NV_VIO_GX_READ_MAP_INDEX
regp->Graphics[NV_VIO_GX_READ_MAP_INDEX] = 0x00;
NVWriteVgaGr(dev, 0, NV_VIO_GX_READ_MAP_INDEX, plane);
gr4 = NVReadVgaGr(dev, 0, NV_VIO_GX_READ_MAP_INDEX);
NVWriteVgaGr(dev, 0, NV_VIO_GX_READ_MAP_INDEX, gr4);