rust/kernel/i2c.rs

// SPDX-License-Identifier: GPL-2.0

//! I2C Driver subsystem

// I2C Driver abstractions.
use crate::{
    acpi,
    container_of,
    device,
    device_id::{
        RawDeviceId,
        RawDeviceIdIndex, //
    },
    devres::Devres,
    driver,
    error::*,
    of,
    prelude::*,
    sync::aref::{
        ARef,
        AlwaysRefCounted, //
    },
    types::Opaque, //
};

use core::{
    marker::PhantomData,
    mem::offset_of,
    ptr::{
        from_ref,
        NonNull, //
    }, //
};

/// An I2C device id table.
#[repr(transparent)]
#[derive(Clone, Copy)]
pub struct DeviceId(bindings::i2c_device_id);

impl DeviceId {
    const I2C_NAME_SIZE: usize = 20;

    /// Create a new device id from an I2C 'id' string.
    #[inline(always)]
    pub const fn new(id: &'static CStr) -> Self {
        let src = id.to_bytes_with_nul();
        build_assert!(src.len() <= Self::I2C_NAME_SIZE, "ID exceeds 20 bytes");
        let mut i2c: bindings::i2c_device_id = pin_init::zeroed();
        let mut i = 0;
        while i < src.len() {
            i2c.name[i] = src[i];
            i += 1;
        }

        Self(i2c)
    }
}

// SAFETY: `DeviceId` is a `#[repr(transparent)]` wrapper of `i2c_device_id` and does not add
// additional invariants, so it's safe to transmute to `RawType`.
unsafe impl RawDeviceId for DeviceId {
    type RawType = bindings::i2c_device_id;
}

// SAFETY: `DRIVER_DATA_OFFSET` is the offset to the `driver_data` field.
unsafe impl RawDeviceIdIndex for DeviceId {
    const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::i2c_device_id, driver_data);
}

/// IdTable type for I2C
pub type IdTable<T> = &'static dyn kernel::device_id::IdTable<DeviceId, T>;

/// Create a I2C `IdTable` with its alias for modpost.
#[macro_export]
macro_rules! i2c_device_table {
    ($($tt:tt)*) => {
        $crate::module_device_table!("i2c", $crate::i2c::DeviceId, $($tt)*);
    };
}

/// An adapter for the registration of I2C drivers.
pub struct Adapter<T: Driver>(T);

// SAFETY:
// - `bindings::i2c_driver` is a C type declared as `repr(C)`.
// - `T::Data` is the type of the driver's device private data.
// - `struct i2c_driver` embeds a `struct device_driver`.
// - `DEVICE_DRIVER_OFFSET` is the correct byte offset to the embedded `struct device_driver`.
unsafe impl<T: Driver> driver::DriverLayout for Adapter<T> {
    type DriverType = bindings::i2c_driver;
    type DriverData<'bound> = T::Data<'bound>;
    const DEVICE_DRIVER_OFFSET: usize = core::mem::offset_of!(Self::DriverType, driver);
}

// SAFETY: A call to `unregister` for a given instance of `DriverType` is guaranteed to be valid if
// a preceding call to `register` has been successful.
unsafe impl<T: Driver> driver::RegistrationOps for Adapter<T> {
    unsafe fn register(
        idrv: &Opaque<Self::DriverType>,
        name: &'static CStr,
        module: &'static ThisModule,
    ) -> Result {
        build_assert!(
            T::ACPI_ID_TABLE.is_some() || T::OF_ID_TABLE.is_some() || T::I2C_ID_TABLE.is_some(),
            "At least one of ACPI/OF/Legacy tables must be present when registering an i2c driver"
        );

        let i2c_table = match T::I2C_ID_TABLE {
            Some(table) => table.as_ptr(),
            None => core::ptr::null(),
        };

        let of_table = match T::OF_ID_TABLE {
            Some(table) => table.as_ptr(),
            None => core::ptr::null(),
        };

        let acpi_table = match T::ACPI_ID_TABLE {
            Some(table) => table.as_ptr(),
            None => core::ptr::null(),
        };

        // SAFETY: It's safe to set the fields of `struct i2c_client` on initialization.
        unsafe {
            (*idrv.get()).driver.name = name.as_char_ptr();
            (*idrv.get()).probe = Some(Self::probe_callback);
            (*idrv.get()).remove = Some(Self::remove_callback);
            (*idrv.get()).shutdown = Some(Self::shutdown_callback);
            (*idrv.get()).id_table = i2c_table;
            (*idrv.get()).driver.of_match_table = of_table;
            (*idrv.get()).driver.acpi_match_table = acpi_table;
        }

        // SAFETY: `idrv` is guaranteed to be a valid `DriverType`.
        to_result(unsafe { bindings::i2c_register_driver(module.as_ptr(), idrv.get()) })
    }

    unsafe fn unregister(idrv: &Opaque<Self::DriverType>) {
        // SAFETY: `idrv` is guaranteed to be a valid `DriverType`.
        unsafe { bindings::i2c_del_driver(idrv.get()) }
    }
}

impl<T: Driver> Adapter<T> {
    extern "C" fn probe_callback(idev: *mut bindings::i2c_client) -> kernel::ffi::c_int {
        // SAFETY: The I2C bus only ever calls the probe callback with a valid pointer to a
        // `struct i2c_client`.
        //
        // INVARIANT: `idev` is valid for the duration of `probe_callback()`.
        let idev = unsafe { &*idev.cast::<I2cClient<device::CoreInternal<'_>>>() };

        let info = Self::i2c_id_info(idev).or_else(|| {
            // SAFETY: `idev` matched data is of type `Self::IdInfo`.
            unsafe { <Self as driver::Adapter>::id_info(idev.as_ref()) }
        });

        from_result(|| {
            let data = T::probe(idev, info);

            idev.as_ref().set_drvdata(data)?;
            Ok(0)
        })
    }

    extern "C" fn remove_callback(idev: *mut bindings::i2c_client) {
        // SAFETY: `idev` is a valid pointer to a `struct i2c_client`.
        let idev = unsafe { &*idev.cast::<I2cClient<device::CoreInternal<'_>>>() };

        // SAFETY: `remove_callback` is only ever called after a successful call to
        // `probe_callback`, hence it's guaranteed that `I2cClient::set_drvdata()` has been called
        // and stored a `Pin<KBox<T::Data<'_>>>`.
        let data = unsafe { idev.as_ref().drvdata_borrow::<T::Data<'_>>() };

        T::unbind(idev, data);
    }

    extern "C" fn shutdown_callback(idev: *mut bindings::i2c_client) {
        // SAFETY: `shutdown_callback` is only ever called for a valid `idev`
        let idev = unsafe { &*idev.cast::<I2cClient<device::CoreInternal<'_>>>() };

        // SAFETY: `shutdown_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 `Pin<KBox<T::Data<'_>>>`.
        let data = unsafe { idev.as_ref().drvdata_borrow::<T::Data<'_>>() };

        T::shutdown(idev, data);
    }

    /// The [`i2c::IdTable`] of the corresponding driver.
    fn i2c_id_table() -> Option<IdTable<<Self as driver::Adapter>::IdInfo>> {
        T::I2C_ID_TABLE
    }

    /// Returns the driver's private data from the matching entry in the [`i2c::IdTable`], if any.
    ///
    /// If this returns `None`, it means there is no match with an entry in the [`i2c::IdTable`].
    fn i2c_id_info(dev: &I2cClient) -> Option<&'static <Self as driver::Adapter>::IdInfo> {
        let table = Self::i2c_id_table()?;

        // SAFETY:
        // - `table` has static lifetime, hence it's valid for reads
        // - `dev` is guaranteed to be valid while it's alive, and so is `dev.as_raw()`.
        let raw_id = unsafe { bindings::i2c_match_id(table.as_ptr(), dev.as_raw()) };

        if raw_id.is_null() {
            return None;
        }

        // SAFETY: `DeviceId` is a `#[repr(transparent)` wrapper of `struct i2c_device_id` and
        // does not add additional invariants, so it's safe to transmute.
        let id = unsafe { &*raw_id.cast::<DeviceId>() };

        // SAFETY: `id` comes from `table` which is of type `IdArray<_, Self::IdInfo>`.
        Some(unsafe { id.info_unchecked::<T::IdInfo>() })
    }
}

impl<T: Driver> driver::Adapter for Adapter<T> {
    type IdInfo = T::IdInfo;

    fn of_id_table() -> Option<of::IdTable<Self::IdInfo>> {
        T::OF_ID_TABLE
    }

    fn acpi_id_table() -> Option<acpi::IdTable<Self::IdInfo>> {
        T::ACPI_ID_TABLE
    }
}

/// Declares a kernel module that exposes a single i2c driver.
///
/// # Examples
///
/// ```ignore
/// kernel::module_i2c_driver! {
///     type: MyDriver,
///     name: "Module name",
///     authors: ["Author name"],
///     description: "Description",
///     license: "GPL v2",
/// }
/// ```
#[macro_export]
macro_rules! module_i2c_driver {
    ($($f:tt)*) => {
        $crate::module_driver!(<T>, $crate::i2c::Adapter<T>, { $($f)* });
    };
}

/// The i2c driver trait.
///
/// Drivers must implement this trait in order to get a i2c driver registered.
///
/// # Example
///
///```
/// # use kernel::{acpi, bindings, device::Core, i2c, of};
///
/// struct MyDriver;
///
/// kernel::acpi_device_table!(
///     ACPI_TABLE,
///     <MyDriver as i2c::Driver>::IdInfo,
///     [
///         (acpi::DeviceId::new(c"LNUXBEEF"), ())
///     ]
/// );
///
/// kernel::i2c_device_table!(
///     I2C_TABLE,
///     <MyDriver as i2c::Driver>::IdInfo,
///     [
///          (i2c::DeviceId::new(c"rust_driver_i2c"), ())
///     ]
/// );
///
/// kernel::of_device_table!(
///     OF_TABLE,
///     <MyDriver as i2c::Driver>::IdInfo,
///     [
///         (of::DeviceId::new(c"test,device"), ())
///     ]
/// );
///
/// impl i2c::Driver for MyDriver {
///     type IdInfo = ();
///     type Data<'bound> = Self;
///     const I2C_ID_TABLE: Option<i2c::IdTable<Self::IdInfo>> = Some(&I2C_TABLE);
///     const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
///     const ACPI_ID_TABLE: Option<acpi::IdTable<Self::IdInfo>> = Some(&ACPI_TABLE);
///
///     fn probe<'bound>(
///         _idev: &'bound i2c::I2cClient<Core<'_>>,
///         _id_info: Option<&'bound Self::IdInfo>,
///     ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound {
///         Err(ENODEV)
///     }
///
///     fn shutdown<'bound>(
///         _idev: &'bound i2c::I2cClient<Core<'_>>,
///         this: Pin<&Self::Data<'bound>>,
///     ) {
///     }
/// }
///```
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 type of the driver's bus device private data.
    type Data<'bound>: Send + 'bound;

    /// The table of device ids supported by the driver.
    const I2C_ID_TABLE: Option<IdTable<Self::IdInfo>> = None;

    /// 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;

    /// I2C driver probe.
    ///
    /// Called when a new i2c client is added or discovered.
    /// Implementers should attempt to initialize the client here.
    fn probe<'bound>(
        dev: &'bound I2cClient<device::Core<'_>>,
        id_info: Option<&'bound Self::IdInfo>,
    ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound;

    /// I2C driver shutdown.
    ///
    /// Called by the kernel during system reboot or power-off to allow the [`Driver`] to bring the
    /// [`I2cClient`] into a safe state. Implementing this callback is optional.
    ///
    /// Typical actions include stopping transfers, disabling interrupts, or resetting the hardware
    /// to prevent undesired behavior during shutdown.
    ///
    /// This callback is distinct from final resource cleanup, as the driver instance remains valid
    /// after it returns. Any deallocation or teardown of driver-owned resources should instead be
    /// handled in `Drop`.
    fn shutdown<'bound>(dev: &'bound I2cClient<device::Core<'_>>, this: Pin<&Self::Data<'bound>>) {
        let _ = (dev, this);
    }

    /// I2C driver unbind.
    ///
    /// Called when the [`I2cClient`] is unbound from its bound [`Driver`]. Implementing this
    /// callback is optional.
    ///
    /// This callback serves as a place for drivers to perform teardown operations that require a
    /// `&Device<Core>` or `&Device<Bound>` reference. For instance, drivers may try to perform I/O
    /// operations to gracefully tear down the device.
    ///
    /// Otherwise, release operations for driver resources should be performed in `Drop`.
    fn unbind<'bound>(dev: &'bound I2cClient<device::Core<'_>>, this: Pin<&Self::Data<'bound>>) {
        let _ = (dev, this);
    }
}

/// The i2c adapter representation.
///
/// This structure represents the Rust abstraction for a C `struct i2c_adapter`. The
/// implementation abstracts the usage of an existing C `struct i2c_adapter` that
/// gets passed from the C side
///
/// # Invariants
///
/// A [`I2cAdapter`] instance represents a valid `struct i2c_adapter` created by the C portion of
/// the kernel.
#[repr(transparent)]
pub struct I2cAdapter<Ctx: device::DeviceContext = device::Normal>(
    Opaque<bindings::i2c_adapter>,
    PhantomData<Ctx>,
);

impl<Ctx: device::DeviceContext> I2cAdapter<Ctx> {
    fn as_raw(&self) -> *mut bindings::i2c_adapter {
        self.0.get()
    }
}

impl I2cAdapter {
    /// Returns the I2C Adapter index.
    #[inline]
    pub fn index(&self) -> i32 {
        // SAFETY: `self.as_raw` is a valid pointer to a `struct i2c_adapter`.
        unsafe { (*self.as_raw()).nr }
    }

    /// Gets pointer to an `i2c_adapter` by index.
    pub fn get(index: i32) -> Result<ARef<Self>> {
        // SAFETY: `index` must refer to a valid I2C adapter; the kernel
        // guarantees that `i2c_get_adapter(index)` returns either a valid
        // pointer or NULL. `NonNull::new` guarantees the correct check.
        let adapter = NonNull::new(unsafe { bindings::i2c_get_adapter(index) }).ok_or(ENODEV)?;

        // SAFETY: `adapter` is non-null and points to a live `i2c_adapter`.
        // `I2cAdapter` is #[repr(transparent)], so this cast is valid.
        // `i2c_get_adapter` returned the adapter with an incremented refcount, which we pass to
        // the `ARef`.
        Ok(unsafe { ARef::from_raw(adapter.cast::<I2cAdapter<device::Normal>>()) })
    }
}

// SAFETY: `I2cAdapter` is a transparent wrapper of a type that doesn't depend on
// `I2cAdapter`'s generic argument.
kernel::impl_device_context_deref!(unsafe { I2cAdapter });
kernel::impl_device_context_into_aref!(I2cAdapter);

// SAFETY: Instances of `I2cAdapter` are always reference-counted.
unsafe impl AlwaysRefCounted for I2cAdapter {
    fn inc_ref(&self) {
        // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
        unsafe { bindings::i2c_get_adapter(self.index()) };
    }

    unsafe fn dec_ref(obj: NonNull<Self>) {
        // SAFETY: The safety requirements guarantee that the refcount is non-zero.
        unsafe { bindings::i2c_put_adapter(obj.as_ref().as_raw()) }
    }
}

/// The i2c board info representation
///
/// This structure represents the Rust abstraction for a C `struct i2c_board_info` structure,
/// which is used for manual I2C client creation.
#[repr(transparent)]
pub struct I2cBoardInfo(bindings::i2c_board_info);

impl I2cBoardInfo {
    const I2C_TYPE_SIZE: usize = 20;
    /// Create a new [`I2cBoardInfo`] for a kernel driver.
    #[inline(always)]
    pub const fn new(type_: &'static CStr, addr: u16) -> Self {
        let src = type_.to_bytes_with_nul();
        build_assert!(src.len() <= Self::I2C_TYPE_SIZE, "Type exceeds 20 bytes");
        let mut i2c_board_info: bindings::i2c_board_info = pin_init::zeroed();
        let mut i: usize = 0;
        while i < src.len() {
            i2c_board_info.type_[i] = src[i];
            i += 1;
        }

        i2c_board_info.addr = addr;
        Self(i2c_board_info)
    }

    fn as_raw(&self) -> *const bindings::i2c_board_info {
        from_ref(&self.0)
    }
}

/// The i2c client representation.
///
/// This structure represents the Rust abstraction for a C `struct i2c_client`. The
/// implementation abstracts the usage of an existing C `struct i2c_client` that
/// gets passed from the C side
///
/// # Invariants
///
/// A [`I2cClient`] instance represents a valid `struct i2c_client` created by the C portion of
/// the kernel.
#[repr(transparent)]
pub struct I2cClient<Ctx: device::DeviceContext = device::Normal>(
    Opaque<bindings::i2c_client>,
    PhantomData<Ctx>,
);

impl<Ctx: device::DeviceContext> I2cClient<Ctx> {
    fn as_raw(&self) -> *mut bindings::i2c_client {
        self.0.get()
    }
}

// SAFETY: `I2cClient` is a transparent wrapper of `struct i2c_client`.
// The offset is guaranteed to point to a valid device field inside `I2cClient`.
unsafe impl<Ctx: device::DeviceContext> device::AsBusDevice<Ctx> for I2cClient<Ctx> {
    const OFFSET: usize = offset_of!(bindings::i2c_client, dev);
}

// SAFETY: `I2cClient` is a transparent wrapper of a type that doesn't depend on
// `I2cClient`'s generic argument.
kernel::impl_device_context_deref!(unsafe { I2cClient });
kernel::impl_device_context_into_aref!(I2cClient);

// SAFETY: Instances of `I2cClient` are always reference-counted.
unsafe impl AlwaysRefCounted for I2cClient {
    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) }
    }
}

impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for I2cClient<Ctx> {
    fn as_ref(&self) -> &device::Device<Ctx> {
        let raw = self.as_raw();
        // SAFETY: By the type invariant of `Self`, `self.as_raw()` is a pointer to a valid
        // `struct i2c_client`.
        let dev = unsafe { &raw mut (*raw).dev };

        // SAFETY: `dev` points to a valid `struct device`.
        unsafe { device::Device::from_raw(dev) }
    }
}

impl<Ctx: device::DeviceContext> TryFrom<&device::Device<Ctx>> for &I2cClient<Ctx> {
    type Error = kernel::error::Error;

    fn try_from(dev: &device::Device<Ctx>) -> Result<Self, Self::Error> {
        // SAFETY: By the type invariant of `Device`, `dev.as_raw()` is a valid pointer to a
        // `struct device`.
        if unsafe { bindings::i2c_verify_client(dev.as_raw()).is_null() } {
            return Err(EINVAL);
        }

        // SAFETY: We've just verified that the type of `dev` equals to
        // `bindings::i2c_client_type`, hence `dev` must be embedded in a valid
        // `struct i2c_client` as guaranteed by the corresponding C code.
        let idev = unsafe { container_of!(dev.as_raw(), bindings::i2c_client, dev) };

        // SAFETY: `idev` is a valid pointer to a `struct i2c_client`.
        Ok(unsafe { &*idev.cast() })
    }
}

// SAFETY: A `I2cClient` is always reference-counted and can be released from any thread.
unsafe impl Send for I2cClient {}

// SAFETY: `I2cClient` can be shared among threads because all methods of `I2cClient`
// (i.e. `I2cClient<Normal>) are thread safe.
unsafe impl Sync for I2cClient {}

/// The registration of an i2c client device.
///
/// This type represents the registration of a [`struct i2c_client`]. When an instance of this
/// type is dropped, its respective i2c client device will be unregistered from the system.
///
/// # Invariants
///
/// `self.0` always holds a valid pointer to an initialized and registered
/// [`struct i2c_client`].
#[repr(transparent)]
pub struct Registration(NonNull<bindings::i2c_client>);

impl Registration {
    /// The C `i2c_new_client_device` function wrapper for manual I2C client creation.
    pub fn new<'a>(
        i2c_adapter: &I2cAdapter,
        i2c_board_info: &I2cBoardInfo,
        parent_dev: &'a device::Device<device::Bound>,
    ) -> impl PinInit<Devres<Self>, Error> + 'a {
        Devres::new(parent_dev, Self::try_new(i2c_adapter, i2c_board_info))
    }

    fn try_new(i2c_adapter: &I2cAdapter, i2c_board_info: &I2cBoardInfo) -> Result<Self> {
        // SAFETY: the kernel guarantees that `i2c_new_client_device()` returns either a valid
        // pointer or NULL. `from_err_ptr` separates errors. Following `NonNull::new`
        // checks for NULL.
        let raw_dev = from_err_ptr(unsafe {
            bindings::i2c_new_client_device(i2c_adapter.as_raw(), i2c_board_info.as_raw())
        })?;

        let dev_ptr = NonNull::new(raw_dev).ok_or(ENODEV)?;

        Ok(Self(dev_ptr))
    }
}

impl Drop for Registration {
    fn drop(&mut self) {
        // SAFETY: `Drop` is only called for a valid `Registration`, which by invariant
        // always contains a non-null pointer to an `i2c_client`.
        unsafe { bindings::i2c_unregister_device(self.0.as_ptr()) }
    }
}

// SAFETY: A `Registration` of a `struct i2c_client` can be released from any thread.
unsafe impl Send for Registration {}

// SAFETY: `Registration` offers no interior mutability (no mutation through &self
// and no mutable access is exposed)
unsafe impl Sync for Registration {}