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rust: i2c: add basic I2C device and driver abstractions

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Implement the core abstractions needed for I2C drivers, including:

* `i2c::Driver` — the trait drivers must implement, including `probe`

* `i2c::I2cClient` — a safe wrapper around `struct i2c_client`

* `i2c::Adapter` — implements `driver::RegistrationOps` to hook into the
  generic `driver::Registration` machinery

* `i2c::DeviceId` — a `RawDeviceIdIndex` implementation for I2C device IDs

Acked-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Igor Korotin <igor.korotin.linux@gmail.com>
Link: https://patch.msgid.link/20251116162144.171469-1-igor.korotin.linux@gmail.com
[ Remove unnecessary safety comment; fix rustdoc `Device` -> `I2cClient`.
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
This commit is contained in:
Igor Korotin
2025-11-16 16:21:44 +00:00
committed by Danilo Krummrich
parent dd6ff5cf56
commit 57c5bd9aee
4 changed files with 445 additions and 0 deletions
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8
MAINTAINERS
View File

@@ -11743,6 +11743,14 @@ F: include/linux/i2c.h
F: include/uapi/linux/i2c-*.h
F: include/uapi/linux/i2c.h
I2C SUBSYSTEM [RUST]
M: Igor Korotin <igor.korotin.linux@gmail.com>
R: Danilo Krummrich <dakr@kernel.org>
R: Daniel Almeida <daniel.almeida@collabora.com>
L: rust-for-linux@vger.kernel.org
S: Maintained
F: rust/kernel/i2c.rs
I2C SUBSYSTEM HOST DRIVERS
M: Andi Shyti <andi.shyti@kernel.org>
L: linux-i2c@vger.kernel.org

1
rust/bindings/bindings_helper.h
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@@ -58,6 +58,7 @@
#include <linux/firmware.h>
#include <linux/interrupt.h>
#include <linux/fs.h>
#include <linux/i2c.h>
#include <linux/ioport.h>
#include <linux/jiffies.h>
#include <linux/jump_label.h>

434
rust/kernel/i2c.rs Normal file
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@@ -0,0 +1,434 @@
// SPDX-License-Identifier: GPL-2.0
//! I2C Driver subsystem
// I2C Driver abstractions.
use crate::{
acpi,
container_of,
device,
device_id::{
RawDeviceId,
RawDeviceIdIndex, //
},
driver,
error::*,
of,
prelude::*,
types::{
AlwaysRefCounted,
Opaque, //
}, //
};
use core::{
marker::PhantomData,
ptr::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 {
build_assert!(
id.len_with_nul() <= Self::I2C_NAME_SIZE,
"ID exceeds 20 bytes"
);
let src = id.as_bytes_with_nul();
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 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 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 {}

2
rust/kernel/lib.rs
View File

@@ -94,6 +94,8 @@ pub mod faux;
pub mod firmware;
pub mod fmt;
pub mod fs;
#[cfg(CONFIG_I2C = "y")]
pub mod i2c;
pub mod id_pool;
pub mod init;
pub mod io;