linux-kernel - Re: [net-next PATCH v11 1/6] net: phy: pass PHY driver to .match_phy

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Message-Id: <D9YA78RFVQMH.QPUFXMHSVU7V@kernel.org>
Date: Sat, 17 May 2025 10:09:53 +0200
From: "Benno Lossin" <lossin@...nel.org>
To: "Christian Marangi" <ansuelsmth@...il.com>, "Andrew Lunn"
 <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, "Eric
 Dumazet" <edumazet@...gle.com>, "Jakub Kicinski" <kuba@...nel.org>, "Paolo
 Abeni" <pabeni@...hat.com>, "Rob Herring" <robh@...nel.org>, "Krzysztof
 Kozlowski" <krzk+dt@...nel.org>, "Conor Dooley" <conor+dt@...nel.org>,
 "Heiner Kallweit" <hkallweit1@...il.com>, "Russell King"
 <linux@...linux.org.uk>, "Florian Fainelli"
 <florian.fainelli@...adcom.com>, "Broadcom internal kernel review list"
 <bcm-kernel-feedback-list@...adcom.com>, Marek Behún
 <kabel@...nel.org>, "Andrei Botila" <andrei.botila@....nxp.com>, "FUJITA
 Tomonori" <fujita.tomonori@...il.com>, "Trevor Gross" <tmgross@...ch.edu>,
 "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>, "Danilo Krummrich" <dakr@...nel.org>,
 "Sabrina Dubroca" <sd@...asysnail.net>, "Michael Klein"
 <michael@...sekall.de>, "Daniel Golle" <daniel@...rotopia.org>,
 <netdev@...r.kernel.org>, <devicetree@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <rust-for-linux@...r.kernel.org>
Cc: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
Subject: Re: [net-next PATCH v11 1/6] net: phy: pass PHY driver to
 .match_phy_device OP

On Fri May 16, 2025 at 11:23 PM CEST, Christian Marangi wrote:
> diff --git a/rust/kernel/net/phy.rs b/rust/kernel/net/phy.rs
> index a59469c785e3..079a0f884887 100644
> --- a/rust/kernel/net/phy.rs
> +++ b/rust/kernel/net/phy.rs
> @@ -418,15 +418,18 @@ impl<T: Driver> Adapter<T> {
>  
>      /// # Safety
>      ///
> -    /// `phydev` must be passed by the corresponding callback in `phy_driver`.
> +    /// `phydev` and `phydrv` must be passed by the corresponding callback in
> +    //  `phy_driver`.
>      unsafe extern "C" fn match_phy_device_callback(
>          phydev: *mut bindings::phy_device,
> +        phydrv: *const bindings::phy_driver,
>      ) -> crate::ffi::c_int {
>          // SAFETY: This callback is called only in contexts
>          // where we hold `phy_device->lock`, so the accessors on
>          // `Device` are okay to call.
>          let dev = unsafe { Device::from_raw(phydev) };
> -        T::match_phy_device(dev) as i32
> +        let drv = unsafe { T::from_raw(phydrv) };
> +        T::match_phy_device(dev, drv) as i32
>      }
>  
>      /// # Safety
> @@ -574,6 +577,19 @@ pub const fn create_phy_driver<T: Driver>() -> DriverVTable {
>  /// This trait is used to create a [`DriverVTable`].
>  #[vtable]
>  pub trait Driver {
> +    /// # Safety
> +    ///
> +    /// For the duration of `'a`, the pointer must point at a valid
> +    /// `phy_driver`, and the caller must be in a context where all
> +    /// methods defined on this struct are safe to call.
> +    unsafe fn from_raw<'a>(ptr: *const bindings::phy_driver) -> &'a DriverVTable {
> +        // CAST: `DriverVTable` is a `repr(transparent)` wrapper around `bindings::phy_driver`.
> +        let ptr = ptr.cast::<DriverVTable>();
> +        // SAFETY: by the function requirements the pointer is const and is
> +        // always valid to access for the duration of `'a`.
> +        unsafe { &*ptr }
> +    }

If we go the way of supplying a `&DriverVTable` in the
`match_phy_device` function, then this should be a function in the impl
block of `DriverVTable` and not in `Driver`.

See my reply to Fujita on the previous version, I don't think that we
need to add the `DriverVTable` to the `match_phy_device` function if we
don't provide accessor methods. Currently that isn't needed, so you only
need the hunks above this one. (I'd wait for Fujita's reply though).

---
Cheers,
Benno

> +
>      /// Defines certain other features this PHY supports.
>      /// It is a combination of the flags in the [`flags`] module.
>      const FLAGS: u32 = 0;
> @@ -602,7 +618,7 @@ fn get_features(_dev: &mut Device) -> Result {
>  
>      /// Returns true if this is a suitable driver for the given phydev.
>      /// If not implemented, matching is based on [`Driver::PHY_DEVICE_ID`].
> -    fn match_phy_device(_dev: &Device) -> bool {
> +    fn match_phy_device(_dev: &mut Device, _drv: &DriverVTable) -> bool {
>          false
>      }
>