3 files changed, 78 insertions, 20 deletions

diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
index 11b03e9d7e89..dd84e2b4d7ae 100644
--- a/rust/kernel/cpufreq.rs
+++ b/rust/kernel/cpufreq.rs
@@ -13,7 +13,7 @@ use crate::{
     cpu::CpuId,
     cpumask,
     device::{Bound, Device},
-    devres::Devres,
+    devres,
     error::{code::*, from_err_ptr, from_result, to_result, Result, VTABLE_DEFAULT_ERROR},
     ffi::{c_char, c_ulong},
     prelude::*,
@@ -1046,10 +1046,13 @@ impl<T: Driver> Registration<T> {
 
     /// Same as [`Registration::new`], but does not return a [`Registration`] instance.
     ///
-    /// Instead the [`Registration`] is owned by [`Devres`] and will be revoked / dropped, once the
+    /// Instead the [`Registration`] is owned by [`devres::register`] and will be dropped, once the
     /// device is detached.
-    pub fn new_foreign_owned(dev: &Device<Bound>) -> Result {
-        Devres::new_foreign_owned(dev, Self::new()?, GFP_KERNEL)
+    pub fn new_foreign_owned(dev: &Device<Bound>) -> Result
+    where
+        T: 'static,
+    {
+        devres::register(dev, Self::new()?, GFP_KERNEL)
     }
 }
 
diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index fd8b75aa03bc..64458ca3d69f 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -9,12 +9,12 @@ use crate::{
     alloc::Flags,
     bindings,
     device::{Bound, Device},
-    error::{Error, Result},
+    error::{to_result, Error, Result},
     ffi::c_void,
     prelude::*,
     revocable::{Revocable, RevocableGuard},
     sync::{rcu, Arc, Completion},
-    types::ARef,
+    types::{ARef, ForeignOwnable},
 };
 
 #[pin_data]
@@ -184,14 +184,6 @@ impl<T: Send> Devres<T> {
         Ok(Devres(inner))
     }
 
-    /// Same as [`Devres::new`], but does not return a `Devres` instance. Instead the given `data`
-    /// is owned by devres and will be revoked / dropped, once the device is detached.
-    pub fn new_foreign_owned(dev: &Device<Bound>, data: T, flags: Flags) -> Result {
-        let _ = DevresInner::new(dev, data, flags)?;
-
-        Ok(())
-    }
-
     /// Obtain `&'a T`, bypassing the [`Revocable`].
     ///
     /// This method allows to directly obtain a `&'a T`, bypassing the [`Revocable`], by presenting
@@ -261,3 +253,64 @@ impl<T: Send> Drop for Devres<T> {
         }
     }
 }
+
+/// Consume `data` and [`Drop::drop`] `data` once `dev` is unbound.
+fn register_foreign<P>(dev: &Device<Bound>, data: P) -> Result
+where
+    P: ForeignOwnable + Send + 'static,
+{
+    let ptr = data.into_foreign();
+
+    #[allow(clippy::missing_safety_doc)]
+    unsafe extern "C" fn callback<P: ForeignOwnable>(ptr: *mut kernel::ffi::c_void) {
+        // SAFETY: `ptr` is the pointer to the `ForeignOwnable` leaked above and hence valid.
+        drop(unsafe { P::from_foreign(ptr.cast()) });
+    }
+
+    // SAFETY:
+    // - `dev.as_raw()` is a pointer to a valid and bound device.
+    // - `ptr` is a valid pointer the `ForeignOwnable` devres takes ownership of.
+    to_result(unsafe {
+        // `devm_add_action_or_reset()` also calls `callback` on failure, such that the
+        // `ForeignOwnable` is released eventually.
+        bindings::devm_add_action_or_reset(dev.as_raw(), Some(callback::<P>), ptr.cast())
+    })
+}
+
+/// Encapsulate `data` in a [`KBox`] and [`Drop::drop`] `data` once `dev` is unbound.
+///
+/// # Examples
+///
+/// ```no_run
+/// use kernel::{device::{Bound, Device}, devres};
+///
+/// /// Registration of e.g. a class device, IRQ, etc.
+/// struct Registration;
+///
+/// impl Registration {
+///     fn new() -> Self {
+///         // register
+///
+///         Self
+///     }
+/// }
+///
+/// impl Drop for Registration {
+///     fn drop(&mut self) {
+///        // unregister
+///     }
+/// }
+///
+/// fn from_bound_context(dev: &Device<Bound>) -> Result {
+///     devres::register(dev, Registration::new(), GFP_KERNEL)
+/// }
+/// ```
+pub fn register<T, E>(dev: &Device<Bound>, data: impl PinInit<T, E>, flags: Flags) -> Result
+where
+    T: Send + 'static,
+    Error: From<E>,
+{
+    let data = KBox::pin_init(data, flags)?;
+
+    register_foreign(dev, data)
+}
diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
index acb638086131..f63addaf7235 100644
--- a/rust/kernel/drm/driver.rs
+++ b/rust/kernel/drm/driver.rs
@@ -5,9 +5,7 @@
 //! C header: [`include/linux/drm/drm_drv.h`](srctree/include/linux/drm/drm_drv.h)
 
 use crate::{
-    bindings, device,
-    devres::Devres,
-    drm,
+    bindings, device, devres, drm,
     error::{to_result, Result},
     prelude::*,
     str::CStr,
@@ -130,18 +128,22 @@ impl<T: Driver> Registration<T> {
     }
 
     /// Same as [`Registration::new`}, but transfers ownership of the [`Registration`] to
-    /// [`Devres`].
+    /// [`devres::register`].
     pub fn new_foreign_owned(
         drm: &drm::Device<T>,
         dev: &device::Device<device::Bound>,
         flags: usize,
-    ) -> Result {
+    ) -> Result
+    where
+        T: 'static,
+    {
         if drm.as_ref().as_raw() != dev.as_raw() {
             return Err(EINVAL);
         }
 
         let reg = Registration::<T>::new(drm, flags)?;
-        Devres::new_foreign_owned(dev, reg, GFP_KERNEL)
+
+        devres::register(dev, reg, GFP_KERNEL)
     }
 
     /// Returns a reference to the `Device` instance for this registration.