[PATCH] drm/amd/display: add cursor pitch check

[Simon Ser]

CC Daniel Vetter and Bas, see below…

On Thursday, November 12, 2020 8:56 PM, Kazlauskas, Nicholas <nicholas.kazlauskas at amd.com> wrote:

> Reviewed-by: Nicholas Kazlauskasnicholas.kazlauskas at amd.com

Thanks for the review!

> > Couple questions:
> >
> > - This implements a single check for all GPU generations. Is my
> >   assumption correct here? It seems like this check is OK for at least
> >   DCN 1.0 and DCN 2.0.
> >
> > - We should really implement better checks. What features are supported
> >   on the cursor plane? Is scaling supported? Is cropping supported? Is
> >   rotation always supported?
> >
>
> On DCE and DCN there is no dedicated hardware cursor plane. You get a
> cursor per pipe but it's going to inherit the scaling and positioning
> from the underlying pipe.
>
> There's software logic to ensure we position the cursor in the correct
> location in CRTC space independent on the underlying DRM plane's scaling
> and positioning but there's no way for us to correct the scaling. Cursor
> will always be 64, 128, or 256 in the pipe's destination space.

Interesting.

Daniel Vetter: what would be the best way to expose this to user-space?
Maybe we should just make atomic commits with a cursor plane fail when
scaling is used on the primary plane?

Disabling the cursor plane sounds better than displaying the wrong
image.

> Cursor can be independently rotated in hardware but this isn't something
> we expose support for to userspace.

Hmm, I see that cursor planes have the "rotation" property exposed:

    "rotation": bitmask {rotate-0, rotate-90, rotate-180, rotate-270}

In fact all planes have it. It's done in amdgpu_dm_plane_init (behind a
`dm->adev->asic_type >= CHIP_BONAIRE` condition).

Is this an oversight?

> The pitch check of 64/128/256 is OK but we don't support 256 on DCE.

Yeah, I've noticed that. The size check right above should catch it
in most cases I think, because max_cursor_size is 128 on DCE. Side
note, max_cursor_size is 64 on DCE 6.0.