NV_PBUS_POWERCTRL_4
saved_powerctrl_4 = nvif_rd32(device, NV_PBUS_POWERCTRL_4);
nvif_wr32(device, NV_PBUS_POWERCTRL_4, saved_powerctrl_4 & 0xffffffcf);
nvif_wr32(device, NV_PBUS_POWERCTRL_4, saved_powerctrl_4);