linux-kernel - Re: [PATCH v2 1/5] rust: Move property

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Message-ID: <Z_0xGRsI74PsAL_E@cassiopeiae>
Date: Mon, 14 Apr 2025 18:00:25 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Remo Senekowitsch <remo@...nzli.dev>
Cc: Rob Herring <robh@...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>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2 1/5] rust: Move property_present to separate file

On Mon, Apr 14, 2025 at 05:26:26PM +0200, Remo Senekowitsch wrote:
> Not all property-related APIs can be exposed directly on a device.
> For example, iterating over child nodes of a device will yield
> fwnode_handle. Thus, in order to access properties on these child nodes,
> duplicate the APIs on a fwnode as they are in C.

What do you mean with "duplicate the APIs"?

Also, this patch does three separate things.

  (1) move property_present() to separate file
  (2) implement FwNode abstraction
  (3) implement Device::fwnode()

I'd rather keep property_present() in device.rs and also move fwnode() into
device.rs, even though in C it's in property.c. impl Device blocks should be in
device.rs.

Hence, please split this in two patches, one for (2) and one for (3).

> +++ b/rust/kernel/property.rs
> @@ -0,0 +1,75 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Unified device property interface.
> +//!
> +//! C header: [`include/linux/property.h`](srctree/include/linux/property.h)
> +
> +use core::ptr;
> +
> +use crate::{bindings, device::Device, str::CStr, types::Opaque};
> +
> +impl Device {
> +    /// Obtain the fwnode corresponding to the device.
> +    fn fwnode(&self) -> &FwNode {
> +        // SAFETY: `self` is valid.
> +        let fwnode_handle = unsafe { bindings::__dev_fwnode(self.as_raw()) };
> +        if fwnode_handle.is_null() {
> +            panic!("fwnode_handle cannot be null");

Please don't use panic!() unless you hit an error condition that is impossible
to handle.

If __dev_fwnode() can ever return NULL, make this function return
Option<&FwNode> instead.