diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index b69440c..75105a2 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -12005,9 +12005,6 @@ intel_compare_link_m_n(const struct intel_link_m_n *m_n,
 			      m2_n2->gmch_m, m2_n2->gmch_n, !adjust) &&
 	    intel_compare_m_n(m_n->link_m, m_n->link_n,
 			      m2_n2->link_m, m2_n2->link_n, !adjust)) {
-		if (adjust)
-			*m2_n2 = *m_n;
-
 		return true;
 	}
 
@@ -13149,6 +13146,33 @@ static int calc_watermark_data(struct intel_atomic_state *state)
 	return 0;
 }
 
+static void intel_crtc_check_fastset(struct intel_crtc_state *old_crtc_state,
+				     struct intel_crtc_state *new_crtc_state)
+{
+	struct drm_i915_private *dev_priv =
+		to_i915(new_crtc_state->base.crtc->dev);
+
+	if (!intel_pipe_config_compare(dev_priv, old_crtc_state,
+				       new_crtc_state, true))
+		return;
+
+	new_crtc_state->base.mode_changed = false;
+	new_crtc_state->update_pipe = true;
+
+	/*
+	 * If we're not doing the full modeset we want to
+	 * keep the current M/N values as they may be
+	 * sufficiently different to the computed values
+	 * to cause problems.
+	 *
+	 * FIXME: should really copy more fuzzy state here
+	 */
+	new_crtc_state->fdi_m_n = old_crtc_state->fdi_m_n;
+	new_crtc_state->dp_m_n = old_crtc_state->dp_m_n;
+	new_crtc_state->dp_m2_n2 = old_crtc_state->dp_m2_n2;
+	new_crtc_state->has_drrs = old_crtc_state->has_drrs;
+}
+
 /**
  * intel_atomic_check - validate state object
  * @dev: drm device
@@ -13197,12 +13221,8 @@ static int intel_atomic_check(struct drm_device *dev,
 			return ret;
 		}
 
-		if (intel_pipe_config_compare(dev_priv,
-					to_intel_crtc_state(old_crtc_state),
-					pipe_config, true)) {
-			crtc_state->mode_changed = false;
-			pipe_config->update_pipe = true;
-		}
+		intel_crtc_check_fastset(to_intel_crtc_state(old_crtc_state),
+					 pipe_config);
 
 		if (needs_modeset(crtc_state))
 			any_ms = true;