drm/i915: Warn when inteldrmfb fails to restore its framebuffer config

While sifting through the inteldrmfb code trying to solve #22040 I found that
the fb restore path doesn't check the return value of
drm_crtc_helper_set_config(), which seems to have all sorts of potential
failure modes. We should warn someone if one of these is triggered.

Signed-Off-By: Ben Gamari <bgamari.foss@gmail.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[anholt: hand-applied, failures are mine]
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/intel_fb.c

@@ -870,7 +870,11 @@ static int intelfb_single_fb_probe(struct drm_device *dev)
  */
 void intelfb_restore(void)
 {
-	drm_crtc_helper_set_config(&kernelfb_mode);
+	int ret;
+	if ((ret = drm_crtc_helper_set_config(&kernelfb_mode)) != 0) {
+		printk(KERN_ERR "Failed to restore crtc configuration: %d\n",
+		       ret);
+	}
 }
 
 static void intelfb_restore_work_fn(struct work_struct *ignored)