[PATCH] drm: rework description of primary and cursor planes

[Simon Ser]

On Wednesday, December 9th, 2020 at 8:40 PM, Daniel Vetter <daniel at ffwll.ch> wrote:

> > But it's not enough, can't have two CRTCs with the same primary plane. Well,
> > I give up, it's just simpler to use Daniel's criteria.
>
> Yeah, also with the validation check we'll now real quick if any driver
> gets it wrong. Then I think we can have a useful discussion about why, and
> what to do with that case. As-is we're kinda drafting specs in the void,
> which is always a bit tough ...
>
> That's kinda another reason for doing the stricter check I proposed, it's
> easier to check and guarantee (on both the driver and compositor side
> hopefully).

Hmm, actually, I'm already hitting a driver which doesn't guarantee that.
amdgpu with my hardware [1] has the first primary plane linked to the the last
CRTC, the second primary plane linked to the second-to-last CRTC, and so on.

[1]: https://drmdb.emersion.fr/devices/129e158a4d9f