This is my very first Rust abstraction in the kernel, I took inspiration from various other abstractions that had already been written.
I only implemented enough to rewrite a very simple driver I wrote in the past, in order to test the API and make sure it’s at least as ergonomic as the C version, without any unsafe at all. Signed-off-by: Link Mauve <[email protected]> --- rust/bindings/bindings_helper.h | 1 + rust/kernel/lib.rs | 2 + rust/kernel/nvmem.rs | 163 ++++++++++++++++++++++++++++++++ 3 files changed, 166 insertions(+) create mode 100644 rust/kernel/nvmem.rs diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index a067038b4b42..522a76b2e294 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -65,6 +65,7 @@ #include <linux/mdio.h> #include <linux/mm.h> #include <linux/miscdevice.h> +#include <linux/nvmem-provider.h> #include <linux/of_device.h> #include <linux/pci.h> #include <linux/phy.h> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 696f62f85eb5..97f3fc1e8e12 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -118,6 +118,8 @@ #[cfg(CONFIG_NET)] pub mod net; pub mod num; +#[cfg(CONFIG_NVMEM)] +pub mod nvmem; pub mod of; #[cfg(CONFIG_PM_OPP)] pub mod opp; diff --git a/rust/kernel/nvmem.rs b/rust/kernel/nvmem.rs new file mode 100644 index 000000000000..4b81fd65c9a7 --- /dev/null +++ b/rust/kernel/nvmem.rs @@ -0,0 +1,163 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! nvmem framework provider. +//! +//! Copyright (C) 2026 Link Mauve <[email protected]> + +use crate::build_error; +use crate::device::Device; +use crate::error::{from_result, VTABLE_DEFAULT_ERROR}; +use crate::prelude::*; +use core::marker::PhantomData; +use macros::vtable; + +/// The possible types for a nvmem provider. +#[derive(Default)] +#[repr(u32)] +pub enum Type { + /// The type of memory is unknown. + #[default] + Unknown = bindings::nvmem_type_NVMEM_TYPE_UNKNOWN, + + /// Electrically erasable programmable ROM. + Eeprom = bindings::nvmem_type_NVMEM_TYPE_EEPROM, + + /// One-time programmable memory. + Otp = bindings::nvmem_type_NVMEM_TYPE_OTP, + + /// This memory is backed by a battery. + BatteryBacked = bindings::nvmem_type_NVMEM_TYPE_BATTERY_BACKED, + + /// Ferroelectric RAM. + Fram = bindings::nvmem_type_NVMEM_TYPE_FRAM, +} + +/// nvmem configuration. +/// +/// Rust abstraction for the C `struct nvmem_config`. +#[derive(Default)] +#[repr(transparent)] +pub struct NvmemConfig<T: NvmemProvider + Default> { + inner: bindings::nvmem_config, + _p: PhantomData<T>, +} + +impl<T: NvmemProvider + Default> NvmemConfig<T> { + /// NvmemConfig's read callback. + /// + /// SAFETY: Called from C. Inputs must be valid pointers. + extern "C" fn reg_read( + context: *mut c_void, + offset: u32, + val: *mut c_void, + bytes: usize, + ) -> i32 { + from_result(|| { + let context = context.cast::<T::Priv>(); + // SAFETY: context is a valid T::Priv as set in Device::nvmem_register(). + let context = unsafe { &*context }; + let val = val.cast::<u8>(); + // SAFETY: val should be non-null, and allocated for bytes bytes. + let data = unsafe { core::slice::from_raw_parts_mut(val, bytes) }; + T::read(context, offset, data).map(|()| 0) + }) + } + + /// NvmemConfig's write callback. + /// + /// SAFETY: Called from C. Inputs must be valid pointers. + extern "C" fn reg_write( + context: *mut c_void, + offset: u32, + // TODO: Change val from void* to const void* in the C API! + val: *mut c_void, + bytes: usize, + ) -> i32 { + from_result(|| { + let context = context.cast::<T::Priv>(); + // SAFETY: context is a valid T::Priv as set in Device::nvmem_register(). + let context = unsafe { &*context }; + let val = val.cast::<u8>().cast_const(); + // SAFETY: val should be non-null, and allocated for bytes bytes. + let data = unsafe { core::slice::from_raw_parts(val, bytes) }; + T::write(context, offset, data).map(|()| 0) + }) + } + + /// Optional name. + pub fn with_name(mut self, name: &CStr) -> Self { + self.inner.name = name.as_char_ptr(); + self + } + + /// Type of the nvmem storage + pub fn with_type(mut self, type_: Type) -> Self { + self.inner.type_ = type_ as u32; + self + } + + /// Device is read-only. + pub fn with_read_only(mut self, read_only: bool) -> Self { + self.inner.read_only = read_only; + self + } + + /// Device is accessibly to root only. + pub fn with_root_only(mut self, root_only: bool) -> Self { + self.inner.root_only = root_only; + self + } + + /// Device size. + pub fn with_size(mut self, size: i32) -> Self { + self.inner.size = size; + self + } + + /// Minimum read/write access granularity. + pub fn with_word_size(mut self, word_size: i32) -> Self { + self.inner.word_size = word_size; + self + } + + /// Minimum read/write access stride. + pub fn with_stride(mut self, stride: i32) -> Self { + self.inner.stride = stride; + self + } +} + +impl Device { + /// Register a managed nvmem provider on the given device. + pub fn nvmem_register<T>(&self, mut config: NvmemConfig<T>, priv_: &T::Priv) + where + T: NvmemProvider + Default, + { + // FIXME: The last cast to mut indicates some unsoundness here. + config.inner.priv_ = core::ptr::from_ref(priv_).cast::<c_void>().cast_mut(); + config.inner.dev = self.as_raw(); + config.inner.reg_read = Some(NvmemConfig::<T>::reg_read); + config.inner.reg_write = Some(NvmemConfig::<T>::reg_write); + // SAFETY: Both self and config can’t be null here, and should have the correct type. + unsafe { bindings::devm_nvmem_register(self.as_raw(), &config.inner) }; + } +} + +/// Helper trait to define the callbacks of a nvmem provider. +#[vtable] +pub trait NvmemProvider { + /// The type passed into the context for read and write functions. + type Priv; + + /// Callback to read data. + #[inline] + fn read(_context: &Self::Priv, _offset: u32, _data: &mut [u8]) -> Result { + build_error!(VTABLE_DEFAULT_ERROR) + } + + /// Callback to write data. + #[inline] + fn write(_context: &Self::Priv, _offset: u32, _data: &[u8]) -> Result { + build_error!(VTABLE_DEFAULT_ERROR) + } +} -- 2.52.0
