Currently, we do not ensure that APIs that require a bound device instance can
only be called with a bound device.

Examples of such APIs are Devres, dma::CoherentAllocation and
pci::Device::iomap_region().

This patch series introduces the "Bound" device context such that we can ensure
to only ever pass a bound device to APIs that require this precondition.

In order to get there, we need some prerequisites:

(1) Implement macros to consistently derive Deref implementations for the
    different device contexts. For instance, Device<Core> can be dereferenced to
    Device<Bound>, since all device references we get from "core" bus callbacks
    are guaranteed to be from a bound device. Device<Bound> can always be
    dereferenced to Device (i.e. Device<Normal>), since the "Normal" device
    context has no specific requirements.

(2) Implement device context support for the generic Device type. Some APIs such
    as Devres and dma::CoherentAllocation work with generic devices.

(3) Preserve device context generics in bus specific device' AsRef
    implementation, such that we can derive the device context when converting
    from a bus specific device reference to a generic device reference.

With this, Devres::new(), for instance, can take a &Device<Bound> argument and
hence ensure that it can't be called with a Device reference that is not
guaranteed to be bound to a driver.

A branch containing the patches can be found in [1].

[1] https://web.git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=rust/device-bound

Changes in v2:
  - add a safety requirement for impl_device_context_deref! (thanks to Benno for
    working this out)

Danilo Krummrich (9):
  rust: device: implement impl_device_context_deref!
  rust: device: implement impl_device_context_into_aref!
  rust: device: implement device context for Device
  rust: platform: preserve device context in AsRef
  rust: pci: preserve device context in AsRef
  rust: device: implement Bound device context
  rust: pci: move iomap_region() to impl Device<Bound>
  rust: devres: require a bound device
  rust: dma: require a bound device

 rust/kernel/device.rs   | 90 ++++++++++++++++++++++++++++++++++++++++-
 rust/kernel/devres.rs   | 17 ++++----
 rust/kernel/dma.rs      | 14 +++----
 rust/kernel/pci.rs      | 33 +++++----------
 rust/kernel/platform.rs | 32 ++++-----------
 5 files changed, 121 insertions(+), 65 deletions(-)


base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
-- 
2.49.0

On Sun, Apr 13, 2025 at 07:36:55PM +0200, Danilo Krummrich wrote:
> Currently, we do not ensure that APIs that require a bound device instance can
> only be called with a bound device.
> 
> Examples of such APIs are Devres, dma::CoherentAllocation and
> pci::Device::iomap_region().
> 
> This patch series introduces the "Bound" device context such that we can ensure
> to only ever pass a bound device to APIs that require this precondition.
> 
> In order to get there, we need some prerequisites:
> 
> (1) Implement macros to consistently derive Deref implementations for the
>     different device contexts. For instance, Device<Core> can be dereferenced to
>     Device<Bound>, since all device references we get from "core" bus callbacks
>     are guaranteed to be from a bound device. Device<Bound> can always be
>     dereferenced to Device (i.e. Device<Normal>), since the "Normal" device
>     context has no specific requirements.
> 
> (2) Implement device context support for the generic Device type. Some APIs such
>     as Devres and dma::CoherentAllocation work with generic devices.
> 
> (3) Preserve device context generics in bus specific device' AsRef
>     implementation, such that we can derive the device context when converting
>     from a bus specific device reference to a generic device reference.
> 
> With this, Devres::new(), for instance, can take a &Device<Bound> argument and
> hence ensure that it can't be called with a Device reference that is not
> guaranteed to be bound to a driver.
> 
> A branch containing the patches can be found in [1].
> 
> [1] https://web.git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=rust/device-bound

With the following changes, applied to driver-core/topic/device-context, thanks!

  *  Add missing `::` prefix in macros.
  *  Fix typos pointed out by Bjorn.

- Danilo