[PATCH] drm/tegra: Add blend mode properties

[PATCH] drm/tegra: Add blend mode properties

[Thierry Reding]

From: Thierry Reding <treding@nvidia.com>

The default programming in the driver matches the "coverage" blend mode,
so add the corresponding pixel blend mode property to let userspace know
about it.

Signed-off-by: Thierry Reding <treding@nvidia.com>
---
 drivers/gpu/drm/tegra/dc.c  | 6 ++++++
 drivers/gpu/drm/tegra/hub.c | 2 ++
 2 files changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
index 0b3fcc7011b35..fefc3761a4bc7 100644
--- a/drivers/gpu/drm/tegra/dc.c
+++ b/drivers/gpu/drm/tegra/dc.c
@@ -904,6 +904,7 @@ static struct drm_plane *tegra_primary_plane_create(struct drm_device *drm,
 						    struct tegra_dc *dc)
 {
 	unsigned long possible_crtcs = tegra_plane_get_possible_crtcs(drm);
+	unsigned int blend_caps = BIT(DRM_MODE_BLEND_COVERAGE);
 	enum drm_plane_type type = DRM_PLANE_TYPE_PRIMARY;
 	struct tegra_plane *plane;
 	unsigned int num_formats;
@@ -939,6 +940,7 @@ static struct drm_plane *tegra_primary_plane_create(struct drm_device *drm,
 	}
 
 	drm_plane_helper_add(&plane->base, &tegra_plane_helper_funcs);
+	drm_plane_create_blend_mode_property(&plane->base, blend_caps);
 	drm_plane_create_zpos_property(&plane->base, plane->index, 0, 255);
 
 	err = drm_plane_create_rotation_property(&plane->base,
@@ -1209,6 +1211,7 @@ static struct drm_plane *tegra_dc_cursor_plane_create(struct drm_device *drm,
 						      struct tegra_dc *dc)
 {
 	unsigned long possible_crtcs = tegra_plane_get_possible_crtcs(drm);
+	unsigned int blend_caps = BIT(DRM_MODE_BLEND_COVERAGE);
 	struct tegra_plane *plane;
 	unsigned int num_formats;
 	const u32 *formats;
@@ -1252,6 +1255,7 @@ static struct drm_plane *tegra_dc_cursor_plane_create(struct drm_device *drm,
 	}
 
 	drm_plane_helper_add(&plane->base, &tegra_cursor_plane_helper_funcs);
+	drm_plane_create_blend_mode_property(&plane->base, blend_caps);
 	drm_plane_create_zpos_immutable_property(&plane->base, 255);
 
 	return &plane->base;
@@ -1356,6 +1360,7 @@ static struct drm_plane *tegra_dc_overlay_plane_create(struct drm_device *drm,
 						       bool cursor)
 {
 	unsigned long possible_crtcs = tegra_plane_get_possible_crtcs(drm);
+	unsigned int blend_caps = BIT(DRM_MODE_BLEND_COVERAGE);
 	struct tegra_plane *plane;
 	unsigned int num_formats;
 	enum drm_plane_type type;
@@ -1394,6 +1399,7 @@ static struct drm_plane *tegra_dc_overlay_plane_create(struct drm_device *drm,
 	}
 
 	drm_plane_helper_add(&plane->base, &tegra_plane_helper_funcs);
+	drm_plane_create_blend_mode_property(&plane->base, blend_caps);
 	drm_plane_create_zpos_property(&plane->base, plane->index, 0, 255);
 
 	err = drm_plane_create_rotation_property(&plane->base,
diff --git a/drivers/gpu/drm/tegra/hub.c b/drivers/gpu/drm/tegra/hub.c
index bd442bfd45407..448f49f3a7d7e 100644
--- a/drivers/gpu/drm/tegra/hub.c
+++ b/drivers/gpu/drm/tegra/hub.c
@@ -759,6 +759,7 @@ struct drm_plane *tegra_shared_plane_create(struct drm_device *drm,
 					    unsigned int index,
 					    enum drm_plane_type type)
 {
+	unsigned int blend_caps = BIT(DRM_MODE_BLEND_COVERAGE);
 	struct tegra_drm *tegra = drm->dev_private;
 	struct tegra_display_hub *hub = tegra->hub;
 	struct tegra_shared_plane *plane;
@@ -797,6 +798,7 @@ struct drm_plane *tegra_shared_plane_create(struct drm_device *drm,
 	}
 
 	drm_plane_helper_add(p, &tegra_shared_plane_helper_funcs);
+	drm_plane_create_blend_mode_property(p, blend_caps);
 	drm_plane_create_zpos_property(p, 0, 0, 255);
 
 	return p;
-- 
2.55.0

Re: [PATCH] drm/tegra: Add blend mode properties

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The newly added pixel_blend_mode property is not initialized in the plane's reset hook, leading to an invalid initial atomic state.
--

commit dea256106aa6a4944ed84de30a43b82c973ff72f
Author: Thierry Reding <treding@nvidia.com>

drm/tegra: Add blend mode properties

The default programming in the driver matches the "coverage" blend mode,
so add the corresponding pixel blend mode property to let userspace know
about it.

> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> index 0b3fcc7011b35..fefc3761a4bc7 100644
> --- a/drivers/gpu/drm/tegra/dc.c
> +++ b/drivers/gpu/drm/tegra/dc.c
> @@ -939,6 +940,7 @@ static struct drm_plane *tegra_primary_plane_create(struct drm_device *drm,
>  	}
>  
>  	drm_plane_helper_add(&plane->base, &tegra_plane_helper_funcs);
> +	drm_plane_create_blend_mode_property(&plane->base, blend_caps);

[Severity: High]
Since tegra_plane_reset() in drivers/gpu/drm/tegra/plane.c uses kzalloc_obj()
to zero-allocate the atomic plane state:

	state = kzalloc_obj(*state);
	if (state) {
		plane->state = &state->base;
		plane->state->plane = plane;

Will this cause atomic commits to fail with -EINVAL if userspace performs a
commit without changing the blend mode?

The pixel_blend_mode field is implicitly left at 0 (DRM_MODE_BLEND_PREMULTI).
Because only DRM_MODE_BLEND_COVERAGE (enum value 1) is exposed in blend_caps,
the core DRM enum validator (drm_property_change_valid_get()) will reject
the 0 value when userspace queries and subsequently commits the state.

Should tegra_plane_reset() be updated to explicitly initialize
pixel_blend_mode to DRM_MODE_BLEND_COVERAGE?

>  	drm_plane_create_zpos_property(&plane->base, plane->index, 0, 255);

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260826105421.1825331-1-thierry.reding@kernel.org?part=1

Re: [PATCH] drm/tegra: Add blend mode properties

[Jon Hunter]

On 26/08/2026 11:54, Thierry Reding wrote:
> From: Thierry Reding <treding@nvidia.com>
> 
> The default programming in the driver matches the "coverage" blend mode,
> so add the corresponding pixel blend mode property to let userspace know
> about it.
> 
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
>   drivers/gpu/drm/tegra/dc.c  | 6 ++++++
>   drivers/gpu/drm/tegra/hub.c | 2 ++
>   2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
> index 0b3fcc7011b35..fefc3761a4bc7 100644
> --- a/drivers/gpu/drm/tegra/dc.c
> +++ b/drivers/gpu/drm/tegra/dc.c
> @@ -904,6 +904,7 @@ static struct drm_plane *tegra_primary_plane_create(struct drm_device *drm,
>   						    struct tegra_dc *dc)
>   {
>   	unsigned long possible_crtcs = tegra_plane_get_possible_crtcs(drm);
> +	unsigned int blend_caps = BIT(DRM_MODE_BLEND_COVERAGE);
>   	enum drm_plane_type type = DRM_PLANE_TYPE_PRIMARY;
>   	struct tegra_plane *plane;
>   	unsigned int num_formats;
> @@ -939,6 +940,7 @@ static struct drm_plane *tegra_primary_plane_create(struct drm_device *drm,
>   	}
>   
>   	drm_plane_helper_add(&plane->base, &tegra_plane_helper_funcs);
> +	drm_plane_create_blend_mode_property(&plane->base, blend_caps);
>   	drm_plane_create_zpos_property(&plane->base, plane->index, 0, 255);
>   
>   	err = drm_plane_create_rotation_property(&plane->base,
> @@ -1209,6 +1211,7 @@ static struct drm_plane *tegra_dc_cursor_plane_create(struct drm_device *drm,
>   						      struct tegra_dc *dc)
>   {
>   	unsigned long possible_crtcs = tegra_plane_get_possible_crtcs(drm);
> +	unsigned int blend_caps = BIT(DRM_MODE_BLEND_COVERAGE);
>   	struct tegra_plane *plane;
>   	unsigned int num_formats;
>   	const u32 *formats;
> @@ -1252,6 +1255,7 @@ static struct drm_plane *tegra_dc_cursor_plane_create(struct drm_device *drm,
>   	}
>   
>   	drm_plane_helper_add(&plane->base, &tegra_cursor_plane_helper_funcs);
> +	drm_plane_create_blend_mode_property(&plane->base, blend_caps);
>   	drm_plane_create_zpos_immutable_property(&plane->base, 255);
>   
>   	return &plane->base;
> @@ -1356,6 +1360,7 @@ static struct drm_plane *tegra_dc_overlay_plane_create(struct drm_device *drm,
>   						       bool cursor)
>   {
>   	unsigned long possible_crtcs = tegra_plane_get_possible_crtcs(drm);
> +	unsigned int blend_caps = BIT(DRM_MODE_BLEND_COVERAGE);
>   	struct tegra_plane *plane;
>   	unsigned int num_formats;
>   	enum drm_plane_type type;
> @@ -1394,6 +1399,7 @@ static struct drm_plane *tegra_dc_overlay_plane_create(struct drm_device *drm,
>   	}
>   
>   	drm_plane_helper_add(&plane->base, &tegra_plane_helper_funcs);
> +	drm_plane_create_blend_mode_property(&plane->base, blend_caps);
>   	drm_plane_create_zpos_property(&plane->base, plane->index, 0, 255);
>   
>   	err = drm_plane_create_rotation_property(&plane->base,
> diff --git a/drivers/gpu/drm/tegra/hub.c b/drivers/gpu/drm/tegra/hub.c
> index bd442bfd45407..448f49f3a7d7e 100644
> --- a/drivers/gpu/drm/tegra/hub.c
> +++ b/drivers/gpu/drm/tegra/hub.c
> @@ -759,6 +759,7 @@ struct drm_plane *tegra_shared_plane_create(struct drm_device *drm,
>   					    unsigned int index,
>   					    enum drm_plane_type type)
>   {
> +	unsigned int blend_caps = BIT(DRM_MODE_BLEND_COVERAGE);
>   	struct tegra_drm *tegra = drm->dev_private;
>   	struct tegra_display_hub *hub = tegra->hub;
>   	struct tegra_shared_plane *plane;
> @@ -797,6 +798,7 @@ struct drm_plane *tegra_shared_plane_create(struct drm_device *drm,
>   	}
>   
>   	drm_plane_helper_add(p, &tegra_shared_plane_helper_funcs);
> +	drm_plane_create_blend_mode_property(p, blend_caps);
>   	drm_plane_create_zpos_property(p, 0, 0, 255);
>   
>   	return p;

Tested-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>

Thanks!
Jon

-- 
nvpublic