linux-kernel - Re: [PATCH v5 2/9] rust: device: Enable accessing the FwNode of a Device

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Message-Id: <DA1UK58JZWCM.CXSOPB8BN4H7@buenzli.dev>
Date: Wed, 21 May 2025 14:45:06 +0200
From: "Remo Senekowitsch" <remo@...nzli.dev>
To: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
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>, "Danilo
 Krummrich" <dakr@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 "Dirk Behme" <dirk.behme@...bosch.com>, <linux-kernel@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Subject: Re: [PATCH v5 2/9] rust: device: Enable accessing the FwNode of a
 Device

On Wed May 21, 2025 at 1:59 PM CEST, Greg Kroah-Hartman wrote:
> On Tue, May 20, 2025 at 10:00:17PM +0200, Remo Senekowitsch wrote:
>> Subsequent patches will add methods for reading properties to FwNode.
>> The first step to accessing these methods will be to access the "root"
>> FwNode of a Device.
>> 
>> Add the method `fwnode` to `Device`.
>> 
>> Signed-off-by: Remo Senekowitsch <remo@...nzli.dev>
>> ---
>>  rust/kernel/device.rs | 15 +++++++++++++++
>>  1 file changed, 15 insertions(+)
>> 
>> diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs
>> index d8619d4485fb4..b4b7056eb80f8 100644
>> --- a/rust/kernel/device.rs
>> +++ b/rust/kernel/device.rs
>> @@ -186,6 +186,21 @@ unsafe fn printk(&self, klevel: &[u8], msg: fmt::Arguments<'_>) {
>>          };
>>      }
>>  
>> +    /// Obtain the [`FwNode`](property::FwNode) corresponding to the device.
>> +    pub fn fwnode(&self) -> Option<&property::FwNode> {
>> +        // SAFETY: `self` is valid.
>> +        let fwnode_handle = unsafe { bindings::__dev_fwnode(self.as_raw()) };
>
> Why isn't this calling __dev_fwnode_const()?  And there's no way to just
> use dev_fwnode() directly?  Ugh, it's a macro...

I think I had that in earlier versions of the patch series. There was
a helper to call the macro from Rust. It was pointed out that this is
not clearly expressing the intent - whether fwnode is mutated or not.
And I think someone said the fwnode can be mutated so __dev_fwnode() is
semantically correct.