On Mon Aug 31, 2026 at 10:42 PM CEST, Gary Guo wrote:
> I think if you change the signatue of `registration_data_with` slightly:
>
> pub fn registration_data_with<'this, F: ForLt + 'static, R>(
> &'this self,
> f: impl for<'a> FnOnce(Pin<&'this F::Of<'a>>) -> R,
> ^ note this is changed from 'a to 'this
> ) -> Result<R>;
>
> then there will be an implied bound available inside the callback where 'a
> outlives 'this, and thus the function callback is able to perform coercion of
> any T<'a> to T<'this> provided that `T` is covariant over lifetime `'a`.
>
> [ The coercion won't work when doing abstract `F::Of` on the bus abstraction
> side, but for any user it is dealing with concrete types so the compiler sees
> specific types and thus can check variance ]
>
> Then your projection can just be
>
> aux.registration_data_project(|x| &x.field)
>
> I haven't tried it out but I think it should work.
I gave this a shot and it seems to work out, it's a good simplification. I think
we don't even need a dedicated project method in this case. We could add an
alias for with() just to clarify the intent, but not sure that's worth.
@Alistair: Here's the diff I tested this with:
diff --git a/drivers/gpu/drm/nova/file.rs b/drivers/gpu/drm/nova/file.rs
index 798b14f33e20..9babaa0b9a5f 100644
--- a/drivers/gpu/drm/nova/file.rs
+++ b/drivers/gpu/drm/nova/file.rs
@@ -13,6 +13,7 @@
gem::BaseObject,
Registered, //
},
+ num::Bounded,
prelude::*,
transmute::AsBytes,
uaccess::UserSlice,
@@ -32,10 +33,12 @@
impl GpuInfo {
fn new(reg_data: &DrmRegData<'_>) -> Self {
+ let spec = reg_data.api.with(|api| api.get_ref().spec());
+
reg_data.api.with(|api| {
Self(uapi::drm_nova_gpu_info {
- architecture: api.architecture(),
- implementation: api.implementation(),
+ architecture: u32::from(Bounded::from(spec.chipset.arch())),
+ implementation: spec.chipset.implementation(),
vram_size: api.vram_size(),
gpu_name: api.gpu_name(),
gpu_short_name: api.gpu_short_name(),
diff --git a/drivers/gpu/nova-core/api.rs b/drivers/gpu/nova-core/api.rs
index c9ae48d278af..6825d3562d56 100644
--- a/drivers/gpu/nova-core/api.rs
+++ b/drivers/gpu/nova-core/api.rs
@@ -13,6 +13,8 @@
types::ForLt, //
};
+pub use crate::gpu::Spec;
+
use crate::gpu::{
Gpu, //
};
@@ -44,14 +46,9 @@ pub fn handle(adev: &auxiliary::Device<Bound>) ->
Result<NovaCoreApiHandle<'_>>
NovaCoreApiHandle::of(adev)
}
- /// Returns the architecture identifier of this GPU.
- pub fn architecture(&self) -> u32 {
- self.gpu.spec.chipset.arch() as u32
- }
-
- /// Returns the implementation identifier of this GPU.
- pub fn implementation(&self) -> u32 {
- self.gpu.spec.chipset.implementation()
+ /// Returns the GPU [`Spec`].
+ pub fn spec(&self) -> &Spec {
+ &self.gpu.spec
}
/// Returns the size of the PCIe BAR used for accessing VRAM, typically
@@ -78,7 +75,9 @@ fn of(adev: &'a auxiliary::Device<Bound>) -> Result<Self> {
}
/// Access the [`NovaCoreApi`] through a closure.
- pub fn with<R>(&self, f: impl for<'b> FnOnce(Pin<&'b NovaCoreApi<'b>>) ->
R) -> R {
+ ///
+ /// References to covariant sub-fields can be returned from the closure
directly.
+ pub fn with<R>(&self, f: impl for<'b> FnOnce(Pin<&'a NovaCoreApi<'b>>) ->
R) -> R {
self.adev
.registration_data_with::<ForLt!(NovaCoreApi<'_>), R>(f)
.expect("TypeId was validated in NovaCoreApiHandle::of()")
diff --git a/drivers/gpu/nova-core/gpu.rs b/drivers/gpu/nova-core/gpu.rs
index 166f4bb55752..04b97b0f89f4 100644
--- a/drivers/gpu/nova-core/gpu.rs
+++ b/drivers/gpu/nova-core/gpu.rs
@@ -42,7 +42,8 @@ macro_rules! define_chipset {
::kernel::macros::paste!(
/// Enum representation of the GPU chipset.
#[derive(fmt::Debug, Copy, Clone, PartialOrd, Ord, PartialEq, Eq)]
- pub(crate) enum Chipset {
+ #[allow(missing_docs)]
+ pub enum Chipset {
$($variant = $value),*,
}
@@ -119,7 +120,8 @@ fn try_from(value: u32) -> Result<Self, Self::Error> {
});
impl Chipset {
- pub(crate) const fn arch(self) -> Architecture {
+ /// Returns the [`Architecture`] generation of this chipset.
+ pub const fn arch(self) -> Architecture {
match self {
Self::TU102 | Self::TU104 | Self::TU106 | Self::TU117 |
Self::TU116 => {
Architecture::Turing
@@ -138,8 +140,8 @@ pub(crate) const fn arch(self) -> Architecture {
}
}
- /// Returns the implementation identifier of this chipset.
- pub(crate) const fn implementation(self) -> u32 {
+ /// Returns the implementation identifier of this chipset within its
architecture.
+ pub const fn implementation(self) -> u32 {
self as u32 & 0xf
}
@@ -167,7 +169,8 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// Enum representation of the GPU generation.
#[derive(fmt::Debug, Copy, Clone)]
#[repr(u32)]
- pub(crate) enum Architecture with TryFrom<Bounded<u32, 6>> {
+ #[allow(missing_docs)]
+ pub enum Architecture with TryFrom<Bounded<u32, 6>> {
Turing = uapi::drm_nova_architecture_NOVA_DRM_ARCHITECTURE_TURING,
Ampere = uapi::drm_nova_architecture_NOVA_DRM_ARCHITECTURE_AMPERE,
Hopper = uapi::drm_nova_architecture_NOVA_DRM_ARCHITECTURE_HOPPER,
@@ -202,8 +205,9 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// Structure holding a basic description of the GPU: `Chipset` and `Revision`.
#[derive(Clone, Copy)]
-pub(crate) struct Spec {
- pub(crate) chipset: Chipset,
+pub struct Spec {
+ /// The GPU chipset.
+ pub chipset: Chipset,
revision: Revision,
}
diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs
index 60dfbec8f330..06f816420790 100644
--- a/rust/kernel/auxiliary.rs
+++ b/rust/kernel/auxiliary.rs
@@ -305,6 +305,10 @@ unsafe fn registration_data_pinned<F: ForLt +
'static>(&self) -> Result<Pin<&F::
/// `F` is the [`ForLt`](trait@ForLt) encoding of the data type. The
closure receives a pinned
/// reference to the registration data.
///
+ /// The outer reference carries the `&self` lifetime while the inner type
carries the HRTB
+ /// lifetime `'a`, implying `'a` outlives `&self`. This allows the closure
to coerce covariant
+ /// sub-fields (e.g. `&'a T` to the caller's lifetime) and return them
directly in `R`.
+ ///
/// For covariant types that implement [`trait@CovariantForLt`], prefer
/// [`registration_data`](Self::registration_data) which returns a direct
reference.
///
@@ -314,13 +318,14 @@ unsafe fn registration_data_pinned<F: ForLt +
'static>(&self) -> Result<Pin<&F::
/// Returns [`ENOENT`] if no registration data has been set, e.g. when the
device was
/// registered by a C driver.
#[inline]
- pub fn registration_data_with<F: ForLt + 'static, R>(
- &self,
- f: impl for<'a> FnOnce(Pin<&'a F::Of<'a>>) -> R,
+ pub fn registration_data_with<'this, F: ForLt + 'static, R>(
+ &'this self,
+ f: impl for<'a> FnOnce(Pin<&'this F::Of<'a>>) -> R,
) -> Result<R> {
- // SAFETY: The HRTB closure prevents the caller from smuggling in
references with a
- // concrete short lifetime, making the round-trip from `'static` sound
regardless of
- // variance.
+ // SAFETY: The HRTB on the inner type prevents the caller from
exploiting a specific
+ // choice of `'a`. Covariant sub-fields can be safely coerced to
`'this`, while
+ // invariant fields cannot be coerced and thus cannot escape with an
incorrect
+ // lifetime.
let pinned = unsafe { self.registration_data_pinned::<F>()? };
Ok(f(pinned))
