[PATCH v6 2/8] rust: pwm: Add Kconfig and basic data structures

From: Michal Wilczynski
Date: Tue Jul 01 2025 - 12:03:50 EST

Introduce the foundational support for PWM abstractions in Rust.

This commit adds the `RUST_PWM_ABSTRACTIONS` Kconfig option to enable
the feature, along with the necessary build-system support and C
helpers.

It also introduces the first set of safe wrappers for the PWM
subsystem, covering the basic data carrying C structs and enums:
- `Polarity`: A safe wrapper for `enum pwm_polarity`.
- `Waveform`: A wrapper for `struct pwm_waveform`.
- `Args`: A wrapper for `struct pwm_args`.
- `State`: A wrapper for `struct pwm_state`.

These types provide memory safe, idiomatic Rust representations of the
core PWM data structures and form the building blocks for the
abstractions that will follow.

Signed-off-by: Michal Wilczynski <m.wilczynski@xxxxxxxxxxx>
---
MAINTAINERS | 6 ++
drivers/pwm/Kconfig | 13 ++++
rust/bindings/bindings_helper.h | 1 +
rust/helpers/helpers.c | 1 +
rust/helpers/pwm.c | 20 ++++++
rust/kernel/lib.rs | 2 +
rust/kernel/pwm.rs | 137 ++++++++++++++++++++++++++++++++++++++++
7 files changed, 180 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index b7c9cba99db27d8a761522f94a1d4c7ef09c8632..fe47833a341f7d25f0f65877ea6bc3dc77261732 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20177,6 +20177,12 @@ F: include/linux/pwm.h
F: include/linux/pwm_backlight.h
K: pwm_(config|apply_might_sleep|apply_atomic|ops)

+PWM SUBSYSTEM BINDINGS [RUST]
+M: Michal Wilczynski <m.wilczynski@xxxxxxxxxxx>
+S: Maintained
+F: rust/helpers/pwm.c
+F: rust/kernel/pwm.rs
+
PXA GPIO DRIVER
M: Robert Jarzmik <robert.jarzmik@xxxxxxx>
L: linux-gpio@xxxxxxxxxxxxxxx
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 3ef1757502ebd92b30584cd10611311a0fbfc03b..c32655566d6ab9eff9d10f29e469f9aef89cecfa 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -799,4 +799,17 @@ config PWM_XILINX
To compile this driver as a module, choose M here: the module
will be called pwm-xilinx.

+ config RUST_PWM_ABSTRACTIONS
+ bool "Rust PWM abstractions support"
+ depends on RUST
+ depends on PWM=y
+ help
+ This option enables the safe Rust abstraction layer for the PWM
+ subsystem. It provides idiomatic wrappers and traits necessary for
+ writing PWM controller drivers in Rust.
+
+ The abstractions handle resource management (like memory and reference
+ counting) and provide safe interfaces to the underlying C core,
+ allowing driver logic to be written in safe Rust.
+
endif
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 5f795e60e889b9fc887013743c81b1cf92a52adb..6a6e1b1736b38f36c1dbdd875defb3b526372b67 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -66,6 +66,7 @@
#include <linux/pm_opp.h>
#include <linux/poll.h>
#include <linux/property.h>
+#include <linux/pwm.h>
#include <linux/refcount.h>
#include <linux/sched.h>
#include <linux/security.h>
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 1f800e78920145fc5149befb15579179dfb6e02e..c449d72fa8b19b2ab084be520466ab916c63cea7 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -35,6 +35,7 @@
#include "pid_namespace.c"
#include "poll.c"
#include "property.c"
+#include "pwm.c"
#include "rbtree.c"
#include "rcu.c"
#include "refcount.c"
diff --git a/rust/helpers/pwm.c b/rust/helpers/pwm.c
new file mode 100644
index 0000000000000000000000000000000000000000..d75c588863685d3990b525bb1b84aa4bc35ac397
--- /dev/null
+++ b/rust/helpers/pwm.c
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2025 Samsung Electronics Co., Ltd.
+// Author: Michal Wilczynski <m.wilczynski@xxxxxxxxxxx>
+
+#include <linux/pwm.h>
+
+struct device *rust_helper_pwmchip_parent(const struct pwm_chip *chip)
+{
+ return pwmchip_parent(chip);
+}
+
+void *rust_helper_pwmchip_get_drvdata(struct pwm_chip *chip)
+{
+ return pwmchip_get_drvdata(chip);
+}
+
+void rust_helper_pwmchip_set_drvdata(struct pwm_chip *chip, void *data)
+{
+ pwmchip_set_drvdata(chip, data);
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 5bbf3627212f0a26d34be0d6c160a370abf1e996..9f7038d3d501982a843d6d86571d20f1213ba9ee 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -106,6 +106,8 @@
pub mod seq_file;
pub mod sizes;
mod static_assert;
+#[cfg(CONFIG_RUST_PWM_ABSTRACTIONS)]
+pub mod pwm;
#[doc(hidden)]
pub mod std_vendor;
pub mod str;
diff --git a/rust/kernel/pwm.rs b/rust/kernel/pwm.rs
new file mode 100644
index 0000000000000000000000000000000000000000..3fad101406eac728d9b12083fad7abf7b7f89b25
--- /dev/null
+++ b/rust/kernel/pwm.rs
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2025 Samsung Electronics Co., Ltd.
+// Author: Michal Wilczynski <m.wilczynski@xxxxxxxxxxx>
+
+//! PWM subsystem abstractions.
+//!
+//! C header: [`include/linux/pwm.h`](srctree/include/linux/pwm.h).
+
+use crate::{
+ bindings,
+ prelude::*,
+ types::Opaque,
+};
+use core::convert::TryFrom;
+
+/// PWM polarity. Mirrors [`enum pwm_polarity`](srctree/include/linux/pwm.h).
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum Polarity {
+ /// Normal polarity (duty cycle defines the high period of the signal).
+ Normal,
+
+ /// Inversed polarity (duty cycle defines the low period of the signal).
+ Inversed,
+}
+
+impl TryFrom<bindings::pwm_polarity> for Polarity {
+ type Error = Error;
+
+ fn try_from(polarity: bindings::pwm_polarity) -> Result<Self, Error> {
+ match polarity {
+ bindings::pwm_polarity_PWM_POLARITY_NORMAL => Ok(Polarity::Normal),
+ bindings::pwm_polarity_PWM_POLARITY_INVERSED => Ok(Polarity::Inversed),
+ _ => Err(EINVAL),
+ }
+ }
+}
+
+impl From<Polarity> for bindings::pwm_polarity {
+ fn from(polarity: Polarity) -> Self {
+ match polarity {
+ Polarity::Normal => bindings::pwm_polarity_PWM_POLARITY_NORMAL,
+ Polarity::Inversed => bindings::pwm_polarity_PWM_POLARITY_INVERSED,
+ }
+ }
+}
+
+/// Represents a PWM waveform configuration.
+/// Mirrors struct [`struct pwm_waveform`](srctree/include/linux/pwm.h).
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
+pub struct Waveform {
+ /// Total duration of one complete PWM cycle, in nanoseconds.
+ pub period_length_ns: u64,
+
+ /// Duty-cycle active time, in nanoseconds.
+ ///
+ /// For a typical normal polarity configuration (active-high) this is the
+ /// high time of the signal.
+ pub duty_length_ns: u64,
+
+ /// Duty-cycle start offset, in nanoseconds.
+ ///
+ /// Delay from the beginning of the period to the first active edge.
+ /// In most simple PWM setups this is `0`, so the duty cycle starts
+ /// immediately at each period’s start.
+ pub duty_offset_ns: u64,
+}
+
+impl From<bindings::pwm_waveform> for Waveform {
+ fn from(wf: bindings::pwm_waveform) -> Self {
+ Waveform {
+ period_length_ns: wf.period_length_ns,
+ duty_length_ns: wf.duty_length_ns,
+ duty_offset_ns: wf.duty_offset_ns,
+ }
+ }
+}
+
+impl From<Waveform> for bindings::pwm_waveform {
+ fn from(wf: Waveform) -> Self {
+ bindings::pwm_waveform {
+ period_length_ns: wf.period_length_ns,
+ duty_length_ns: wf.duty_length_ns,
+ duty_offset_ns: wf.duty_offset_ns,
+ }
+ }
+}
+
+/// Wrapper for board-dependent PWM arguments [`struct pwm_args`](srctree/include/linux/pwm.h).
+#[repr(transparent)]
+pub struct Args(Opaque<bindings::pwm_args>);
+
+impl Args {
+ /// Creates an `Args` wrapper from a C struct pointer.
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that `c_args_ptr` is a valid, non-null pointer
+ /// to `bindings::pwm_args` and that the pointed-to data is valid
+ /// for the duration of this function call (as data is copied).
+ unsafe fn from_c_ptr(c_args_ptr: *const bindings::pwm_args) -> Self {
+ // SAFETY: Caller guarantees `c_args_ptr` is valid. We dereference it to copy.
+ Args(Opaque::new(unsafe { *c_args_ptr }))
+ }
+
+ /// Returns the period of the PWM signal in nanoseconds.
+ pub fn period(&self) -> u64 {
+ // SAFETY: `self.0.get()` returns a pointer to the `bindings::pwm_args`
+ // managed by the `Opaque` wrapper. This pointer is guaranteed to be
+ // valid and aligned for the lifetime of `self` because `Opaque` owns a copy.
+ unsafe { (*self.0.get()).period }
+ }
+
+ /// Returns the polarity of the PWM signal.
+ pub fn polarity(&self) -> Result<Polarity, Error> {
+ // SAFETY: `self.0.get()` returns a pointer to the `bindings::pwm_args`
+ // managed by the `Opaque` wrapper. This pointer is guaranteed to be
+ // valid and aligned for the lifetime of `self`.
+ let raw_polarity = unsafe { (*self.0.get()).polarity };
+ Polarity::try_from(raw_polarity)
+ }
+}
+
+/// Wrapper for PWM state [`struct pwm_state`](srctree/include/linux/pwm.h).
+#[repr(transparent)]
+pub struct State(bindings::pwm_state);
+
+impl State {
+ /// Creates a `State` wrapper by taking ownership of a C `pwm_state` value.
+ pub(crate) fn from_c(c_state: bindings::pwm_state) -> Self {
+ State(c_state)
+ }
+
+ /// Returns `true` if the PWM signal is enabled.
+ pub fn enabled(&self) -> bool {
+ self.0.enabled
+ }
+}

--
2.34.1