drm/rockchip: Disable blending for win0

Blending win0 with the background color doesn't seem to work
correctly. We only get the background color, no matter the contents of
the win0 framebuffer.  However, blending pre-multiplied color with the
default opaque black default background color is a no-op, so we can
just disable blending to get the correct result.
Signed-off-by: Kristian H. Kristensen <hoegsberg@chromium.org>
Cc: Sandy Huang <hjc@rock-chips.com>
Cc: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180418173152.93246-1-hoegsberg@chromium.org

drivers/gpu/drm/rockchip/rockchip_drm_vop.c

@@ -76,6 +76,9 @@
 #define VOP_WIN_GET_YRGBADDR(vop, win) \
 		vop_readl(vop, win->base + win->phy->yrgb_mst.offset)
 
+#define VOP_WIN_TO_INDEX(vop_win) \
+	((vop_win) - (vop_win)->vop->win)
+
 #define to_vop(x) container_of(x, struct vop, crtc)
 #define to_vop_win(x) container_of(x, struct vop_win, base)
 
@@ -708,6 +711,7 @@ static void vop_plane_atomic_update(struct drm_plane *plane,
 	dma_addr_t dma_addr;
 	uint32_t val;
 	bool rb_swap;
+	int win_index = VOP_WIN_TO_INDEX(vop_win);
 	int format;
 
 	/*
@@ -777,7 +781,14 @@ static void vop_plane_atomic_update(struct drm_plane *plane,
 	rb_swap = has_rb_swapped(fb->format->format);
 	VOP_WIN_SET(vop, win, rb_swap, rb_swap);
 
-	if (fb->format->has_alpha) {
+	/*
+	 * Blending win0 with the background color doesn't seem to work
+	 * correctly. We only get the background color, no matter the contents
+	 * of the win0 framebuffer.  However, blending pre-multiplied color
+	 * with the default opaque black default background color is a no-op,
+	 * so we can just disable blending to get the correct result.
+	 */
+	if (fb->format->has_alpha && win_index > 0) {
 		VOP_WIN_SET(vop, win, dst_alpha_ctl,
 			    DST_FACTOR_M0(ALPHA_SRC_INVERSE));
 		val = SRC_ALPHA_EN(1) | SRC_COLOR_M0(ALPHA_SRC_PRE_MUL) |