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A TypeId is stored alongside the data for runtime type > checking, making Device::registration_data() a safe method. I wonder if we could require auxillary drivers to specify a type, and then = the abstraction would check if the type matches; if it matches, it create a `&Device` and `probe`, otherwise it skips over the driver complete= ly. This gets rid of the failure path. > > Signed-off-by: Danilo Krummrich > --- > drivers/gpu/nova-core/driver.rs | 10 +- > include/linux/auxiliary_bus.h | 4 + > rust/kernel/auxiliary.rs | 208 ++++++++++++++++++-------- > samples/rust/rust_driver_auxiliary.rs | 40 +++-- > 4 files changed, 180 insertions(+), 82 deletions(-) > > diff --git a/drivers/gpu/nova-core/driver.rs b/drivers/gpu/nova-core/driv= er.rs > index 84b0e1703150..8fe484d357f6 100644 > --- a/drivers/gpu/nova-core/driver.rs > +++ b/drivers/gpu/nova-core/driver.rs > @@ -32,8 +32,7 @@ > pub(crate) struct NovaCore { > #[pin] > pub(crate) gpu: Gpu, > - #[pin] > - _reg: Devres, > + _reg: Devres>, > } > =20 > const BAR0_SIZE: usize =3D SZ_16M; > @@ -96,14 +95,15 @@ fn probe(pdev: &pci::Device, _info: &Self::IdIn= fo) -> impl PinInit =20 > Ok(try_pin_init!(Self { > gpu <- Gpu::new(pdev, bar.clone(), bar.access(pdev.as_re= f())?), > - _reg <- auxiliary::Registration::new( > + _reg: auxiliary::Registration::new( > pdev.as_ref(), > c"nova-drm", > // TODO[XARR]: Use XArray or perhaps IDA for proper = ID allocation/recycling. For > // now, use a simple atomic counter that never recyc= les IDs. > AUXILIARY_ID_COUNTER.fetch_add(1, Relaxed), > - crate::MODULE_NAME > - ), > + crate::MODULE_NAME, > + (), > + )?, > })) > }) > } > diff --git a/include/linux/auxiliary_bus.h b/include/linux/auxiliary_bus.= h > index bc09b55e3682..4e1ad8ccbcdd 100644 > --- a/include/linux/auxiliary_bus.h > +++ b/include/linux/auxiliary_bus.h > @@ -62,6 +62,9 @@ > * @sysfs.irqs: irqs xarray contains irq indices which are used by the d= evice, > * @sysfs.lock: Synchronize irq sysfs creation, > * @sysfs.irq_dir_exists: whether "irqs" directory exists, > + * @registration_data_rust: private data owned by the registering (paren= t) > + * driver; valid for as long as the device is > + * registered with the driver core, > * > * An auxiliary_device represents a part of its parent device's function= ality. > * It is given a name that, combined with the registering drivers > @@ -148,6 +151,7 @@ struct auxiliary_device { > struct mutex lock; /* Synchronize irq sysfs creation */ > bool irq_dir_exists; > } sysfs; > + void *registration_data_rust; > }; > =20 > /** > diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs > index 93c0db1f6655..467befea8e44 100644 > --- a/rust/kernel/auxiliary.rs > +++ b/rust/kernel/auxiliary.rs > @@ -19,12 +19,17 @@ > to_result, // > }, > prelude::*, > - types::Opaque, > + types::{ > + ForeignOwnable, > + Opaque, // > + }, > ThisModule, // > }; > use core::{ > + any::TypeId, > marker::PhantomData, > mem::offset_of, > + pin::Pin, > ptr::{ > addr_of_mut, > NonNull, // > @@ -257,6 +262,40 @@ pub fn parent(&self) -> &device::Device { > // SAFETY: A bound auxiliary device always has a bound parent de= vice. > unsafe { parent.as_bound() } > } > + > + /// Returns a pinned reference to the registration data set by the r= egistering (parent) driver. > + /// > + /// Returns [`EINVAL`] if `T` does not match the type used by the pa= rent driver when calling > + /// [`Registration::new()`]. > + /// > + /// Returns [`ENOENT`] if no registration data has been set, e.g. wh= en the device was > + /// registered by a C driver. > + pub fn registration_data(&self) -> Result> { Any reason that this is not just `Result<&T>`? > + // SAFETY: By the type invariant, `self.as_raw()` is a valid `st= ruct auxiliary_device`. > + let ptr =3D unsafe { (*self.as_raw()).registration_data_rust }; > + if ptr.is_null() { I think we could treat C-registered aux devices as if their data is `()`. So you could do if TypeId::of::() !=3D TypeId::of::<()> { return Err(EINVAL); } return Ok(Pin::static_ref(&())); here. Best, Gary > + dev_warn!( > + self.as_ref(), > + "No registration data set; parent is not a Rust driver.\= n" > + ); > + return Err(ENOENT); > + } > + > + // SAFETY: `ptr` is non-null and was set via `into_foreign()` in= `Registration::new()`; > + // `RegistrationData` is `#[repr(C)]` with `type_id` at offset 0= , so reading a `TypeId` > + // at the start of the allocation is valid regardless of `T`. > + let type_id =3D unsafe { ptr.cast::().read() }; > + if type_id !=3D TypeId::of::() { > + return Err(EINVAL); > + } > + > + // SAFETY: The `TypeId` check above confirms that the stored typ= e is `T`; `ptr` remains > + // valid until `Registration::drop()` calls `from_foreign()`. > + let wrapper =3D unsafe { Pin::>>::borro= w(ptr) }; > + > + // SAFETY: `data` is a structurally pinned field of `Registratio= nData`. > + Ok(unsafe { wrapper.map_unchecked(|w| &w.data) }) > + } > } > =20