rust: drm: Add Driver::ParentDevice associated type

Add a ParentDevice associated type to the Driver trait, allowing each
DRM driver to declare its parent bus device type (e.g.
auxiliary::Device, platform::Device).

Change UnregisteredDevice::new() to take &T::ParentDevice<Bound>,
ensuring at the type level that the DRM device's parent matches the
declared bus device type.

Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Deborah Brouwer <deborah.brouwer@collabora.com>
Link: https://patch.msgid.link/20260628145406.2107056-5-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

3 files changed, 10 insertions, 4 deletions

diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
index 35ff9c6942d8..343c0ef63c6c 100644
--- a/rust/kernel/drm/device.rs
+++ b/rust/kernel/drm/device.rs
@@ -178,7 +178,10 @@ impl<T: drm::Driver> UnregisteredDevice<T> {
     /// Create a new `UnregisteredDevice` for a `drm::Driver`.
     ///
     /// This can be used to create a [`Registration`](kernel::drm::Registration).
-    pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<Self> {
+    pub fn new(
+        dev: &T::ParentDevice<device::Bound>,
+        data: impl PinInit<T::Data, Error>,
+    ) -> Result<Self> {
         // `__drm_dev_alloc` uses `kmalloc()` to allocate memory, hence ensure a `kmalloc()`
         // compatible `Layout`.
         let layout = Kmalloc::aligned_layout(Layout::new::<Device<T, Normal>>());
@@ -195,7 +198,7 @@ impl<T: drm::Driver> UnregisteredDevice<T> {
         // - `dev` is valid by its type invarants,
         let raw_drm: *mut Device<T, Normal> = unsafe {
             bindings::__drm_dev_alloc(
-                dev.as_raw(),
+                dev.as_ref().as_raw(),
                 &alloc_vtable,
                 layout.size(),
                 mem::offset_of!(Device<T, Normal>, dev),
diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
index 25f7e233884d..802e7fc13e30 100644
--- a/rust/kernel/drm/driver.rs
+++ b/rust/kernel/drm/driver.rs
@@ -116,6 +116,9 @@ pub trait Driver {
     /// The type used to represent a DRM File (client)
     type File: drm::file::DriverFile;
 
+    /// The bus device type of the parent device that the DRM device is associated with.
+    type ParentDevice<Ctx: device::DeviceContext>: device::AsBusDevice<Ctx>;
+
     /// Driver metadata
     const INFO: DriverInfo;
 
diff --git a/rust/kernel/drm/gem/shmem.rs b/rust/kernel/drm/gem/shmem.rs
index 52de59b14dad..cbcfc7e4edb6 100644
--- a/rust/kernel/drm/gem/shmem.rs
+++ b/rust/kernel/drm/gem/shmem.rs
@@ -684,6 +684,7 @@ mod tests {
         type Data = KunitData;
         type File = KunitFile;
         type Object<Ctx: DeviceContext> = Object<KunitObject, Ctx>;
+        type ParentDevice<Ctx: device::DeviceContext> = faux::Device<Ctx>;
 
         const INFO: drm::DriverInfo = INFO;
         const IOCTLS: &'static [drm::ioctl::DrmIoctlDescriptor] = &[];
@@ -694,8 +695,7 @@ mod tests {
         let data = try_pin_init!(KunitData {});
         let reg = faux::Registration::new(c"Kunit", None)?;
         let fdev = reg.as_ref();
-        let dev = fdev.as_ref();
-        let drm = UnregisteredDevice::new(dev, data)?;
+        let drm = UnregisteredDevice::new(fdev, data)?;
 
         Ok((reg, drm))
     }