[PATCH v2 1/4] drm/ast: create blend mode property on cursor plane

[Qinyun Tan <qinyuntan@linux.alibaba.com>]

Since commit 860e748bddcc ("drm: ensure blend mode supported if pixel
format with alpha exposed"), drm_mode_config_validate() warns when a
plane exposes an alpha pixel format but not the "pixel blend mode"
property. The ast cursor plane (ARGB4444, ARGB8888) trips this on
driver load:

  [PLANE:37:plane-1] pixel format with alpha exposed but blend mode not setup
  WARNING: drivers/gpu/drm/drm_mode_config.c:872 at drm_mode_config_validate+0x48f/0x510 [drm]
  ...
  Call Trace:
   drm_dev_register+0x1ce/0x290 [drm]
   ast_pci_probe+0x19d/0x3f0 [ast]
   local_pci_probe+0x41/0x90

Per Thomas Zimmermann's review, the ASPEED documentation describes the
hardware cursor as blending with straight (non-pre-multiplied) alpha,
which corresponds to DRM_MODE_BLEND_COVERAGE. Expose a "pixel blend
mode" property advertising only DRM_MODE_BLEND_COVERAGE to make the
hardware semantics explicit and silence the warning.

Fixes: 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
Suggested-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.com>
---
v2: advertise DRM_MODE_BLEND_COVERAGE instead of PREMULTI, per Thomas
Zimmermann's review and the ASPEED documentation.

 drivers/gpu/drm/ast/ast_cursor.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/ast/ast_cursor.c b/drivers/gpu/drm/ast/ast_cursor.c
index fd19c45f2abe2..690d4cd1db5ee 100644
--- a/drivers/gpu/drm/ast/ast_cursor.c
+++ b/drivers/gpu/drm/ast/ast_cursor.c
@@ -25,6 +25,7 @@
 #include <linux/sizes.h>
 
 #include <drm/drm_atomic.h>
+#include <drm/drm_blend.h>
 #include <drm/drm_damage_helper.h>
 #include <drm/drm_format_helper.h>
 #include <drm/drm_gem_atomic_helper.h>
@@ -355,6 +356,8 @@ int ast_cursor_plane_init(struct ast_device *ast)
 	}
 	drm_plane_helper_add(cursor_plane, &ast_cursor_plane_helper_funcs);
 	drm_plane_enable_fb_damage_clips(cursor_plane);
+	drm_plane_create_blend_mode_property(cursor_plane,
+					     BIT(DRM_MODE_BLEND_COVERAGE));
 
 	return 0;
 }
-- 
2.43.7