rust/kernel/driver.rs

// SPDX-License-Identifier: GPL-2.0

//! Generic support for drivers of different buses (e.g., PCI, Platform, Amba, etc.).
//!
//! This documentation describes how to implement a bus specific driver API and how to align it with
//! the design of (bus specific) devices.
//!
//! Note: Readers are expected to know the content of the documentation of [`Device`] and
//! [`DeviceContext`].
//!
//! # Driver Trait
//!
//! The main driver interface is defined by a bus specific driver trait. For instance:
//!
//! ```ignore
//! pub trait Driver {
//!     /// The type holding information about each device ID supported by the driver.
//!     type IdInfo: 'static;
//!
//!     /// The type of the driver's bus device private data.
//!     type Data<'bound>: Send + 'bound;
//!
//!     /// The table of OF device ids supported by the driver.
//!     const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = None;
//!
//!     /// The table of ACPI device ids supported by the driver.
//!     const ACPI_ID_TABLE: Option<acpi::IdTable<Self::IdInfo>> = None;
//!
//!     /// Driver probe.
//!     fn probe<'bound>(
//!         dev: &'bound Device<device::Core<'_>>,
//!         id_info: &'bound Self::IdInfo,
//!     ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound;
//!
//!     /// Driver unbind (optional).
//!     fn unbind<'bound>(
//!         dev: &'bound Device<device::Core<'_>>,
//!         this: Pin<&Self::Data<'bound>>,
//!     ) {
//!         let _ = (dev, this);
//!     }
//! }
//! ```
//!
//! For specific examples see:
//!
//! * [`platform::Driver`](kernel::platform::Driver)
#![cfg_attr(
    CONFIG_AUXILIARY_BUS,
    doc = "* [`auxiliary::Driver`](kernel::auxiliary::Driver)"
)]
#![cfg_attr(CONFIG_PCI, doc = "* [`pci::Driver`](kernel::pci::Driver)")]
//!
//! The `probe()` callback should return a
//! `impl PinInit<Self::Data<'bound>, Error>`, i.e. the driver's private data. The bus
//! abstraction should store the pointer in the corresponding bus device. The generic
//! [`Device`] infrastructure provides common helpers for this purpose on its
//! [`Device<CoreInternal>`] implementation.
//!
//! All driver callbacks should provide a reference to the driver's private data. Once the driver
//! is unbound from the device, the bus abstraction should take back the ownership of the driver's
//! private data from the corresponding [`Device`] and [`drop`] it.
//!
//! All driver callbacks should provide a [`Device<Core>`] reference (see also [`device::Core`]).
//!
//! # Adapter
//!
//! The adapter implementation of a bus represents the abstraction layer between the C bus
//! callbacks and the Rust bus callbacks. It therefore has to be generic over an implementation of
//! the [driver trait](#driver-trait).
//!
//! ```ignore
//! pub struct Adapter<T: Driver>;
//! ```
//!
//! There's a common [`Adapter`] trait that can be implemented to inherit common driver
//! infrastructure, such as finding the ID info from an [`of::IdTable`] or [`acpi::IdTable`].
//!
//! # Driver Registration
//!
//! In order to register C driver types (such as `struct platform_driver`) the [adapter](#adapter)
//! should implement the [`RegistrationOps`] trait.
//!
//! This trait implementation can be used to create the actual registration with the common
//! [`Registration`] type.
//!
//! Typically, bus abstractions want to provide a bus specific `module_bus_driver!` macro, which
//! creates a kernel module with exactly one [`Registration`] for the bus specific adapter.
//!
//! The generic driver infrastructure provides a helper for this with the [`module_driver`] macro.
//!
//! # Device IDs
//!
//! Besides the common device ID types, such as [`of::DeviceId`] and [`acpi::DeviceId`], most buses
//! may need to implement their own device ID types.
//!
//! For this purpose the generic infrastructure in [`device_id`] should be used.
//!
//! [`Core`]: device::Core
//! [`Device`]: device::Device
//! [`Device<Core>`]: device::Device<device::Core>
//! [`Device<CoreInternal>`]: device::Device<device::CoreInternal>
//! [`DeviceContext`]: device::DeviceContext
//! [`device_id`]: kernel::device_id
//! [`module_driver`]: kernel::module_driver

use crate::{
    acpi,
    device,
    of,
    prelude::*,
    types::Opaque,
    ThisModule, //
};

/// Trait describing the layout of a specific device driver.
///
/// This trait describes the layout of a specific driver structure, such as `struct pci_driver` or
/// `struct platform_driver`.
///
/// # Safety
///
/// Implementors must guarantee that:
/// - `DriverType` is `repr(C)`,
/// - `DriverData` is the type of the driver's device private data.
/// - `DriverType` embeds a valid `struct device_driver` at byte offset `DEVICE_DRIVER_OFFSET`.
pub unsafe trait DriverLayout {
    /// The specific driver type embedding a `struct device_driver`.
    type DriverType: Default;

    /// The type of the driver's bus device private data.
    type DriverData<'bound>;

    /// Byte offset of the embedded `struct device_driver` within `DriverType`.
    ///
    /// This must correspond exactly to the location of the embedded `struct device_driver` field.
    const DEVICE_DRIVER_OFFSET: usize;
}

/// The [`RegistrationOps`] trait serves as generic interface for subsystems (e.g., PCI, Platform,
/// Amba, etc.) to provide the corresponding subsystem specific implementation to register /
/// unregister a driver of the particular type (`DriverType`).
///
/// For instance, the PCI subsystem would set `DriverType` to `bindings::pci_driver` and call
/// `bindings::__pci_register_driver` from `RegistrationOps::register` and
/// `bindings::pci_unregister_driver` from `RegistrationOps::unregister`.
///
/// # Safety
///
/// A call to [`RegistrationOps::unregister`] for a given instance of `DriverType` is only valid if
/// a preceding call to [`RegistrationOps::register`] has been successful.
pub unsafe trait RegistrationOps: DriverLayout {
    /// Registers a driver.
    ///
    /// # Safety
    ///
    /// On success, `reg` must remain pinned and valid until the matching call to
    /// [`RegistrationOps::unregister`].
    unsafe fn register(
        reg: &Opaque<Self::DriverType>,
        name: &'static CStr,
        module: &'static ThisModule,
    ) -> Result;

    /// Unregisters a driver previously registered with [`RegistrationOps::register`].
    ///
    /// # Safety
    ///
    /// Must only be called after a preceding successful call to [`RegistrationOps::register`] for
    /// the same `reg`.
    unsafe fn unregister(reg: &Opaque<Self::DriverType>);
}

/// A [`Registration`] is a generic type that represents the registration of some driver type (e.g.
/// `bindings::pci_driver`). Therefore a [`Registration`] must be initialized with a type that
/// implements the [`RegistrationOps`] trait, such that the generic `T::register` and
/// `T::unregister` calls result in the subsystem specific registration calls.
///
///Once the `Registration` structure is dropped, the driver is unregistered.
#[pin_data(PinnedDrop)]
pub struct Registration<T: RegistrationOps> {
    #[pin]
    reg: Opaque<T::DriverType>,
}

// 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: RegistrationOps> Sync for Registration<T> {}

// SAFETY: Both registration and unregistration are implemented in C and safe to be performed from
// any thread, so `Registration` is `Send`.
unsafe impl<T: RegistrationOps> Send for Registration<T> {}

impl<T: RegistrationOps> Registration<T> {
    extern "C" fn post_unbind_callback(dev: *mut bindings::device) {
        // SAFETY: The driver core only ever calls the post unbind callback with a valid pointer to
        // a `struct device`.
        //
        // INVARIANT: `dev` is valid for the duration of the `post_unbind_callback()`.
        let dev = unsafe { &*dev.cast::<device::Device<device::CoreInternal<'_>>>() };

        // `remove()` has been completed at this point; devres resources are still valid and will
        // be released after the driver's bus device private data is dropped.
        //
        // SAFETY: By the safety requirements of the `Driver` trait, `T::DriverData` is the
        // driver's bus device private data type.
        drop(unsafe { dev.drvdata_obtain::<T::DriverData<'_>>() });
    }

    /// Attach generic `struct device_driver` callbacks.
    fn callbacks_attach(drv: &Opaque<T::DriverType>) {
        let ptr = drv.get().cast::<u8>();

        // SAFETY:
        // - `drv.get()` yields a valid pointer to `Self::DriverType`.
        // - Adding `DEVICE_DRIVER_OFFSET` yields the address of the embedded `struct device_driver`
        //   as guaranteed by the safety requirements of the `Driver` trait.
        let base = unsafe { ptr.add(T::DEVICE_DRIVER_OFFSET) };

        // CAST: `base` points to the offset of the embedded `struct device_driver`.
        let base = base.cast::<bindings::device_driver>();

        // SAFETY: It is safe to set the fields of `struct device_driver` on initialization.
        unsafe { (*base).p_cb.post_unbind_rust = Some(Self::post_unbind_callback) };
    }

    /// Creates a new instance of the registration object.
    pub fn new(name: &'static CStr, module: &'static ThisModule) -> impl PinInit<Self, Error>
    where
        T: 'static,
    {
        try_pin_init!(Self {
            reg <- Opaque::try_ffi_init(|ptr: *mut T::DriverType| {
                // SAFETY: `try_ffi_init` guarantees that `ptr` is valid for write.
                unsafe { ptr.write(T::DriverType::default()) };

                // SAFETY: `try_ffi_init` guarantees that `ptr` is valid for write, and it has
                // just been initialised above, so it's also valid for read.
                let drv = unsafe { &*(ptr as *const Opaque<T::DriverType>) };

                Self::callbacks_attach(drv);

                // SAFETY: `drv` is guaranteed to be pinned until `T::unregister`.
                unsafe { T::register(drv, name, module) }
            }),
        })
    }
}

#[pinned_drop]
impl<T: RegistrationOps> PinnedDrop for Registration<T> {
    fn drop(self: Pin<&mut Self>) {
        // SAFETY: The existence of `self` guarantees that `self.reg` has previously been
        // successfully registered with `T::register`
        unsafe { T::unregister(&self.reg) };
    }
}

/// Declares a kernel module that exposes a single driver.
///
/// It is meant to be used as a helper by other subsystems so they can more easily expose their own
/// macros.
#[macro_export]
macro_rules! module_driver {
    (<$gen_type:ident>, $driver_ops:ty, { type: $type:ty, $($f:tt)* }) => {
        type Ops<$gen_type> = $driver_ops;

        #[$crate::prelude::pin_data]
        struct DriverModule {
            #[pin]
            _driver: $crate::driver::Registration<Ops<$type>>,
        }

        impl $crate::InPlaceModule for DriverModule {
            fn init(
                module: &'static $crate::ThisModule
            ) -> impl ::pin_init::PinInit<Self, $crate::error::Error> {
                $crate::try_pin_init!(Self {
                    _driver <- $crate::driver::Registration::new(
                        <Self as $crate::ModuleMetadata>::NAME,
                        module,
                    ),
                })
            }
        }

        $crate::prelude::module! {
            type: DriverModule,
            $($f)*
        }
    }
}

/// The bus independent adapter to match a drivers and a devices.
///
/// This trait should be implemented by the bus specific adapter, which represents the connection
/// of a device and a driver.
///
/// It provides bus independent functions for device / driver interactions.
pub trait Adapter {
    /// The type holding driver private data about each device id supported by the driver.
    type IdInfo: 'static;

    /// The [`acpi::IdTable`] of the corresponding driver
    fn acpi_id_table() -> Option<acpi::IdTable<Self::IdInfo>>;

    /// The [`of::IdTable`] of the corresponding driver.
    fn of_id_table() -> Option<of::IdTable<Self::IdInfo>>;

    /// Returns the driver's private data from the matching entry of any of the ID tables, if any.
    ///
    /// If this returns `None`, it means that there is no match in any of the ID tables directly
    /// associated with a [`device::Device`].
    ///
    /// # Safety
    ///
    /// The caller must ensure that the `dev` matched data is of type `Self::IdInfo`.
    #[inline]
    unsafe fn id_info(dev: &device::Device) -> Option<&'static Self::IdInfo> {
        // SAFETY: `dev` is guaranteed to be valid while it's alive, and so is `dev.as_raw()`.
        let data = unsafe { bindings::device_get_match_data(dev.as_raw()) };

        // SAFETY: Per safety requirement, `data` is of type `Self::IdInfo`.
        unsafe { data.cast::<Self::IdInfo>().as_ref() }
    }
}