* [PATCH v3 1/3] rust/drm: Introduce DeviceContext
2026-01-22 22:46 [PATCH v3 0/3] Introduce DeviceContext Lyude Paul
@ 2026-01-22 22:46 ` Lyude Paul
2026-01-23 1:41 ` Daniel Almeida
2026-01-23 17:09 ` Danilo Krummrich
2026-01-22 22:46 ` [PATCH v3 2/3] rust/drm: Don't setup private driver data until registration Lyude Paul
2026-01-22 22:46 ` [PATCH v3 3/3] rust/drm/gem: Use DeviceContext with GEM objects Lyude Paul
2 siblings, 2 replies; 10+ messages in thread
From: Lyude Paul @ 2026-01-22 22:46 UTC (permalink / raw)
To: linux-kernel, dri-devel, rust-for-linux, Danilo Krummrich
Cc: nouveau, Miguel Ojeda, Simona Vetter, Alice Ryhl, Shankari Anand,
David Airlie, Benno Lossin, Asahi Lina, Daniel Almeida,
Lyude Paul
One of the tricky things about DRM bindings in Rust is the fact that
initialization of a DRM device is a multi-step process. It's quite normal
for a device driver to start making use of its DRM device for tasks like
creating GEM objects before userspace registration happens. This is an
issue in rust though, since prior to userspace registration the device is
only partly initialized. This means there's a plethora of DRM device
operations we can't yet expose without opening up the door to UB if the DRM
device in question isn't yet registered.
Additionally, this isn't something we can reliably check at runtime. And
even if we could, performing an operation which requires the device be
registered when the device isn't actually registered is a programmer bug,
meaning there's no real way to gracefully handle such a mistake at runtime.
And even if that wasn't the case, it would be horrendously annoying and
noisy to have to check if a device is registered constantly throughout a
driver.
In order to solve this, we first take inspiration from
`kernel::device::DeviceContext` and introduce `kernel::drm::DeviceContext`.
This provides us with a ZST type that we can generalize over to represent
contexts where a device is known to have been registered with userspace at
some point in time (`Registered`), along with contexts where we can't make
such a guarantee (`Uninit`).
It's important to note we intentionally do not provide a `DeviceContext`
which represents an unregistered device. This is because there's no
reasonable way to guarantee that a device with long-living references to
itself will not be registered eventually with userspace. Instead, we
provide a new-type for this: `UnregisteredDevice` which can
provide a guarantee that the `Device` has never been registered with
userspace. To ensure this, we modify `Registration` so that creating a new
`Registration` requires passing ownership of an `UnregisteredDevice`.
Signed-off-by: Lyude Paul <lyude@redhat.com>
---
V2:
* Make sure that `UnregisteredDevice` is not thread-safe (since DRM device
initialization is also not thread-safe)
* Rename from AnyCtx to Uninit, I think this name actually makes a bit more
sense.
* Change assume_registered() to assume_ctx()
Since it looks like in some situations, we'll want to update the
DeviceContext of a object to the latest DeviceContext we know the Device
to be in.
* Rename Init to Uninit
When we eventually add KMS support, we're going to have 3 different
DeviceContexts - Uninit, Init, Registered. Additionally, aside from not
being registered there are a number of portions of the rest of the Device
which also aren't usable before at least the Init context - so the naming
of Uninit makes this a little clearer.
* s/DeviceContext/DeviceContext/
For consistency with the rest of the kernel
* Drop as_ref::<Device<T, Uninit>>() for now since I don't actually think
we need this quite yet
V3:
* Get rid of drm_dev_ctx!, as we don't actually need to implement Send or
Sync ourselves
* Remove mention of C function in drm::device::Registration rustdoc
* Add more documentation to the DeviceContext trait, go into detail about
the various setup phases and such.
* Add missing period to comment in `UnregisteredDevice::new()`.
drivers/gpu/drm/nova/driver.rs | 8 +-
drivers/gpu/drm/tyr/driver.rs | 10 +-
rust/kernel/drm/device.rs | 179 +++++++++++++++++++++++++++------
rust/kernel/drm/driver.rs | 38 +++++--
rust/kernel/drm/mod.rs | 4 +
5 files changed, 193 insertions(+), 46 deletions(-)
diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs
index b1af0a099551d..99d6841b69cbc 100644
--- a/drivers/gpu/drm/nova/driver.rs
+++ b/drivers/gpu/drm/nova/driver.rs
@@ -21,7 +21,7 @@ pub(crate) struct NovaDriver {
}
/// Convienence type alias for the DRM device type for this driver
-pub(crate) type NovaDevice = drm::Device<NovaDriver>;
+pub(crate) type NovaDevice<Ctx = drm::Registered> = drm::Device<NovaDriver, Ctx>;
#[pin_data]
pub(crate) struct NovaData {
@@ -56,10 +56,10 @@ impl auxiliary::Driver for NovaDriver {
fn probe(adev: &auxiliary::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<Self, Error> {
let data = try_pin_init!(NovaData { adev: adev.into() });
- let drm = drm::Device::<Self>::new(adev.as_ref(), data)?;
- drm::Registration::new_foreign_owned(&drm, adev.as_ref(), 0)?;
+ let drm = drm::UnregisteredDevice::<Self>::new(adev.as_ref(), data)?;
+ let drm = drm::Registration::new_foreign_owned(drm, adev.as_ref(), 0)?;
- Ok(Self { drm })
+ Ok(Self { drm: drm.into() })
}
}
diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs
index 2a45d02888253..ac265a60f5667 100644
--- a/drivers/gpu/drm/tyr/driver.rs
+++ b/drivers/gpu/drm/tyr/driver.rs
@@ -30,7 +30,7 @@
pub(crate) type IoMem = kernel::io::mem::IoMem<SZ_2M>;
/// Convenience type alias for the DRM device type for this driver.
-pub(crate) type TyrDevice = drm::Device<TyrDriver>;
+pub(crate) type TyrDevice<Ctx = drm::Registered> = drm::Device<TyrDriver, Ctx>;
#[pin_data(PinnedDrop)]
pub(crate) struct TyrDriver {
@@ -133,10 +133,12 @@ fn probe(
gpu_info,
});
- let tdev: ARef<TyrDevice> = drm::Device::new(pdev.as_ref(), data)?;
- drm::driver::Registration::new_foreign_owned(&tdev, pdev.as_ref(), 0)?;
+ let tdev = drm::UnregisteredDevice::<Self>::new(pdev.as_ref(), data)?;
+ let tdev = drm::driver::Registration::new_foreign_owned(tdev, pdev.as_ref(), 0)?;
- let driver = TyrDriver { device: tdev };
+ let driver = TyrDriver {
+ device: tdev.into(),
+ };
// We need this to be dev_info!() because dev_dbg!() does not work at
// all in Rust for now, and we need to see whether probe succeeded.
diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
index 30116d78cabe0..f529bc7fc4032 100644
--- a/rust/kernel/drm/device.rs
+++ b/rust/kernel/drm/device.rs
@@ -10,7 +10,8 @@
device, //
drm::{
self,
- driver::AllocImpl, //
+ driver::AllocImpl,
+ private::Sealed, //
},
error::from_err_ptr,
prelude::*,
@@ -18,10 +19,14 @@
ARef,
AlwaysRefCounted, //
},
- types::Opaque,
+ types::{
+ NotThreadSafe,
+ Opaque, //
+ },
};
use core::{
alloc::Layout,
+ marker::PhantomData,
mem,
ops::Deref,
ptr::{
@@ -61,26 +66,98 @@ macro_rules! drm_legacy_fields {
}
}
-/// A typed DRM device with a specific `drm::Driver` implementation.
+/// A trait implemented by all possible contexts a [`Device`] can be used in.
+///
+/// Setting up a new [`Device`] is a multi-stage process. Each step of the process that a user
+/// interacts with in Rust has a respective [`DeviceContext`] typestate. For example,
+/// `Device<T, Registered>` would be a [`Device`] that reached the [`Registered`] [`DeviceContext`].
+///
+/// Each stage of this process is described below:
///
-/// The device is always reference-counted.
+/// ```text
+/// 1 2 3
+/// +--------------+ +------------------+ +-----------------------+
+/// |Device created| → |Device initialized| → |Registered w/ userspace|
+/// +--------------+ +------------------+ +-----------------------+
+/// (Uninit) (Registered)
+/// ```
+///
+/// 1. The [`Device`] is in the [`Uninit`] context and is not guaranteed to be initialized or
+/// registered with userspace. Only a limited subset of DRM core functionality is available.
+/// 2. The [`Device`] is guaranteed to be fully initialized, but is not guaranteed to be registered
+/// with userspace. All DRM core functionality which doesn't interact with userspace is
+/// available. We currently don't have a context for representing this.
+/// 3. The [`Device`] is guaranteed to be fully initialized, and is guaranteed to have been
+/// registered with userspace at some point - thus putting it in the [`Registered`] context.
+///
+/// An important caveat of [`DeviceContext`] which must be kept in mind: when used as a typestate
+/// for a reference type, it can only guarantee that a [`Device`] reached a particular stage in the
+/// initialization process _at the time the reference was taken_. No guarantee is made in regards to
+/// what stage of the process the [`Device`] is currently in. This means for instance that a
+/// `&Device<T, Uninit>` may actually be registered with userspace, it just wasn't known to be
+/// registered at the time the reference was taken.
+pub trait DeviceContext: Sealed + Send + Sync {}
+
+/// The [`DeviceContext`] of a [`Device`] that was registered with userspace at some point.
+///
+/// This represents a [`Device`] which is guaranteed to have been registered with userspace at
+/// some point in time. Such a DRM device is guaranteed to have been fully-initialized.
+///
+/// Note: A device in this context is not guaranteed to remain registered with userspace for its
+/// entire lifetime, as this is impossible to guarantee at compile-time.
///
/// # Invariants
///
-/// `self.dev` is a valid instance of a `struct device`.
-#[repr(C)]
-pub struct Device<T: drm::Driver> {
- dev: Opaque<bindings::drm_device>,
- data: T::Data,
+/// A [`Device`] in this [`DeviceContext`] is guaranteed to have been registered with userspace
+/// at some point in time.
+pub struct Registered;
+
+impl Sealed for Registered {}
+impl DeviceContext for Registered {}
+
+/// The [`DeviceContext`] of a [`Device`] that may be unregistered and partly uninitialized.
+///
+/// A [`Device`] in this context is only guaranteed to be partly initialized, and may or may not
+/// be registered with userspace. Thus operations which depend on the [`Device`] being fully
+/// initialized, or which depend on the [`Device`] being registered with userspace are not
+/// available through this [`DeviceContext`].
+///
+/// A [`Device`] in this context can be used to create a
+/// [`Registration`](drm::driver::Registration).
+pub struct Uninit;
+
+impl Sealed for Uninit {}
+impl DeviceContext for Uninit {}
+
+/// A [`Device`] which is known at compile-time to be unregistered with userspace.
+///
+/// This type allows performing operations which are only safe to do before userspace registration,
+/// and can be used to create a [`Registration`](drm::driver::Registration) once the driver is ready
+/// to register the device with userspace.
+///
+/// Since DRM device initialization must be single-threaded, this object is not thread-safe.
+///
+/// # Invariants
+///
+/// The device in `self.0` is guaranteed to be a newly created [`Device`] that has not yet been
+/// registered with userspace until this type is dropped.
+pub struct UnregisteredDevice<T: drm::Driver>(ARef<Device<T, Uninit>>, NotThreadSafe);
+
+impl<T: drm::Driver> Deref for UnregisteredDevice<T> {
+ type Target = Device<T, Uninit>;
+
+ fn deref(&self) -> &Self::Target {
+ &self.0
+ }
}
-impl<T: drm::Driver> Device<T> {
+impl<T: drm::Driver> UnregisteredDevice<T> {
const VTABLE: bindings::drm_driver = drm_legacy_fields! {
load: None,
open: Some(drm::File::<T::File>::open_callback),
postclose: Some(drm::File::<T::File>::postclose_callback),
unload: None,
- release: Some(Self::release),
+ release: Some(Device::<T>::release),
master_set: None,
master_drop: None,
debugfs_init: None,
@@ -108,8 +185,10 @@ impl<T: drm::Driver> Device<T> {
const GEM_FOPS: bindings::file_operations = drm::gem::create_fops();
- /// Create a new `drm::Device` for a `drm::Driver`.
- pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<ARef<Self>> {
+ /// Create a new `UnregisteredDevice` for a `drm::Driver`.
+ ///
+ /// This can be used to create a [`Registration`](kernel::drm::Registration).
+ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<Self> {
// `__drm_dev_alloc` uses `kmalloc()` to allocate memory, hence ensure a `kmalloc()`
// compatible `Layout`.
let layout = Kmalloc::aligned_layout(Layout::new::<Self>());
@@ -117,12 +196,12 @@ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<A
// SAFETY:
// - `VTABLE`, as a `const` is pinned to the read-only section of the compilation,
// - `dev` is valid by its type invarants,
- let raw_drm: *mut Self = unsafe {
+ let raw_drm: *mut Device<T, Uninit> = unsafe {
bindings::__drm_dev_alloc(
dev.as_raw(),
&Self::VTABLE,
layout.size(),
- mem::offset_of!(Self, dev),
+ mem::offset_of!(Device<T, Uninit>, dev),
)
}
.cast();
@@ -137,7 +216,7 @@ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<A
unsafe { data.__pinned_init(raw_data) }.inspect_err(|_| {
// SAFETY: `raw_drm` is a valid pointer to `Self`, given that `__drm_dev_alloc` was
// successful.
- let drm_dev = unsafe { Self::into_drm_device(raw_drm) };
+ let drm_dev = unsafe { Device::into_drm_device(raw_drm) };
// SAFETY: `__drm_dev_alloc()` was successful, hence `drm_dev` must be valid and the
// refcount must be non-zero.
@@ -146,9 +225,40 @@ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<A
// SAFETY: The reference count is one, and now we take ownership of that reference as a
// `drm::Device`.
- Ok(unsafe { ARef::from_raw(raw_drm) })
+ // INVARIANT: We just created the device above, but have yet to call `drm_dev_register`.
+ // `Self` cannot be copied or sent to another thread - ensuring that `drm_dev_register`
+ // won't be called during its lifetime and that the device is unregistered.
+ Ok(Self(unsafe { ARef::from_raw(raw_drm) }, NotThreadSafe))
}
+}
+
+/// A typed DRM device with a specific [`drm::Driver`] implementation and [`DeviceContext`].
+///
+/// Since DRM devices can be used before being fully initialized and registered with userspace, `C`
+/// represents the furthest [`DeviceContext`] we can guarantee that this [`Device`] has reached.
+///
+/// Keep in mind: this means that an unregistered device can still have the registration state
+/// [`Registered`] as long as it was registered with userspace once in the past, and that the
+/// behavior of such a device is still well-defined. In such a situation, the behavior of any
+/// functions which interact with userspace will simply be no-ops. Additionally, a device with the
+/// registration state [`Uninit`] simply does not have a guaranteed registration state at compile
+/// time, and could be either registered or unregistered. Since there is no way to guarantee a
+/// long-lived reference to an unregistered device would remain unregistered, we do not provide a
+/// [`DeviceContext`] for this.
+///
+/// # Invariants
+///
+/// * `self.dev` is a valid instance of a `struct device`.
+/// * The data layout of `Self` remains the same across all implementations of `C`.
+/// * Any invariants for `C` also apply.
+#[repr(C)]
+pub struct Device<T: drm::Driver, C: DeviceContext = Registered> {
+ dev: Opaque<bindings::drm_device>,
+ data: T::Data,
+ _ctx: PhantomData<C>,
+}
+impl<T: drm::Driver, C: DeviceContext> Device<T, C> {
pub(crate) fn as_raw(&self) -> *mut bindings::drm_device {
self.dev.get()
}
@@ -174,13 +284,13 @@ unsafe fn into_drm_device(ptr: NonNull<Self>) -> *mut bindings::drm_device {
///
/// # Safety
///
- /// Callers must ensure that `ptr` is valid, non-null, and has a non-zero reference count,
- /// i.e. it must be ensured that the reference count of the C `struct drm_device` `ptr` points
- /// to can't drop to zero, for the duration of this function call and the entire duration when
- /// the returned reference exists.
- ///
- /// Additionally, callers must ensure that the `struct device`, `ptr` is pointing to, is
- /// embedded in `Self`.
+ /// * Callers must ensure that `ptr` is valid, non-null, and has a non-zero reference count,
+ /// i.e. it must be ensured that the reference count of the C `struct drm_device` `ptr` points
+ /// to can't drop to zero, for the duration of this function call and the entire duration when
+ /// the returned reference exists.
+ /// * Additionally, callers must ensure that the `struct device`, `ptr` is pointing to, is
+ /// embedded in `Self`.
+ /// * Callers promise that any type invariants of `C` will be upheld.
#[doc(hidden)]
pub unsafe fn from_raw<'a>(ptr: *const bindings::drm_device) -> &'a Self {
// SAFETY: By the safety requirements of this function `ptr` is a valid pointer to a
@@ -200,9 +310,20 @@ extern "C" fn release(ptr: *mut bindings::drm_device) {
// - `this` is valid for dropping.
unsafe { core::ptr::drop_in_place(this) };
}
+
+ /// Change the [`DeviceContext`] for a [`Device`].
+ ///
+ /// # Safety
+ ///
+ /// The caller promises that `self` fulfills all of the guarantees provided by the given
+ /// [`DeviceContext`].
+ pub(crate) unsafe fn assume_ctx<NewCtx: DeviceContext>(&self) -> &Device<T, NewCtx> {
+ // SAFETY: The data layout is identical via our type invariants.
+ unsafe { mem::transmute(self) }
+ }
}
-impl<T: drm::Driver> Deref for Device<T> {
+impl<T: drm::Driver, C: DeviceContext> Deref for Device<T, C> {
type Target = T::Data;
fn deref(&self) -> &Self::Target {
@@ -212,7 +333,7 @@ fn deref(&self) -> &Self::Target {
// SAFETY: DRM device objects are always reference counted and the get/put functions
// satisfy the requirements.
-unsafe impl<T: drm::Driver> AlwaysRefCounted for Device<T> {
+unsafe impl<T: drm::Driver, C: DeviceContext> AlwaysRefCounted for Device<T, C> {
fn inc_ref(&self) {
// SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
unsafe { bindings::drm_dev_get(self.as_raw()) };
@@ -227,7 +348,7 @@ unsafe fn dec_ref(obj: NonNull<Self>) {
}
}
-impl<T: drm::Driver> AsRef<device::Device> for Device<T> {
+impl<T: drm::Driver, C: DeviceContext> AsRef<device::Device> for Device<T, C> {
fn as_ref(&self) -> &device::Device {
// SAFETY: `bindings::drm_device::dev` is valid as long as the DRM device itself is valid,
// which is guaranteed by the type invariant.
@@ -236,8 +357,8 @@ fn as_ref(&self) -> &device::Device {
}
// SAFETY: A `drm::Device` can be released from any thread.
-unsafe impl<T: drm::Driver> Send for Device<T> {}
+unsafe impl<T: drm::Driver, C: DeviceContext> Send for Device<T, C> {}
// SAFETY: A `drm::Device` can be shared among threads because all immutable methods are protected
// by the synchronization in `struct drm_device`.
-unsafe impl<T: drm::Driver> Sync for Device<T> {}
+unsafe impl<T: drm::Driver, C: DeviceContext> Sync for Device<T, C> {}
diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
index 5233bdebc9fcd..da9f1bfef1f14 100644
--- a/rust/kernel/drm/driver.rs
+++ b/rust/kernel/drm/driver.rs
@@ -13,6 +13,10 @@
prelude::*,
sync::aref::ARef, //
};
+use core::{
+ mem,
+ ptr::NonNull, //
+};
/// Driver use the GEM memory manager. This should be set for all modern drivers.
pub(crate) const FEAT_GEM: u32 = bindings::drm_driver_feature_DRIVER_GEM;
@@ -123,31 +127,47 @@ pub trait Driver {
pub struct Registration<T: Driver>(ARef<drm::Device<T>>);
impl<T: Driver> Registration<T> {
- fn new(drm: &drm::Device<T>, flags: usize) -> Result<Self> {
+ fn new(drm: drm::UnregisteredDevice<T>, flags: usize) -> Result<Self> {
// SAFETY: `drm.as_raw()` is valid by the invariants of `drm::Device`.
to_result(unsafe { bindings::drm_dev_register(drm.as_raw(), flags) })?;
- Ok(Self(drm.into()))
+ // SAFETY: We just called `drm_dev_register` above
+ let new = NonNull::from(unsafe { drm.assume_ctx() });
+
+ // Leak the ARef from UnregisteredDevice in preparation for transferring its ownership.
+ mem::forget(drm);
+
+ // SAFETY: `drm`'s `Drop` constructor was never called, ensuring that there remains at least
+ // one reference to the device - which we take ownership over here.
+ let new = unsafe { ARef::from_raw(new) };
+
+ Ok(Self(new))
}
- /// Registers a new [`Device`](drm::Device) with userspace.
+ /// Registers a new [`UnregisteredDevice`](drm::UnregisteredDevice) with userspace.
///
/// Ownership of the [`Registration`] object is passed to [`devres::register`].
- pub fn new_foreign_owned(
- drm: &drm::Device<T>,
- dev: &device::Device<device::Bound>,
+ pub fn new_foreign_owned<'a>(
+ drm: drm::UnregisteredDevice<T>,
+ dev: &'a device::Device<device::Bound>,
flags: usize,
- ) -> Result
+ ) -> Result<&'a drm::Device<T>>
where
T: 'static,
{
- if drm.as_ref().as_raw() != dev.as_raw() {
+ let this_dev: &device::Device = drm.as_ref();
+ if this_dev.as_raw() != dev.as_raw() {
return Err(EINVAL);
}
let reg = Registration::<T>::new(drm, flags)?;
+ let drm = NonNull::from(reg.device());
+
+ devres::register(dev, reg, GFP_KERNEL)?;
- devres::register(dev, reg, GFP_KERNEL)
+ // SAFETY: Since `reg` was passed to devres::register(), the device now owns the lifetime
+ // of the DRM registration - ensuring that this references lives for at least as long as 'a.
+ Ok(unsafe { drm.as_ref() })
}
/// Returns a reference to the `Device` instance for this registration.
diff --git a/rust/kernel/drm/mod.rs b/rust/kernel/drm/mod.rs
index 1b82b6945edf2..64a43cb0fe57c 100644
--- a/rust/kernel/drm/mod.rs
+++ b/rust/kernel/drm/mod.rs
@@ -9,6 +9,10 @@
pub mod ioctl;
pub use self::device::Device;
+pub use self::device::DeviceContext;
+pub use self::device::Registered;
+pub use self::device::Uninit;
+pub use self::device::UnregisteredDevice;
pub use self::driver::Driver;
pub use self::driver::DriverInfo;
pub use self::driver::Registration;
--
2.52.0
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH v3 1/3] rust/drm: Introduce DeviceContext
2026-01-22 22:46 ` [PATCH v3 1/3] rust/drm: " Lyude Paul
@ 2026-01-23 1:41 ` Daniel Almeida
2026-01-23 17:09 ` Danilo Krummrich
1 sibling, 0 replies; 10+ messages in thread
From: Daniel Almeida @ 2026-01-23 1:41 UTC (permalink / raw)
To: Lyude Paul
Cc: linux-kernel, dri-devel, rust-for-linux, Danilo Krummrich,
nouveau, Miguel Ojeda, Simona Vetter, Alice Ryhl, Shankari Anand,
David Airlie, Benno Lossin, Asahi Lina
Hi Lyude,
> On 22 Jan 2026, at 19:46, Lyude Paul <lyude@redhat.com> wrote:
>
> One of the tricky things about DRM bindings in Rust is the fact that
> initialization of a DRM device is a multi-step process. It's quite normal
> for a device driver to start making use of its DRM device for tasks like
> creating GEM objects before userspace registration happens. This is an
> issue in rust though, since prior to userspace registration the device is
> only partly initialized. This means there's a plethora of DRM device
> operations we can't yet expose without opening up the door to UB if the DRM
> device in question isn't yet registered.
>
> Additionally, this isn't something we can reliably check at runtime. And
> even if we could, performing an operation which requires the device be
> registered when the device isn't actually registered is a programmer bug,
> meaning there's no real way to gracefully handle such a mistake at runtime.
> And even if that wasn't the case, it would be horrendously annoying and
> noisy to have to check if a device is registered constantly throughout a
> driver.
>
> In order to solve this, we first take inspiration from
> `kernel::device::DeviceContext` and introduce `kernel::drm::DeviceContext`.
> This provides us with a ZST type that we can generalize over to represent
> contexts where a device is known to have been registered with userspace at
> some point in time (`Registered`), along with contexts where we can't make
> such a guarantee (`Uninit`).
>
> It's important to note we intentionally do not provide a `DeviceContext`
> which represents an unregistered device. This is because there's no
> reasonable way to guarantee that a device with long-living references to
> itself will not be registered eventually with userspace. Instead, we
> provide a new-type for this: `UnregisteredDevice` which can
> provide a guarantee that the `Device` has never been registered with
> userspace. To ensure this, we modify `Registration` so that creating a new
> `Registration` requires passing ownership of an `UnregisteredDevice`.
>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
>
> ---
> V2:
> * Make sure that `UnregisteredDevice` is not thread-safe (since DRM device
> initialization is also not thread-safe)
> * Rename from AnyCtx to Uninit, I think this name actually makes a bit more
> sense.
> * Change assume_registered() to assume_ctx()
> Since it looks like in some situations, we'll want to update the
> DeviceContext of a object to the latest DeviceContext we know the Device
> to be in.
> * Rename Init to Uninit
> When we eventually add KMS support, we're going to have 3 different
> DeviceContexts - Uninit, Init, Registered. Additionally, aside from not
> being registered there are a number of portions of the rest of the Device
> which also aren't usable before at least the Init context - so the naming
> of Uninit makes this a little clearer.
> * s/DeviceContext/DeviceContext/
> For consistency with the rest of the kernel
> * Drop as_ref::<Device<T, Uninit>>() for now since I don't actually think
> we need this quite yet
> V3:
> * Get rid of drm_dev_ctx!, as we don't actually need to implement Send or
> Sync ourselves
> * Remove mention of C function in drm::device::Registration rustdoc
> * Add more documentation to the DeviceContext trait, go into detail about
> the various setup phases and such.
> * Add missing period to comment in `UnregisteredDevice::new()`.
>
> drivers/gpu/drm/nova/driver.rs | 8 +-
> drivers/gpu/drm/tyr/driver.rs | 10 +-
> rust/kernel/drm/device.rs | 179 +++++++++++++++++++++++++++------
> rust/kernel/drm/driver.rs | 38 +++++--
> rust/kernel/drm/mod.rs | 4 +
> 5 files changed, 193 insertions(+), 46 deletions(-)
>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH v3 1/3] rust/drm: Introduce DeviceContext
2026-01-22 22:46 ` [PATCH v3 1/3] rust/drm: " Lyude Paul
2026-01-23 1:41 ` Daniel Almeida
@ 2026-01-23 17:09 ` Danilo Krummrich
1 sibling, 0 replies; 10+ messages in thread
From: Danilo Krummrich @ 2026-01-23 17:09 UTC (permalink / raw)
To: Lyude Paul
Cc: linux-kernel, dri-devel, rust-for-linux, nouveau, Miguel Ojeda,
Simona Vetter, Alice Ryhl, Shankari Anand, David Airlie,
Benno Lossin, Asahi Lina, Daniel Almeida
On Thu Jan 22, 2026 at 11:46 PM CET, Lyude Paul wrote:
> diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs
> index b1af0a099551d..99d6841b69cbc 100644
> --- a/drivers/gpu/drm/nova/driver.rs
> +++ b/drivers/gpu/drm/nova/driver.rs
> @@ -21,7 +21,7 @@ pub(crate) struct NovaDriver {
> }
>
> /// Convienence type alias for the DRM device type for this driver
> -pub(crate) type NovaDevice = drm::Device<NovaDriver>;
> +pub(crate) type NovaDevice<Ctx = drm::Registered> = drm::Device<NovaDriver, Ctx>;
Nothing for this patch (series), but I think we should get rid of this type
alias, I think it's confusing.
> +/// A typed DRM device with a specific [`drm::Driver`] implementation and [`DeviceContext`].
> +///
> +/// Since DRM devices can be used before being fully initialized and registered with userspace, `C`
> +/// represents the furthest [`DeviceContext`] we can guarantee that this [`Device`] has reached.
> +///
> +/// Keep in mind: this means that an unregistered device can still have the registration state
> +/// [`Registered`] as long as it was registered with userspace once in the past, and that the
> +/// behavior of such a device is still well-defined. In such a situation, the behavior of any
> +/// functions which interact with userspace will simply be no-ops. Additionally, a device with the
This is still not correct, the are not guaranteed to be no-ops. We can still
have callbacks from userspace after the DRM device is unregistered.
> +/// registration state [`Uninit`] simply does not have a guaranteed registration state at compile
> +/// time, and could be either registered or unregistered. Since there is no way to guarantee a
> +/// long-lived reference to an unregistered device would remain unregistered, we do not provide a
> +/// [`DeviceContext`] for this.
> +///
> +/// # Invariants
> +///
> +/// * `self.dev` is a valid instance of a `struct device`.
> +/// * The data layout of `Self` remains the same across all implementations of `C`.
> +/// * Any invariants for `C` also apply.
> +#[repr(C)]
> +pub struct Device<T: drm::Driver, C: DeviceContext = Registered> {
> + dev: Opaque<bindings::drm_device>,
> + data: T::Data,
> + _ctx: PhantomData<C>,
> +}
<snip>
> - /// Registers a new [`Device`](drm::Device) with userspace.
> + /// Registers a new [`UnregisteredDevice`](drm::UnregisteredDevice) with userspace.
> ///
> /// Ownership of the [`Registration`] object is passed to [`devres::register`].
> - pub fn new_foreign_owned(
> - drm: &drm::Device<T>,
> - dev: &device::Device<device::Bound>,
> + pub fn new_foreign_owned<'a>(
> + drm: drm::UnregisteredDevice<T>,
> + dev: &'a device::Device<device::Bound>,
> flags: usize,
> - ) -> Result
> + ) -> Result<&'a drm::Device<T>>
> where
> T: 'static,
> {
> - if drm.as_ref().as_raw() != dev.as_raw() {
> + let this_dev: &device::Device = drm.as_ref();
> + if this_dev.as_raw() != dev.as_raw() {
I still think this change is unnecessary and the name 'this_dev' is misleading,
as it actually is the parent device.
> return Err(EINVAL);
> }
>
> let reg = Registration::<T>::new(drm, flags)?;
> + let drm = NonNull::from(reg.device());
> +
> + devres::register(dev, reg, GFP_KERNEL)?;
>
> - devres::register(dev, reg, GFP_KERNEL)
> + // SAFETY: Since `reg` was passed to devres::register(), the device now owns the lifetime
> + // of the DRM registration - ensuring that this references lives for at least as long as 'a.
> + Ok(unsafe { drm.as_ref() })
> }
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH v3 2/3] rust/drm: Don't setup private driver data until registration
2026-01-22 22:46 [PATCH v3 0/3] Introduce DeviceContext Lyude Paul
2026-01-22 22:46 ` [PATCH v3 1/3] rust/drm: " Lyude Paul
@ 2026-01-22 22:46 ` Lyude Paul
2026-01-23 1:52 ` Daniel Almeida
2026-01-22 22:46 ` [PATCH v3 3/3] rust/drm/gem: Use DeviceContext with GEM objects Lyude Paul
2 siblings, 1 reply; 10+ messages in thread
From: Lyude Paul @ 2026-01-22 22:46 UTC (permalink / raw)
To: linux-kernel, dri-devel, rust-for-linux, Danilo Krummrich
Cc: nouveau, Miguel Ojeda, Simona Vetter, Alice Ryhl, Shankari Anand,
David Airlie, Benno Lossin, Asahi Lina, Daniel Almeida,
Lyude Paul
Now that we have a DeviceContext that we can use to represent whether a
Device is known to have been registered, we can make it so that drivers can
create their Devices but wait until the registration phase to assign their
private data to the Device. This is desirable as some drivers need to make
use of the DRM device early on before finalizing their private driver data.
As such, this change makes it so that the driver's private data can
currently only be accessed through Device<T, Registered> types and not
Device<T, Uninit>.
Signed-off-by: Lyude Paul <lyude@redhat.com>
---
drivers/gpu/drm/nova/driver.rs | 4 +--
drivers/gpu/drm/tyr/driver.rs | 4 +--
rust/kernel/drm/device.rs | 63 ++++++++++++++++++++--------------
rust/kernel/drm/driver.rs | 19 ++++++++--
4 files changed, 58 insertions(+), 32 deletions(-)
diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs
index 99d6841b69cbc..8cea5f68c3b04 100644
--- a/drivers/gpu/drm/nova/driver.rs
+++ b/drivers/gpu/drm/nova/driver.rs
@@ -56,8 +56,8 @@ impl auxiliary::Driver for NovaDriver {
fn probe(adev: &auxiliary::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<Self, Error> {
let data = try_pin_init!(NovaData { adev: adev.into() });
- let drm = drm::UnregisteredDevice::<Self>::new(adev.as_ref(), data)?;
- let drm = drm::Registration::new_foreign_owned(drm, adev.as_ref(), 0)?;
+ let drm = drm::UnregisteredDevice::<Self>::new(adev.as_ref())?;
+ let drm = drm::Registration::new_foreign_owned(drm, adev.as_ref(), data, 0)?;
Ok(Self { drm: drm.into() })
}
diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs
index ac265a60f5667..e73c56659ea75 100644
--- a/drivers/gpu/drm/tyr/driver.rs
+++ b/drivers/gpu/drm/tyr/driver.rs
@@ -133,8 +133,8 @@ fn probe(
gpu_info,
});
- let tdev = drm::UnregisteredDevice::<Self>::new(pdev.as_ref(), data)?;
- let tdev = drm::driver::Registration::new_foreign_owned(tdev, pdev.as_ref(), 0)?;
+ let tdev = drm::UnregisteredDevice::<Self>::new(pdev.as_ref())?;
+ let tdev = drm::driver::Registration::new_foreign_owned(tdev, pdev.as_ref(), data, 0)?;
let driver = TyrDriver {
device: tdev.into(),
diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
index f529bc7fc4032..0e81957cf8c28 100644
--- a/rust/kernel/drm/device.rs
+++ b/rust/kernel/drm/device.rs
@@ -26,13 +26,15 @@
};
use core::{
alloc::Layout,
+ cell::UnsafeCell,
marker::PhantomData,
- mem,
- ops::Deref,
- ptr::{
+ mem::{
self,
- NonNull, //
+ MaybeUninit, //
},
+ ops::Deref,
+ ptr::NonNull,
+ sync::atomic::*,
};
#[cfg(CONFIG_DRM_LEGACY)]
@@ -141,7 +143,7 @@ impl DeviceContext for Uninit {}
///
/// The device in `self.0` is guaranteed to be a newly created [`Device`] that has not yet been
/// registered with userspace until this type is dropped.
-pub struct UnregisteredDevice<T: drm::Driver>(ARef<Device<T, Uninit>>, NotThreadSafe);
+pub struct UnregisteredDevice<T: drm::Driver>(pub(crate) ARef<Device<T, Uninit>>, NotThreadSafe);
impl<T: drm::Driver> Deref for UnregisteredDevice<T> {
type Target = Device<T, Uninit>;
@@ -188,7 +190,7 @@ impl<T: drm::Driver> UnregisteredDevice<T> {
/// Create a new `UnregisteredDevice` for a `drm::Driver`.
///
/// This can be used to create a [`Registration`](kernel::drm::Registration).
- pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<Self> {
+ pub fn new(dev: &device::Device) -> Result<Self> {
// `__drm_dev_alloc` uses `kmalloc()` to allocate memory, hence ensure a `kmalloc()`
// compatible `Layout`.
let layout = Kmalloc::aligned_layout(Layout::new::<Self>());
@@ -207,22 +209,6 @@ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<S
.cast();
let raw_drm = NonNull::new(from_err_ptr(raw_drm)?).ok_or(ENOMEM)?;
- // SAFETY: `raw_drm` is a valid pointer to `Self`.
- let raw_data = unsafe { ptr::addr_of_mut!((*raw_drm.as_ptr()).data) };
-
- // SAFETY:
- // - `raw_data` is a valid pointer to uninitialized memory.
- // - `raw_data` will not move until it is dropped.
- unsafe { data.__pinned_init(raw_data) }.inspect_err(|_| {
- // SAFETY: `raw_drm` is a valid pointer to `Self`, given that `__drm_dev_alloc` was
- // successful.
- let drm_dev = unsafe { Device::into_drm_device(raw_drm) };
-
- // SAFETY: `__drm_dev_alloc()` was successful, hence `drm_dev` must be valid and the
- // refcount must be non-zero.
- unsafe { bindings::drm_dev_put(drm_dev) };
- })?;
-
// SAFETY: The reference count is one, and now we take ownership of that reference as a
// `drm::Device`.
// INVARIANT: We just created the device above, but have yet to call `drm_dev_register`.
@@ -254,7 +240,15 @@ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<S
#[repr(C)]
pub struct Device<T: drm::Driver, C: DeviceContext = Registered> {
dev: Opaque<bindings::drm_device>,
- data: T::Data,
+
+ /// Keeps track of whether we've initialized the device data yet.
+ pub(crate) data_is_init: AtomicBool,
+
+ /// The Driver's private data.
+ ///
+ /// This must only be written to from [`drm::Registration::new`].
+ pub(crate) data: UnsafeCell<MaybeUninit<T::Data>>,
+
_ctx: PhantomData<C>,
}
@@ -305,6 +299,21 @@ extern "C" fn release(ptr: *mut bindings::drm_device) {
// SAFETY: `ptr` is a valid pointer to a `struct drm_device` and embedded in `Self`.
let this = unsafe { Self::from_drm_device(ptr) };
+ {
+ // SAFETY:
+ // - Since we are in release(), we are guaranteed that no one else has access to `this`.
+ // - We confirmed above that `this` is a valid pointer to an initialized `Self`.
+ let this = unsafe { &mut *this };
+ if this.data_is_init.load(Ordering::Relaxed) {
+ // SAFETY:
+ // - Since we are in release(), we are guaranteed that no one else has access to
+ // `this`.
+ // - We checked that the data is initialized above.
+ // - We do not use `data` any point after calling this function.
+ unsafe { (&mut *this.data.get()).assume_init_drop() };
+ }
+ }
+
// SAFETY:
// - When `release` runs it is guaranteed that there is no further access to `this`.
// - `this` is valid for dropping.
@@ -323,11 +332,15 @@ pub(crate) unsafe fn assume_ctx<NewCtx: DeviceContext>(&self) -> &Device<T, NewC
}
}
-impl<T: drm::Driver, C: DeviceContext> Deref for Device<T, C> {
+impl<T: drm::Driver> Deref for Device<T, Registered> {
type Target = T::Data;
fn deref(&self) -> &Self::Target {
- &self.data
+ // SAFETY:
+ // - `data` is initialized before any `Device`s with the `Registered` context are available
+ // to the user.
+ // - `data` is only written to once in `Registration::new()`, so this read will never race.
+ unsafe { (&*self.data.get()).assume_init_ref() }
}
}
diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
index da9f1bfef1f14..a16605b407159 100644
--- a/rust/kernel/drm/driver.rs
+++ b/rust/kernel/drm/driver.rs
@@ -15,7 +15,8 @@
};
use core::{
mem,
- ptr::NonNull, //
+ ptr::NonNull,
+ sync::atomic::*, //
};
/// Driver use the GEM memory manager. This should be set for all modern drivers.
@@ -127,7 +128,18 @@ pub trait Driver {
pub struct Registration<T: Driver>(ARef<drm::Device<T>>);
impl<T: Driver> Registration<T> {
- fn new(drm: drm::UnregisteredDevice<T>, flags: usize) -> Result<Self> {
+ fn new(
+ drm: drm::UnregisteredDevice<T>,
+ data: impl PinInit<T::Data, Error>,
+ flags: usize,
+ ) -> Result<Self> {
+ // SAFETY:
+ // - `raw_data` is a valid pointer to uninitialized memory.
+ // - `raw_data` will not move until it is dropped.
+ unsafe { data.__pinned_init(drm.0.data.get().cast()) }?;
+
+ drm.data_is_init.store(true, Ordering::Relaxed);
+
// SAFETY: `drm.as_raw()` is valid by the invariants of `drm::Device`.
to_result(unsafe { bindings::drm_dev_register(drm.as_raw(), flags) })?;
@@ -150,6 +162,7 @@ fn new(drm: drm::UnregisteredDevice<T>, flags: usize) -> Result<Self> {
pub fn new_foreign_owned<'a>(
drm: drm::UnregisteredDevice<T>,
dev: &'a device::Device<device::Bound>,
+ data: impl PinInit<T::Data, Error>,
flags: usize,
) -> Result<&'a drm::Device<T>>
where
@@ -160,7 +173,7 @@ pub fn new_foreign_owned<'a>(
return Err(EINVAL);
}
- let reg = Registration::<T>::new(drm, flags)?;
+ let reg = Registration::<T>::new(drm, data, flags)?;
let drm = NonNull::from(reg.device());
devres::register(dev, reg, GFP_KERNEL)?;
--
2.52.0
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH v3 2/3] rust/drm: Don't setup private driver data until registration
2026-01-22 22:46 ` [PATCH v3 2/3] rust/drm: Don't setup private driver data until registration Lyude Paul
@ 2026-01-23 1:52 ` Daniel Almeida
2026-01-23 17:00 ` lyude
0 siblings, 1 reply; 10+ messages in thread
From: Daniel Almeida @ 2026-01-23 1:52 UTC (permalink / raw)
To: Lyude Paul
Cc: linux-kernel, dri-devel, rust-for-linux, Danilo Krummrich,
nouveau, Miguel Ojeda, Simona Vetter, Alice Ryhl, Shankari Anand,
David Airlie, Benno Lossin, Asahi Lina
Hi Lyude,
> On 22 Jan 2026, at 19:46, Lyude Paul <lyude@redhat.com> wrote:
>
> Now that we have a DeviceContext that we can use to represent whether a
> Device is known to have been registered, we can make it so that drivers can
> create their Devices but wait until the registration phase to assign their
> private data to the Device. This is desirable as some drivers need to make
> use of the DRM device early on before finalizing their private driver data.
>
> As such, this change makes it so that the driver's private data can
> currently only be accessed through Device<T, Registered> types and not
> Device<T, Uninit>.
>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> ---
> drivers/gpu/drm/nova/driver.rs | 4 +--
> drivers/gpu/drm/tyr/driver.rs | 4 +--
> rust/kernel/drm/device.rs | 63 ++++++++++++++++++++--------------
> rust/kernel/drm/driver.rs | 19 ++++++++--
> 4 files changed, 58 insertions(+), 32 deletions(-)
>
> diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs
> index 99d6841b69cbc..8cea5f68c3b04 100644
> --- a/drivers/gpu/drm/nova/driver.rs
> +++ b/drivers/gpu/drm/nova/driver.rs
> @@ -56,8 +56,8 @@ impl auxiliary::Driver for NovaDriver {
> fn probe(adev: &auxiliary::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<Self, Error> {
> let data = try_pin_init!(NovaData { adev: adev.into() });
>
> - let drm = drm::UnregisteredDevice::<Self>::new(adev.as_ref(), data)?;
> - let drm = drm::Registration::new_foreign_owned(drm, adev.as_ref(), 0)?;
> + let drm = drm::UnregisteredDevice::<Self>::new(adev.as_ref())?;
> + let drm = drm::Registration::new_foreign_owned(drm, adev.as_ref(), data, 0)?;
>
> Ok(Self { drm: drm.into() })
> }
> diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs
> index ac265a60f5667..e73c56659ea75 100644
> --- a/drivers/gpu/drm/tyr/driver.rs
> +++ b/drivers/gpu/drm/tyr/driver.rs
> @@ -133,8 +133,8 @@ fn probe(
> gpu_info,
> });
>
> - let tdev = drm::UnregisteredDevice::<Self>::new(pdev.as_ref(), data)?;
> - let tdev = drm::driver::Registration::new_foreign_owned(tdev, pdev.as_ref(), 0)?;
> + let tdev = drm::UnregisteredDevice::<Self>::new(pdev.as_ref())?;
> + let tdev = drm::driver::Registration::new_foreign_owned(tdev, pdev.as_ref(), data, 0)?;
>
> let driver = TyrDriver {
> device: tdev.into(),
> diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
> index f529bc7fc4032..0e81957cf8c28 100644
> --- a/rust/kernel/drm/device.rs
> +++ b/rust/kernel/drm/device.rs
> @@ -26,13 +26,15 @@
> };
> use core::{
> alloc::Layout,
> + cell::UnsafeCell,
> marker::PhantomData,
> - mem,
> - ops::Deref,
> - ptr::{
> + mem::{
> self,
> - NonNull, //
> + MaybeUninit, //
> },
> + ops::Deref,
> + ptr::NonNull,
> + sync::atomic::*,
> };
>
> #[cfg(CONFIG_DRM_LEGACY)]
> @@ -141,7 +143,7 @@ impl DeviceContext for Uninit {}
> ///
> /// The device in `self.0` is guaranteed to be a newly created [`Device`] that has not yet been
> /// registered with userspace until this type is dropped.
> -pub struct UnregisteredDevice<T: drm::Driver>(ARef<Device<T, Uninit>>, NotThreadSafe);
> +pub struct UnregisteredDevice<T: drm::Driver>(pub(crate) ARef<Device<T, Uninit>>, NotThreadSafe);
>
> impl<T: drm::Driver> Deref for UnregisteredDevice<T> {
> type Target = Device<T, Uninit>;
> @@ -188,7 +190,7 @@ impl<T: drm::Driver> UnregisteredDevice<T> {
> /// Create a new `UnregisteredDevice` for a `drm::Driver`.
> ///
> /// This can be used to create a [`Registration`](kernel::drm::Registration).
> - pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<Self> {
> + pub fn new(dev: &device::Device) -> Result<Self> {
> // `__drm_dev_alloc` uses `kmalloc()` to allocate memory, hence ensure a `kmalloc()`
> // compatible `Layout`.
> let layout = Kmalloc::aligned_layout(Layout::new::<Self>());
> @@ -207,22 +209,6 @@ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<S
> .cast();
> let raw_drm = NonNull::new(from_err_ptr(raw_drm)?).ok_or(ENOMEM)?;
>
> - // SAFETY: `raw_drm` is a valid pointer to `Self`.
> - let raw_data = unsafe { ptr::addr_of_mut!((*raw_drm.as_ptr()).data) };
> -
> - // SAFETY:
> - // - `raw_data` is a valid pointer to uninitialized memory.
> - // - `raw_data` will not move until it is dropped.
> - unsafe { data.__pinned_init(raw_data) }.inspect_err(|_| {
> - // SAFETY: `raw_drm` is a valid pointer to `Self`, given that `__drm_dev_alloc` was
> - // successful.
> - let drm_dev = unsafe { Device::into_drm_device(raw_drm) };
> -
> - // SAFETY: `__drm_dev_alloc()` was successful, hence `drm_dev` must be valid and the
> - // refcount must be non-zero.
> - unsafe { bindings::drm_dev_put(drm_dev) };
> - })?;
> -
> // SAFETY: The reference count is one, and now we take ownership of that reference as a
> // `drm::Device`.
> // INVARIANT: We just created the device above, but have yet to call `drm_dev_register`.
> @@ -254,7 +240,15 @@ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<S
> #[repr(C)]
> pub struct Device<T: drm::Driver, C: DeviceContext = Registered> {
> dev: Opaque<bindings::drm_device>,
> - data: T::Data,
> +
> + /// Keeps track of whether we've initialized the device data yet.
> + pub(crate) data_is_init: AtomicBool,
Why don’t we make the data a member of the Registered context?
> +
> + /// The Driver's private data.
> + ///
> + /// This must only be written to from [`drm::Registration::new`].
> + pub(crate) data: UnsafeCell<MaybeUninit<T::Data>>,
> +
> _ctx: PhantomData<C>,
> }
>
> @@ -305,6 +299,21 @@ extern "C" fn release(ptr: *mut bindings::drm_device) {
> // SAFETY: `ptr` is a valid pointer to a `struct drm_device` and embedded in `Self`.
> let this = unsafe { Self::from_drm_device(ptr) };
>
> + {
> + // SAFETY:
> + // - Since we are in release(), we are guaranteed that no one else has access to `this`.
> + // - We confirmed above that `this` is a valid pointer to an initialized `Self`.
> + let this = unsafe { &mut *this };
> + if this.data_is_init.load(Ordering::Relaxed) {
> + // SAFETY:
> + // - Since we are in release(), we are guaranteed that no one else has access to
> + // `this`.
> + // - We checked that the data is initialized above.
> + // - We do not use `data` any point after calling this function.
> + unsafe { (&mut *this.data.get()).assume_init_drop() };
> + }
> + }
> +
> // SAFETY:
> // - When `release` runs it is guaranteed that there is no further access to `this`.
> // - `this` is valid for dropping.
> @@ -323,11 +332,15 @@ pub(crate) unsafe fn assume_ctx<NewCtx: DeviceContext>(&self) -> &Device<T, NewC
> }
> }
>
> -impl<T: drm::Driver, C: DeviceContext> Deref for Device<T, C> {
> +impl<T: drm::Driver> Deref for Device<T, Registered> {
> type Target = T::Data;
>
> fn deref(&self) -> &Self::Target {
> - &self.data
> + // SAFETY:
> + // - `data` is initialized before any `Device`s with the `Registered` context are available
> + // to the user.
> + // - `data` is only written to once in `Registration::new()`, so this read will never race.
> + unsafe { (&*self.data.get()).assume_init_ref() }
> }
> }
>
> diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
> index da9f1bfef1f14..a16605b407159 100644
> --- a/rust/kernel/drm/driver.rs
> +++ b/rust/kernel/drm/driver.rs
> @@ -15,7 +15,8 @@
> };
> use core::{
> mem,
> - ptr::NonNull, //
> + ptr::NonNull,
> + sync::atomic::*, //
> };
>
> /// Driver use the GEM memory manager. This should be set for all modern drivers.
> @@ -127,7 +128,18 @@ pub trait Driver {
> pub struct Registration<T: Driver>(ARef<drm::Device<T>>);
>
> impl<T: Driver> Registration<T> {
> - fn new(drm: drm::UnregisteredDevice<T>, flags: usize) -> Result<Self> {
> + fn new(
> + drm: drm::UnregisteredDevice<T>,
> + data: impl PinInit<T::Data, Error>,
> + flags: usize,
> + ) -> Result<Self> {
IIUC this consumes UnregisteredDevice and returns
Registration<T: Driver>(ARef<drm::Device<T>>);
i.e.:
Registration<T: Driver>(ARef<drm::Device<T, C = Registered>>);
Again, the Registered typestate seems like the perfect place to store T::Data.
> + // SAFETY:
> + // - `raw_data` is a valid pointer to uninitialized memory.
> + // - `raw_data` will not move until it is dropped.
> + unsafe { data.__pinned_init(drm.0.data.get().cast()) }?;
> +
> + drm.data_is_init.store(true, Ordering::Relaxed);
> +
> // SAFETY: `drm.as_raw()` is valid by the invariants of `drm::Device`.
> to_result(unsafe { bindings::drm_dev_register(drm.as_raw(), flags) })?;
>
> @@ -150,6 +162,7 @@ fn new(drm: drm::UnregisteredDevice<T>, flags: usize) -> Result<Self> {
> pub fn new_foreign_owned<'a>(
> drm: drm::UnregisteredDevice<T>,
> dev: &'a device::Device<device::Bound>,
> + data: impl PinInit<T::Data, Error>,
> flags: usize,
> ) -> Result<&'a drm::Device<T>>
> where
> @@ -160,7 +173,7 @@ pub fn new_foreign_owned<'a>(
> return Err(EINVAL);
> }
>
> - let reg = Registration::<T>::new(drm, flags)?;
> + let reg = Registration::<T>::new(drm, data, flags)?;
> let drm = NonNull::from(reg.device());
>
> devres::register(dev, reg, GFP_KERNEL)?;
> --
> 2.52.0
>
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH v3 2/3] rust/drm: Don't setup private driver data until registration
2026-01-23 1:52 ` Daniel Almeida
@ 2026-01-23 17:00 ` lyude
0 siblings, 0 replies; 10+ messages in thread
From: lyude @ 2026-01-23 17:00 UTC (permalink / raw)
To: Daniel Almeida
Cc: linux-kernel, dri-devel, rust-for-linux, Danilo Krummrich,
nouveau, Miguel Ojeda, Simona Vetter, Alice Ryhl, Shankari Anand,
David Airlie, Benno Lossin, Asahi Lina
On Thu, 2026-01-22 at 22:52 -0300, Daniel Almeida wrote:
> > @@ -254,7 +240,15 @@ pub fn new(dev: &device::Device, data: impl
> > PinInit<T::Data, Error>) -> Result<S
> > #[repr(C)]
> > pub struct Device<T: drm::Driver, C: DeviceContext = Registered> {
> > dev: Opaque<bindings::drm_device>,
> > - data: T::Data,
> > +
> > + /// Keeps track of whether we've initialized the device data
> > yet.
> > + pub(crate) data_is_init: AtomicBool,
>
> Why don’t we make the data a member of the Registered context?
A couple of different reasons. For one: not having it embedded as part
of Device would complicate trying to go from the device's private data
using container_of! to the actual Device struct, which isn't great for
workqueues.
The other much more important reason is that Registered isn't going to
be the only typestate that has access to the driver's private data in
the future. With KMS, nearly all of the modesetting callbacks for a
driver can be invoked before userspace registration. E.g. consider a
modesetting driver that needs to perform a modeset pre-registration so
that the hardware is in a known good state before being exposed to
userspace.
To clarify what this looks like: you'll recall that I made a diagram
showing a high-level overview of the DRM initialization process for the
documentation for DeviceContext. The second stage in that diagram,
which I'm currently calling Init, is the context that we're going to
need to eventually add a typestate for.
FWIW, this is more or less what the flow will look like with this new
context. Indenting indicates calling down to a function from within the
function above
* UnregisteredDevice::new(d: device::Device) -> UnregisteredDevice<T>
- // Creates Crtcs, Connectors, etc.
KmsDriver::probe(d: &UninitializedKmsDevice)
* // The driver sets stuff up
* Registration::new_foreign_owned(
dev: UnregisteredDevice,
data: impl PinInit<T::Data>
):
- // Initialize `data`, so driver data is ready at this point
- KmsDriver::pre_registration_init(d: &Device<T, Init>)
- // Perform actual userspace registration
If it wasn't clear too: this means tyr won't really need to do anything
when we add the new DeviceContext typestate :)
>
> > +
> > + /// The Driver's private data.
> > + ///
> > + /// This must only be written to from
> > [`drm::Registration::new`].
> > + pub(crate) data: UnsafeCell<MaybeUninit<T::Data>>,
> > +
> > _ctx: PhantomData<C>,
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH v3 3/3] rust/drm/gem: Use DeviceContext with GEM objects
2026-01-22 22:46 [PATCH v3 0/3] Introduce DeviceContext Lyude Paul
2026-01-22 22:46 ` [PATCH v3 1/3] rust/drm: " Lyude Paul
2026-01-22 22:46 ` [PATCH v3 2/3] rust/drm: Don't setup private driver data until registration Lyude Paul
@ 2026-01-22 22:46 ` Lyude Paul
2026-01-23 1:56 ` Daniel Almeida
2 siblings, 1 reply; 10+ messages in thread
From: Lyude Paul @ 2026-01-22 22:46 UTC (permalink / raw)
To: linux-kernel, dri-devel, rust-for-linux, Danilo Krummrich
Cc: nouveau, Miguel Ojeda, Simona Vetter, Alice Ryhl, Shankari Anand,
David Airlie, Benno Lossin, Asahi Lina, Daniel Almeida,
Lyude Paul
Now that we have the ability to represent the context in which a DRM device
is in at compile-time, we can start carrying around this context with GEM
object types in order to allow a driver to safely create GEM objects before
a DRM device has registered with userspace.
Signed-off-by: Lyude Paul <lyude@redhat.com>
---
drivers/gpu/drm/nova/driver.rs | 2 +-
drivers/gpu/drm/nova/gem.rs | 11 +++---
drivers/gpu/drm/tyr/driver.rs | 2 +-
drivers/gpu/drm/tyr/gem.rs | 3 +-
rust/kernel/drm/device.rs | 14 ++++----
rust/kernel/drm/driver.rs | 2 +-
rust/kernel/drm/gem/mod.rs | 64 +++++++++++++++++++++++-----------
7 files changed, 63 insertions(+), 35 deletions(-)
diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs
index 8cea5f68c3b04..2c13261450406 100644
--- a/drivers/gpu/drm/nova/driver.rs
+++ b/drivers/gpu/drm/nova/driver.rs
@@ -67,7 +67,7 @@ fn probe(adev: &auxiliary::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<S
impl drm::Driver for NovaDriver {
type Data = NovaData;
type File = File;
- type Object = gem::Object<NovaObject>;
+ type Object<Ctx: drm::DeviceContext> = gem::Object<NovaObject, Ctx>;
const INFO: drm::DriverInfo = INFO;
diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs
index 6ccfa5da57617..f6e98b9db58d8 100644
--- a/drivers/gpu/drm/nova/gem.rs
+++ b/drivers/gpu/drm/nova/gem.rs
@@ -2,7 +2,7 @@
use kernel::{
drm,
- drm::{gem, gem::BaseObject},
+ drm::{gem, gem::BaseObject, DeviceContext},
page,
prelude::*,
sync::aref::ARef,
@@ -20,20 +20,23 @@ pub(crate) struct NovaObject {}
impl gem::DriverObject for NovaObject {
type Driver = NovaDriver;
- fn new(_dev: &NovaDevice, _size: usize) -> impl PinInit<Self, Error> {
+ fn new<Ctx: DeviceContext>(_dev: &NovaDevice<Ctx>, _size: usize) -> impl PinInit<Self, Error> {
try_pin_init!(NovaObject {})
}
}
impl NovaObject {
/// Create a new DRM GEM object.
- pub(crate) fn new(dev: &NovaDevice, size: usize) -> Result<ARef<gem::Object<Self>>> {
+ pub(crate) fn new<Ctx: DeviceContext>(
+ dev: &NovaDevice<Ctx>,
+ size: usize,
+ ) -> Result<ARef<gem::Object<Self, Ctx>>> {
if size == 0 {
return Err(EINVAL);
}
let aligned_size = page::page_align(size).ok_or(EINVAL)?;
- gem::Object::new(dev, aligned_size)
+ gem::Object::<Self, Ctx>::new(dev, aligned_size)
}
/// Look up a GEM object handle for a `File` and return an `ObjectRef` for it.
diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs
index e73c56659ea75..03e337d95521c 100644
--- a/drivers/gpu/drm/tyr/driver.rs
+++ b/drivers/gpu/drm/tyr/driver.rs
@@ -177,7 +177,7 @@ fn drop(self: Pin<&mut Self>) {
impl drm::Driver for TyrDriver {
type Data = TyrData;
type File = File;
- type Object = drm::gem::Object<TyrObject>;
+ type Object<R: drm::DeviceContext> = drm::gem::Object<TyrObject, R>;
const INFO: drm::DriverInfo = INFO;
diff --git a/drivers/gpu/drm/tyr/gem.rs b/drivers/gpu/drm/tyr/gem.rs
index 1273bf89dbd5d..00804f8c14bd4 100644
--- a/drivers/gpu/drm/tyr/gem.rs
+++ b/drivers/gpu/drm/tyr/gem.rs
@@ -3,6 +3,7 @@
use crate::driver::TyrDevice;
use crate::driver::TyrDriver;
use kernel::drm::gem;
+use kernel::drm::DeviceContext;
use kernel::prelude::*;
/// GEM Object inner driver data
@@ -12,7 +13,7 @@ pub(crate) struct TyrObject {}
impl gem::DriverObject for TyrObject {
type Driver = TyrDriver;
- fn new(_dev: &TyrDevice, _size: usize) -> impl PinInit<Self, Error> {
+ fn new<Ctx: DeviceContext>(_dev: &TyrDevice<Ctx>, _size: usize) -> impl PinInit<Self, Error> {
try_pin_init!(TyrObject {})
}
}
diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
index 0e81957cf8c28..4c03105e6a817 100644
--- a/rust/kernel/drm/device.rs
+++ b/rust/kernel/drm/device.rs
@@ -163,13 +163,13 @@ impl<T: drm::Driver> UnregisteredDevice<T> {
master_set: None,
master_drop: None,
debugfs_init: None,
- gem_create_object: T::Object::ALLOC_OPS.gem_create_object,
- prime_handle_to_fd: T::Object::ALLOC_OPS.prime_handle_to_fd,
- prime_fd_to_handle: T::Object::ALLOC_OPS.prime_fd_to_handle,
- gem_prime_import: T::Object::ALLOC_OPS.gem_prime_import,
- gem_prime_import_sg_table: T::Object::ALLOC_OPS.gem_prime_import_sg_table,
- dumb_create: T::Object::ALLOC_OPS.dumb_create,
- dumb_map_offset: T::Object::ALLOC_OPS.dumb_map_offset,
+ gem_create_object: T::Object::<Uninit>::ALLOC_OPS.gem_create_object,
+ prime_handle_to_fd: T::Object::<Uninit>::ALLOC_OPS.prime_handle_to_fd,
+ prime_fd_to_handle: T::Object::<Uninit>::ALLOC_OPS.prime_fd_to_handle,
+ gem_prime_import: T::Object::<Uninit>::ALLOC_OPS.gem_prime_import,
+ gem_prime_import_sg_table: T::Object::<Uninit>::ALLOC_OPS.gem_prime_import_sg_table,
+ dumb_create: T::Object::<Uninit>::ALLOC_OPS.dumb_create,
+ dumb_map_offset: T::Object::<Uninit>::ALLOC_OPS.dumb_map_offset,
show_fdinfo: None,
fbdev_probe: None,
diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
index a16605b407159..94ebaf19ac069 100644
--- a/rust/kernel/drm/driver.rs
+++ b/rust/kernel/drm/driver.rs
@@ -110,7 +110,7 @@ pub trait Driver {
type Data: Sync + Send;
/// The type used to manage memory for this driver.
- type Object: AllocImpl;
+ type Object<Ctx: drm::DeviceContext>: AllocImpl;
/// The type used to represent a DRM File (client)
type File: drm::file::DriverFile;
diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs
index b4199945db378..3af9f52f8eda4 100644
--- a/rust/kernel/drm/gem/mod.rs
+++ b/rust/kernel/drm/gem/mod.rs
@@ -8,6 +8,10 @@
bindings,
drm::{
self,
+ device::{
+ DeviceContext,
+ Registered, //
+ },
driver::{
AllocImpl,
AllocOps, //
@@ -22,6 +26,7 @@
types::Opaque,
};
use core::{
+ marker::PhantomData,
ops::Deref,
ptr::NonNull, //
};
@@ -33,21 +38,30 @@
/// [`DriverFile`]: drm::file::DriverFile
pub type DriverFile<T> = drm::File<<<T as DriverObject>::Driver as drm::Driver>::File>;
+/// A type alias for retrieving the current [`AllocImpl`] for a given [`DriverObject`].
+///
+/// [`Driver`]: drm::Driver
+pub type DriverAllocImpl<T, Ctx = Registered> =
+ <<T as DriverObject>::Driver as drm::Driver>::Object<Ctx>;
+
/// GEM object functions, which must be implemented by drivers.
pub trait DriverObject: Sync + Send + Sized {
/// Parent `Driver` for this object.
type Driver: drm::Driver;
/// Create a new driver data object for a GEM object of a given size.
- fn new(dev: &drm::Device<Self::Driver>, size: usize) -> impl PinInit<Self, Error>;
+ fn new<Ctx: DeviceContext>(
+ dev: &drm::Device<Self::Driver, Ctx>,
+ size: usize,
+ ) -> impl PinInit<Self, Error>;
/// Open a new handle to an existing object, associated with a File.
- fn open(_obj: &<Self::Driver as drm::Driver>::Object, _file: &DriverFile<Self>) -> Result {
+ fn open(_obj: &DriverAllocImpl<Self>, _file: &DriverFile<Self>) -> Result {
Ok(())
}
/// Close a handle to an existing object, associated with a File.
- fn close(_obj: &<Self::Driver as drm::Driver>::Object, _file: &DriverFile<Self>) {}
+ fn close(_obj: &DriverAllocImpl<Self>, _file: &DriverFile<Self>) {}
}
/// Trait that represents a GEM object subtype
@@ -73,9 +87,12 @@ extern "C" fn open_callback<T: DriverObject>(
// SAFETY: `open_callback` is only ever called with a valid pointer to a `struct drm_file`.
let file = unsafe { DriverFile::<T>::from_raw(raw_file) };
- // SAFETY: `open_callback` is specified in the AllocOps structure for `DriverObject<T>`,
- // ensuring that `raw_obj` is contained within a `DriverObject<T>`
- let obj = unsafe { <<T::Driver as drm::Driver>::Object as IntoGEMObject>::from_raw(raw_obj) };
+ // SAFETY:
+ // * `open_callback` is specified in the AllocOps structure for `DriverObject`, ensuring that
+ // `raw_obj` is contained within a `DriverAllocImpl<T>`
+ // * It is only possible for `open_callback` to be called after device registration, ensuring
+ // that the object's device is in the `Registered` state.
+ let obj: &DriverAllocImpl<T> = unsafe { IntoGEMObject::from_raw(raw_obj) };
match T::open(obj, file) {
Err(e) => e.to_errno(),
@@ -92,12 +109,12 @@ extern "C" fn close_callback<T: DriverObject>(
// SAFETY: `close_callback` is specified in the AllocOps structure for `Object<T>`, ensuring
// that `raw_obj` is indeed contained within a `Object<T>`.
- let obj = unsafe { <<T::Driver as drm::Driver>::Object as IntoGEMObject>::from_raw(raw_obj) };
+ let obj: &DriverAllocImpl<T> = unsafe { IntoGEMObject::from_raw(raw_obj) };
T::close(obj, file);
}
-impl<T: DriverObject> IntoGEMObject for Object<T> {
+impl<T: DriverObject, Ctx: DeviceContext> IntoGEMObject for Object<T, Ctx> {
fn as_raw(&self) -> *mut bindings::drm_gem_object {
self.obj.get()
}
@@ -105,7 +122,7 @@ fn as_raw(&self) -> *mut bindings::drm_gem_object {
unsafe fn from_raw<'a>(self_ptr: *mut bindings::drm_gem_object) -> &'a Self {
// SAFETY: `obj` is guaranteed to be in an `Object<T>` via the safety contract of this
// function
- unsafe { &*crate::container_of!(Opaque::cast_from(self_ptr), Object<T>, obj) }
+ unsafe { &*crate::container_of!(Opaque::cast_from(self_ptr), Object<T, Ctx>, obj) }
}
}
@@ -122,7 +139,7 @@ fn size(&self) -> usize {
fn create_handle<D, F>(&self, file: &drm::File<F>) -> Result<u32>
where
Self: AllocImpl<Driver = D>,
- D: drm::Driver<Object = Self, File = F>,
+ D: drm::Driver<Object<Registered> = Self, File = F>,
F: drm::file::DriverFile<Driver = D>,
{
let mut handle: u32 = 0;
@@ -137,7 +154,7 @@ fn create_handle<D, F>(&self, file: &drm::File<F>) -> Result<u32>
fn lookup_handle<D, F>(file: &drm::File<F>, handle: u32) -> Result<ARef<Self>>
where
Self: AllocImpl<Driver = D>,
- D: drm::Driver<Object = Self, File = F>,
+ D: drm::Driver<Object<Registered> = Self, File = F>,
F: drm::file::DriverFile<Driver = D>,
{
// SAFETY: The arguments are all valid per the type invariants.
@@ -177,16 +194,18 @@ impl<T: IntoGEMObject> BaseObject for T {}
///
/// # Invariants
///
-/// - `self.obj` is a valid instance of a `struct drm_gem_object`.
+/// * `self.obj` is a valid instance of a `struct drm_gem_object`.
+/// * Any type invariants of `Ctx` apply to the parent DRM device for this GEM object.
#[repr(C)]
#[pin_data]
-pub struct Object<T: DriverObject + Send + Sync> {
+pub struct Object<T: DriverObject + Send + Sync, Ctx: DeviceContext = Registered> {
obj: Opaque<bindings::drm_gem_object>,
#[pin]
data: T,
+ _ctx: PhantomData<Ctx>,
}
-impl<T: DriverObject> Object<T> {
+impl<T: DriverObject, Ctx: DeviceContext> Object<T, Ctx> {
const OBJECT_FUNCS: bindings::drm_gem_object_funcs = bindings::drm_gem_object_funcs {
free: Some(Self::free_callback),
open: Some(open_callback::<T>),
@@ -206,11 +225,12 @@ impl<T: DriverObject> Object<T> {
};
/// Create a new GEM object.
- pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
+ pub fn new(dev: &drm::Device<T::Driver, Ctx>, size: usize) -> Result<ARef<Self>> {
let obj: Pin<KBox<Self>> = KBox::pin_init(
try_pin_init!(Self {
obj: Opaque::new(bindings::drm_gem_object::default()),
data <- T::new(dev, size),
+ _ctx: PhantomData,
}),
GFP_KERNEL,
)?;
@@ -219,6 +239,8 @@ pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
unsafe { (*obj.as_raw()).funcs = &Self::OBJECT_FUNCS };
// SAFETY: The arguments are all valid per the type invariants.
+ // INVARIANT: We use `dev` for creating the GEM object, which is known to be in state `Ctx` -
+ // ensuring that the GEM object's pointer to the DRM device is always in the same state.
to_result(unsafe { bindings::drm_gem_object_init(dev.as_raw(), obj.obj.get(), size) })?;
// SAFETY: We will never move out of `Self` as `ARef<Self>` is always treated as pinned.
@@ -232,13 +254,15 @@ pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
}
/// Returns the `Device` that owns this GEM object.
- pub fn dev(&self) -> &drm::Device<T::Driver> {
+ pub fn dev(&self) -> &drm::Device<T::Driver, Ctx> {
// SAFETY:
// - `struct drm_gem_object.dev` is initialized and valid for as long as the GEM
// object lives.
// - The device we used for creating the gem object is passed as &drm::Device<T::Driver> to
// Object::<T>::new(), so we know that `T::Driver` is the right generic parameter to use
// here.
+ // - Any type invariants of `Ctx` are upheld by using the same `Ctx` for the `Device` we
+ // return.
unsafe { drm::Device::from_raw((*self.as_raw()).dev) }
}
@@ -264,7 +288,7 @@ extern "C" fn free_callback(obj: *mut bindings::drm_gem_object) {
}
// SAFETY: Instances of `Object<T>` are always reference-counted.
-unsafe impl<T: DriverObject> crate::sync::aref::AlwaysRefCounted for Object<T> {
+unsafe impl<T: DriverObject, Ctx: DeviceContext> AlwaysRefCounted for Object<T, Ctx> {
fn inc_ref(&self) {
// SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
unsafe { bindings::drm_gem_object_get(self.as_raw()) };
@@ -279,9 +303,9 @@ unsafe fn dec_ref(obj: NonNull<Self>) {
}
}
-impl<T: DriverObject> super::private::Sealed for Object<T> {}
+impl<T: DriverObject, Ctx: DeviceContext> super::private::Sealed for Object<T, Ctx> {}
-impl<T: DriverObject> Deref for Object<T> {
+impl<T: DriverObject, Ctx: DeviceContext> Deref for Object<T, Ctx> {
type Target = T;
fn deref(&self) -> &Self::Target {
@@ -289,7 +313,7 @@ fn deref(&self) -> &Self::Target {
}
}
-impl<T: DriverObject> AllocImpl for Object<T> {
+impl<T: DriverObject, Ctx: DeviceContext> AllocImpl for Object<T, Ctx> {
type Driver = T::Driver;
const ALLOC_OPS: AllocOps = AllocOps {
--
2.52.0
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH v3 3/3] rust/drm/gem: Use DeviceContext with GEM objects
2026-01-22 22:46 ` [PATCH v3 3/3] rust/drm/gem: Use DeviceContext with GEM objects Lyude Paul
@ 2026-01-23 1:56 ` Daniel Almeida
2026-01-23 22:52 ` lyude
0 siblings, 1 reply; 10+ messages in thread
From: Daniel Almeida @ 2026-01-23 1:56 UTC (permalink / raw)
To: Lyude Paul
Cc: linux-kernel, dri-devel, rust-for-linux, Danilo Krummrich,
nouveau, Miguel Ojeda, Simona Vetter, Alice Ryhl, Shankari Anand,
David Airlie, Benno Lossin, Asahi Lina
Hi Lyude,
> On 22 Jan 2026, at 19:46, Lyude Paul <lyude@redhat.com> wrote:
>
> Now that we have the ability to represent the context in which a DRM device
> is in at compile-time, we can start carrying around this context with GEM
> object types in order to allow a driver to safely create GEM objects before
> a DRM device has registered with userspace.
>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> ---
> drivers/gpu/drm/nova/driver.rs | 2 +-
> drivers/gpu/drm/nova/gem.rs | 11 +++---
> drivers/gpu/drm/tyr/driver.rs | 2 +-
> drivers/gpu/drm/tyr/gem.rs | 3 +-
> rust/kernel/drm/device.rs | 14 ++++----
> rust/kernel/drm/driver.rs | 2 +-
> rust/kernel/drm/gem/mod.rs | 64 +++++++++++++++++++++++-----------
> 7 files changed, 63 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/gpu/drm/nova/driver.rs b/drivers/gpu/drm/nova/driver.rs
> index 8cea5f68c3b04..2c13261450406 100644
> --- a/drivers/gpu/drm/nova/driver.rs
> +++ b/drivers/gpu/drm/nova/driver.rs
> @@ -67,7 +67,7 @@ fn probe(adev: &auxiliary::Device<Core>, _info: &Self::IdInfo) -> impl PinInit<S
> impl drm::Driver for NovaDriver {
> type Data = NovaData;
> type File = File;
> - type Object = gem::Object<NovaObject>;
> + type Object<Ctx: drm::DeviceContext> = gem::Object<NovaObject, Ctx>;
>
> const INFO: drm::DriverInfo = INFO;
>
> diff --git a/drivers/gpu/drm/nova/gem.rs b/drivers/gpu/drm/nova/gem.rs
> index 6ccfa5da57617..f6e98b9db58d8 100644
> --- a/drivers/gpu/drm/nova/gem.rs
> +++ b/drivers/gpu/drm/nova/gem.rs
> @@ -2,7 +2,7 @@
>
> use kernel::{
> drm,
> - drm::{gem, gem::BaseObject},
> + drm::{gem, gem::BaseObject, DeviceContext},
> page,
> prelude::*,
> sync::aref::ARef,
> @@ -20,20 +20,23 @@ pub(crate) struct NovaObject {}
> impl gem::DriverObject for NovaObject {
> type Driver = NovaDriver;
>
> - fn new(_dev: &NovaDevice, _size: usize) -> impl PinInit<Self, Error> {
> + fn new<Ctx: DeviceContext>(_dev: &NovaDevice<Ctx>, _size: usize) -> impl PinInit<Self, Error> {
> try_pin_init!(NovaObject {})
> }
> }
>
> impl NovaObject {
> /// Create a new DRM GEM object.
> - pub(crate) fn new(dev: &NovaDevice, size: usize) -> Result<ARef<gem::Object<Self>>> {
> + pub(crate) fn new<Ctx: DeviceContext>(
> + dev: &NovaDevice<Ctx>,
> + size: usize,
> + ) -> Result<ARef<gem::Object<Self, Ctx>>> {
> if size == 0 {
> return Err(EINVAL);
> }
> let aligned_size = page::page_align(size).ok_or(EINVAL)?;
>
> - gem::Object::new(dev, aligned_size)
> + gem::Object::<Self, Ctx>::new(dev, aligned_size)
> }
>
> /// Look up a GEM object handle for a `File` and return an `ObjectRef` for it.
> diff --git a/drivers/gpu/drm/tyr/driver.rs b/drivers/gpu/drm/tyr/driver.rs
> index e73c56659ea75..03e337d95521c 100644
> --- a/drivers/gpu/drm/tyr/driver.rs
> +++ b/drivers/gpu/drm/tyr/driver.rs
> @@ -177,7 +177,7 @@ fn drop(self: Pin<&mut Self>) {
> impl drm::Driver for TyrDriver {
> type Data = TyrData;
> type File = File;
> - type Object = drm::gem::Object<TyrObject>;
> + type Object<R: drm::DeviceContext> = drm::gem::Object<TyrObject, R>;
>
> const INFO: drm::DriverInfo = INFO;
>
> diff --git a/drivers/gpu/drm/tyr/gem.rs b/drivers/gpu/drm/tyr/gem.rs
> index 1273bf89dbd5d..00804f8c14bd4 100644
> --- a/drivers/gpu/drm/tyr/gem.rs
> +++ b/drivers/gpu/drm/tyr/gem.rs
> @@ -3,6 +3,7 @@
> use crate::driver::TyrDevice;
> use crate::driver::TyrDriver;
> use kernel::drm::gem;
> +use kernel::drm::DeviceContext;
> use kernel::prelude::*;
>
> /// GEM Object inner driver data
> @@ -12,7 +13,7 @@ pub(crate) struct TyrObject {}
> impl gem::DriverObject for TyrObject {
> type Driver = TyrDriver;
>
> - fn new(_dev: &TyrDevice, _size: usize) -> impl PinInit<Self, Error> {
> + fn new<Ctx: DeviceContext>(_dev: &TyrDevice<Ctx>, _size: usize) -> impl PinInit<Self, Error> {
> try_pin_init!(TyrObject {})
> }
> }
> diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
> index 0e81957cf8c28..4c03105e6a817 100644
> --- a/rust/kernel/drm/device.rs
> +++ b/rust/kernel/drm/device.rs
> @@ -163,13 +163,13 @@ impl<T: drm::Driver> UnregisteredDevice<T> {
> master_set: None,
> master_drop: None,
> debugfs_init: None,
> - gem_create_object: T::Object::ALLOC_OPS.gem_create_object,
> - prime_handle_to_fd: T::Object::ALLOC_OPS.prime_handle_to_fd,
> - prime_fd_to_handle: T::Object::ALLOC_OPS.prime_fd_to_handle,
> - gem_prime_import: T::Object::ALLOC_OPS.gem_prime_import,
> - gem_prime_import_sg_table: T::Object::ALLOC_OPS.gem_prime_import_sg_table,
> - dumb_create: T::Object::ALLOC_OPS.dumb_create,
> - dumb_map_offset: T::Object::ALLOC_OPS.dumb_map_offset,
> + gem_create_object: T::Object::<Uninit>::ALLOC_OPS.gem_create_object,
> + prime_handle_to_fd: T::Object::<Uninit>::ALLOC_OPS.prime_handle_to_fd,
> + prime_fd_to_handle: T::Object::<Uninit>::ALLOC_OPS.prime_fd_to_handle,
> + gem_prime_import: T::Object::<Uninit>::ALLOC_OPS.gem_prime_import,
> + gem_prime_import_sg_table: T::Object::<Uninit>::ALLOC_OPS.gem_prime_import_sg_table,
> + dumb_create: T::Object::<Uninit>::ALLOC_OPS.dumb_create,
> + dumb_map_offset: T::Object::<Uninit>::ALLOC_OPS.dumb_map_offset,
Why are we specifically going with Uninit here?
> show_fdinfo: None,
> fbdev_probe: None,
>
> diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
> index a16605b407159..94ebaf19ac069 100644
> --- a/rust/kernel/drm/driver.rs
> +++ b/rust/kernel/drm/driver.rs
> @@ -110,7 +110,7 @@ pub trait Driver {
> type Data: Sync + Send;
>
> /// The type used to manage memory for this driver.
> - type Object: AllocImpl;
> + type Object<Ctx: drm::DeviceContext>: AllocImpl;
>
> /// The type used to represent a DRM File (client)
> type File: drm::file::DriverFile;
> diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs
> index b4199945db378..3af9f52f8eda4 100644
> --- a/rust/kernel/drm/gem/mod.rs
> +++ b/rust/kernel/drm/gem/mod.rs
> @@ -8,6 +8,10 @@
> bindings,
> drm::{
> self,
> + device::{
> + DeviceContext,
> + Registered, //
> + },
> driver::{
> AllocImpl,
> AllocOps, //
> @@ -22,6 +26,7 @@
> types::Opaque,
> };
> use core::{
> + marker::PhantomData,
> ops::Deref,
> ptr::NonNull, //
> };
> @@ -33,21 +38,30 @@
> /// [`DriverFile`]: drm::file::DriverFile
> pub type DriverFile<T> = drm::File<<<T as DriverObject>::Driver as drm::Driver>::File>;
>
> +/// A type alias for retrieving the current [`AllocImpl`] for a given [`DriverObject`].
> +///
> +/// [`Driver`]: drm::Driver
> +pub type DriverAllocImpl<T, Ctx = Registered> =
> + <<T as DriverObject>::Driver as drm::Driver>::Object<Ctx>;
Should this be a follow up patch instead?
> +
> /// GEM object functions, which must be implemented by drivers.
> pub trait DriverObject: Sync + Send + Sized {
> /// Parent `Driver` for this object.
> type Driver: drm::Driver;
>
> /// Create a new driver data object for a GEM object of a given size.
> - fn new(dev: &drm::Device<Self::Driver>, size: usize) -> impl PinInit<Self, Error>;
> + fn new<Ctx: DeviceContext>(
> + dev: &drm::Device<Self::Driver, Ctx>,
> + size: usize,
> + ) -> impl PinInit<Self, Error>;
>
> /// Open a new handle to an existing object, associated with a File.
> - fn open(_obj: &<Self::Driver as drm::Driver>::Object, _file: &DriverFile<Self>) -> Result {
> + fn open(_obj: &DriverAllocImpl<Self>, _file: &DriverFile<Self>) -> Result {
> Ok(())
> }
>
> /// Close a handle to an existing object, associated with a File.
> - fn close(_obj: &<Self::Driver as drm::Driver>::Object, _file: &DriverFile<Self>) {}
> + fn close(_obj: &DriverAllocImpl<Self>, _file: &DriverFile<Self>) {}
> }
>
> /// Trait that represents a GEM object subtype
> @@ -73,9 +87,12 @@ extern "C" fn open_callback<T: DriverObject>(
> // SAFETY: `open_callback` is only ever called with a valid pointer to a `struct drm_file`.
> let file = unsafe { DriverFile::<T>::from_raw(raw_file) };
>
> - // SAFETY: `open_callback` is specified in the AllocOps structure for `DriverObject<T>`,
> - // ensuring that `raw_obj` is contained within a `DriverObject<T>`
> - let obj = unsafe { <<T::Driver as drm::Driver>::Object as IntoGEMObject>::from_raw(raw_obj) };
> + // SAFETY:
> + // * `open_callback` is specified in the AllocOps structure for `DriverObject`, ensuring that
> + // `raw_obj` is contained within a `DriverAllocImpl<T>`
> + // * It is only possible for `open_callback` to be called after device registration, ensuring
> + // that the object's device is in the `Registered` state.
> + let obj: &DriverAllocImpl<T> = unsafe { IntoGEMObject::from_raw(raw_obj) };
>
> match T::open(obj, file) {
> Err(e) => e.to_errno(),
> @@ -92,12 +109,12 @@ extern "C" fn close_callback<T: DriverObject>(
>
> // SAFETY: `close_callback` is specified in the AllocOps structure for `Object<T>`, ensuring
> // that `raw_obj` is indeed contained within a `Object<T>`.
> - let obj = unsafe { <<T::Driver as drm::Driver>::Object as IntoGEMObject>::from_raw(raw_obj) };
> + let obj: &DriverAllocImpl<T> = unsafe { IntoGEMObject::from_raw(raw_obj) };
>
> T::close(obj, file);
> }
>
> -impl<T: DriverObject> IntoGEMObject for Object<T> {
> +impl<T: DriverObject, Ctx: DeviceContext> IntoGEMObject for Object<T, Ctx> {
> fn as_raw(&self) -> *mut bindings::drm_gem_object {
> self.obj.get()
> }
> @@ -105,7 +122,7 @@ fn as_raw(&self) -> *mut bindings::drm_gem_object {
> unsafe fn from_raw<'a>(self_ptr: *mut bindings::drm_gem_object) -> &'a Self {
> // SAFETY: `obj` is guaranteed to be in an `Object<T>` via the safety contract of this
> // function
> - unsafe { &*crate::container_of!(Opaque::cast_from(self_ptr), Object<T>, obj) }
> + unsafe { &*crate::container_of!(Opaque::cast_from(self_ptr), Object<T, Ctx>, obj) }
> }
> }
>
> @@ -122,7 +139,7 @@ fn size(&self) -> usize {
> fn create_handle<D, F>(&self, file: &drm::File<F>) -> Result<u32>
> where
> Self: AllocImpl<Driver = D>,
> - D: drm::Driver<Object = Self, File = F>,
> + D: drm::Driver<Object<Registered> = Self, File = F>,
> F: drm::file::DriverFile<Driver = D>,
> {
> let mut handle: u32 = 0;
> @@ -137,7 +154,7 @@ fn create_handle<D, F>(&self, file: &drm::File<F>) -> Result<u32>
> fn lookup_handle<D, F>(file: &drm::File<F>, handle: u32) -> Result<ARef<Self>>
> where
> Self: AllocImpl<Driver = D>,
> - D: drm::Driver<Object = Self, File = F>,
> + D: drm::Driver<Object<Registered> = Self, File = F>,
> F: drm::file::DriverFile<Driver = D>,
> {
> // SAFETY: The arguments are all valid per the type invariants.
> @@ -177,16 +194,18 @@ impl<T: IntoGEMObject> BaseObject for T {}
> ///
> /// # Invariants
> ///
> -/// - `self.obj` is a valid instance of a `struct drm_gem_object`.
> +/// * `self.obj` is a valid instance of a `struct drm_gem_object`.
> +/// * Any type invariants of `Ctx` apply to the parent DRM device for this GEM object.
> #[repr(C)]
> #[pin_data]
> -pub struct Object<T: DriverObject + Send + Sync> {
> +pub struct Object<T: DriverObject + Send + Sync, Ctx: DeviceContext = Registered> {
> obj: Opaque<bindings::drm_gem_object>,
> #[pin]
> data: T,
> + _ctx: PhantomData<Ctx>,
> }
>
> -impl<T: DriverObject> Object<T> {
> +impl<T: DriverObject, Ctx: DeviceContext> Object<T, Ctx> {
> const OBJECT_FUNCS: bindings::drm_gem_object_funcs = bindings::drm_gem_object_funcs {
> free: Some(Self::free_callback),
> open: Some(open_callback::<T>),
> @@ -206,11 +225,12 @@ impl<T: DriverObject> Object<T> {
> };
>
> /// Create a new GEM object.
> - pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
> + pub fn new(dev: &drm::Device<T::Driver, Ctx>, size: usize) -> Result<ARef<Self>> {
> let obj: Pin<KBox<Self>> = KBox::pin_init(
> try_pin_init!(Self {
> obj: Opaque::new(bindings::drm_gem_object::default()),
> data <- T::new(dev, size),
> + _ctx: PhantomData,
> }),
> GFP_KERNEL,
> )?;
> @@ -219,6 +239,8 @@ pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
> unsafe { (*obj.as_raw()).funcs = &Self::OBJECT_FUNCS };
>
> // SAFETY: The arguments are all valid per the type invariants.
> + // INVARIANT: We use `dev` for creating the GEM object, which is known to be in state `Ctx` -
> + // ensuring that the GEM object's pointer to the DRM device is always in the same state.
> to_result(unsafe { bindings::drm_gem_object_init(dev.as_raw(), obj.obj.get(), size) })?;
>
> // SAFETY: We will never move out of `Self` as `ARef<Self>` is always treated as pinned.
> @@ -232,13 +254,15 @@ pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
> }
>
> /// Returns the `Device` that owns this GEM object.
> - pub fn dev(&self) -> &drm::Device<T::Driver> {
> + pub fn dev(&self) -> &drm::Device<T::Driver, Ctx> {
> // SAFETY:
> // - `struct drm_gem_object.dev` is initialized and valid for as long as the GEM
> // object lives.
> // - The device we used for creating the gem object is passed as &drm::Device<T::Driver> to
> // Object::<T>::new(), so we know that `T::Driver` is the right generic parameter to use
> // here.
> + // - Any type invariants of `Ctx` are upheld by using the same `Ctx` for the `Device` we
> + // return.
> unsafe { drm::Device::from_raw((*self.as_raw()).dev) }
> }
>
> @@ -264,7 +288,7 @@ extern "C" fn free_callback(obj: *mut bindings::drm_gem_object) {
> }
>
> // SAFETY: Instances of `Object<T>` are always reference-counted.
> -unsafe impl<T: DriverObject> crate::sync::aref::AlwaysRefCounted for Object<T> {
> +unsafe impl<T: DriverObject, Ctx: DeviceContext> AlwaysRefCounted for Object<T, Ctx> {
> fn inc_ref(&self) {
> // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero.
> unsafe { bindings::drm_gem_object_get(self.as_raw()) };
> @@ -279,9 +303,9 @@ unsafe fn dec_ref(obj: NonNull<Self>) {
> }
> }
>
> -impl<T: DriverObject> super::private::Sealed for Object<T> {}
> +impl<T: DriverObject, Ctx: DeviceContext> super::private::Sealed for Object<T, Ctx> {}
>
> -impl<T: DriverObject> Deref for Object<T> {
> +impl<T: DriverObject, Ctx: DeviceContext> Deref for Object<T, Ctx> {
> type Target = T;
>
> fn deref(&self) -> &Self::Target {
> @@ -289,7 +313,7 @@ fn deref(&self) -> &Self::Target {
> }
> }
>
> -impl<T: DriverObject> AllocImpl for Object<T> {
> +impl<T: DriverObject, Ctx: DeviceContext> AllocImpl for Object<T, Ctx> {
> type Driver = T::Driver;
>
> const ALLOC_OPS: AllocOps = AllocOps {
> --
> 2.52.0
>
>
^ permalink raw reply [flat|nested] 10+ messages in thread* Re: [PATCH v3 3/3] rust/drm/gem: Use DeviceContext with GEM objects
2026-01-23 1:56 ` Daniel Almeida
@ 2026-01-23 22:52 ` lyude
0 siblings, 0 replies; 10+ messages in thread
From: lyude @ 2026-01-23 22:52 UTC (permalink / raw)
To: Daniel Almeida
Cc: linux-kernel, dri-devel, rust-for-linux, Danilo Krummrich,
nouveau, Miguel Ojeda, Simona Vetter, Alice Ryhl, Shankari Anand,
David Airlie, Benno Lossin, Asahi Lina
On Thu, 2026-01-22 at 22:56 -0300, Daniel Almeida wrote:
> > }
> > }
> > diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs
> > index 0e81957cf8c28..4c03105e6a817 100644
> > --- a/rust/kernel/drm/device.rs
> > +++ b/rust/kernel/drm/device.rs
> > @@ -163,13 +163,13 @@ impl<T: drm::Driver> UnregisteredDevice<T> {
> > master_set: None,
> > master_drop: None,
> > debugfs_init: None,
> > - gem_create_object: T::Object::ALLOC_OPS.gem_create_object,
> > - prime_handle_to_fd:
> > T::Object::ALLOC_OPS.prime_handle_to_fd,
> > - prime_fd_to_handle:
> > T::Object::ALLOC_OPS.prime_fd_to_handle,
> > - gem_prime_import: T::Object::ALLOC_OPS.gem_prime_import,
> > - gem_prime_import_sg_table:
> > T::Object::ALLOC_OPS.gem_prime_import_sg_table,
> > - dumb_create: T::Object::ALLOC_OPS.dumb_create,
> > - dumb_map_offset: T::Object::ALLOC_OPS.dumb_map_offset,
> > + gem_create_object:
> > T::Object::<Uninit>::ALLOC_OPS.gem_create_object,
> > + prime_handle_to_fd:
> > T::Object::<Uninit>::ALLOC_OPS.prime_handle_to_fd,
> > + prime_fd_to_handle:
> > T::Object::<Uninit>::ALLOC_OPS.prime_fd_to_handle,
> > + gem_prime_import:
> > T::Object::<Uninit>::ALLOC_OPS.gem_prime_import,
> > + gem_prime_import_sg_table:
> > T::Object::<Uninit>::ALLOC_OPS.gem_prime_import_sg_table,
> > + dumb_create: T::Object::<Uninit>::ALLOC_OPS.dumb_create,
> > + dumb_map_offset:
> > T::Object::<Uninit>::ALLOC_OPS.dumb_map_offset,
>
> Why are we specifically going with Uninit here?
I think this was just an assumption that similarly to KMS callbacks,
gem callbacks can also happen before registration. except, that some of
these clearly can't happen before registration - whoops.
But this being said - it doesn't really make any difference what the
DeviceContext is here. The DeviceContext generic here isn't actually
used in any way, nor is it used by the C callback, it's just here
because we have to specify it on the associated type.
>
> > show_fdinfo: None,
> > fbdev_probe: None,
> >
> > diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
> > index a16605b407159..94ebaf19ac069 100644
> > --- a/rust/kernel/drm/driver.rs
> > +++ b/rust/kernel/drm/driver.rs
> > @@ -110,7 +110,7 @@ pub trait Driver {
> > type Data: Sync + Send;
> >
> > /// The type used to manage memory for this driver.
> > - type Object: AllocImpl;
> > + type Object<Ctx: drm::DeviceContext>: AllocImpl;
> >
> > /// The type used to represent a DRM File (client)
> > type File: drm::file::DriverFile;
> > diff --git a/rust/kernel/drm/gem/mod.rs
> > b/rust/kernel/drm/gem/mod.rs
> > index b4199945db378..3af9f52f8eda4 100644
> > --- a/rust/kernel/drm/gem/mod.rs
> > +++ b/rust/kernel/drm/gem/mod.rs
> > @@ -8,6 +8,10 @@
> > bindings,
> > drm::{
> > self,
> > + device::{
> > + DeviceContext,
> > + Registered, //
> > + },
> > driver::{
> > AllocImpl,
> > AllocOps, //
> > @@ -22,6 +26,7 @@
> > types::Opaque,
> > };
> > use core::{
> > + marker::PhantomData,
> > ops::Deref,
> > ptr::NonNull, //
> > };
> > @@ -33,21 +38,30 @@
> > /// [`DriverFile`]: drm::file::DriverFile
> > pub type DriverFile<T> = drm::File<<<T as DriverObject>::Driver as
> > drm::Driver>::File>;
> >
> > +/// A type alias for retrieving the current [`AllocImpl`] for a
> > given [`DriverObject`].
> > +///
> > +/// [`Driver`]: drm::Driver
> > +pub type DriverAllocImpl<T, Ctx = Registered> =
> > + <<T as DriverObject>::Driver as drm::Driver>::Object<Ctx>;
>
> Should this be a follow up patch instead?
>
> > +
> > /// GEM object functions, which must be implemented by drivers.
> > pub trait DriverObject: Sync + Send + Sized {
> > /// Parent `Driver` for this object.
> > type Driver: drm::Driver;
> >
> > /// Create a new driver data object for a GEM object of a given
> > size.
> > - fn new(dev: &drm::Device<Self::Driver>, size: usize) -> impl
> > PinInit<Self, Error>;
> > + fn new<Ctx: DeviceContext>(
> > + dev: &drm::Device<Self::Driver, Ctx>,
> > + size: usize,
> > + ) -> impl PinInit<Self, Error>;
> >
> > /// Open a new handle to an existing object, associated with a
> > File.
> > - fn open(_obj: &<Self::Driver as drm::Driver>::Object, _file:
> > &DriverFile<Self>) -> Result {
> > + fn open(_obj: &DriverAllocImpl<Self>, _file:
> > &DriverFile<Self>) -> Result {
> > Ok(())
> > }
> >
> > /// Close a handle to an existing object, associated with a
> > File.
> > - fn close(_obj: &<Self::Driver as drm::Driver>::Object, _file:
> > &DriverFile<Self>) {}
> > + fn close(_obj: &DriverAllocImpl<Self>, _file:
> > &DriverFile<Self>) {}
> > }
> >
> > /// Trait that represents a GEM object subtype
> > @@ -73,9 +87,12 @@ extern "C" fn open_callback<T: DriverObject>(
> > // SAFETY: `open_callback` is only ever called with a valid
> > pointer to a `struct drm_file`.
> > let file = unsafe { DriverFile::<T>::from_raw(raw_file) };
> >
> > - // SAFETY: `open_callback` is specified in the AllocOps
> > structure for `DriverObject<T>`,
> > - // ensuring that `raw_obj` is contained within a
> > `DriverObject<T>`
> > - let obj = unsafe { <<T::Driver as drm::Driver>::Object as
> > IntoGEMObject>::from_raw(raw_obj) };
> > + // SAFETY:
> > + // * `open_callback` is specified in the AllocOps structure
> > for `DriverObject`, ensuring that
> > + // `raw_obj` is contained within a `DriverAllocImpl<T>`
> > + // * It is only possible for `open_callback` to be called
> > after device registration, ensuring
> > + // that the object's device is in the `Registered` state.
> > + let obj: &DriverAllocImpl<T> = unsafe {
> > IntoGEMObject::from_raw(raw_obj) };
> >
> > match T::open(obj, file) {
> > Err(e) => e.to_errno(),
> > @@ -92,12 +109,12 @@ extern "C" fn close_callback<T: DriverObject>(
> >
> > // SAFETY: `close_callback` is specified in the AllocOps
> > structure for `Object<T>`, ensuring
> > // that `raw_obj` is indeed contained within a `Object<T>`.
> > - let obj = unsafe { <<T::Driver as drm::Driver>::Object as
> > IntoGEMObject>::from_raw(raw_obj) };
> > + let obj: &DriverAllocImpl<T> = unsafe {
> > IntoGEMObject::from_raw(raw_obj) };
> >
> > T::close(obj, file);
> > }
> >
> > -impl<T: DriverObject> IntoGEMObject for Object<T> {
> > +impl<T: DriverObject, Ctx: DeviceContext> IntoGEMObject for
> > Object<T, Ctx> {
> > fn as_raw(&self) -> *mut bindings::drm_gem_object {
> > self.obj.get()
> > }
> > @@ -105,7 +122,7 @@ fn as_raw(&self) -> *mut
> > bindings::drm_gem_object {
> > unsafe fn from_raw<'a>(self_ptr: *mut bindings::drm_gem_object)
> > -> &'a Self {
> > // SAFETY: `obj` is guaranteed to be in an `Object<T>` via
> > the safety contract of this
> > // function
> > - unsafe {
> > &*crate::container_of!(Opaque::cast_from(self_ptr), Object<T>, obj)
> > }
> > + unsafe {
> > &*crate::container_of!(Opaque::cast_from(self_ptr), Object<T, Ctx>,
> > obj) }
> > }
> > }
> >
> > @@ -122,7 +139,7 @@ fn size(&self) -> usize {
> > fn create_handle<D, F>(&self, file: &drm::File<F>) ->
> > Result<u32>
> > where
> > Self: AllocImpl<Driver = D>,
> > - D: drm::Driver<Object = Self, File = F>,
> > + D: drm::Driver<Object<Registered> = Self, File = F>,
> > F: drm::file::DriverFile<Driver = D>,
> > {
> > let mut handle: u32 = 0;
> > @@ -137,7 +154,7 @@ fn create_handle<D, F>(&self, file:
> > &drm::File<F>) -> Result<u32>
> > fn lookup_handle<D, F>(file: &drm::File<F>, handle: u32) ->
> > Result<ARef<Self>>
> > where
> > Self: AllocImpl<Driver = D>,
> > - D: drm::Driver<Object = Self, File = F>,
> > + D: drm::Driver<Object<Registered> = Self, File = F>,
> > F: drm::file::DriverFile<Driver = D>,
> > {
> > // SAFETY: The arguments are all valid per the type
> > invariants.
> > @@ -177,16 +194,18 @@ impl<T: IntoGEMObject> BaseObject for T {}
> > ///
> > /// # Invariants
> > ///
> > -/// - `self.obj` is a valid instance of a `struct drm_gem_object`.
> > +/// * `self.obj` is a valid instance of a `struct drm_gem_object`.
> > +/// * Any type invariants of `Ctx` apply to the parent DRM device
> > for this GEM object.
> > #[repr(C)]
> > #[pin_data]
> > -pub struct Object<T: DriverObject + Send + Sync> {
> > +pub struct Object<T: DriverObject + Send + Sync, Ctx:
> > DeviceContext = Registered> {
> > obj: Opaque<bindings::drm_gem_object>,
> > #[pin]
> > data: T,
> > + _ctx: PhantomData<Ctx>,
> > }
> >
> > -impl<T: DriverObject> Object<T> {
> > +impl<T: DriverObject, Ctx: DeviceContext> Object<T, Ctx> {
> > const OBJECT_FUNCS: bindings::drm_gem_object_funcs =
> > bindings::drm_gem_object_funcs {
> > free: Some(Self::free_callback),
> > open: Some(open_callback::<T>),
> > @@ -206,11 +225,12 @@ impl<T: DriverObject> Object<T> {
> > };
> >
> > /// Create a new GEM object.
> > - pub fn new(dev: &drm::Device<T::Driver>, size: usize) ->
> > Result<ARef<Self>> {
> > + pub fn new(dev: &drm::Device<T::Driver, Ctx>, size: usize) ->
> > Result<ARef<Self>> {
> > let obj: Pin<KBox<Self>> = KBox::pin_init(
> > try_pin_init!(Self {
> > obj:
> > Opaque::new(bindings::drm_gem_object::default()),
> > data <- T::new(dev, size),
> > + _ctx: PhantomData,
> > }),
> > GFP_KERNEL,
> > )?;
> > @@ -219,6 +239,8 @@ pub fn new(dev: &drm::Device<T::Driver>, size:
> > usize) -> Result<ARef<Self>> {
> > unsafe { (*obj.as_raw()).funcs = &Self::OBJECT_FUNCS };
> >
> > // SAFETY: The arguments are all valid per the type
> > invariants.
> > + // INVARIANT: We use `dev` for creating the GEM object,
> > which is known to be in state `Ctx` -
> > + // ensuring that the GEM object's pointer to the DRM
> > device is always in the same state.
> > to_result(unsafe {
> > bindings::drm_gem_object_init(dev.as_raw(), obj.obj.get(), size)
> > })?;
> >
> > // SAFETY: We will never move out of `Self` as `ARef<Self>`
> > is always treated as pinned.
> > @@ -232,13 +254,15 @@ pub fn new(dev: &drm::Device<T::Driver>,
> > size: usize) -> Result<ARef<Self>> {
> > }
> >
> > /// Returns the `Device` that owns this GEM object.
> > - pub fn dev(&self) -> &drm::Device<T::Driver> {
> > + pub fn dev(&self) -> &drm::Device<T::Driver, Ctx> {
> > // SAFETY:
> > // - `struct drm_gem_object.dev` is initialized and valid
> > for as long as the GEM
> > // object lives.
> > // - The device we used for creating the gem object is
> > passed as &drm::Device<T::Driver> to
> > // Object::<T>::new(), so we know that `T::Driver` is the
> > right generic parameter to use
> > // here.
> > + // - Any type invariants of `Ctx` are upheld by using the
> > same `Ctx` for the `Device` we
> > + // return.
> > unsafe { drm::Device::from_raw((*self.as_raw()).dev) }
> > }
> >
> > @@ -264,7 +288,7 @@ extern "C" fn free_callback(obj: *mut
> > bindings::drm_gem_object) {
> > }
> >
> > // SAFETY: Instances of `Object<T>` are always reference-counted.
> > -unsafe impl<T: DriverObject> crate::sync::aref::AlwaysRefCounted
> > for Object<T> {
> > +unsafe impl<T: DriverObject, Ctx: DeviceContext> AlwaysRefCounted
> > for Object<T, Ctx> {
> > fn inc_ref(&self) {
> > // SAFETY: The existence of a shared reference guarantees
> > that the refcount is non-zero.
> > unsafe { bindings::drm_gem_object_get(self.as_raw()) };
> > @@ -279,9 +303,9 @@ unsafe fn dec_ref(obj: NonNull<Self>) {
> > }
> > }
> >
> > -impl<T: DriverObject> super::private::Sealed for Object<T> {}
> > +impl<T: DriverObject, Ctx: DeviceContext> super::private::Sealed
> > for Object<T, Ctx> {}
> >
> > -impl<T: DriverObject> Deref for Object<T> {
> > +impl<T: DriverObject, Ctx: DeviceContext> Deref for Object<T, Ctx>
> > {
> > type Target = T;
> >
> > fn deref(&self) -> &Self::Target {
> > @@ -289,7 +313,7 @@ fn deref(&self) -> &Self::Target {
> > }
> > }
> >
> > -impl<T: DriverObject> AllocImpl for Object<T> {
> > +impl<T: DriverObject, Ctx: DeviceContext> AllocImpl for Object<T,
> > Ctx> {
> > type Driver = T::Driver;
> >
> > const ALLOC_OPS: AllocOps = AllocOps {
> > --
> > 2.52.0
> >
> >
^ permalink raw reply [flat|nested] 10+ messages in thread