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

This patch depends on:

"[PATCH v2 01/19] drm/fourcc: Add a alpha field to drm_format_info"
Signed-off-by: Ayan Kumar Halder <ayan.halder@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>

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)
@@ -274,6 +277,7 @@ 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;
+	bool format_has_alpha = plane->state->fb->format->has_alpha;
 
 	mp = to_malidp_plane(plane);
 
@@ -325,12 +329,25 @@ 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 (format_has_alpha) {
+
+		/*
+		 * 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) {