linux-kernel - Re: [PATCH 10/10] samples: rust: platform: Add property read examples

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Message-Id: <D8QJSRGJIYHS.K4H9W8N8N0YO@buenzli.dev>
Date: Wed, 26 Mar 2025 23:23:51 +0100
From: "Remo Senekowitsch" <remo@...nzli.dev>
To: "Rob Herring" <robh@...nel.org>
Cc: "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>, "Daniel Scally"
 <djrscally@...il.com>, "Heikki Krogerus" <heikki.krogerus@...ux.intel.com>,
 "Sakari Ailus" <sakari.ailus@...ux.intel.com>, "Dirk Behme"
 <dirk.behme@...bosch.com>, "Greg Kroah-Hartman"
 <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 "Danilo Krummrich" <dakr@...nel.org>, "Saravana Kannan"
 <saravanak@...gle.com>, "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" <benno.lossin@...ton.me>,
 "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice Ryhl"
 <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 <linux-kernel@...r.kernel.org>, <linux-acpi@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH 10/10] samples: rust: platform: Add property read
 examples

On Wed Mar 26, 2025 at 11:01 PM CET, Rob Herring wrote:
>>
>> +        let prop = dev
>> +            .property_read::<bool>(c_str!("test,bool-prop"))
>> +            .required()?;
>
> The 'required' is kind of odd for boolean properties. They are never 
> required as not present is the only way to to get false.

Agreed. I can think of a few alternatives:

* Make the trait `Property` more flexible to allow each implementor to specify
  what its output type for the `read` function is, via an associated type.
  I really don't like this idea, because overly generic APIs can mess with type
  inference and become less ergonomic because of it.

* Use `propert_present` instead. That doesn't perfectly express the intention,
  because it doesn't warn if the property is present but has a type other than
  bool.

* Add an additional inherent method `property_read_bool`, which returns a plain
  `bool` instead of `PropertyGuard<bool>`. Then there will be three slightly
  different ways to read a bool: `property_present`, `property_read_bool` and
  `property_read::<bool>`. Maybe that's confusing.

* Add `property_read_bool` and remove `impl Property for bool`. That would avoid
  confusion between `property_read_bool` and `property_read::<bool>`, only the
  former would work.