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

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Message-ID: <20250618113232.6d237208@bootlin.com>
Date: Wed, 18 Jun 2025 11:32:32 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, David Gibson
 <david@...son.dropbear.id.au>, Ayush Singh <ayush@...gleboard.org>, Rob
 Herring <robh@...nel.org>
Cc: 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

Hi Krzysztof,

On Wed, 4 Jun 2025 20:35:51 +0200
Krzysztof Kozlowski <krzk@...nel.org> wrote:

...

> > 
> > Symbols are exported only when an overlay is applied on the node where the
> > export-symbols node is available. Those symbols are visible only from the
> > overlay applied. Symbols exported thanks to export-symbols are not global
> > to the all device-tree (it is not __symbols__) but local to a node.
> > 
> > If an overlay is applied at connector1 node, it can use the 'connector'
> > symbols and thanks to export-symbols, the 'connector' symbol will be
> > resolved to foo_connector.
> > 
> > If the overlay is applied at connector2 node, the 'connector' symbol is then
> > resolved to bar_connector.  
> 
> OK, this explains a lot. Unless I missed it, would be nice to include it
> in binding description.

Sure, I will add something in the next iteration.

...

> >>> +patternProperties:
> >>> +  "^[a-zA-Z_]?[a-zA-Z0-9_]*$":    
> >>
> >> This messes up with coding style which I would prefer keep intact.
> >> Basically these properties will be using label style.  
> > 
> > Yes, those properties remap phandles.
> > 
> > Their names are the name of the label used from the overlay and their
> > values are the phandle mapped.
> > 
> > You already have this kind properties using label style in __symbols__,
> > __fixups__, __local_fixups__ nodes.  
> 
> I have them in DTB, but I don't have these in DTS. The exported-symbols
> would be in the DTS and that is what coding style is about.
> 

I think export-symbols has to be in DTS.
Maybe it could be described in an other way in order to avoid the coding style
issue you reported.

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