linux-kernel - Re: [PATCH v3 04/14] rust: drm: gem: Support driver-private GEM object types

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Message-ID: <1e486de119bb2335b71018417800c8e90172202b.camel@redhat.com>
Date: Mon, 08 Sep 2025 13:39:11 -0400
From: Lyude Paul <lyude@...hat.com>
To: Daniel Almeida <daniel.almeida@...labora.com>
Cc: dri-devel@...ts.freedesktop.org, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Danilo Krummrich <dakr@...nel.org>, Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann	 <tzimmermann@...e.de>, David
 Airlie <airlied@...il.com>, Simona Vetter	 <simona@...ll.ch>, Miguel Ojeda
 <ojeda@...nel.org>, Alex Gaynor	 <alex.gaynor@...il.com>, Boqun Feng
 <boqun.feng@...il.com>, Gary Guo	 <gary@...yguo.net>,
 Björn Roy Baron	 <bjorn3_gh@...tonmail.com>, Benno
 Lossin <lossin@...nel.org>, Andreas Hindborg	 <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross	 <tmgross@...ch.edu>, Asahi
 Lina <lina+kernel@...hilina.net>, "open list:DRM DRIVER FOR NVIDIA GPUS
 [RUST]"	 <nouveau@...ts.freedesktop.org>
Subject: Re: [PATCH v3 04/14] rust: drm: gem: Support driver-private GEM
 object types

On Thu, 2025-09-04 at 09:51 -0300, Daniel Almeida wrote:
> > -        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: DriverAllocImpl::<T>::ALLOC_OPS.gem_create_object,
> > +        prime_handle_to_fd: DriverAllocImpl::<T>::ALLOC_OPS.prime_handle_to_fd,
> > +        prime_fd_to_handle: DriverAllocImpl::<T>::ALLOC_OPS.prime_fd_to_handle,
> > +        gem_prime_import: DriverAllocImpl::<T>::ALLOC_OPS.gem_prime_import,
> > +        gem_prime_import_sg_table: DriverAllocImpl::<T>::ALLOC_OPS.gem_prime_import_sg_table,
> > +        dumb_create: DriverAllocImpl::<T>::ALLOC_OPS.dumb_create,
> > +        dumb_map_offset: DriverAllocImpl::<T>::ALLOC_OPS.dumb_map_offset,
> 
> There are now possibly infinitely many ALLOC_OPS. Is it a problem that
> we’re choosing a particular one here?

I haven't tested this, but I'm fairly certain it should be fine - gem objects
already have their own drm_gem_object_funcs, and all of these callbacks are
concerned with driver-wide gem hooks that expect the default gem object type
that the driver uses. If I did things properly, it should only really be
possible to create a driver-private GEM object from within the driver -
meaning that none of these callbacks will ever be invoked for one and can be
safely ignored there.

TBH - on the nova side we decided that I shouldn't spend too much time on this
aspect of the gem patch series since I don't think any driver has an immediate
usecase for driver-private object GEM types. So if we'd rather consider this
patch in the future vs. now I'm totally fine with that.

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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