Re: [RFC PATCH 02/12] drm/dep: Add DRM dependency queue layer

[Daniel Almeida]

> On 17 Mar 2026, at 09:31, Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
> 
> On Tue Mar 17, 2026 at 3:47 AM CET, Daniel Almeida wrote:
>> I agree with what Danilo said below, i.e.:  IMHO, with the direction that DRM
>> is going, it is much more ergonomic to add a Rust component with a nice C
>> interface than doing it the other way around.
> 
> This is not exactly what I said. I was talking about the maintainance aspects
> and that a Rust Jobqueue implementation (for the reasons explained in my initial
> reply) is easily justifiable in this aspect, whereas another C implementation,
> that does *not* replace the existing DRM scheduler entirely, is much harder to
> justify from a maintainance perspective.

Ok, I misunderstood your point a bit.

> 
> I'm also not sure whether a C interface from the Rust side is easy to establish.
> We don't want to limit ourselves in terms of language capabilities for this and
> passing through all the additional infromation Rust carries in the type system
> might not be straight forward.
> 
> It would be an experiment, and it was one of the ideas behind the Rust Jobqueue
> to see how it turns if we try. Always with the fallback of having C
> infrastructure as an alternative when it doesn't work out well.

From previous experience in doing Rust to C FFI in NVK, I don’t see, at
first, why this can’t work. But I agree with you, there may very well be
unanticipated things here and this part is indeed an experiment. No argument
from me here.

> 
> Having this said, I don't see an issue with the drm_dep thing going forward if
> there is a path to replacing DRM sched entirely.

The issues I pointed out remain. Even if the plan is to have drm_dep + JobQueue
(and no drm_sched). I feel that my point of considering doing it in Rust remains.

> 
> The Rust component should remain independent from this for the reasons mentioned
> in [1].
> 
> [1] https://lore.kernel.org/dri-devel/DH51W6XRQXYX.3M30IRYIWZLFG@xxxxxxxxxx/

Ok

— Daniel