[PATCH v20 3/3] rust: leds: add multicolor classdev abstractions

[Markus Probst]

Implement the abstractions needed for multicolor led class devices,
including:

* `led::MultiColor` - the led mode implementation

* `MultiColorSubLed` - a safe wrapper arround `mc_subled`

* `led::MultiColorDevice` - a safe wrapper around `led_classdev_mc`

* `led::DeviceBuilder::build_multicolor` - a function to register a new
  multicolor led class device

Signed-off-by: Markus Probst <markus.probst@xxxxxxxxx>
---
 rust/bindings/bindings_helper.h |   1 +
 rust/kernel/led.rs              |  34 ++-
 rust/kernel/led/multicolor.rs   | 460 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 494 insertions(+), 1 deletion(-)

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 1124785e210b..821f539e597e 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -68,6 +68,7 @@
 #include <linux/iosys-map.h>
 #include <linux/jiffies.h>
 #include <linux/jump_label.h>
+#include <linux/led-class-multicolor.h>
 #include <linux/mdio.h>
 #include <linux/mm.h>
 #include <linux/miscdevice.h>
diff --git a/rust/kernel/led.rs b/rust/kernel/led.rs
index 9e4c8726390b..83d47c2c9778 100644
--- a/rust/kernel/led.rs
+++ b/rust/kernel/led.rs
@@ -33,8 +33,16 @@
     types::Opaque, //
 };
 
+#[cfg(CONFIG_LEDS_CLASS_MULTICOLOR)]
+mod multicolor;
 mod normal;
 
+#[cfg(CONFIG_LEDS_CLASS_MULTICOLOR)]
+pub use multicolor::{
+    MultiColor,
+    MultiColorDevice,
+    MultiColorSubLed, //
+};
 pub use normal::{
     Device,
     Normal, //
@@ -258,7 +266,24 @@ pub enum Color {
     Violet = bindings::LED_COLOR_ID_VIOLET,
     Yellow = bindings::LED_COLOR_ID_YELLOW,
     Ir = bindings::LED_COLOR_ID_IR,
+    #[cfg_attr(
+        CONFIG_LEDS_CLASS_MULTICOLOR,
+        doc = "Use this color for a [`MultiColor`] led."
+    )]
+    #[cfg_attr(
+        not(CONFIG_LEDS_CLASS_MULTICOLOR),
+        doc = "Use this color for a `MultiColor` led."
+    )]
+    /// If the led supports RGB, use [`Color::Rgb`] instead.
     Multi = bindings::LED_COLOR_ID_MULTI,
+    #[cfg_attr(
+        CONFIG_LEDS_CLASS_MULTICOLOR,
+        doc = "Use this color for a [`MultiColor`] led with rgb support."
+    )]
+    #[cfg_attr(
+        not(CONFIG_LEDS_CLASS_MULTICOLOR),
+        doc = "Use this color for a `MultiColor` led with rgb support."
+    )]
     Rgb = bindings::LED_COLOR_ID_RGB,
     Purple = bindings::LED_COLOR_ID_PURPLE,
     Orange = bindings::LED_COLOR_ID_ORANGE,
@@ -299,7 +324,14 @@ fn try_from(value: u32) -> core::result::Result<Self, Self::Error> {
 ///
 /// Each led mode has its own led class device type with different capabilities.
 ///
-/// See [`Normal`].
+#[cfg_attr(
+    CONFIG_LEDS_CLASS_MULTICOLOR,
+    doc = "See [`Normal`] and [`MultiColor`]."
+)]
+#[cfg_attr(
+    not(CONFIG_LEDS_CLASS_MULTICOLOR),
+    doc = "See [`Normal`] and `MultiColor`."
+)]
 pub trait Mode: private::Sealed {
     /// The class device for the led mode.
     type Device<'bound, T: LedOps<Mode = Self> + 'bound>;
diff --git a/rust/kernel/led/multicolor.rs b/rust/kernel/led/multicolor.rs
new file mode 100644
index 000000000000..9a341b333648
--- /dev/null
+++ b/rust/kernel/led/multicolor.rs
@@ -0,0 +1,460 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Led mode for the `struct led_classdev_mc`.
+//!
+//! C header: [`include/linux/led-class-multicolor.h`](srctree/include/linux/led-class-multicolor.h)
+
+use core::{
+    cell::UnsafeCell,
+    num::NonZero,
+    ptr, //
+};
+
+use crate::types::ScopeGuard;
+
+use super::*;
+
+/// The led mode for the `struct led_classdev_mc`. Leds with this mode can have multiple colors.
+pub enum MultiColor {}
+impl Mode for MultiColor {
+    type Device<'bound, T: LedOps<Mode = Self> + 'bound> = MultiColorDevice<'bound, T>;
+}
+impl private::Sealed for MultiColor {}
+
+/// The multicolor sub led info representation.
+///
+/// This structure represents the Rust abstraction for a C `struct mc_subled`.
+#[repr(C)]
+#[derive(Debug)]
+#[non_exhaustive]
+pub struct MultiColorSubLed {
+    /// The color of the sub led
+    pub color: Color,
+    brightness: UnsafeCell<u32>,
+    intensity: UnsafeCell<u32>,
+    /// The maximum supported intensity value.
+    ///
+    /// If None the maximum intensity equals to [`LedOps::MAX_BRIGHTNESS`].
+    pub max_intensity: Option<NonZero<u32>>,
+    /// Arbitrary data for the driver to store.
+    pub channel: u32,
+}
+
+// SAFETY: `MultiColorSubLed` can be shared among threads.
+unsafe impl Sync for MultiColorSubLed {}
+
+impl Clone for MultiColorSubLed {
+    fn clone(&self) -> Self {
+        Self {
+            color: self.color,
+            brightness: self.brightness().into(),
+            intensity: self.intensity().into(),
+            max_intensity: self.max_intensity,
+            channel: self.channel,
+        }
+    }
+}
+
+// We directly pass a reference to the `subled_info` field in `led_classdev_mc` to the driver via
+// `Device::subleds()`.
+// We need safeguards to ensure `MultiColorSubLed` and `mc_subled` stay identical.
+const _: () = {
+    use core::mem::offset_of;
+
+    const fn assert_same_type<T>(_: &T, _: &T) {}
+
+    let rust_zeroed = MultiColorSubLed {
+        color: Color::White,
+        brightness: UnsafeCell::new(0),
+        intensity: UnsafeCell::new(0),
+        max_intensity: None,
+        channel: 0,
+    };
+    let c_zeroed = bindings::mc_subled {
+        color_index: 0,
+        brightness: 0,
+        intensity: 0,
+        max_intensity: 0,
+        channel: 0,
+    };
+
+    assert!(offset_of!(MultiColorSubLed, color) == offset_of!(bindings::mc_subled, color_index));
+    assert!(
+        offset_of!(MultiColorSubLed, brightness) == offset_of!(bindings::mc_subled, brightness)
+    );
+    assert!(offset_of!(MultiColorSubLed, intensity) == offset_of!(bindings::mc_subled, intensity));
+    assert!(
+        offset_of!(MultiColorSubLed, max_intensity)
+            == offset_of!(bindings::mc_subled, max_intensity)
+    );
+    assert!(offset_of!(MultiColorSubLed, channel) == offset_of!(bindings::mc_subled, channel));
+
+    assert_same_type(&0u32, &c_zeroed.color_index);
+    assert_same_type(&rust_zeroed.brightness.into_inner(), &c_zeroed.brightness);
+    assert_same_type(&rust_zeroed.intensity.into_inner(), &c_zeroed.intensity);
+    assert!(size_of_val(&rust_zeroed.max_intensity) == size_of_val(&c_zeroed.max_intensity));
+    assert_same_type(&rust_zeroed.channel, &c_zeroed.channel);
+
+    assert!(size_of::<MultiColorSubLed>() == size_of::<bindings::mc_subled>());
+};
+
+impl MultiColorSubLed {
+    /// Create a new multicolor sub led info.
+    #[inline]
+    pub const fn new(color: Color) -> Self {
+        Self {
+            color,
+            brightness: UnsafeCell::new(0),
+            intensity: UnsafeCell::new(0),
+            max_intensity: None,
+            channel: 0,
+        }
+    }
+
+    /// Set arbitrary data for the driver.
+    #[inline]
+    pub const fn channel(mut self, channel: u32) -> Self {
+        self.channel = channel;
+        self
+    }
+
+    /// Set the initial intensity of the subled.
+    #[inline]
+    pub const fn initial_intensity(mut self, intensity: u32) -> Self {
+        self.intensity = UnsafeCell::new(intensity);
+        self
+    }
+
+    /// Set the maximum supported intensity of the subled.
+    #[inline]
+    pub const fn max_intensity(mut self, max_intensity: NonZero<u32>) -> Self {
+        self.max_intensity = Some(max_intensity);
+        self
+    }
+
+    /// The intensity of the sub led.
+    #[inline]
+    pub const fn intensity(&self) -> u32 {
+        // SAFETY:
+        // - `self.intensity.get()` is a valid pointer to `u32`.
+        // - We don't have exclusive or immutable access to `self.intensity`,
+        //   but the alignment should prevent "load tearing".
+        unsafe { *self.intensity.get() }
+    }
+
+    /// The brightness of the sub led.
+    #[inline]
+    pub const fn brightness(&self) -> u32 {
+        // SAFETY:
+        // - `self.intensity.get()` is a valid pointer to `u32`.
+        // - We don't have exclusive or immutable access to `self.brightness`,
+        //   but the alignment should prevent "load tearing".
+        unsafe { *self.brightness.get() }
+    }
+}
+
+/// The multicolor led class device representation.
+///
+/// This structure represents the Rust abstraction for a multicolor led class device.
+#[pin_data(PinnedDrop)]
+pub struct MultiColorDevice<'bound, T: LedOps<Mode = MultiColor> + 'bound> {
+    #[pin]
+    ops: T,
+    #[pin]
+    classdev: Opaque<bindings::led_classdev_mc>,
+    _p: PhantomData<&'bound ()>,
+}
+
+impl<'a, S: DeviceBuilderState> DeviceBuilder<'a, S> {
+    /// Registers a new [`MulticolorDevice`].
+    pub fn build_multicolor<'bound: 'a, T: LedOps<Mode = MultiColor> + 'bound>(
+        self,
+        parent: &'bound T::Bus,
+        ops: impl PinInit<T, Error> + 'a,
+        subleds: &'a [MultiColorSubLed],
+    ) -> impl PinInit<MultiColorDevice<'bound, T>, Error> + 'a {
+        const_assert!(T::MAX_BRIGHTNESS <= i32::MAX.unsigned_abs() || !T::HAS_BRIGHTNESS_GET);
+
+        try_pin_init!(MultiColorDevice {
+            ops <- ops,
+            classdev <- Opaque::try_ffi_init(|ptr: *mut bindings::led_classdev_mc| {
+                let mut colors = [false; bindings::LED_COLOR_ID_MAX as usize];
+                for subled in subleds {
+                    if colors[subled.color as usize] {
+                        dev_err!(parent.as_ref(), "duplicate color in multicolor led\n");
+                        return Err(EINVAL);
+                    }
+                    colors[subled.color as usize] = true;
+                }
+                let subleds_box = KBox::pin_slice(
+                    |index| Ok::<_, Error>(subleds[index].clone()),
+                    subleds.len(),
+                    GFP_KERNEL,
+                )?;
+                let subleds_box_raw = KBox::into_raw(Pin::into_inner(subleds_box));
+
+                let subled_guard = ScopeGuard::new(|| {
+                    // SAFETY: `subleds_box_raw` is guaranteed to be a valid pointer to
+                    // `[MultiColorSubLed]`.
+                    drop(unsafe { <KBox<[MultiColorSubLed]>>::from_raw(subleds_box_raw) });
+                });
+
+                // SAFETY: `try_ffi_init` guarantees that `ptr` is valid for write.
+                // `led_classdev_mc` gets fully initialized in-place by
+                // `led_classdev_multicolor_register_ext` including `mutex` and `list_head`.
+                unsafe {
+                    ptr.write(bindings::led_classdev_mc {
+                        led_cdev: bindings::led_classdev {
+                            brightness_set: (!T::BLOCKING)
+                                .then_some(Adapter::<T>::brightness_set_callback),
+                            brightness_set_blocking: T::BLOCKING
+                                .then_some(Adapter::<T>::brightness_set_blocking_callback),
+                            brightness_get: T::HAS_BRIGHTNESS_GET
+                                .then_some(Adapter::<T>::brightness_get_callback),
+                            blink_set: T::HAS_BLINK_SET.then_some(Adapter::<T>::blink_set_callback),
+                            max_brightness: T::MAX_BRIGHTNESS,
+                            brightness: self.initial_brightness,
+                            color: self.color as u32,
+                            name: self.name.map_or(core::ptr::null(), CStrExt::as_char_ptr),
+                            ..bindings::led_classdev::default()
+                        },
+                        num_colors: u32::try_from(subleds_box_raw.len())?,
+                        // CAST: The safeguards in the const block ensure that
+                        // `MultiColorSubLed` has an identical layout to `mc_subled`.
+                        subled_info: subleds_box_raw.cast::<bindings::mc_subled>(),
+                    })
+                };
+
+                let mut init_data = bindings::led_init_data {
+                    fwnode: self
+                        .fwnode
+                        .as_ref()
+                        .map_or(core::ptr::null_mut(), |fwnode| fwnode.as_raw()),
+                    default_label: core::ptr::null(),
+                    devicename: self
+                        .devicename
+                        .map_or(core::ptr::null(), CStrExt::as_char_ptr),
+                    devname_mandatory: self.devname_mandatory,
+                };
+
+                // SAFETY:
+                // - `parent.as_ref().as_raw()` is guaranteed to be a pointer to a valid
+                //    `device`.
+                // - `ptr` is guaranteed to be a pointer to an initialized `led_classdev_mc`.
+                to_result(unsafe {
+                    bindings::led_classdev_multicolor_register_ext(
+                        parent.as_ref().as_raw(),
+                        ptr,
+                        if self.name.is_none() {
+                            &raw mut init_data
+                        } else {
+                            core::ptr::null_mut()
+                        },
+                    )
+                })?;
+
+                subled_guard.dismiss();
+
+                core::mem::forget(self.fwnode); // keep the reference count incremented
+
+                Ok::<_, Error>(())
+            }),
+            _p: PhantomData,
+        })
+    }
+}
+
+impl<'bound, T: LedOps<Mode = MultiColor> + 'bound> MultiColorDevice<'bound, T> {
+    /// # Safety
+    /// `led_cdev` must be a valid pointer to a `led_classdev` embedded within a
+    /// `led::MultiColorDevice`.
+    #[inline]
+    unsafe fn from_raw<'a>(led_cdev: *mut bindings::led_classdev) -> &'a Self {
+        // SAFETY: The function's contract guarantees that `led_cdev` points to a `led_classdev`
+        // field embedded within a valid `led::MultiColorDevice`. `container_of!` can therefore
+        // safely calculate the address of the containing struct.
+        let led_mc_cdev = unsafe { container_of!(led_cdev, bindings::led_classdev_mc, led_cdev) };
+
+        // SAFETY: It is guaranteed that `led_mc_cdev` points to a `led_classdev_mc`
+        // field embedded within a valid `led::MultiColorDevice`. `container_of!` can therefore
+        // safely calculate the address of the containing struct.
+        unsafe { &*container_of!(Opaque::cast_from(led_mc_cdev), Self, classdev) }
+    }
+
+    #[inline]
+    fn parent(&self) -> &'bound device::Device<Bound> {
+        // SAFETY: `self.classdev.get()` is guaranteed to be a valid pointer to `led_classdev_mc`.
+        unsafe { device::Device::from_raw((*(*self.classdev.get()).led_cdev.dev).parent) }
+    }
+
+    /// Returns the subleds passed to [`Device::new_multicolor`].
+    #[inline]
+    pub fn subleds(&self) -> &[MultiColorSubLed] {
+        // SAFETY: The existence of `self` guarantees that `self.classdev.get()` is a pointer to a
+        // valid `led_classdev_mc`.
+        let raw = unsafe { &*self.classdev.get() };
+        // SAFETY: `raw.subled_info` is a valid pointer to `mc_subled[num_colors]`.
+        // CAST: The safeguards in the const block ensure that `MultiColorSubLed` has an identical
+        // layout to `mc_subled`.
+        unsafe {
+            core::slice::from_raw_parts(
+                raw.subled_info.cast::<MultiColorSubLed>(),
+                // CAST: It is guaranteed that `num_colors` fits into an `usize`.
+                raw.num_colors as usize,
+            )
+        }
+    }
+}
+
+// SAFETY: A `led::MultiColorDevice` can be unregistered from any thread.
+unsafe impl<'bound, T: LedOps<Mode = MultiColor> + 'bound + Send> Send
+    for MultiColorDevice<'bound, T>
+{
+}
+
+// SAFETY: `led::MultiColorDevice` can be shared among threads because all methods of `led::Device`
+// are thread safe.
+unsafe impl<'bound, T: LedOps<Mode = MultiColor> + 'bound + Sync> Sync
+    for MultiColorDevice<'bound, T>
+{
+}
+
+struct Adapter<T: LedOps<Mode = MultiColor>> {
+    _p: PhantomData<T>,
+}
+
+impl<T: LedOps<Mode = MultiColor>> Adapter<T> {
+    /// # Safety
+    /// `led_cdev` must be a valid pointer to a `led_classdev` embedded within a
+    /// `led::MultiColorDevice`.
+    /// This function is called on setting the brightness of a led.
+    unsafe extern "C" fn brightness_set_callback(
+        led_cdev: *mut bindings::led_classdev,
+        brightness: u32,
+    ) {
+        // SAFETY: The function's contract guarantees that `led_cdev` is a valid pointer to a
+        // `led_classdev` embedded within a `led::MultiColorDevice`.
+        let classdev = unsafe { MultiColorDevice::<T>::from_raw(led_cdev) };
+        // SAFETY: `classdev.parent()` is guaranteed to be contained in `T::Bus`.
+        let parent = unsafe { T::Bus::from_device(classdev.parent()) };
+
+        // SAFETY: `classdev.classdev.get()` is guaranteed to be a pointer to a valid
+        // `led_classdev_mc`.
+        unsafe { bindings::led_mc_calc_color_components(classdev.classdev.get(), brightness) };
+
+        let _ = classdev.ops.brightness_set(parent, classdev, brightness);
+    }
+
+    /// # Safety
+    /// `led_cdev` must be a valid pointer to a `led_classdev` embedded within a
+    /// `led::MultiColorDevice`.
+    /// This function is called on setting the brightness of a led immediately.
+    unsafe extern "C" fn brightness_set_blocking_callback(
+        led_cdev: *mut bindings::led_classdev,
+        brightness: u32,
+    ) -> i32 {
+        from_result(|| {
+            // SAFETY: The function's contract guarantees that `led_cdev` is a valid pointer to a
+            // `led_classdev` embedded within a `led::MultiColorDevice`.
+            let classdev = unsafe { MultiColorDevice::<T>::from_raw(led_cdev) };
+            // SAFETY: `classdev.parent()` is guaranteed to be contained in `T::Bus`.
+            let parent = unsafe { T::Bus::from_device(classdev.parent()) };
+
+            // SAFETY: `classdev.classdev.get()` is guaranteed to be a pointer to a valid
+            // `led_classdev_mc`.
+            unsafe { bindings::led_mc_calc_color_components(classdev.classdev.get(), brightness) };
+
+            classdev.ops.brightness_set(parent, classdev, brightness)?;
+            Ok(0)
+        })
+    }
+
+    /// # Safety
+    /// `led_cdev` must be a valid pointer to a `led_classdev` embedded within a
+    /// `led::MultiColorDevice`.
+    /// This function is called on getting the brightness of a led.
+    unsafe extern "C" fn brightness_get_callback(led_cdev: *mut bindings::led_classdev) -> u32 {
+        // SAFETY: The function's contract guarantees that `led_cdev` is a valid pointer to a
+        // `led_classdev` embedded within a `led::MultiColorDevice`.
+        let classdev = unsafe { MultiColorDevice::<T>::from_raw(led_cdev) };
+        // SAFETY: `classdev.parent()` is guaranteed to be contained in `T::Bus`.
+        let parent = unsafe { T::Bus::from_device(classdev.parent()) };
+
+        // CAST: Resulting value will be casted back to i32 in the led subsystem.
+        from_result(|| {
+            classdev
+                .ops
+                .brightness_get(parent, classdev)
+                .inspect(|val| debug_assert!(*val <= T::MAX_BRIGHTNESS))
+                .and_then(|val| Ok(i32::try_from(val)?))
+        }) as u32
+    }
+
+    /// # Safety
+    /// `led_cdev` must be a valid pointer to a `led_classdev` embedded within a
+    /// `led::MultiColorDevice`.
+    /// `delay_on` and `delay_off` must be valid pointers to `usize` and have
+    /// exclusive access for the period of this function.
+    /// This function is called on enabling hardware accelerated blinking.
+    unsafe extern "C" fn blink_set_callback(
+        led_cdev: *mut bindings::led_classdev,
+        delay_on: *mut usize,
+        delay_off: *mut usize,
+    ) -> i32 {
+        from_result(|| {
+            // SAFETY: The function's contract guarantees that `led_cdev` is a valid pointer to a
+            // `led_classdev` embedded within a `led::MultiColorDevice`.
+            let classdev = unsafe { MultiColorDevice::<T>::from_raw(led_cdev) };
+            // SAFETY: `classdev.parent()` is guaranteed to be contained in `T::Bus`.
+            let parent = unsafe { T::Bus::from_device(classdev.parent()) };
+
+            classdev.ops.blink_set(
+                parent,
+                classdev,
+                // SAFETY: The function's contract guarantees that `delay_on` points to a `usize`
+                // and is exclusive for the period of this function.
+                unsafe { &mut *delay_on },
+                // SAFETY: The function's contract guarantees that `delay_off` points to a `usize`
+                // and is exclusive for the period of this function.
+                unsafe { &mut *delay_off },
+            )?;
+            Ok(0)
+        })
+    }
+}
+
+#[pinned_drop]
+impl<'bound, T: LedOps<Mode = MultiColor> + 'bound> PinnedDrop for MultiColorDevice<'bound, T> {
+    fn drop(self: Pin<&mut Self>) {
+        let raw = self.classdev.get();
+        // SAFETY: The existence of `self` guarantees that `self.classdev.get()` is a pointer to a
+        // valid `led_classdev_mc`.
+        let dev: &device::Device = unsafe { device::Device::from_raw((*raw).led_cdev.dev) };
+
+        if let Some(fwnode) = dev.fwnode() {
+            // SAFETY: the reference count of `fwnode` has previously been incremented in
+            // `led::DeviceBuilder::build_multicolor`.
+            unsafe { FwNode::dec_ref(NonNull::from(fwnode)) };
+        }
+
+        // SAFETY: The existence of `self` guarantees that `self.classdev` has previously been
+        // successfully registered with `led_classdev_multicolor_register_ext`.
+        unsafe { bindings::led_classdev_multicolor_unregister(raw) };
+
+        // SAFETY: `raw` is guaranteed to be a valid pointer to `led_classdev_mc`.
+        let led_cdev = unsafe { &*raw };
+
+        // SAFETY: `led_cdev.subled_info` is guaranteed to be a valid pointer to
+        // `[MultiColorSubLed]` with length of `led_cdev.num_colors`.
+        // See `led::DeviceBuilder::build_multicolor`.
+        drop(unsafe {
+            KBox::from_raw(ptr::slice_from_raw_parts_mut(
+                led_cdev.subled_info.cast::<MultiColorSubLed>(),
+                // CAST: `num_colors` was originally converted from a `usize` in
+                // `DeviceBuilder::build_multicolor`. Thus it is guaranteed that
+                // `num_colors` fits into an usize.
+                led_cdev.num_colors as usize,
+            ))
+        });
+    }
+}

-- 
2.53.0