Re: [PATCH 5/5] rust: serdev: Pause receive callback before calling unbind

[Markus Probst <markus.probst@posteo.de>]

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On Sun, 2026-09-06 at 18:20 +0200, Danilo Krummrich wrote:
> On Sun Sep 6, 2026 at 5:55 PM CEST, Markus Probst wrote:
> > @@ -200,10 +203,14 @@ extern "C" fn receive_buf_callback(
> >          // INVARIANT: `sdev` is valid for the duration of `receive_buf_callback()`.
> >          let sdev = unsafe { &*sdev.cast::<Device<device::BoundInternal>>() };
> >  
> > -        // SAFETY: `receive_buf_callback` is only ever called after a successful call to
> > -        // `probe_callback`, hence it's guaranteed that `Device::set_drvdata()` has been called
> > -        // and stored a `Pin<KBox<PrivateData<'_, T>>>`.
> > -        let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
> > +        // SAFETY:
> > +        // - `receive_buf_callback` is only ever called after a successful call to `probe_callback`,
> > +        //   hence it's guaranteed that `Device::set_drvdata()` has been called and stored a
> > +        //   `Pin<KBox<PrivateData<'_, T>>>`.
> > +        // - `unbind_callback` calls `serdev_device_pause_rx` before accessing the driver data,
> > +        //   which guarantees that this function will not overlap with it. Thus we have exclusive
> > +        //   access.
> > +        let private_data = unsafe { sdev.as_ref().drvdata_borrow_mut::<PrivateData<'_, T>>() };
> 
> This would break the driver core's lifetime design. Any kind of registration
> (such as class device, auxiliary, IRQ, etc.) may borrow fields from the bus
> device private data. The whole design is based on the guarantee that we never
> construct a mutable reference of the bus device private data.
Thanks for the info.

That explains why unbind doesn't provide a mutable reference on
platform drivers either.

I will drop the 2 patches in the next revision.

Thanks
- Markus Probst

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