[Description]:

Add a feature flag in Uhci & Ehci to disable legacy USB SMI.
[Impaction]:
  Platform integrator can choose to legacy USB SMI or not.
[Reference Info]
  EDK Tracker 1082

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@5081 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Bus/Pci/UhciDxe/Uhci.c

@@ -1658,7 +1658,9 @@ UhciDriverBindingStart (
   // Robustnesss improvement such as for UoL
   // Default is not required.
   //
-  // UhciTurnOffUsbEmulation (PciIo);
+  if (FeaturePcdGet (PcdUsbLegacySupport)) {
+    UhciTurnOffUsbEmulation (PciIo);
+  }
 
   Status = PciIo->Attributes (
                     PciIo,