[RFC PATCH hwc] drm_hwcomposer: set CRTC background color when available

[Maarten Lankhorst]

Op 22-02-18 om 04:54 schreef Stefan Schake:
> Android assumes an implicit black background layer is always present
> behind all layers it specifies for composition. drm_hwcomposer currently
> punts responsibility for this to the kernel/DRM platform and puts layers
> with per-pixel alpha content on the primary plane when requested.
>
> On some platforms (e.g. VC4) a background color fill has a cycle cost for
> the hardware composer and is not enabled by default. Instead, userland can
> request a background color through a CRTC property. Use this property to
> specify the implicit black background Android expects.
>
> Signed-off-by: Stefan Schake <stschake at gmail.com>
> ---
> Kernel changes for this (background_color) are available here:
>
> https://github.com/stschake/linux/commits/background-upstream
>
> Sending as RFC because I'm not entirely clear on whose responsibility
> this should be, on most DRM drivers it seems to be implicit. I think
> a case could also be made that VC4 should not accept alpha formats on
> the lowest layer or enable background color fill when given one anyway.
> On the other hand, userland control over background color seems desirable
> regardless and is a feature of multiple hardware composers (i915, vc4, omap).
Ping? Would be nice if we were moving forward. :)