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

Ville Syrjälä syrjala at sci.fi
Tue Apr 26 08:20:03 PDT 2011

On Mon, Apr 25, 2011 at 04:16:18PM -0700, Keith Packard wrote:
> On Mon, 25 Apr 2011 15:12:20 -0700, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> > Overlays are a bit like half-CRTCs.  They have a location and fb, but
> > don't drive outputs directly.  Add support for handling them to the core
> > KMS code.
> Are overlays/underlays not associated with a specific CRTC? To my mind,
> overlays are another scanout buffer associated with a specific CRTC, so
> you'd create a scanout buffer and attach that to a specific scanout slot
> in a crtc, with the 'default' slot being the usual graphics plane.

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.

Also a glance at DirectFB and OpenWF Display APIs might be helpful.

Ville Syrjälä
syrjala at sci.fi

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