"Kristian H. Kristensen" <hoegsberg@gmail.com> writes:

> Rockchip doesn't support per-pixel alpha blending for the lowest
> window in the stack. While the hw supports restacking the windows, we
> don't expose that in KMS, so just filter out alpha formats for the
> primary plane.

In discussing this for VC4, we noted that an alternative is to just set
up the lowest plane as an RGBX format, since alpha is premultiplied and
the background is black.