drm/vc4: Fix the "no scaling" case on multi-planar YUV formats

When there's no scaling requested ->is_unity should be true no matter
the format.

Also, when no scaling is requested and we have a multi-planar YUV
format, we should leave ->y_scaling[0] to VC4_SCALING_NONE and only
set ->x_scaling[0] to VC4_SCALING_PPF.

Doing this fixes an hardly visible artifact (seen when using modetest
and a rather big overlay plane in YUV420).

Fixes: fc04023fafec ("drm/vc4: Add support for YUV planes.")
Cc: <stable@vger.kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20180725122907.13702-1-boris.brezillon@bootlin.com
Signed-off-by: Sean Paul <seanpaul@chromium.org>

drivers/gpu/drm/vc4/vc4_plane.c

@@ -297,6 +297,9 @@ static int vc4_plane_setup_clipping_and_scaling(struct drm_plane_state *state)
 	vc4_state->y_scaling[0] = vc4_get_scaling_mode(vc4_state->src_h[0],
 						       vc4_state->crtc_h);
 
+	vc4_state->is_unity = (vc4_state->x_scaling[0] == VC4_SCALING_NONE &&
+			       vc4_state->y_scaling[0] == VC4_SCALING_NONE);
+
 	if (num_planes > 1) {
 		vc4_state->is_yuv = true;
 
@@ -312,24 +315,17 @@ static int vc4_plane_setup_clipping_and_scaling(struct drm_plane_state *state)
 			vc4_get_scaling_mode(vc4_state->src_h[1],
 					     vc4_state->crtc_h);
 
-		/* YUV conversion requires that scaling be enabled,
-		 * even on a plane that's otherwise 1:1.  Choose TPZ
-		 * for simplicity.
+		/* YUV conversion requires that horizontal scaling be enabled,
+		 * even on a plane that's otherwise 1:1. Looks like only PPF
+		 * works in that case, so let's pick that one.
 		 */
-		if (vc4_state->x_scaling[0] == VC4_SCALING_NONE)
-			vc4_state->x_scaling[0] = VC4_SCALING_TPZ;
-		if (vc4_state->y_scaling[0] == VC4_SCALING_NONE)
-			vc4_state->y_scaling[0] = VC4_SCALING_TPZ;
+		if (vc4_state->is_unity)
+			vc4_state->x_scaling[0] = VC4_SCALING_PPF;
 	} else {
 		vc4_state->x_scaling[1] = VC4_SCALING_NONE;
 		vc4_state->y_scaling[1] = VC4_SCALING_NONE;
 	}
 
-	vc4_state->is_unity = (vc4_state->x_scaling[0] == VC4_SCALING_NONE &&
-			       vc4_state->y_scaling[0] == VC4_SCALING_NONE &&
-			       vc4_state->x_scaling[1] == VC4_SCALING_NONE &&
-			       vc4_state->y_scaling[1] == VC4_SCALING_NONE);
-
 	/* No configuring scaling on the cursor plane, since it gets
 	   non-vblank-synced updates, and scaling requires requires
 	   LBM changes which have to be vblank-synced.
@@ -672,7 +668,10 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
 		vc4_dlist_write(vc4_state, SCALER_CSC2_ITR_R_601_5);
 	}
 
-	if (!vc4_state->is_unity) {
+	if (vc4_state->x_scaling[0] != VC4_SCALING_NONE ||
+	    vc4_state->x_scaling[1] != VC4_SCALING_NONE ||
+	    vc4_state->y_scaling[0] != VC4_SCALING_NONE ||
+	    vc4_state->y_scaling[1] != VC4_SCALING_NONE) {
 		/* LBM Base Address. */
 		if (vc4_state->y_scaling[0] != VC4_SCALING_NONE ||
 		    vc4_state->y_scaling[1] != VC4_SCALING_NONE) {