netdev - Re: [net-next PATCH v10 7/7] rust: net::phy sync with match_phy

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Message-Id: <20250517.152735.1375764560545086525.fujita.tomonori@gmail.com>
Date: Sat, 17 May 2025 15:27:35 +0900 (JST)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: lossin@...nel.org
Cc: ansuelsmth@...il.com, fujita.tomonori@...il.com, andrew+netdev@...n.ch,
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Subject: Re: [net-next PATCH v10 7/7] rust: net::phy sync with
 match_phy_device C changes

Thanks for the review!

On Fri, 16 May 2025 22:16:23 +0200
"Benno Lossin" <lossin@...nel.org> wrote:

> On Fri May 16, 2025 at 5:12 PM CEST, Christian Marangi wrote:
>> On Fri, May 16, 2025 at 04:48:53PM +0200, Benno Lossin wrote:
>>> On Fri May 16, 2025 at 2:30 PM CEST, FUJITA Tomonori wrote:
>>> > On Thu, 15 May 2025 13:27:12 +0200
>>> > Christian Marangi <ansuelsmth@...il.com> wrote:
>>> >> @@ -574,6 +577,23 @@ 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 Self
>>> >> +    where
>>> >> +        Self: Sized,
>>> >> +    {
>>> >> +        // CAST: `Self` is a `repr(transparent)` wrapper around `bindings::phy_driver`.
>>> >> +        let ptr = ptr.cast::<Self>();
>>> >> +        // SAFETY: by the function requirements the pointer is valid and we have unique access for
>>> >> +        // the duration of `'a`.
>>> >> +        unsafe { &*ptr }
>>> >> +    }
>>> >
>>> > We might need to update the comment. phy_driver is const so I think
>>> > that we can access to it any time.
>>> 
>>> Why is any type implementing `Driver` a transparent wrapper around
>>> `bindings::phy_driver`?
>>> 
>>
>> Is this referred to a problem with using from_raw or more of a general
>> question on how the rust wrapper are done for phy code?
> 
> I looked at the `phy.rs` file again and now I'm pretty sure the above
> code is wrong. `Self` can be implemented on any type (even types like
> `Infallible` that do not have any valid bit patterns, since it's an
> empty enum). The abstraction for `bindings::phy_driver` is
> `DriverVTable` not an object of type `Self`, so you should cast to that
> pointer instead.

Yeah.

I don't want to delay this patchset due to Rust side changes so
casting a pointer to bindings::phy_driver to DriverVTable is ok but
the following signature doesn't look useful for Rust phy drivers:

fn match_phy_device(_dev: &mut Device, _drv: &DriverVTable) -> bool

struct DriverVTable is only used to create an array of
bindings::phy_driver for C side, and it doesn't provide any
information to the Rust driver.

In match_phy_device(), for example, a device driver accesses to
PHY_DEVICE_ID, which the Driver trait provides. I think we need to
create an instance of the device driver's own type that implements the
Driver trait and make it accessible.