[PATCH v2] rust: drm/gem: Remove Object.dev

[PATCH v2] rust: drm/gem: Remove Object.dev

[Lyude Paul]

I noticed by chance that there's actually already a pointer to this in
struct drm_gem_object. So, no use in carrying this around!

Signed-off-by: Lyude Paul <lyude@redhat.com>
Acked-by: Danilo Krummrich <dakr@kernel.org>
---
V2:
* Improve safety comment in Object.dev()

 rust/kernel/drm/gem/mod.rs | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs
index 30c853988b942..d984148403679 100644
--- a/rust/kernel/drm/gem/mod.rs
+++ b/rust/kernel/drm/gem/mod.rs
@@ -187,12 +187,10 @@ impl<T: IntoGEMObject> BaseObject for T {}
 /// Invariants
 ///
 /// - `self.obj` is a valid instance of a `struct drm_gem_object`.
-/// - `self.dev` is always a valid pointer to a `struct drm_device`.
 #[repr(C)]
 #[pin_data]
 pub struct Object<T: DriverObject + Send + Sync> {
     obj: Opaque<bindings::drm_gem_object>,
-    dev: NonNull<drm::Device<T::Driver>>,
     #[pin]
     data: T,
 }
@@ -222,9 +220,6 @@ pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
             try_pin_init!(Self {
                 obj: Opaque::new(bindings::drm_gem_object::default()),
                 data <- T::new(dev, size),
-                // INVARIANT: The drm subsystem guarantees that the `struct drm_device` will live
-                // as long as the GEM object lives.
-                dev: dev.into(),
             }),
             GFP_KERNEL,
         )?;
@@ -247,9 +242,13 @@ pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
 
     /// Returns the `Device` that owns this GEM object.
     pub fn dev(&self) -> &drm::Device<T::Driver> {
-        // SAFETY: The DRM subsystem guarantees that the `struct drm_device` will live as long as
-        // the GEM object lives, hence the pointer must be valid.
-        unsafe { self.dev.as_ref() }
+        // SAFETY:
+        // - `struct drm_gem_object.dev` is initialized and valid for as long as the GEM
+        //   object lives.
+        // - The device we used for creating the gem object is passed as &drm::Device<T::Driver> to
+        //   Object::<T>::new(), so we know that `T::Driver` is the right generic parameter to use
+        //   here.
+        unsafe { drm::Device::from_raw((*self.as_raw()).dev) }
     }
 
     fn as_raw(&self) -> *mut bindings::drm_gem_object {

base-commit: 77ed4376d7c5de8be1f2612d6b4777077fb5fdb2
-- 
2.51.0

Re: [PATCH v2] rust: drm/gem: Remove Object.dev

[Alice Ryhl]

On Tue, Oct 21, 2025 at 7:22 PM Lyude Paul <lyude@redhat.com> wrote:
>
> I noticed by chance that there's actually already a pointer to this in
> struct drm_gem_object. So, no use in carrying this around!
>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Acked-by: Danilo Krummrich <dakr@kernel.org>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>