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Subject: Re: [RFC PATCH] drm: Add per-plane pixel blend mode property
To:     Lowry Li <lowry.li@arm.com>, liviu.dudau@arm.com
Cc:     airlied@linux.ie, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, daniel.vetter@intel.com,
        nd@arm.com
References: <1525775676-32158-1-git-send-email-lowry.li@arm.com>
From:   Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Message-ID: <9e753dbc-1e58-6ac2-cd0e-4c02ab387c5f@linux.intel.com>
Date:   Thu, 17 May 2018 10:05:35 +0200
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Op 08-05-18 om 12:34 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.
>
> Add 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.
>
> 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         | 95 +++++++++++++++++++++++++++++++++++++
>  include/drm/drm_blend.h             |  6 +++
>  include/drm/drm_plane.h             |  7 +++
>  5 files changed, 113 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index a567310..0bb6de1 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -764,6 +764,8 @@ int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		state->src_w = val;
>  	} else if (property == config->prop_src_h) {
>  		state->src_h = 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_ROTATE_MASK))
>  			return -EINVAL;
> @@ -826,6 +828,8 @@ int drm_atomic_plane_set_property(struct drm_plane *plane,
>  		*val = state->src_w;
>  	} else if (property == config->prop_src_h) {
>  		*val = state->src_h;
> +	} 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 01d936b..e4377fd 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -3133,6 +3133,7 @@ void drm_atomic_helper_plane_reset(struct drm_plane *plane)
>  	if (plane->state) {
>  		plane->state->plane = plane;
>  		plane->state->rotation = DRM_ROTATE_0;
> +		plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
>  	}
>  }
>  EXPORT_SYMBOL(drm_atomic_helper_plane_reset);
> diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> index 665aafc..bb938de 100644
> --- a/drivers/gpu/drm/drm_blend.c
> +++ b/drivers/gpu/drm/drm_blend.c
> @@ -98,6 +98,12 @@
>   *   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.
> + *
>   * 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).
> @@ -405,3 +411,92 @@ 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)
> + *
> + * 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:
> + *
> + * DRM_MODE_BLEND_PIXEL_NONE: Blend formula that ignores the pixel alpha.
> + *	"None"
> + *	out.rgb = plane.alpha * pixel.rgb + (1 - plane.alpha) * bg.rgb
> + *
> + * DRM_MODE_BLEND_PREMULTI: Blend formula that assumes the pixel color values
> + *			    have been already pre-multiplied with the alpha
> + *			    channel values.
> + *	"Pre-multiplied"
> + *	out.rgb = plane.alpha * pixel.rgb +
> + *	      (1 - (plane.alpha * pixel.alpha)) * bg.rgb
> + *
> + * DRM_MODE_BLEND_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.
> + *	"Coverage"
> + *	out.rgb = plane.alpha * pixel.alpha * pixel.rgb +
> + *	      (1 - (plane.alpha * pixel.alpha)) * bg.rgb
> + *
> + * This property has no effect on formats with no pixel alpha, as pixel.alpha
> + * is assumed to be 1.0. If the plane does not expose the "alpha" property, then
> + * plane.alpha is assumed to be 1.0, otherwise, it is the value of the "alpha"
> + * property.
> + *
> + * 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, j = 0;
> +
> +	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));

Just a small nitpick: all other crtc properties appear to use upper case
and underscores instead of spaces and lowercase for the property name.
For the value names I would imagine it's fine, but probably best to be
consistent for the name.

:)

All in all with the review comments from the others addressed, I think this looks good.

~Maarten

> +	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, j++, 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 13221cf..6bf95a4 100644
> --- a/include/drm/drm_blend.h
> +++ b/include/drm/drm_blend.h
> @@ -26,6 +26,10 @@
>  #include <linux/list.h>
>  #include <linux/ctype.h>
>  
> +#define DRM_MODE_BLEND_PIXEL_NONE	0
> +#define DRM_MODE_BLEND_PREMULTI		1
> +#define DRM_MODE_BLEND_COVERAGE		2
> +
>  struct drm_device;
>  struct drm_atomic_state;
Seems in general when such values are defined, they're put inside uapi/drm/drm_mode.h :)

> @@ -65,4 +69,6 @@ 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 20867b4..f9cbfee 100644
> --- a/include/drm/drm_plane.h
> +++ b/include/drm/drm_plane.h
> @@ -41,6 +41,8 @@
>   *	plane (in 16.16)
>   * @src_w: width of visible portion of plane (in 16.16)
>   * @src_h: height of visible portion of plane (in 16.16)
> + * @pixel_blend_mode: how the plane's framebuffer alpha channel is used when
> + *	blending with the background colour.
>   * @rotation: rotation of the plane
>   * @zpos: priority of the given plane on crtc (optional)
>   *	Note that multiple active planes on the same crtc can have an identical
> @@ -104,6 +106,9 @@ struct drm_plane_state {
>  	uint32_t src_x, src_y;
>  	uint32_t src_h, src_w;
>  
> +	/* Plane pixel blend mode */
> +	uint16_t pixel_blend_mode;
> +
>  	/* Plane rotation */
>  	unsigned int rotation;
>  
> @@ -459,6 +464,7 @@ enum drm_plane_type {
>   * @state: current atomic state for this plane
>   * @zpos_property: zpos property for this plane
>   * @rotation_property: rotation property for this plane
> + * @blend_mode_property: blend mode property for this plane
>   * @helper_private: mid-layer private data
>   */
>  struct drm_plane {
> @@ -506,6 +512,7 @@ struct drm_plane {
>  
>  	struct drm_property *zpos_property;
>  	struct drm_property *rotation_property;
> +	struct drm_property *blend_mode_property;
>  };
>  
>  #define obj_to_plane(x) container_of(x, struct drm_plane, base)