warnings from validate_blend_mode_for_alpha_formats() in next-20260715

warnings from validate_blend_mode_for_alpha_formats() in next-20260715

[Bert Karwatzki]

commit 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
introduces validate_blend_mode_for_alpha_formats() which prints warnings for amdpgu as 
amdgpu only set blend_mode_property for planes of type DRM_PLANE_TYPE_OVERLAY. I tried to fix
this by removing he (plane->type == DRM_PLANE_TYPE_OVERLAY) check in amdgpu_dm_plane_init():

	printk(KERN_INFO "%s: plane=%px plane->type=0x%x plane_cap=%px\n", __func__, plane, plane->type, plane_cap);
	if (plane_cap)
		printk(KERN_INFO "%s: per_pixel_alpha =%u\n", __func__, plane_cap->per_pixel_alpha);
	if (plane_cap && plane_cap->per_pixel_alpha) {
		unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
					  BIT(DRM_MODE_BLEND_PREMULTI) |
					  BIT(DRM_MODE_BLEND_COVERAGE);

		printk(KERN_INFO "%s: creating alpha and blend mode properties for plane %px\n", __func__, plane);
		drm_plane_create_alpha_property(plane);
		drm_plane_create_blend_mode_property(plane, blend_caps);
	}

But this does not completely silence the warnings becuase for planes of type DRM_PLANE_TYPE_CURSOR plane_cap is NULL.
Is this a problem that should be fixed in amdgpu or is should validate_blend_mode_for_alpha_formats() only be called
for planes of certain types?

Bert Karwatzki
   

Re: warnings from validate_blend_mode_for_alpha_formats() in next-20260715

[Alex Deucher]

+ Some display folks

On Fri, Jul 17, 2026 at 9:04 AM Bert Karwatzki <spasswolf@web.de> wrote:
>
> commit 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
> introduces validate_blend_mode_for_alpha_formats() which prints warnings for amdpgu as
> amdgpu only set blend_mode_property for planes of type DRM_PLANE_TYPE_OVERLAY. I tried to fix
> this by removing he (plane->type == DRM_PLANE_TYPE_OVERLAY) check in amdgpu_dm_plane_init():
>
>         printk(KERN_INFO "%s: plane=%px plane->type=0x%x plane_cap=%px\n", __func__, plane, plane->type, plane_cap);
>         if (plane_cap)
>                 printk(KERN_INFO "%s: per_pixel_alpha =%u\n", __func__, plane_cap->per_pixel_alpha);
>         if (plane_cap && plane_cap->per_pixel_alpha) {
>                 unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
>                                           BIT(DRM_MODE_BLEND_PREMULTI) |
>                                           BIT(DRM_MODE_BLEND_COVERAGE);
>
>                 printk(KERN_INFO "%s: creating alpha and blend mode properties for plane %px\n", __func__, plane);
>                 drm_plane_create_alpha_property(plane);
>                 drm_plane_create_blend_mode_property(plane, blend_caps);
>         }
>
> But this does not completely silence the warnings becuase for planes of type DRM_PLANE_TYPE_CURSOR plane_cap is NULL.
> Is this a problem that should be fixed in amdgpu or is should validate_blend_mode_for_alpha_formats() only be called
> for planes of certain types?
>
> Bert Karwatzki
>

Re: warnings from validate_blend_mode_for_alpha_formats() in next-20260715

[Leandro Ribeiro]

On 7/17/26 11:55 AM, Alex Deucher wrote:
> + Some display folks
> 
> On Fri, Jul 17, 2026 at 9:04 AM Bert Karwatzki <spasswolf@web.de> wrote:
>>
>> commit 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
>> introduces validate_blend_mode_for_alpha_formats() which prints warnings for amdpgu as
>> amdgpu only set blend_mode_property for planes of type DRM_PLANE_TYPE_OVERLAY. I tried to fix
>> this by removing he (plane->type == DRM_PLANE_TYPE_OVERLAY) check in amdgpu_dm_plane_init():
>>
>>         printk(KERN_INFO "%s: plane=%px plane->type=0x%x plane_cap=%px\n", __func__, plane, plane->type, plane_cap);
>>         if (plane_cap)
>>                 printk(KERN_INFO "%s: per_pixel_alpha =%u\n", __func__, plane_cap->per_pixel_alpha);
>>         if (plane_cap && plane_cap->per_pixel_alpha) {
>>                 unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
>>                                           BIT(DRM_MODE_BLEND_PREMULTI) |
>>                                           BIT(DRM_MODE_BLEND_COVERAGE);
>>
>>                 printk(KERN_INFO "%s: creating alpha and blend mode properties for plane %px\n", __func__, plane);
>>                 drm_plane_create_alpha_property(plane);
>>                 drm_plane_create_blend_mode_property(plane, blend_caps);
>>         }
>>
>> But this does not completely silence the warnings becuase for planes of type DRM_PLANE_TYPE_CURSOR plane_cap is NULL.
>> Is this a problem that should be fixed in amdgpu or is should validate_blend_mode_for_alpha_formats() only be called
>> for planes of certain types?

IMO validate_blend_mode_for_alpha_formats() should be called for all
types of planes. I can't think of anything special about a cursor plane
that would justify it being allowed to expose formats with alpha but not
the blend mode property.

I'm not familiar with the AMD codebase to suggest the best fix, but the
driver would need some way to know whether cursor planes are exposing
formats with alpha.

>>
>> Bert Karwatzki
>>

-- 
Leandro Ribeiro

Re: warnings from validate_blend_mode_for_alpha_formats() in next-20260715

[Bert Karwatzki]

Am Freitag, dem 17.07.2026 um 19:54 -0300 schrieb Leandro Ribeiro:
> 
> On 7/17/26 11:55 AM, Alex Deucher wrote:
> > + Some display folks
> > 
> > On Fri, Jul 17, 2026 at 9:04 AM Bert Karwatzki <spasswolf@web.de> wrote:
> > > 
> > > commit 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
> > > introduces validate_blend_mode_for_alpha_formats() which prints warnings for amdpgu as
> > > amdgpu only set blend_mode_property for planes of type DRM_PLANE_TYPE_OVERLAY. I tried to fix
> > > this by removing he (plane->type == DRM_PLANE_TYPE_OVERLAY) check in amdgpu_dm_plane_init():
> > > 
> > >         printk(KERN_INFO "%s: plane=%px plane->type=0x%x plane_cap=%px\n", __func__, plane, plane->type, plane_cap);
> > >         if (plane_cap)
> > >                 printk(KERN_INFO "%s: per_pixel_alpha =%u\n", __func__, plane_cap->per_pixel_alpha);
> > >         if (plane_cap && plane_cap->per_pixel_alpha) {
> > >                 unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
> > >                                           BIT(DRM_MODE_BLEND_PREMULTI) |
> > >                                           BIT(DRM_MODE_BLEND_COVERAGE);
> > > 
> > >                 printk(KERN_INFO "%s: creating alpha and blend mode properties for plane %px\n", __func__, plane);
> > >                 drm_plane_create_alpha_property(plane);
> > >                 drm_plane_create_blend_mode_property(plane, blend_caps);
> > >         }
> > > 
> > > But this does not completely silence the warnings becuase for planes of type DRM_PLANE_TYPE_CURSOR plane_cap is NULL.
> > > Is this a problem that should be fixed in amdgpu or is should validate_blend_mode_for_alpha_formats() only be called
> > > for planes of certain types?
> 
> IMO validate_blend_mode_for_alpha_formats() should be called for all
> types of planes. I can't think of anything special about a cursor plane
> that would justify it being allowed to expose formats with alpha but not
> the blend mode property.
> 
> I'm not familiar with the AMD codebase to suggest the best fix, but the
> driver would need some way to know whether cursor planes are exposing
> formats with alpha.
> 
> > > 
> > > Bert Karwatzki
> > > 

So I looked through the code and found that the cursor planes are initiallized by 
amdgpu_dm_crtc_init() which calls amdgpu_dm_plane_init() with plane_cap = NULL.
So I was able to silence the warning by introducing a dummy_plane_cap in amdgpu_dm_crtc_init()
and dropping the plane->type check in amdgpu_dm_plane_init().

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
index d63688b9d93d..7fb118444d14 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
@@ -731,13 +731,17 @@ int amdgpu_dm_crtc_init(struct amdgpu_display_manager *dm,
        struct drm_plane *cursor_plane;
        bool has_degamma;
        int res = -ENOMEM;
+       struct dc_plane_cap dummy_cap = {
+               .type = DC_PLANE_TYPE_DCE_RGB,
+               .per_pixel_alpha = 1,
+       };
 
        cursor_plane = kzalloc_obj(*cursor_plane);
        if (!cursor_plane)
                goto fail;
 
        cursor_plane->type = DRM_PLANE_TYPE_CURSOR;
-       res = amdgpu_dm_plane_init(dm, cursor_plane, 0, NULL);
+       res = amdgpu_dm_plane_init(dm, cursor_plane, 0, &dummy_cap);
 
        acrtc = kzalloc_obj(struct amdgpu_crtc);
        if (!acrtc)
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
index 26f35434a92f..20785fb451dd 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
@@ -1932,8 +1932,7 @@ int amdgpu_dm_plane_init(struct amdgpu_display_manager *dm,
        if (res)
                return res;
 
-       if (plane->type == DRM_PLANE_TYPE_OVERLAY &&
-           plane_cap && plane_cap->per_pixel_alpha) {
+       if (plane_cap && plane_cap->per_pixel_alpha) {
                unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
                                          BIT(DRM_MODE_BLEND_PREMULTI) |
                                          BIT(DRM_MODE_BLEND_COVERAGE);

One can probably also omit the .type field in the dummy_cap struct and
also does not have to check if plance_cap is NULL anymore.

Bert Karwatzki

Re: warnings from validate_blend_mode_for_alpha_formats() in next-20260715

[Bert Karwatzki]

Am Samstag, dem 18.07.2026 um 11:21 +0200 schrieb Bert Karwatzki:
> Am Freitag, dem 17.07.2026 um 19:54 -0300 schrieb Leandro Ribeiro:
> > 
> > On 7/17/26 11:55 AM, Alex Deucher wrote:
> > > + Some display folks
> > > 
> > > On Fri, Jul 17, 2026 at 9:04 AM Bert Karwatzki <spasswolf@web.de> wrote:
> > > > 
> > > > commit 860e748bddcc ("drm: ensure blend mode supported if pixel format with alpha exposed")
> > > > introduces validate_blend_mode_for_alpha_formats() which prints warnings for amdpgu as
> > > > amdgpu only set blend_mode_property for planes of type DRM_PLANE_TYPE_OVERLAY. I tried to fix
> > > > this by removing he (plane->type == DRM_PLANE_TYPE_OVERLAY) check in amdgpu_dm_plane_init():
> > > > 
> > > >         printk(KERN_INFO "%s: plane=%px plane->type=0x%x plane_cap=%px\n", __func__, plane, plane->type, plane_cap);
> > > >         if (plane_cap)
> > > >                 printk(KERN_INFO "%s: per_pixel_alpha =%u\n", __func__, plane_cap->per_pixel_alpha);
> > > >         if (plane_cap && plane_cap->per_pixel_alpha) {
> > > >                 unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
> > > >                                           BIT(DRM_MODE_BLEND_PREMULTI) |
> > > >                                           BIT(DRM_MODE_BLEND_COVERAGE);
> > > > 
> > > >                 printk(KERN_INFO "%s: creating alpha and blend mode properties for plane %px\n", __func__, plane);
> > > >                 drm_plane_create_alpha_property(plane);
> > > >                 drm_plane_create_blend_mode_property(plane, blend_caps);
> > > >         }
> > > > 
> > > > But this does not completely silence the warnings becuase for planes of type DRM_PLANE_TYPE_CURSOR plane_cap is NULL.
> > > > Is this a problem that should be fixed in amdgpu or is should validate_blend_mode_for_alpha_formats() only be called
> > > > for planes of certain types?
> > 
> > IMO validate_blend_mode_for_alpha_formats() should be called for all
> > types of planes. I can't think of anything special about a cursor plane
> > that would justify it being allowed to expose formats with alpha but not
> > the blend mode property.
> > 
> > I'm not familiar with the AMD codebase to suggest the best fix, but the
> > driver would need some way to know whether cursor planes are exposing
> > formats with alpha.
> > 
> > > > 
> > > > Bert Karwatzki
> > > > 
> 
> So I looked through the code and found that the cursor planes are initiallized by 
> amdgpu_dm_crtc_init() which calls amdgpu_dm_plane_init() with plane_cap = NULL.
> So I was able to silence the warning by introducing a dummy_plane_cap in amdgpu_dm_crtc_init()
> and dropping the plane->type check in amdgpu_dm_plane_init().
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> index d63688b9d93d..7fb118444d14 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c
> @@ -731,13 +731,17 @@ int amdgpu_dm_crtc_init(struct amdgpu_display_manager *dm,
>         struct drm_plane *cursor_plane;
>         bool has_degamma;
>         int res = -ENOMEM;
> +       struct dc_plane_cap dummy_cap = {
> +               .type = DC_PLANE_TYPE_DCE_RGB,
> +               .per_pixel_alpha = 1,
> +       };
>  
>         cursor_plane = kzalloc_obj(*cursor_plane);
>         if (!cursor_plane)
>                 goto fail;
>  
>         cursor_plane->type = DRM_PLANE_TYPE_CURSOR;
> -       res = amdgpu_dm_plane_init(dm, cursor_plane, 0, NULL);
> +       res = amdgpu_dm_plane_init(dm, cursor_plane, 0, &dummy_cap);
>  
>         acrtc = kzalloc_obj(struct amdgpu_crtc);
>         if (!acrtc)
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> index 26f35434a92f..20785fb451dd 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> @@ -1932,8 +1932,7 @@ int amdgpu_dm_plane_init(struct amdgpu_display_manager *dm,
>         if (res)
>                 return res;
>  
> -       if (plane->type == DRM_PLANE_TYPE_OVERLAY &&
> -           plane_cap && plane_cap->per_pixel_alpha) {
> +       if (plane_cap && plane_cap->per_pixel_alpha) {
>                 unsigned int blend_caps = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
>                                           BIT(DRM_MODE_BLEND_PREMULTI) |
>                                           BIT(DRM_MODE_BLEND_COVERAGE);
> 
> One can probably also omit the .type field in the dummy_cap struct and
> also does not have to check if plance_cap is NULL anymore.
> 
> Bert Karwatzki

This might seem problematic as this unconditionally sets per_pixel_alpha = true for cursor planes,
but currently the only pixel format used for cursor planes in amdgpu is DRM_FORMAT_ARGB8888:

$ grep -B 1 -A 3 'cursor_formats\[\]' drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c

static const u32 cursor_formats[] = {
	DRM_FORMAT_ARGB8888
};

Bert Karwatzki