From 33026ad7c540512bd18dbc7ca7c58e12cba47e54 Mon Sep 17 00:00:00 2001
From: Danilo Krummrich <dakr@kernel.org>
Date: Wed, 21 Aug 2024 04:48:16 +0200
Subject: rust: driver: generalize `Registration` structure

Generalize the `Registration` structure to be used commonly by
subsystems / busses.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/driver.rs | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs    |  1 +
 2 files changed, 90 insertions(+)
 create mode 100644 rust/kernel/driver.rs

diff --git a/rust/kernel/driver.rs b/rust/kernel/driver.rs
new file mode 100644
index 000000000000..4fec6ee1a90d
--- /dev/null
+++ b/rust/kernel/driver.rs
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Generic driver support
+
+use core::cell::UnsafeCell;
+use core::marker::PhantomData;
+use kernel::{alloc::flags::*, prelude::*};
+
+/// The [`RegistrationOps`] trait serves as generic interface for subsystems (e.g., PCI, Platform,
+/// Amba, etc.) to privide the corresponding subsystem specific implementation to register /
+/// unregister a driver of the particular type (`RegType`).
+///
+/// For instance, the PCI subsystem would set `RegType` to `bindings::pci_driver` and call
+/// `bindings::__pci_register_driver` from `RegistrationOps::register` and
+/// `bindings::pci_unregister_driver` from `RegistrationOps::unregister`.
+pub trait RegistrationOps {
+    /// The type that holds information about the registration. This is typically a struct defined
+    /// by the C portion of the kernel, e.g. `bindings::pci_driver.
+    type RegType: Default;
+
+    /// Registers a driver.
+    ///
+    /// # Safety
+    ///
+    /// `reg` must point to valid, initialised, and writable memory. It may be modified by this
+    /// function to hold registration state.
+    ///
+    /// On success, `reg` must remain pinned and valid until the matching call to
+    /// [`RegistrationOps::unregister`].
+    unsafe fn register(
+        reg: *mut Self::RegType,
+        name: &'static CStr,
+        module: &'static ThisModule,
+    ) -> Result;
+
+    /// Unregisters a driver previously registered with [`RegistrationOps::register`].
+    ///
+    /// # Safety
+    ///
+    /// `reg` must point to valid writable memory, initialised by a previous successful call to
+    /// [`RegistrationOps::register`].
+    unsafe fn unregister(reg: *mut Self::RegType);
+}
+
+/// Registration structure for a driver.
+///
+/// The existance of an instance of this structure implies that the corresponding driver is
+/// currently registered.
+pub struct Registration<T: RegistrationOps> {
+    driver: Pin<KBox<UnsafeCell<T::RegType>>>,
+    _p: PhantomData<T>,
+}
+
+impl<T> Registration<T>
+where
+    T: RegistrationOps,
+{
+    /// Register a new driver from `T::RegType`.
+    pub fn new(name: &'static CStr, module: &'static ThisModule) -> Result<Self> {
+        let driver = KBox::pin(UnsafeCell::new(T::RegType::default()), GFP_KERNEL)?;
+
+        // SAFETY: `driver` has just been initialized; it's only freed after `Self::drop`, which
+        // calls `T::unregister` first.
+        unsafe { T::register(driver.get(), name, module) }?;
+
+        Ok(Self {
+            driver,
+            _p: PhantomData::<T>,
+        })
+    }
+}
+
+impl<T> Drop for Registration<T>
+where
+    T: RegistrationOps,
+{
+    fn drop(&mut self) {
+        // SAFETY: Only ever called if the `Registration` was created successfully.
+        unsafe { T::unregister(self.driver.get()) };
+    }
+}
+
+// SAFETY: `Registration` has no fields or methods accessible via `&Registration`, so it is safe to
+// share references to it with multiple threads as nothing can be done.
+unsafe impl<T> Sync for Registration<T> where T: RegistrationOps {}
+
+// SAFETY: Both registration and unregistration are implemented in C and safe to be performed from
+// any thread, so `Registration` is `Send`.
+unsafe impl<T> Send for Registration<T> where T: RegistrationOps {}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index ab8f3cf7fb40..2ef77187c5c7 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -31,6 +31,7 @@ pub mod block;
 mod build_assert;
 pub mod cred;
 pub mod device;
+pub mod driver;
 pub mod error;
 #[cfg(CONFIG_RUST_FW_LOADER_ABSTRACTIONS)]
 pub mod firmware;
-- 
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