Message-ID: <854b4448-3ff1-4fb4-b58f-21136f5ec3e4@gmx.de>
Date: Thu, 25 Dec 2025 19:06:05 +0100
From: Armin Wolf <W_Armin@....de>
To: Gladyshev Ilya <foxido@...ido.dev>,
 "foxido @ foxido . dev-cc= Rafael J. Wysocki" <rafael@...nel.org>
Cc: Len Brown <lenb@...nel.org>, Miguel Ojeda <ojeda@...nel.org>,
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
 Danilo Krummrich <dakr@...nel.org>, Tamir Duberstein <tamird@...il.com>,
 platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
 rust-for-linux@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [RFC PATCH 2/3] rust: introduce WMI abstractions

Am 21.12.25 um 19:22 schrieb Gladyshev Ilya:

> Implement the basic WMI subsystem abstractions required to write a
> WMI device driver with or without the need for initial device data.
> This includes the following data structures:
>
> The `wmi::Driver` trait represents the interface to the driver.
>
> The `wmi::Device` abstraction represents a `struct wmi_device`.
>
> In order to provide the WMI specific parts to a generic
> `driver::Registration` the `driver::RegistrationOps` trait is
> implemented by `wmi::Adapter`.
>
> Everything from C side is supported, except shutdown action
>
> Signed-off-by: Gladyshev Ilya <foxido@...ido.dev>
> ---
>   rust/bindings/bindings_helper.h |   1 +
>   rust/kernel/lib.rs              |   2 +
>   rust/kernel/wmi.rs              | 267 ++++++++++++++++++++++++++++++++
>   3 files changed, 270 insertions(+)
>   create mode 100644 rust/kernel/wmi.rs
>
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index a067038b4b42..f9671280c6b5 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -85,6 +85,7 @@
>   #include <linux/usb.h>
>   #include <linux/wait.h>
>   #include <linux/workqueue.h>
> +#include <linux/wmi.h>
>   #include <linux/xarray.h>
>   #include <trace/events/rust_sample.h>
>   
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index f812cf120042..db3e649d26eb 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -151,6 +151,8 @@
>   pub mod uaccess;
>   #[cfg(CONFIG_USB = "y")]
>   pub mod usb;
> +#[cfg(CONFIG_ACPI_WMI)]
> +pub mod wmi;
>   pub mod workqueue;
>   pub mod xarray;
>   
> diff --git a/rust/kernel/wmi.rs b/rust/kernel/wmi.rs
> new file mode 100644
> index 000000000000..018e88d01e8c
> --- /dev/null
> +++ b/rust/kernel/wmi.rs
> @@ -0,0 +1,267 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +//! Abstractions for the WMI devices.
> +//!
> +//! C header: [`include/linux/wmi.h`](srctree/include/linux/wmi.h)
> +
> +use crate::{
> +    acpi::AcpiObject,
> +    device,
> +    device_id::{RawDeviceId, RawDeviceIdIndex},
> +    driver,
> +    error::{from_result, to_result, VTABLE_DEFAULT_ERROR},
> +    prelude::*,
> +    types::Opaque,
> +};
> +use core::{
> +    marker::PhantomData,
> +    mem::MaybeUninit,
> +    ptr::{addr_of_mut, NonNull},
> +};
> +use macros::vtable;
> +
> +/// [`IdTable`](kernel::device_id::IdTable) type for WMI.
> +pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<DeviceId, T>;
> +
> +/// The WMI driver trait.
> +#[vtable]
> +pub trait Driver: Send {
> +    /// The type holding information about each one of the device ids supported by the driver.
> +    type IdInfo: 'static;
> +
> +    /// The table of device ids supported by the driver.
> +    const TABLE: IdTable<Self::IdInfo>;
> +
> +    /// WMI driver probe.
> +    ///
> +    /// Called when a new WMI device is bound to this driver.
> +    /// Implementers should attempt to initialize the driver here.
> +    fn probe(dev: &Device<device::Core>, id_info: &Self::IdInfo) -> impl PinInit<Self, Error>;
> +
> +    /// WMI device notify.
> +    ///
> +    /// Called when new WMI event received from bounded device
> +    fn notify(&self, _dev: &Device<device::Core>, _event: &AcpiObject) {
> +        build_error!(VTABLE_DEFAULT_ERROR);
> +    }
> +
> +    /// WMI driver remove.
> +    fn remove(self: Pin<KBox<Self>>, _dev: &Device<device::Core>) {
> +        build_error!(VTABLE_DEFAULT_ERROR);
> +    }
> +}
> +
> +/// A WMI device.
> +///
> +/// This structure represents the Rust abstraction for a C [`struct wmi_device`].
> +/// The implementation abstracts the usage of a C [`struct wmi_device`] passed
> +/// in from the C side.
> +pub struct Device<Cxt: device::DeviceContext = device::Normal> {
> +    inner: Opaque<bindings::wmi_device>,
> +    _p: PhantomData<Cxt>,
> +}
> +
> +impl<Cxt: device::DeviceContext> Device<Cxt> {
> +    fn as_raw(&self) -> *mut bindings::wmi_device {
> +        self.inner.get()
> +    }
> +}
> +
> +/// An adapter for the registration of WMI 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::wmi_driver;
> +
> +    unsafe fn register(
> +        wdrv: &Opaque<Self::RegType>,
> +        name: &'static CStr,
> +        module: &'static ThisModule,
> +    ) -> Result {
> +        macro_rules! map_callback {
> +            ($flag:ident -> $callback:ident) => {
> +                if T::$flag {
> +                    Some(Self::$callback)
> +                } else {
> +                    None
> +                }
> +            };
> +        }
> +
> +        // SAFETY: It's safe to set the fields of `struct wmi_driver` on initialization.
> +        unsafe {
> +            (*wdrv.get()).driver.name = name.as_char_ptr();
> +            (*wdrv.get()).driver.probe_type = bindings::probe_type_PROBE_PREFER_ASYNCHRONOUS;
> +            (*wdrv.get()).id_table = T::TABLE.as_ptr();
> +            (*wdrv.get()).probe = map_callback!(HAS_PROBE -> probe_callback);
> +            (*wdrv.get()).notify = map_callback!(HAS_NOTIFY -> notify_callback);

I think it should be possible to handle WMI drivers requiring .no_notify_data to be set. Is there
a way to declare the WMI event data passed to the notify() callback as optional? If yes, then i suggest
that we always set .no_notify_data and simply require the WMI drivers themselves to verify that a given
WMI event does contain additional event data.

(Said no_notify_data flag only exists because most WMI drivers currently assume that the event data
passed to the .notify() callback is not NULL)

Thanks,
Armin Wolf

> +            (*wdrv.get()).remove = map_callback!(HAS_REMOVE -> remove_callback);
> +            (*wdrv.get()).shutdown = None;
> +            (*wdrv.get()).no_singleton = true;
> +        }
> +
> +        // SAFETY: `wdrv` is guaranteed to be a valid `RegType`.
> +        to_result(unsafe { bindings::__wmi_driver_register(wdrv.get(), module.0) })
> +    }
> +
> +    unsafe fn unregister(wdrv: &Opaque<Self::RegType>) {
> +        // SAFETY: `wdrv` is guaranteed to be a valid `RegType`.
> +        unsafe { bindings::wmi_driver_unregister(wdrv.get()) };
> +    }
> +}
> +
> +impl<T: Driver + 'static> Adapter<T> {
> +    extern "C" fn probe_callback(
> +        wdev: *mut bindings::wmi_device,
> +        id: *const c_void,
> +    ) -> kernel::ffi::c_int {
> +        // SAFETY: The WMI core only ever calls the probe callback with a valid pointer to a
> +        // `struct wmi_device`.
> +        //
> +        // INVARIANT: `wdev` is valid for the duration of `probe_callback()`.
> +        let wdev = unsafe { &*wdev.cast::<Device<device::CoreInternal>>() };
> +
> +        let id = id as usize;
> +        let info = T::TABLE.info(id);
> +
> +        from_result(|| {
> +            let data = T::probe(wdev, info);
> +
> +            wdev.as_ref().set_drvdata(data)?;
> +            Ok(0)
> +        })
> +    }
> +
> +    extern "C" fn notify_callback(
> +        wdev: *mut bindings::wmi_device,
> +        obj: *mut bindings::acpi_object,
> +    ) {
> +        // SAFETY: The WMI system only ever calls the notify callback with a valid pointer to a
> +        // `struct wmi_device`.
> +        let wdev = unsafe { &*wdev.cast::<Device<device::CoreInternal>>() };
> +        // SAFETY: AcpiObject is repr(transparent) wrapper
> +        let obj: &AcpiObject = unsafe { &*(obj as *const AcpiObject) };
> +
> +        // SAFETY: `notify_callback` is only ever called after a successful call to
> +        // `probe_callback`, hence it's guaranteed that `Device::set_drvdata()` has been called
> +        // and stored a `T`.
> +        let this: &T = unsafe { &wdev.as_ref().drvdata_borrow::<T>() };
> +        this.notify(wdev, obj);
> +    }
> +
> +    extern "C" fn remove_callback(wdev: *mut bindings::wmi_device) {
> +        // SAFETY: The WMI system only ever calls the remove callback with a valid pointer to a
> +        // `struct wmi_device`.
> +        let wdev = unsafe { &*wdev.cast::<Device<device::CoreInternal>>() };
> +
> +        // SAFETY: `remove_callback` is only ever called after a successful call to
> +        // `probe_callback`, hence it's guaranteed that `Device::set_drvdata()` has been called
> +        // and stored a `T`.
> +        let this = unsafe { wdev.as_ref().drvdata_obtain::<T>() };
> +        this.remove(wdev);
> +    }
> +}
> +
> +impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for Device<Ctx> {
> +    fn as_ref(&self) -> &device::Device<Ctx> {
> +        // SAFETY: By the type invariant of `Self`, `self.as_raw()` is a pointer to a valid
> +        // `struct platform_device`.
> +        let dev = unsafe { addr_of_mut!((*self.inner.get()).dev) };
> +
> +        // SAFETY: `dev` points to a valid `struct device`.
> +        unsafe { device::Device::from_raw(dev) }
> +    }
> +}
> +
> +kernel::impl_device_context_deref!(unsafe { Device });
> +kernel::impl_device_context_into_aref!(Device);
> +
> +// SAFETY: Instances of `Device` are always reference-counted.
> +unsafe impl crate::sync::aref::AlwaysRefCounted for Device {
> +    fn inc_ref(&self) {
> +        // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
> +        unsafe { bindings::get_device(self.as_ref().as_raw()) };
> +    }
> +
> +    unsafe fn dec_ref(obj: NonNull<Self>) {
> +        // SAFETY: The safety requirements guarantee that the refcount is non-zero.
> +        unsafe { bindings::put_device(&raw mut (*obj.as_ref().as_raw()).dev) }
> +    }
> +}
> +
> +/// Abstraction for the WMI device ID structure, i.e. [`struct wmi_device_id`].
> +#[repr(transparent)]
> +pub struct DeviceId(bindings::wmi_device_id);
> +
> +impl DeviceId {
> +    /// Constructs new DeviceId from GUID string
> +    pub const fn new(guid: &[u8; bindings::UUID_STRING_LEN as usize]) -> Self {
> +        // SAFETY: FFI type is valid to be zero-initialized.
> +        let mut inner: bindings::wmi_device_id = unsafe { MaybeUninit::zeroed().assume_init() };
> +
> +        build_assert!(inner.guid_string.len() == bindings::UUID_STRING_LEN as usize + 1);
> +
> +        // SAFETY: It's safe to copy UUID_STRING_LEN, because we validated lengths
> +        // Also we leave last byte zeroed -> guid_string is valid C string
> +        unsafe {
> +            ::core::ptr::copy_nonoverlapping(
> +                guid.as_ptr(),
> +                &raw mut inner.guid_string[0],
> +                bindings::UUID_STRING_LEN as usize,
> +            );
> +        }
> +
> +        Self(inner)
> +    }
> +}
> +
> +// SAFETY: `DeviceId` is a `#[repr(transparent)]` wrapper of `wmi_device_id` and does not add
> +// additional invariants, so it's safe to transmute to `RawType`.
> +unsafe impl RawDeviceId for DeviceId {
> +    type RawType = bindings::wmi_device_id;
> +}
> +
> +// SAFETY: `DRIVER_DATA_OFFSET` is the offset to the `context` field.
> +unsafe impl RawDeviceIdIndex for DeviceId {
> +    const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::wmi_device_id, context);
> +
> +    fn index(&self) -> usize {
> +        self.0.context as usize
> +    }
> +}
> +
> +/// Declares a kernel module that exposes a single WMI driver.
> +///
> +/// # Examples
> +///
> +/// ```ignore
> +/// module_wmi_driver! {
> +///     type: MyDriver,
> +///     name: "Module name",
> +///     author: ["Author name"],
> +///     description: "Description",
> +///     license: "GPL v2",
> +/// }
> +/// ```
> +#[macro_export]
> +macro_rules! module_wmi_driver {
> +    ($($f:tt)*) => {
> +        $crate::module_driver!(<T>, $crate::wmi::Adapter<T>, { $($f)* });
> +    }
> +}
> +
> +/// Create a WMI `IdTable` with its alias for modpost.
> +#[macro_export]
> +macro_rules! wmi_device_table {
> +    ($table_name:ident, $module_table_name:ident, $id_info_type: ty, $table_data: expr) => {
> +        const $table_name: $crate::device_id::IdArray<
> +            $crate::wmi::DeviceId,
> +            $id_info_type,
> +            { $table_data.len() },
> +        > = $crate::device_id::IdArray::new($table_data);
> +
> +        $crate::module_device_table!("wmi", $module_table_name, $table_name);
> +    };
> +}

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