On 9/8/25 8:46 PM, Lyude Paul wrote:
> Now that my rust skills have been honed, I noticed that there's a lot of
> generics in our gem bindings that don't actually need to be here. Currently
> the hierarchy of traits in our gem bindings looks like this:
>
> * Drivers implement:
> * BaseDriverObject<T: DriverObject> (has the callbacks)
> * DriverObject (has the drm::Driver type)
> * Crate implements:
> * IntoGEMObject for Object<T> where T: DriverObject
> Handles conversion to/from raw object pointers
> * BaseObject for T where T: IntoGEMObject
> Provides methods common to all gem interfaces
>
> Also of note, this leaves us with two different drm::Driver associated
> types:
> * DriverObject::Driver
> * IntoGEMObject::Driver
>
> I'm not entirely sure of the original intent here unfortunately (if anyone
> is, please let me know!), but my guess is that the idea would be that some
> objects can implement IntoGEMObject using a different ::Driver than
> DriverObject - presumably to enable the usage of gem objects from different
> drivers. A reasonable usecase of course.
>
> However - if I'm not mistaken, I don't think that this is actually how
> things would go in practice. Driver implementations are of course
> implemented by their associated drivers, and generally drivers are not
> linked to each-other when building the kernel. Which is to say that even in
> a situation where we would theoretically deal with gem objects from another
> driver, we still wouldn't have access to its drm::driver::Driver
> implementation. It's more likely we would simply want a variant of gem
> objects in such a situation that have no association with a
> drm::driver::Driver type.
>
> Taking that into consideration, we can assume the following:
> * Anything that implements BaseDriverObject will implement DriverObject
> In other words, all BaseDriverObjects indirectly have an associated
> ::Driver type - so the two traits can be combined into one with no
> generics.
> * Not everything that implements IntoGEMObject will have an associated
> ::Driver, and that's OK.
>
> And with this, we now can do quite a bit of cleanup with the use of
> generics here. As such, this commit:
>
> * Removes the generics on BaseDriverObject
> * Moves DriverObject::Driver into BaseDriverObject
> * Removes DriverObject
> * Removes IntoGEMObject::Driver
> * Add AllocImpl::Driver, which we can use as a binding to figure out the
> correct File type for BaseObject
>
> Leaving us with a simpler trait hierarchy that now looks like this:
>
> * Drivers implement: BaseDriverObject
> * Crate implements:
> * IntoGEMObject for Object<T> where T: DriverObject
> * BaseObject for T where T: IntoGEMObject
>
> Which makes the code a lot easier to understand and build on :).
>
> Signed-off-by: Lyude Paul <ly...@redhat.com>
> Reviewed-by: Daniel Almeida <daniel.alme...@collabora.com>
Acked-by: Danilo Krummrich <d...@kernel.org>
