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.

Tested-by: Drew Fustini <fustini@kernel.org>
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 MAINTAINERS                     |   8 +++
 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, 182 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index a92290fffa163f9fe8fe3f04bf66426f9a894409..778c668066dda09f304b19e2366e9011a6843dab 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20070,6 +20070,14 @@ 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@samsung.com>
+L:	linux-pwm@vger.kernel.org
+L:	rust-for-linux@vger.kernel.org
+S:	Maintained
+F:	rust/helpers/pwm.c
+F:	rust/kernel/pwm.rs
+
 PXA GPIO DRIVER
 M:	Robert Jarzmik <robert.jarzmik@free.fr>
 L:	linux-gpio@vger.kernel.org
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index d9bcd1e8413eaed1602d6686873e263767c58f5f..cfddeae0eab3523f04f361fb41ccd1345c0c937b 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -790,4 +790,17 @@ 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 bc494745f67b82e7a3a6f53055ece0fc3acf6e0d..e794dada5537c53f8aeae425d181ec339c10f9d0 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -63,6 +63,7 @@
 #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 0f1b5d11598591bc62bb6439747211af164b76d6..73902d8bd87e93cb3bc3c501360c37e29e8dde19 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -30,6 +30,7 @@
 #include "platform.c"
 #include "pci.c"
 #include "pid_namespace.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@samsung.com>
+
+#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 6b4774b2b1c37f4da1866e993be6230bc6715841..ce1d08b14e456905dbe7b625bbb8ca8b08deae2a 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -105,6 +105,8 @@
 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@samsung.com>
+
+//! 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

Hi Michal,


Overall looks good, a few minor comments:

[…]

> +
> +/// 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 }))
> +    }

from_raw()


> +
> +    /// 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);

No Opaque<T>?

> +
> +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
> 
> 

If the lack of Opaque<T> is not a problem for whatever reason:

Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>

— Daniel

On 7/25/25 17:08, Daniel Almeida wrote:
> Hi Michal,
> 
> 
> Overall looks good, a few minor comments:

Hi,
Congratulations for getting your IoMem series merged. Thank you for your
work, as it will allow me to proceed and re-add the driver part for this
series.

> 
> […]
> 
>> +
>> +/// 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 }))
>> +    }
> 
> from_raw()
> 
> 
>> +
>> +    /// 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);
> 
> No Opaque<T>?

Since this is a copy of the state it's fine. The Args above should
follow similar pattern, the divergence stemmed when iterating with this
series. So I would rather fix the Args to also not be Opaque as it
doesn't need to be, since it's also a copy of the original (since it's
so small and read only).

> 
>> +
>> +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
>>
>>
> 
> If the lack of Opaque<T> is not a problem for whatever reason:
> 
> Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
> 
> — Daniel
> 
> 

Best regards,
-- 
Michal Wilczynski <m.wilczynski@samsung.com>