Re: [WIP RFC v2 28/35] rust: drm/kms: Add RawPlane::framebuffer()

[Lyude Paul <lyude@redhat.com>]

On Thu, 2024-11-28 at 11:29 -0300, Daniel Almeida wrote:
> Hi Lyude,
> 
> > On 30 Sep 2024, at 20:10, Lyude Paul <lyude@redhat.com> wrote:
> > 
> > Returns the Framebuffer currently assigned in an atomic plane state.
> 
> A bit unrelated to this patch, but can you have more than one framebuffer active? 

Not on a single display plane, but you can have multiple display planes active
on the same CRTC that each have their own framebuffer. Also, some framebuffers
can have more than a single buffer object attached to them (for stuff like
stereoscopic displays).

> 
> i.e.: for things like overlays, etc

JFYI an overlay is basically just a type of display plane, but has limitations
a universal display plane doesn't have. You see it mostly on older hardware,
where I think the common usecase was to do video decoding and isolate it to a
single display plane to lower the resource usage of actually compositing the
resulting video onto the display.

> 
> > 
> > Signed-off-by: Lyude Paul <lyude@redhat.com>
> > ---
> > rust/kernel/drm/kms/plane.rs | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> > 
> > diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
> > index cd5167e6441f1..15efa53fda8d3 100644
> > --- a/rust/kernel/drm/kms/plane.rs
> > +++ b/rust/kernel/drm/kms/plane.rs
> > @@ -31,6 +31,7 @@
> >     StaticModeObject,
> >     atomic::*,
> >     crtc::*,
> > +    framebuffer::*,
> > };
> > 
> > /// The main trait for implementing the [`struct drm_plane`] API for [`Plane`]
> > @@ -521,6 +522,13 @@ fn atomic_helper_check<S>(
> >             )
> >         })
> >     }
> > +
> > +    /// Return the framebuffer currently set for this plane state
> > +    #[inline]
> > +    fn framebuffer(&self) -> Option<&Framebuffer<<Self::Plane as ModeObject>::Driver>> {
> > +        // SAFETY: The layout of Framebuffer<T> is identical to `fb`
> > +        unsafe { self.as_raw().fb.as_ref().map(|fb| Framebuffer::from_raw(fb)) }
> > +    }
> > }
> > impl<T: AsRawPlaneState + ?Sized> RawPlaneState for T {}
> > 
> > -- 
> > 2.46.1
> > 
> > 
> 
> LGTM
> 
> — Daniel
> 

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

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