netdev - Re: [PATCH net-next v7 1/5] rust: core abstractions for network PHY drivers

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Message-ID: <0e858596-51b7-458c-a4eb-fa1e192e1ab3@proton.me>
Date: Sat, 28 Oct 2023 18:45:40 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Andrew Lunn <andrew@...n.ch>
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>, boqun.feng@...il.com, netdev@...r.kernel.org, rust-for-linux@...r.kernel.org, tmgross@...ch.edu, miguel.ojeda.sandonis@...il.com, wedsonaf@...il.com
Subject: Re: [PATCH net-next v7 1/5] rust: core abstractions for network PHY drivers

On 28.10.23 20:23, Andrew Lunn wrote:
> On Sat, Oct 28, 2023 at 04:37:53PM +0000, Benno Lossin wrote:
>> On 28.10.23 11:27, FUJITA Tomonori wrote:
>>> On Fri, 27 Oct 2023 21:19:38 +0000
>>> Benno Lossin <benno.lossin@...ton.me> wrote:
>>>> I did not notice this before, but this means we cannot use the `link`
>>>> function from bindgen, since that takes `&self`. We would need a
>>>> function that takes `*const Self` instead.
>>>
>>> Implementing functions to access to a bitfield looks tricky so we need
>>> to add such feature to bindgen or we add getters to the C side?
>>
>> Indeed, I just opened an issue [1] on the bindgen repo.
>>
>> [1]: https://github.com/rust-lang/rust-bindgen/issues/2674
> 
> Please could you help me understand the consequences here. Are you
> saying the rust toolchain is fatally broken here, it cannot generate
> valid code at the moment? As a result we need to wait for a new
> version of bindgen?
This only affects bitfields, since they require special accessor functions
generated by bindgen, so I would not say that the toolchain is fatally broken.
It also is theoretically possible to manually access the bitfields in a correct
manner, but that is error prone (which is why we use the accessor functions
provided by bindgen).

In this particular case we have three options:
1. wait until bindgen provides a raw accessor function that allows to use
    only raw pointers.
2. create some C helper functions for the bitfield access that will be replaced
    by the bindgen functions once bindgen has updated.
3. Since for the `phy_device` bindings, we only ever call functions while holding
    the `phy_device.lock` lock (at least I think that this is correct) we might be
    able to get away with creating a reference to the object and use the current
    accessor functions anyway.

But for point 3 I will have to consult the others.

-- 
Cheers,
Benno