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

[Thomas Zimmermann]

Hi,

thanks for the updated patch.

Did you see the review from the Sashiko bot?  The default value is 
PRE_MULTI, but the driver only supports COVERAGE.  This needs to be 
changed as part of this patch. The default assignment is at [1] in 
__drm_atomic_helper_plane_state_init().

The ast driver needs to override drm_plane_funcs.atomic_create_state for 
the cursor plane to update the value pixel_blend to COVERAGE for new 
plane states. Same goes for vbox.

[1] 
https://gitlab.freedesktop.org/drm/misc/kernel/-/blob/drm-misc-next/drivers/gpu/drm/drm_atomic_state_helper.c?ref_type=heads#L281

Best regards
Thomas


Am 01.09.26 um 10:32 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
>
> 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@xxxxxxx>
> Signed-off-by: Qinyun Tan <qinyuntan@xxxxxxxxxxxxxxxxx>
> ---
> 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;
>   }

--
--
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)