drm/i915: Update dbuf slices only with full modeset

During full modeset, global state(i.e dev_priv) is protected
by locking the crtcs in state, otherwise global state is not
serialized. Also if it is not a full modeset, we anyway
don't need to change DBuf slice configuration as Pipe configuration
doesn't change.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200202230630.8975-4-stanislav.lisovskiy@intel.com

drivers/gpu/drm/i915/display/intel_display.c

@@ -15720,7 +15720,8 @@ static void intel_atomic_commit_tail(struct intel_atomic_state *state)
 		intel_encoders_update_prepare(state);
 
 	/* Enable all new slices, we might need */
-	icl_dbuf_slice_pre_update(state);
+	if (state->modeset)
+		icl_dbuf_slice_pre_update(state);
 
 	/* Now enable the clocks, plane, pipe, and connectors that we set up. */
 	dev_priv->display.commit_modeset_enables(state);
@@ -15776,7 +15777,8 @@ static void intel_atomic_commit_tail(struct intel_atomic_state *state)
 	}
 
 	/* Disable all slices, we don't need */
-	icl_dbuf_slice_post_update(state);
+	if (state->modeset)
+		icl_dbuf_slice_post_update(state);
 
 	for_each_oldnew_intel_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
 		intel_post_plane_update(state, crtc);