try another idea

bbswitch.c

@@ -436,6 +436,7 @@ static int __init bbswitch_init(void) {
                 dev_name(&pdev->dev), (char *)buf.pointer);
         } else {
             dis_dev = pdev;
+            pci_d3cold_enable(pdev);
             dis_handle = handle;
             pr_info("Found discrete VGA device %s: %s\n",
                 dev_name(&pdev->dev), (char *)buf.pointer);