drm/exynos: Don't blend mixer layer 0

This patch disables blending the mixer's layer 0 onto the background
(solid color). It doesn't make sense to blend this layer by default,
and causes color distortion if the layer is used for arbitrary content.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_mixer.c

@@ -643,12 +643,14 @@ static void mixer_win_reset(struct mixer_context *ctx)
 	/* setting graphical layers */
 	val  = MXR_GRP_CFG_COLOR_KEY_DISABLE; /* no blank key */
 	val |= MXR_GRP_CFG_WIN_BLEND_EN;
-	val |= MXR_GRP_CFG_BLEND_PRE_MUL;
-	val |= MXR_GRP_CFG_PIXEL_BLEND_EN;
 	val |= MXR_GRP_CFG_ALPHA_VAL(0xff); /* non-transparent alpha */
 
-	/* the same configuration for both layers */
+	/* Don't blend layer 0 onto the mixer background */
 	mixer_reg_write(res, MXR_GRAPHIC_CFG(0), val);
+
+	/* Blend layer 1 into layer 0 */
+	val |= MXR_GRP_CFG_BLEND_PRE_MUL;
+	val |= MXR_GRP_CFG_PIXEL_BLEND_EN;
 	mixer_reg_write(res, MXR_GRAPHIC_CFG(1), val);
 
 	/* setting video layers */