[PATCH v2 2/4] rust: nvmem: Add an abstraction for nvmem providers

Link Mauve
2026-02-04T04:05:33Z

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 <linkmauve@linkmauve.fr>
---
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 <linkmauve@linkmauve.fr>
+
+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