[PATCH 0/4] drm: create blend mode property on alpha-capable planes of simple drivers

[PATCH 0/4] drm: create blend mode property on alpha-capable planes of simple drivers

[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 does not create the "pixel
blend mode" property. Several simple/virtual drivers trip this on
driver load. I hit the ast one on an ASPEED AST2600 BMC:

  [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

These four drivers share the same gap; this series covers ast, qxl,
virtio-gpu and vboxvideo.

These planes have always blended with pre-multiplied alpha: the
hardware (or host-side compositor for the virtual drivers) is fixed
function with no configurable blend mode, and userspace has
historically assumed pre-multiplied blending when the property is not
attached, which is also the documented default of the property. So
each patch simply exposes the "pixel blend mode" property advertising
only DRM_MODE_BLEND_PREMULTI, making the existing semantics explicit
and silencing the warning. No functional change.

This follows the same approach as the already-merged i915 and nouveau
fixes:

  67e955e073c6 ("drm/i915/display: expose blend mode on alpha-capable planes")
  df0311845915 ("drm/nouveau/kms/nv50-: Unconditionally create blend_mode prop for wndws")

The ast patch is verified on AST2600 hardware: the warning is gone and
the cursor plane now exposes the "pixel blend mode" property with
Pre-multiplied as the only and current value. The qxl, virtio and
vboxvideo patches follow the identical pattern and are compile-tested.

Qinyun Tan (4):
  drm/ast: create blend mode property on cursor plane
  drm/qxl: create blend mode property on primary and cursor planes
  drm/virtio: create blend mode property on cursor plane
  drm/vboxvideo: create blend mode property on planes

 drivers/gpu/drm/ast/ast_cursor.c       | 3 +++
 drivers/gpu/drm/qxl/qxl_display.c      | 4 ++++
 drivers/gpu/drm/vboxvideo/vbox_mode.c  | 4 ++++
 drivers/gpu/drm/virtio/virtgpu_plane.c | 4 ++++
 4 files changed, 15 insertions(+)

-- 
2.43.7

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

[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@linux.alibaba.com>
---
 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));
 
 	return 0;
 }
-- 
2.43.7

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@linux.alibaba.com>
> ---
>   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)

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

[钦云谭]

Hi Thomas,

在 2026/9/1 15:03, Thomas Zimmermann 写道:
> 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@linux.alibaba.com>
>> ---
>>   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.
> 

Thanks for the correction.

I'll send a v2 that declares DRM_MODE_BLEND_COVERAGE for the ast
cursor plane instead.

> Best regards
> Thomas
> 
>>         return 0;
>>   }
> 

[PATCH 2/4] drm/qxl: create blend mode property on primary and cursor planes

[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. Both the qxl primary and cursor planes expose ARGB8888 and
trip this on driver load.

The planes have 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@linux.alibaba.com>
---
 drivers/gpu/drm/qxl/qxl_display.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
index 7f4178800afd7..0cd1456cca347 100644
--- a/drivers/gpu/drm/qxl/qxl_display.c
+++ b/drivers/gpu/drm/qxl/qxl_display.c
@@ -30,6 +30,7 @@
 #include <drm/drm_drv.h>
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_blend.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_encoder.h>
 #include <drm/drm_framebuffer.h>
@@ -993,6 +994,9 @@ static struct drm_plane *qxl_create_plane(struct qxl_device *qdev,
 
 	drm_plane_helper_add(plane, helper_funcs);
 
+	drm_plane_create_blend_mode_property(plane,
+					     BIT(DRM_MODE_BLEND_PREMULTI));
+
 	return plane;
 
 free_plane:
-- 
2.43.7

[PATCH 3/4] drm/virtio: create blend mode property on cursor plane

[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 virtio-gpu cursor plane (HOST_ARGB8888) trips this.

The 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. The
primary plane only exposes HOST_XRGB8888, so the call is gated to the
cursor. No functional change.

Fixes: 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
Signed-off-by: Qinyun Tan <qinyuntan@linux.alibaba.com>
---
 drivers/gpu/drm/virtio/virtgpu_plane.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/virtio/virtgpu_plane.c b/drivers/gpu/drm/virtio/virtgpu_plane.c
index 1d1b27ece62a7..640815af40980 100644
--- a/drivers/gpu/drm/virtio/virtgpu_plane.c
+++ b/drivers/gpu/drm/virtio/virtgpu_plane.c
@@ -24,6 +24,7 @@
  */
 
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_blend.h>
 #include <drm/drm_damage_helper.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_gem_atomic_helper.h>
@@ -609,6 +610,9 @@ struct drm_plane *virtio_gpu_plane_init(struct virtio_gpu_device *vgdev,
 
 	if (type == DRM_PLANE_TYPE_PRIMARY)
 		drm_plane_enable_fb_damage_clips(plane);
+	else if (type == DRM_PLANE_TYPE_CURSOR)
+		drm_plane_create_blend_mode_property(plane,
+						     BIT(DRM_MODE_BLEND_PREMULTI));
 
 	return plane;
 }
-- 
2.43.7

[PATCH 4/4] drm/vboxvideo: create blend mode property on planes

[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. Both the vboxvideo primary and cursor planes expose ARGB8888
and trip this on driver load.

The planes have 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@linux.alibaba.com>
---
 drivers/gpu/drm/vboxvideo/vbox_mode.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/vboxvideo/vbox_mode.c b/drivers/gpu/drm/vboxvideo/vbox_mode.c
index 8e4e5fc9d3c5a..658803646eee2 100644
--- a/drivers/gpu/drm/vboxvideo/vbox_mode.c
+++ b/drivers/gpu/drm/vboxvideo/vbox_mode.c
@@ -15,6 +15,7 @@
 
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_blend.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_fb_helper.h>
 #include <drm/drm_fourcc.h>
@@ -540,6 +541,9 @@ static struct drm_plane *vbox_create_plane(struct vbox_private *vbox,
 
 	drm_plane_helper_add(plane, helper_funcs);
 
+	drm_plane_create_blend_mode_property(plane,
+					     BIT(DRM_MODE_BLEND_PREMULTI));
+
 	return plane;
 
 free_plane:
-- 
2.43.7