Re: [PATCH v3 1/2] rust: miscdevice: add additional data to MiscDeviceRegistration

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Wed, May 21, 2025 at 01:55:36PM +0200, Greg Kroah-Hartman wrote:
> On Sat, May 17, 2025 at 03:42:29PM +0200, Danilo Krummrich wrote:
> > On Sat, May 17, 2025 at 01:33:49PM +0200, Christian Schrefl wrote:
> > > +pub struct MiscDeviceRegistration<T: MiscDevice> {
> > >      #[pin]
> > >      inner: Opaque<bindings::miscdevice>,
> > > +    #[pin]
> > > +    data: UnsafePinned<T::RegistrationData>,
> > >      _t: PhantomData<T>,
> > >  }
> > 
> > I recommend not to store data within a Registration type itself.
> > 
> > I know that this is designed with the focus on using misc device directly from
> > the module scope; and in this context it works great.
> > 
> > However, it becomes quite suboptimal when used from a driver scope. For
> > instance, if the misc device is registered within a platform driver's probe()
> > function.
> > 
> > I know this probably isn't supported yet. At least, I assume it isn't supported
> > "officially", given that the abstraction does not provide an option to set a
> > parent device. Yet I think we should consider it.
> 
> It's going to be a requirement to properly set the parent device, and
> as you point out, this really should be in some sort of scope, not just
> a module.
> 
> But, we have two types of users of a misc device, one like this is
> written, for a module-scope, and one for the "normal" device scope.  The
> device scope is going to be tricker as it can, and will, get
> disconnected from the device separately from the misc device lifespan,
> so when that logic is added, it's going to be tricky as you point out.
> 
> So I'll take this now, but in the future this is going to have to be
> cleaned up and modified.

Nope, can't take it, it breaks the build from my tree:

error[E0432]: unresolved import `crate::types::UnsafePinned`
  --> rust/kernel/miscdevice.rs:20:37
   |
20 |     types::{ForeignOwnable, Opaque, UnsafePinned},
   |                                     ^^^^^^^^^^^^ no `UnsafePinned` in `types`

error[E0432]: unresolved import `pin_init::Wrapper`
  --> rust/kernel/miscdevice.rs:23:5
   |
23 | use pin_init::Wrapper;
   |     ^^^^^^^^^^^^^^^^^ no `Wrapper` in the root

error: aborting due to 2 previous errors

:(