I assume the USB controller is still asserting its event. You'll need to clear USB1_EN in GPE0_EN. That should stop it. From what I can tell in the code GPE0_EN is only messed with when entering S5. So you may want to ensure that is cleared when setting up SMIs in coreboot.
-Aaron
Ok, i can disable USB1_EN, and it helps. But i want to enable it before jump to OS waking vector, to be able to resume from USB keyboard again. And once i enable it, coreboot starts these endless SMIs. How can i stop USB controller from asserting this event?