Currently, the driver's device private data is allocated and initialized
from driver core code called from bus abstractions after the driver's
probe() callback returned the corresponding initializer.

Similarly, the driver's device private data is dropped within the
remove() callback of bus abstractions after calling the remove()
callback of the corresponding driver.

However, commit 6f61a2637abe ("rust: device: introduce
Device::drvdata()") introduced an accessor for the driver's device
private data for a Device<Bound>, i.e. a device that is currently bound
to a driver.

Obviously, this is in conflict with dropping the driver's device private
data in remove(), since a device can not be considered to be fully
unbound after remove() has finished:

We also have to consider registrations guarded by devres - such as IRQ
or class device registrations - which are torn down after remove() in
devres_release_all().

Thus, it can happen that, for instance, a class device or IRQ callback
still calls Device::drvdata(), which then runs concurrently to remove()
(which sets dev->driver_data to NULL and drops the driver's device
private data), before devres_release_all() started to tear down the
corresponding registration. This is because devres guarded registrations
can, as expected, access the corresponding Device<Bound> that defines
their scope.

In C it simply is the driver's responsibility to ensure that its device
private data is freed after e.g. an IRQ registration is unregistered.

Typically, C drivers achieve this by allocating their device private data
with e.g. devm_kzalloc() before doing anything else, i.e. before e.g.
registering an IRQ with devm_request_threaded_irq(), relying on the
reverse order cleanup of devres.

Technically, we could do something similar in Rust. However, the
resulting code would be pretty messy:

In Rust we have to differentiate between allocated but uninitialized
memory and initialized memory in the type system. Thus, we would need to
somehow keep track of whether the driver's device private data object
has been initialized (i.e. probe() was successful and returned a valid
initializer for this memory) and conditionally call the destructor of
the corresponding object when it is freed.

This is because we'd need to allocate and register the memory of the
driver's device private data *before* it is initialized by the
initializer returned by the driver's probe() callback, because the
driver could already register devres guarded registrations within
probe() outside of the driver's device private data initializer.

Luckily there is a much simpler solution: Instead of dropping the
driver's device private data at the end of remove(), we just drop it
after the device has been fully unbound, i.e. after all devres callbacks
have been processed.

For this, we introduce a new post_unbind() callback private to the
driver-core, i.e. the callback is neither exposed to drivers, nor to bus
abstractions.

This way, the driver-core code can simply continue to conditionally
allocate the memory for the driver's device private data when the
driver's initializer is returned from probe() - no change needed - and
drop it when the driver-core code receives the post_unbind() callback.

Closes: https://lore.kernel.org/all/DEZMS6Y4A7XE.XE7EUBT5SJFJ@kernel.org/
Fixes: 6f61a2637abe ("rust: device: introduce Device::drvdata()")
Acked-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Igor Korotin <igor.korotin.linux@gmail.com>
Link: https://patch.msgid.link/20260107103511.570525-7-dakr@kernel.org
[ Remove #ifdef CONFIG_RUST, rename post_unbind() to post_unbind_rust().
 - Danilo]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Add an associated type DriverData to the DriverLayout trait indicating
the type of the driver's device private data.

Acked-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Igor Korotin <igor.korotin.linux@gmail.com>
Link: https://patch.msgid.link/20260107103511.570525-6-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Add an associated const DEVICE_DRIVER_OFFSET to the DriverLayout trait
indicating the offset of the embedded struct device_driver within
Self::DriverType, i.e. the specific driver structs, such as struct
pci_driver or struct platform_driver.

Acked-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Igor Korotin <igor.korotin.linux@gmail.com>
Link: https://patch.msgid.link/20260107103511.570525-5-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

The DriverLayout trait describes the layout of a specific driver
structure, such as `struct pci_driver` or `struct platform_driver`.

In a first step, this replaces the associated type RegType of the
RegistrationOps with the DriverLayout::DriverType associated type.

Acked-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Igor Korotin <igor.korotin.linux@gmail.com>
Link: https://patch.msgid.link/20260107103511.570525-4-dakr@kernel.org
[ Rename driver::Driver to driver::DriverLayout, as it represents the
  layout of a driver structure rather than the driver structure itself.
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Implement the `AsBusDevice` trait for converting a `Device` reference to a
bus device reference for all bus devices.

The `AsBusDevice` trait allows abstractions to provide the bus device in
class device callbacks. It must not be used by drivers and is intended for
bus and class device abstractions only.

Signed-off-by: Markus Probst <markus.probst@posteo.de>
Link: https://patch.msgid.link/20251027200547.1038967-2-markus.probst@posteo.de
[ * Remove unused import.
  * Change visibility of AsBusDevice to public.
  * Fix build for USB.
  * Add impl for I2cClient.
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Currently request_irq_by_index() returns

        Result<impl PinInit<irq::Registration<T>, Error> + 'a>

which may carry an error in the Result or the initializer; the same is
true for the other IRQ methods.

Use pin_init::pin_init_scope() to get rid of this redundancy.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251103203053.2348783-2-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Let T be the actual private driver data type without the surrounding
box, as it leaves less room for potential bugs.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

The driver model defines the lifetime of the private data stored in (and
owned by) a bus device to be valid from when the driver is bound to a
device (i.e. from successful probe()) until the driver is unbound from
the device.

This is already taken care of by the Rust implementation of the driver
model. However, we still ask drivers to return a Result<Pin<KBox<Self>>>
from probe().

Unlike in C, where we do not have the concept of initializers, but
rather deal with uninitialized memory, drivers can just return an
impl PinInit<Self, Error> instead.

This contributes to more clarity to the fact that a driver returns it's
device private data in probe() and the Rust driver model owns the data,
manages the lifetime and - considering the lifetime - provides (safe)
accessors for the driver.

Hence, let probe() functions return an impl PinInit<Self, Error> instead
of Result<Pin<KBox<Self>>>.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Update call sites in the driver-core files and its related samples
to import `ARef` and `AlwaysRefCounted` from `sync::aref`
instead of `types`.

This aligns with the ongoing effort to move `ARef` and
`AlwaysRefCounted` to sync.

Suggested-by: Benno Lossin <lossin@kernel.org>
Link: https://github.com/Rust-for-Linux/linux/issues/1173
Signed-off-by: Shankari Anand <shankari.ak0208@gmail.com>
Link: https://lore.kernel.org/r/20250814104615.355106-1-shankari.ak0208@gmail.com
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

These accessors can be used to retrieve a irq::Registration and
irq::ThreadedRegistration from a platform device by
index or name. Alternatively, drivers can retrieve an IrqRequest from a
bound platform device for later use.

These accessors ensure that only valid IRQ lines can ever be registered.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Joel Fernandes <joelagnelf@nvidia.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://lore.kernel.org/r/20250811-topics-tyr-request_irq2-v9-5-0485dcd9bcbf@collabora.com
[ Remove expect(dead_code) from IrqRequest::new(), re-format macros and
  macro invocations to not exceed 100 characters line length. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>