drm/vc4: plane: TPZ scaling modes cannot reduce lbm size when alpha-less

spec says "Note that there is not an extra mode to save memory
for alpha-less formats" in the TPZ section.

Currently, if first plane is RGB888 and scaled down (TPZ)
a second plane will corrupt the LBM and result in garbage

I've also folded in the modification to components to the
function as it seems misplaced

Signed-off-by: Dom Cobley <popcornmix@gmail.com>

Author: popcornmix

drivers/gpu/drm/vc4/vc4_plane.c

@@ -805,7 +805,10 @@ static unsigned int vc4_lbm_components(const struct drm_plane_state *state,
 	if (info->is_yuv)
 		return channel ? 2 : 1;
 
-	if (info->has_alpha)
+	if (vc4_state->y_scaling[channel] == VC4_SCALING_TPZ)
+		return 4;
+
+	if (info->has_alpha && state->alpha == DRM_BLEND_ALPHA_OPAQUE)
 		return 4;
 
 	return 3;
@@ -836,9 +839,6 @@ static unsigned int vc4_lbm_channel_size(const struct drm_plane_state *state,
 	if (!components)
 		return 0;
 
-	if (state->alpha != DRM_BLEND_ALPHA_OPAQUE && info->has_alpha)
-		components -= 1;
-
 	words = width * wpc * components;
 
 	lines = DIV_ROUND_UP(words, 128 / info->hsub);