Re: [PATCH v5 13/19] rust: drm: Wrap ioctl dispatch in RegistrationGuard

On Sun Jun 28, 2026 at 11:53 PM JST, Danilo Krummrich wrote:
> Ioctl handlers now receive a &Device<T, Registered> reference, proving
> at the type level that the device is registered and its parent bus
> device is bound.

nit: the non-imperative style makes it sound a bit like this is the
pre-patch state. Maybe change to something like "Make ioctl handlers
receive...".

>
> This is achieved by calling registration_guard() on the Device<T, Ioctl>
> obtained in ioctl dispatch context. If the device has been unplugged,
> the ioctl returns -ENODEV without calling the handler.
>
> To resolve the driver type parameter T for type inference, which the
> compiler cannot propagate through method resolution and associated-type
> projections alone, a dead-code closure and a helper function are used as
> a type-inference anchor.
>
> Reviewed-by: Lyude Paul <[email protected]>
> Signed-off-by: Danilo Krummrich <[email protected]>
> ---
>  drivers/gpu/drm/nova/file.rs | 12 ++++++----
>  drivers/gpu/drm/tyr/file.rs  |  7 ++++--
>  rust/kernel/drm/ioctl.rs     | 45 +++++++++++++++++++++++++++++++++---
>  3 files changed, 55 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/nova/file.rs b/drivers/gpu/drm/nova/file.rs
> index a3b7bd36792c..19fb89b28984 100644
> --- a/drivers/gpu/drm/nova/file.rs
> +++ b/drivers/gpu/drm/nova/file.rs
> @@ -4,7 +4,11 @@
>  use crate::gem::NovaObject;
>  use kernel::{
>      alloc::flags::*,
> -    drm::{self, gem::BaseObject},
> +    drm::{
> +        self,
> +        gem::BaseObject,
> +        Registered, //
> +    },
>      pci,
>      prelude::*,
>      uapi,
> @@ -23,7 +27,7 @@ fn open(_dev: &NovaDevice) -> Result<Pin<KBox<Self>>> {
>  impl File {
>      /// IOCTL: get_param: Query GPU / driver metadata.
>      pub(crate) fn get_param(
> -        dev: &NovaDevice,
> +        dev: &NovaDevice<Registered>,
>          getparam: &mut uapi::drm_nova_getparam,
>          _file: &drm::File<File>,
>      ) -> Result<u32> {
> @@ -43,7 +47,7 @@ pub(crate) fn get_param(
>  
>      /// IOCTL: gem_create: Create a new DRM GEM object.
>      pub(crate) fn gem_create(
> -        dev: &NovaDevice,
> +        dev: &NovaDevice<Registered>,
>          req: &mut uapi::drm_nova_gem_create,
>          file: &drm::File<File>,
>      ) -> Result<u32> {
> @@ -56,7 +60,7 @@ pub(crate) fn gem_create(
>  
>      /// IOCTL: gem_info: Query GEM metadata.
>      pub(crate) fn gem_info(
> -        _dev: &NovaDevice,
> +        _dev: &NovaDevice<Registered>,
>          req: &mut uapi::drm_nova_gem_info,
>          file: &drm::File<File>,
>      ) -> Result<u32> {
> diff --git a/drivers/gpu/drm/tyr/file.rs b/drivers/gpu/drm/tyr/file.rs
> index 31411da203c5..fb9233eae01c 100644
> --- a/drivers/gpu/drm/tyr/file.rs
> +++ b/drivers/gpu/drm/tyr/file.rs
> @@ -1,7 +1,10 @@
>  // SPDX-License-Identifier: GPL-2.0 or MIT
>  
>  use kernel::{
> -    drm,
> +    drm::{
> +        self,
> +        Registered, //
> +    },
>      prelude::*,
>      uaccess::UserSlice,
>      uapi, //
> @@ -28,7 +31,7 @@ fn open(_dev: &drm::Device<Self::Driver>) -> Result<Pin<KBox<Self>>> {
>  
>  impl TyrDrmFileData {
>      pub(crate) fn dev_query(
> -        ddev: &TyrDrmDevice,
> +        ddev: &TyrDrmDevice<Registered>,
>          devquery: &mut uapi::drm_panthor_dev_query,
>          _file: &TyrDrmFile,
>      ) -> Result<u32> {
> diff --git a/rust/kernel/drm/ioctl.rs b/rust/kernel/drm/ioctl.rs
> index 6f5a9877bdae..f24cf7b146a8 100644
> --- a/rust/kernel/drm/ioctl.rs
> +++ b/rust/kernel/drm/ioctl.rs
> @@ -70,6 +70,18 @@ pub mod internal {
>      pub use bindings::drm_device;
>      pub use bindings::drm_file;
>      pub use bindings::drm_ioctl_desc;
> +
> +    /// Reinterpret a pointer to a DRM device with a different [`DeviceContext`], preserving the

This sentence makes it sound like the origin and destination contexts
are parameters, but this helper only does `Ioctl` to `Registered`.

> +    /// driver type parameter `T`.
> +    ///
> +    /// Used by [`declare_drm_ioctls!`] to anchor type inference.
> +    #[doc(hidden)]
> +    #[inline]
> +    pub const fn __dev_ctx_cast<T: crate::drm::Driver>(
> +        ptr: *const crate::drm::Device<T, crate::drm::Ioctl>,
> +    ) -> *const crate::drm::Device<T, crate::drm::Registered> {
> +        ptr.cast()
> +    }
>  }

The points above really are nits though.

Reviewed-by: Alexandre Courbot <[email protected]>