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Howlett" , Uladzislau Rezki , Boqun Feng , Gary Guo , bjorn3_gh@protonmail.com, Benno Lossin , Andreas Hindborg , Trevor Gross , rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, linux-leds@vger.kernel.org Content-Type: text/plain; charset="utf-8" On Thu, Oct 09, 2025 at 06:12:34PM +0000, Markus Probst wrote: > Implement the core abstractions needed for led class devices, including: > > * `led::Handler` - the trait for handling leds, including > `brightness_set` > > * `led::InitData` - data set for the led class device > > * `led::Device` - a safe wrapper around `led_classdev` > > Signed-off-by: Markus Probst > +/// The led class device representation. > +/// > +/// This structure represents the Rust abstraction for a C `struct led_classdev`. > +#[pin_data(PinnedDrop)] > +pub struct Device { > + handler: KBox, > + #[pin] > + classdev: Opaque, > +} Is it not possible to use Device with a `handler: T` field here? That avoids the box. I don't think other abstractions have needed that. If it's needed, then why is LED special? > +/// The led handler trait. > +/// > +/// # Examples > +/// > +///``` > +/// # use kernel::{c_str, led, alloc::KBox, error::{Result, code::ENOSYS}}; > +/// # use core::pin::Pin; > +/// > +/// struct MyHandler; > +/// > +/// > +/// impl led::Handler for MyHandler { > +/// const BLOCKING = false; > +/// const MAX_BRIGHTNESS = 255; > +/// > +/// fn brightness_set(&self, _brightness: u32) -> Result<()> { > +/// // Set the brightness for the led here > +/// Ok(()) > +/// } > +/// } > +/// > +/// fn register_my_led() -> Result>> { > +/// let handler = MyHandler; > +/// KBox::pin_init(led::Device::new( > +/// None, > +/// None, > +/// led::InitData::new() > +/// .default_label(c_str!("my_led")), > +/// handler, > +/// )) > +/// } > +///``` > +/// Led drivers must implement this trait in order to register and handle a [`Device`]. > +pub trait Handler { > + /// If set true, [`Handler::brightness_set`] and [`Handler::blink_set`] must not sleep > + /// and perform the operation immediately. > + const BLOCKING: bool; > + /// Set this to true, if [`Handler::blink_set`] is implemented. > + const BLINK: bool = false; We have a macro called #[vtable] that automatically generates this kind of constant for you. Please use it. > +impl Device { > + /// Registers a new led classdev. > + /// > + /// The [`Device`] will be unregistered and drop. > + pub fn new<'a, T: Handler + 'static>( > + parent: Option<&'a device::Device>, > + init_data: InitData<'a>, > + handler: T, > + ) -> impl PinInit + use<'a, T> { > + try_pin_init!(Self { > + handler <- { > + let handler: KBox = KBox::::new(handler, GFP_KERNEL)?; > + Ok::<_, Error>(handler) > + }, > + classdev <- Opaque::try_ffi_init(|ptr: *mut bindings::led_classdev| { > + // SAFETY: `try_ffi_init` guarantees that `ptr` is valid for write. > + unsafe { ptr.write(bindings::led_classdev { > + max_brightness: T::MAX_BRIGHTNESS, > + brightness_set: T::BLOCKING.then_some( > + brightness_set as unsafe extern "C" fn(*mut bindings::led_classdev, u32) > + ), > + brightness_set_blocking: (!T::BLOCKING).then_some( > + brightness_set_blocking > + as unsafe extern "C" fn(*mut bindings::led_classdev,u32) -> i32 > + ), > + blink_set: T::BLINK.then_some( > + blink_set > + as unsafe extern "C" fn(*mut bindings::led_classdev, *mut usize, > + *mut usize) -> i32 I think you can just do `blink_set as _`. > + ), > + .. bindings::led_classdev::default() > + }) }; > + > + let mut init_data = bindings::led_init_data { > + fwnode: init_data.fwnode.map_or(core::ptr::null_mut(), FwNode::as_raw), > + default_label: init_data.default_label > + .map_or(core::ptr::null(), CStr::as_char_ptr), > + devicename: init_data.devicename.map_or(core::ptr::null(), CStr::as_char_ptr), > + devname_mandatory: init_data.devname_mandatory, > + }; > + > + let parent = parent > + .map_or(core::ptr::null_mut(), device::Device::as_raw); > + > + // SAFETY: > + // - `parent` is guaranteed to be a pointer to a valid `device` > + // or a null pointer. > + // - `ptr` is guaranteed to be a pointer to an initialized `led_classdev`. > + to_result(unsafe { > + bindings::led_classdev_register_ext(parent, ptr, &mut init_data) So it's ok that `init_data` is valid for the duration of this call and no longer? It doesn't stash a pointer to it anywhere? > +extern "C" fn brightness_set(led_cdev: *mut bindings::led_classdev, brightness: u32) { > + // SAFETY: `led_cdev` is a valid pointer to a `led_classdev` stored inside a `Device`. > + let classdev = unsafe { > + &*container_of!( > + led_cdev.cast::>(), Please use Opaque::cast_from instead. > + // SAFETY: `led_cdev` is a valid pointer to a `led_classdev` stored inside a `Device`. > + let classdev = unsafe { > + &*container_of!( > + led_cdev.cast::>(), > + Device, > + classdev > + ) > + }; Instead of repeating this logic many times, I suggest a Device::from_raw method. > +extern "C" fn blink_set( > + led_cdev: *mut bindings::led_classdev, > + delay_on: *mut usize, > + delay_off: *mut usize, > +) -> i32 { > + // SAFETY: `led_cdev` is a valid pointer to a `led_classdev` stored inside a `Device`. > + let classdev = unsafe { > + &*container_of!( > + led_cdev.cast::>(), > + Device, > + classdev > + ) > + }; > + from_result(|| { > + classdev.handler.blink_set( > + // SAFETY: `delay_on` is guaranteed to be a valid pointer to usize > + unsafe { &mut *delay_on }, > + // SAFETY: `delay_on` is guaranteed to be a valid pointer to usize > + unsafe { &mut *delay_off }, To create a mutable reference, this safety comment should argue why it is the case that nobody will access these fields for the duration of `blink_set`. (For example, from another thread?) Alice