drm/i915: Make sure cursor has enough ddb for the selected wm level

We use a fixed ddb allocation for the cursor. Now the calculation
actually makes sure we have enough ddb space, but let's double check
anyway.

Cc: Neel Desai <neel.desai@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190312205844.6339-6-ville.syrjala@linux.intel.comReviewed-by: Matt Roper <matthew.d.roper@intel.com>

drivers/gpu/drm/i915/intel_pm.c

@@ -4401,10 +4401,17 @@ skl_allocate_pipe_ddb(struct intel_crtc_state *cstate,
 	for (level = ilk_wm_max_level(dev_priv); level >= 0; level--) {
 		blocks = 0;
 		for_each_plane_id_on_crtc(intel_crtc, plane_id) {
-			if (plane_id == PLANE_CURSOR)
+			wm = &cstate->wm.skl.optimal.planes[plane_id];
+
+			if (plane_id == PLANE_CURSOR) {
+				if (WARN_ON(wm->wm[level].min_ddb_alloc >
+					    total[PLANE_CURSOR])) {
+					blocks = U32_MAX;
+					break;
+				}
 				continue;
+			}
 
-			wm = &cstate->wm.skl.optimal.planes[plane_id];
 			blocks += wm->wm[level].min_ddb_alloc;
 			blocks += wm->uv_wm[level].min_ddb_alloc;
 		}