Message-ID: <20240930233257.1189730-7-lyude@redhat.com>
Date: Mon, 30 Sep 2024 19:09:49 -0400
From: Lyude Paul <lyude@...hat.com>
To: dri-devel@...ts.freedesktop.org,
	rust-for-linux@...r.kernel.org
Cc: Asahi Lina <lina@...hilina.net>,
	Danilo Krummrich <dakr@...nel.org>,
	mcanal@...lia.com,
	airlied@...hat.com,
	zhiw@...dia.com,
	cjia@...dia.com,
	jhubbard@...dia.com,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Boqun Feng <boqun.feng@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Trevor Gross <tmgross@...ch.edu>,
	linux-kernel@...r.kernel.org (open list)
Subject: [WIP RFC v2 06/35] rust: drm/kms: Add drm_plane bindings

The next step is adding a set of basic bindings to create a plane, which
has to happen before we can create a CRTC (since we need to be able to at
least specify a primary plane for a CRTC upon creation). This mostly
follows the same general pattern as connectors (AsRawPlane,
AsRawPlaneState, etc.).

There is one major difference with planes vs. other types of atomic mode
objects: drm_plane_state isn't the only base plane struct used in DRM
drivers, as some drivers will use helpers like drm_shadow_plane_state which
have a drm_plane_state embedded within them.

Since we'll eventually be adding bindings for shadow planes, we introduce a
PlaneStateHelper trait - which represents any data type which can be used
as the main wrapping structure around a drm_plane_state - and we implement
this trait for PlaneState<T>. This trait can be used in our C callbacks to
allow for drivers to use different wrapping structures without needing to
implement a separate set of FFI callbacks for each type. Currently planes
are the only type I'm aware of which do this.

Signed-off-by: Lyude Paul <lyude@...hat.com>

---

V2:
* Start using Gerry Guo's updated #[vtable] function so that our driver
  operations table has a static location in memory

Signed-off-by: Lyude Paul <lyude@...hat.com>
---
 rust/kernel/drm/kms.rs       |   1 +
 rust/kernel/drm/kms/plane.rs | 504 +++++++++++++++++++++++++++++++++++
 2 files changed, 505 insertions(+)
 create mode 100644 rust/kernel/drm/kms/plane.rs

diff --git a/rust/kernel/drm/kms.rs b/rust/kernel/drm/kms.rs
index 0138e6830b48c..5b075794a1155 100644
--- a/rust/kernel/drm/kms.rs
+++ b/rust/kernel/drm/kms.rs
@@ -4,6 +4,7 @@
 
 pub mod connector;
 pub mod fbdev;
+pub mod plane;
 
 use crate::{
     drm::{
diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
new file mode 100644
index 0000000000000..3040c4546b121
--- /dev/null
+++ b/rust/kernel/drm/kms/plane.rs
@@ -0,0 +1,504 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+//! Bindings for [`struct drm_plane`] and friends.
+//!
+//! [`struct drm_plane`]: srctree/include/drm/drm_plane.h
+
+use alloc::boxed::Box;
+use crate::{
+    bindings,
+    drm::{device::Device, drv::Driver, fourcc::*},
+    error::{to_result, from_result, Error},
+    init::Zeroable,
+    prelude::*,
+    types::{ARef, Opaque},
+    private::Sealed,
+};
+use core::{
+    cell::Cell,
+    pin::Pin,
+    slice,
+    mem::{self, size_of, ManuallyDrop},
+    ptr::{self, null, null_mut, NonNull},
+    marker::*,
+    ops::*,
+};
+use macros::pin_data;
+use super::{
+    KmsDriver,
+    UnregisteredKmsDevice,
+    ModeObject,
+    StaticModeObject,
+};
+
+/// The main trait for implementing the [`struct drm_plane`] API for [`Plane`]
+///
+/// Any KMS driver should have at least one implementation of this type, which allows them to create
+/// [`Plane`] objects. Additionally, a driver may store driver-private data within the type that
+/// implements [`DriverPlane`] - and it will be made available when using a fully typed [`Plane`]
+/// object.
+///
+/// # Invariants
+///
+/// - Any C FFI callbacks generated using this trait are guaranteed that passed-in
+///   [`struct drm_plane`] pointers are contained within a [`Plane<Self>`].
+/// - Any C FFI callbacks generated using this trait are guaranteed that passed-in
+///   [`struct drm_plane_state`] pointers are contained within a [`PlaneState<Self::State>`].
+///
+/// [`struct drm_plane`]: srctree/include/drm/drm_plane.h
+/// [`struct drm_plane_state`]: srctree/include/drm/drm_plane.h
+#[vtable]
+pub trait DriverPlane: Send + Sync + Sized {
+    /// The generated C vtable for this [`DriverPlane`] implementation.
+    #[unique]
+    const OPS: &'static DriverPlaneOps = &DriverPlaneOps {
+        funcs: bindings::drm_plane_funcs {
+            update_plane: Some(bindings::drm_atomic_helper_update_plane),
+            disable_plane: Some(bindings::drm_atomic_helper_disable_plane),
+            destroy: Some(plane_destroy_callback::<Self>),
+            reset: Some(plane_reset_callback::<Self>),
+            set_property: None,
+            atomic_duplicate_state: Some(atomic_duplicate_state_callback::<Self::State>),
+            atomic_destroy_state: Some(atomic_destroy_state_callback::<Self::State>),
+            atomic_set_property: None, // TODO someday
+            atomic_get_property: None, // TODO someday
+            late_register: None, // TODO someday
+            early_unregister: None, // TODO someday
+            atomic_print_state: None, // TODO: Display someday???
+            format_mod_supported: None // TODO someday
+        },
+
+        helper_funcs: bindings::drm_plane_helper_funcs {
+            prepare_fb: None,
+            cleanup_fb: None,
+            begin_fb_access: None, // TODO: someday?
+            end_fb_access: None, // TODO: someday?
+            atomic_check: None,
+            atomic_update: None,
+            atomic_enable: None, // TODO
+            atomic_disable: None, // TODO
+            atomic_async_check: None, // TODO
+            atomic_async_update: None, // TODO
+            panic_flush: None,
+            get_scanout_buffer: None
+        }
+    };
+
+    /// The type to pass to the `args` field of [`Plane::new`].
+    ///
+    /// This type will be made available in in the `args` argument of [`Self::new`]. Drivers which
+    /// don't need this can simply pass [`()`] here.
+    type Args;
+
+    /// The parent [`Driver`] implementation.
+    type Driver: KmsDriver;
+
+    /// The [`DriverPlaneState`] implementation for this [`DriverPlane`].
+    ///
+    /// See [`DriverPlaneState`] for more info.
+    type State: DriverPlaneState;
+
+    /// The constructor for creating a [`Plane`] using this [`DriverPlane`] implementation.
+    ///
+    /// Drivers may use this to instantiate their [`DriverPlane`] object.
+    fn new(device: &Device<Self::Driver>, args: Self::Args) -> impl PinInit<Self, Error>;
+}
+
+/// The generated C vtable for a [`DriverPlane`].
+///
+/// This type is created internally by DRM.
+pub struct DriverPlaneOps {
+    funcs: bindings::drm_plane_funcs,
+    helper_funcs: bindings::drm_plane_helper_funcs,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[repr(u32)]
+/// An enumerator describing a type of [`Plane`].
+///
+/// This is mainly just relevant for DRM legacy drivers.
+pub enum PlaneType {
+    /// Overlay planes represent all non-primary, non-cursor planes. Some drivers refer to these
+    /// types of planes as "sprites" internally.
+    OVERLAY = bindings::drm_plane_type_DRM_PLANE_TYPE_OVERLAY,
+
+    /// A primary plane attached to a CRTC that is the most likely to be able to light up the CRTC
+    /// when no scaling/cropping is used, and the plane covers the whole CRTC.
+    PRIMARY = bindings::drm_plane_type_DRM_PLANE_TYPE_PRIMARY,
+
+    /// A cursor plane attached to a CRTC that is more likely to be enabled when no scaling/cropping
+    /// is used, and the framebuffer has the size indicated by [`ModeConfigInfo::max_cursor`].
+    ///
+    /// [`ModeConfigInfo::max_cursor`]: crate::drm::kms::ModeConfigInfo
+    CURSOR = bindings::drm_plane_type_DRM_PLANE_TYPE_CURSOR,
+}
+
+/// The main interface for a [`struct drm_plane`].
+///
+/// This type is the main interface for dealing with DRM planes. In addition, it also allows
+/// immutable access to whatever private data is contained within an implementor's [`DriverPlane`]
+/// type.
+///
+/// # Invariants
+///
+/// - `plane` and `inner` are initialized for as long as this object is made available to users.
+/// - The data layout of this structure begins with [`struct drm_plane`].
+/// - The atomic state for this type can always be assumed to be of type [`PlaneState<T::State>`].
+///
+/// [`struct drm_plane`]: srctree/include/drm/drm_plane.h
+#[repr(C)]
+#[pin_data]
+pub struct Plane<T: DriverPlane> {
+    /// The FFI drm_plane object
+    plane: Opaque<bindings::drm_plane>,
+    /// The driver's private inner data
+    #[pin]
+    inner: T,
+    #[pin]
+    _p: PhantomPinned,
+}
+
+unsafe impl Zeroable for bindings::drm_plane {}
+
+impl<T: DriverPlane> Sealed for Plane<T> {}
+
+impl<T: DriverPlane> Deref for Plane<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl<T: DriverPlane> Plane<T> {
+    /// Construct a new [`Plane`].
+    ///
+    /// A driver may use this from their [`Kms::create_objects`] callback in order to construct new
+    /// [`Plane`] objects.
+    ///
+    /// [`Kms::create_objects`]: kernel::drm::kms::Kms::create_objects
+    pub fn new<'a, 'b: 'a, const FMT_COUNT: usize, const MOD_COUNT: usize>(
+        dev: &'a UnregisteredKmsDevice<'a, T::Driver>,
+        possible_crtcs: u32,
+        formats: &'static FormatList<FMT_COUNT>,
+        format_modifiers: Option<&'static ModifierList<MOD_COUNT>>,
+        type_: PlaneType,
+        name: Option<&CStr>,
+        args: T::Args,
+    ) -> Result<&'b Self> {
+        let this: Pin<Box<Self>> = Box::try_pin_init(
+            try_pin_init!(Self {
+                plane: Opaque::new(bindings::drm_plane {
+                    helper_private: &T::OPS.helper_funcs,
+                    ..Default::default()
+                }),
+                inner <- T::new(dev, args),
+                _p: PhantomPinned
+            }),
+            GFP_KERNEL
+        )?;
+
+        // SAFETY: FFI call with no special requirements
+        to_result(unsafe {
+            bindings::drm_universal_plane_init(
+                dev.as_raw(),
+                this.as_raw(),
+                possible_crtcs,
+                &T::OPS.funcs,
+                formats.as_ptr(),
+                formats.raw_len() as _,
+                format_modifiers.map_or(null(), |f| f.as_ptr()),
+                type_ as _,
+                name.map_or(null(), |n| n.as_char_ptr())
+            )
+        })?;
+
+        // Convert the box into a raw pointer, we'll re-assemble it in plane_destroy_callback()
+        // SAFETY: We don't move anything
+        Ok(unsafe { &*Box::into_raw(Pin::into_inner_unchecked(this)) })
+    }
+}
+
+/// A trait implemented by any type that acts as a [`struct drm_plane`] interface.
+///
+/// This is implemented internally by DRM.
+///
+/// [`struct drm_plane`]: srctree/include/drm/drm_plane.h
+pub trait AsRawPlane: StaticModeObject {
+    /// The type that should be used to represent an atomic state for this plane interface.
+    type State: FromRawPlaneState;
+
+    /// Return the raw `bindings::drm_plane` for this DRM plane.
+    ///
+    /// Drivers should never use this directly.
+    fn as_raw(&self) -> *mut bindings::drm_plane;
+
+    /// Convert a raw `bindings::drm_plane` pointer into an object of this type.
+    ///
+    /// SAFETY: Callers promise that `ptr` points to a valid instance of this type
+    unsafe fn from_raw<'a>(ptr: *mut bindings::drm_plane) -> &'a Self;
+}
+
+impl<T: DriverPlane> AsRawPlane for Plane<T> {
+    type State = PlaneState<T::State>;
+
+    fn as_raw(&self) -> *mut bindings::drm_plane {
+        self.plane.get()
+    }
+
+    unsafe fn from_raw<'a>(ptr: *mut bindings::drm_plane) -> &'a Self {
+        // SAFETY: Our data layout starts with `bindings::drm_plane`
+        unsafe { &*ptr.cast() }
+    }
+}
+
+impl<T: DriverPlane> ModeObject for Plane<T> {
+    type Driver = T::Driver;
+
+    fn drm_dev(&self) -> &Device<Self::Driver> {
+        // SAFETY: DRM planes exist for as long as the device does, so this pointer is always valid
+        unsafe { Device::borrow((*self.as_raw()).dev) }
+    }
+
+    fn raw_mode_obj(&self) -> *mut bindings::drm_mode_object {
+        // SAFETY: We don't expose DRM planes to users before `base` is initialized
+        unsafe { &mut ((*self.as_raw()).base) }
+    }
+}
+
+// SAFETY: Planes do not have a refcount
+unsafe impl<T: DriverPlane> StaticModeObject for Plane<T> {}
+
+// SAFETY: Our interface is thread-safe.
+unsafe impl<T: DriverPlane> Send for Plane<T> {}
+
+// SAFETY: Our interface is thread-safe.
+unsafe impl<T: DriverPlane> Sync for Plane<T> {}
+
+/// A trait implemented by any type which can produce a reference to a [`struct drm_plane_state`].
+///
+/// This is implemented internally by DRM.
+///
+/// [`struct drm_plane_state`]: srctree/include/drm/drm_plane.h
+pub trait AsRawPlaneState: private::AsRawPlaneState {
+    /// The type that this plane state interface returns to represent the parent DRM plane
+    type Plane: AsRawPlane;
+}
+
+pub(crate) mod private {
+    /// Trait for retrieving references to the base plane state contained within any plane state
+    /// compatible type
+    #[doc(hidden)]
+    pub trait AsRawPlaneState {
+        /// Return an immutable reference to the raw plane state
+        fn as_raw(&self) -> &bindings::drm_plane_state;
+
+        /// Get a mutable reference to the raw `bindings::drm_plane_state` contained within this
+        /// type.
+        ///
+        /// # Safety
+        ///
+        /// The caller promises this mutable reference will not be used to modify any contents of
+        /// `bindings::drm_plane_state` which DRM would consider to be static - like the backpointer
+        /// to the DRM plane that owns this state. This also means the mutable reference should
+        /// never be exposed outside of this crate.
+        unsafe fn as_raw_mut(&mut self) -> &mut bindings::drm_plane_state;
+    }
+}
+
+pub(crate) use private::AsRawPlaneState as AsRawPlaneStatePrivate;
+
+/// A trait implemented for any type which can be constructed directly from a
+/// [`struct drm_plane_state`] pointer.
+///
+/// This is implemented internally by DRM.
+///
+/// [`struct drm_plane_state`]: srctree/include/drm/drm_plane.h
+pub trait FromRawPlaneState: AsRawPlaneState {
+    /// Get an immutable reference to this type from the given raw `bindings::drm_plane_state`
+    /// pointer
+    ///
+    /// # Safety
+    ///
+    /// The caller guarantees `ptr` is contained within a valid instance of `Self`
+    unsafe fn from_raw<'a>(ptr: *const bindings::drm_plane_state) -> &'a Self;
+
+    /// Get a mutable reference to this type from the given raw `bindings::drm_plane_state` pointer
+    ///
+    /// # Safety
+    ///
+    /// The caller guarantees `ptr` is contained within a valid instance of `Self`, and that no
+    /// other references (mutable or immutable) to `ptr` exist.
+    unsafe fn from_raw_mut<'a>(ptr: *mut bindings::drm_plane_state) -> &'a mut Self;
+}
+
+/// The main interface for a [`struct drm_plane_state`].
+///
+/// This type is the main interface for dealing with the atomic state of DRM planes. In addition, it
+/// allows access to whatever private data is contained within an implementor's [`DriverPlaneState`]
+/// type.
+///
+/// # Invariants
+///
+/// - The DRM C API and our interface guarantees that only the user has mutable access to `state`,
+///   up until [`drm_atomic_helper_commit_hw_done`] is called. Therefore, `plane` follows rust's
+///   data aliasing rules and does not need to be behind an [`Opaque`] type.
+/// - `state` and `inner` initialized for as long as this object is exposed to users.
+/// - The data layout of this structure begins with [`struct drm_plane_state`].
+/// - The plane for this atomic state can always be assumed to be of type [`Plane<T::Plane>`].
+///
+/// [`struct drm_plane_state`]: srctree/include/drm/drm_plane.h
+/// [`drm_atomic_helper_commit_hw_done`]: srctree/include/drm/drm_atomic_helper.h
+#[derive(Default)]
+#[repr(C)]
+pub struct PlaneState<T: DriverPlaneState> {
+    state: bindings::drm_plane_state,
+    inner: T,
+}
+
+/// The main trait for implementing the [`struct drm_plane_state`] API for a [`Plane`].
+///
+/// A driver may store driver-private data within the implementor's type, which will be available
+/// when using a full typed [`PlaneState`] object.
+///
+/// # Invariants
+///
+/// - Any C FFI callbacks generated using this trait are guaranteed that passed-in
+///   [`struct drm_plane`] pointers are contained within a [`Plane<Self::Plane>`].
+/// - Any C FFI callbacks generated using this trait are guaranteed that passed-in
+///   [`struct drm_plane_state`] pointers are contained within a [`PlaneState<Self>`].
+///
+/// [`struct drm_plane`]: srctree/include/drm_plane.h
+/// [`struct drm_plane_state`]: srctree/include/drm_plane.h
+pub trait DriverPlaneState: Clone + Default + Sized {
+    /// The type for this driver's drm_plane implementation
+    type Plane: DriverPlane;
+}
+
+impl<T: DriverPlaneState> Sealed for PlaneState<T> {}
+
+impl<T: DriverPlaneState> AsRawPlaneState for PlaneState<T> {
+    type Plane = Plane<T::Plane>;
+}
+
+impl<T: DriverPlaneState> private::AsRawPlaneState for PlaneState<T> {
+    fn as_raw(&self) -> &bindings::drm_plane_state {
+        &self.state
+    }
+
+    unsafe fn as_raw_mut(&mut self) -> &mut bindings::drm_plane_state {
+        &mut self.state
+    }
+}
+
+impl<T: DriverPlaneState> FromRawPlaneState for PlaneState<T> {
+    unsafe fn from_raw<'a>(ptr: *const bindings::drm_plane_state) -> &'a Self {
+        // SAFETY: Our data layout starts with `bindings::drm_plane_state`
+        unsafe { &*ptr.cast() }
+    }
+
+    unsafe fn from_raw_mut<'a>(ptr: *mut bindings::drm_plane_state) -> &'a mut Self {
+        // SAFETY: Our data layout starts with `bindings::drm_plane_state`
+        unsafe { &mut *ptr.cast() }
+    }
+}
+
+unsafe impl Zeroable for bindings::drm_plane_state {}
+
+impl<T: DriverPlaneState> Deref for PlaneState<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl<T: DriverPlaneState> DerefMut for PlaneState<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.inner
+    }
+}
+
+unsafe extern "C" fn plane_destroy_callback<T: DriverPlane>(
+    plane: *mut bindings::drm_plane
+) {
+    // SAFETY: DRM guarantees that `plane` points to a valid initialized `drm_plane`.
+    unsafe { bindings::drm_plane_cleanup(plane) };
+
+    // SAFETY:
+    // - DRM guarantees we are now the only one with access to this [`drm_plane`].
+    // - This cast is safe via `DriverPlane`s type invariants.
+    drop(unsafe { Box::from_raw(plane as *mut Plane<T>) });
+}
+
+unsafe extern "C" fn atomic_duplicate_state_callback<T: DriverPlaneState>(
+    plane: *mut bindings::drm_plane
+) -> *mut bindings::drm_plane_state {
+    // SAFETY: DRM guarantees that `plane` points to a valid initialized `drm_plane`.
+    let state = unsafe { (*plane).state };
+    if state.is_null() {
+        return null_mut();
+    }
+
+    // SAFETY: This cast is safe via `DriverPlaneState`s type invariants.
+    let state = unsafe { PlaneState::<T>::from_raw(state) };
+
+    let new = Box::try_init(
+        try_init!(PlaneState::<T> {
+            state: bindings::drm_plane_state { ..Default::default() },
+            inner: state.inner.clone()
+        }),
+        GFP_KERNEL
+    );
+
+    if let Ok(mut new) = new {
+        // SAFETY: Just a lil' FFI call, nothing special here
+        unsafe {
+            bindings::__drm_atomic_helper_plane_duplicate_state(plane, new.as_raw_mut())
+        };
+
+        Box::into_raw(new).cast()
+    } else {
+        null_mut()
+    }
+}
+
+unsafe extern "C" fn atomic_destroy_state_callback<T: DriverPlaneState>(
+    _plane: *mut bindings::drm_plane,
+    state: *mut bindings::drm_plane_state
+) {
+    // SAFETY: DRM guarantees that `state` points to a valid instance of `drm_plane_state`
+    unsafe { bindings::__drm_atomic_helper_plane_destroy_state(state) };
+
+    // SAFETY:
+    // * DRM guarantees we are the only one with access to this `drm_plane_state`
+    // * This cast is safe via our type invariants.
+    drop(unsafe { Box::from_raw(state.cast::<PlaneState<T>>()) });
+}
+
+unsafe extern "C" fn plane_reset_callback<T: DriverPlane>(
+    plane: *mut bindings::drm_plane,
+) {
+    // SAFETY: DRM guarantees that `state` points to a valid instance of `drm_plane_state`
+    let state = unsafe { (*plane).state };
+    if !state.is_null() {
+        // SAFETY:
+        // * We're guaranteed `plane` is `Plane<T>` via type invariants
+        // * We're guaranteed `state` is `PlaneState<T>` via type invariants.
+        unsafe { atomic_destroy_state_callback::<T::State>(plane, state) }
+
+        // SAFETY: No special requirements here, DRM expects this to be NULL
+        unsafe { (*plane).state = null_mut(); }
+    }
+
+    // Unfortunately, this is the best we can do at the moment as this FFI callback was mistakenly
+    // presumed to be infallible :(
+    let new = Box::new(PlaneState::<T::State>::default(), GFP_KERNEL)
+        .expect("Blame the API, sorry!");
+
+    // DRM takes ownership of the state from here, resets it, and then assigns it to the plane
+    // SAFETY:
+    // - DRM guarantees that `plane` points to a valid instance of `drm_plane`.
+    // - The cast to `drm_plane_state` is safe via `PlaneState`s type invariants.
+    unsafe { bindings::__drm_atomic_helper_plane_reset(plane, Box::into_raw(new).cast()) };
+}
-- 
2.46.1

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