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charset=utf-8 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.700.81\)) Subject: Re: [PATCH v4 1/3] rust: i2c: add basic I2C device and driver abstractions From: Daniel Almeida In-Reply-To: <20250820151913.1814284-1-igor.korotin.linux@gmail.com> Date: Wed, 27 Aug 2025 15:37:36 -0300 Cc: Miguel Ojeda , Alex Gaynor , Wolfram Sang , Boqun Feng , Gary Guo , =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Greg Kroah-Hartman , Viresh Kumar , Asahi Lina , Wedson Almeida Filho , Alex Hung , Tamir Duberstein , Xiangfei Ding , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-i2c@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: References: <20250820151427.1812482-1-igor.korotin.linux@gmail.com> <20250820151913.1814284-1-igor.korotin.linux@gmail.com> To: Igor Korotin X-Mailer: Apple Mail (2.3826.700.81) X-ZohoMailClient: External Hi Igor, > On 20 Aug 2025, at 12:19, Igor Korotin = wrote: >=20 > Implement the core abstractions needed for I2C drivers, including: >=20 > - `i2c::Driver` =E2=80=94 the trait drivers must implement, including = `probe` >=20 > - `i2c::I2cClient` =E2=80=94 a safe wrapper around `struct i2c_client` >=20 > - `i2c::Adapter` =E2=80=94 implements `driver::RegistrationOps` to = hook into the > generic `driver::Registration` machinery >=20 > - `i2c::DeviceId` =E2=80=94 a `RawDeviceIdIndex` implementation for = I2C > device IDs >=20 > Signed-off-by: Igor Korotin > --- > MAINTAINERS | 8 + > rust/bindings/bindings_helper.h | 1 + > rust/kernel/i2c.rs | 396 ++++++++++++++++++++++++++++++++ > rust/kernel/lib.rs | 2 + > 4 files changed, 407 insertions(+) > create mode 100644 rust/kernel/i2c.rs >=20 > diff --git a/MAINTAINERS b/MAINTAINERS > index fe168477caa4..c44c7ac317b1 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -11516,6 +11516,14 @@ F: include/linux/i2c.h > F: include/uapi/linux/i2c-*.h > F: include/uapi/linux/i2c.h >=20 > +I2C SUBSYSTEM [RUST] > +M: Igor Korotin > +R: Danilo Krummrich > +R: Daniel Almeida > +L: rust-for-linux@vger.kernel.org > +S: Maintained > +F: rust/kernel/i2c.rs > + > I2C SUBSYSTEM HOST DRIVERS > M: Andi Shyti > L: linux-i2c@vger.kernel.org > diff --git a/rust/bindings/bindings_helper.h = b/rust/bindings/bindings_helper.h > index 84d60635e8a9..81796d5e16e8 100644 > --- a/rust/bindings/bindings_helper.h > +++ b/rust/bindings/bindings_helper.h > @@ -53,6 +53,7 @@ > #include > #include > #include > +#include > #include > #include > #include > diff --git a/rust/kernel/i2c.rs b/rust/kernel/i2c.rs > new file mode 100644 > index 000000000000..f5e8c4bc1b7d > --- /dev/null > +++ b/rust/kernel/i2c.rs > @@ -0,0 +1,396 @@ > +// 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::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 =3D 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() <=3D Self::I2C_NAME_SIZE, > + "ID exceeds 20 bytes" > + ); > + let src =3D id.as_bytes_with_nul(); > + // Replace with `bindings::acpi_device_id::default()` once = stabilized for `const`. > + // SAFETY: FFI type is valid to be zero-initialized. > + let mut i2c: bindings::i2c_device_id =3D unsafe { = core::mem::zeroed() }; > + let mut i =3D 0; > + while i < src.len() { > + i2c.name[i] =3D src[i]; > + i +=3D 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 =3D 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 =3D = 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 =3D &'static dyn = kernel::device_id::IdTable; > + > +/// 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) =3D> { > + const $table_name: $crate::device_id::IdArray< > + $crate::i2c::DeviceId, > + $id_info_type, > + { $table_data.len() }, > + > =3D $crate::device_id::IdArray::new($table_data); > + > + $crate::module_device_table!("i2c", $module_table_name, = $table_name); > + }; > +} > + > +/// An adapter for the registration of I2C drivers. > +pub struct Adapter(T); > + > +// 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 driver::RegistrationOps for = Adapter { > + type RegType =3D bindings::i2c_driver; > + > + unsafe fn register( > + idrv: &Opaque, > + 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" > + ); =E2=80=A6=E2=80=9Dwhen registering an i2c driver=E2=80=9D. The generated error is cryptic, so we should add as much information as = possible. > + > + let i2c_table =3D match T::I2C_ID_TABLE { > + Some(table) =3D> table.as_ptr(), > + None =3D> core::ptr::null(), > + }; > + > + let of_table =3D match T::OF_ID_TABLE { > + Some(table) =3D> table.as_ptr(), > + None =3D> core::ptr::null(), > + }; > + > + let acpi_table =3D match T::ACPI_ID_TABLE { > + Some(table) =3D> table.as_ptr(), > + None =3D> core::ptr::null(), > + }; > + > + // SAFETY: It's safe to set the fields of `struct i2c_client` = on initialization. > + unsafe { > + (*idrv.get()).driver.name =3D name.as_char_ptr(); > + (*idrv.get()).probe =3D Some(Self::probe_callback); > + (*idrv.get()).remove =3D Some(Self::remove_callback); > + (*idrv.get()).shutdown =3D Some(Self::shutdown_callback); > + (*idrv.get()).id_table =3D i2c_table; > + (*idrv.get()).driver.of_match_table =3D of_table; > + (*idrv.get()).driver.acpi_match_table =3D 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) { > + // SAFETY: `idrv` is guaranteed to be a valid `RegType`. > + unsafe { bindings::i2c_del_driver(idrv.get()) } > + } > +} > + > +impl Adapter { > + 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 =3D unsafe { = &*idev.cast::>() }; > + > + let info =3D > + Self::i2c_id_info(idev).or_else(|| ::id_info(idev.as_ref())); I wonder if these should be private member functions? > + > + from_result(|| { > + let data =3D 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 =3D unsafe { = &*idev.cast::>() }; > + > + // 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>`. > + drop(unsafe { idev.as_ref().drvdata_obtain::>>() = }); > + } > + > + extern "C" fn shutdown_callback(idev: *mut bindings::i2c_client) = { > + // SAFETY: `shutdown_callback` is only ever called for a = valid `idev` > + let idev =3D unsafe { = &*idev.cast::>() }; > + > + T::shutdown(idev); > + } > + > + /// The [`i2c::IdTable`] of the corresponding driver. > + fn i2c_id_table() -> Option::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 ::IdInfo> { Again, perhaps a private member function? I=E2=80=99m trying to simplify = the syntax here. > + let table =3D 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 `idev.as_raw()`. I don=E2=80=99t see an =E2=80=9Cidev=E2=80=9D in scope? Perhaps you = meant =E2=80=9Cdev=E2=80=9D ? > + let raw_id =3D 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 =3D unsafe { &*raw_id.cast::() }; > + > + Some(table.info(::index(id))) Do we really need to use the fully-qualified syntax here? > + } > +} > + > +impl driver::Adapter for Adapter { > + type IdInfo =3D T::IdInfo; > + > + fn of_id_table() -> Option> { > + T::OF_ID_TABLE > + } > + > + fn acpi_id_table() -> Option> { > + 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)*) =3D> { > + $crate::module_driver!(, $crate::i2c::Adapter, { $($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, > +/// ::IdInfo, > +/// [ > +/// (acpi::DeviceId::new(c_str!("LNUXBEEF")), ()) > +/// ] > +/// ); > +/// > +/// kernel::i2c_device_table!( > +/// I2C_TABLE, > +/// MODULE_I2C_TABLE, > +/// ::IdInfo, > +/// [ > +/// (i2c::DeviceId::new(c_str!("rust_driver_i2c")), ()) > +/// ] > +/// ); > +/// > +/// kernel::of_device_table!( > +/// OF_TABLE, > +/// MODULE_OF_TABLE, > +/// ::IdInfo, > +/// [ > +/// (of::DeviceId::new(c_str!("test,device")), ()) > +/// ] > +/// ); > +/// > +/// impl i2c::Driver for MyDriver { > +/// type IdInfo =3D (); > +/// const I2C_ID_TABLE: Option> =3D = Some(&I2C_TABLE); > +/// const OF_ID_TABLE: Option> =3D = Some(&OF_TABLE); > +/// const ACPI_ID_TABLE: Option> =3D = Some(&ACPI_TABLE); > +/// > +/// fn probe( > +/// _idev: &i2c::I2cClient, > +/// _id_info: Option<&Self::IdInfo>, > +/// ) -> Result>> { > +/// Err(ENODEV) > +/// } > +/// > +/// fn shutdown(_idev: &i2c::I2cClient) { > +/// } > +/// } > +///``` > +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 =3D (); > + // ``` > + type IdInfo: 'static; > + > + /// The table of device ids supported by the driver. > + const I2C_ID_TABLE: Option> =3D None; > + > + /// The table of OF device ids supported by the driver. > + const OF_ID_TABLE: Option> =3D None; > + > + /// The table of ACPI device ids supported by the driver. > + const ACPI_ID_TABLE: Option> =3D = 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, > + id_info: Option<&Self::IdInfo>, > + ) -> Result>>; > + > + /// I2C driver shutdown > + /// > + /// Called when > + fn shutdown(dev: &I2cClient) { > + let _ =3D dev; > + } > +} > + > +/// 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( > + Opaque, > + PhantomData, > +); > + > +impl I2cClient { > + 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 crate::types::AlwaysRefCounted for I2cClient { I=E2=80=99d import this. > + 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) { > + // SAFETY: The safety requirements guarantee that the = refcount is non-zero. > + unsafe { bindings::put_device(&raw mut = (*obj.as_ref().as_raw()).dev) } > + } > +} > + > +impl AsRef> for = I2cClient { > + fn as_ref(&self) -> &device::Device { > + let raw =3D self.as_raw(); > + // SAFETY: By the type invariant of `Self`, `self.as_raw()` = is a pointer to a valid > + // `struct i2c_client`. > + let dev =3D unsafe { &raw mut (*raw).dev }; > + > + // SAFETY: `dev` points to a valid `struct device`. > + unsafe { device::Device::from_raw(dev) } > + } > +} > + > +impl TryFrom<&device::Device> for = &I2cClient { > + type Error =3D kernel::error::Error; > + > + fn try_from(dev: &device::Device) -> Result { > + // 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 =3D 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) are thread safe. > +unsafe impl Sync for I2cClient {} > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs > index ed53169e795c..a5e97a9b1546 100644 > --- a/rust/kernel/lib.rs > +++ b/rust/kernel/lib.rs > @@ -89,6 +89,8 @@ > pub mod firmware; > pub mod fmt; > pub mod fs; > +#[cfg(CONFIG_I2C =3D "y")] > +pub mod i2c; > pub mod init; > pub mod io; > pub mod ioctl; > --=20 > 2.43.0 >=20 >=20