On 2026-09-01 at 06:42 +1000, Gary Guo <[email protected]> wrote... > On Mon Aug 31, 2026 at 9:08 PM BST, Danilo Krummrich wrote: > > On Fri Aug 28, 2026 at 5:35 AM CEST, Alistair Popple wrote: > >> +/// API handle for the auxiliary bus child drivers to interact with > >> nova-core. > >> +pub struct NovaCoreApi<'bound> { > >> + #[expect(unused)] > >> + pub(crate) gpu: Pin<&'bound Gpu<'bound>>, > >> +} > >> + > >> +impl NovaCoreApi<'_> { > >> + /// Obtain a [`NovaCoreApi`] handle from an auxiliary device > >> registered > >> + /// by nova-core. > >> + pub fn of(adev: &auxiliary::Device<Bound>) -> > >> Result<Pin<&NovaCoreApi<'_>>> { > >> + adev.registration_data::<CovariantForLt!(NovaCoreApi<'_>)>() > >> + } > >> +} > > > > CovariantForLt does not hold anymore on latest drm-rust-next, as Cmdq has a > > Mutex. So, this needs ForLt now and therefore the approach that I shared in > > [1] > > a while ago. I applied the changes in [2] to fix it up.
I can see why the mutex means covariance no longer holds, but I would kind of also expect it to not compile given it surely can't be safe here to treat an invariant type as covariant. Is this just a limitation of the current CovariantForLt implementation not being able to prove covariance or am I missing something else? Thanks. - Alistair
