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Subject: Re: [PATCH v4 1/2] drm: Add per-plane pixel blend mode property
To:     Lowry Li <lowry.li@arm.com>, liviu.dudau@arm.com
Cc:     gustavo@padovan.org, daniel.vetter@intel.com,
        seanpaul@chromium.org, airlied@linux.ie,
        ville.syrjala@linux.intel.com, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org, brian.starkey@arm.com,
        malidp@foss.arm.com, emil.l.velikov@gmail.com, nd@arm.com
References: <1534314933-23182-1-git-send-email-lowry.li@arm.com>
 <1534314933-23182-2-git-send-email-lowry.li@arm.com>
From:   Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Message-ID: <226092b6-315d-b4b8-1c3f-b5d6cdc7da3f@linux.intel.com>
Date:   Wed, 22 Aug 2018 15:27:44 +0200
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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