Message-ID: <20240930233257.1189730-6-lyude@redhat.com>
Date: Mon, 30 Sep 2024 19:09:48 -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 05/35] rust: drm/kms: Add bindings for drm_connector

We start off by introducing wrappers for the first important type of mode
object: a DRM display connector. This introduces Connector<T:
DriverConnector> and ConnectorState<T: DriverConnectorState>. Both
DriverConnector and DriverConnectorState must be implemented by KMS
drivers, and a driver may have as many implementations of these two traits
as it needs. This also introduces the general data pattern we'll be using
for all of the core mode objects that can be used in atomic commits.

It's important to note that both Connector<T> and ConnectorState<T> are
intended to be "subclassable". To explain what this means, we need to look
at how a DRM driver normally uses objects like DRM connectors.

Typically, a driver in C will define its connectors like so:

struct foo_connector {
  struct drm_connector base;
  int bar;
}

Note that we have a drm_connector struct embedded in foo_connector, but we
have data which comes after it which is defined by the driver. This is
important for a number of reasons: connectors can have their own mutexes
and various other hardware-specific information that a driver may want
access to at any time. The same goes for drm_connector_state, where drivers
will subclass this struct in the same way. It's worth noting as well that
it isn't uncommon for a driver to have multiple types of connectors, but
we'll handle in a later commit.

As a result, we've designed Connector<T> and ConnectorState<T> so that for
both types: a DRM driver can add custom data into the T. As well, there's
some basic limitations on how this data may be accessed:

* Data within the `DriverConnector` struct is pinned in order to allow
  mutexes and other structs which need pinning to be stored within it. As
  well, it is impossible to get a direct mutable reference to the data
  within DriverConnector - as there's no locks for doing so which would
  cause a race condition.
* Data within the `DriverConnectorState` struct is currently not pinned.
  While it's not unheard of for a driver to put something like a mutex in
  its atomic states, (VKMS actually does this in some spots) this quickly
  complicates things especially with nonblocking modesets - and doesn't
  really fit into the philosophy of an atomic state anyway. We may add
  support for this in the future later if this does end up being needed,
  but for now we hold back in order to make it much easier for drivers to
  access private data within the atomic state.
  As well, the functions we provide for converting to/from raw connector
  state pointers are notably different from many other rust types in the
  kernel. Instead of converting raw state pointers to raw ConnectorState<T>
  pointers, we allow for direct immutable and mutable references. The
  reason for this is that it makes accessing private driver data in the
  state much easier, and unlike Connector<T> - we can actually uphold
  all of the required data aliasing rules thanks to states only being
  mutable by a single thread before they've been swapped in.
  Note that currently, we don't provide a way to access said private data
  for ConnectorState<T> since allowing direct access to a &mut
  ConnectorState<T> could allow a caller to modify portions of
  drm_connector_state which are meant to be invariant throughout the
  lifetime of the connector state. We'll address this in the next few
  commits when we introduce the global atomic state type.

And finally - we introduce the following internal traits for the crate side
of things:

  * AsRawConnector - any type which can spit out a *mut
    bindings::drm_connector or be recovered from one
  * AsRawConnectorState - any type which can return a reference to a
    bindings::drm_connector_state
  * private::AsRawConnectorState - just methods for AsRawConnectorState
    that we don't want to be accessible to our users (since they could be
    used to introduce UB)
  * FromRawConnectorState - any type which can be recovered from a raw
    pointer to a bindings::drm_connector_state

The reason for having AsRawConnectorState and FromRawConnectorState as
separate traits unlike AsRawConnector is due to the fact that we'll
introduce objects later on which can be used as DRM connector states, but
cannot be directly derived from a *mut bindings::drm_connector_state
because they hold additional state or have additional side-effects.

Likewise, we'll also have other objects which can be used as raw DRM
connectors - hence AsRawConnector.

Signed-off-by: Lyude Paul <lyude@...hat.com>
---
 rust/kernel/drm/kms.rs           |   1 +
 rust/kernel/drm/kms/connector.rs | 531 +++++++++++++++++++++++++++++++
 2 files changed, 532 insertions(+)
 create mode 100644 rust/kernel/drm/kms/connector.rs

diff --git a/rust/kernel/drm/kms.rs b/rust/kernel/drm/kms.rs
index f1a8ba4b7e296..0138e6830b48c 100644
--- a/rust/kernel/drm/kms.rs
+++ b/rust/kernel/drm/kms.rs
@@ -2,6 +2,7 @@
 
 //! KMS driver abstractions for rust.
 
+pub mod connector;
 pub mod fbdev;
 
 use crate::{
diff --git a/rust/kernel/drm/kms/connector.rs b/rust/kernel/drm/kms/connector.rs
new file mode 100644
index 0000000000000..0fa927a3743b2
--- /dev/null
+++ b/rust/kernel/drm/kms/connector.rs
@@ -0,0 +1,531 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+//! Rust bindings for DRM connectors
+
+use crate::{
+    bindings,
+    sync::ArcBorrow,
+    drm::{
+        drv::{Driver, FEAT_MODESET},
+        device::Device,
+    },
+    types::{AlwaysRefCounted, Opaque, ARef},
+    prelude::*,
+    init::Zeroable,
+    error::{to_result, from_result},
+    build_error,
+    private::Sealed,
+};
+use core::{
+    marker::*,
+    ptr::null_mut,
+    mem,
+    ptr::{self, NonNull, addr_of_mut},
+    ffi::*,
+    ops::*,
+    cell::Cell,
+};
+use super::{
+    ModeObject,
+    RcModeObject,
+    KmsDriver,
+};
+use macros::pin_data;
+
+// XXX: This is :\, figure out a better way at some point?
+pub use bindings::{
+    DRM_MODE_CONNECTOR_Unknown,
+    DRM_MODE_CONNECTOR_VGA,
+    DRM_MODE_CONNECTOR_DVII,
+    DRM_MODE_CONNECTOR_DVID,
+    DRM_MODE_CONNECTOR_DVIA,
+    DRM_MODE_CONNECTOR_Composite,
+    DRM_MODE_CONNECTOR_SVIDEO,
+    DRM_MODE_CONNECTOR_LVDS,
+    DRM_MODE_CONNECTOR_Component,
+    DRM_MODE_CONNECTOR_9PinDIN,
+    DRM_MODE_CONNECTOR_DisplayPort,
+    DRM_MODE_CONNECTOR_HDMIA,
+    DRM_MODE_CONNECTOR_HDMIB,
+    DRM_MODE_CONNECTOR_TV,
+    DRM_MODE_CONNECTOR_eDP,
+    DRM_MODE_CONNECTOR_VIRTUAL,
+    DRM_MODE_CONNECTOR_DSI,
+    DRM_MODE_CONNECTOR_DPI,
+    DRM_MODE_CONNECTOR_WRITEBACK,
+    DRM_MODE_CONNECTOR_SPI,
+    DRM_MODE_CONNECTOR_USB,
+};
+
+/// The main trait for implementing the [`struct drm_connector`] API for [`Connector`].
+///
+/// Any KMS driver should have at least one implementation of this type, which allows them to create
+/// [`Connector`] objects. Additionally, a driver may store driver-private data within the type that
+/// implements [`DriverConnector`] - and it will be made available when using a fully typed
+/// [`Connector`] object.
+///
+/// # Invariants
+///
+/// - Any C FFI callbacks generated using this trait are guaranteed that passed-in
+///   [`struct drm_connector`] pointers are contained within a [`Connector<Self>`].
+/// - Any C FFI callbacks generated using this trait are guaranteed that passed-in
+///   [`struct drm_connector_state`] pointers are contained within a
+///   [`ConnectorState<Self::State>`].
+///
+/// [`struct drm_connector`]: srctree/include/drm/drm_connector.h
+/// [`struct drm_connector_state`]: srctree/include/drm/drm_connector.h
+#[vtable]
+pub trait DriverConnector: Send + Sync + Sized {
+    /// The generated C vtable for this [`DriverConnector`] implementation
+    #[unique]
+    const OPS: &'static DriverConnectorOps = &DriverConnectorOps {
+        funcs: bindings::drm_connector_funcs {
+            dpms: None,
+            atomic_get_property: None,
+            atomic_set_property: None,
+            early_unregister: None,
+            late_register: None,
+            set_property: None,
+            reset: Some(connector_reset_callback::<Self::State>),
+            atomic_print_state: None,
+            atomic_destroy_state: Some(atomic_destroy_state_callback::<Self::State>),
+            destroy: Some(connector_destroy_callback::<Self>),
+            force: None,
+            detect: None,
+            fill_modes: None,
+            debugfs_init: None,
+            oob_hotplug_event: None,
+            atomic_duplicate_state: Some(atomic_duplicate_state_callback::<Self::State>),
+        },
+        helper_funcs: bindings::drm_connector_helper_funcs {
+            mode_valid: None,
+            atomic_check: None,
+            get_modes: None,
+            detect_ctx: None,
+            enable_hpd: None,
+            disable_hpd: None,
+            best_encoder: None,
+            atomic_commit: None,
+            mode_valid_ctx: None,
+            atomic_best_encoder: None,
+            prepare_writeback_job: None,
+            cleanup_writeback_job: None,
+        }
+    };
+
+    /// The type to pass to the `args` field of [`Connector::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 [`DriverConnectorState`] implementation for this [`DriverConnector`].
+    ///
+    /// See [`DriverConnectorState`] for more info.
+    type State: DriverConnectorState;
+
+    /// The constructor for creating a [`Connector`] using this [`DriverConnector`] implementation.
+    ///
+    /// Drivers may use this to instantiate their [`DriverConnector`] object.
+    fn new(device: &Device<Self::Driver>, args: Self::Args) -> impl PinInit<Self, Error>;
+}
+
+/// The generated C vtable for a [`DriverConnector`].
+///
+/// This type is created internally by DRM.
+pub struct DriverConnectorOps {
+    funcs: bindings::drm_connector_funcs,
+    helper_funcs: bindings::drm_connector_helper_funcs,
+}
+
+/// The main interface for a [`struct drm_connector`].
+///
+/// This type is the main interface for dealing with DRM connectors. In addition, it also allows
+/// immutable access to whatever private data is contained within an implementor's
+/// [`DriverConnector`] 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.
+/// - `connector` 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_connector`].
+/// - The atomic state for this type can always be assumed to be of type
+///   [`ConnectorState<T::State>`].
+///
+/// [`struct drm_connector`]: srctree/include/drm/drm_connector.h
+/// [`drm_atomic_helper_commit_hw_done`]: srctree/include/drm/drm_atomic_helper.h
+#[repr(C)]
+#[pin_data]
+pub struct Connector<T: DriverConnector> {
+    connector: Opaque<bindings::drm_connector>,
+    #[pin]
+    inner: T,
+    #[pin]
+    _p: PhantomPinned
+}
+
+impl<T: DriverConnector> Sealed for Connector<T> { }
+
+// SAFETY: DRM expects this struct to be zero-initialized
+unsafe impl Zeroable for bindings::drm_connector { }
+
+impl<T: DriverConnector> Deref for Connector<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl<T: DriverConnector> Connector<T> {
+    /// Construct a new [`Connector`].
+    ///
+    /// A driver may use this to create new [`Connector`] objects.
+    ///
+    /// TODO: Add a way to handle creating connectors after device registration. Also, that's why we
+    /// don't ask for a UnregisteredKms device here.
+    ///
+    /// [`Kms::create_objects`]: kernel::drm::kms::Kms::create_objects
+    pub fn new(
+        dev: &Device<T::Driver>,
+        type_: u32,
+        args: T::Args,
+    ) -> Result<ARef<Self>> {
+        let new: Pin<Box<Self>> = Box::try_pin_init(
+            try_pin_init!(Self {
+                connector: Opaque::new(bindings::drm_connector {
+                    helper_private: &T::OPS.helper_funcs,
+                    ..Default::default()
+                }),
+                inner <- T::new(dev, args),
+                _p: PhantomPinned
+            }),
+            GFP_KERNEL
+        )?;
+
+        // SAFETY: FFI call with no special safety requirements
+        to_result(unsafe {
+            bindings::drm_connector_init(
+                dev.as_raw(),
+                new.as_raw(),
+                &T::OPS.funcs,
+                type_ as i32
+            )
+        })?;
+
+        // Convert the connector into an ARef so the caller has proper ownership over a refcount to
+        // it. Also, the Box we consume here will be reconstructed in connector_destroy_callback()
+        // once the connector's refcount drops to zero.
+        // SAFETY: We currently hold ownership of the Box containing the connector and it's
+        // refcount. As well, this operation will not move the contents of the Box.
+        Ok(unsafe {
+            ARef::from_raw(NonNull::new_unchecked(Box::into_raw(Pin::into_inner_unchecked(new))))
+        })
+    }
+}
+
+/// A trait implemented by any type that acts as a [`struct drm_connector`] interface.
+///
+/// This is implemented internally by DRM.
+///
+/// [`struct drm_connector`]: srctree/include/drm/drm_connector.h
+pub trait AsRawConnector: RcModeObject {
+    /// The parent [`Driver`] for this [`Connector`] interface
+    ///
+    /// TODO: get rid of this
+    type Driver: KmsDriver;
+
+    /// The type this connector interface returns for its atomic state
+    type State: FromRawConnectorState;
+
+    /// Return the raw [`struct drm_connector`] for this DRM connector.
+    ///
+    /// Drivers should never use this directly
+    ///
+    /// [`struct drm_Connector`]: srctree/include/drm/drm_connector.h
+    fn as_raw(&self) -> *mut bindings::drm_connector;
+
+    /// Convert a raw `bindings::drm_connector` 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_connector) -> &'a Self;
+}
+
+// SAFETY: Our connector interfaces are guaranteed to be thread-safe
+unsafe impl<T: DriverConnector> Send for Connector<T> {}
+
+// SAFETY: Our connector interfaces are guaranteed to be thread-safe
+unsafe impl<T: DriverConnector> Sync for Connector<T> {}
+
+impl<T: DriverConnector> ModeObject for Connector<T> {
+    type Driver = T::Driver;
+
+    fn drm_dev(&self) -> &Device<Self::Driver> {
+        // SAFETY: The parent device for a DRM connector will never outlive the connector, and this
+        // pointer is invariant through the lifetime of the connector
+        unsafe { Device::borrow((*self.as_raw()).dev) }
+    }
+
+    fn raw_mode_obj(&self) -> *mut bindings::drm_mode_object {
+        // SAFETY: We don't expose DRM connectors to users before `base` is initialized
+        unsafe { &mut (*self.as_raw()).base }
+    }
+}
+
+// SAFETY: DRM connectors are refcounted mode objects
+unsafe impl<T: DriverConnector> RcModeObject for Connector<T> {}
+
+impl<T: DriverConnector> AsRawConnector for Connector<T> {
+    type Driver = T::Driver;
+    type State = ConnectorState<T::State>;
+
+    fn as_raw(&self) -> *mut bindings::drm_connector {
+        self.connector.get()
+    }
+
+    unsafe fn from_raw<'a>(ptr: *mut bindings::drm_connector) -> &'a Self {
+        // SAFETY: Our data layout starts with `bindings::drm_connector`
+        unsafe { &*ptr.cast() }
+    }
+}
+
+unsafe extern "C" fn connector_destroy_callback<T: DriverConnector>(
+    connector: *mut bindings::drm_connector,
+) {
+    // SAFETY: DRM guarantees that `connector` points to a valid initialized `drm_connector`.
+    unsafe {
+        bindings::drm_connector_unregister(connector);
+        bindings::drm_connector_cleanup(connector);
+    };
+
+    // SAFETY:
+    // * We originally created the connector in a `Box`
+    // * We are guaranteed to hold the last remaining reference to this connector
+    // * This cast is safe via `DriverConnector`s type invariants.
+    drop(unsafe { Box::from_raw(connector as *mut Connector<T>) });
+}
+
+// SAFETY: DRM expects this struct to be zero-initialized
+unsafe impl Zeroable for bindings::drm_connector_state {}
+
+/// A trait implemented by any type which can produce a reference to a [`struct drm_connector_state`].
+///
+/// This is implemented internally by DRM.
+///
+/// [`struct drm_connector_state`]: srctree/include/drm/drm_connector.h
+pub trait AsRawConnectorState: private::AsRawConnectorState {
+    /// The type that represents this connector state's DRM connector.
+    type Connector: AsRawConnector;
+}
+
+pub(super) mod private {
+    use super::*;
+
+    /// Trait for retrieving references to the base connector state contained within any connector
+    /// state compatible type
+    #[doc(hidden)]
+    pub trait AsRawConnectorState {
+        /// Return an immutable reference to the raw connector state.
+        fn as_raw(&self) -> &bindings::drm_connector_state;
+
+        /// Get a mutable reference to the raw [`struct drm_connector_state`] contained within this
+        /// type.
+        ///
+        ///
+        /// # Safety
+        ///
+        /// The caller promises this mutable reference will not be used to modify any contents of
+        /// [`struct drm_connector_state`] which DRM would consider to be static - like the
+        /// backpointer to the DRM connector that owns this state. This also means the mutable
+        /// reference should never be exposed outside of this crate.
+        ///
+        /// [`struct drm_connector_state`]: srctree/include/drm/drm_connector.h
+        unsafe fn as_raw_mut(&mut self) -> &mut bindings::drm_connector_state;
+    }
+}
+
+pub(super) use private::AsRawConnectorState as AsRawConnectorStatePrivate;
+
+/// A trait implemented for any type which can be constructed directly from a
+/// [`struct drm_connector_state`] pointer.
+///
+/// This is implemented internally by DRM.
+///
+/// [`struct drm_connector_state`]: srctree/include/drm/drm_connector.h
+pub trait FromRawConnectorState: AsRawConnectorState {
+    /// Get an immutable reference to this type from the given raw [`struct drm_connector_state`]
+    /// pointer
+    ///
+    /// # Safety
+    ///
+    /// The caller guarantees `ptr` is contained within a valid instance of `Self`
+    ///
+    /// [`struct drm_connector_state`]: srctree/include/drm/drm_connector.h
+    unsafe fn from_raw<'a>(ptr: *const bindings::drm_connector_state) -> &'a Self;
+
+    /// Get a mutable reference to this type from the given raw [`struct drm_connector_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.
+    ///
+    /// [`struct drm_connector_state`]: srctree/include/drm/drm_connector.h
+    unsafe fn from_raw_mut<'a>(ptr: *mut bindings::drm_connector_state) -> &'a mut Self;
+}
+
+/// The main interface for a [`struct drm_connector_state`].
+///
+/// This type is the main interface for dealing with the atomic state of DRM connectors. In
+/// addition, it allows access to whatever private data is contained within an implementor's
+/// [`DriverConnectorState`] 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, `connector` 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_connector_state`].
+/// - The connector for this atomic state can always be assumed to be of type
+///   [`Connector<T::Connector>`].
+///
+/// [`struct drm_connector_state`]: srctree/include/drm/drm_connector.h
+/// [`drm_atomic_helper_commit_hw_done`]: srctree/include/drm/drm_atomic_helper.h
+#[derive(Default)]
+#[repr(C)]
+pub struct ConnectorState<T: DriverConnectorState> {
+    state: bindings::drm_connector_state,
+    inner: T,
+}
+
+/// The main trait for implementing the [`struct drm_connector_state`] API for a [`Connector`].
+///
+/// A driver may store driver-private data within the implementor's type, which will be available
+/// when using a full typed [`ConnectorState`] object.
+///
+/// # Invariants
+///
+/// - Any C FFI callbacks generated using this trait are guaranteed that passed-in
+///   [`struct drm_connector`] pointers are contained within a [`Connector<Self::Connector>`].
+/// - Any C FFI callbacks generated using this trait are guaranteed that passed-in
+///   [`struct drm_connector_state`] pointers are contained within a [`ConnectorState<Self>`].
+///
+/// [`struct drm_connector`]: srctree/include/drm_connector.h
+/// [`struct drm_connector_state`]: srctree/include/drm_connector.h
+pub trait DriverConnectorState: Clone + Default + Sized {
+    /// The parent [`DriverConnector`].
+    type Connector: DriverConnector;
+}
+
+impl<T: DriverConnectorState> Sealed for ConnectorState<T> {}
+
+impl<T: DriverConnectorState> AsRawConnectorState for ConnectorState<T> {
+    type Connector = Connector<T::Connector>;
+}
+
+impl<T: DriverConnectorState> private::AsRawConnectorState for ConnectorState<T> {
+    fn as_raw(&self) -> &bindings::drm_connector_state {
+        &self.state
+    }
+
+    unsafe fn as_raw_mut(&mut self) -> &mut bindings::drm_connector_state {
+        &mut self.state
+    }
+}
+
+impl<T: DriverConnectorState> FromRawConnectorState for ConnectorState<T> {
+    unsafe fn from_raw<'a>(ptr: *const bindings::drm_connector_state) -> &'a Self {
+        // SAFETY: Our data layout starts with `bindings::drm_connector_state`
+        unsafe { &*ptr.cast() }
+    }
+
+    unsafe fn from_raw_mut<'a>(ptr: *mut bindings::drm_connector_state) -> &'a mut Self {
+        // SAFETY: Our data layout starts with `bindings::drm_connector_state`
+        unsafe { &mut *ptr.cast() }
+    }
+}
+
+unsafe extern "C" fn atomic_duplicate_state_callback<T: DriverConnectorState>(
+    connector: *mut bindings::drm_connector
+) -> *mut bindings::drm_connector_state
+{
+    // SAFETY: DRM guarantees that `connector` points to a valid initialized `drm_connector`.
+    let state = unsafe { (*connector).state };
+    if state.is_null() {
+        return null_mut();
+    }
+
+    // SAFETY:
+    // - We just verified that `state` is non-null
+    // * This cast is guaranteed to be safe via our type invariants.
+    let state = unsafe { ConnectorState::<T>::from_raw(state) };
+
+    let new = Box::try_init(
+        try_init!(ConnectorState::<T> {
+            state: bindings::drm_connector_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_connector_duplicate_state(connector, new.as_raw_mut())
+        };
+
+        Box::into_raw(new).cast()
+    } else {
+        null_mut()
+    }
+}
+
+unsafe extern "C" fn atomic_destroy_state_callback<T: DriverConnectorState>(
+    _connector: *mut bindings::drm_connector,
+    connector_state: *mut bindings::drm_connector_state
+) {
+    // SAFETY: DRM guarantees that `state` points to a valid instance of `drm_connector_state`
+    unsafe { bindings::__drm_atomic_helper_connector_destroy_state(connector_state) };
+
+    // SAFETY:
+    // * DRM guarantees we are the only one with access to this `drm_connector_state`
+    // * This cast is safe via our type invariants.
+    drop(unsafe { Box::from_raw(connector_state.cast::<ConnectorState<T>>()) });
+}
+
+unsafe extern "C" fn connector_reset_callback<T: DriverConnectorState>(
+    connector: *mut bindings::drm_connector,
+) {
+    // SAFETY: DRM guarantees that `state` points to a valid instance of `drm_connector_state`
+    let state = unsafe { (*connector).state };
+    if !state.is_null() {
+        // SAFETY:
+        // * We're guaranteed `connector` is `Connector<T>` via type invariants
+        // * We're guaranteed `state` is `ConnectorState<T>` via type invariants.
+        unsafe { atomic_destroy_state_callback::<T>(connector, state) }
+
+        // SAFETY: No special requirements here, DRM expects this to be NULL
+        unsafe { (*connector).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(ConnectorState::<T>::default(), GFP_KERNEL).expect("Blame the API, sorry!");
+
+    // DRM takes ownership of the state from here, resets it, and then assigns it to the connector
+    // SAFETY:
+    // - DRM guarantees that `connector` points to a valid instance of `drm_connector`.
+    // - The cast to `drm_connector_state` is safe via `ConnectorState`s type invariants.
+    unsafe {
+        bindings::__drm_atomic_helper_connector_reset(connector, Box::into_raw(new).cast())
+    };
+}
-- 
2.46.1

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