From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A69BB322B; Tue, 27 May 2025 18:31:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748370680; cv=none; b=nNvKHbTGYpSBe0EagKHgz/1ZJKEakO07NpAJ5Xy4Zb0j+oLZhl5Er6E4Urhw3Fv0nruQAvfN9u98+pS6jx8T//vGGFg/mQi5koAwciKOPWKs4/pOE0z5ppvTHfdE3DG3FLB1ZtSpOkEamUpp0VGnyUKs7C+DsDHGaio0lCneENg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748370680; c=relaxed/simple; bh=2sS44xR4BqP6ZT0NN2NeXbfkEpdZ2MWF4j4vm7U0nFI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GqUKlvlG6IiBaj0Kq6N39YG9RjXDB/RgfAc2mwttlKDc68uq5pZTSO26OeoqVJb3cPY+O237rbNRLCo6nOYuSmYeoJbj+4bJ020JfNzwUKddfo/uTZOx+Y8Eqsr7C5Nn42TMexQZ6NS2kdttFYagh0mQJOMk6LTIGx8mSgmckfI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bD4yA/gq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bD4yA/gq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A332C4CEE9; Tue, 27 May 2025 18:31:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748370680; bh=2sS44xR4BqP6ZT0NN2NeXbfkEpdZ2MWF4j4vm7U0nFI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=bD4yA/gqzIQ5hqCFevY/dvtWDUmxbVKqNuChwp6MgejkpWYhmc/xF9+/nRxDPye5Q YotGrFfYdZA0lrLKEoXCUh/jINCYq7758mEYK8eAeEmshBEdfNNfyl/djy7zF8gvS+ XwSCHB7sBqQaLWriY6ubfg1gbrpC9p8TathnrfH5z14K6m44eT1WmRSWP6Y0lsZb2u NqQNmRQNwTfYSh9gM/3iqtaSFc+FVzfJyqt+ts6E8NulLYNp8HIIUryiZ0oLzunb2E HDzdDpHgC1x+f0LOxYCd9+pSITvWGbJcL+1O2oYvkSNhzsvq5z6NGZ7Y4K7ucD/e9+ endILuZuq0AVA== Message-ID: <0770a47e-fd2f-4b6f-9a9a-b0d539ace30c@kernel.org> Date: Tue, 27 May 2025 20:31:14 +0200 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/7] dt-bindings: Add support for export-symbols node To: Herve Codina , David Gibson , Andrew Davis , Ayush Singh , Geert Uytterhoeven , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Arnd Bergmann , Greg Kroah-Hartman , Saravana Kannan Cc: devicetree@vger.kernel.org, devicetree-compiler@vger.kernel.org, linux-kernel@vger.kernel.org, Luca Ceresoli , Thomas Petazzoni References: <20250430125154.195498-1-herve.codina@bootlin.com> <20250430125154.195498-2-herve.codina@bootlin.com> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 30/04/2025 14:51, Herve Codina 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. I have impression that this is being discussed in three places simultaneously - here, DT spec and DT schema. I don't know how to solve the multiplication, but I will keep answering here, because that's my part. > > 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>; > }; > }; > ... And what would this mean? Which symbol is exported - foo or bar? > > - Base device tree board B: > ... > front_connector: addon-connector { > export-symbols { > connector = <&front_connector>; > }; > }; Another problem is that the board DTS should not care about overlays. It feels like breaking encapsulation and I cannot imagine now adding 1000 export-symbols, because every i2c, spi, mikrobus or PCI slot could have an overlay applied. You could argue that only few nodes will be exported like this, so only real mikrobus connectors. Then I will argue: look at aliases. People alias everything everywhere, not following the guidelines. If we assume that such overlays are designed for specific boards, thus there will be only one or two exported symbols not 1000, then what is the benefit of export symbols comparing to referencing by full path? And with above assumption - such overlays designed per board - plus my first point about duplicated exports: connector = <&foo_connector>; connector = <&bar_connector>; why not exporting the symbol with the same name? E.g.: foo_connector: connector1 { export-symbols { whatever-property-style = <&foo_connector>; }; }; and overlay: node { ... connector = <&foo_connector>; ... }; Or even annotation? foo_connector: connector1 __exported_symbol__ { .... }; node { ... connector = <&foo_connector>; ... }; ? This also answers my further question about DTS style (see at the bottom) > ... > > - 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 > Tested-by: Ayush Singh I would argue you cannot test a binding, because testing here is part of a process, but what do I know... > --- > .../devicetree/bindings/export-symbols.yaml | 43 +++++++++++++++++++ > 1 file changed, 43 insertions(+) > create mode 100644 Documentation/devicetree/bindings/export-symbols.yaml > > diff --git a/Documentation/devicetree/bindings/export-symbols.yaml b/Documentation/devicetree/bindings/export-symbols.yaml > new file mode 100644 > index 000000000000..0e404eff8937 > --- /dev/null > +++ b/Documentation/devicetree/bindings/export-symbols.yaml > @@ -0,0 +1,43 @@ > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause) > +%YAML 1.2 > +--- > +$id: http://devicetree.org/schemas/export-symbols.yaml# > +$schema: http://devicetree.org/meta-schemas/core.yaml# > + > +title: Export symbols > + > +maintainers: > + - Herve Codina > + > +description: | > + 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. > + > +properties: > + $nodename: > + const: export-symbols > + > +patternProperties: > + "^[a-zA-Z_]?[a-zA-Z0-9_]*$": This messes up with coding style which I would prefer keep intact. Basically these properties will be using label style. > + $ref: /schemas/types.yaml#/definitions/phandle > + description: > + A symbol exported in the form =. > + > +additionalProperties: false > + Best regards, Krzysztof