Merge tag 'driver-core-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-coreHEADtorvalds/mastertorvalds/HEADmaster

Pull driver core updates from Danilo Krummrich:
 "Arch Topology:
   - Move parse_acpi_topology() from arm64 to common code for reuse in
     RISC-V

  CPU:
   - Expose housekeeping CPUs through /sys/devices/system/cpu/housekeeping
   - Print a newline (or 0x0A) instead of '(null)' reading
     /sys/devices/system/cpu/nohz_full when nohz_full= is not set

  debugfs
   - Remove (broken) 'no-mount' mode
   - Remove redundant access mode checks in debugfs_get_tree() and
     debugfs_create_*() functions

  Devres:
   - Remove unused devm_free_percpu() helper
   - Move devm_alloc_percpu() from device.h to devres.h

  Firmware Loader:
   - Replace simple_strtol() with kstrtoint()
   - Do not call cancel_store() when no upload is in progress

  kernfs:
   - Increase struct super_block::maxbytes to MAX_LFS_FILESIZE
   - Fix a missing unwind path in __kernfs_new_node()

  Misc:
   - Increase the name size in struct auxiliary_device_id to 40
     characters
   - Replace system_unbound_wq with system_dfl_wq and add WQ_PERCPU to
     alloc_workqueue()

  Platform:
   - Replace ERR_PTR() with IOMEM_ERR_PTR() in platform ioremap
     functions

  Rust:
   - Auxiliary:
      - Unregister auxiliary device on parent device unbind
      - Move parent() to impl Device; implement device context aware
        parent() for Device<Bound>
      - Illustrate how to safely obtain a driver's device private data
        when calling from an auxiliary driver into the parant device
        driver

   - DebugFs:
      - Implement support for binary large objects

   - Device:
      - Let probe() return the driver's device private data as pinned
        initializer, i.e. impl PinInit<Self, Error>
      - Implement safe accessor for a driver's device private data for
        Device<Bound> (returned reference can't out-live driver binding
        and guarantees the correct private data type)
      - Implement AsBusDevice trait, to be used by class device
        abstractions to derive the bus device type of the parent device

   - DMA:
      - Store raw pointer of allocation as NonNull
      - Use start_ptr() and start_ptr_mut() to inherit correct
        mutability of self

   - FS:
      - Add file::Offset type alias

   - I2C:
      - Add abstractions for I2C device / driver infrastructure
      - Implement abstractions for manual I2C device registrations

   - I/O:
      - Use "kernel vertical" style for imports
      - Define ResourceSize as resource_size_t
      - Move ResourceSize to top-level I/O module
      - Add type alias for phys_addr_t
      - Implement Rust version of read_poll_timeout_atomic()

   - PCI:
      - Use "kernel vertical" style for imports
      - Move I/O and IRQ infrastructure to separate files
      - Add support for PCI interrupt vectors
      - Implement TryInto<IrqRequest<'a>> for IrqVector<'a> to convert
        an IrqVector bound to specific pci::Device into an IrqRequest
        bound to the same pci::Device's parent Device
      - Leverage pin_init_scope() to get rid of redundant Result in IRQ
        methods

   - PinInit:
      - Add {pin_}init_scope() to execute code before creating an
        initializer

   - Platform:
      - Leverage pin_init_scope() to get rid of redundant Result in IRQ
        methods

   - Timekeeping:
      - Implement abstraction of udelay()

   - Uaccess:
      - Implement read_slice_partial() and read_slice_file() for
        UserSliceReader
      - Implement write_slice_partial() and write_slice_file() for
        UserSliceWriter

  sysfs:
   - Prepare the constification of struct attribute"

* tag 'driver-core-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/driver-core/driver-core: (75 commits)
  rust: pci: fix build failure when CONFIG_PCI_MSI is disabled
  debugfs: Fix default access mode config check
  debugfs: Remove broken no-mount mode
  debugfs: Remove redundant access mode checks
  driver core: Check drivers_autoprobe for all added devices
  driver core: WQ_PERCPU added to alloc_workqueue users
  driver core: replace use of system_unbound_wq with system_dfl_wq
  tick/nohz: Expose housekeeping CPUs in sysfs
  tick/nohz: avoid showing '(null)' if nohz_full= not set
  sysfs/cpu: Use DEVICE_ATTR_RO for nohz_full attribute
  kernfs: fix memory leak of kernfs_iattrs in __kernfs_new_node
  fs/kernfs: raise sb->maxbytes to MAX_LFS_FILESIZE
  mod_devicetable: Bump auxiliary_device_id name size
  sysfs: simplify attribute definition macros
  samples/kobject: constify 'struct foo_attribute'
  samples/kobject: add is_visible() callback to attribute group
  sysfs: attribute_group: enable const variants of is_visible()
  sysfs: introduce __SYSFS_FUNCTION_ALTERNATIVE()
  sysfs: transparently handle const pointers in ATTRIBUTE_GROUPS()
  sysfs: attribute_group: allow registration of const attribute
  ...

1 files changed, 586 insertions, 0 deletions

diff --git a/rust/kernel/i2c.rs b/rust/kernel/i2c.rs
new file mode 100644
index 000000000000..491e6cc25cf4
--- /dev/null
+++ b/rust/kernel/i2c.rs
@@ -0,0 +1,586 @@
+// 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::*,
+    types::{
+        AlwaysRefCounted,
+        Opaque, //
+    }, //
+};
+
+use core::{
+    marker::PhantomData,
+    mem::offset_of,
+    ptr::{
+        from_ref,
+        NonNull, //
+    }, //
+};
+
+use kernel::types::ARef;
+
+/// 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);
+
+    fn index(&self) -> usize {
+        self.0.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 {
+    ($table_name:ident, $module_table_name:ident, $id_info_type: ty, $table_data: expr) => {
+        const $table_name: $crate::device_id::IdArray<
+            $crate::i2c::DeviceId,
+            $id_info_type,
+            { $table_data.len() },
+        > = $crate::device_id::IdArray::new($table_data);
+
+        $crate::module_device_table!("i2c", $module_table_name, $table_name);
+    };
+}
+
+/// An adapter for the registration of I2C 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::i2c_driver;
+
+    unsafe fn register(
+        idrv: &Opaque<Self::RegType>,
+        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 `RegType`.
+        to_result(unsafe { bindings::i2c_register_driver(module.0, idrv.get()) })
+    }
+
+    unsafe fn unregister(idrv: &Opaque<Self::RegType>) {
+        // SAFETY: `idrv` is guaranteed to be a valid `RegType`.
+        unsafe { bindings::i2c_del_driver(idrv.get()) }
+    }
+}
+
+impl<T: Driver + 'static> 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(|| <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>>`.
+        let data = unsafe { idev.as_ref().drvdata_obtain::<T>() };
+
+        T::unbind(idev, data.as_ref());
+    }
+
+    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>>`.
+        let data = unsafe { idev.as_ref().drvdata_obtain::<T>() };
+
+        T::shutdown(idev, data.as_ref());
+    }
+
+    /// 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>() };
+
+        Some(table.info(<DeviceId as RawDeviceIdIndex>::index(id)))
+    }
+}
+
+impl<T: Driver + 'static> 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, c_str, device::Core, i2c, of};
+///
+/// struct MyDriver;
+///
+/// kernel::acpi_device_table!(
+///     ACPI_TABLE,
+///     MODULE_ACPI_TABLE,
+///     <MyDriver as i2c::Driver>::IdInfo,
+///     [
+///         (acpi::DeviceId::new(c_str!("LNUXBEEF")), ())
+///     ]
+/// );
+///
+/// kernel::i2c_device_table!(
+///     I2C_TABLE,
+///     MODULE_I2C_TABLE,
+///     <MyDriver as i2c::Driver>::IdInfo,
+///     [
+///          (i2c::DeviceId::new(c_str!("rust_driver_i2c")), ())
+///     ]
+/// );
+///
+/// kernel::of_device_table!(
+///     OF_TABLE,
+///     MODULE_OF_TABLE,
+///     <MyDriver as i2c::Driver>::IdInfo,
+///     [
+///         (of::DeviceId::new(c_str!("test,device")), ())
+///     ]
+/// );
+///
+/// impl i2c::Driver for MyDriver {
+///     type IdInfo = ();
+///     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(
+///         _idev: &i2c::I2cClient<Core>,
+///         _id_info: Option<&Self::IdInfo>,
+///     ) -> impl PinInit<Self, Error> {
+///         Err(ENODEV)
+///     }
+///
+///     fn shutdown(_idev: &i2c::I2cClient<Core>, this: Pin<&Self>) {
+///     }
+/// }
+///```
+pub trait Driver: Send {
+    /// 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 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(
+        dev: &I2cClient<device::Core>,
+        id_info: Option<&Self::IdInfo>,
+    ) -> impl PinInit<Self, Error>;
+
+    /// 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 `Self::drop`.
+    fn shutdown(dev: &I2cClient<device::Core>, this: Pin<&Self>) {
+        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 `Self::drop`.
+    fn unbind(dev: &I2cClient<device::Core>, this: Pin<&Self>) {
+        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.
+        Ok(unsafe { (&*adapter.as_ptr().cast::<I2cAdapter<device::Normal>>()).into() })
+    }
+}
+
+// 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 crate::types::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 {}