[RFC] drm: add overlays as first class KMS objects

[Alan Cox]

> And what if you don't have a "default" plane as such. For example, OMAP3 
> has one graphics plane and two video planes, and two output paths. Each
> of the planes can be assigned to zero or one outputs. To accomodate this,
> the design should allow for CRTCs without any scanout buffers.

Some TV type stuff is a bit like that - well there may be a scanout buffer
but its on a protected hardware path and no part of the system except
certain bits of hardware can touch it from decrypt to output connector.

Clearly a scanout buffer isn't the only way to describe what a crtc is
outputting and you need a somewhat more flexible handle including one you
can acquire somehow to represent other objects like capture buffers,
protected planes and live video merges.

Alan