Some hardware only supports the COVERAGE blend mode and lacks PREMULTI
support entirely. DRM currently requires that PREMULTI is present when
creating a blend mode property, which prevents such drivers from being
properly upstreamed.

This series removes this restriction and allows drivers to create a blend
mode property without PREMULTI.

On Weston (userspace), we are working [1] towards adding support for
this kind of hardware.

[1] https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/2046

v4:
- Trigger warnings instead of errors when pixel format with alpha is
  exposed but blend mode is not setup.
- Require blend mode only when plane exposes pixel formats with alpha, not
  when it supports the alpha property.

v3:
- Changed where we enforce drivers to expose blend mode for planes that
  support the alpha property or pixel formats with alpha.
- Fixed missing check to forbid calling
  drm_plane_create_blend_mode_property() with a zero bitmask of
  supported modes.

v2:
- Force drivers to expose blend mode if plane supports alpha property
  or pixel format with alpha.

Leandro Ribeiro (2):
  drm/drm_blend: allow blend mode property without PREMULTI
  drm: ensure blend mode supported if pixel format with alpha exposed

 drivers/gpu/drm/drm_blend.c       | 20 ++++++++++++++------
 drivers/gpu/drm/drm_mode_config.c | 21 +++++++++++++++++++++
 2 files changed, 35 insertions(+), 6 deletions(-)

-- 
2.54.0