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

David Gibson <[email protected]> Mon, 8 Sep 2025 14:48:25 +1000
Newsgroups	org.kernel.vger.devicetree-compiler,org.kernel.vger.linux-devicetree,org.kernel.vger.linux-kernel
Message-ID	<aL5gGRlnbVuAQk-t@zatzit>
On Mon, Aug 18, 2025 at 11:07:57PM +0530, Ayush Singh wrote:
> 
> On 8/18/25 22:35, Rob Herring wrote:
> > On Sun, Aug 17, 2025 at 3:42 AM Ayush Singh <[email protected]> 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.

We're already on v17 of DTB (although only 5 of those version numbers
were actually used).

It shouldn't actually be that hard to extend it in a number of ways
without having to completely redefine it.

-- 
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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