drm/i915: Move the SKL+ zero constant alpha handling

Let's run through the entire plane check even when the plane
is invisible due to zero constant alpha. This makes for more
consistent behaviour since we check the src/dst coordinates,
stride etc. against the hardware limits.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181018195921.9898-2-ville.syrjala@linux.intel.comReviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -3113,10 +3113,6 @@ int skl_check_plane_surface(struct intel_plane_state *plane_state)
 	if (ret)
 		return ret;
 
-	/* HW only has 8 bits pixel precision, disable plane if invisible */
-	if (!(plane_state->base.alpha >> 8))
-		plane_state->base.visible = false;
-
 	if (!plane_state->base.visible)
 		return 0;
 

drivers/gpu/drm/i915/intel_sprite.c

@@ -1405,6 +1405,10 @@ static int skl_plane_check(struct intel_crtc_state *crtc_state,
 	if (ret)
 		return ret;
 
+	/* HW only has 8 bits pixel precision, disable plane if invisible */
+	if (!(plane_state->base.alpha >> 8))
+		plane_state->base.visible = false;
+
 	plane_state->ctl = skl_plane_ctl(crtc_state, plane_state);
 
 	if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))