Re: [PATCH v8 3/5] rust: add basic serial device bus abstractions

[Markus Probst]

On Sat, 2026-05-30 at 18:14 +0200, Danilo Krummrich wrote:
> On Sat May 30, 2026 at 4:51 PM CEST, Markus Probst wrote:
> > On Sat, 2026-05-30 at 16:35 +0200, Danilo Krummrich wrote:
> > > On Sat May 30, 2026 at 4:27 PM CEST, Markus Probst wrote:
> > > > This would work, but I don't see how it would get rid of rust_private_data in
> > > > this way. The device private data will but the private bus abstraction data
> > > > needs to outlive the devres callbacks (which is done by rust_private_data).
> > > 
> > > Why? You only ever use it in the receive callback, which won't be called after
> > > device unbind anymore.
> > Because the possibility exists that some classdev ops or Drop calls
> > e.g. sdev.set_baudrate. This is a null pointer dereference after
> > serdev_device_close has been called. I interpreted it to add a state to
> > the abstraction private data which would prevent those calls (early
> > return with error) after serdev_device_close has been called, but this
> > would only work if it outlives these calls.
> > 
> > But it seems you were refering to something else with the state?
> 
> Yes, but I just notice that I'm a step ahead. With the lifetime model class
> device registrations shouldn't be guarded with Devres anymore, but with a
> lifetime.
> 
> (This also entirely eliminates the need for having different devres stages to
> prevent drivers from smuggling a newly created Devres object into an existing
> Devres<Registration<T>>'s data, which would be unsound for obvious reasons.)
> 
> With this there is no way there are still class device callbacks after the bus
> device private data has been dropped in the first place.
There would still be Drop, which can access the device.
Drop happens after remove_callback.

Might be simpler for now: I can use a mutex to prevent calls in
receive_buf after remove_callback has been called.

Thanks
- Markus Probst

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