Re: [WIP RFC v2 26/35] WIP: rust: drm/kms: Add RawPlaneState::atomic_helper_check()

[Lyude Paul]

On Thu, 2024-11-28 at 11:04 -0300, Daniel Almeida wrote:
> Hi Lyude,
> 
> > On 30 Sep 2024, at 20:10, Lyude Paul <lyude@xxxxxxxxxx> wrote:
> > 
> > Add a binding for drm_atomic_helper_check_plane_state(). Since we want to
> > make sure that the user is passing in the new state for a Crtc instead of
> > an old state, we explicitly ask for a reference to a BorrowedCrtcState.
> > 
> > Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> > 
> > ---
> > 
> > TODO:
> > * Add support for scaling options
> 
> Can / should this be a separate commit? This would allow this one to go in earlier.

It could be but I don't have any implementation of this yet, which is why it's
mentioned as a todo.

> 
> > 
> > Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> > ---
> > rust/kernel/drm/kms/plane.rs | 25 +++++++++++++++++++++++++
> > 1 file changed, 25 insertions(+)
> > 
> > diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
> > index 4d16d53179fca..cd5167e6441f1 100644
> > --- a/rust/kernel/drm/kms/plane.rs
> > +++ b/rust/kernel/drm/kms/plane.rs
> > @@ -496,6 +496,31 @@ fn crtc<'a, 'b: 'a>(&'a self) -> Option<&'b OpaqueCrtc<<Self::Plane as ModeObjec
> >         // SAFETY: This cast is guaranteed safe by `OpaqueCrtc`s invariants.
> >         NonNull::new(self.as_raw().crtc).map(|c| unsafe { OpaqueCrtc::from_raw(c.as_ptr()) })
> >     }
> > +
> > +    /// Run the atomic check helper for this plane and the given CRTC state
> > +    fn atomic_helper_check<S>(
> > +        &mut self,
> > +        crtc_state: &BorrowedCrtcState<'_, S>,
> > +        can_position: bool,
> > +        can_update_disabled: bool
> > +    ) -> Result
> 
> Some docs on the arguments would be nice IMHO. Things like `can_position` and `can_update_disabled`
> seem a bit opaque.
> 

I'm curious if you have any idea whether we can link back to kernel docs in
rust? We have pretty extensive documentation written up on almost all of this
already, I just have no idea how to incorporate it on the rust side.

> > +    where
> > +        S: FromRawCrtcState,
> > +        S::Crtc: AsRawCrtc<Driver = <Self::Plane as ModeObject>::Driver>
> > +    {
> > +        // SAFETY: We're passing the mutable reference from `self.as_raw_mut()` directly to DRM,
> > +        // which is safe.
> > +        to_result(unsafe {
> > +            bindings::drm_atomic_helper_check_plane_state(
> > +                self.as_raw_mut(),
> > +                crtc_state.as_raw(),
> > +                bindings::DRM_PLANE_NO_SCALING as _, // TODO: add parameters for scaling
> > +                bindings::DRM_PLANE_NO_SCALING as _,
> 
> No scaling means that you can only select the display’s highest resolution?

No, I believe (correct me if I'm wrong here chat) that this is about plane
scaling rather than resolution. A lot of display hardware has the ability to
do hardware-scaling of individual display planes, so that the input
framebuffer for a plane can be larger than the actual display plane that's on-
screen.

> 
> > +                can_position,
> > +                can_update_disabled
> > +            )
> > +        })
> > +    }
> > }
> > impl<T: AsRawPlaneState + ?Sized> RawPlaneState for T {}
> > 
> > -- 
> > 2.46.1
> > 
> 
> Barring the comment above about the docs, this looks good.
> 
> — Daniel
> 

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

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