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

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Message-ID: <aL5fl0GhUdZbIZA3@zatzit>
Date: Mon, 8 Sep 2025 14:46:15 +1000
From: David Gibson <david@...son.dropbear.id.au>
To: Ayush Singh <ayush@...gleboard.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
	Herve Codina <herve.codina@...tlin.com>,
	Rob Herring <robh@...nel.org>, Andrew Davis <afd@...com>,
	Geert Uytterhoeven <geert@...ux-m68k.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,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 1/7] dt-bindings: Add support for export-symbols node

On Sun, Aug 17, 2025 at 02:12:28PM +0530, Ayush Singh wrote:
> On 8/17/25 13:52, Krzysztof Kozlowski wrote:
> 
> > On 17/08/2025 10:18, Ayush Singh wrote:
> > > > > > Hardware:
> > > > > >      i2c0 from SoC --------- connector 1, I2C A signals
> > > > > >      i2c1 from SoC --------- connector 1, I2C B signals
> > > > > > 
> > > > > >      connector1 {
> > > > > >          export-symbols {
> > > > > > 	  i2c_a = <&i2c0>;
> > > > > > 	  i2c_b = <&i2c1>;
> > > > > >          };
> > > > > >      };
> > > > > > 
> > > > > > In order to avoid the coding style issue, this could be replace
> > > > > > with:
> > > > > >     connector1 {
> > > > > >          export-symbols {
> > > > > > 	  symbol-names = "i2c_a", "i2c_b";
> > > > > > 	  symbols = <&i2c0>, <&i2c1>;
> > > > > >          };
> > > > > >      };
> > > > > > 
> > > > > > Krzysztof, Rob, do you think this could be accepted ?
> > > > > > 
> > > > > > Ayush, David, do you thing this could be easily implemented in fdtoverlay ?
> > > > > > 
> > > > > > Best regards,
> > > > > > Hervé
> > > > > > 
> > > > > Well, it is possible.
> > > > > 
> > > > > However, on connectors like pb2 header, there will be 50-100 export
> > > > > symbols. So it will start becoming difficult to maintain.
> > > > And the first syntax solves this how? I don't see the practical difference.
> > > 
> > > Well, I was more worried about matching which phandle belongs to which
> > > symbol easily. Let us assume that 2 symbols will be in each line (after
> > > accounting for the indention and 80 char limit) and we have 70 symbols,
> > > so 35 lines. To check which phandle belongs to the 2nd symbol on line
> > > 25th line of  symbol-names, well, you would at the best case need to
> > > have something like relative line numbers in your editor. Then you know
> > > that the 35th line from the current one is where you need to look.
> > > 
> > > In the current syntax, the symbol name and phandle are on the same line.
> > > So well, easy to see which symbols refers to which phandle.
> > OK, that's valid point. Any ideas how to solve it without introducing
> > underscores for properties?
> > 
> > Best regards,
> > Krzysztof
> 
> 
> Well, we can modify `get_phandle_from_symbols_node` to allow matching `*_*`
> to `*-*`. And we can do the same in devicetree easily enough. Not sure if
> implicit loose matching like that are the best idea.
> 
> Zephyr does something similar for compatible strings. It pretty much
> replaces the all non alphanumeric characters with `_` in compatible string
> match. Although that is more to do with the limitation they are working
> with, i.e. the devicetree being converted to static headers instead of being
> runtime thing.

This is another reason to consider doing this in a new out-of-band
extension to dtb, rather than as "regular" device tree properties.  In
that case you can redefine your naming conventions to suit your needs.

-- 
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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