[PATCH v3 5/8] rust: drm: add debugfs_init callback to Driver trait

[Alvin Sun <alvin.sun@linux.dev>]

Add debugfs_init method to the Driver trait, enabling Rust DRM drivers
to populate debugfs entries during device registration.

Signed-off-by: Alvin Sun <alvin.sun@linux.dev>
---
 rust/kernel/drm/device.rs | 41 ++++++++++++++++++++++++++++++++++++++++-
 rust/kernel/drm/driver.rs | 11 +++++++++++
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
index 7a3a0e21e9557..35fd514fec274 100644
--- a/rust/kernel/drm/device.rs
+++ b/rust/kernel/drm/device.rs
@@ -7,6 +7,7 @@
 use crate::{
     alloc::allocator::Kmalloc,
     bindings,
+    debugfs,
     device,
     drm::{
         self,
@@ -170,7 +171,7 @@ const fn compute_features() -> u32 {
         release: Some(Device::<T>::release),
         master_set: None,
         master_drop: None,
-        debugfs_init: None,
+        debugfs_init: Some(Device::<T>::debugfs_init_callback),
 
         gem_create_object: T::Object::ALLOC_OPS.gem_create_object,
         prime_handle_to_fd: T::Object::ALLOC_OPS.prime_handle_to_fd,
@@ -353,6 +354,44 @@ extern "C" fn release(ptr: *mut bindings::drm_device) {
         unsafe { core::ptr::drop_in_place(this) };
     }
 
+    /// C callback for `drm_driver.debugfs_init`.
+    ///
+    /// # Safety
+    ///
+    /// The DRM core guarantees that `minor` is valid and non-null, that
+    /// `minor->dev` is a valid `drm_device` embedded in a `Device<T>`.
+    unsafe extern "C" fn debugfs_init_callback(minor: *mut bindings::drm_minor) {
+        // SAFETY: `minor` is valid and non-null per the function's safety
+        // precondition.
+        let dev_ptr = unsafe { (*minor).dev };
+        // SAFETY: `minor` is valid per the function's safety precondition.
+        let debugfs_root = unsafe { (*minor).debugfs_root };
+
+        // Debugfs may be disabled.
+        if debugfs_root.is_null() {
+            return;
+        }
+
+        // SAFETY: `dev_ptr` points to a valid `drm_device` embedded in
+        // `Device<T>`.
+        let dev = unsafe { Self::from_raw(dev_ptr) };
+
+        // SAFETY: The device is in the registered state per the function's
+        // safety precondition.
+        let dev = unsafe { dev.assume_ctx::<Registered>() };
+
+        dev.registration_data_with(|reg_data| {
+            // SAFETY: `debugfs_root` is valid as long as the DRM device is
+            // registered. The debugfs proxy fops wait for in-progress file
+            // operations and block new ones during `debugfs_remove()`, so no
+            // access to `reg_data` can outlive it. `debugfs_remove()` runs
+            // before `Registration::drop` frees `reg_data`.
+            let dir = unsafe { debugfs::ScopeRef::new(debugfs_root, reg_data) };
+
+            T::debugfs_init(&dir);
+        });
+    }
+
     /// Change the [`DeviceContext`] for a [`Device`].
     ///
     /// # Safety
diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
index 08b2a318cf02a..f850b11fd5c53 100644
--- a/rust/kernel/drm/driver.rs
+++ b/rust/kernel/drm/driver.rs
@@ -6,6 +6,7 @@
 
 use crate::{
     bindings,
+    debugfs,
     device,
     drm,
     error::to_result,
@@ -138,6 +139,16 @@ pub trait Driver {
     /// usable from the render node (i.e. marked DRM_RENDER_ALLOW), whereas
     /// userspace processes using the master node can invoke any ioctl.
     const FEAT_RENDER: bool = false;
+
+    /// Populates debugfs for this DRM device.
+    ///
+    /// Called by the DRM core during registration. The `ScopeRef` provides
+    /// access to the device's `RegistrationData` for creating debugfs files.
+    fn debugfs_init(_dir: &debugfs::ScopeRef<'_, Self::RegistrationData<'_>>)
+    where
+        Self: Sized,
+    {
+    }
 }
 
 /// The registration type of a `drm::Device`.

-- 
2.43.0