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

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Message-ID: <ef7720ae-bada-4133-a685-d277cd4aa7e6@beagleboard.org>
Date: Mon, 18 Aug 2025 23:07:57 +0530
From: Ayush Singh <ayush@...gleboard.org>
To: Rob Herring <robh@...nel.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
 Herve Codina <herve.codina@...tlin.com>,
 David Gibson <david@...son.dropbear.id.au>, 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 8/18/25 22:35, Rob Herring wrote:
> On Sun, Aug 17, 2025 at 3:42 AM Ayush Singh <ayush@...gleboard.org> 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 just going from bad to worse... If there's a real need to use
> underscores, then use underscores. But that's all beside the point. I
> didn't like v1 and nothing has changed in v2 to change that.
>
> This looks like continuing down the path of working around DTB format
> limitations like DT overlays originally did (which both David (IIRC)
> and I think was a mistake). But now instead of somewhat hidden,
> generated data, you're adding manually written/maintained data. I
> don't have any suggestion currently how to avoid that other than we
> need to rev the DTB format which no one really wants to hear. Maybe
> there's some other solution, but I don't have one ATM.
>
> Rob

Well, if anyone decides to do a v2 of DTB, I would love to help in any 
way I can.


Best Regards,

Ayush Singh