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

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 01.09.26 um 14:51 schrieb Qinyun Tan:
> Hi Thomas,
>
> On 9/1/26 8:30 PM, Thomas Zimmermann wrote:
>> Hi
>>
>> Am 01.09.26 um 13:54 schrieb 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.
>> Or even better: I just sent out a patch to pick the right default value for the plane state. Let's first see what comes out of this. Patch is at [1].
>>
>> [1] https://lore.kernel.org/dri-devel/20260901122731.83854-1-tzimmermann@suse.de/
>>
>> Best regards
>> Thomas
>>
>   
> Thanks! I did see the Sashiko bot report and had started on a v3 that
> overrides drm_plane_funcs.atomic_create_state in ast and vboxvideo
> (for vboxvideo on both the primary and cursor planes).
>
> But your approach looks better to me: drm_plane_create_blend_mode_property()
> already picks DRM_MODE_BLEND_COVERAGE as the property default when
> PREMULTI is not supported, so initializing the plane state from the
> property default fixes this for every COVERAGE-only plane without
> per-driver boilerplate.
>
> I'll hold off on v3 until your patch has settled.

Another patch just landed that fixes the problem:

https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/c3080b58d81d3699cbf4dfd5ba860630fca96f4a

So I acked the rest of your series and I'll merge it in a few days. 
Thanks again for taking care of these drivers.

Best regards
Thomas


>
> Best regards,
> Qinyun
>
>
>>> [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@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;
>>>>    }

-- 
--
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)