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

Stéphane Marchesin stephane.marchesin at gmail.com
Mon Apr 25 16:35:20 PDT 2011

On Mon, Apr 25, 2011 at 16:22, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> On Mon, 25 Apr 2011 16:16:18 -0700
> Keith Packard <keithp at keithp.com> 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.
> Yes, that matches my understanding as well.  I've deliberately made the
> implementation flexible there though, under the assumption that some
> hardware allows a plane to be directed at more than one CRTC (though
> probably not simultaneously).
> Arguably, this is something we should have done when the
> connector/encoder split was done (making planes in general first class
> objects).  But with today's code, treating a CRTC as a pixel pump and a
> primary plane seems fine, with overlays tacked onto the side as
> secondary pixel sources but tied to a specific CRTC.

What is the plan for supporting multiple formats? When I looked at
this for nouveau it ended up growing out of control when adding
support for all the YUV (planar, packed, 12 or 16 bpp formats) and RGB
format combinations.


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