netdev - Re: [PATCH net-next v10 1/4] rust: core abstractions for network PHY drivers

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Message-ID: <ccf2b9af-1c8c-44c4-bb93-51dd9ea1cccf@ryhl.io>
Date: Mon, 11 Dec 2023 22:46:01 +0100
From: Alice Ryhl <alice@...l.io>
To: FUJITA Tomonori <fujita.tomonori@...il.com>, netdev@...r.kernel.org
Cc: rust-for-linux@...r.kernel.org, andrew@...n.ch, tmgross@...ch.edu,
 miguel.ojeda.sandonis@...il.com, benno.lossin@...ton.me, wedsonaf@...il.com,
 aliceryhl@...gle.com, boqun.feng@...il.com
Subject: Re: [PATCH net-next v10 1/4] rust: core abstractions for network PHY
 drivers

On 12/11/23 00:49, FUJITA Tomonori wrote:
> This patch adds abstractions to implement network PHY drivers; the
> driver registration and bindings for some of callback functions in
> struct phy_driver and many genphy_ functions.
> 
> This feature is enabled with CONFIG_RUST_PHYLIB_ABSTRACTIONS=y.
> 
> This patch enables unstable const_maybe_uninit_zeroed feature for
> kernel crate to enable unsafe code to handle a constant value with
> uninitialized data. With the feature, the abstractions can initialize
> a phy_driver structure with zero easily; instead of initializing all
> the members by hand. It's supposed to be stable in the not so distant
> future.
> 
> Link: https://github.com/rust-lang/rust/pull/116218
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>

Overall looks fine to me. Just a few comments below that confuse me:

> +    /// Gets the state of PHY state machine states.
> +    pub fn state(&self) -> DeviceState {
> +        let phydev = self.0.get();
> +        // SAFETY: The struct invariant ensures that we may access
> +        // this field without additional synchronization.
> +        let state = unsafe { (*phydev).state };
> +        // TODO: this conversion code will be replaced with automatically generated code by bindgen
> +        // when it becomes possible.
> +        // better to call WARN_ONCE() when the state is out-of-range.

Did you mix up two comments here? This doesn't parse in my brain.
> +    /// Reads a given C22 PHY register.
> +    // This function reads a hardware register and updates the stats so takes `&mut self`.
> +    pub fn read(&mut self, regnum: u16) -> Result<u16> {
> +        let phydev = self.0.get();
> +        // SAFETY: `phydev` is pointing to a valid object by the type invariant of `Self`.
> +        // So an FFI call with a valid pointer.

This sentence also doesn't parse in my brain. Perhaps "So it's just an 
FFI call" or similar?

Alice