linux-kernel - Re: [PATCH v1 3/3] samples: rust: platform: Add property child and reference args examples

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Message-Id: <DAPMND2X0QHE.1N0NF7R1F8J1G@buenzli.dev>
Date: Wed, 18 Jun 2025 13:37:08 +0200
From: "Remo Senekowitsch" <remo@...nzli.dev>
To: "Danilo Krummrich" <dakr@...nel.org>, "Rob Herring" <robh@...nel.org>
Cc: "Saravana Kannan" <saravanak@...gle.com>, "Greg Kroah-Hartman"
 <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor" <alex.gaynor@...il.com>,
 "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo" <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>, "Mark
 Brown" <broonie@...nel.org>, "Dirk Behme" <dirk.behme@...bosch.com>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v1 3/3] samples: rust: platform: Add property child and
 reference args examples

On Tue Jun 17, 2025 at 3:11 PM CEST, Danilo Krummrich wrote:
> On Tue, Jun 17, 2025 at 08:01:08AM -0500, Rob Herring wrote:
>> On Mon, Jun 16, 2025 at 10:45 AM Remo Senekowitsch <remo@...nzli.dev> wrote:
>> > @@ -91,6 +95,13 @@ fn properties_parse(dev: &device::Device) -> Result {
>> >          let prop: KVec<i16> = fwnode.property_read_array_vec(name, 4)?.required_by(dev)?;
>> >          dev_info!(dev, "'{name}'='{prop:?}' (KVec)\n");
>> >
>> > +        for child in fwnode.children() {
>> > +            let name = c_str!("test,ref-arg");
>> > +            let nargs = NArgs::N(2);
>> > +            let prop: FwNodeReferenceArgs = child.property_get_reference_args(name, nargs, 0)?;
>> 
>> Is there some reason we can just pass 2 in rather than nargs? Seems
>> overly verbose for my tastes.
>
> It's because you could also pass NArgs::Prop("foo-bar") to indicate the the
> name of the property telling the number of arguments.
>
> NArgs is defined as
>
> 	pub enum NArgs<'a> {
> 	    /// The name of the property of the reference indicating the number of
> 	    /// arguments.
> 	    Prop(&'a CStr),
> 	    /// The known number of arguments.
> 	    N(u32),
> 	}
>
> and FwNode::property_get_reference_args() can match against the corresponding
> enum variant to cover both cases.

I guess we could make the function generic if that's deemed worth it?
A trait and an implementation for `u32` and `&CStr` each. Similar to how
we made `property_read` generic.

>> > +            dev_info!(dev, "'{name}'='{prop:?}'\n");
>> > +        }
>> > +
>> >          Ok(())
>> >      }
>> >  }
>> > --
>> > 2.49.0
>> >