[PATCH v3 0/9] Rust Abstractions for PWM subsystem with TH1520 PWM driver

[PATCH v3 0/9] Rust Abstractions for PWM subsystem with TH1520 PWM driver

[Michal Wilczynski]

This patch series introduces Rust support for the T-HEAD TH1520 PWM
controller and demonstrates its use for fan control on the Sipeed Lichee
Pi 4A board.

The primary goal of this patch series is to introduce a basic set of
Rust abstractions for the Linux PWM subsystem. As a first user and
practical demonstration of these abstractions, the series also provides
a functional PWM driver for the T-HEAD TH1520 SoC. This allows control
of its PWM channels and ultimately enables temperature controlled fan
support for the Lichee Pi 4A board. This work aims to explore the use of
Rust for PWM drivers and lay a foundation for potential future
Rust based PWM drivers.

The core of this series is a new rust/kernel/pwm.rs module that provides
abstractions for writing PWM chip provider drivers in Rust. This has
been significantly reworked from v1 based on extensive feedback. The key
features of the new abstraction layer include:

 - Ownership and Lifetime Management: The pwm::Chip wrapper is managed
   by ARef, correctly tying its lifetime to its embedded struct device
   reference counter. Chip registration is handled by a pwm::Registration
   RAII guard, which guarantees that pwmchip_add is always paired with
   pwmchip_remove, preventing resource leaks.

 - Modern and Safe API: The PwmOps trait is now based on the modern
   waveform API (round_waveform_tohw, write_waveform, etc.) as recommended
   by the subsystem maintainer. It is generic over a driver's
   hardware specific data structure, moving all unsafe serialization logic
   into the abstraction layer and allowing drivers to be written in 100%
   safe Rust.

 - Ergonomics: The API provides safe, idiomatic wrappers for other PWM
   types (State, Args, Device, etc.) and uses standard kernel error
   handling patterns.

The series is structured as follows:
 - Rust PWM Abstractions: The new safe abstraction layer.
 - TH1520 PWM Driver: A new Rust driver for the TH1520 SoC, built on
   top of the new abstractions.
 - Clock Fix: A necessary fix to the TH1520 clock driver to ensure bus
   clocks remain enabled.
 - Device Tree Bindings & Nodes: The remaining patches add the necessary
   DT bindings and nodes for the TH1520 PWM controller, a thermal
   sensor, and the PWM fan configuration for the Lichee Pi 4A board.

Testing:
Tested on the TH1520 SoC. The fan works correctly. The duty/period
calculaties are correct. Fan starts slow when the chip is not hot and
gradually increases the speed when PVT reports higher temperatures.

The patches are based on mainline, with some dependencies which are not
merged yet - platform Io support [1] and math wrapper [2].

Reference repository with all the patches together can be found on
github [3].

[1] - https://lore.kernel.org/rust-for-linux/20250509-topics-tyr-platform_iomem-v8-0-e9f1725a40da@collabora.com/
[2] - https://lore.kernel.org/all/20250609-math-rust-v1-v1-1-285fac00031f@samsung.com/
[3] - https://github.com/mwilczy/linux/commits/rust-next-pwm-working-fan-for-sending-v7/

---
Changes in v3:
 - Addressed feedback from Uwe by making multiple changes to the TH1520
   driver and the abstraction layer.
 - Split the core PWM abstractions into three focused commits to ease
   review per Benno request.
 - Confirmed the driver now works correctly with CONFIG_PWM_DEBUG enabled
   by implementing the full waveform API, which correctly reads the
   hardware state.
 - Refactored the Rust code to build cleanly with
   CONFIG_RUST_BUILD_ASSERT_ALLOW=n, primarily by using the try_* family of
   functions for IoMem access.
 - Included several cosmetic changes and cleanups to the abstractions
   per Miguel review.

- Link to v2: https://lore.kernel.org/r/20250610-rust-next-pwm-working-fan-for-sending-v2-0-753e2955f110@samsung.com

Changes in v2:
 - Reworked the PWM abstraction layer based on extensive feedback.
 - Replaced initial devm allocation with a proper ARef<Chip> lifetime model
   using AlwaysRefCounted.
 - Implemented a Registration RAII guard to ensure safe chip add/remove.
 - Migrated the PwmOps trait from the legacy .apply callback to the modern
   waveform API.
 - Refactored the TH1520 driver to use the new, safer abstractions.
 - Added a patch to mark essential bus clocks as CLK_IGNORE_UNUSED to fix
   boot hangs when the PWM and thermal sensors are enabled.
- Link to v1: https://lore.kernel.org/r/20250524-rust-next-pwm-working-fan-for-sending-v1-0-bdd2d5094ff7@samsung.com

---
Michal Wilczynski (9):
      rust: pwm: Add Kconfig and basic data structures
      rust: pwm: Add core 'Device' and 'Chip' object wrappers
      rust: pwm: Add driver operations trait and registration support
      pwm: Add Rust driver for T-HEAD TH1520 SoC
      clk: thead: Mark essential bus clocks as CLK_IGNORE_UNUSED
      dt-bindings: pwm: thead: Add T-HEAD TH1520 PWM controller
      riscv: dts: thead: Add PWM controller node
      riscv: dts: thead: Add PVT node
      riscv: dts: thead: Add PWM fan and thermal control

 .../devicetree/bindings/pwm/thead,th1520-pwm.yaml  |  48 ++
 MAINTAINERS                                        |   8 +
 arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts  |  67 ++
 arch/riscv/boot/dts/thead/th1520.dtsi              |  18 +
 drivers/clk/thead/clk-th1520-ap.c                  |   5 +-
 drivers/pwm/Kconfig                                |  23 +
 drivers/pwm/Makefile                               |   1 +
 drivers/pwm/pwm_th1520.rs                          | 328 ++++++++
 rust/bindings/bindings_helper.h                    |   1 +
 rust/helpers/helpers.c                             |   1 +
 rust/kernel/lib.rs                                 |   2 +
 rust/kernel/pwm.rs                                 | 886 +++++++++++++++++++++
 12 files changed, 1386 insertions(+), 2 deletions(-)
---
base-commit: 79b01ff21368605a62b76535ab1ab5f1f726de60
change-id: 20250524-rust-next-pwm-working-fan-for-sending-552ad2d1b193

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


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[PATCH v3 1/9] rust: pwm: Add Kconfig and basic data structures

[Michal Wilczynski]

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@samsung.com>
---
 MAINTAINERS                     |   6 ++
 drivers/pwm/Kconfig             |  13 +++
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers/helpers.c          |   1 +
 rust/kernel/lib.rs              |   2 +
 rust/kernel/pwm.rs              | 198 ++++++++++++++++++++++++++++++++++++++++
 6 files changed, 221 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 0c1d245bf7b84f8a78b811e0c9c5a3edc09edc22..a575622454a2ef57ce055c8a8c4765fa4fddc490 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -20073,6 +20073,12 @@ 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@samsung.com>
+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 693cdd01f9290fa01375cf78cac0e5a90df74c6c..6fe7dd529577952bf7adb4fe0526b0d5fbd6f3bd 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -64,6 +64,7 @@
 #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 16fa9bca5949b85e8d4cdcfe8e6886124f72d8d8..60879e6d794ce0f87e39caafc5495bf5e8acf8f0 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -31,6 +31,7 @@
 #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/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..ed681b228c414e7ae8bf80ca649ad497c9dc4ec3
--- /dev/null
+++ b/rust/kernel/pwm.rs
@@ -0,0 +1,198 @@
+// 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;
+
+/// Maximum size for the hardware-specific waveform representation buffer.
+///
+/// From C: `#define WFHWSIZE 20`
+pub const WFHW_MAX_SIZE: usize = 20;
+
+/// 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 Default for State {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl State {
+    /// Creates a new zeroed `State`.
+    pub fn new() -> Self {
+        State(bindings::pwm_state::default())
+    }
+
+    /// 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)
+    }
+
+    /// Gets the period of the PWM signal in nanoseconds.
+    pub fn period(&self) -> u64 {
+        self.0.period
+    }
+
+    /// Sets the period of the PWM signal in nanoseconds.
+    pub fn set_period(&mut self, period_ns: u64) {
+        self.0.period = period_ns;
+    }
+
+    /// Gets the duty cycle of the PWM signal in nanoseconds.
+    pub fn duty_cycle(&self) -> u64 {
+        self.0.duty_cycle
+    }
+
+    /// Sets the duty cycle of the PWM signal in nanoseconds.
+    pub fn set_duty_cycle(&mut self, duty_ns: u64) {
+        self.0.duty_cycle = duty_ns;
+    }
+
+    /// Returns `true` if the PWM signal is enabled.
+    pub fn enabled(&self) -> bool {
+        self.0.enabled
+    }
+
+    /// Sets the enabled state of the PWM signal.
+    pub fn set_enabled(&mut self, enabled: bool) {
+        self.0.enabled = enabled;
+    }
+
+    /// Gets the polarity of the PWM signal.
+    pub fn polarity(&self) -> Result<Polarity, Error> {
+        Polarity::try_from(self.0.polarity)
+    }
+
+    /// Sets the polarity of the PWM signal.
+    pub fn set_polarity(&mut self, polarity: Polarity) {
+        self.0.polarity = polarity.into();
+    }
+
+    /// Returns `true` if the PWM signal is configured for power usage hint.
+    pub fn usage_power(&self) -> bool {
+        self.0.usage_power
+    }
+
+    /// Sets the power usage hint for the PWM signal.
+    pub fn set_usage_power(&mut self, usage_power: bool) {
+        self.0.usage_power = usage_power;
+    }
+}

-- 
2.34.1


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[PATCH v3 2/9] rust: pwm: Add core 'Device' and 'Chip' object wrappers

[Michal Wilczynski]

Building on the basic data types, this commit introduces the central
object abstractions for the PWM subsystem: Device and Chip. It also
includes the core trait implementations that make the Chip wrapper a
complete, safe, and managed object.

The main components of this change are:
 - Device and Chip Structs: These structs wrap the underlying struct
   pwm_device and struct pwm_chip C objects, providing safe, idiomatic
   methods to access their fields.

 - Core Trait Implementations for Chip:
    - AlwaysRefCounted: Links the Chip's lifetime to its embedded
      struct device reference counter. This enables automatic lifetime
      management via ARef.
    - Send and Sync: Marks the Chip wrapper as safe for use across
      threads. This is sound because the C core handles all necessary
      locking for the underlying object's state.

These wrappers and traits form a robust foundation for building PWM
drivers in Rust.

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 rust/kernel/pwm.rs | 227 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 225 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/pwm.rs b/rust/kernel/pwm.rs
index ed681b228c414e7ae8bf80ca649ad497c9dc4ec3..8c4c27a4e4fc9da2fc8ea5015df2a315cfc6b932 100644
--- a/rust/kernel/pwm.rs
+++ b/rust/kernel/pwm.rs
@@ -8,10 +8,12 @@
 
 use crate::{
     bindings,
+    device,
+    error,
     prelude::*,
-    types::Opaque,
+    types::{ARef, AlwaysRefCounted, ForeignOwnable, Opaque},
 };
-use core::convert::TryFrom;
+use core::{convert::TryFrom, ptr::NonNull};
 
 /// Maximum size for the hardware-specific waveform representation buffer.
 ///
@@ -196,3 +198,224 @@ pub fn set_usage_power(&mut self, usage_power: bool) {
         self.0.usage_power = usage_power;
     }
 }
+
+/// 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 temporary `&mut Device` from a raw C pointer for use in callbacks.
+    ///
+    /// It returns a mutable reference (`&mut Self`) because the underlying C APIs
+    /// for PWM operations use non-const pointers (`struct pwm_device *`). This
+    /// signals that the functions in the vtable are permitted to mutate the
+    /// device's state (e.g., by writing to hardware registers). Using `&mut`
+    /// allows the `PwmOps` trait to accurately model this behavior and leverage
+    /// Rust's aliasing rules for greater safety.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `ptr` is a valid, non-null pointer to
+    /// `bindings::pwm_device` that is properly initialized.
+    /// The `pwm_device` must remain valid for the lifetime `'a`.
+    /// The caller must also ensure that Rust's aliasing rules are upheld.
+    pub(crate) unsafe fn from_ptr<'a>(ptr: *mut bindings::pwm_device) -> &'a mut Self {
+        // SAFETY: Caller guarantees `ptr` is valid and meets lifetime/aliasing.
+        // `Self` is `#[repr(transparent)]`, so casting is valid.
+        unsafe { &mut *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(&self) -> &Chip {
+        // 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_ptr's safety conditions must be met.
+        unsafe { Chip::from_ptr((*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() {
+            None
+        } else {
+            // 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 board-dependent arguments for this PWM device.
+    pub fn args(&self) -> Args {
+        // SAFETY: self.as_raw() gives a valid pointer to `pwm_device`.
+        // The `args` field is a valid `pwm_args` struct embedded within `pwm_device`.
+        // `Args::from_c_ptr`'s safety conditions are met by providing this pointer.
+        unsafe { Args::from_c_ptr(&(*self.as_raw()).args) }
+    }
+
+    /// 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 })
+    }
+
+    /// Returns `true` if the PWM signal is currently enabled based on its state.
+    pub fn is_enabled(&self) -> bool {
+        self.state().enabled()
+    }
+}
+
+/// Wrapper for a PWM chip/controller ([`struct pwm_chip`](srctree/include/linux/pwm.h)).
+#[repr(transparent)]
+pub struct Chip(Opaque<bindings::pwm_chip>);
+
+impl Chip {
+    /// Creates a temporary `&mut Chip` from a raw C pointer for use in callbacks.
+    ///
+    /// It returns a mutable reference (`&mut Self`) because the underlying C APIs
+    /// for PWM operations use non-const pointers (`struct pwm_chip *`). This
+    /// signals that the functions in the vtable are permitted to mutate the
+    /// chip's state (e.g., by calling `set_drvdata` or through operations that
+    /// modify hardware registers). Using `&mut` is essential for these cases.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `ptr` is a valid, non-null pointer to
+    /// `bindings::pwm_chip` that is properly initialized.
+    /// The `pwm_chip` must remain valid for the lifetime `'a`.
+    /// The caller must also ensure that Rust's aliasing rules are upheld.
+    pub(crate) unsafe fn from_ptr<'a>(ptr: *mut bindings::pwm_chip) -> &'a mut Self {
+        // SAFETY: Caller guarantees `ptr` is valid and meets lifetime/aliasing.
+        // `Self` is `#[repr(transparent)]`, so casting is valid.
+        unsafe { &mut *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 npwm(&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`.
+        let dev_field_ptr = unsafe { core::ptr::addr_of!((*self.as_raw()).dev) };
+        // SAFETY: `dev_field_ptr` is a valid pointer to `bindings::device`.
+        // Casting and dereferencing is safe due to `repr(transparent)` and lifetime.
+        unsafe { &*(dev_field_ptr.cast::<device::Device>()) }
+    }
+
+    /// Returns a reference to the parent device of this PWM chip's device.
+    pub fn parent_device(&self) -> Option<&device::Device> {
+        self.device().parent()
+    }
+
+    /// Gets the *typed* driver-specific data associated with this chip's embedded device.
+    pub fn drvdata<T: 'static>(&self) -> Option<&T> {
+        // SAFETY: `self.as_raw()` gives a valid pwm_chip pointer.
+        // `bindings::pwmchip_get_drvdata` is the C function to retrieve driver data.
+        let ptr = unsafe { bindings::pwmchip_get_drvdata(self.as_raw()) };
+        if ptr.is_null() {
+            None
+        } else {
+            // SAFETY: `ptr` is non-null. Caller ensures `T` is the correct type.
+            // Lifetime of data is managed by the driver that set it.
+            unsafe { Some(&*(ptr.cast::<T>())) }
+        }
+    }
+
+    /// Sets the *typed* driver-specific data associated with this chip's embedded device.
+    pub fn set_drvdata<T: 'static + ForeignOwnable>(&self, data: T) {
+        // SAFETY: `self.as_raw()` gives a valid pwm_chip pointer.
+        // `bindings::pwmchip_set_drvdata` is the C function to set driver data.
+        // `data.into_foreign()` provides a valid `*mut c_void`.
+        unsafe { bindings::pwmchip_set_drvdata(self.as_raw(), data.into_foreign().cast()) }
+    }
+
+    /// 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, npwm: u32, sizeof_priv: usize) -> Result<ARef<Self>> {
+        // SAFETY: `parent_device_for_dev_field.as_raw()` is valid.
+        // `bindings::pwmchip_alloc` returns a valid `*mut bindings::pwm_chip` (refcount 1)
+        // or an ERR_PTR.
+        let c_chip_ptr_raw =
+            unsafe { bindings::pwmchip_alloc(parent_dev.as_raw(), npwm, sizeof_priv) };
+
+        let c_chip_ptr: *mut bindings::pwm_chip = error::from_err_ptr(c_chip_ptr_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 AlwaysRefCounted for Chip {
+    #[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(core::ptr::addr_of_mut!((*self.0.get()).dev));
+        }
+    }
+
+    #[inline]
+    unsafe fn dec_ref(obj: NonNull<Chip>) {
+        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(core::ptr::addr_of_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 Send for Chip {}
+
+// 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 Sync for Chip {}

-- 
2.34.1


_______________________________________________
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http://lists.infradead.org/mailman/listinfo/linux-riscv

[PATCH v3 3/9] rust: pwm: Add driver operations trait and registration support

[Michal Wilczynski]

Complete the PWM abstraction layer by adding the final components
required to implement and register a driver.

The main additions are:

 - PwmOps Trait: An interface that drivers can implement to provide
   their hardware specific logic. It mirrors the C pwm_ops interface,
   providing hooks for standard PWM operations like apply, request, and
   waveform handling.

 - FFI VTable and Adapter: The Adapter struct, PwmOpsVTable wrapper, and
   create_pwm_ops function are introduced. This scaffolding handles the
   unsafe FFI translation, bridging the gap between the idiomatic PwmOps
   trait and the C kernel's function-pointer-based vtable.

 - Registration Guard: A final RAII guard that uses the vtable to safely
   register a Chip with the PWM core via pwmchip_add. Its Drop
   implementation guarantees that pwmchip_remove is always called,
   preventing resource leaks.

With this patch, the PWM abstraction layer is now complete and ready to
be used for writing PWM chip drivers in Rust.

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 rust/kernel/pwm.rs | 471 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 468 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/pwm.rs b/rust/kernel/pwm.rs
index 8c4c27a4e4fc9da2fc8ea5015df2a315cfc6b932..64210411450cd3d964d21f1e712fcfd4d8aed988 100644
--- a/rust/kernel/pwm.rs
+++ b/rust/kernel/pwm.rs
@@ -8,12 +8,12 @@
 
 use crate::{
     bindings,
-    device,
-    error,
+    device::{self, Bound},
+    error::{self, to_result},
     prelude::*,
     types::{ARef, AlwaysRefCounted, ForeignOwnable, Opaque},
 };
-use core::{convert::TryFrom, ptr::NonNull};
+use core::{convert::TryFrom, marker::PhantomData, mem::ManuallyDrop, ptr::NonNull};
 
 /// Maximum size for the hardware-specific waveform representation buffer.
 ///
@@ -419,3 +419,468 @@ unsafe impl Send for Chip {}
 // kernel locks, which the C core is responsible for. Any interior mutability is
 // handled and synchronized by the C kernel code.
 unsafe impl Sync for Chip {}
+
+/// Manages the registration of a PWM chip, ensuring `pwmchip_remove` is called on drop.
+pub struct Registration {
+    chip: ManuallyDrop<ARef<Chip>>,
+}
+
+impl Registration {
+    /// Registers a PWM chip (obtained via `Chip::new`) with the PWM subsystem.
+    ///
+    /// Takes an [`ARef<Chip>`]. On `Drop` of the returned `Registration` object,
+    /// `pwmchip_remove` is called for the chip.
+    pub fn new(chip: ARef<Chip>, ops_vtable: &'static PwmOpsVTable) -> Result<Self> {
+        // Get the raw C pointer from ARef<Chip>.
+        let c_chip_ptr = chip.as_raw().cast::<bindings::pwm_chip>();
+
+        // SAFETY: `c_chip_ptr` is valid (guaranteed by ARef existing).
+        // `ops_vtable.as_raw()` provides a valid `*const bindings::pwm_ops`.
+        // `bindings::__pwmchip_add` preconditions (valid pointers, ops set on chip) are met.
+        unsafe {
+            (*c_chip_ptr).ops = ops_vtable.as_raw();
+            to_result(bindings::__pwmchip_add(c_chip_ptr, core::ptr::null_mut()))?;
+        }
+        Ok(Registration {
+            chip: ManuallyDrop::new(chip),
+        })
+    }
+}
+
+impl Drop for Registration {
+    fn drop(&mut self) {
+        let chip = &**self.chip;
+        let chip_raw: *mut bindings::pwm_chip = chip.as_raw();
+
+        // SAFETY: `chip_raw` points to a chip that was successfully registered via `Self::new`.
+        // `bindings::pwmchip_remove` is the correct C function to unregister it.
+        unsafe {
+            bindings::pwmchip_remove(chip_raw);
+            ManuallyDrop::drop(&mut self.chip); // Drops the ARef<Chip>
+        }
+    }
+}
+
+/// 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 [`WFHW_MAX_SIZE`].
+    type WfHw: Copy + Default;
+
+    /// Optional hook to atomically apply a new PWM config.
+    fn apply(
+        _chip: &mut Chip,
+        _pwm: &mut Device,
+        _state: &State,
+        _parent_dev: &device::Device<Bound>,
+    ) -> Result {
+        Err(ENOTSUPP)
+    }
+
+    /// Optional hook for when a PWM device is requested.
+    fn request(_chip: &mut Chip, _pwm: &mut Device, _parent_dev: &device::Device<Bound>) -> Result {
+        Ok(())
+    }
+
+    /// Optional hook for when a PWM device is freed.
+    fn free(_chip: &mut Chip, _pwm: &mut Device, _parent_dev: &device::Device<Bound>) {}
+
+    /// Optional hook for capturing a PWM signal.
+    fn capture(
+        _chip: &mut Chip,
+        _pwm: &mut Device,
+        _result: &mut bindings::pwm_capture,
+        _timeout: usize,
+        _parent_dev: &device::Device<Bound>,
+    ) -> Result {
+        Err(ENOTSUPP)
+    }
+
+    /// Optional hook to get the current hardware state.
+    fn get_state(
+        _chip: &mut Chip,
+        _pwm: &mut Device,
+        _state: &mut State,
+        _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: &mut Chip,
+        _pwm: &mut Device,
+        _wf: &Waveform,
+    ) -> Result<(c_int, 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: &mut Chip,
+        _pwm: &Device,
+        _wfhw: &Self::WfHw,
+        _wf: &mut Waveform,
+    ) -> Result<c_int> {
+        Err(ENOTSUPP)
+    }
+
+    /// Read the current hardware configuration into the hardware-specific representation.
+    fn read_waveform(
+        _chip: &mut Chip,
+        _pwm: &mut Device,
+        _parent_dev: &device::Device<Bound>,
+    ) -> Result<Self::WfHw> {
+        Err(ENOTSUPP)
+    }
+
+    /// Write a hardware-specific waveform configuration to the hardware.
+    fn write_waveform(
+        _chip: &mut Chip,
+        _pwm: &mut 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> {
+    /// # 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>();
+        if size > WFHW_MAX_SIZE {
+            return Err(EINVAL);
+        }
+
+        // SAFETY: The caller ensures `wfhw_ptr` is valid for `size` bytes.
+        unsafe {
+            core::ptr::copy_nonoverlapping(wfhw as *const _ as *const u8, wfhw_ptr.cast(), 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>();
+        if size > WFHW_MAX_SIZE {
+            return Err(EINVAL);
+        }
+
+        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(), &mut wfhw as *mut _ as *mut u8, size);
+        }
+
+        Ok(wfhw)
+    }
+
+    /// # Safety
+    ///
+    /// Pointers from C must be valid.
+    unsafe extern "C" fn apply_callback(
+        c: *mut bindings::pwm_chip,
+        p: *mut bindings::pwm_device,
+        s: *const bindings::pwm_state,
+    ) -> c_int {
+        // SAFETY: This block relies on the function's safety contract: the C caller
+        // provides valid pointers. `Chip::from_ptr` and `Device::from_ptr` are `unsafe fn`
+        // whose preconditions are met by this contract.
+        let (chip, pwm) = unsafe { (Chip::from_ptr(c), Device::from_ptr(p)) };
+        let parent_dev = match chip.parent_device() {
+            Some(dev) => dev,
+            None => {
+                return EINVAL.to_errno();
+            }
+        };
+
+        // SAFETY: The PWM core guarantees callbacks only happen on a live, bound device.
+        let bound_parent =
+            unsafe { &*(parent_dev as *const device::Device as *const device::Device<Bound>) };
+
+        // SAFETY: The state provided by the callback is guaranteed to be valid
+        let state = State::from_c(unsafe { *s });
+        match T::apply(chip, pwm, &state, bound_parent) {
+            Ok(()) => 0,
+            Err(e) => e.to_errno(),
+        }
+    }
+
+    /// # Safety
+    ///
+    /// Pointers from C must be valid.
+    unsafe extern "C" fn request_callback(
+        c: *mut bindings::pwm_chip,
+        p: *mut bindings::pwm_device,
+    ) -> c_int {
+        // SAFETY: PWM core guarentees `c` and `p` are valid pointers.
+        let (chip, pwm) = unsafe { (Chip::from_ptr(c), Device::from_ptr(p)) };
+        let parent_dev = match chip.parent_device() {
+            Some(dev) => dev,
+            None => {
+                return EINVAL.to_errno();
+            }
+        };
+
+        let bound_parent =
+	// SAFETY: The PWM core guarantees the device is bound during callbacks.
+            unsafe { &*(parent_dev as *const device::Device as *const device::Device<Bound>) };
+        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 free_callback(c: *mut bindings::pwm_chip, p: *mut bindings::pwm_device) {
+        // SAFETY: Relies on the function's contract that `c` and `p` are valid pointers.
+        let (chip, pwm) = unsafe { (Chip::from_ptr(c), Device::from_ptr(p)) };
+        let parent_dev = match chip.parent_device() {
+            Some(dev) => dev,
+            None => {
+                return;
+            }
+        };
+
+        let bound_parent =
+	// SAFETY: The PWM core guarantees the device is bound during callbacks.
+            unsafe { &*(parent_dev as *const device::Device as *const device::Device<Bound>) };
+        T::free(chip, pwm, bound_parent);
+    }
+
+    /// # Safety
+    ///
+    /// Pointers from C must be valid.
+    unsafe extern "C" fn capture_callback(
+        c: *mut bindings::pwm_chip,
+        p: *mut bindings::pwm_device,
+        res: *mut bindings::pwm_capture,
+        timeout: usize,
+    ) -> c_int {
+        // SAFETY: Relies on the function's contract that `c` and `p` are valid pointers.
+        let (chip, pwm, result) = unsafe { (Chip::from_ptr(c), Device::from_ptr(p), &mut *res) };
+        let parent_dev = match chip.parent_device() {
+            Some(dev) => dev,
+            None => {
+                return EINVAL.to_errno();
+            }
+        };
+
+        let bound_parent =
+	        // SAFETY: The PWM core guarantees the device is bound during callbacks.
+            unsafe { &*(parent_dev as *const device::Device as *const device::Device<Bound>) };
+        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 get_state_callback(
+        c: *mut bindings::pwm_chip,
+        p: *mut bindings::pwm_device,
+        s: *mut bindings::pwm_state,
+    ) -> c_int {
+        // SAFETY: Relies on the function's contract that `c` and `p` are valid pointers.
+        let (chip, pwm) = unsafe { (Chip::from_ptr(c), Device::from_ptr(p)) };
+        let parent_dev = match chip.parent_device() {
+            Some(dev) => dev,
+            None => {
+                return EINVAL.to_errno();
+            }
+        };
+        let bound_parent =
+	// SAFETY: The PWM core guarantees the device is bound during callbacks.
+            unsafe { &*(parent_dev as *const device::Device as *const device::Device<Bound>) };
+        let mut rust_state = State::new();
+        match T::get_state(chip, pwm, &mut rust_state, bound_parent) {
+            Ok(()) => {
+                // SAFETY: `s` is guaranteed valid by the C caller.
+                unsafe {
+                    *s = rust_state.0;
+                };
+                0
+            }
+            Err(e) => e.to_errno(),
+        }
+    }
+
+    /// # Safety
+    ///
+    /// Pointers from C must be valid.
+    unsafe extern "C" fn round_waveform_tohw_callback(
+        c: *mut bindings::pwm_chip,
+        p: *mut bindings::pwm_device,
+        w: *const bindings::pwm_waveform,
+        wh: *mut c_void,
+    ) -> c_int {
+        // SAFETY: Relies on the function's contract that `c` and `p` are valid pointers.
+        let (chip, pwm, wf) =
+            unsafe { (Chip::from_ptr(c), Device::from_ptr(p), Waveform::from(*w)) };
+        match T::round_waveform_tohw(chip, pwm, &wf) {
+            Ok((status, wfhw)) => {
+                // SAFETY: `wh` is valid per this function's safety contract.
+                if unsafe { Self::serialize_wfhw(&wfhw, wh) }.is_err() {
+                    return EINVAL.to_errno();
+                }
+                status
+            }
+            Err(e) => e.to_errno(),
+        }
+    }
+
+    /// # Safety
+    ///
+    /// Pointers from C must be valid.
+    unsafe extern "C" fn round_waveform_fromhw_callback(
+        c: *mut bindings::pwm_chip,
+        p: *mut bindings::pwm_device,
+        wh: *const c_void,
+        w: *mut bindings::pwm_waveform,
+    ) -> c_int {
+        // SAFETY: Relies on the function's contract that `c` and `p` are valid pointers.
+        let (chip, pwm) = unsafe { (Chip::from_ptr(c), Device::from_ptr(p)) };
+        // SAFETY: `deserialize_wfhw`'s safety contract is met by this function's contract.
+        let wfhw = match unsafe { Self::deserialize_wfhw(wh) } {
+            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(ret) => {
+                // SAFETY: `w` is guaranteed valid by the C caller.
+                unsafe {
+                    *w = rust_wf.into();
+                };
+                ret
+            }
+            Err(e) => e.to_errno(),
+        }
+    }
+
+    /// # Safety
+    ///
+    /// Pointers from C must be valid.
+    unsafe extern "C" fn read_waveform_callback(
+        c: *mut bindings::pwm_chip,
+        p: *mut bindings::pwm_device,
+        wh: *mut c_void,
+    ) -> c_int {
+        // SAFETY: Relies on the function's contract that `c` and `p` are valid pointers.
+        let (chip, pwm) = unsafe { (Chip::from_ptr(c), Device::from_ptr(p)) };
+        let parent_dev = match chip.parent_device() {
+            Some(dev) => dev,
+            None => {
+                return EINVAL.to_errno();
+            }
+        };
+
+        let bound_parent =
+	// SAFETY: The PWM core guarantees the device is bound during callbacks.
+            unsafe { &*(parent_dev as *const device::Device as *const device::Device<Bound>) };
+        match T::read_waveform(chip, pwm, bound_parent) {
+            // SAFETY: `wh` is valid per this function's safety contract.
+            Ok(wfhw) => match unsafe { Self::serialize_wfhw(&wfhw, wh) } {
+                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(
+        c: *mut bindings::pwm_chip,
+        p: *mut bindings::pwm_device,
+        wh: *const c_void,
+    ) -> c_int {
+        // SAFETY: Relies on the function's contract that `c` and `p` are valid pointers.
+        let (chip, pwm) = unsafe { (Chip::from_ptr(c), Device::from_ptr(p)) };
+        let parent_dev = match chip.parent_device() {
+            Some(dev) => dev,
+            None => {
+                return EINVAL.to_errno();
+            }
+        };
+
+        let bound_parent =
+	        // SAFETY: The PWM core guarantees the device is bound during callbacks.
+            unsafe { &*(parent_dev as *const device::Device as *const device::Device<Bound>) };
+        // SAFETY: `wh` is valid per this function's safety contract.
+        let wfhw = match unsafe { Self::deserialize_wfhw(wh) } {
+            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(Opaque<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.get()
+    }
+}
+
+/// 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.apply = Some(Adapter::<T>::apply_callback);
+    ops.request = Some(Adapter::<T>::request_callback);
+    ops.free = Some(Adapter::<T>::free_callback);
+    ops.capture = Some(Adapter::<T>::capture_callback);
+    ops.get_state = Some(Adapter::<T>::get_state_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(Opaque::new(ops))
+}

-- 
2.34.1


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Re: [PATCH v3 3/9] rust: pwm: Add driver operations trait and registration support

[Danilo Krummrich]

On Tue, Jun 17, 2025 at 04:07:26PM +0200, Michal Wilczynski wrote:
> +/// Manages the registration of a PWM chip, ensuring `pwmchip_remove` is called on drop.
> +pub struct Registration {
> +    chip: ManuallyDrop<ARef<Chip>>,

Why is this ManuallyDrop when you call ManuallyDrop::drop(&mut self.chip) as
the last thing in Registration::drop()?

I think you don't need ManuallyDrop here.

> +}
> +
> +impl Registration {
> +    /// Registers a PWM chip (obtained via `Chip::new`) with the PWM subsystem.
> +    ///
> +    /// Takes an [`ARef<Chip>`]. On `Drop` of the returned `Registration` object,
> +    /// `pwmchip_remove` is called for the chip.
> +    pub fn new(chip: ARef<Chip>, ops_vtable: &'static PwmOpsVTable) -> Result<Self> {

For the reason mentioned in [1] this should either return Result<Devres<Self>>
or just Result, if you use Devres::new_foreign_owned() (see also [2]).

In case of the latter, the Registration instance is automatically dropped once
the parent device is unbound.

If you go with the first, you can drop the Devres<Registration> (and hence the
inner Registration) at any arbitrary point of time, but Devres will still
gurarantee that the inner Registration is dropped once the parent device is
unbound, i.e. it can't out-live driver unbind.

This guarantees that the &Device<Bound> instance you provide in the callbacks
below is guaranteed to be valid.

[1] https://lore.kernel.org/lkml/aFF7qqlexxh540FW@pollux/
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/rust/kernel/drm/driver.rs#n134

> +        // Get the raw C pointer from ARef<Chip>.
> +        let c_chip_ptr = chip.as_raw().cast::<bindings::pwm_chip>();
> +
> +        // SAFETY: `c_chip_ptr` is valid (guaranteed by ARef existing).
> +        // `ops_vtable.as_raw()` provides a valid `*const bindings::pwm_ops`.
> +        // `bindings::__pwmchip_add` preconditions (valid pointers, ops set on chip) are met.
> +        unsafe {
> +            (*c_chip_ptr).ops = ops_vtable.as_raw();
> +            to_result(bindings::__pwmchip_add(c_chip_ptr, core::ptr::null_mut()))?;
> +        }

Please split this up into separate unsafe blocks.

> +        Ok(Registration {
> +            chip: ManuallyDrop::new(chip),
> +        })
> +    }
> +}
> +
> +impl Drop for Registration {
> +    fn drop(&mut self) {
> +        let chip = &**self.chip;
> +        let chip_raw: *mut bindings::pwm_chip = chip.as_raw();
> +
> +        // SAFETY: `chip_raw` points to a chip that was successfully registered via `Self::new`.
> +        // `bindings::pwmchip_remove` is the correct C function to unregister it.
> +        unsafe {
> +            bindings::pwmchip_remove(chip_raw);
> +            ManuallyDrop::drop(&mut self.chip); // Drops the ARef<Chip>
> +        }

Same here, but I don't think ManuallyDrop is needed anyways.

> +    }
> +}

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[PATCH v3 4/9] pwm: Add Rust driver for T-HEAD TH1520 SoC

[Michal Wilczynski]

Introduce a PWM driver for the T-HEAD TH1520 SoC, written in Rust and
utilizing the safe PWM abstractions from the preceding commit.

The driver implements the pwm::PwmOps trait using the modern waveform
API (round_waveform_tohw, write_waveform, etc.) to support configuration
of period, duty cycle, and polarity for the TH1520's PWM channels.

Resource management is handled using idiomatic Rust patterns. The PWM
chip object is allocated via pwm::Chip::new and its registration with
the PWM core is managed by the pwm::Registration RAII guard. This
ensures pwmchip_remove is always called when the driver unbinds,
preventing resource leaks. Device managed resources are used for the
MMIO region, and the clock lifecycle is correctly managed in the
driver's private data Drop implementation.

The driver's core logic is written entirely in safe Rust, with no unsafe
blocks.

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 MAINTAINERS               |   1 +
 drivers/pwm/Kconfig       |  10 ++
 drivers/pwm/Makefile      |   1 +
 drivers/pwm/pwm_th1520.rs | 328 ++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 340 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index a575622454a2ef57ce055c8a8c4765fa4fddc490..879870471e86dcec4a0e8f5c45d2cc3409411fdd 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -21402,6 +21402,7 @@ F:	drivers/mailbox/mailbox-th1520.c
 F:	drivers/net/ethernet/stmicro/stmmac/dwmac-thead.c
 F:	drivers/pinctrl/pinctrl-th1520.c
 F:	drivers/pmdomain/thead/
+F:	drivers/pwm/pwm_th1520.rs
 F:	drivers/reset/reset-th1520.c
 F:	include/dt-bindings/clock/thead,th1520-clk-ap.h
 F:	include/dt-bindings/power/thead,th1520-power.h
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index cfddeae0eab3523f04f361fb41ccd1345c0c937b..a675b3bd68392d1b05a47a2a1390c5606647ca15 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -719,6 +719,16 @@ config PWM_TEGRA
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-tegra.
 
+config PWM_TH1520
+	tristate "TH1520 PWM support"
+	depends on RUST_PWM_ABSTRACTIONS
+	help
+	  This option enables the driver for the PWM controller found on the
+	  T-HEAD TH1520 SoC.
+
+	  To compile this driver as a module, choose M here; the module
+	  will be called pwm-th1520. If you are unsure, say N.
+
 config PWM_TIECAP
 	tristate "ECAP PWM support"
 	depends on ARCH_OMAP2PLUS || ARCH_DAVINCI_DA8XX || ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index 96160f4257fcb0e0951581af0090615c0edf5260..a410747095327a315a6bcd24ae343ce7857fe323 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -66,6 +66,7 @@ obj-$(CONFIG_PWM_STMPE)		+= pwm-stmpe.o
 obj-$(CONFIG_PWM_SUN4I)		+= pwm-sun4i.o
 obj-$(CONFIG_PWM_SUNPLUS)	+= pwm-sunplus.o
 obj-$(CONFIG_PWM_TEGRA)		+= pwm-tegra.o
+obj-$(CONFIG_PWM_TH1520)	+= pwm_th1520.o
 obj-$(CONFIG_PWM_TIECAP)	+= pwm-tiecap.o
 obj-$(CONFIG_PWM_TIEHRPWM)	+= pwm-tiehrpwm.o
 obj-$(CONFIG_PWM_TWL)		+= pwm-twl.o
diff --git a/drivers/pwm/pwm_th1520.rs b/drivers/pwm/pwm_th1520.rs
new file mode 100644
index 0000000000000000000000000000000000000000..7869a118be94068861a64346258732aeec13a521
--- /dev/null
+++ b/drivers/pwm/pwm_th1520.rs
@@ -0,0 +1,328 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2025 Samsung Electronics Co., Ltd.
+// Author: Michal Wilczynski <m.wilczynski@samsung.com>
+
+//! Rust T-HEAD TH1520 PWM driver
+//!
+//! Limitations:
+//! - The period and duty cycle are controlled by 32-bit hardware registers,
+//!   limiting the maximum resolution.
+//! - The driver supports continuous output mode only; one-shot mode is not
+//!   implemented.
+//! - The controller hardware provides up to 6 PWM channels.
+//!
+
+use core::ops::Deref;
+use kernel::{
+    c_str,
+    clk::Clk,
+    device::{Bound, Core, Device},
+    devres,
+    io::mem::IoMem,
+    of, platform,
+    prelude::*,
+    pwm, time,
+};
+
+const MAX_PWM_NUM: u32 = 6;
+
+// Register offsets
+const fn th1520_pwm_chn_base(n: u32) -> usize {
+    (n * 0x20) as usize
+}
+
+const fn th1520_pwm_ctrl(n: u32) -> usize {
+    th1520_pwm_chn_base(n)
+}
+
+const fn th1520_pwm_per(n: u32) -> usize {
+    th1520_pwm_chn_base(n) + 0x08
+}
+
+const fn th1520_pwm_fp(n: u32) -> usize {
+    th1520_pwm_chn_base(n) + 0x0c
+}
+
+// Control register bits
+const PWM_START: u32 = 1 << 0;
+const PWM_CFG_UPDATE: u32 = 1 << 2;
+const PWM_CONTINUOUS_MODE: u32 = 1 << 5;
+const PWM_FPOUT: u32 = 1 << 8;
+
+const TH1520_PWM_REG_SIZE: usize = 0xB0;
+
+fn ns_to_cycles(ns: u64, rate_hz: u64) -> u64 {
+    const NSEC_PER_SEC_U64: u64 = time::NSEC_PER_SEC as u64;
+
+    match ns.checked_mul(rate_hz) {
+        Some(product) => product / NSEC_PER_SEC_U64,
+        None => u64::MAX,
+    }
+}
+
+fn cycles_to_ns(cycles: u64, rate_hz: u64) -> u64 {
+    const NSEC_PER_SEC_U64: u64 = time::NSEC_PER_SEC as u64;
+
+    // Round up
+    let Some(numerator) = cycles
+        .checked_mul(NSEC_PER_SEC_U64)
+        .and_then(|p| p.checked_add(rate_hz - 1))
+    else {
+        return u64::MAX;
+    };
+
+    numerator / rate_hz
+}
+
+/// Hardware-specific waveform representation for TH1520.
+#[derive(Copy, Clone, Debug, Default)]
+struct Th1520WfHw {
+    period_cycles: u32,
+    duty_cycles: u32,
+    ctrl_val: u32,
+    enabled: bool,
+}
+
+/// The driver's private data struct. It holds all necessary devres managed resources.
+struct Th1520PwmDriverData {
+    iomem: devres::Devres<IoMem<TH1520_PWM_REG_SIZE>>,
+    clk: Clk,
+}
+
+impl pwm::PwmOps for Th1520PwmDriverData {
+    type WfHw = Th1520WfHw;
+
+    fn round_waveform_tohw(
+        chip: &mut pwm::Chip,
+        _pwm: &mut pwm::Device,
+        wf: &pwm::Waveform,
+    ) -> Result<(c_int, Self::WfHw)> {
+        let data: &Self = chip.drvdata().ok_or(EINVAL)?;
+
+        if wf.period_length_ns == 0 {
+            return Ok((
+                0,
+                Th1520WfHw {
+                    enabled: false,
+                    ..Default::default()
+                },
+            ));
+        }
+
+        let rate_hz = data.clk.rate().as_hz() as u64;
+
+        let period_cycles = ns_to_cycles(wf.period_length_ns, rate_hz).min(u32::MAX as u64);
+        let mut duty_cycles = ns_to_cycles(wf.duty_length_ns, rate_hz).min(u32::MAX as u64);
+
+        let mut ctrl_val = PWM_CONTINUOUS_MODE;
+
+        if wf.duty_offset_ns == 0 {
+            ctrl_val |= PWM_FPOUT;
+        } else {
+            duty_cycles = period_cycles - duty_cycles;
+        }
+
+        let wfhw = Th1520WfHw {
+            period_cycles: period_cycles as u32,
+            duty_cycles: duty_cycles as u32,
+            ctrl_val,
+            enabled: true,
+        };
+
+        dev_dbg!(
+            chip.device(),
+            "Requested: period {}ns, duty {}ns, offset {}ns -> HW: period {} cyc, duty {} cyc, ctrl 0x{:x}\n",
+            wf.period_length_ns,
+            wf.duty_length_ns,
+            wf.duty_offset_ns,
+            wfhw.period_cycles,
+            wfhw.duty_cycles,
+            wfhw.ctrl_val
+        );
+
+        Ok((0, wfhw))
+    }
+
+    fn round_waveform_fromhw(
+        chip: &mut pwm::Chip,
+        _pwm: &pwm::Device,
+        wfhw: &Self::WfHw,
+        wf: &mut pwm::Waveform,
+    ) -> Result<c_int> {
+        let data: &Self = chip.drvdata().ok_or(EINVAL)?;
+        let rate_hz = data.clk.rate().as_hz() as u64;
+
+        wf.period_length_ns = cycles_to_ns(wfhw.period_cycles as u64, rate_hz);
+
+        let duty_cycles = wfhw.duty_cycles as u64;
+
+        if (wfhw.ctrl_val & PWM_FPOUT) != 0 {
+            wf.duty_length_ns = cycles_to_ns(duty_cycles, rate_hz);
+            wf.duty_offset_ns = 0;
+        } else {
+            let period_cycles = wfhw.period_cycles as u64;
+            let original_duty_cycles = period_cycles.saturating_sub(duty_cycles);
+
+            wf.duty_length_ns = cycles_to_ns(original_duty_cycles, rate_hz);
+            // We can't recover the original non-zero offset, so we just set it
+            // to a representative non-zero value.
+            wf.duty_offset_ns = 1;
+        }
+
+        Ok(0)
+    }
+
+    fn read_waveform(
+        chip: &mut pwm::Chip,
+        pwm: &mut pwm::Device,
+        parent_dev: &Device<Bound>,
+    ) -> Result<Self::WfHw> {
+        let data: &Self = chip.drvdata().ok_or(EINVAL)?;
+        let hwpwm = pwm.hwpwm();
+        let iomem_guard = data.iomem.access(parent_dev)?;
+        let iomap = iomem_guard.deref();
+
+        let ctrl = iomap.try_read32(th1520_pwm_ctrl(hwpwm))?;
+        let period_cycles = iomap.try_read32(th1520_pwm_per(hwpwm))?;
+        let duty_cycles = iomap.try_read32(th1520_pwm_fp(hwpwm))?;
+
+        let wfhw = Th1520WfHw {
+            period_cycles,
+            duty_cycles,
+            ctrl_val: ctrl,
+            enabled: duty_cycles != 0,
+        };
+
+        dev_dbg!(
+            chip.device(),
+            "PWM-{}: read_waveform: Read hw state - period: {}, duty: {}, ctrl: 0x{:x}, enabled: {}",
+            hwpwm,
+            wfhw.period_cycles,
+            wfhw.duty_cycles,
+            wfhw.ctrl_val,
+            wfhw.enabled
+        );
+
+        Ok(wfhw)
+    }
+
+    fn write_waveform(
+        chip: &mut pwm::Chip,
+        pwm: &mut pwm::Device,
+        wfhw: &Self::WfHw,
+        parent_dev: &Device<Bound>,
+    ) -> Result {
+        let data: &Self = chip.drvdata().ok_or(EINVAL)?;
+        let hwpwm = pwm.hwpwm();
+        let iomem_guard = data.iomem.access(parent_dev)?;
+        let iomap = iomem_guard.deref();
+        let was_enabled = pwm.state().enabled();
+
+        if !wfhw.enabled {
+            if was_enabled {
+                iomap.try_write32(wfhw.ctrl_val, th1520_pwm_ctrl(hwpwm))?;
+                iomap.try_write32(0, th1520_pwm_fp(hwpwm))?;
+                iomap.try_write32(wfhw.ctrl_val | PWM_CFG_UPDATE, th1520_pwm_ctrl(hwpwm))?;
+            }
+            return Ok(());
+        }
+
+        iomap.try_write32(wfhw.ctrl_val, th1520_pwm_ctrl(hwpwm))?;
+        iomap.try_write32(wfhw.period_cycles, th1520_pwm_per(hwpwm))?;
+        iomap.try_write32(wfhw.duty_cycles, th1520_pwm_fp(hwpwm))?;
+        iomap.try_write32(wfhw.ctrl_val | PWM_CFG_UPDATE, th1520_pwm_ctrl(hwpwm))?;
+
+        // The `PWM_START` bit must be written in a separate, final transaction, and
+        // only when enabling the channel from a disabled state.
+        if !was_enabled {
+            iomap.try_write32(wfhw.ctrl_val | PWM_START, th1520_pwm_ctrl(hwpwm))?;
+        }
+
+        dev_dbg!(
+            chip.device(),
+            "PWM-{}: Wrote (per: {}, duty: {})",
+            hwpwm,
+            wfhw.period_cycles,
+            wfhw.duty_cycles,
+        );
+
+        Ok(())
+    }
+}
+
+impl Drop for Th1520PwmDriverData {
+    fn drop(&mut self) {
+        self.clk.disable_unprepare();
+    }
+}
+
+static TH1520_PWM_OPS: pwm::PwmOpsVTable = pwm::create_pwm_ops::<Th1520PwmDriverData>();
+
+struct Th1520PwmPlatformDriver {
+    _registration: pwm::Registration,
+}
+
+kernel::of_device_table!(
+    OF_TABLE,
+    MODULE_OF_TABLE,
+    <Th1520PwmPlatformDriver as platform::Driver>::IdInfo,
+    [(of::DeviceId::new(c_str!("thead,th1520-pwm")), ())]
+);
+
+impl platform::Driver for Th1520PwmPlatformDriver {
+    type IdInfo = ();
+    const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
+
+    fn probe(
+        pdev: &platform::Device<Core>,
+        _id_info: Option<&Self::IdInfo>,
+    ) -> Result<Pin<KBox<Self>>> {
+        let dev = pdev.as_ref();
+        let resource = pdev.resource(0).ok_or(ENODEV)?;
+        let iomem = pdev.ioremap_resource_sized::<TH1520_PWM_REG_SIZE>(resource)?;
+        let clk = Clk::get(pdev.as_ref(), None)?;
+
+        clk.prepare_enable()?;
+
+        // TODO: Get exclusive ownership of the clock to prevent rate changes.
+        // The Rust equivalent of `clk_rate_exclusive_get()` is not yet available.
+        // This should be updated once it is implemented.
+        let rate_hz = clk.rate().as_hz();
+        if rate_hz == 0 {
+            dev_err!(dev, "Clock rate is zero\n");
+            return Err(EINVAL);
+        }
+
+        if rate_hz > time::NSEC_PER_SEC as usize {
+            dev_err!(
+                dev,
+                "Clock rate {} Hz is too high, not supported.\n",
+                rate_hz
+            );
+            return Err(ERANGE);
+        }
+
+        let chip = pwm::Chip::new(dev, MAX_PWM_NUM, 0)?;
+
+        let drvdata = KBox::new(Th1520PwmDriverData { iomem, clk }, GFP_KERNEL)?;
+        chip.set_drvdata(drvdata);
+
+        let registration = pwm::Registration::new(chip, &TH1520_PWM_OPS)?;
+
+        Ok(KBox::new(
+            Th1520PwmPlatformDriver {
+                _registration: registration,
+            },
+            GFP_KERNEL,
+        )?
+        .into())
+    }
+}
+
+kernel::module_platform_driver! {
+    type: Th1520PwmPlatformDriver,
+    name: "pwm-th1520",
+    authors: ["Michal Wilczynski <m.wilczynski@samsung.com>"],
+    description: "T-HEAD TH1520 PWM driver",
+    license: "GPL v2",
+}

-- 
2.34.1


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Re: [PATCH v3 4/9] pwm: Add Rust driver for T-HEAD TH1520 SoC

[Danilo Krummrich]

On Tue, Jun 17, 2025 at 04:07:27PM +0200, Michal Wilczynski wrote:
> +    fn write_waveform(
> +        chip: &mut pwm::Chip,
> +        pwm: &mut pwm::Device,

I think you can't hand out mutable references here. This would allow things like
mem::swap(), which I think are not valid on those structures.

> +        wfhw: &Self::WfHw,
> +        parent_dev: &Device<Bound>,
> +    ) -> Result {
> +        let data: &Self = chip.drvdata().ok_or(EINVAL)?;
> +        let hwpwm = pwm.hwpwm();
> +        let iomem_guard = data.iomem.access(parent_dev)?;

Technically, this isn't a guard, hence would't call it that way.

> +        let iomap = iomem_guard.deref();
> +        let was_enabled = pwm.state().enabled();
> +
> +        if !wfhw.enabled {
> +            if was_enabled {
> +                iomap.try_write32(wfhw.ctrl_val, th1520_pwm_ctrl(hwpwm))?;
> +                iomap.try_write32(0, th1520_pwm_fp(hwpwm))?;
> +                iomap.try_write32(wfhw.ctrl_val | PWM_CFG_UPDATE, th1520_pwm_ctrl(hwpwm))?;
> +            }
> +            return Ok(());
> +        }
> +
> +        iomap.try_write32(wfhw.ctrl_val, th1520_pwm_ctrl(hwpwm))?;
> +        iomap.try_write32(wfhw.period_cycles, th1520_pwm_per(hwpwm))?;
> +        iomap.try_write32(wfhw.duty_cycles, th1520_pwm_fp(hwpwm))?;
> +        iomap.try_write32(wfhw.ctrl_val | PWM_CFG_UPDATE, th1520_pwm_ctrl(hwpwm))?;

None of the offsets are known at compile time? :(

> +
> +        // The `PWM_START` bit must be written in a separate, final transaction, and
> +        // only when enabling the channel from a disabled state.
> +        if !was_enabled {
> +            iomap.try_write32(wfhw.ctrl_val | PWM_START, th1520_pwm_ctrl(hwpwm))?;
> +        }
> +
> +        dev_dbg!(
> +            chip.device(),
> +            "PWM-{}: Wrote (per: {}, duty: {})",
> +            hwpwm,
> +            wfhw.period_cycles,
> +            wfhw.duty_cycles,
> +        );
> +
> +        Ok(())
> +    }
> +}

<snip>

> +impl platform::Driver for Th1520PwmPlatformDriver {
> +    type IdInfo = ();
> +    const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
> +
> +    fn probe(
> +        pdev: &platform::Device<Core>,
> +        _id_info: Option<&Self::IdInfo>,
> +    ) -> Result<Pin<KBox<Self>>> {
> +        let dev = pdev.as_ref();
> +        let resource = pdev.resource(0).ok_or(ENODEV)?;
> +        let iomem = pdev.ioremap_resource_sized::<TH1520_PWM_REG_SIZE>(resource)?;
> +        let clk = Clk::get(pdev.as_ref(), None)?;
> +
> +        clk.prepare_enable()?;
> +
> +        // TODO: Get exclusive ownership of the clock to prevent rate changes.
> +        // The Rust equivalent of `clk_rate_exclusive_get()` is not yet available.
> +        // This should be updated once it is implemented.
> +        let rate_hz = clk.rate().as_hz();
> +        if rate_hz == 0 {
> +            dev_err!(dev, "Clock rate is zero\n");
> +            return Err(EINVAL);
> +        }
> +
> +        if rate_hz > time::NSEC_PER_SEC as usize {
> +            dev_err!(
> +                dev,
> +                "Clock rate {} Hz is too high, not supported.\n",
> +                rate_hz
> +            );
> +            return Err(ERANGE);
> +        }
> +
> +        let chip = pwm::Chip::new(dev, MAX_PWM_NUM, 0)?;
> +
> +        let drvdata = KBox::new(Th1520PwmDriverData { iomem, clk }, GFP_KERNEL)?;
> +        chip.set_drvdata(drvdata);
> +
> +        let registration = pwm::Registration::new(chip, &TH1520_PWM_OPS)?;
> +
> +        Ok(KBox::new(
> +            Th1520PwmPlatformDriver {
> +                _registration: registration,
> +            },
> +            GFP_KERNEL,
> +        )?
> +        .into())

Here you are setting up the registration for the correct lifetime, however
drivers could extend the lifetime of the registration arbitrarily, which would
break the guarantee of the &Device<Bound> we rely on in the callbacks above
(e.g. write_waveform()).

Hence, pwm::Registration's lifetime has to be controlled by Devres. I'll also
add a corresponding comment in your registration patch.

> +    }
> +}

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Re: [PATCH v3 4/9] pwm: Add Rust driver for T-HEAD TH1520 SoC

[Michal Wilczynski]

On 6/17/25 16:28, Danilo Krummrich wrote:
> On Tue, Jun 17, 2025 at 04:07:27PM +0200, Michal Wilczynski wrote:
>> +    fn write_waveform(
>> +        chip: &mut pwm::Chip,
>> +        pwm: &mut pwm::Device,
> 
> I think you can't hand out mutable references here. This would allow things like
> mem::swap(), which I think are not valid on those structures.
> 
>> +        wfhw: &Self::WfHw,
>> +        parent_dev: &Device<Bound>,
>> +    ) -> Result {
>> +        let data: &Self = chip.drvdata().ok_or(EINVAL)?;
>> +        let hwpwm = pwm.hwpwm();
>> +        let iomem_guard = data.iomem.access(parent_dev)?;
> 
> Technically, this isn't a guard, hence would't call it that way.
> 
>> +        let iomap = iomem_guard.deref();
>> +        let was_enabled = pwm.state().enabled();
>> +
>> +        if !wfhw.enabled {
>> +            if was_enabled {
>> +                iomap.try_write32(wfhw.ctrl_val, th1520_pwm_ctrl(hwpwm))?;
>> +                iomap.try_write32(0, th1520_pwm_fp(hwpwm))?;
>> +                iomap.try_write32(wfhw.ctrl_val | PWM_CFG_UPDATE, th1520_pwm_ctrl(hwpwm))?;
>> +            }
>> +            return Ok(());
>> +        }
>> +
>> +        iomap.try_write32(wfhw.ctrl_val, th1520_pwm_ctrl(hwpwm))?;
>> +        iomap.try_write32(wfhw.period_cycles, th1520_pwm_per(hwpwm))?;
>> +        iomap.try_write32(wfhw.duty_cycles, th1520_pwm_fp(hwpwm))?;
>> +        iomap.try_write32(wfhw.ctrl_val | PWM_CFG_UPDATE, th1520_pwm_ctrl(hwpwm))?;
> 
> None of the offsets are known at compile time? :(

Sadly they are computed based on runtime parameter hwpwm, so Rust can't
guarantee correctness during compilation :-(.

Thank you for your other feedback, appreciate it !

> 
>> +
>> +        // The `PWM_START` bit must be written in a separate, final transaction, and
>> +        // only when enabling the channel from a disabled state.
>> +        if !was_enabled {
>> +            iomap.try_write32(wfhw.ctrl_val | PWM_START, th1520_pwm_ctrl(hwpwm))?;
>> +        }
>> +
>> +        dev_dbg!(
>> +            chip.device(),
>> +            "PWM-{}: Wrote (per: {}, duty: {})",
>> +            hwpwm,
>> +            wfhw.period_cycles,
>> +            wfhw.duty_cycles,
>> +        );
>> +
>> +        Ok(())
>> +    }
>> +}
> 
> <snip>
> 
>> +impl platform::Driver for Th1520PwmPlatformDriver {
>> +    type IdInfo = ();
>> +    const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
>> +
>> +    fn probe(
>> +        pdev: &platform::Device<Core>,
>> +        _id_info: Option<&Self::IdInfo>,
>> +    ) -> Result<Pin<KBox<Self>>> {
>> +        let dev = pdev.as_ref();
>> +        let resource = pdev.resource(0).ok_or(ENODEV)?;
>> +        let iomem = pdev.ioremap_resource_sized::<TH1520_PWM_REG_SIZE>(resource)?;
>> +        let clk = Clk::get(pdev.as_ref(), None)?;
>> +
>> +        clk.prepare_enable()?;
>> +
>> +        // TODO: Get exclusive ownership of the clock to prevent rate changes.
>> +        // The Rust equivalent of `clk_rate_exclusive_get()` is not yet available.
>> +        // This should be updated once it is implemented.
>> +        let rate_hz = clk.rate().as_hz();
>> +        if rate_hz == 0 {
>> +            dev_err!(dev, "Clock rate is zero\n");
>> +            return Err(EINVAL);
>> +        }
>> +
>> +        if rate_hz > time::NSEC_PER_SEC as usize {
>> +            dev_err!(
>> +                dev,
>> +                "Clock rate {} Hz is too high, not supported.\n",
>> +                rate_hz
>> +            );
>> +            return Err(ERANGE);
>> +        }
>> +
>> +        let chip = pwm::Chip::new(dev, MAX_PWM_NUM, 0)?;
>> +
>> +        let drvdata = KBox::new(Th1520PwmDriverData { iomem, clk }, GFP_KERNEL)?;
>> +        chip.set_drvdata(drvdata);
>> +
>> +        let registration = pwm::Registration::new(chip, &TH1520_PWM_OPS)?;
>> +
>> +        Ok(KBox::new(
>> +            Th1520PwmPlatformDriver {
>> +                _registration: registration,
>> +            },
>> +            GFP_KERNEL,
>> +        )?
>> +        .into())
> 
> Here you are setting up the registration for the correct lifetime, however
> drivers could extend the lifetime of the registration arbitrarily, which would
> break the guarantee of the &Device<Bound> we rely on in the callbacks above
> (e.g. write_waveform()).
> 
> Hence, pwm::Registration's lifetime has to be controlled by Devres. I'll also
> add a corresponding comment in your registration patch.
> 
>> +    }
>> +}
> 

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

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[PATCH v3 5/9] clk: thead: Mark essential bus clocks as CLK_IGNORE_UNUSED

[Michal Wilczynski]

Probing peripherals in the AON and PERI domains, such as the PVT thermal
sensor and the PWM controller, can lead to boot hangs or unresponsive
devices on the LPi4A board. The root cause is that their parent bus
clocks ('CLK_CPU2AON_X2H' and the 'CLK_PERISYS_APB' clocks) are
automatically gated by the kernel's power-saving mechanisms when the bus
is perceived as idle.

Alternative solutions were investigated, including modeling the parent
bus in the Device Tree with 'simple-pm-bus' or refactoring the clock
driver's parentage. The 'simple-pm-bus' approach is not viable due to
the lack of defined bus address ranges in the hardware manual and its
creation of improper dependencies on the 'pm_runtime' API for consumer
drivers.

Therefore, applying the'`CLK_IGNORE_UNUSED' flag directly to the
essential bus clocks is the most direct and targeted fix. This prevents
the kernel from auto-gating these buses and ensures peripherals remain
accessible.

This change fixes the boot hang associated with the PVT sensor and
resolves the functional issues with the PWM controller.

Link: https://lore.kernel.org/all/9e8a12db-236d-474c-b110-b3be96edf057@samsung.com/ [1]

Reviewed-by: Drew Fustini <drew@pdp7.com>
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 drivers/clk/thead/clk-th1520-ap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/thead/clk-th1520-ap.c b/drivers/clk/thead/clk-th1520-ap.c
index ebfb1d59401d05443716eb0029403b01775e8f73..cf7f6bd428a0faa4611b3fc61edbbc6690e565d9 100644
--- a/drivers/clk/thead/clk-th1520-ap.c
+++ b/drivers/clk/thead/clk-th1520-ap.c
@@ -792,11 +792,12 @@ static CCU_GATE(CLK_AON2CPU_A2X, aon2cpu_a2x_clk, "aon2cpu-a2x", axi4_cpusys2_ac
 		0x134, BIT(8), 0);
 static CCU_GATE(CLK_X2X_CPUSYS, x2x_cpusys_clk, "x2x-cpusys", axi4_cpusys2_aclk_pd,
 		0x134, BIT(7), 0);
-static CCU_GATE(CLK_CPU2AON_X2H, cpu2aon_x2h_clk, "cpu2aon-x2h", axi_aclk_pd, 0x138, BIT(8), 0);
+static CCU_GATE(CLK_CPU2AON_X2H, cpu2aon_x2h_clk, "cpu2aon-x2h", axi_aclk_pd,
+		0x138, BIT(8), CLK_IGNORE_UNUSED);
 static CCU_GATE(CLK_CPU2PERI_X2H, cpu2peri_x2h_clk, "cpu2peri-x2h", axi4_cpusys2_aclk_pd,
 		0x140, BIT(9), CLK_IGNORE_UNUSED);
 static CCU_GATE(CLK_PERISYS_APB1_HCLK, perisys_apb1_hclk, "perisys-apb1-hclk", perisys_ahb_hclk_pd,
-		0x150, BIT(9), 0);
+		0x150, BIT(9), CLK_IGNORE_UNUSED);
 static CCU_GATE(CLK_PERISYS_APB2_HCLK, perisys_apb2_hclk, "perisys-apb2-hclk", perisys_ahb_hclk_pd,
 		0x150, BIT(10), CLK_IGNORE_UNUSED);
 static CCU_GATE(CLK_PERISYS_APB3_HCLK, perisys_apb3_hclk, "perisys-apb3-hclk", perisys_ahb_hclk_pd,

-- 
2.34.1


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[PATCH v3 6/9] dt-bindings: pwm: thead: Add T-HEAD TH1520 PWM controller

[Michal Wilczynski]

Add the Device Tree binding documentation for the T-HEAD
TH1520 SoC PWM controller.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 .../devicetree/bindings/pwm/thead,th1520-pwm.yaml  | 48 ++++++++++++++++++++++
 MAINTAINERS                                        |  1 +
 2 files changed, 49 insertions(+)

diff --git a/Documentation/devicetree/bindings/pwm/thead,th1520-pwm.yaml b/Documentation/devicetree/bindings/pwm/thead,th1520-pwm.yaml
new file mode 100644
index 0000000000000000000000000000000000000000..855aec59ac53c430adc849271235686e87b10e6c
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/thead,th1520-pwm.yaml
@@ -0,0 +1,48 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/pwm/thead,th1520-pwm.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: T-HEAD TH1520 PWM controller
+
+maintainers:
+  - Michal Wilczynski <m.wilczynski@samsung.com>
+
+allOf:
+  - $ref: pwm.yaml#
+
+properties:
+  compatible:
+    const: thead,th1520-pwm
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    items:
+      - description: SoC PWM clock
+
+  "#pwm-cells":
+    const: 3
+
+required:
+  - compatible
+  - reg
+  - clocks
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/thead,th1520-clk-ap.h>
+    soc {
+      #address-cells = <2>;
+      #size-cells = <2>;
+      pwm@ffec01c000 {
+          compatible = "thead,th1520-pwm";
+          reg = <0xff 0xec01c000 0x0 0x4000>;
+          clocks = <&clk CLK_PWM>;
+          #pwm-cells = <3>;
+      };
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index 879870471e86dcec4a0e8f5c45d2cc3409411fdd..8a55e8d88394a269aa152e80a03c439a36e6062e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -21394,6 +21394,7 @@ F:	Documentation/devicetree/bindings/firmware/thead,th1520-aon.yaml
 F:	Documentation/devicetree/bindings/mailbox/thead,th1520-mbox.yaml
 F:	Documentation/devicetree/bindings/net/thead,th1520-gmac.yaml
 F:	Documentation/devicetree/bindings/pinctrl/thead,th1520-pinctrl.yaml
+F:	Documentation/devicetree/bindings/pwm/thead,th1520-pwm.yaml
 F:	Documentation/devicetree/bindings/reset/thead,th1520-reset.yaml
 F:	arch/riscv/boot/dts/thead/
 F:	drivers/clk/thead/clk-th1520-ap.c

-- 
2.34.1


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[PATCH v3 7/9] riscv: dts: thead: Add PWM controller node

[Michal Wilczynski]

Add the Device Tree node for the T-HEAD TH1520 SoC's PWM controller.

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 arch/riscv/boot/dts/thead/th1520.dtsi | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/riscv/boot/dts/thead/th1520.dtsi b/arch/riscv/boot/dts/thead/th1520.dtsi
index 1db0054c4e093400e9dbebcee5fcfa5b5cae6e32..26996422e1efe5d2dde68819c2cec1c3fa782a23 100644
--- a/arch/riscv/boot/dts/thead/th1520.dtsi
+++ b/arch/riscv/boot/dts/thead/th1520.dtsi
@@ -490,6 +490,13 @@ uart2: serial@ffec010000 {
 			status = "disabled";
 		};
 
+		pwm: pwm@ffec01c000 {
+			compatible = "thead,th1520-pwm";
+			reg = <0xff 0xec01c000 0x0 0x4000>;
+			clocks = <&clk CLK_PWM>;
+			#pwm-cells = <3>;
+		};
+
 		clk: clock-controller@ffef010000 {
 			compatible = "thead,th1520-clk-ap";
 			reg = <0xff 0xef010000 0x0 0x1000>;

-- 
2.34.1


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[PATCH v3 8/9] riscv: dts: thead: Add PVT node

[Michal Wilczynski]

Add PVT DT node for thermal sensor.

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 arch/riscv/boot/dts/thead/th1520.dtsi | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/riscv/boot/dts/thead/th1520.dtsi b/arch/riscv/boot/dts/thead/th1520.dtsi
index 26996422e1efe5d2dde68819c2cec1c3fa782a23..bef30780034e06b07aa29b27b0225ea891a4b531 100644
--- a/arch/riscv/boot/dts/thead/th1520.dtsi
+++ b/arch/riscv/boot/dts/thead/th1520.dtsi
@@ -669,6 +669,17 @@ padctrl_aosys: pinctrl@fffff4a000 {
 			thead,pad-group = <1>;
 		};
 
+		pvt: pvt@fffff4e000 {
+			compatible = "moortec,mr75203";
+			reg = <0xff 0xfff4e000 0x0 0x80>,
+			      <0xff 0xfff4e080 0x0 0x100>,
+			      <0xff 0xfff4e180 0x0 0x680>,
+			      <0xff 0xfff4e800 0x0 0x600>;
+			reg-names = "common", "ts", "pd", "vm";
+			clocks = <&aonsys_clk>;
+			#thermal-sensor-cells = <1>;
+		};
+
 		gpio@fffff52000 {
 			compatible = "snps,dw-apb-gpio";
 			reg = <0xff 0xfff52000 0x0 0x1000>;

-- 
2.34.1


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[PATCH v3 9/9] riscv: dts: thead: Add PWM fan and thermal control

[Michal Wilczynski]

Add Device Tree nodes to enable a PWM controlled fan and it's associated
thermal management for the Lichee Pi 4A board.

This enables temperature-controlled active cooling for the Lichee Pi 4A
board based on SoC temperature.

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts | 67 +++++++++++++++++++++++
 1 file changed, 67 insertions(+)

diff --git a/arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts b/arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts
index 4020c727f09e8e2286fdc7fecd79dbd8eba69556..c58c2085ca92a3234f1350500cedae4157f0c35f 100644
--- a/arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts
+++ b/arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts
@@ -28,9 +28,76 @@ aliases {
 	chosen {
 		stdout-path = "serial0:115200n8";
 	};
+
+	thermal-zones {
+		cpu-thermal {
+			polling-delay = <1000>;
+			polling-delay-passive = <1000>;
+			thermal-sensors = <&pvt 0>;
+
+			trips {
+				fan_config0: fan-trip0 {
+					temperature = <39000>;
+					hysteresis = <5000>;
+					type = "active";
+				};
+
+				fan_config1: fan-trip1 {
+					temperature = <50000>;
+					hysteresis = <5000>;
+					type = "active";
+				};
+
+				fan_config2: fan-trip2 {
+					temperature = <60000>;
+					hysteresis = <5000>;
+					type = "active";
+				};
+			};
+
+			cooling-maps {
+				map-active-0 {
+					cooling-device = <&fan 1 1>;
+					trip = <&fan_config0>;
+				};
+
+				map-active-1 {
+					cooling-device = <&fan 2 2>;
+					trip = <&fan_config1>;
+				};
+
+				map-active-2 {
+					cooling-device = <&fan 3 3>;
+					trip = <&fan_config2>;
+				};
+			};
+		};
+	};
+
+	fan: pwm-fan {
+		pinctrl-names = "default";
+		pinctrl-0 = <&fan_pins>;
+		compatible = "pwm-fan";
+		#cooling-cells = <2>;
+		pwms = <&pwm 1 10000000 0>;
+		cooling-levels = <0 66 196 255>;
+	};
+
 };
 
 &padctrl0_apsys {
+	fan_pins: fan-0 {
+		pwm1-pins {
+			pins = "GPIO3_3"; /* PWM1 */
+			function = "pwm";
+			bias-disable;
+			drive-strength = <25>;
+			input-disable;
+			input-schmitt-disable;
+			slew-rate = <0>;
+		};
+	};
+
 	uart0_pins: uart0-0 {
 		tx-pins {
 			pins = "UART0_TXD";

-- 
2.34.1


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