Message-ID: <20250312002741.453350-3-dakr@kernel.org>
Date: Wed, 12 Mar 2025 01:19:08 +0100
From: Danilo Krummrich <dakr@...nel.org>
To: gregkh@...uxfoundation.org,
	rafael@...nel.org,
	ojeda@...nel.org,
	alex.gaynor@...il.com,
	boqun.feng@...il.com,
	gary@...yguo.net,
	bjorn3_gh@...tonmail.com,
	benno.lossin@...ton.me,
	a.hindborg@...nel.org,
	aliceryhl@...gle.com,
	tmgross@...ch.edu,
	airlied@...il.com,
	acourbot@...dia.com,
	jhubbard@...dia.com
Cc: linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org,
	Danilo Krummrich <dakr@...nel.org>
Subject: [PATCH 2/4] rust: auxiliary: add auxiliary driver abstractions

Implement the basic auxiliary abstractions required to implement a
driver matching an auxiliary device.

The design and implementation is analogous to PCI and platform and is
based on the generic device / driver abstractions.

Signed-off-by: Danilo Krummrich <dakr@...nel.org>
---
 MAINTAINERS                     |   1 +
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers/auxiliary.c        |  23 ++++
 rust/helpers/helpers.c          |   1 +
 rust/kernel/auxiliary.rs        | 233 ++++++++++++++++++++++++++++++++
 rust/kernel/lib.rs              |   2 +
 6 files changed, 261 insertions(+)
 create mode 100644 rust/helpers/auxiliary.c
 create mode 100644 rust/kernel/auxiliary.rs

diff --git a/MAINTAINERS b/MAINTAINERS
index f5c7022937a7..0a737b28cdfa 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7114,6 +7114,7 @@ F:	include/linux/kobj*
 F:	include/linux/property.h
 F:	include/linux/sysfs.h
 F:	lib/kobj*
+F:	rust/kernel/auxiliary.rs
 F:	rust/kernel/device.rs
 F:	rust/kernel/device_id.rs
 F:	rust/kernel/devres.rs
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index f46cf3bb7069..83026b6e53b2 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -7,6 +7,7 @@
  */
 
 #include <kunit/test.h>
+#include <linux/auxiliary_bus.h>
 #include <linux/blk-mq.h>
 #include <linux/blk_types.h>
 #include <linux/blkdev.h>
diff --git a/rust/helpers/auxiliary.c b/rust/helpers/auxiliary.c
new file mode 100644
index 000000000000..0db3860d774e
--- /dev/null
+++ b/rust/helpers/auxiliary.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/auxiliary_bus.h>
+
+void rust_helper_auxiliary_set_drvdata(struct auxiliary_device *adev, void *data)
+{
+	auxiliary_set_drvdata(adev, data);
+}
+
+void *rust_helper_auxiliary_get_drvdata(struct auxiliary_device *adev)
+{
+	return auxiliary_get_drvdata(adev);
+}
+
+void rust_helper_auxiliary_device_uninit(struct auxiliary_device *adev)
+{
+	return auxiliary_device_uninit(adev);
+}
+
+void rust_helper_auxiliary_device_delete(struct auxiliary_device *adev)
+{
+	return auxiliary_device_delete(adev);
+}
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 0640b7e115be..d744af85e3b2 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -7,6 +7,7 @@
  * Sorted alphabetically.
  */
 
+#include "auxiliary.c"
 #include "blk.c"
 #include "bug.c"
 #include "build_assert.c"
diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
new file mode 100644
index 000000000000..3bdd690990aa
--- /dev/null
+++ b/rust/kernel/auxiliary.rs
@@ -0,0 +1,233 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Abstractions for the auxiliary bus.
+//!
+//! C header: [`include/linux/auxiliary_bus.h`](srctree/include/linux/auxiliary_bus.h)
+
+use crate::{
+    bindings, container_of, device,
+    device_id::RawDeviceId,
+    driver,
+    error::{to_result, Result},
+    prelude::*,
+    str::CStr,
+    types::{ARef, ForeignOwnable, Opaque},
+    ThisModule,
+};
+use core::ptr::addr_of_mut;
+
+/// An adapter for the registration of auxiliary drivers.
+pub struct Adapter<T: Driver>(T);
+
+// SAFETY: A call to `unregister` for a given instance of `RegType` is guaranteed to be valid if
+// a preceding call to `register` has been successful.
+unsafe impl<T: Driver + 'static> driver::RegistrationOps for Adapter<T> {
+    type RegType = bindings::auxiliary_driver;
+
+    unsafe fn register(
+        adrv: &Opaque<Self::RegType>,
+        name: &'static CStr,
+        module: &'static ThisModule,
+    ) -> Result {
+        // SAFETY: It's safe to set the fields of `struct auxiliary_driver` on initialization.
+        unsafe {
+            (*adrv.get()).name = name.as_char_ptr();
+            (*adrv.get()).probe = Some(Self::probe_callback);
+            (*adrv.get()).remove = Some(Self::remove_callback);
+            (*adrv.get()).id_table = T::ID_TABLE.as_ptr();
+        }
+
+        // SAFETY: `adrv` is guaranteed to be a valid `RegType`.
+        to_result(unsafe {
+            bindings::__auxiliary_driver_register(adrv.get(), module.0, name.as_char_ptr())
+        })
+    }
+
+    unsafe fn unregister(adrv: &Opaque<Self::RegType>) {
+        // SAFETY: `adrv` is guaranteed to be a valid `RegType`.
+        unsafe { bindings::auxiliary_driver_unregister(adrv.get()) }
+    }
+}
+
+impl<T: Driver + 'static> Adapter<T> {
+    extern "C" fn probe_callback(
+        adev: *mut bindings::auxiliary_device,
+        id: *const bindings::auxiliary_device_id,
+    ) -> core::ffi::c_int {
+        // SAFETY: The auxiliary bus only ever calls the probe callback with a valid pointer to a
+        // `struct auxiliary_device`.
+        let dev = unsafe { device::Device::get_device(addr_of_mut!((*adev).dev)) };
+        // SAFETY: `dev` is guaranteed to be embedded in a valid `struct auxiliary_device` by the
+        // call above.
+        let mut adev = unsafe { Device::from_dev(dev) };
+
+        // SAFETY: `DeviceId` is a `#[repr(transparent)` wrapper of `struct auxiliary_device_id` and
+        // does not add additional invariants, so it's safe to transmute.
+        let id = unsafe { &*id.cast::<DeviceId>() };
+        let info = T::ID_TABLE.info(id.index());
+
+        match T::probe(&mut adev, info) {
+            Ok(data) => {
+                // Let the `struct auxiliary_device` own a reference of the driver's private data.
+                // SAFETY: By the type invariant `adev.as_raw` returns a valid pointer to a
+                // `struct auxiliary_device`.
+                unsafe { bindings::auxiliary_set_drvdata(adev.as_raw(), data.into_foreign()) };
+            }
+            Err(err) => return Error::to_errno(err),
+        }
+
+        0
+    }
+
+    extern "C" fn remove_callback(adev: *mut bindings::auxiliary_device) {
+        // SAFETY: The auxiliary bus only ever calls the remove callback with a valid pointer to a
+        // `struct auxiliary_device`.
+        let ptr = unsafe { bindings::auxiliary_get_drvdata(adev) };
+
+        // SAFETY: `remove_callback` is only ever called after a successful call to
+        // `probe_callback`, hence it's guaranteed that `ptr` points to a valid and initialized
+        // `KBox<T>` pointer created through `KBox::into_foreign`.
+        let _ = unsafe { KBox::<T>::from_foreign(ptr) };
+    }
+}
+
+/// Declares a kernel module that exposes a single auxiliary driver.
+#[macro_export]
+macro_rules! module_auxiliary_driver {
+    ($($f:tt)*) => {
+        $crate::module_driver!(<T>, $crate::auxiliary::Adapter<T>, { $($f)* });
+    };
+}
+
+/// Abstraction for `bindings::auxiliary_device_id`.
+#[repr(transparent)]
+#[derive(Clone, Copy)]
+pub struct DeviceId(bindings::auxiliary_device_id);
+
+impl DeviceId {
+    /// Create a new [`DeviceId`] from name.
+    pub const fn new(modname: &'static CStr, name: &'static CStr) -> Self {
+        let name = name.as_bytes_with_nul();
+        let modname = modname.as_bytes_with_nul();
+
+        // TODO: Replace with `bindings::auxiliary_device_id::default()` once stabilized for
+        // `const`.
+        //
+        // SAFETY: FFI type is valid to be zero-initialized.
+        let mut id: bindings::auxiliary_device_id = unsafe { core::mem::zeroed() };
+
+        let mut i = 0;
+        while i < modname.len() {
+            id.name[i] = modname[i];
+            i += 1;
+        }
+
+        // Reuse the space of the NULL terminator.
+        id.name[i - 1] = b'.';
+
+        let mut j = 0;
+        while j < name.len() {
+            id.name[i] = name[j];
+            i += 1;
+            j += 1;
+        }
+
+        Self(id)
+    }
+}
+
+// SAFETY:
+// * `DeviceId` is a `#[repr(transparent)` wrapper of `auxiliary_device_id` and does not add
+//   additional invariants, so it's safe to transmute to `RawType`.
+// * `DRIVER_DATA_OFFSET` is the offset to the `driver_data` field.
+unsafe impl RawDeviceId for DeviceId {
+    type RawType = bindings::auxiliary_device_id;
+
+    const DRIVER_DATA_OFFSET: usize =
+        core::mem::offset_of!(bindings::auxiliary_device_id, driver_data);
+
+    fn index(&self) -> usize {
+        self.0.driver_data
+    }
+}
+
+/// IdTable type for auxiliary drivers.
+pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<DeviceId, T>;
+
+/// Create a auxiliary `IdTable` with its alias for modpost.
+#[macro_export]
+macro_rules! auxiliary_device_table {
+    ($table_name:ident, $module_table_name:ident, $id_info_type: ty, $table_data: expr) => {
+        const $table_name: $crate::device_id::IdArray<
+            $crate::auxiliary::DeviceId,
+            $id_info_type,
+            { $table_data.len() },
+        > = $crate::device_id::IdArray::new($table_data);
+
+        $crate::module_device_table!("auxiliary", $module_table_name, $table_name);
+    };
+}
+
+/// The auxiliary driver trait.
+///
+/// Drivers must implement this trait in order to get an auxiliary driver registered.
+pub trait Driver {
+    /// The type holding information about each device id supported by the driver.
+    ///
+    /// TODO: Use associated_type_defaults once stabilized:
+    ///
+    /// type IdInfo: 'static = ();
+    type IdInfo: 'static;
+
+    /// The table of device ids supported by the driver.
+    const ID_TABLE: IdTable<Self::IdInfo>;
+
+    /// Auxiliary driver probe.
+    ///
+    /// Called when a new auxiliary device is added or discovered. Implementers should attempt
+    /// to initialize the device here.
+    fn probe(dev: &mut Device, id_info: &Self::IdInfo) -> Result<Pin<KBox<Self>>>;
+}
+
+/// The auxiliary device representation.
+///
+/// An auxiliary device is based on an always reference counted [`device::Device`] instance. Cloning
+/// an auxiliary device, hence, also increments the base device' reference count.
+///
+/// # Invariants
+///
+/// [`Device`] holds a valid reference of `ARef<device::Device>` whose underlying `struct device` is
+/// a member of a `struct auxiliary_device`.
+#[derive(Clone)]
+pub struct Device(ARef<device::Device>);
+
+impl Device {
+    /// Create an auxiliary [`Device`] instance from an existing [`device::Device`].
+    ///
+    /// # Safety
+    ///
+    /// `dev` must be an `ARef<device::Device>` whose underlying `bindings::device` is a member of
+    /// a `bindings::auxiliary_device`.
+    unsafe fn from_dev(dev: ARef<device::Device>) -> Self {
+        Self(dev)
+    }
+
+    fn as_raw(&self) -> *mut bindings::auxiliary_device {
+        // SAFETY: By the type invariant `self.0.as_raw` is a pointer to the `struct device`
+        // embedded in `struct auxiliary_device`.
+        unsafe { container_of!(self.0.as_raw(), bindings::auxiliary_device, dev).cast_mut() }
+    }
+
+    /// Returns the auxiliary device' id.
+    pub fn id(&self) -> u32 {
+        // SAFETY: By the type invariant `self.as_raw()` is a valid pointer to a
+        // `struct auxiliary_device`.
+        unsafe { (*self.as_raw()).id }
+    }
+}
+
+impl AsRef<device::Device> for Device {
+    fn as_ref(&self) -> &device::Device {
+        &self.0
+    }
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 398242f92a96..d9a2ca9d1f20 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -36,6 +36,8 @@
 pub use ffi;
 
 pub mod alloc;
+#[cfg(CONFIG_AUXILIARY_BUS)]
+pub mod auxiliary;
 #[cfg(CONFIG_BLOCK)]
 pub mod block;
 #[doc(hidden)]
-- 
2.48.1

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