drm/i915: Don't clobber crtc->new_config when nothing changes

When doing a nop modeset we currently leave crtc->new_config point at
the already freed temporary pipe_config. That will anger the sanity
checks in intel_modeset_update_state() when the nop modeset gets
followed by a GPU reset on gen3/4 where the display block gets fully
reinitialized during the reset.

So leave crtc->new_config alone until we know a modeset is actually
required.

Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -10907,7 +10907,6 @@ intel_modeset_compute_config(struct drm_crtc *crtc,
 	}
 	intel_dump_pipe_config(to_intel_crtc(crtc), pipe_config,
 			       "[modeset]");
-	to_intel_crtc(crtc)->new_config = pipe_config;
 
 out:
 	return pipe_config;
@@ -10933,6 +10932,9 @@ static int __intel_set_mode(struct drm_crtc *crtc,
 
 	*saved_mode = crtc->mode;
 
+	if (modeset_pipes)
+		to_intel_crtc(crtc)->new_config = pipe_config;
+
 	/*
 	 * See if the config requires any additional preparation, e.g.
 	 * to adjust global state with pipes off.  We need to do this
@@ -11466,12 +11468,12 @@ static int intel_crtc_set_config(struct drm_mode_set *set)
 		ret = PTR_ERR(pipe_config);
 		goto fail;
 	} else if (pipe_config) {
-		if (to_intel_crtc(set->crtc)->new_config->has_audio !=
+		if (pipe_config->has_audio !=
 		    to_intel_crtc(set->crtc)->config.has_audio)
 			config->mode_changed = true;
 
 		/* Force mode sets for any infoframe stuff */
-		if (to_intel_crtc(set->crtc)->new_config->has_infoframe ||
+		if (pipe_config->has_infoframe ||
 		    to_intel_crtc(set->crtc)->config.has_infoframe)
 			config->mode_changed = true;
 	}