drm/vc4: Make vc4_lbm_size() return 0 when vertical scaling is disabled

LBM is not needed when vertical scaling is disabled. Return 0 in this
case to avoid allocating LBM memory that will anyway be unused.

While at it, drop the test on ->is_unity which is now redundant.
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20181130090254.594-1-boris.brezillon@bootlin.com

drivers/gpu/drm/vc4/vc4_plane.c

@@ -395,10 +395,13 @@ static u32 vc4_lbm_size(struct drm_plane_state *state)
 	u32 pix_per_line = max(vc4_state->src_w[0], (u32)vc4_state->crtc_w);
 	u32 lbm;
 
-	if (!vc4_state->is_yuv) {
-		if (vc4_state->is_unity)
+	/* LBM is not needed when there's no vertical scaling. */
+	if (vc4_state->y_scaling[0] == VC4_SCALING_NONE &&
+	    vc4_state->y_scaling[1] == VC4_SCALING_NONE)
 		return 0;
-		else if (vc4_state->y_scaling[0] == VC4_SCALING_TPZ)
+
+	if (!vc4_state->is_yuv) {
+		if (vc4_state->y_scaling[0] == VC4_SCALING_TPZ)
 			lbm = pix_per_line * 8;
 		else {
 			/* In special cases, this multiplier might be 12. */