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

[Thomas Zimmermann]

Hi

Am 01.09.26 um 08:50 schrieb Qinyun Tan:
> 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
>
> The hardware cursor has always blended with pre-multiplied alpha and
> userspace assumes that blend mode when the property is not attached.
> Expose a "pixel blend mode" property advertising only
> DRM_MODE_BLEND_PREMULTI to make the existing semantics explicit and
> silence the warning. No functional change.
>
> Fixes: 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
> Signed-off-by: Qinyun Tan <qinyuntan@xxxxxxxxxxxxxxxxx>
> ---
>   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..08d93ac7f7cb8 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_PREMULTI));

AFAIU the available documentation, AST hardware corresponds to 
DRM_MODE_BLEND_COVERAGE.

Best regards
Thomas

>   
>   	return 0;
>   }

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, (HRB 36809, AG Nürnberg)