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 825452459EA; Wed, 28 May 2025 08:06:40 +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=1748419600; cv=none; b=leAZFwzOEE8OtRGJi/Hr1Q+dGs+Z3FW2xdrTYoQjjkIYm9e9y37t38x/8i/pSYn4NEqydcFv+1Np52NbhCAsnSR4DUKMHeMGwmz13+wBwCf5WmK+qPvJTfEeO8kPn4EsgulxDHhpncW0OmPGry+DF2fP8ZBMASWiqcW3LlPszwE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748419600; c=relaxed/simple; bh=SW97+/6o0Bda4FjXubNbdRzpoyh+i+v91gUy6eOTLnw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Zc53j/kawKnTqE5C6fNhEMWdYnnQtl2sC2Sl4jaPd3QDVb81rWxggr2c3mSfqEl5/WVTuVftQsZSHte9h2zE9lLCJihaHgicQu+6EdvvIWdlyV12g8/+UJb+HjWO9xtrLXtgDiz1moGXitQ6RsadbaaDqy6DNbgCEMlqefkdgos= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MnXdCUZ4; 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="MnXdCUZ4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5CBC9C4CEEF; Wed, 28 May 2025 08:06:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1748419600; bh=SW97+/6o0Bda4FjXubNbdRzpoyh+i+v91gUy6eOTLnw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=MnXdCUZ4xGgmcADcuH8m4JaGdkcG7IZRZVNxJV6pOk2wBRf6P7LFmWZg8ikKdSok5 c/F6aAGMEBlRBrDRt/0v57upw4kP0EuWXE3UrGyatLFJvYRMzBLHPmvkdmB5d/oLKr slMAAbBnaKTMUsEm9zidYETJLxMPMUI4n/LVANKTGj/1E3nz3lcaimGUT1lc1WIdiW 4wVWMcfPU3OM16wZ8rC56c78a9qnN65CRqByN+++s3UEbs4rM9K34I1zAD79FqWiEb /BnkFFncv1s8JN4vK6Sr8HmTzANGCdWgoCSkrr8XsiSSNdfc46VhNvD6TwAMmvIMJ2 NzdPz5jnu8OOQ== Message-ID: <412231e0-5fcf-4708-aeab-cc3aa38c817e@kernel.org> Date: Wed, 28 May 2025 10:06:34 +0200 Precedence: bulk X-Mailing-List: devicetree-compiler@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: Ayush Singh , Herve Codina , David Gibson , Andrew Davis , 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> <0770a47e-fd2f-4b6f-9a9a-b0d539ace30c@kernel.org> <6c61a101-6ec7-4350-bfa7-5b7d32177818@beagleboard.org> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 28/05/2025 09:59, Ayush Singh wrote: > On 5/28/25 00:01, Krzysztof Kozlowski wrote: > >> 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? >> > > Can you explain how referencing by full path will work in connector + > addon board setups? > > The full path will be dependent on the connector, which means the same > addon  board overlay cannot work for different connectors. That was the assumption. > > >> >> 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>; >> ... >> }; > > > Isn't this overlay tied to `foo_connector`, i.e. it cannot be used with > `bar_connector`? I don't know what the example tried to say. I asked the question, so don't ask question to my question. We both apparently do not know. What is the meaning of that example I questioned? To which connector this is an overlay? Which symbol is exported for that example? Best regards, Krzysztof