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[v4,1/2] drm: Add per-plane pixel blend mode property

Message ID 1534314933-23182-2-git-send-email-lowry.li@arm.com (mailing list archive)
State New, archived
Headers show
Series drm/blend: Add per-plane pixel blend mode property | expand

Commit Message

Lowry Li (Arm Technology China) Aug. 15, 2018, 6:35 a.m. UTC
Pixel blend modes represent the alpha blending equation
selection, describing how the pixels from the current
plane are composited with the background.

Adds a pixel_blend_mode to drm_plane_state and a
blend_mode_property to drm_plane, and related support
functions.

Defines three blend modes in drm_blend.h.

Changes since v1:
 - Moves the blending equation into the DOC comment
 - Refines the comments of drm_plane_create_blend_mode_property to not
   enumerate the #defines, but instead the string values
 - Uses fg.* instead of pixel.* and plane_alpha instead of plane.alpha
Changes since v2:
 - Refines the comments of drm_plane_create_blend_mode_property:
      1) Puts the descriptions (after the ":") on a new line
      2) Adds explaining why @supported_modes need PREMUL as default
Changes since v3:
 - Refines drm_plane_create_blend_mode_property(). drm_property_add_enum()
   can calculate the index itself just fine, so no point in having the
   caller pass it in.
 - Since the current DRM assumption is that alpha is premultiplied
   as default, define DRM_MODE_BLEND_PREMULTI as 0 will be better.
 - Refines some comments.

Signed-off-by: Lowry Li <lowry.li@arm.com>
---
 drivers/gpu/drm/drm_atomic.c        |   4 ++
 drivers/gpu/drm/drm_atomic_helper.c |   1 +
 drivers/gpu/drm/drm_blend.c         | 126 ++++++++++++++++++++++++++++++++++++
 include/drm/drm_blend.h             |   6 ++
 include/drm/drm_plane.h             |   2 +
 5 files changed, 139 insertions(+)

Comments

Liviu Dudau Aug. 15, 2018, 10:10 a.m. UTC | #1
On Wed, Aug 15, 2018 at 02:35:32PM +0800, Lowry Li wrote:
> Pixel blend modes represent the alpha blending equation
> selection, describing how the pixels from the current
> plane are composited with the background.
> 
> Adds a pixel_blend_mode to drm_plane_state and a
> blend_mode_property to drm_plane, and related support
> functions.
> 
> Defines three blend modes in drm_blend.h.
> 
> Changes since v1:
>  - Moves the blending equation into the DOC comment
>  - Refines the comments of drm_plane_create_blend_mode_property to not
>    enumerate the #defines, but instead the string values
>  - Uses fg.* instead of pixel.* and plane_alpha instead of plane.alpha
> Changes since v2:
>  - Refines the comments of drm_plane_create_blend_mode_property:
>       1) Puts the descriptions (after the ":") on a new line
>       2) Adds explaining why @supported_modes need PREMUL as default
> Changes since v3:
>  - Refines drm_plane_create_blend_mode_property(). drm_property_add_enum()
>    can calculate the index itself just fine, so no point in having the
>    caller pass it in.
>  - Since the current DRM assumption is that alpha is premultiplied
>    as default, define DRM_MODE_BLEND_PREMULTI as 0 will be better.
>  - Refines some comments.
> 
> Signed-off-by: Lowry Li <lowry.li@arm.com>

Looks good to me!

Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>

Thanks,
Liviu

> ---
>  drivers/gpu/drm/drm_atomic.c        |   4 ++
>  drivers/gpu/drm/drm_atomic_helper.c |   1 +
>  drivers/gpu/drm/drm_blend.c         | 126 ++++++++++++++++++++++++++++++++++++
>  include/drm/drm_blend.h             |   6 ++
>  include/drm/drm_plane.h             |   2 +
>  5 files changed, 139 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 3eb061e..d0478ab 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -895,6 +895,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		state->src_h = val;
>  	} else if (property == plane->alpha_property) {
>  		state->alpha = val;
> +	} else if (property == plane->blend_mode_property) {
> +		state->pixel_blend_mode = val;
>  	} else if (property == plane->rotation_property) {
>  		if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK)) {
>  			DRM_DEBUG_ATOMIC("[PLANE:%d:%s] bad rotation bitmask: 0x%llx\n",
> @@ -968,6 +970,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		*val = state->src_h;
>  	} else if (property == plane->alpha_property) {
>  		*val = state->alpha;
> +	} else if (property == plane->blend_mode_property) {
> +		*val = state->pixel_blend_mode;
>  	} else if (property == plane->rotation_property) {
>  		*val = state->rotation;
>  	} else if (property == plane->zpos_property) {
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 6dd5036..563af09 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -3569,6 +3569,7 @@ void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
>  	/* Reset the alpha value to fully opaque if it matters */
>  	if (plane->alpha_property)
>  		state->alpha = plane->alpha_property->values[1];
> +	plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
>  
>  	plane->state = state;
>  }
> diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> index a16a74d..24016c9 100644
> --- a/drivers/gpu/drm/drm_blend.c
> +++ b/drivers/gpu/drm/drm_blend.c
> @@ -107,6 +107,52 @@
>   *	planes. Without this property the primary plane is always below the cursor
>   *	plane, and ordering between all other planes is undefined.
>   *
> + * pixel blend mode:
> + *	Pixel blend mode is set up with drm_plane_create_blend_mode_property().
> + *	It adds a blend mode for alpha blending equation selection, describing
> + *	how the pixels from the current plane are composited with the
> + *	background.
> + *
> + *	 Three alpha blending equations are defined:
> + *
> + *	 "None":
> + *		 Blend formula that ignores the pixel alpha::
> + *
> + *			 out.rgb = plane_alpha * fg.rgb +
> + *				 (1 - plane_alpha) * bg.rgb
> + *
> + *	 "Pre-multiplied":
> + *		 Blend formula that assumes the pixel color values
> + *		 have been already pre-multiplied with the alpha
> + *		 channel values::
> + *
> + *			 out.rgb = plane_alpha * fg.rgb +
> + *				 (1 - (plane_alpha * fg.alpha)) * bg.rgb
> + *
> + *	 "Coverage":
> + *		 Blend formula that assumes the pixel color values have not
> + *		 been pre-multiplied and will do so when blending them to the
> + *		 background color values::
> + *
> + *			 out.rgb = plane_alpha * fg.alpha * fg.rgb +
> + *				 (1 - (plane_alpha * fg.alpha)) * bg.rgb
> + *
> + *	 Using the following symbols:
> + *
> + *	 "fg.rgb":
> + *		 Each of the RGB component values from the plane's pixel
> + *	 "fg.alpha":
> + *		 Alpha component value from the plane's pixel. If the plane's
> + *		 pixel format has no alpha component, then this is assumed to be
> + *		 1.0. In these cases, this property has no effect, as all three
> + *		 equations become equivalent.
> + *	 "bg.rgb":
> + *		 Each of the RGB component values from the background
> + *	 "plane_alpha":
> + *		 Plane alpha value set by the plane "alpha" property. If the
> + *		 plane does not expose the "alpha" property, then this is
> + *		 assumed to be 1.0
> + *
>   * Note that all the property extensions described here apply either to the
>   * plane or the CRTC (e.g. for the background color, which currently is not
>   * exposed and assumed to be black).
> @@ -448,3 +494,83 @@ int drm_atomic_normalize_zpos(struct drm_device *dev,
>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_atomic_normalize_zpos);
> +
> +/**
> + * drm_plane_create_blend_mode_property - create a new blend mode property
> + * @plane: drm plane
> + * @supported_modes: bitmask of supported modes, must include
> + *		     BIT(DRM_MODE_BLEND_PREMULTI). Current DRM assumption is
> + *		     that alpha is premultiplied, and old userspace can break if
> + *		     the property defaults to anything else.
> + *
> + * This creates a new property describing the blend mode.
> + *
> + * The property exposed to userspace is an enumeration property (see
> + * drm_property_create_enum()) called "pixel blend mode" and has the
> + * following enumeration values:
> + *
> + * "None":
> + *	Blend formula that ignores the pixel alpha.
> + *
> + * "Pre-multiplied":
> + *	Blend formula that assumes the pixel color values have been already
> + *	pre-multiplied with the alpha channel values.
> + *
> + * "Coverage":
> + *	Blend formula that assumes the pixel color values have not been
> + *	pre-multiplied and will do so when blending them to the background color
> + *	values.
> + *
> + * RETURNS:
> + * Zero for success or -errno
> + */
> +int drm_plane_create_blend_mode_property(struct drm_plane *plane,
> +					 unsigned int supported_modes)
> +{
> +	struct drm_device *dev = plane->dev;
> +	struct drm_property *prop;
> +	static const struct drm_prop_enum_list props[] = {
> +		{ DRM_MODE_BLEND_PIXEL_NONE, "None" },
> +		{ DRM_MODE_BLEND_PREMULTI, "Pre-multiplied" },
> +		{ DRM_MODE_BLEND_COVERAGE, "Coverage" },
> +	};
> +	unsigned int valid_mode_mask = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
> +				       BIT(DRM_MODE_BLEND_PREMULTI)   |
> +				       BIT(DRM_MODE_BLEND_COVERAGE);
> +	int i;
> +
> +	if (WARN_ON((supported_modes & ~valid_mode_mask) ||
> +		    ((supported_modes & BIT(DRM_MODE_BLEND_PREMULTI)) == 0)))
> +		return -EINVAL;
> +
> +	prop = drm_property_create(dev, DRM_MODE_PROP_ENUM,
> +				   "pixel blend mode",
> +				   hweight32(supported_modes));
> +	if (!prop)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < ARRAY_SIZE(props); i++) {
> +		int ret;
> +
> +		if (!(BIT(props[i].type) & supported_modes))
> +			continue;
> +
> +		ret = drm_property_add_enum(prop, props[i].type,
> +					    props[i].name);
> +
> +		if (ret) {
> +			drm_property_destroy(dev, prop);
> +
> +			return ret;
> +		}
> +	}
> +
> +	drm_object_attach_property(&plane->base, prop, DRM_MODE_BLEND_PREMULTI);
> +	plane->blend_mode_property = prop;
> +
> +	if (plane->state)
> +		plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_plane_create_blend_mode_property);
> diff --git a/include/drm/drm_blend.h b/include/drm/drm_blend.h
> index 330c561..88bdfec 100644
> --- a/include/drm/drm_blend.h
> +++ b/include/drm/drm_blend.h
> @@ -27,6 +27,10 @@
>  #include <linux/ctype.h>
>  #include <drm/drm_mode.h>
>  
> +#define DRM_MODE_BLEND_PREMULTI		0
> +#define DRM_MODE_BLEND_COVERAGE		1
> +#define DRM_MODE_BLEND_PIXEL_NONE	2
> +
>  struct drm_device;
>  struct drm_atomic_state;
>  struct drm_plane;
> @@ -52,4 +56,6 @@ int drm_plane_create_zpos_immutable_property(struct drm_plane *plane,
>  					     unsigned int zpos);
>  int drm_atomic_normalize_zpos(struct drm_device *dev,
>  			      struct drm_atomic_state *state);
> +int drm_plane_create_blend_mode_property(struct drm_plane *plane,
> +					 unsigned int supported_modes);
>  #endif
> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> index 8a152dc..c52614a 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -117,6 +117,7 @@ struct drm_plane_state {
>  	 * details.
>  	 */
>  	u16 alpha;
> +	uint16_t pixel_blend_mode;
>  
>  	/**
>  	 * @rotation:
> @@ -659,6 +660,7 @@ struct drm_plane {
>  	 * drm_plane_create_rotation_property().
>  	 */
>  	struct drm_property *rotation_property;
> +	struct drm_property *blend_mode_property;
>  
>  	/**
>  	 * @color_encoding_property:
> -- 
> 1.9.1
>
Sean Paul Aug. 22, 2018, 12:39 p.m. UTC | #2
On Wed, Aug 15, 2018 at 02:35:32PM +0800, Lowry Li wrote:
> Pixel blend modes represent the alpha blending equation
> selection, describing how the pixels from the current
> plane are composited with the background.
> 
> Adds a pixel_blend_mode to drm_plane_state and a
> blend_mode_property to drm_plane, and related support
> functions.
> 
> Defines three blend modes in drm_blend.h.
> 
> Changes since v1:
>  - Moves the blending equation into the DOC comment
>  - Refines the comments of drm_plane_create_blend_mode_property to not
>    enumerate the #defines, but instead the string values
>  - Uses fg.* instead of pixel.* and plane_alpha instead of plane.alpha
> Changes since v2:
>  - Refines the comments of drm_plane_create_blend_mode_property:
>       1) Puts the descriptions (after the ":") on a new line
>       2) Adds explaining why @supported_modes need PREMUL as default
> Changes since v3:
>  - Refines drm_plane_create_blend_mode_property(). drm_property_add_enum()
>    can calculate the index itself just fine, so no point in having the
>    caller pass it in.
>  - Since the current DRM assumption is that alpha is premultiplied
>    as default, define DRM_MODE_BLEND_PREMULTI as 0 will be better.
>  - Refines some comments.
> 
> Signed-off-by: Lowry Li <lowry.li@arm.com>
> ---
>  drivers/gpu/drm/drm_atomic.c        |   4 ++
>  drivers/gpu/drm/drm_atomic_helper.c |   1 +
>  drivers/gpu/drm/drm_blend.c         | 126 ++++++++++++++++++++++++++++++++++++
>  include/drm/drm_blend.h             |   6 ++
>  include/drm/drm_plane.h             |   2 +
>  5 files changed, 139 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 3eb061e..d0478ab 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -895,6 +895,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		state->src_h = val;
>  	} else if (property == plane->alpha_property) {
>  		state->alpha = val;
> +	} else if (property == plane->blend_mode_property) {
> +		state->pixel_blend_mode = val;
>  	} else if (property == plane->rotation_property) {
>  		if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK)) {
>  			DRM_DEBUG_ATOMIC("[PLANE:%d:%s] bad rotation bitmask: 0x%llx\n",
> @@ -968,6 +970,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		*val = state->src_h;
>  	} else if (property == plane->alpha_property) {
>  		*val = state->alpha;
> +	} else if (property == plane->blend_mode_property) {
> +		*val = state->pixel_blend_mode;
>  	} else if (property == plane->rotation_property) {
>  		*val = state->rotation;
>  	} else if (property == plane->zpos_property) {
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 6dd5036..563af09 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -3569,6 +3569,7 @@ void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
>  	/* Reset the alpha value to fully opaque if it matters */
>  	if (plane->alpha_property)
>  		state->alpha = plane->alpha_property->values[1];
> +	plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;

Shouldn't this be state->pixel_blend_mode instead of
plane->state->pixel_blend_mode?

>  
>  	plane->state = state;
>  }

/snip
Maarten Lankhorst Aug. 22, 2018, 1:27 p.m. UTC | #3
Op 15-08-18 om 08:35 schreef Lowry Li:
> Pixel blend modes represent the alpha blending equation
> selection, describing how the pixels from the current
> plane are composited with the background.
>
> Adds a pixel_blend_mode to drm_plane_state and a
> blend_mode_property to drm_plane, and related support
> functions.
>
> Defines three blend modes in drm_blend.h.
>
> Changes since v1:
>  - Moves the blending equation into the DOC comment
>  - Refines the comments of drm_plane_create_blend_mode_property to not
>    enumerate the #defines, but instead the string values
>  - Uses fg.* instead of pixel.* and plane_alpha instead of plane.alpha
> Changes since v2:
>  - Refines the comments of drm_plane_create_blend_mode_property:
>       1) Puts the descriptions (after the ":") on a new line
>       2) Adds explaining why @supported_modes need PREMUL as default
> Changes since v3:
>  - Refines drm_plane_create_blend_mode_property(). drm_property_add_enum()
>    can calculate the index itself just fine, so no point in having the
>    caller pass it in.
>  - Since the current DRM assumption is that alpha is premultiplied
>    as default, define DRM_MODE_BLEND_PREMULTI as 0 will be better.
>  - Refines some comments.
>
> Signed-off-by: Lowry Li <lowry.li@arm.com>
> ---
>  drivers/gpu/drm/drm_atomic.c        |   4 ++
>  drivers/gpu/drm/drm_atomic_helper.c |   1 +
>  drivers/gpu/drm/drm_blend.c         | 126 ++++++++++++++++++++++++++++++++++++
>  include/drm/drm_blend.h             |   6 ++
>  include/drm/drm_plane.h             |   2 +
>  5 files changed, 139 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 3eb061e..d0478ab 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -895,6 +895,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		state->src_h = val;
>  	} else if (property == plane->alpha_property) {
>  		state->alpha = val;
> +	} else if (property == plane->blend_mode_property) {
> +		state->pixel_blend_mode = val;
>  	} else if (property == plane->rotation_property) {
>  		if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK)) {
>  			DRM_DEBUG_ATOMIC("[PLANE:%d:%s] bad rotation bitmask: 0x%llx\n",
> @@ -968,6 +970,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		*val = state->src_h;
>  	} else if (property == plane->alpha_property) {
>  		*val = state->alpha;
> +	} else if (property == plane->blend_mode_property) {
> +		*val = state->pixel_blend_mode;
>  	} else if (property == plane->rotation_property) {
>  		*val = state->rotation;
>  	} else if (property == plane->zpos_property) {
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 6dd5036..563af09 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -3569,6 +3569,7 @@ void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
>  	/* Reset the alpha value to fully opaque if it matters */
>  	if (plane->alpha_property)
>  		state->alpha = plane->alpha_property->values[1];
> +	plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
>  
>  	plane->state = state;
>  }
> diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> index a16a74d..24016c9 100644
> --- a/drivers/gpu/drm/drm_blend.c
> +++ b/drivers/gpu/drm/drm_blend.c
> @@ -107,6 +107,52 @@
>   *	planes. Without this property the primary plane is always below the cursor
>   *	plane, and ordering between all other planes is undefined.
>   *
> + * pixel blend mode:
> + *	Pixel blend mode is set up with drm_plane_create_blend_mode_property().
> + *	It adds a blend mode for alpha blending equation selection, describing
> + *	how the pixels from the current plane are composited with the
> + *	background.
> + *
> + *	 Three alpha blending equations are defined:
> + *
> + *	 "None":
> + *		 Blend formula that ignores the pixel alpha::
> + *
> + *			 out.rgb = plane_alpha * fg.rgb +
> + *				 (1 - plane_alpha) * bg.rgb
> + *
> + *	 "Pre-multiplied":
> + *		 Blend formula that assumes the pixel color values
> + *		 have been already pre-multiplied with the alpha
> + *		 channel values::
> + *
> + *			 out.rgb = plane_alpha * fg.rgb +
> + *				 (1 - (plane_alpha * fg.alpha)) * bg.rgb
> + *
> + *	 "Coverage":
> + *		 Blend formula that assumes the pixel color values have not
> + *		 been pre-multiplied and will do so when blending them to the
> + *		 background color values::
> + *
> + *			 out.rgb = plane_alpha * fg.alpha * fg.rgb +
> + *				 (1 - (plane_alpha * fg.alpha)) * bg.rgb
> + *
> + *	 Using the following symbols:
> + *
> + *	 "fg.rgb":
> + *		 Each of the RGB component values from the plane's pixel
> + *	 "fg.alpha":
> + *		 Alpha component value from the plane's pixel. If the plane's
> + *		 pixel format has no alpha component, then this is assumed to be
> + *		 1.0. In these cases, this property has no effect, as all three
> + *		 equations become equivalent.
> + *	 "bg.rgb":
> + *		 Each of the RGB component values from the background
> + *	 "plane_alpha":
> + *		 Plane alpha value set by the plane "alpha" property. If the
> + *		 plane does not expose the "alpha" property, then this is
> + *		 assumed to be 1.0
> + *
>   * Note that all the property extensions described here apply either to the
>   * plane or the CRTC (e.g. for the background color, which currently is not
>   * exposed and assumed to be black).
> @@ -448,3 +494,83 @@ int drm_atomic_normalize_zpos(struct drm_device *dev,
>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_atomic_normalize_zpos);
> +
> +/**
> + * drm_plane_create_blend_mode_property - create a new blend mode property
> + * @plane: drm plane
> + * @supported_modes: bitmask of supported modes, must include
> + *		     BIT(DRM_MODE_BLEND_PREMULTI). Current DRM assumption is
> + *		     that alpha is premultiplied, and old userspace can break if
> + *		     the property defaults to anything else.
> + *
> + * This creates a new property describing the blend mode.
> + *
> + * The property exposed to userspace is an enumeration property (see
> + * drm_property_create_enum()) called "pixel blend mode" and has the
> + * following enumeration values:
> + *
> + * "None":
> + *	Blend formula that ignores the pixel alpha.
> + *
> + * "Pre-multiplied":
> + *	Blend formula that assumes the pixel color values have been already
> + *	pre-multiplied with the alpha channel values.
> + *
> + * "Coverage":
> + *	Blend formula that assumes the pixel color values have not been
> + *	pre-multiplied and will do so when blending them to the background color
> + *	values.
> + *
> + * RETURNS:
> + * Zero for success or -errno
> + */
> +int drm_plane_create_blend_mode_property(struct drm_plane *plane,
> +					 unsigned int supported_modes)
> +{
> +	struct drm_device *dev = plane->dev;
> +	struct drm_property *prop;
> +	static const struct drm_prop_enum_list props[] = {
> +		{ DRM_MODE_BLEND_PIXEL_NONE, "None" },
> +		{ DRM_MODE_BLEND_PREMULTI, "Pre-multiplied" },
> +		{ DRM_MODE_BLEND_COVERAGE, "Coverage" },
> +	};
> +	unsigned int valid_mode_mask = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
> +				       BIT(DRM_MODE_BLEND_PREMULTI)   |
> +				       BIT(DRM_MODE_BLEND_COVERAGE);
> +	int i;
> +
> +	if (WARN_ON((supported_modes & ~valid_mode_mask) ||
> +		    ((supported_modes & BIT(DRM_MODE_BLEND_PREMULTI)) == 0)))
> +		return -EINVAL;
> +
> +	prop = drm_property_create(dev, DRM_MODE_PROP_ENUM,
> +				   "pixel blend mode",
> +				   hweight32(supported_modes));
> +	if (!prop)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < ARRAY_SIZE(props); i++) {
> +		int ret;
> +
> +		if (!(BIT(props[i].type) & supported_modes))
> +			continue;
> +
> +		ret = drm_property_add_enum(prop, props[i].type,
> +					    props[i].name);
> +
> +		if (ret) {
> +			drm_property_destroy(dev, prop);
> +
> +			return ret;
> +		}
> +	}
> +
> +	drm_object_attach_property(&plane->base, prop, DRM_MODE_BLEND_PREMULTI);
Do we still care about !atomic kernel drivers?
> +	plane->blend_mode_property = prop;
> +
> +	if (plane->state)
> +		plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;

Is this still needed with the hunk in __drm_atomic_helper_plane_reset() ? I would just remove it.


> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_plane_create_blend_mode_property);
> diff --git a/include/drm/drm_blend.h b/include/drm/drm_blend.h
> index 330c561..88bdfec 100644
> --- a/include/drm/drm_blend.h
> +++ b/include/drm/drm_blend.h
> @@ -27,6 +27,10 @@
>  #include <linux/ctype.h>
>  #include <drm/drm_mode.h>
>  
> +#define DRM_MODE_BLEND_PREMULTI		0
> +#define DRM_MODE_BLEND_COVERAGE		1
> +#define DRM_MODE_BLEND_PIXEL_NONE	2
> +
>  struct drm_device;
>  struct drm_atomic_state;
>  struct drm_plane;
> @@ -52,4 +56,6 @@ int drm_plane_create_zpos_immutable_property(struct drm_plane *plane,
>  					     unsigned int zpos);
>  int drm_atomic_normalize_zpos(struct drm_device *dev,
>  			      struct drm_atomic_state *state);
> +int drm_plane_create_blend_mode_property(struct drm_plane *plane,
> +					 unsigned int supported_modes);
>  #endif
> diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> index 8a152dc..c52614a 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -117,6 +117,7 @@ struct drm_plane_state {
>  	 * details.
>  	 */
>  	u16 alpha;
> +	uint16_t pixel_blend_mode;
>  
>  	/**
>  	 * @rotation:
> @@ -659,6 +660,7 @@ struct drm_plane {
>  	 * drm_plane_create_rotation_property().
>  	 */
>  	struct drm_property *rotation_property;
> +	struct drm_property *blend_mode_property;
>  
>  	/**
>  	 * @color_encoding_property:

These need to be documented.

With those changes:

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

~Maarten
Lowry Li (Arm Technology China) Aug. 23, 2018, 7:19 a.m. UTC | #4
On Wed, Aug 22, 2018 at 03:27:44PM +0200, Maarten Lankhorst wrote:
> Op 15-08-18 om 08:35 schreef Lowry Li:
> > Pixel blend modes represent the alpha blending equation
> > selection, describing how the pixels from the current
> > plane are composited with the background.
> >
> > Adds a pixel_blend_mode to drm_plane_state and a
> > blend_mode_property to drm_plane, and related support
> > functions.
> >
> > Defines three blend modes in drm_blend.h.
> >
> > Changes since v1:
> >  - Moves the blending equation into the DOC comment
> >  - Refines the comments of drm_plane_create_blend_mode_property to not
> >    enumerate the #defines, but instead the string values
> >  - Uses fg.* instead of pixel.* and plane_alpha instead of plane.alpha
> > Changes since v2:
> >  - Refines the comments of drm_plane_create_blend_mode_property:
> >       1) Puts the descriptions (after the ":") on a new line
> >       2) Adds explaining why @supported_modes need PREMUL as default
> > Changes since v3:
> >  - Refines drm_plane_create_blend_mode_property(). drm_property_add_enum()
> >    can calculate the index itself just fine, so no point in having the
> >    caller pass it in.
> >  - Since the current DRM assumption is that alpha is premultiplied
> >    as default, define DRM_MODE_BLEND_PREMULTI as 0 will be better.
> >  - Refines some comments.
> >
> > Signed-off-by: Lowry Li <lowry.li@arm.com>
> > ---
> >  drivers/gpu/drm/drm_atomic.c        |   4 ++
> >  drivers/gpu/drm/drm_atomic_helper.c |   1 +
> >  drivers/gpu/drm/drm_blend.c         | 126 ++++++++++++++++++++++++++++++++++++
> >  include/drm/drm_blend.h             |   6 ++
> >  include/drm/drm_plane.h             |   2 +
> >  5 files changed, 139 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index 3eb061e..d0478ab 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -895,6 +895,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
> >  		state->src_h = val;
> >  	} else if (property == plane->alpha_property) {
> >  		state->alpha = val;
> > +	} else if (property == plane->blend_mode_property) {
> > +		state->pixel_blend_mode = val;
> >  	} else if (property == plane->rotation_property) {
> >  		if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK)) {
> >  			DRM_DEBUG_ATOMIC("[PLANE:%d:%s] bad rotation bitmask: 0x%llx\n",
> > @@ -968,6 +970,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
> >  		*val = state->src_h;
> >  	} else if (property == plane->alpha_property) {
> >  		*val = state->alpha;
> > +	} else if (property == plane->blend_mode_property) {
> > +		*val = state->pixel_blend_mode;
> >  	} else if (property == plane->rotation_property) {
> >  		*val = state->rotation;
> >  	} else if (property == plane->zpos_property) {
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 6dd5036..563af09 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -3569,6 +3569,7 @@ void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
> >  	/* Reset the alpha value to fully opaque if it matters */
> >  	if (plane->alpha_property)
> >  		state->alpha = plane->alpha_property->values[1];
> > +	plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
> >  
> >  	plane->state = state;
> >  }
> > diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> > index a16a74d..24016c9 100644
> > --- a/drivers/gpu/drm/drm_blend.c
> > +++ b/drivers/gpu/drm/drm_blend.c
> > @@ -107,6 +107,52 @@
> >   *	planes. Without this property the primary plane is always below the cursor
> >   *	plane, and ordering between all other planes is undefined.
> >   *
> > + * pixel blend mode:
> > + *	Pixel blend mode is set up with drm_plane_create_blend_mode_property().
> > + *	It adds a blend mode for alpha blending equation selection, describing
> > + *	how the pixels from the current plane are composited with the
> > + *	background.
> > + *
> > + *	 Three alpha blending equations are defined:
> > + *
> > + *	 "None":
> > + *		 Blend formula that ignores the pixel alpha::
> > + *
> > + *			 out.rgb = plane_alpha * fg.rgb +
> > + *				 (1 - plane_alpha) * bg.rgb
> > + *
> > + *	 "Pre-multiplied":
> > + *		 Blend formula that assumes the pixel color values
> > + *		 have been already pre-multiplied with the alpha
> > + *		 channel values::
> > + *
> > + *			 out.rgb = plane_alpha * fg.rgb +
> > + *				 (1 - (plane_alpha * fg.alpha)) * bg.rgb
> > + *
> > + *	 "Coverage":
> > + *		 Blend formula that assumes the pixel color values have not
> > + *		 been pre-multiplied and will do so when blending them to the
> > + *		 background color values::
> > + *
> > + *			 out.rgb = plane_alpha * fg.alpha * fg.rgb +
> > + *				 (1 - (plane_alpha * fg.alpha)) * bg.rgb
> > + *
> > + *	 Using the following symbols:
> > + *
> > + *	 "fg.rgb":
> > + *		 Each of the RGB component values from the plane's pixel
> > + *	 "fg.alpha":
> > + *		 Alpha component value from the plane's pixel. If the plane's
> > + *		 pixel format has no alpha component, then this is assumed to be
> > + *		 1.0. In these cases, this property has no effect, as all three
> > + *		 equations become equivalent.
> > + *	 "bg.rgb":
> > + *		 Each of the RGB component values from the background
> > + *	 "plane_alpha":
> > + *		 Plane alpha value set by the plane "alpha" property. If the
> > + *		 plane does not expose the "alpha" property, then this is
> > + *		 assumed to be 1.0
> > + *
> >   * Note that all the property extensions described here apply either to the
> >   * plane or the CRTC (e.g. for the background color, which currently is not
> >   * exposed and assumed to be black).
> > @@ -448,3 +494,83 @@ int drm_atomic_normalize_zpos(struct drm_device *dev,
> >  	return 0;
> >  }
> >  EXPORT_SYMBOL(drm_atomic_normalize_zpos);
> > +
> > +/**
> > + * drm_plane_create_blend_mode_property - create a new blend mode property
> > + * @plane: drm plane
> > + * @supported_modes: bitmask of supported modes, must include
> > + *		     BIT(DRM_MODE_BLEND_PREMULTI). Current DRM assumption is
> > + *		     that alpha is premultiplied, and old userspace can break if
> > + *		     the property defaults to anything else.
> > + *
> > + * This creates a new property describing the blend mode.
> > + *
> > + * The property exposed to userspace is an enumeration property (see
> > + * drm_property_create_enum()) called "pixel blend mode" and has the
> > + * following enumeration values:
> > + *
> > + * "None":
> > + *	Blend formula that ignores the pixel alpha.
> > + *
> > + * "Pre-multiplied":
> > + *	Blend formula that assumes the pixel color values have been already
> > + *	pre-multiplied with the alpha channel values.
> > + *
> > + * "Coverage":
> > + *	Blend formula that assumes the pixel color values have not been
> > + *	pre-multiplied and will do so when blending them to the background color
> > + *	values.
> > + *
> > + * RETURNS:
> > + * Zero for success or -errno
> > + */
> > +int drm_plane_create_blend_mode_property(struct drm_plane *plane,
> > +					 unsigned int supported_modes)
> > +{
> > +	struct drm_device *dev = plane->dev;
> > +	struct drm_property *prop;
> > +	static const struct drm_prop_enum_list props[] = {
> > +		{ DRM_MODE_BLEND_PIXEL_NONE, "None" },
> > +		{ DRM_MODE_BLEND_PREMULTI, "Pre-multiplied" },
> > +		{ DRM_MODE_BLEND_COVERAGE, "Coverage" },
> > +	};
> > +	unsigned int valid_mode_mask = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
> > +				       BIT(DRM_MODE_BLEND_PREMULTI)   |
> > +				       BIT(DRM_MODE_BLEND_COVERAGE);
> > +	int i;
> > +
> > +	if (WARN_ON((supported_modes & ~valid_mode_mask) ||
> > +		    ((supported_modes & BIT(DRM_MODE_BLEND_PREMULTI)) == 0)))
> > +		return -EINVAL;
> > +
> > +	prop = drm_property_create(dev, DRM_MODE_PROP_ENUM,
> > +				   "pixel blend mode",
> > +				   hweight32(supported_modes));
> > +	if (!prop)
> > +		return -ENOMEM;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(props); i++) {
> > +		int ret;
> > +
> > +		if (!(BIT(props[i].type) & supported_modes))
> > +			continue;
> > +
> > +		ret = drm_property_add_enum(prop, props[i].type,
> > +					    props[i].name);
> > +
> > +		if (ret) {
> > +			drm_property_destroy(dev, prop);
> > +
> > +			return ret;
> > +		}
> > +	}
> > +
> > +	drm_object_attach_property(&plane->base, prop, DRM_MODE_BLEND_PREMULTI);
> Do we still care about !atomic kernel drivers?
Hi Maarten,
Thanks for your comments. We don't need to care about this. And
DRM_MODE_BLEND_PREMULTI is zero as default.

> > +	plane->blend_mode_property = prop;
> > +
> > +	if (plane->state)
> > +		plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
> 
> Is this still needed with the hunk in __drm_atomic_helper_plane_reset() ? I would just remove it.
Totally agree. Will remove this. Thanks a lot:)
 
> > +
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL(drm_plane_create_blend_mode_property);
> > diff --git a/include/drm/drm_blend.h b/include/drm/drm_blend.h
> > index 330c561..88bdfec 100644
> > --- a/include/drm/drm_blend.h
> > +++ b/include/drm/drm_blend.h
> > @@ -27,6 +27,10 @@
> >  #include <linux/ctype.h>
> >  #include <drm/drm_mode.h>
> >  
> > +#define DRM_MODE_BLEND_PREMULTI		0
> > +#define DRM_MODE_BLEND_COVERAGE		1
> > +#define DRM_MODE_BLEND_PIXEL_NONE	2
> > +
> >  struct drm_device;
> >  struct drm_atomic_state;
> >  struct drm_plane;
> > @@ -52,4 +56,6 @@ int drm_plane_create_zpos_immutable_property(struct drm_plane *plane,
> >  					     unsigned int zpos);
> >  int drm_atomic_normalize_zpos(struct drm_device *dev,
> >  			      struct drm_atomic_state *state);
> > +int drm_plane_create_blend_mode_property(struct drm_plane *plane,
> > +					 unsigned int supported_modes);
> >  #endif
> > diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
> > index 8a152dc..c52614a 100644
> > --- a/include/drm/drm_plane.h
> > +++ b/include/drm/drm_plane.h
> > @@ -117,6 +117,7 @@ struct drm_plane_state {
> >  	 * details.
> >  	 */
> >  	u16 alpha;
> > +	uint16_t pixel_blend_mode;
> >  
> >  	/**
> >  	 * @rotation:
> > @@ -659,6 +660,7 @@ struct drm_plane {
> >  	 * drm_plane_create_rotation_property().
> >  	 */
> >  	struct drm_property *rotation_property;
> > +	struct drm_property *blend_mode_property;
> >  
> >  	/**
> >  	 * @color_encoding_property:
> 
> These need to be documented.
Yes, will add this. Thanks.

> With those changes:
> 
> Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> 
> ~Maarten
Lowry Li (Arm Technology China) Aug. 23, 2018, 7:23 a.m. UTC | #5
On Wed, Aug 22, 2018 at 08:39:49AM -0400, Sean Paul wrote:
> On Wed, Aug 15, 2018 at 02:35:32PM +0800, Lowry Li wrote:
> > Pixel blend modes represent the alpha blending equation
> > selection, describing how the pixels from the current
> > plane are composited with the background.
> > 
> > Adds a pixel_blend_mode to drm_plane_state and a
> > blend_mode_property to drm_plane, and related support
> > functions.
> > 
> > Defines three blend modes in drm_blend.h.
> > 
> > Changes since v1:
> >  - Moves the blending equation into the DOC comment
> >  - Refines the comments of drm_plane_create_blend_mode_property to not
> >    enumerate the #defines, but instead the string values
> >  - Uses fg.* instead of pixel.* and plane_alpha instead of plane.alpha
> > Changes since v2:
> >  - Refines the comments of drm_plane_create_blend_mode_property:
> >       1) Puts the descriptions (after the ":") on a new line
> >       2) Adds explaining why @supported_modes need PREMUL as default
> > Changes since v3:
> >  - Refines drm_plane_create_blend_mode_property(). drm_property_add_enum()
> >    can calculate the index itself just fine, so no point in having the
> >    caller pass it in.
> >  - Since the current DRM assumption is that alpha is premultiplied
> >    as default, define DRM_MODE_BLEND_PREMULTI as 0 will be better.
> >  - Refines some comments.
> > 
> > Signed-off-by: Lowry Li <lowry.li@arm.com>
> > ---
> >  drivers/gpu/drm/drm_atomic.c        |   4 ++
> >  drivers/gpu/drm/drm_atomic_helper.c |   1 +
> >  drivers/gpu/drm/drm_blend.c         | 126 ++++++++++++++++++++++++++++++++++++
> >  include/drm/drm_blend.h             |   6 ++
> >  include/drm/drm_plane.h             |   2 +
> >  5 files changed, 139 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index 3eb061e..d0478ab 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -895,6 +895,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
> >  		state->src_h = val;
> >  	} else if (property == plane->alpha_property) {
> >  		state->alpha = val;
> > +	} else if (property == plane->blend_mode_property) {
> > +		state->pixel_blend_mode = val;
> >  	} else if (property == plane->rotation_property) {
> >  		if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK)) {
> >  			DRM_DEBUG_ATOMIC("[PLANE:%d:%s] bad rotation bitmask: 0x%llx\n",
> > @@ -968,6 +970,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
> >  		*val = state->src_h;
> >  	} else if (property == plane->alpha_property) {
> >  		*val = state->alpha;
> > +	} else if (property == plane->blend_mode_property) {
> > +		*val = state->pixel_blend_mode;
> >  	} else if (property == plane->rotation_property) {
> >  		*val = state->rotation;
> >  	} else if (property == plane->zpos_property) {
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 6dd5036..563af09 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -3569,6 +3569,7 @@ void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
> >  	/* Reset the alpha value to fully opaque if it matters */
> >  	if (plane->alpha_property)
> >  		state->alpha = plane->alpha_property->values[1];
> > +	plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
> 
> Shouldn't this be state->pixel_blend_mode instead of
> plane->state->pixel_blend_mode?
Hi Sean,
Yeah, will refine this. Thanks for your comments:) 
> >  
> >  	plane->state = state;
> >  }
> 
> /snip
> 
> -- 
> Sean Paul, Software Engineer, Google / Chromium OS
diff mbox series

Patch

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 3eb061e..d0478ab 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -895,6 +895,8 @@  static int drm_atomic_plane_set_property(struct drm_plane *plane,
 		state->src_h = val;
 	} else if (property == plane->alpha_property) {
 		state->alpha = val;
+	} else if (property == plane->blend_mode_property) {
+		state->pixel_blend_mode = val;
 	} else if (property == plane->rotation_property) {
 		if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK)) {
 			DRM_DEBUG_ATOMIC("[PLANE:%d:%s] bad rotation bitmask: 0x%llx\n",
@@ -968,6 +970,8 @@  static int drm_atomic_plane_set_property(struct drm_plane *plane,
 		*val = state->src_h;
 	} else if (property == plane->alpha_property) {
 		*val = state->alpha;
+	} else if (property == plane->blend_mode_property) {
+		*val = state->pixel_blend_mode;
 	} else if (property == plane->rotation_property) {
 		*val = state->rotation;
 	} else if (property == plane->zpos_property) {
diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 6dd5036..563af09 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -3569,6 +3569,7 @@  void __drm_atomic_helper_plane_reset(struct drm_plane *plane,
 	/* Reset the alpha value to fully opaque if it matters */
 	if (plane->alpha_property)
 		state->alpha = plane->alpha_property->values[1];
+	plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
 
 	plane->state = state;
 }
diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
index a16a74d..24016c9 100644
--- a/drivers/gpu/drm/drm_blend.c
+++ b/drivers/gpu/drm/drm_blend.c
@@ -107,6 +107,52 @@ 
  *	planes. Without this property the primary plane is always below the cursor
  *	plane, and ordering between all other planes is undefined.
  *
+ * pixel blend mode:
+ *	Pixel blend mode is set up with drm_plane_create_blend_mode_property().
+ *	It adds a blend mode for alpha blending equation selection, describing
+ *	how the pixels from the current plane are composited with the
+ *	background.
+ *
+ *	 Three alpha blending equations are defined:
+ *
+ *	 "None":
+ *		 Blend formula that ignores the pixel alpha::
+ *
+ *			 out.rgb = plane_alpha * fg.rgb +
+ *				 (1 - plane_alpha) * bg.rgb
+ *
+ *	 "Pre-multiplied":
+ *		 Blend formula that assumes the pixel color values
+ *		 have been already pre-multiplied with the alpha
+ *		 channel values::
+ *
+ *			 out.rgb = plane_alpha * fg.rgb +
+ *				 (1 - (plane_alpha * fg.alpha)) * bg.rgb
+ *
+ *	 "Coverage":
+ *		 Blend formula that assumes the pixel color values have not
+ *		 been pre-multiplied and will do so when blending them to the
+ *		 background color values::
+ *
+ *			 out.rgb = plane_alpha * fg.alpha * fg.rgb +
+ *				 (1 - (plane_alpha * fg.alpha)) * bg.rgb
+ *
+ *	 Using the following symbols:
+ *
+ *	 "fg.rgb":
+ *		 Each of the RGB component values from the plane's pixel
+ *	 "fg.alpha":
+ *		 Alpha component value from the plane's pixel. If the plane's
+ *		 pixel format has no alpha component, then this is assumed to be
+ *		 1.0. In these cases, this property has no effect, as all three
+ *		 equations become equivalent.
+ *	 "bg.rgb":
+ *		 Each of the RGB component values from the background
+ *	 "plane_alpha":
+ *		 Plane alpha value set by the plane "alpha" property. If the
+ *		 plane does not expose the "alpha" property, then this is
+ *		 assumed to be 1.0
+ *
  * Note that all the property extensions described here apply either to the
  * plane or the CRTC (e.g. for the background color, which currently is not
  * exposed and assumed to be black).
@@ -448,3 +494,83 @@  int drm_atomic_normalize_zpos(struct drm_device *dev,
 	return 0;
 }
 EXPORT_SYMBOL(drm_atomic_normalize_zpos);
+
+/**
+ * drm_plane_create_blend_mode_property - create a new blend mode property
+ * @plane: drm plane
+ * @supported_modes: bitmask of supported modes, must include
+ *		     BIT(DRM_MODE_BLEND_PREMULTI). Current DRM assumption is
+ *		     that alpha is premultiplied, and old userspace can break if
+ *		     the property defaults to anything else.
+ *
+ * This creates a new property describing the blend mode.
+ *
+ * The property exposed to userspace is an enumeration property (see
+ * drm_property_create_enum()) called "pixel blend mode" and has the
+ * following enumeration values:
+ *
+ * "None":
+ *	Blend formula that ignores the pixel alpha.
+ *
+ * "Pre-multiplied":
+ *	Blend formula that assumes the pixel color values have been already
+ *	pre-multiplied with the alpha channel values.
+ *
+ * "Coverage":
+ *	Blend formula that assumes the pixel color values have not been
+ *	pre-multiplied and will do so when blending them to the background color
+ *	values.
+ *
+ * RETURNS:
+ * Zero for success or -errno
+ */
+int drm_plane_create_blend_mode_property(struct drm_plane *plane,
+					 unsigned int supported_modes)
+{
+	struct drm_device *dev = plane->dev;
+	struct drm_property *prop;
+	static const struct drm_prop_enum_list props[] = {
+		{ DRM_MODE_BLEND_PIXEL_NONE, "None" },
+		{ DRM_MODE_BLEND_PREMULTI, "Pre-multiplied" },
+		{ DRM_MODE_BLEND_COVERAGE, "Coverage" },
+	};
+	unsigned int valid_mode_mask = BIT(DRM_MODE_BLEND_PIXEL_NONE) |
+				       BIT(DRM_MODE_BLEND_PREMULTI)   |
+				       BIT(DRM_MODE_BLEND_COVERAGE);
+	int i;
+
+	if (WARN_ON((supported_modes & ~valid_mode_mask) ||
+		    ((supported_modes & BIT(DRM_MODE_BLEND_PREMULTI)) == 0)))
+		return -EINVAL;
+
+	prop = drm_property_create(dev, DRM_MODE_PROP_ENUM,
+				   "pixel blend mode",
+				   hweight32(supported_modes));
+	if (!prop)
+		return -ENOMEM;
+
+	for (i = 0; i < ARRAY_SIZE(props); i++) {
+		int ret;
+
+		if (!(BIT(props[i].type) & supported_modes))
+			continue;
+
+		ret = drm_property_add_enum(prop, props[i].type,
+					    props[i].name);
+
+		if (ret) {
+			drm_property_destroy(dev, prop);
+
+			return ret;
+		}
+	}
+
+	drm_object_attach_property(&plane->base, prop, DRM_MODE_BLEND_PREMULTI);
+	plane->blend_mode_property = prop;
+
+	if (plane->state)
+		plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_plane_create_blend_mode_property);
diff --git a/include/drm/drm_blend.h b/include/drm/drm_blend.h
index 330c561..88bdfec 100644
--- a/include/drm/drm_blend.h
+++ b/include/drm/drm_blend.h
@@ -27,6 +27,10 @@ 
 #include <linux/ctype.h>
 #include <drm/drm_mode.h>
 
+#define DRM_MODE_BLEND_PREMULTI		0
+#define DRM_MODE_BLEND_COVERAGE		1
+#define DRM_MODE_BLEND_PIXEL_NONE	2
+
 struct drm_device;
 struct drm_atomic_state;
 struct drm_plane;
@@ -52,4 +56,6 @@  int drm_plane_create_zpos_immutable_property(struct drm_plane *plane,
 					     unsigned int zpos);
 int drm_atomic_normalize_zpos(struct drm_device *dev,
 			      struct drm_atomic_state *state);
+int drm_plane_create_blend_mode_property(struct drm_plane *plane,
+					 unsigned int supported_modes);
 #endif
diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
index 8a152dc..c52614a 100644
--- a/include/drm/drm_plane.h
+++ b/include/drm/drm_plane.h
@@ -117,6 +117,7 @@  struct drm_plane_state {
 	 * details.
 	 */
 	u16 alpha;
+	uint16_t pixel_blend_mode;
 
 	/**
 	 * @rotation:
@@ -659,6 +660,7 @@  struct drm_plane {
 	 * drm_plane_create_rotation_property().
 	 */
 	struct drm_property *rotation_property;
+	struct drm_property *blend_mode_property;
 
 	/**
 	 * @color_encoding_property: