linux-kernel - [PATCH] drm/arm/malidp: Disable pixel alpha blending for colors that do not have alpha

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Date:   Fri, 12 Jan 2018 16:33:07 +0000
From:   Ayan Halder <ayan.halder@....com>
To:     liviu.dudau@....com, brian.starkey@....com, malidp@...s.arm.com,
        airlied@...ux.ie, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     nd@....com, Ayan Halder <ayan.halder@....com>
Subject: [PATCH] drm/arm/malidp: Disable pixel alpha blending for colors that do not have alpha

Mali dp needs to disable pixel alpha blending (use layer alpha blending) to
display color formats that do not contain alpha bits per pixel

Signed-off-by: Ayan Kumar Halder <ayan.halder@....com>
---
 drivers/gpu/drm/arm/malidp_planes.c | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/arm/malidp_planes.c b/drivers/gpu/drm/arm/malidp_planes.c
index e741979..4d7d564 100644
--- a/drivers/gpu/drm/arm/malidp_planes.c
+++ b/drivers/gpu/drm/arm/malidp_planes.c
@@ -35,6 +35,9 @@
 #define   LAYER_COMP_MASK		(0x3 << 12)
 #define   LAYER_COMP_PIXEL		(0x3 << 12)
 #define   LAYER_COMP_PLANE		(0x2 << 12)
+#define   LAYER_ALPHA_OFFSET	(16)
+#define   LAYER_ALPHA_MASK		(0xff)
+#define	  LAYER_ALPHA(x)		(((x) & LAYER_ALPHA_MASK) << LAYER_ALPHA_OFFSET)
 #define MALIDP_LAYER_COMPOSE		0x008
 #define MALIDP_LAYER_SIZE		0x00c
 #define   LAYER_H_VAL(x)		(((x) & 0x1fff) << 0)
@@ -268,6 +271,7 @@ static void malidp_de_plane_update(struct drm_plane *plane,
 	struct malidp_plane_state *ms = to_malidp_plane_state(plane->state);
 	u32 src_w, src_h, dest_w, dest_h, val;
 	int i;
+	u8 alpha_bits = plane->state->fb->format->alpha;
 
 	mp = to_malidp_plane(plane);
 
@@ -319,12 +323,25 @@ static void malidp_de_plane_update(struct drm_plane *plane,
 	if (plane->state->rotation & DRM_MODE_REFLECT_Y)
 		val |= LAYER_V_FLIP;
 
-	/*
-	 * always enable pixel alpha blending until we have a way to change
-	 * blend modes
-	 */
 	val &= ~LAYER_COMP_MASK;
-	val |= LAYER_COMP_PIXEL;
+	if (alpha_bits > 0) {
+
+		/*
+		 * always enable pixel alpha blending until we have a way to change
+		 * blend modes
+		 */
+		val |= LAYER_COMP_PIXEL;
+	} else {
+
+		/*
+		 * do not enable pixel alpha blending as the color channel does not
+		 * have any alpha information
+		 */
+		val |= LAYER_COMP_PLANE;
+
+		/* Set layer alpha coefficient to 0xff ie fully opaque */
+		val |= LAYER_ALPHA(0xff);
+	}
 
 	val &= ~LAYER_FLOWCFG(LAYER_FLOWCFG_MASK);
 	if (plane->state->crtc) {
-- 
2.7.4