drm/i915/gen9: Propagate watermark calculation failures up the call chain

Once we move watermark calculation to the atomic check phase, we'll want
to start rejecting display configurations that exceed out watermark
limits.  At the moment we just assume that there's always a valid set of
watermarks, even though this may not actually be true.  Let's prepare by
passing return codes up through the call stack in preparation.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1463061971-19638-15-git-send-email-matthew.d.roper@intel.com
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 325e75f..94804d9 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13309,7 +13309,7 @@
  * phase.  The code here should be run after the per-crtc and per-plane 'check'
  * handlers to ensure that all derived state has been updated.
  */
-static void calc_watermark_data(struct drm_atomic_state *state)
+static int calc_watermark_data(struct drm_atomic_state *state)
 {
 	struct drm_device *dev = state->dev;
 	struct drm_i915_private *dev_priv = to_i915(dev);
@@ -13345,7 +13345,9 @@
 
 	/* Is there platform-specific watermark information to calculate? */
 	if (dev_priv->display.compute_global_watermarks)
-		dev_priv->display.compute_global_watermarks(state);
+		return dev_priv->display.compute_global_watermarks(state);
+
+	return 0;
 }
 
 /**
@@ -13432,9 +13434,7 @@
 		return ret;
 
 	intel_fbc_choose_crtc(dev_priv, state);
-	calc_watermark_data(state);
-
-	return 0;
+	return calc_watermark_data(state);
 }
 
 static int intel_atomic_prepare_commit(struct drm_device *dev,