GMAC_RXMACCONFIG
x = gmac_read_reg(sc, GMAC_RXMACCONFIG);
gmac_write_reg(sc, GMAC_RXMACCONFIG, x);
x = gmac_read_reg(sc, GMAC_RXMACCONFIG);
gmac_write_reg(sc, GMAC_RXMACCONFIG, x);
v = gmac_read_reg(sc, GMAC_RXMACCONFIG);
gmac_write_reg(sc, GMAC_RXMACCONFIG, v);