drm: Add per-plane pixel blend mode property

Pixel blend modes represent the alpha blending equation
selection, describing how the pixels from the current
plane are composited with the background.

Adds a pixel_blend_mode to drm_plane_state and a
blend_mode_property to drm_plane, and related support
functions.

Defines three blend modes in drm_blend.h.

Changes since v1:
 - Moves the blending equation into the DOC comment
 - Refines the comments of drm_plane_create_blend_mode_property to not
   enumerate the #defines, but instead the string values
 - Uses fg.* instead of pixel.* and plane_alpha instead of plane.alpha
Changes since v2:
 - Refines the comments of drm_plane_create_blend_mode_property:
      1) Puts the descriptions (after the ":") on a new line
      2) Adds explaining why @supported_modes need PREMUL as default
Changes since v3:
 - Refines drm_plane_create_blend_mode_property(). drm_property_add_enum()
   can calculate the index itself just fine, so no point in having the
   caller pass it in.
 - Since the current DRM assumption is that alpha is premultiplied
   as default, define DRM_MODE_BLEND_PREMULTI as 0 will be better.
 - Refines some comments.
Changes since v4:
 - Adds comments in drm_blend.h.
 - Removes setting default value in drm_plane_create_blend_mode_property()
   as it is already in __drm_atomic_helper_plane_reset().
 - Fixes to use state->pixel_blend_mode instead of using
   plane->state->pixel_blend_mode in reset function.
 - Rebases on drm-misc-next.

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Lowry Li <lowry.li@arm.com>
Signed-off-by: Ayan Kumar Halder <ayan.halder@arm.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/245734/

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 6dd5036545ec..284a5d2bc11d 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -3569,6 +3569,7 @@ void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
 	/* Reset the alpha value to fully opaque if it matters */
 	if (plane->alpha_property)
 		state->alpha = plane->alpha_property->values[1];
+	state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
 
 	plane->state = state;
 }