linux-kernel - Re: [PATCH RFC 2/4] rust: add basic serial device bus abstractions

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Message-ID: <40a161f055ad3410bba82c1a07fb3c674241c599.camel@posteo.de>
Date: Sun, 08 Feb 2026 14:30:54 +0000
From: Markus Probst <markus.probst@...teo.de>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Kari Argillander <kari.argillander@...il.com>, Rob Herring
 <robh@...nel.org>,  Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri
 Slaby <jirislaby@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,  Boqun Feng
 <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron	 <bjorn3_gh@...tonmail.com>, Benno
 Lossin <lossin@...nel.org>, Andreas Hindborg	 <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross	 <tmgross@...ch.edu>,
 linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH RFC 2/4] rust: add basic serial device bus abstractions

On Tue, 2026-01-13 at 18:37 +0100, Danilo Krummrich wrote:
> On Tue Jan 13, 2026 at 5:15 PM CET, Markus Probst wrote:
> > > > +impl<T: Driver + 'static> Adapter<T> {
> > > > +    const OPS: &'static bindings::serdev_device_ops = &bindings::serdev_device_ops {
> > > > +        receive_buf: if T::HAS_RECEIVE {
> > > > +            Some(Self::receive_buf_callback)
> > > > +        } else {
> > > > +            None
> > > > +        },
> > > > +        write_wakeup: if T::HAS_WRITE_WAKEUP {
> > > > +            Some(Self::write_wakeup_callback)
> > > > +        } else {
> > > > +            Some(bindings::serdev_device_write_wakeup)
> > > > +        },
> > > > +    };
> > > > +    const INITIAL_OPS: &'static bindings::serdev_device_ops = &bindings::serdev_device_ops {
> > > > +        receive_buf: Some(Self::initial_receive_buf_callback),
> > > > +        write_wakeup: if T::HAS_WRITE_WAKEUP_INITIAL {
> > > > +            Some(Self::initial_write_wakeup_callback)
> > > > +        } else {
> > > > +            Some(bindings::serdev_device_write_wakeup)
> > > > +        },
> > > > +    };
> > > > +    const NO_OPS: &'static bindings::serdev_device_ops = &bindings::serdev_device_ops {
> > > > +        receive_buf: None,
> > > > +        write_wakeup: Some(bindings::serdev_device_write_wakeup),
> > > > +    };
> > > > +
> > > > +    extern "C" fn probe_callback(sdev: *mut bindings::serdev_device) -> kernel::ffi::c_int {
> > > > +        // SAFETY: The serial device bus only ever calls the probe callback with a valid pointer to
> > > > +        // a `struct serdev_device`.
> > > > +        //
> > > > +        // INVARIANT: `sdev` is valid for the duration of `probe_callback()`.
> > > > +        let sdev = unsafe { &*sdev.cast::<Device<device::CoreInternal>>() };
> > > > +        let info = <Self as driver::Adapter>::id_info(sdev.as_ref());
> > > > +
> > > > +        from_result(|| {
> > > > +            let data = try_pin_init!(Drvdata {
> > > > +                driver <- T::probe(sdev, info),
> > > > +                initial_data: Some(Default::default()).into(),
> > > > +                late_probe_data: None.into(),
> > > > +            });
> > > > +
> > > > +            sdev.as_ref().set_drvdata(data)?;
> 
> This does not work, a driver can obtain its device private data with
> Device::<Bound>::drvdata() [1].
> 
> For this the driver must assert the correct type, but since you use a private
> type instead of the type given by the driver, i.e. T, Device::<Bound>::drvdata()
> will always fail for the driver.
> 
> [1] https://rust.docs.kernel.org/kernel/device/struct.Device.html#method.drvdata
> 
What do you suggest as alternative? Besides from the "initial data"
debate, I still need to store at least one `Completion` to ensure
safety.

Thanks
- Markus Probst

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