:45 +0200
Herve Codina <herve.codina@...tlin.com> wrote:

> An export-symbols node allows to export symbols for symbols resolution
> performed when applying a device tree overlay.
> 
> When a device tree overlay is applied on a node having an export-symbols
> node, symbols listed in the export-symbols node are used to resolve
> undefined symbols referenced from the overlay.
> 
> This allows:
>   - Referencing symbols from an device tree overlay without the need to
>     know the full base board. Only the connector definition is needed.
> 
>   - Using the exact same overlay on several connectors available on a given
>     board.
> 
> For instance, the following description is supported with the
> export-symbols node:
>  - Base device tree board A:
>     ...
>     foo_connector: connector1 {
>         export-symbols {
>            connector = <&foo_connector>;
>         };
>     };
> 
>     bar_connector: connector2 {
>         export-symbols {
>            connector = <&bar_connector>;
>         };
>     };
>     ...
> 
>  - Base device tree board B:
>     ...
>     front_connector: addon-connector {
>         export-symbols {
>            connector = <&front_connector>;
>         };
>     };
>     ...
> 
>  - Overlay describing an addon board the can be connected on connectors:
>     ...
>     node {
>         ...
>         connector = <&connector>;
>         ...
>     };
>     ...
> 
> Thanks to the export-symbols node, the overlay can be applied on
> connector1 or connector2 available on board A but also on
> addon-connector available on board B.
> 
> Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> Tested-by: Ayush Singh <ayush@...gleboard.org>

Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com