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

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Message-ID: <Z-UoapC4zkKFOD9-@pollux>
Date: Thu, 27 Mar 2025 11:28:58 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: Remo Senekowitsch <remo@...nzli.dev>
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>,
	Rob Herring <robh@...nel.org>, Dirk Behme <dirk.behme@...bosch.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...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 06:13:49PM +0100, Remo Senekowitsch wrote:
> --- a/samples/rust/rust_driver_platform.rs
> +++ b/samples/rust/rust_driver_platform.rs
> @@ -2,7 +2,7 @@
>  
>  //! Rust Platform driver sample.
>  
> -use kernel::{c_str, of, platform, prelude::*};
> +use kernel::{c_str, of, platform, prelude::*, str::CString};
>  
>  struct SampleDriver {
>      pdev: platform::Device,
> @@ -28,6 +28,60 @@ fn probe(pdev: &mut platform::Device, info: Option<&Self::IdInfo>) -> Result<Pin
>              dev_info!(pdev.as_ref(), "Probed with info: '{}'.\n", info.0);
>          }
>  
> +        let dev = pdev.as_ref();
> +        if let Ok(idx) = dev.property_match_string(c_str!("compatible"), c_str!("test,rust-device"))
> +        {
> +            dev_info!(pdev.as_ref(), "matched compatible string idx = {}\n", idx);
> +        }
> +
> +        if let Ok(str) = dev
> +            .property_read::<CString>(c_str!("compatible"))
> +            .required()
> +        {
> +            dev_info!(pdev.as_ref(), "compatible string = {:?}\n", str);
> +        }
> +
> +        let prop = dev
> +            .property_read::<bool>(c_str!("test,bool-prop"))
> +            .required()?;
> +        dev_info!(dev, "bool prop is {}\n", prop);
> +
> +        if dev.property_present(c_str!("test,u32-prop")) {
> +            dev_info!(dev, "'test,u32-prop' is present\n");
> +        }
> +
> +        let prop = dev
> +            .property_read::<u32>(c_str!("test,u32-optional-prop"))
> +            .or(0x12);
> +        dev_info!(
> +            dev,
> +            "'test,u32-optional-prop' is {:#x} (default = {:#x})\n",
> +            prop,
> +            0x12
> +        );

Printing the default value looks more like a test, rather than a sample.

> +
> +        // Missing property without a default will print an error
> +        let _ = dev
> +            .property_read::<u32>(c_str!("test,u32-required-prop"))
> +            .required()?;
> +
> +        let prop: u32 = dev.property_read(c_str!("test,u32-prop")).required()?;
> +        dev_info!(dev, "'test,u32-prop' is {:#x}\n", prop);
> +
> +        let prop: [i16; 4] = dev.property_read(c_str!("test,i16-array")).required()?;
> +        dev_info!(dev, "'test,i16-array' is {:?}\n", prop);
> +        dev_info!(
> +            dev,
> +            "'test,i16-array' length is {}\n",
> +            dev.property_count_elem::<u16>(c_str!("test,i16-array"))
> +                .unwrap()

Please no unwrap() in the kernel, it may panic.

> +        );
> +
> +        let prop: KVec<i16> = dev
> +            .property_read_array_vec(c_str!("test,i16-array"), 4)?
> +            .required()?;
> +        dev_info!(dev, "'test,i16-array' is KVec {:?}\n", prop);
> +

Please move this code to a new function, e.g.

	impl SampleDriver {
	   fn properties_parse(dev: &device::Device)) -> Result;
	}

in order to keep probe() as clean as possible. If we put too much stuff in
there, it might become too confusing to serve as a simple example showing how to
implement a platform driver in Rust.

Besides that, are we sure we really want to print everything?