From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailout2.w1.samsung.com (mailout2.w1.samsung.com [210.118.77.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9A71929CB2D for ; Mon, 23 Jun 2025 18:09:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=210.118.77.12 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750702146; cv=none; b=NFWWSiyNII+ikqWe05O4JA+T/8vaPnEsA6WImN/HcxbfCkzQUqHCsG7UdRU4VYcTwjGRw6wDGyyfiU3WnR7MKbdDnJUSHhCH/tfELWyYt1PjLk31ycS3LxC+AbdCr6E2voSG4LKz8cYZ2+PpNZEcusryq96l0VkQKyXBQfuGk1s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750702146; c=relaxed/simple; bh=/91B2CzNMGbRXodYmqOCSlR4bAJtUWi40/XcvLYxN8U=; h=From:Date:Subject:MIME-Version:Message-Id:In-Reply-To:To:Cc: Content-Type:References; b=boli2sFhm02T8c/u7Ps27DChqN9AXoYb/4b08poorlttT7aUt7ZJwma1wVc5DZ3EQLw3irrISCOlnSuw/CYcaPg+NVJTKvcGGkdNPjgUzM/WaYaby0D3gVv7RCWU1ECL5zGZM9CQp+czD/mue9dkUKESZcWP7o/7Z9f2+prxO+k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=samsung.com; spf=pass smtp.mailfrom=samsung.com; dkim=pass (1024-bit key) header.d=samsung.com header.i=@samsung.com header.b=Wr9cReU7; arc=none smtp.client-ip=210.118.77.12 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=samsung.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=samsung.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=samsung.com header.i=@samsung.com header.b="Wr9cReU7" Received: from eucas1p2.samsung.com (unknown [182.198.249.207]) by mailout2.w1.samsung.com (KnoxPortal) with ESMTP id 20250623180900euoutp02909f313e76a16621863940eb03861208~LvlI5RYwZ2683926839euoutp02H for ; Mon, 23 Jun 2025 18:09:00 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 mailout2.w1.samsung.com 20250623180900euoutp02909f313e76a16621863940eb03861208~LvlI5RYwZ2683926839euoutp02H DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=samsung.com; s=mail20170921; t=1750702140; bh=dOEnl37kGZbQWiL7Vd5sBbmWXQBqlqQFKLHeDuUvdbM=; h=From:Date:Subject:In-Reply-To:To:Cc:References:From; b=Wr9cReU7XYTZnDyDxY8/k9ccarqfjdr1zZ01qakij5t6n29XRKjVRq9pVcZA/GXBr O5E/MD20ibCmu/Dx60ZJNRAJXLYxChiBNBx4S03nc7eUYL3H2rIGSEJQnj0Fb0sNST eeFLlIynLU1fQOzJ9P6UWj+yL98rsX2nUWOMiUPQ= Received: from eusmtip1.samsung.com (unknown [203.254.199.221]) by eucas1p1.samsung.com (KnoxPortal) with ESMTPA id 20250623180859eucas1p10ebb40f33046d52618ba738ebbbaa664~LvlIBokMx2898428984eucas1p1V; Mon, 23 Jun 2025 18:08:59 +0000 (GMT) Received: from AMDC4942.eu.corp.samsungelectronics.net (unknown [106.210.136.40]) by eusmtip1.samsung.com (KnoxPortal) with ESMTPA id 20250623180858eusmtip1324346555bbdcfb27d05677fe34e757c~LvlG5dpgr3150531505eusmtip1x; Mon, 23 Jun 2025 18:08:58 +0000 (GMT) From: Michal Wilczynski Date: Mon, 23 Jun 2025 20:08:50 +0200 Subject: [PATCH v5 2/9] rust: pwm: Add core 'Device' and 'Chip' object wrappers Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Message-Id: <20250623-rust-next-pwm-working-fan-for-sending-v5-2-0ca23747c23e@samsung.com> In-Reply-To: <20250623-rust-next-pwm-working-fan-for-sending-v5-0-0ca23747c23e@samsung.com> To: =?utf-8?q?Uwe_Kleine-K=C3=B6nig?= , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Michal Wilczynski , Drew Fustini , Guo Ren , Fu Wei , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Marek Szyprowski , Benno Lossin , Michael Turquette , Stephen Boyd , Benno Lossin Cc: linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-clk@vger.kernel.org X-Mailer: b4 0.15-dev X-CMS-MailID: 20250623180859eucas1p10ebb40f33046d52618ba738ebbbaa664 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-RootMTR: 20250623180859eucas1p10ebb40f33046d52618ba738ebbbaa664 X-EPHeader: CA X-CMS-RootMailID: 20250623180859eucas1p10ebb40f33046d52618ba738ebbbaa664 References: <20250623-rust-next-pwm-working-fan-for-sending-v5-0-0ca23747c23e@samsung.com> 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 --- rust/kernel/pwm.rs | 216 ++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 214 insertions(+), 2 deletions(-) diff --git a/rust/kernel/pwm.rs b/rust/kernel/pwm.rs index ed681b228c414e7ae8bf80ca649ad497c9dc4ec3..3865b43ec47df6cb0c09bc74a228535512b6b1a8 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 +198,213 @@ 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); + +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 as_ref<'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::() } + } + + /// 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::as_ref's safety conditions must be met. + unsafe { Chip::as_ref((*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); + +impl Chip { + /// 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 as_ref<'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::() } + } + + /// 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::()) } + } + + /// 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(&self) -> &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()) }; + + // SAFETY: The only way to create a chip is through Chip::new, which initializes + // this pointer. + unsafe { &*ptr.cast::() } + } + + /// Sets the *typed* driver-specific data associated with this chip's embedded device. + pub fn set_drvdata(&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`] managing the chip's lifetime via refcounting + /// on its embedded `struct device`. + pub fn new( + parent_dev: &device::Device, + npwm: u32, + sizeof_priv: usize, + drvdata: T, + ) -> Result> { + // 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`, and + // `Opaque` is `repr(transparent)` over `T`. + let chip_ptr_as_self = c_chip_ptr.cast::(); + + // SAFETY: The pointer is valid, so we can create a temporary ref to set data. + let chip_ref = unsafe { &*chip_ptr_as_self }; + chip_ref.set_drvdata(drvdata); + + // 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) { + let c_chip_ptr = obj.cast::().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