AHCI_CAP
cap = AHCI_READ(sc, AHCI_CAP);
AHCI_WRITE(sc, AHCI_CAP, sc->sc_init_data.cap);
sc->sc_init_data.cap = AHCI_READ(sc, AHCI_CAP);
sc->sc_ahci_cap = AHCI_READ(sc, AHCI_CAP);
ahci_cap_64bit = (AHCI_READ(sc, AHCI_CAP) & AHCI_CAP_64BIT) != 0;
ahci_cap = AHCI_READ(sc, AHCI_CAP);