drm: xlnx: zynqmp_dpsub: Fix graphics layer blending

To display the graphics layer, the global alpha needs to be enabled.
Enable it when the graphics plane is enabled (with full opacity), and
disable it otherwise.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/gpu/drm/xlnx/zynqmp_disp.c

@@ -415,6 +415,11 @@ static void zynqmp_disp_avbuf_write(struct zynqmp_disp *disp, int reg, u32 val)
 	writel(val, disp->avbuf.base + reg);
 }
 
+static bool zynqmp_disp_layer_is_gfx(const struct zynqmp_disp_layer *layer)
+{
+	return layer->id == ZYNQMP_DISP_LAYER_GFX;
+}
+
 static bool zynqmp_disp_layer_is_video(const struct zynqmp_disp_layer *layer)
 {
 	return layer->id == ZYNQMP_DISP_LAYER_VID;
@@ -1157,6 +1162,9 @@ zynqmp_disp_plane_atomic_disable(struct drm_plane *plane,
 		return;
 
 	zynqmp_disp_layer_disable(layer);
+
+	if (zynqmp_disp_layer_is_gfx(layer))
+		zynqmp_disp_blend_set_global_alpha(layer->disp, false, 0);
 }
 
 static void
@@ -1186,6 +1194,9 @@ zynqmp_disp_plane_atomic_update(struct drm_plane *plane,
 
 	zynqmp_disp_layer_update(layer, new_state);
 
+	if (zynqmp_disp_layer_is_gfx(layer))
+		zynqmp_disp_blend_set_global_alpha(layer->disp, true, 255);
+
 	/* Enable or re-enable the plane is the format has changed. */
 	if (format_changed)
 		zynqmp_disp_layer_enable(layer);
@@ -1447,7 +1458,6 @@ zynqmp_disp_crtc_atomic_enable(struct drm_crtc *crtc,
 
 	zynqmp_disp_blend_set_output_format(disp, ZYNQMP_DPSUB_FORMAT_RGB);
 	zynqmp_disp_blend_set_bg_color(disp, 0, 0, 0);
-	zynqmp_disp_blend_set_global_alpha(disp, false, 0);
 
 	zynqmp_disp_enable(disp);