[PATCH v15 3/7] rust: pwm: Add complete abstraction layer

Michal Wilczynski
2025-09-30T12:27:49Z

Introduce a comprehensive abstraction layer for the PWM subsystem to
enable writing drivers in Rust.

Because `Device`, `Chip`, and `PwmOps` all refer to each other, they
form a single, indivisible unit with circular dependencies. They are
introduced together in this single commit to create a complete,
compilable abstraction layer.

The main components are:
- Data Wrappers: Safe, idiomatic wrappers for core C types like
`pwm_device`, and `pwm_chip`.

- PwmOps Trait: An interface that drivers can implement to provide
their hardware-specific logic, mirroring the C `pwm_ops` interface.

- FFI VTable and Adapter: A bridge to connect the high-level PwmOps trait
to the C kernel's pwm_ops vtable.

- Allocation and Lifetime Management: A high-level `Chip::new()`
API to safely allocate a chip and a `Registration` guard that integrates
with `devres` to manage the chip's registration with the PWM core.
An `AlwaysRefCounted` implementation and a custom release handler
prevent memory leaks by managing the chip's lifetime and freeing
driver data correctly.

Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
rust/kernel/pwm.rs | 664 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 662 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/pwm.rs b/rust/kernel/pwm.rs
index beabf0086a2f1beea01e0b0a9f6540c601f77a49..79fbb13cd47f75681283648ddc4fffb7889be930 100644
--- a/rust/kernel/pwm.rs
+++ b/rust/kernel/pwm.rs
@@ -8,10 +8,14 @@

use crate::{
bindings,
+ container_of,
+ device::{self, Bound},
+ devres,
+ error::{self, to_result},
prelude::*,
- types::Opaque,
+ types::{ARef, AlwaysRefCounted, Opaque},
};
-use core::convert::TryFrom;
+use core::{convert::TryFrom, marker::PhantomData, ptr::NonNull};

/// PWM polarity. Mirrors [`enum pwm_polarity`](srctree/include/linux/pwm.h).
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -100,3 +104,659 @@ pub fn enabled(&self) -> bool {
self.0.enabled
}
}
+
+/// Describes the outcome of a `round_waveform` operation.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum RoundingOutcome {
+ /// The requested waveform was achievable exactly or by rounding values down.
+ ExactOrRoundedDown,
+
+ /// The requested waveform could only be achieved by rounding up.
+ RoundedUp,
+}
+
+/// Wrapper for a PWM device [`struct pwm_device`](srctree/include/linux/pwm.h).
+#[repr(transparent)]
+pub struct Device(Opaque<bindings::pwm_device>);
+
+impl Device {
+ /// Creates a reference to a [`Device`] from a valid C pointer.
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that `ptr` is valid and remains valid for the lifetime of the
+ /// returned [`Device`] reference.
+ pub(crate) unsafe fn from_raw<'a>(ptr: *mut bindings::pwm_device) -> &'a Self {
+ // SAFETY: The safety requirements guarantee the validity of the dereference, while the
+ // `Device` type being transparent makes the cast ok.
+ unsafe { &*ptr.cast::<Self>() }
+ }
+
+ /// Returns a raw pointer to the underlying `pwm_device`.
+ fn as_raw(&self) -> *mut bindings::pwm_device {
+ self.0.get()
+ }
+
+ /// Gets the hardware PWM index for this device within its chip.
+ pub fn hwpwm(&self) -> u32 {
+ // SAFETY: `self.as_raw()` provides a valid pointer for `self`'s lifetime.
+ unsafe { (*self.as_raw()).hwpwm }
+ }
+
+ /// Gets a reference to the parent `Chip` that this device belongs to.
+ pub fn chip<T: PwmOps>(&self) -> &Chip<T> {
+ // SAFETY: `self.as_raw()` provides a valid pointer. (*self.as_raw()).chip
+ // is assumed to be a valid pointer to `pwm_chip` managed by the kernel.
+ // Chip::from_raw's safety conditions must be met.
+ unsafe { Chip::<T>::from_raw((*self.as_raw()).chip) }
+ }
+
+ /// Gets the label for this PWM device, if any.
+ pub fn label(&self) -> Option<&CStr> {
+ // SAFETY: self.as_raw() provides a valid pointer.
+ let label_ptr = unsafe { (*self.as_raw()).label };
+ if label_ptr.is_null() {
+ return None
+ }
+
+ // SAFETY: label_ptr is non-null and points to a C string
+ // managed by the kernel, valid for the lifetime of the PWM device.
+ Some(unsafe { CStr::from_char_ptr(label_ptr) })
+ }
+
+ /// Gets a copy of the current state of this PWM device.
+ pub fn state(&self) -> State {
+ // SAFETY: `self.as_raw()` gives a valid pointer. `(*self.as_raw()).state`
+ // is a valid `pwm_state` struct. `State::from_c` copies this data.
+ State::from_c(unsafe { (*self.as_raw()).state })
+ }
+
+ /// Sets the PWM waveform configuration and enables the PWM signal.
+ pub fn set_waveform(&self, wf: &Waveform, exact: bool) -> Result {
+ let c_wf = bindings::pwm_waveform::from(*wf);
+
+ // SAFETY: `self.as_raw()` provides a valid `*mut pwm_device` pointer.
+ // `&c_wf` is a valid pointer to a `pwm_waveform` struct. The C function
+ // handles all necessary internal locking.
+ let ret = unsafe { bindings::pwm_set_waveform_might_sleep(self.as_raw(), &c_wf, exact) };
+ to_result(ret)
+ }
+
+ /// Queries the hardware for the configuration it would apply for a given
+ /// request.
+ pub fn round_waveform(&self, wf: &mut Waveform) -> Result<RoundingOutcome> {
+ let mut c_wf = bindings::pwm_waveform::from(*wf);
+
+ // SAFETY: `self.as_raw()` provides a valid `*mut pwm_device` pointer.
+ // `&mut c_wf` is a valid pointer to a mutable `pwm_waveform` struct that
+ // the C function will update.
+ let ret = unsafe { bindings::pwm_round_waveform_might_sleep(self.as_raw(), &mut c_wf) };
+
+ to_result(ret)?;
+
+ *wf = Waveform::from(c_wf);
+
+ if ret == 1 {
+ Ok(RoundingOutcome::RoundedUp)
+ } else {
+ Ok(RoundingOutcome::ExactOrRoundedDown)
+ }
+ }
+
+ /// Reads the current waveform configuration directly from the hardware.
+ pub fn get_waveform(&self) -> Result<Waveform> {
+ let mut c_wf = bindings::pwm_waveform::default();
+
+ // SAFETY: `self.as_raw()` is a valid pointer. We provide a valid pointer
+ // to a stack-allocated `pwm_waveform` struct for the kernel to fill.
+ let ret = unsafe { bindings::pwm_get_waveform_might_sleep(self.as_raw(), &mut c_wf) };
+
+ to_result(ret)?;
+
+ Ok(Waveform::from(c_wf))
+ }
+}
+
+/// The result of a `round_waveform_tohw` operation.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct RoundedWaveform<WfHw> {
+ /// A status code, 0 for success or 1 if values were rounded up.
+ pub status: c_int,
+ /// The driver-specific hardware representation of the waveform.
+ pub hardware_waveform: WfHw,
+}
+
+/// Trait defining the operations for a PWM driver.
+pub trait PwmOps: 'static + Sized {
+ /// The driver-specific hardware representation of a waveform.
+ ///
+ /// This type must be [`Copy`], [`Default`], and fit within `PWM_WFHWSIZE`.
+ type WfHw: Copy + Default;
+
+ /// Optional hook for when a PWM device is requested.
+ fn request(
+ _chip: &Chip<Self>,
+ _pwm: &Device,
+ _parent_dev: &device::Device<Bound>,
+ ) -> Result {
+ Ok(())
+ }
+
+ /// Optional hook for capturing a PWM signal.
+ fn capture(
+ _chip: &Chip<Self>,
+ _pwm: &Device,
+ _result: &mut bindings::pwm_capture,
+ _timeout: usize,
+ _parent_dev: &device::Device<Bound>,
+ ) -> Result {
+ Err(ENOTSUPP)
+ }
+
+ /// Convert a generic waveform to the hardware-specific representation.
+ /// This is typically a pure calculation and does not perform I/O.
+ fn round_waveform_tohw(
+ _chip: &Chip<Self>,
+ _pwm: &Device,
+ _wf: &Waveform,
+ ) -> Result<RoundedWaveform<Self::WfHw>> {
+ Err(ENOTSUPP)
+ }
+
+ /// Convert a hardware-specific representation back to a generic waveform.
+ /// This is typically a pure calculation and does not perform I/O.
+ fn round_waveform_fromhw(
+ _chip: &Chip<Self>,
+ _pwm: &Device,
+ _wfhw: &Self::WfHw,
+ _wf: &mut Waveform,
+ ) -> Result {
+ Err(ENOTSUPP)
+ }
+
+ /// Read the current hardware configuration into the hardware-specific representation.
+ fn read_waveform(
+ _chip: &Chip<Self>,
+ _pwm: &Device,
+ _parent_dev: &device::Device<Bound>,
+ ) -> Result<Self::WfHw> {
+ Err(ENOTSUPP)
+ }
+
+ /// Write a hardware-specific waveform configuration to the hardware.
+ fn write_waveform(
+ _chip: &Chip<Self>,
+ _pwm: &Device,
+ _wfhw: &Self::WfHw,
+ _parent_dev: &device::Device<Bound>,
+ ) -> Result {
+ Err(ENOTSUPP)
+ }
+}
+
+/// Bridges Rust `PwmOps` to the C `pwm_ops` vtable.
+struct Adapter<T: PwmOps> {
+ _p: PhantomData<T>,
+}
+
+impl<T: PwmOps> Adapter<T> {
+ const VTABLE: PwmOpsVTable = create_pwm_ops::<T>();
+
+ /// # Safety
+ ///
+ /// `wfhw_ptr` must be valid for writes of `size_of::<T::WfHw>()` bytes.
+ unsafe fn serialize_wfhw(wfhw: &T::WfHw, wfhw_ptr: *mut c_void) -> Result {
+ let size = core::mem::size_of::<T::WfHw>();
+
+ build_assert!(size <= bindings::PWM_WFHWSIZE as usize);
+
+ // SAFETY: The caller ensures `wfhw_ptr` is valid for `size` bytes.
+ unsafe {
+ core::ptr::copy_nonoverlapping(
+ core::ptr::from_ref::<T::WfHw>(wfhw).cast::<u8>(),
+ wfhw_ptr.cast::<u8>(),
+ size,
+ );
+ }
+
+ Ok(())
+ }
+
+ /// # Safety
+ ///
+ /// `wfhw_ptr` must be valid for reads of `size_of::<T::WfHw>()` bytes.
+ unsafe fn deserialize_wfhw(wfhw_ptr: *const c_void) -> Result<T::WfHw> {
+ let size = core::mem::size_of::<T::WfHw>();
+
+ build_assert!(size <= bindings::PWM_WFHWSIZE as usize);
+
+ let mut wfhw = T::WfHw::default();
+ // SAFETY: The caller ensures `wfhw_ptr` is valid for `size` bytes.
+ unsafe {
+ core::ptr::copy_nonoverlapping(
+ wfhw_ptr.cast::<u8>(),
+ core::ptr::from_mut::<T::WfHw>(&mut wfhw).cast::<u8>(),
+ size,
+ );
+ }
+
+ Ok(wfhw)
+ }
+
+ /// # Safety
+ ///
+ /// `dev` must be a valid pointer to a `bindings::device` embedded within a
+ /// `bindings::pwm_chip`. This function is called by the device core when the
+ /// last reference to the device is dropped.
+ unsafe extern "C" fn release_callback(dev: *mut bindings::device) {
+ // SAFETY: The function's contract guarantees that `dev` points to a `device`
+ // field embedded within a valid `pwm_chip`. `container_of!` can therefore
+ // safely calculate the address of the containing struct.
+ let c_chip_ptr = unsafe { container_of!(dev, bindings::pwm_chip, dev) };
+
+ // SAFETY: `c_chip_ptr` is a valid pointer to a `pwm_chip` as established
+ // above. Calling this FFI function is safe.
+ let drvdata_ptr = unsafe { bindings::pwmchip_get_drvdata(c_chip_ptr) };
+
+ // SAFETY: The driver data was initialized in `new`. We run its destructor here.
+ unsafe { core::ptr::drop_in_place(drvdata_ptr.cast::<T>()) };
+
+ // Now, call the original release function to free the `pwm_chip` itself.
+ // SAFETY: `dev` is the valid pointer passed into this callback, which is
+ // the expected argument for `pwmchip_release`.
+ unsafe { bindings::pwmchip_release(dev); }
+ }
+
+ /// # Safety
+ ///
+ /// Pointers from C must be valid.
+ unsafe extern "C" fn request_callback(
+ chip_ptr: *mut bindings::pwm_chip,
+ pwm_ptr: *mut bindings::pwm_device,
+ ) -> c_int {
+ // SAFETY: PWM core guarentees `chip_ptr` and `pwm_ptr` are valid pointers.
+ let (chip, pwm) = unsafe { (Chip::<T>::from_raw(chip_ptr), Device::from_raw(pwm_ptr)) };
+
+ // SAFETY: The PWM core guarantees the parent device exists and is bound during callbacks.
+ let bound_parent = unsafe { chip.bound_parent_device() };
+ match T::request(chip, pwm, bound_parent) {
+ Ok(()) => 0,
+ Err(e) => e.to_errno(),
+ }
+ }
+
+ /// # Safety
+ ///
+ /// Pointers from C must be valid.
+ unsafe extern "C" fn capture_callback(
+ chip_ptr: *mut bindings::pwm_chip,
+ pwm_ptr: *mut bindings::pwm_device,
+ res: *mut bindings::pwm_capture,
+ timeout: usize,
+ ) -> c_int {
+ // SAFETY: Relies on the function's contract that `chip_ptr` and `pwm_ptr` are valid
+ // pointers.
+ let (chip, pwm, result) = unsafe {
+ (
+ Chip::<T>::from_raw(chip_ptr),
+ Device::from_raw(pwm_ptr),
+ &mut *res,
+ )
+ };
+
+ // SAFETY: The PWM core guarantees the parent device exists and is bound during callbacks.
+ let bound_parent = unsafe { chip.bound_parent_device() };
+ match T::capture(chip, pwm, result, timeout, bound_parent) {
+ Ok(()) => 0,
+ Err(e) => e.to_errno(),
+ }
+ }
+
+ /// # Safety
+ ///
+ /// Pointers from C must be valid.
+ unsafe extern "C" fn round_waveform_tohw_callback(
+ chip_ptr: *mut bindings::pwm_chip,
+ pwm_ptr: *mut bindings::pwm_device,
+ wf_ptr: *const bindings::pwm_waveform,
+ wfhw_ptr: *mut c_void,
+ ) -> c_int {
+ // SAFETY: Relies on the function's contract that `chip_ptr` and `pwm_ptr` are valid
+ // pointers.
+ let (chip, pwm, wf) = unsafe {
+ (
+ Chip::<T>::from_raw(chip_ptr),
+ Device::from_raw(pwm_ptr),
+ Waveform::from(*wf_ptr),
+ )
+ };
+ match T::round_waveform_tohw(chip, pwm, &wf) {
+ Ok(rounded) => {
+ // SAFETY: `wfhw_ptr` is valid per this function's safety contract.
+ if unsafe { Self::serialize_wfhw(&rounded.hardware_waveform, wfhw_ptr) }.is_err() {
+ return EINVAL.to_errno();
+ }
+ rounded.status
+ }
+ Err(e) => e.to_errno(),
+ }
+ }
+
+ /// # Safety
+ ///
+ /// Pointers from C must be valid.
+ unsafe extern "C" fn round_waveform_fromhw_callback(
+ chip_ptr: *mut bindings::pwm_chip,
+ pwm_ptr: *mut bindings::pwm_device,
+ wfhw_ptr: *const c_void,
+ wf_ptr: *mut bindings::pwm_waveform,
+ ) -> c_int {
+ // SAFETY: Relies on the function's contract that `chip_ptr` and `pwm_ptr` are valid
+ // pointers.
+ let (chip, pwm) = unsafe { (Chip::<T>::from_raw(chip_ptr), Device::from_raw(pwm_ptr)) };
+ // SAFETY: `deserialize_wfhw`'s safety contract is met by this function's contract.
+ let wfhw = match unsafe { Self::deserialize_wfhw(wfhw_ptr) } {
+ Ok(v) => v,
+ Err(e) => return e.to_errno(),
+ };
+
+ let mut rust_wf = Waveform::default();
+ match T::round_waveform_fromhw(chip, pwm, &wfhw, &mut rust_wf) {
+ Ok(()) => {
+ // SAFETY: `wf_ptr` is guaranteed valid by the C caller.
+ unsafe {
+ *wf_ptr = rust_wf.into();
+ };
+ 0
+ }
+ Err(e) => e.to_errno(),
+ }
+ }
+
+ /// # Safety
+ ///
+ /// Pointers from C must be valid.
+ unsafe extern "C" fn read_waveform_callback(
+ chip_ptr: *mut bindings::pwm_chip,
+ pwm_ptr: *mut bindings::pwm_device,
+ wfhw_ptr: *mut c_void,
+ ) -> c_int {
+ // SAFETY: Relies on the function's contract that `chip_ptr` and `pwm_ptr` are valid
+ // pointers.
+ let (chip, pwm) = unsafe { (Chip::<T>::from_raw(chip_ptr), Device::from_raw(pwm_ptr)) };
+
+ // SAFETY: The PWM core guarantees the parent device exists and is bound during callbacks.
+ let bound_parent = unsafe { chip.bound_parent_device() };
+ match T::read_waveform(chip, pwm, bound_parent) {
+ // SAFETY: `wfhw_ptr` is valid per this function's safety contract.
+ Ok(wfhw) => match unsafe { Self::serialize_wfhw(&wfhw, wfhw_ptr) } {
+ Ok(()) => 0,
+ Err(e) => e.to_errno(),
+ },
+ Err(e) => e.to_errno(),
+ }
+ }
+
+ /// # Safety
+ ///
+ /// Pointers from C must be valid.
+ unsafe extern "C" fn write_waveform_callback(
+ chip_ptr: *mut bindings::pwm_chip,
+ pwm_ptr: *mut bindings::pwm_device,
+ wfhw_ptr: *const c_void,
+ ) -> c_int {
+ // SAFETY: Relies on the function's contract that `chip_ptr` and `pwm_ptr` are valid
+ // pointers.
+ let (chip, pwm) = unsafe { (Chip::<T>::from_raw(chip_ptr), Device::from_raw(pwm_ptr)) };
+
+ // SAFETY: The PWM core guarantees the parent device exists and is bound during callbacks.
+ let bound_parent = unsafe { chip.bound_parent_device() };
+
+ // SAFETY: `wfhw_ptr` is valid per this function's safety contract.
+ let wfhw = match unsafe { Self::deserialize_wfhw(wfhw_ptr) } {
+ Ok(v) => v,
+ Err(e) => return e.to_errno(),
+ };
+ match T::write_waveform(chip, pwm, &wfhw, bound_parent) {
+ Ok(()) => 0,
+ Err(e) => e.to_errno(),
+ }
+ }
+}
+
+/// VTable structure wrapper for PWM operations.
+/// Mirrors [`struct pwm_ops`](srctree/include/linux/pwm.h).
+#[repr(transparent)]
+pub struct PwmOpsVTable(bindings::pwm_ops);
+
+// SAFETY: PwmOpsVTable is Send. The vtable contains only function pointers
+// and a size, which are simple data types that can be safely moved across
+// threads. The thread-safety of calling these functions is handled by the
+// kernel's locking mechanisms.
+unsafe impl Send for PwmOpsVTable {}
+
+// SAFETY: PwmOpsVTable is Sync. The vtable is immutable after it is created,
+// so it can be safely referenced and accessed concurrently by multiple threads
+// e.g. to read the function pointers.
+unsafe impl Sync for PwmOpsVTable {}
+
+impl PwmOpsVTable {
+ /// Returns a raw pointer to the underlying `pwm_ops` struct.
+ pub(crate) fn as_raw(&self) -> *const bindings::pwm_ops {
+ &self.0
+ }
+}
+
+/// Creates a PWM operations vtable for a type `T` that implements `PwmOps`.
+///
+/// This is used to bridge Rust trait implementations to the C `struct pwm_ops`
+/// expected by the kernel.
+pub const fn create_pwm_ops<T: PwmOps>() -> PwmOpsVTable {
+ // SAFETY: `core::mem::zeroed()` is unsafe. For `pwm_ops`, all fields are
+ // `Option<extern "C" fn(...)>` or data, so a zeroed pattern (None/0) is valid initially.
+ let mut ops: bindings::pwm_ops = unsafe { core::mem::zeroed() };
+
+ ops.request = Some(Adapter::<T>::request_callback);
+ ops.capture = Some(Adapter::<T>::capture_callback);
+
+ ops.round_waveform_tohw = Some(Adapter::<T>::round_waveform_tohw_callback);
+ ops.round_waveform_fromhw = Some(Adapter::<T>::round_waveform_fromhw_callback);
+ ops.read_waveform = Some(Adapter::<T>::read_waveform_callback);
+ ops.write_waveform = Some(Adapter::<T>::write_waveform_callback);
+ ops.sizeof_wfhw = core::mem::size_of::<T::WfHw>();
+
+ PwmOpsVTable(ops)
+}
+
+/// Wrapper for a PWM chip/controller ([`struct pwm_chip`](srctree/include/linux/pwm.h)).
+#[repr(transparent)]
+pub struct Chip<T: PwmOps>(Opaque<bindings::pwm_chip>, PhantomData<T>);
+
+impl<T: PwmOps> Chip<T> {
+ /// Creates a reference to a [`Chip`] from a valid pointer.
+ ///
+ /// # Safety
+ ///
+ /// The caller must ensure that `ptr` is valid and remains valid for the lifetime of the
+ /// returned [`Chip`] reference.
+ pub(crate) unsafe fn from_raw<'a>(ptr: *mut bindings::pwm_chip) -> &'a Self {
+ // SAFETY: The safety requirements guarantee the validity of the dereference, while the
+ // `Chip` type being transparent makes the cast ok.
+ unsafe { &*ptr.cast::<Self>() }
+ }
+
+ /// Returns a raw pointer to the underlying `pwm_chip`.
+ pub(crate) fn as_raw(&self) -> *mut bindings::pwm_chip {
+ self.0.get()
+ }
+
+ /// Gets the number of PWM channels (hardware PWMs) on this chip.
+ pub fn num_channels(&self) -> u32 {
+ // SAFETY: `self.as_raw()` provides a valid pointer for `self`'s lifetime.
+ unsafe { (*self.as_raw()).npwm }
+ }
+
+ /// Returns `true` if the chip supports atomic operations for configuration.
+ pub fn is_atomic(&self) -> bool {
+ // SAFETY: `self.as_raw()` provides a valid pointer for `self`'s lifetime.
+ unsafe { (*self.as_raw()).atomic }
+ }
+
+ /// Returns a reference to the embedded `struct device` abstraction.
+ pub fn device(&self) -> &device::Device {
+ // SAFETY:
+ // - `self.as_raw()` provides a valid pointer to `bindings::pwm_chip`.
+ // - The `dev` field is an instance of `bindings::device` embedded
+ // within `pwm_chip`.
+ // - Taking a pointer to this embedded field is valid.
+ // - `device::Device` is `#[repr(transparent)]`.
+ // - The lifetime of the returned reference is tied to `self`.
+ unsafe { device::Device::from_raw(&raw mut (*self.as_raw()).dev) }
+ }
+
+ /// Gets the typed driver specific data associated with this chip's embedded device.
+ pub fn drvdata(&self) -> &T {
+ // SAFETY: `pwmchip_get_drvdata` returns the pointer to the private data area,
+ // which we know holds our `T`. The pointer is valid for the lifetime of `self`.
+ unsafe { &*bindings::pwmchip_get_drvdata(self.as_raw()).cast::<T>() }
+ }
+
+ /// Returns a reference to the parent device of this PWM chip's device.
+ ///
+ /// # Safety
+ ///
+ /// The caller must guarantee that the parent device exists and is bound.
+ /// This is guaranteed by the PWM core during `PwmOps` callbacks.
+ unsafe fn bound_parent_device(&self) -> &device::Device<Bound> {
+ // SAFETY: Per the function's safety contract, the parent device exists.
+ let parent = unsafe { self.device().parent().unwrap_unchecked() };
+
+ // SAFETY: Per the function's safety contract, the parent device is bound.
+ // This is guaranteed by the PWM core during `PwmOps` callbacks.
+ unsafe { parent.as_bound() }
+ }
+
+ /// Allocates and wraps a PWM chip using `bindings::pwmchip_alloc`.
+ ///
+ /// Returns an [`ARef<Chip>`] managing the chip's lifetime via refcounting
+ /// on its embedded `struct device`.
+ pub fn new(
+ parent_dev: &device::Device,
+ num_channels: u32,
+ data: impl pin_init::PinInit<T, Error>,
+ ) -> Result<ARef<Self>> {
+ let sizeof_priv = core::mem::size_of::<T>();
+ // SAFETY: `pwmchip_alloc` allocates memory for the C struct and our private data.
+ let c_chip_ptr_raw = unsafe {
+ bindings::pwmchip_alloc(parent_dev.as_raw(), num_channels, sizeof_priv)
+ };
+
+ let c_chip_ptr: *mut bindings::pwm_chip = error::from_err_ptr(c_chip_ptr_raw)?;
+
+ // SAFETY: The `drvdata` pointer is the start of the private area, which is where
+ // we will construct our `T` object.
+ let drvdata_ptr = unsafe { bindings::pwmchip_get_drvdata(c_chip_ptr) };
+
+ // SAFETY: We construct the `T` object in-place in the allocated private memory.
+ unsafe { data.__pinned_init(drvdata_ptr.cast())? };
+
+ // SAFETY: `c_chip_ptr` points to a valid chip.
+ unsafe { (*c_chip_ptr).dev.release = Some(Adapter::<T>::release_callback); }
+
+ // SAFETY: `c_chip_ptr` points to a valid chip.
+ // The `Adapter`'s `VTABLE` has a 'static lifetime, so the pointer
+ // returned by `as_raw()` is always valid.
+ unsafe { (*c_chip_ptr).ops = Adapter::<T>::VTABLE.as_raw(); }
+
+ // Cast the `*mut bindings::pwm_chip` to `*mut Chip`. This is valid because
+ // `Chip` is `repr(transparent)` over `Opaque<bindings::pwm_chip>`, and
+ // `Opaque<T>` is `repr(transparent)` over `T`.
+ let chip_ptr_as_self = c_chip_ptr.cast::<Self>();
+
+ // SAFETY: `chip_ptr_as_self` points to a valid `Chip` (layout-compatible with
+ // `bindings::pwm_chip`) whose embedded device has refcount 1.
+ // `ARef::from_raw` takes this pointer and manages it via `AlwaysRefCounted`.
+ Ok(unsafe { ARef::from_raw(NonNull::new_unchecked(chip_ptr_as_self)) })
+ }
+}
+
+// SAFETY: Implements refcounting for `Chip` using the embedded `struct device`.
+unsafe impl<T: PwmOps> AlwaysRefCounted for Chip<T> {
+ #[inline]
+ fn inc_ref(&self) {
+ // SAFETY: `self.0.get()` points to a valid `pwm_chip` because `self` exists.
+ // The embedded `dev` is valid. `get_device` increments its refcount.
+ unsafe { bindings::get_device(&raw mut (*self.0.get()).dev); }
+ }
+
+ #[inline]
+ unsafe fn dec_ref(obj: NonNull<Chip<T>>) {
+ let c_chip_ptr = obj.cast::<bindings::pwm_chip>().as_ptr();
+
+ // SAFETY: `obj` is a valid pointer to a `Chip` (and thus `bindings::pwm_chip`)
+ // with a non-zero refcount. `put_device` handles decrement and final release.
+ unsafe { bindings::put_device(&raw mut (*c_chip_ptr).dev); }
+ }
+}
+
+// SAFETY: `Chip` is a wrapper around `*mut bindings::pwm_chip`. The underlying C
+// structure's state is managed and synchronized by the kernel's device model
+// and PWM core locking mechanisms. Therefore, it is safe to move the `Chip`
+// wrapper (and the pointer it contains) across threads.
+unsafe impl<T: PwmOps + Send> Send for Chip<T> {}
+
+// SAFETY: It is safe for multiple threads to have shared access (`&Chip`) because
+// the `Chip` data is immutable from the Rust side without holding the appropriate
+// kernel locks, which the C core is responsible for. Any interior mutability is
+// handled and synchronized by the C kernel code.
+unsafe impl<T: PwmOps + Sync> Sync for Chip<T> {}
+
+/// A resource guard that ensures `pwmchip_remove` is called on drop.
+///
+/// This struct is intended to be managed by the `devres` framework by transferring its ownership
+/// via [`Devres::register`]. This ties the lifetime of the PWM chip registration
+/// to the lifetime of the underlying device.
+pub struct Registration<T: PwmOps> {
+ chip: ARef<Chip<T>>,
+}
+
+impl<T: 'static + PwmOps + Send + Sync> Registration<T> {
+ /// Registers a PWM chip with the PWM subsystem.
+ ///
+ /// Transfers its ownership to the `devres` framework, which ties its lifetime
+ /// to the parent device.
+ /// On unbind of the parent device, the `devres` entry will be dropped, automatically
+ /// calling `pwmchip_remove`. This function should be called from the driver's `probe`.
+ pub fn register(
+ dev: &device::Device<Bound>,
+ chip: ARef<Chip<T>>,
+ ) -> Result {
+ let chip_parent = chip.device().parent().ok_or(EINVAL)?;
+ if dev.as_raw() != chip_parent.as_raw() {
+ return Err(EINVAL);
+ }
+
+ let c_chip_ptr = chip.as_raw();
+
+ // SAFETY: `c_chip_ptr` points to a valid chip with its ops initialized.
+ // `__pwmchip_add` is the C function to register the chip with the PWM core.
+ unsafe {
+ to_result(bindings::__pwmchip_add(c_chip_ptr, core::ptr::null_mut()))?;
+ }
+
+ let registration = Registration { chip };
+
+ devres::register(dev, registration, GFP_KERNEL)
+ }
+}
+
+impl<T: PwmOps> Drop for Registration<T> {
+ fn drop(&mut self) {
+ let chip_raw = self.chip.as_raw();
+
+ // SAFETY: `chip_raw` points to a chip that was successfully registered.
+ // `bindings::pwmchip_remove` is the correct C function to unregister it.
+ // This `drop` implementation is called automatically by `devres` on driver unbind.
+ unsafe { bindings::pwmchip_remove(chip_raw); }
+ }
+}

--
2.34.1